/conducted by the Texas Coastal and Marine Council [for] General Land Office of Texas. Texas Coastal and Marine Council. Texas.General Land Office. [Austin, Tex.] :The Council,1976. Building, Stormproof Texas. Hurricane protection Texas. Construction contracts Texas. c oas'tal Lonedel Minlifurn Cent er ___ rricane Resistsant for thelTexas 4iI Property of cSC Library MODEL MINIMUM HURRICANE-RESISTANT BUILDING STANDARDS FOR THE TEXAS GULF COAST U. S. DEPARTMENT OF COMMERCE NOAA COASTAL SERVICES CENTER 2234 SOUTH HOBSON AVENUE CHARLESTON, SC 29405-2413 CONDUCTED BY THE TEXAS COASTAL AND MARINE COUNCIL SENATOR A. R. "BABE" SCHWARTZ, CHAIRMAN JOE C. MOSELEY II, EXECUTIVE DIRECTOR propeOrty of CSC Library General Land Office of Texas Bob Armstrong, Commissioner U. S. DEPARTMENT OF COMMERCE NOAA COASTAL SERVICES CENTER 2234 SOUTH HOBSON AVENUE CHARLESTON, SC 29405-2413 SEPTEMBER, 1976 This study was funded in part through financial assistance provided by the Coastal Zone g 'L/Management Act of 1972, administered by the Office of Coastal Zone Management, ,. National Oceanic and Atmospheric Administration. - 3COASTAL AND MARINE COUNCIL July 21, 1976 Son. A. R. "Babe" Schwartz Chalvestn The Honorable Bob Armstrong Commi ssioner Richard Keith Arnold General Land Office Austin Stephen F. Austin Building Truman G. Blocker, Jr., MD Austin, Texas Galveston Dear Commissioner Armstrong: John C. Calhoun, Jr. College Station Enclosed is a copy of the report entitled, "Model Minimum Hurricane- Sen Ry Fraee Resistant Building Standards for the Texas Gulf Coast," that the Wichitay Fallse Texas Coastal and Marine Council contracted to produce for the Wicit Fals General Land Office under the terms of IAC(76-77)717. James J. Flanagan Port Arthur This report contains three principal efforts: Sen. Roy Harrington a An analytical procedure for determining the degree of Port Arthurexposure to reasonably "probable" hurricane conditions Joe S. Harris along the Texas coast. V Austin Edward H. Harte * A model minimum building standard, in a building code Corpus Christi format, that, if implemented as an adjunct to common codes--such as the Southern Standard Building Code-- Mrs. J.W. Hershey should reduce damages due to hurricane forces. Application Houston of these standards would raise the building cost only Rep. Joe A. Hubenalk 3-8%. Rosenberg A thorough discussion of the natural hazards of the Robert L. Massey Texas Gulf coast. I nez Rep Grg ontyaThe Council is also working on a similar effort Linder a mandate of R Elsrg noa the Texas Legislature (S.R. 268) to develop model minimum standards Ela and to examine other related issues. This report is due in about six Rep. Pike Powers months. We would appreciate receiving copies of any comments that Beaumont you may receive on this report for incorporation into our report to the 65th Texas Legislature. We are currently reviewing this George Fred Rhodes document in detail with the affected professional groups (engineers, Port Lavaca contractors, architects, insurance and local government) and Charles P. Turco anticipate some revision. Beaumont JoeC. oseeyIf we can be of any further assistance on this matter, please let Executive Director m nw Sincerely, Jo .Moseley II, P.E." POST OFFICE BOX 13407/AUSTIN, TEXAS 78711I/PHONE (512) 475-5849 TABLE OF CONTENTS Page Preface ..................................................... i Section I - INTRODUCTION - Countering the Hurricane Hazard with Special Building Practices ........................ 1-1 Section II - NATURAL HAZARDS OF THE TEXAS COASTAL ZONE INTRODUCTION ........................................... 11-1 HURRICANES ............................................. 11-4 FLOODING ............................................... 11-16 SHORELINE EROSION ...................................... 11-23 LAND-SURFACE SUBSIDENCE ................................ 11-30 FAULTING ............................................... 11-35 CONCLUSIONS ............................................ 11-39 SELECTED REFERENCES .................................... 11-40 Section III - HAZARD ZONE DELINEATION FOR STANDARDS AND CODES 111-1 Annex A - Computation of Hurricane Tides at the Open Coast ................................................ III-A-1 Annex B - Conceptual Basis for Computing Inland Flooding III-B-1 Annex C - Procedures for Computing Inland Flooding ..... III-C-1 Section IV - MODEL MINIMUM STANDARD CHAPTER 1 - INTRODUCTION ............................... IV-1 CHAPTER 2 - ADMINISTRATION ............................. IV-3 CHAPTER 3 - DEFINITIONS OF TERMS ....................... IV-20 CHAPTER 4 - HURRICANE HAZARD ZONES ..................... IV-24 CHAPTER 5 - WAVE AND SCOUR ACTION ...................... IV-26 CHAPTER 6 - BATTERING BY DEBRIS ........................ IV-32 CHAPTER 7 - FLOODING ................................... IV-33 CHAPTER 8- WIND ....................................... IV-65 CHAPTER 9 - FOUNDATIONS ................................ IV-83 CHAPTER 10 - MASONRY WALLS ............................. IV-85 CHAPTER 11 - STEEL AND IRON ............................ IV-87 CHAPTER 12 - WOOD ...................................... IV-89 CHAPTER 13 - CONCRETE .................................. IV-91 CHAPTER 14 - CLADDING AND GLAZING ...................... IV-93 CHAPTER 15 - ROOF COVERING ............................. IV-95 Selected References - HAZARD ZONE DELINEATION ............... IV-98 Selected References - MODEL MINIMUM BUILDING STANDARDS . ..... IV-100 Municipalities Using the Southern Standard Building Code .... IV-102 PREFACE Hurricanes have been a major threat to life and property along the Atlantic and Gulf coasts. Although catastrophic loss of life has been avoided since the 1900 Hurricane killed 6,000 persons in Galveston, Texas, conditions are now developing which lead officials to fear another major killer. The contributing factors include the following: * Rapidly increasing development in low-lying coastal areas, many of which are reachable only over long stretches of exposed low highways. a Massive influx of persons from non-coastal areas who fail to appreciate how devastating a major hurricane can be. This problem is compounded by the fact that many persons have experienced a near miss or only a minor storm and thus have a casual attitude toward these storms. * Warning systems have improved much in recent years, contributing to complacency among both officials and the public. However, a plateau has been reached, and additional significant improvements are not anti ci pated. The best way--from a technical, political, and economic standpoint--to significantly reduce hurricane damage on a wide scale is through the use of hurricane-resistant building practices. If proper standards are developed and thoughtfully applied in a manner consistent with the exposure to hurricane dangers, damage can be greatly reduced at a modest cost. Since a substantial portion of the population inevitably refuses to evacuate during a warning, the use of stronger structures will obviously result in lower loss of life during the storms. This report was prepared to serve two purposes: 1. Develop for the Texas Coastal Management Program of the General Land Office hurricane-resistant building standards as part of their overall coastal management program effort. 2. Partially satisfy the requirements of S.R. 268, which calls for examination of hurricane hazards, develop- ment of hurricane-resistant performance criteria, drafting of a model minimum building standard, and preparation of institutional alternatives for implementation.* While this procedure and these standards were developed with the Texas coast in mind, almost all elements are generally applicable for all coastal states from Texas to Maine. To accomplish the tasks set out in S.R. 268, a group of experts was assembled. Those persons, along with their principal responsibilities, are as follows: 1. Determination of Hazard Areas and Types of Destructive Forces Associated Therewith: Dr. Robert Simpson, consulting meteorologist, former director of the National Hurricane Center of the National Weather Service and world-renowned hurricane expert. Dr. Simpson was responsible for devising the overall methodology for delineating hazard areas. Dr. Robert Morton, Bureau of Economic Geology, University of Texas at Austin. Dr. Morton shared the responsibility for delineating hazard areas and provided guidance on geological conditions and development. Dr. John Freeman, director of the Institute for Storm Research, University of St. Thomas in Houston. Dr. Freeman, in cooperation with Dr. Simpson, developed the technique for determining the inland boundaries of surge distribution. 2. Drafting of Model Minimum Building Standards: Mr. Herbert Saffir, P.E., consulting engineer, Coral Gables, Florida, a well-known expert on hurricane resistant codes. Helped to set minimum standards and assisted with standards development. Dr. Charles Hix, P.E., consulting engineer and staff member of the Engineering Extension Service, Texas A&M University. Dr. Hix drafted the model standards. Mr. James A. Goldston, P.E., President of the Goldston Construction Company, Corpus Christi. Served in a consultative capacity to insure that decisions/actions were reasonable in view of construction practices and conditions along the Texas coast. 3. State government officials involved in the preparation of this report were: Mr. Art Eatman, P.E., of RPC, Inc., who served as project Follow-up work is continuing in a report of the other aspects that will be ready to submit to the Texas Legislature in January of 1977. ii officer for the General Land Office. Mr. Frank Cox and Mr. Ashley Eledge, Governor's Office, Division of Disaster Emergency Services, served as liaison with that office. The Division of Disaster Emergency Services is responsible for disaster planning. Dr. Joe Moseley, P.E., Executive Director of the Texas Coastal and Marine Council, was responsible for overall conceptualization and management of the project. SECTION I I NTRODUCT ION Hurricanes pose a very significant threat to lives and property in coastal areas. Texas is hit by a hurricane on the average of once every other year. Only recently has attention in coastal management deliberations been focused on hurricane hazards. Development in Texas' coastal areas is increasing, and this trend will continue. This is to be expected, as the coast offers many economic and aesthetic amenities. Since hurricanes are inevitable, it is desirable to develop hazard- prone areas in a fashion that will (a) avoid as many hazards as practical; (b) withstand those forces that cannot be avoided when economically feasible; (c) absorb the inevitable losses; and (d) most important, reduce the loss of life as much as possible. One viable way to accommodate growth in high-risk areas is to develop and implement minimum building standards that will reduce the hurricane risk to life and will reduce the risk to property to an acceptable level and in an equitable manner. Such action sounds deceptively simple * but requires a complex and controversial mix of scientific, engineering, legal and political actions. This report presents such an approach. Principal elements include: * A discussion of the hurricane-related processes impacting the Texas coast; * A description of the nature and magnitude of the destructive forces associated with the hurricane process, and the synthesis of parameters for a ''Texas Design Hurricane;` * An analytical procedure, based upon accepted scientific methods, for spatially delineating the varying degrees of exposure to the design hurricane's destructive forces in coastal areas-- i.e., establishing "hazard zones;" * A set of minimum performance criteria for structures in each of the hazard zones, and * A draft minimum model building standard which complements the Southern Standard Building Code and which contains hurricane-resistant wind and flood requirements which are compatible with accepted design and construction practices and 1-1 economic realities. This model can be used to implement the performance criteria in each hazard zone. MODEL STANDARDS Actions by other entities, standard engineering practices, and experience were all heavily relied upon in an attempt to make the product--i.e., the MODEL HURRICANE BUILDING STANDARDS--as practical as possible. The result is a model code that is: * Based on common design and construction practices with minimal modifications for wind-resistant and flood-resistant requirements (where applicable); a Readily usable by practicing architects and engineers with a minimum of special efforts; e Very economical to the builder/consumer. (Without any cosmetic frills,* it is estimated that the use of this standard, with its hurricane-resistant provisions, will add a maximum of 3-8% over the basic structural cost of the same building constructed to the Southern Standard Building Code now commonly used.**) * In its present form, the Model Standard could be easily adopted by local governments, and, if they already use the Southern Standard Building Code, incorporation of these special provisions would be very simple. LEGAL AND INSTITUTIONAL CONSIDERATIONS Under Texas law, municipalities have the power to adopt ordinances, including building codes. With few exceptions, counties do not have this power. Thus, under existing law, implementation of building standards will *Opponents of any special hurricane-resistant codes often point to codes like that used in Coral Gables., Florida, and note that use of such a code may greatly increase the cost of a structure. However, such codes frequently contain many additional provisions for architectural appearance, etc., that have nothing to do with hurricane resistance. A special analysis is underway which develops detailed cost estimates for common coastal structures, both using and not using these special hurricane-resistant standards. It will be ready by December, 1976. **Appendix C to Section IV contains a listing of Texas coastal municipalities using the Southern Standard Code, and other common Texas practices. I-2 generally fall to coastal municipalities. Legislative action could extend this power to coastal counties, if it were politically palatable. The state, although it has no general authority to set or enforce building codes, can do so in special hazard situations, such as under the disaster planning and special, high-risk insurance statutes. Hurricanes Carla and Celia caused many coastal residents to lose their insurance. As a result, the Legislature established the Texas Catastrophe Property Insurance Pool Act (passed in 1971) which requires all property insurers in the state to pool their resources and provide insurance in high-risk areas. Special rates may be charged in the high-risk areas, and upon approval of the Insurance Board, special building requirements may be imposed in such areas as a condition of insurability.* The 1973 Texas Disaster Act, which was updated in 1975, was the first of its kind in the nation, and brings a major new dimension to the state involvement with disasters. Previously, virtually all state disaster and civil defense activities had been oriented to rescue, relief and recovery. The new law stresses preventive measures by establishing a new policy and setting up new administrative and legal mechanisms. One provision specifically authorizes the governor to suspend any local building code or land use ordinance and place one of his own choosing in effect if he finds a disaster or a threat of disaster. This would include imposition of such requirements in areas where none now exist. Implementation is still in its infancy, and, since some of the preventive steps will be unpopular in many quarters, it is impossible to preduct the ultimate effective- ness of this law. In 1975 the Legislature passed a resolution (S.R. 268) which mandated the development of model minimum building standards for high-risk coastal areas. This report is part of the response to that mandate. The federal government has many programs and policies that relate to disaster exposure, risk and recovery. The Corps of Engineers has countless projects aimed at the construction of protective facilities to minimize damage from flooding and erosion. The nationally subsidized federal flood insurance program, which requires participation of any new construction utilizing federal guaranteed loans, requires local governments to adopt flood management programs. This has been unpopular in many quarters, and the ultimate effect is uncertain. *This provision has never been utiZized, although there is currently (Summer '76) an effort to apply it to mobile homes. Some believe this needs clarification. I-3 The Disaster Relief Act of 1974 constitutes a major change in the federal approach, shifting much emphasis from recovery to prevention. Relatively little has been done by the responsible agency, HUD, to implement this law. When such an attempt is made, there may be more protest than there was over the flood insurance program. Another well-known federal effort is the hurricane warning system headed by the National Weather Service. While strong governmental actions are theoretically possible--such as a construction moratorium in high-hazard areas or the direct establishment and enforcement of state building codes--they are unlikely. Such actions would raise Constitutional questions about the use of private property, and could severely restrict the opportunity of citizens to use and enjoy coastal resources. Considering the size and diversity of the Texas coastal area, such actions would be impractical to administer. More realistic avenues are available. * Increased public awareness of the potential hazards and actions that individuals can take to counter them is a first step. Two specific actions should be explored: (a) the current Hurricane Awareness Program should be continued for current coastal residents, and (b) a disclosure of potential hazards should be provided to all new residents. The purpose of the latter is not to "scare" potential buyers away, but to inform them of hazards and appro- pri ate countermeasures. * Insurance availability and cost should be tied to the strength of a given structure, and its exposure to a hurricane hazard. Currently, the Texas Catastrophe Property Insurance Pool Act has very nebulous provisions for basing rates on the strength of a structure and none on its degree of exposure except in the Pool area. The possibility of such an amendment should be examined. * The current mix of federal and state disaster related programs is very complex. In some cases, the laws and regulations seem to work against each other, or even to promote the creation of "disaster-prone" situations.* The state should make a careful assessment of the impact of these programs. *Assessment of Research on Natural IHazards, G.F. White and JT.E. Haas, MIT Press: 1975. I-4 These and other matters are still being considered by the Texas Coastal and Marine Council as part of its legislative mandate under S.R. 268. The report on this is due in December, 1976. DELINEATION OF HAZARD ZONES A first step in developing a hurricane-resistant building standard is to spatially describe the physical forces of the hurricane in a quantitative manner. Much work has been done on the subject. A relatively simple procedure was developed to be used in conjunction with developing and applying minimum hurricane-resistant standards. This procedure utilizes a combination of analytical procedures and prima facie conditions* and draws heavily on existing practices. The result is four "zones," reflecting four different levels of exposure. They are: Zone A - Scour - Battering with Debris - Flooding - Wind (140 mph) Zone B - Battering with Debris - Flooding - Wind (140 mph) Zone C - Flooding - Wind (140 mph) Zone D - Wind (140 mph) Figures 1-1 and 1-2 illustrate the four zones and the type of destructive forces present in each. Section III is devoted entirely to how to determine the degree of exposure and Section II contains an extensive discussion of the processes involved. A brief discussion of a typical situation in each exposure zone is useful. e Zone A: An example of Zone A may occur on a barrier island and near the beach. The full fury of the storm's wind obviously strikes here. Much of the area is likely to be below 15 feet above sea level, and flooding is very possible. The waters could be moving at a velocity of several knots and be topped with violent waves of 5-10 feet. The water mass itself can exert a significant force, but this is compounded greatly with floating objects As used herein "prima facie conditions" refer to physical evidence, meteorological, geological, topographical, or hydrological, which may be in disagreement with the analytical results. In such cases, the specified prima facie evidence will govern. I-5 such as boats, vehicles, parts of other structures, etc. Few, if any, residential structures could be expected to survive the impact of a one-ton object moving at 10 feet per second (7 miles per hour). This violent water action can also be a very effective "ditch digger" and cause scour around foundations, walls, etc., and undermine structures that would otherwise survive. Figure 1-3 shows what kind of damage scour can do. While this condition will usually occur on a barrier island or on a Gulf-front area of the mainland where there is no barrier island, it could also occur on the shores of the major bays. o Zone B: The middle part of a barrier island, not at an exceptionally high elevation, and away from a washover channel would likely fall into Zone B. Such a place would be subject to the same destructive forces as Zone A, except scour, and could be located on the mainland near a bayshore. a Zone C: This zone could occur on the mainland at a considerable distance inland. Hurricane Carla (1961) caused saltwater flooding 10-15 miles inland across the low-lying coastal plain. Flooding is apt to occur even further inland along the many bayous, streams and other watercourses. * Zone D: Hurricane force winds (74 mph) may extend hundreds of miles inland. However, the extreme winds, i.e., 140 mph, begin to reduce rapidly as the storm loses energy as it moves over land. A procedure is given in Section III for estimating this wind reduction away from the water. These hazard zones are defined for a fairly narrow purpose: to enable a competent engineer to estimate the physical forces that are likely to be encountered at a specific building site. This information is then used to select the proper specifications from the model standard. When the specific parameters from the "Design Hurricane" are used in the analytical procedure, the result will be a location in one of these zones. 1-6 WIN 'tur FIGURE I-1 TYPES OF HURRICANE DAMAGE FOR DIFFERENT DEGREES OF EXPOSURE ," . ll l ..,-, . ,2 ,,--- --'--B-.. .. ... .- ` '-' b '- - " ' - -'- ' .' ._ ---vc ' - ov IGR I-1 TYE F URCAN DgAMAG F O IFEET ERESO XPSR W(IN Zones <T40 MpI A. I- -- . - - N WIND FLOODING j : ..ii.....ii .ii.i .......ii BATTERING S CO R :: SCOUR WIND 140 MPH C--.--7 B. WIND BA> X NBA-fTErIN6 WIND 140 MPH C. - WIMD fLODDING WIND 140- 0I0MPH <"; D .- v WI ND FIGURE I-2 (SAME AS FIGURE II-1) SCHEMATIC REPRESENTATION OF HAZARD ZONES A TO D IN TEXAS COASTAL AREAS. I-8 IAVE SC i JR STR UtTURES -AEN1M SECTION II NATURAL HAZARDS OF THE TEXAS COASTAL ZONE --: L. F. Brown, Jr., Robert A. Morton, Joseph H. McGowen, Charles W. Kreitler, and W. L. Fisher *CONTENTS. Introduction I Shoreline erosion 23 General statement I General statement 23 Natural hazards and land use 3 Shoreline monitoring program 23 Natural hazards of the Texas Coastal Zone 8 General methods and procedures 23 Acknowledgments 3 Definition 23 Hurricanes 4 Sources of data 23 General statement 4 Procedure 23 Development of tropical cyclones 4 Factors affecting accuracy of data 24 Characteristics of hurricanes 5 Original data 24 Related storm effects 7 Topographic surveys 24 Changes in water level 7 Aerial photographs 24 Waves 7 Interpretation of photographs 25 Development of washover (breach) channels 7 Cartographic procedure 25 Rainfall 8 Topographic charts 25 Wind S Aerial photographs 25 Generalized hurricane model S Measurements and calculated rates 25 Storm approach S Justification of method and limitations 26 Landfall S Results of historical monitoring program 26 Hurricane aftermath 9 Gulf shoreline erosion 26 Types of hurricanes 9 Bay shoreline erosion 27 Hurricane Carla 9 Factors affecting shoreline changes 27 Hurricane Beulah 10 Climate 27 Hurricane Celia 11 Storm frequency and intensity 28 Factors influencing severity of hurricane impact 11 Local and worldwide sea-level conditions 28 Nature of the storm 11 Sediment budget 28 Shoreline characteristics 12 Factors aggravating erosion 29 Population density 14 Long-term trends in shoreline position 29 Prediction of severe hurricane damage 14 Potential mitigation of shoreline erosion 29 Mitigation of hurricane impact 14 Land-surface subsidence 30 Flooding 16 General statement 30 General statement 16 Cause and mechanisms of land subsidence 31 Flooding processes 17 Extent of land subsidence 33 Hurricanes and tropical storms 17 Problems caused by land subsidence 34 Storm-surge tides 17 Mitigation of land subsidence and associated problems 34 Rainfall flooding 17 Faulting 3 Frontal-related storms 17 General statement 35 Flood-prone areas i s Extent of active faulting 35 Storm-surge tidal flooding i s Identification of active faults 35 Stream flooding and ponding 20 Gooi otoso alig3 Predicting flood-prone areas 21 Gooi otoso alig3 Mitigation and aggravation of flooding 21 Methods of fault activation 36 Natural flood protection 22 Mitigation of problems associated with faulting 38 Land use and coastal flooding 22 Conclusions 39 Flood prevention structures 22 Selected reference 41 * INTRODUCTION * The Texas shoreline is characterized by inter- connecting natural waterways, restricted bays, lagoons, and estuaries, low to moderate fresh-water inflow, long and narrow barrier islands, and extremely low astro- nomical tidal range. Combined with these natural The Texas Coastal Zone is marked by diversity in coastal environments are bayside and intrabay oil gIis richly fields, bayside refineries and petrochemical plants, geogrphyresorcesclimte, nd inustr. Itdredged intracoastal canals and channels, and satellite endowed with extensive petroleum reserves, sulfur and salt, seaports, intracoastal waterways, mild climate, industries. Exploration and development of offshore good water supplies, abundant wildlife, rich agricul- oil and gas resources are also under way. tural lands, commercial fishing resources, unusual recreational potential, and large tracts of uncrowded Tea foastaliZon, hati on, an recre area for industrialization, urbanization, and recre- land. The Coastal Zone, as herein defined, is a vast ational development. The zone is characterized by a area of about 18,000 square miles, including approx- imately 2,075 square miles of bays and estuaries, 367 chemic al physical concern and mile ofGulfcoatlin, ad 1,00 ilesof ay, chemical processes. Of critical concern to Texans, however, are those natural processes which constitute estuary, and lagoon shoreline (table 1). About a hazards, both to property and life in the Texas Coastal quarter of the State's population and a third of its Zone. This atlas is dedicated to a better understanding economic resources are concentrated in the Coastal of these natural hazards, their processes, impact, and Zone, an area including about 6 percent of the total possible mitigation. area of the State. Texas is subjected to a diversity of natural haz- ards, most of which impact upon the dynamic Coastal Table 1. Statistical information for the area covered by Zone and immediately adjacent inland areas. Principal the Natural Hazards Maps. All data by Texas Bureau of among these natural hazards are (1) shoreline erosion, Economic Geology, except areas of Hurricanes Carla and Beulah (2) land-surface subsidence, especially in the upper salt-water flooding and areas of Beulah rainfall flooding. After Coastal Zone, (3) frequent and damaging hurricanes, U. S. Army Corps of Engineers (1962, 1968). (4) flooding from streams and hurricane-tidal surges, and (5) active surface faulting. Each of these hazards Number of hurricane landfalls, 1900-1972 27 results in substantial physical and monetary losses; Area (square miles) of salt-water flooding, Hurricanes hazards such as flooding and hurricane impact also Carla and Beulah 3,164 have resulted in the loss of many lives. In addition, Area (square miles) of fresh-water flooding, Hurricane the areal extent of certain of the hazards, such as Beulah 2,187 subsidence and active faulting, is increasing in size Area (square miles) of fresh-water flooding by hurricane each year. In all cases, more extensive development in rainfall (floodplains), northern part of Coastal the Coastal Zone means that there will be greater Zone only 2,073 impact from natural hazards in the future unless Area (square miles) below elevation of 20 feet (MSL): adequate mitigation is undertaken. subject to salt-water flooding by tidal surge 5,787 Number of active or potential hurricane washover The most effective and, in some cases, the only channels 137 mitigation of natural hazards and resulting damage is Number of miles of Gulf beach erosion: greater than 10 to avoid certain uses of hazard-prone lands. Mitigation feet per year (long term) 47 by selected use requires, however, that the extent, Number of miles of Gulf beach erosion: from 5 to 10 feet frequency, and impact of natural hazards be known. per year (long term) 50 The basic goal of this atlas, "Natural Hazards of the Number of miles of Gulf beach erosion: from 0 to 5 feet Texas Coastal Zone," is identification of the principal per year (long term) 104 natural hazards of the Coastal Zone (fig. 1), delinea- Number of miles of bay and lagoon shoreline erosion 408 tion of hazard occurrence and distribution, recognition Area (square miles) of land subsidence: greater than 5 feet 227 of the natural and man-induced causes of these haz- Area (square miles) of land subsidence: from 1 to 5 feet 1,080 ards, and evaluation of measures that may lead to Area (square miles) of land subsidence: from 0.2 to 1 foot 5,422 mitigation of hazard impact. Number of miles of known active surface faults 96 Number of miles of Gulf shoreline 367 The Bureau of Economic Geology, The University Number of miles of bay-lagoon shoreline 1,100 j of Texas at Austin, has conducted a variety of re- Area (square miles) of bays and lagoons 2,075 [ search programs in the Texas Coastal Zone. The Area (square miles) of land in map area 18,000 primary program has been the preparation of an extensive "Environmental Geologic Atlas of the Texas Coastal Zone." The Environmental Geologic Atlas is a TEXAS ORINGE . HOUSTON , AHUR INDEX COLORADO 9 sEAUMONT- W . \ PRT ARTHUR AREA ' ALVESTON-HOUSTON g \ m AVREA ./,CRX- t \BAY CITY- I \_ .' ' 9 ' J /BY CITY-FRMEEPORT ARE I- - ad AREA RONVILL- 0 0 cto / PORT LAVACA X1 \-- K)H AREAIGEN A ."CO H$ FRPU S CHRISTI i ,/I CHRISTI am AREA IONZ. KINGSVILLE AREA BROWNSVILLE / AREA ' I hiOALGO \ 1 __<-W 0 HARIN GEN , Scale in Miles Figure 1. Index of Natural Hazards Maps of the Texas Coastal Zone. series of seven individual atlases designed to provide a intervals using available, controlled aerial photographs comprehensive inventory of the land, water, and and coastal charts, along with surveyed beach profiles, natural resources of the Texas Coastal Zone. Further, the historical rate of change of the Gulf shoreline and the 63d Legislature of the State of Texas, through a related natural features has been determined. Recogni- special line appropriation, directed the Bureau of tion of the major natural hazards of the Coastal Zone Economic Geology to conduct a program involving the and consequent impact was an outgrowth of these historical monitoring of the Texas Gulf shoreline. By investigations of shoreline change, as well as the result mapping the shoreline position at selected historical of mapping and analysis as a part of the "Environ- II-2 mental Geologic Atlas of the Texas Coastal Zone." In this atlas, natural hazards are discussed in Various natural hazards in the Texas Coastal Zone terms of distribution and occurrence, processes and have been evaluated in a number of reports already causes, impacts, and mitigation and reduction. This published or currently in preparation. This report is text, as well as the figures and tables, is intended to intended primarily to summarize in a general way the provide a perspective which will enable the reader to current knowledge of the distribution, nature, and better understand and interpret the maps of the atlas. impact of these natural coastal hazards. Inclusion of areas of coastal hazards, except for the flood-prone areas of the upper Texas Coastal Zone, is based on actual, recent occurrences that have been NATURAL HAZARDS AND LAND USE observed, monitored, or measured. The hazards are The subject of land use, and especially any defined on the basis of data available in 1974; addi- Tcnsideration of land- use m anagement, is complex. In tional information in the future certainly may permit consideration of land-use management, is complex. In the case of lands subjected to hazardous coastal pro- improvement of the accuracy of the maps. cesses, however, the application of any measures, The seven maps of the atlas (fig. 1) each contain whether voluntary or obligatory, structural or non- ae lend as was o h convn a descriptive legend, as well as other conventional map structural, that lead to the reduction and mitigation of symbols. The base map was constructed from 350 symbols. The base map was constructed from 350 damage caused by these natural hazards, is beneficial. U. S. Geological Survey 7.5-minute quadrangle maps Nevertheless, a number of problems are involved in propvermitigti rs, ana umbe offrobemus a r by the cartography section of the Bureau of Economic proper mitigation. First, an adequate effort must be Geology. The scale of the maps is 1:250,000 or 4 expended in delineating hazard-prone lands and in determining the economic impact of selected use of miles per inch. Sources of map data, as well as credits, determining the economic impact of selected use of are listed in the legend of each map and are further hazard-prone lands. Second, the economic incentive are listed in the l egend of each map and are further for mitigation is largely negative; it is unlike the documented in the following text. Although this atlas is the collective product of the listed writers, each positive incentives for the effective management of individual writer assumed principal responsibility for agricultural lands. Finally, the kinds of cost-to-benefit preparation of one or more secti ons: Introduction and preparation of one or more sections: Introduction and ratios involved for various, specific uses of hazard- Conclusions-. L. Fisher and L. F. Brown, Jr.; Conclusions--W. L. Fisher and L. F. Brown, Jr.; prone lands must be determined. In some cases, prone lands must be determined. In some cases, Hurricanes-J. H. McGowen; Flooding-L. F. Brown, damages and losses sustained in utilizing certain Jr . ; Shoreline Erosion-R. A. Morton; Land-Surface Jr.; Shoreline Erosion--R. A. Morton; Land-Surface hazard-prone lands may be offset by significant eco- nomic gain. For example, the agricultural use of Subsidence--W. L. Fisher; and Faulting--C. W. Kreitler. nomic gain. For example, the agricultural use of floodplains may result in periodic crop damage and loss by flooding, but the overall high yield from these Information and data for several of the natural fertile lands justifies their continued use. Clearly, a hazards reported herein are available in more detailed different cost-to-benefit ratio exists in the use of form and on more detailed base maps; these sources floodplains for residential development. In another are cited in this report. In addition, more detailed example, the use of ground water in the Coastal Zone information on shoreline erosion exists on work maps results in substantial annual savings over the cost of on file at the Bureau of Economic Geology. transport and treatment of surface water. The with- drawal df ground water, however, causes subsidence ACKNOWLEDGMENTS and some associated problems which result in property damage and land loss. Natural hazards and measures Many staff members of the Bureau of Economic for reduction of losses should be considered logically Geology contributed to the preparation of this report. in the context of both costs and benefits for specific Cartographic preparation of the maps was by R. L. uses of hazard-prone lands. Dillon, Barbara Hartmann, and D. F. Scranton under the direction of J. W. Macon, chief cartographer. NATURAL HAZARDS OF THE TEXAS Research assistance was provided by the following COASTAL ZONE staff members: M. Amdurer, J. L. Brewton, C. L. Burton, A. C. Funk, M. K. Pieper, and P. M. Walters. Natural hazards in the Texas Coastal Zone and The manuscript was typed by Sharon E. Polensky and immediately adjacent land areas can be classified into Jamie L. Tillerson. The report was edited by Kelley two general categories. Some of these hazards are two general categories. Some of these hazards are Kennedy, Elizabeth T. Moore, Leslie Jones, and Karen dynamic, relatively short-term events, such as hurri- M. White. Camera-ready copy was prepared by Fannie M. White. Camera-ready copy was prepared by Fannie canes and flooding; the more obvious impacts are M. Sellingsloh and Dawn M·. Weiler. known, even if not always fully respected. Other hazards, such as shoreline erosion, land-surface subsi- The manuscript was reviewed by E. G. Wermund dence, arid active surface faulting, are relatively long- and M. K. Pieper, Bureau of Ecanomic Geology; R. 0. term processes; they are commonly less dramatic and, Kehle, Department of Geological Sciences, The for the most part, are neither widely recognized nor University of Texas at Austin; and J. C. Moseley, appreciated. Executive Director, Texas Coastal and Marine Council. II-3 * HURRICANES 0 Table 2. Beaufort scale of wind force. After Dunn and GENERAL STATEMENT Miller (1964). Hurricane approach and landfall may drastically Beaufort No. MPH Knots ClassificatherBuea change the shoreline and damage or destroy man-made Casfcto structures. Large, steep waves riding the crest of a storm surge erode beaches, dunes, and cliffed bay 0 1 1 shores and destroy inadequately designed buildings. 1 1-3 1-3 Light The storm surge inundates low-lying areas along Gulf 2 4-7 4-6 and mainland shorelines with salt water, and severe storm-surge flooding may destroy large areas of natural 3 8-12 7-10 Gentle vegetation and agricultural crops. Fresh-water flooding 4 13-18 11-16 Moderate produced by torrential hurricane rainfall may be par- 5 19-24 17-21 Fresh ticularly destructive along natural drainage systems. Hurricane winds may damage or destroy man-made 6 25-31 22-27 Srn structures, with mobile homes particularly vulnerable 7 32-38 28-33 Srn to wind damage. Because of the direct and pervasive relationship of hurricanes and many natural coastal 8 39-46 34-40 Gl hazards, an understanding of hurricanes is important. 9 47-54 41-47 Gl DEVELOPMENT OF TROPICAL CYCLONES 10 55-63 48-55 WoeGl 11 64-73 56-63 WoeGl A hurricane is a storm of tropical origin with a cyclonic wind circulation of 74 miles per hour or 12 74 or 64 or Hurricane higher (Dunn and Miller, 1964). The cyclonic atmo- >74 > 64 spheric system is characterized by decreasing baro- metric pressure toward the center and by surface winds. In the northern hemisphere, these surface winds spiral counterclockwise upward, lifting the air and eventually producing clouds and precipitation. strike the Texas Coast occur most frequently in August and September (fig. 3). The mean storm track The hurricane is the devastating end member of and the area of most frequent origin change from the tropical cyclone class of storms. The classification month to month during the hurricane season. Storms that is commonly used in the Atlantic region (table 2) spawned at a particular time and place have a pre- is as follows: (1) tropical disturbance-rotary circula- ferred landfall area (Dunn and Miller, 1964). The most tion slight or absent on the surface; no closed isobars frequent landfall area for storms that develop in the (contours of equal pressure) or strong winds; common northwestern Caribbean or the Gulf of Mexico in June throughout the tropics; (2) tropical depression-one or is the Texas Coast. The Texas Coast is rarely struck by more closed isobars; wind equal to or less than hurricanes after the middle of September. Beaufort 7; (3) tropical storm-closed isobars; wind greater than Beaufort 7 but less than 12; and (4) hurricane-wind force of Beaufort 12, or 74 mph or greater.20 0lO 0 0900 30 0 000 0 The precise details of physical processes that > produce hurricanes are not well understood. It is I j( j70 known, nevertheless, that the mechanism producing hurricanes must supply (1) low-level atmfospheric con-- vergence of sufficient strength to lift the moist layer; > J (2) high-level atmospheric divergence to remove accu- o - mulated air and yield a pressure drop at the surface; -- and (3) energy to maintain the atmospherict- tj circulation.V1- t Conditions favorable for tropical cyclone develop- ment exist in the North Atlantic Ocean, the Caribbean Figure 2. Areas of tropical cyclone development. After Dunn Sea, and the Gulf of Mexico from June through and Miller (1964). October (fig. 2). Tropical storms and hurricanes that 11-4 hurricane vortex. The Intertropical Convergence Zone 200- is the area where winds from the North and South Atlantic converge. When the ICZ moves north or south 190- of the equator, the Earth's rotation imparts a spin to W)180- TROPICAL CYCLONES converging currents, thereby developing tropical cy- a, clones. In the North Atlantic this occurs near Cape .170- HURRICANES ' Verde. A polar trough is a low-pressure zone which OD0_ I migrates from west to east within the prevailing -160- HURRICANES THAT westerles. The westerlies lie north of the Azores- STRUCK THE TEXAS 50U- TCOAST / Bermuda High. When the polar trough is very strong _150t- / \ or when the Azores-Bermuda High is weak, the trough 40- may penetrate the tropics. Its influence on the devel- 130 - opment of tropical cyclones is greatest either early or 130 - | tlate in the hurricane season. 120- - "l / I 0- / 100o 80 600 400 20° 0o 0100- ' I <50 - IL 40- 10 zo 38 0- r I t\k I ,a0° 4 81 ¢ L;'? 61° ' B o 400 20 720- Figure 4. Mean position of the Azores-Bermuda High during z0 - Dunnand Miller (1964). m/ .10 00 1 /"X MONTHS OF THE YEAR A hurricane runs on heat. Its formation and Figure 3. Frequency of Atlantic tropical es and maintenance depend upon en -Bermuda High dring hurricanes and the number of hurricanes that struck the Texasr Coast between 1887 and 1958. Data from Dunn and Miller ocean surface. Hurricanes form over comparatively (1964). warm water with a temperature above 79°F. Warm moist air moves across the ocean surface spiraling inward into the hurricane circulation. As it rises to hurricanes and the number of hurricanes that struck the Texas Atmospheric conditions or elements that directly higher elevations, it expands under reduced pressure. or indirectly contribute to the formation of tropical When the air becomes saturated, moisture condenses cyclones are (1) the Azores-Bermuda High, (2) easterly waves, (3) the Intertropical Convergence Zone, and (4) and releases heat to the surrounding atmosphere. polar troughs. The Azores-Bermuda High is a large Energy is partly dissipated in the upper anticyclonic anticyclone extending from the Iberian Peninsula to flow by surface and internal friction. the southeastern United States (fig. 4). It is the dominant atmospheric system for the Atlantic during summer and early fall when the High oscillates from CHARACTERISTICS OF HURRICANES north to south (Dunn and Miller, 1964). Persistent departures from normal position have a significant The principal features of a hurricane are (1) the effect on hurricane frequency and paths. The easterly eye, surrounded by convective clouds; (2) low-level wave is a low-pressure trough which is imbedded in cyclonic winds; (3) upper level anticyclonic winds; and the easterly current lying south of the Azores-Bermuda (4) a vertical circulation system in which air flows into High. A stable wave may move from east to west as the eye at low levels, flowing upward within the much as 3,000 miles without any change. Deviation convective clouds, outward in the upper levels, and from the norm indicates that the wave is developing a downward in the outer parts of the storm (fig. 5). TT-5 Table 3. Hurricane classification. After Dunn and Miller Y ----- _50,000 (1964). ' -- --------------- opooo .... . ' , - -, -4 ....'-'-= -- .0,000 20,000 EClassification Maximum winds Minimum central pressure ;----20,000 Classification (mph) (inches Hg) iO.000 ' (i) Minor Less than 74 More than 29.40 LEFT SIDE RIGHT SIDE Pr,-ory Energy Cell ( Hol Towers") Coneecfive Clouds M Allootrls Corrus Minimal 74 to 100 29.03 to 29.40 Figure 5. Hurricane model. The primary energy cell (convective chimney) is located in the area enclosed by the broken line. After Major 101 to 135 28.01 to 29.00 Carr (1967). Extreme 136 and higher 28.00 or less The eye of the hurricane is a low-pressure area where wind velocities are only 10 to 20 mph. The eye may be relatively small, only 4 miles in diameter, or Table 4. The nature of hurricanes striking the Texas Coast large, up to 25 miles in diameter. Average diameter is between 1900 and 1972. Dash indicates that data are unavailable. about 14 miles (Dunn and Miller, 1964). Data from National Oceanic and Atmospheric Administration- National Hurricane Center (1900-1974). Note that data do not necessarily agree with that provided by U. S. Army Corps of Air flows from high-pressure areas toward the Engineers (1962, 1968, 1971a). low-pressure storm center. The pressure differential results primarily from temperature differences. Strongest hurricane winds are near the storm center .... r .. [.. .. because this is the area with the steepest pressure .. No, .. 2.5 -o 270 Or 50 000 6 6a 'Leon ' gradient (fig. 6). Lower level winds have sustained 9............. velocities ranging from 74 to 200 mph; the velocity of [ III.. Coor. .. 1510 Son, 70 lI 120 N -p a gusts may exceed sustained winds by 30 to 50 per- rrd cent. Winds are stronger on the right side of the N`.. . .10- -. 00 . ... hurricane eye (fig. 5) because the forward motion of .......... O975 1 70 -7 orpo b.ro 000G 6 S IC6 r 500000 rrr 21 the storm is added to the rotational wind velocities. oI ]19o Por o 0016 App 70 II mph6 730m -o 000 00' Oor2 o Oolt d 07 00 0000 00 Nolrornd PaOolodtre s oIn ol; · l( ..... 7070 Sop' 70 73 nor 700 oor 0799 70 Coo,- 2000 ro 000 , Noo1'oI- 0 0,0d 000 120 I I Ip I 1 0 21 ll 5 Ir I SSoOno lal 20 ... . ....... rr......r, I 7002 00 h 0 1p0 Oro 61 2lon S, 5000000 00 lit 0 ,,19233 5ep t 4-6 linpr OOmph 0000 1 r,,. 012000000 40 CON No1 name 35rawnswfico ?0 6g 0mp0 0- 0p 08 8 " 2 la 1 aI SI 500r00OpS 80- Al ESTHER oo or 0 o - / 'P \oo'\ 7007 14 sopt 03 1 3 mo 90-p 0007 2 3 1 '00 5 agn 6000 000 4 Rn i 'L DOSTNC NP IAL ........... UJ N. Nrd O Figure 6, Wind profiles in Hurricanes Donna, 1960, Esther, t .. d a Do a 6. N DONNA 754 4o 000 - 2 r78 ' 090 P 0,otliohoo -l 5 000000 UJl ao An, PS. , opn . 0,66a, u3 ! / " ' ANNA 194S I U ) .:N$ .S O27 Omh 10 p 2851 IS olaa 20?133,000 3 4 0 -4 -l. ....... ..,o Ia o G O 1 I 1'N 1900 Aug 0 30 0 ,r j4 770 ob 3070 Sabine Pa S20. 0 I000 I 9194 Oc 3 1 3ml 135 mb 28 I 10 Fre-ot S6.o 1Ono0S 20 1959 5oocoo .,0. , 9 1 no l 1r 00r9 Opool oIh Slhrro'COOO- 4 00 29 07 2 N8o' 000y00700 $oO 196o Sep0 [ - P3noh [ 750" 'ooo L 5300,000 ,3 2 Cn 50700r 0'¢o0n0, 70 00 70or I0 Io I 000 I Ira000, 6100303 9070000, h 0p ro94o1 - 2Hg114i 1 700 9117700 3 20 40 60 8 - OO 120 Oro. 00704.6 0201 ...6o. . ....ooooo 0.... RADIAL DISTANCE (NAUTICAL MILES) 730 20 80 0 I- 000 I0 Figure 6. Wind profiles in Hurricanes Donna, 1960, Esther, [s7, r 0 000000 1961, and Anna, 1961. After Col6n (1966). 11-6 Hurricane size is commonly expressed in terms of Waves diameter of hurricane and gale winds or by diameter of the outer closed isobar. Average diameters of Principal damage to man-made structures and hurricane and gale winds are about 100 and 400 miles, severe erosion of shorelines are produced by storm respectively. There is a wide range in the size of waves superimposed on the storm surge. The power hurricanes. The Great Atlantic Hurricane of 1944 had generated by a breaking wave can be visualized by hurricane winds with a diameter of 600 miles (Dunn considering that a cubic yard of water weighs about and Miller, 1964). Hurricane Carla, in 1961, had 1,500 pounds and that waves may be moving at a hurricane-force winds with a diameter of about 300 velocity of about 70 to 80 feet per second. Breaking miles (Colon, 1966; Hayes, 1967), and in 1970, Celia's waves alone can destroy many buildings, but their hurricane wind diameter was about 80 miles. destructive potential is significantly increased by tree trunks, pilings, and other debris that act as battering Hurricane size and intensity are not directly rams. Appropriately designed structures, nevertheless, related. The most intense hurricanes are not neces- can withstand flooding associated with the forerunner sarily the largest; for example, the diameter of cy- and storm surge. clonic circulation tends to increase during the decaying stage (Colo'n, 1966). Low barometric pressure and The shoreline may retreat several hundred feet relatively high wind velocity are common to all trop- during a few hours when under attack by storm waves ical disturbances (table 3), and these parameters are (Shepard, 1973; McGowen and Brewton, 1975). more suitable for classifying hurricanes (Dunn and Between hurricanes, accretion may restore much of Miller, 1964). the shoreline lost during the storm. Maximum surge height is commonly associated Average fife of a hurricane, determined by time with a storm which has a track perpendicular to the and place of origin and rate of forward movement, is shoreline. It is also greatest along coasts, such as the about nine days. Most hurricanes move forward at a Texas Gulf Coast, that are concave and adjacent to rate of about 12 mph. The forward speed of hurri- wide, gently sloping shelves. If the hurricane landfall canes that have struck the Texas Coast in August and coincides with the astronomical high tide, surge height September has averaged 8 to 12 mph. Hurricanes that will be even greater. struck the Texas Coast between 1900 and 1972 The rare "hurricane wave" or seiche has caused exhibit a wide variety of characteristics (table 4). some of the world's greatest natural disasters (Dunn and Miller, 1964). It may result from resonance that produces a huge wave, or it may be a rapidly rising RELATED STORM EFFECTS and abnormally high storm surge. The hurricane that struck Galveston on 8 September 1900 may have been Hurricanes produce striking changes in the sea; accompanied by such a hurricane wave. During the huge waves and storm tides are generated. Hurricanes Galveston storm, water level rose steadily from 3:00 also trigger heavy rainfall, create high-velocity winds, to 7:30 p.m., at which time there was an abrupt rise, and spawn tornadoes. As the storm approaches and of about 4 feet in as many seconds (Dunn and Miller, makes landfall, each of these related phenomena 1964). becomes increasingly more important because hurri- canes have the potential to alter the shoreline by Development of Washover (Breach) Channels erosion or deposition, to flood low-lying areas, and to damage or destroy man-made structures. One of the principal effects of the storm surge is the development of washover channels that breach Changes in Water Level barrier islands or peninsulas. These channels readily develop at the sites of eolian erosion (blowouts) or in A slow rise in water level occurs when oceanic areas with poorly developed fore-island dune ridges swells generated by a distant storm approach the and beach ridges. Tidal waters flow landward through coast. This rise in water level is known as the fore- the channels, scouring sand and depositing the sedi- runner. A rise in water level of 3 to 4 feet, produced ment in washover fans within the adjacent bay or by the forerunner, can affect several hundred miles of lagoon. Following passage of the hurricane, the coast (Dunn and Miller, 1964). Storm surge, on the channels serve to return the elevated waters of the other hand, is a rapid rise in water level generated by bays and lagoons to the open Gulf. The surge channels onshore hurricane winds and decreasing barometric are active only during the brief period of hurricane pressure. Maximum storm surge generally occurs 10 to approach, landfall, and immediate aftermath; storms 20 miles to the right of the storm track, but it may tend to reactivate the same wash-over channels. Marine occur to the left of the storm if counterclockwise shoreline processes close the gulfward end of the north winds stack water against an obstruction, such channel within a few days. Water may stand in the as the back side of a barrier island. abandoned channel for months following the storm. 11- 7 In general, the density of washover channels Storm Approach increases southwestward along the Texas Coast. This regional increase in channels results principally from Storm approach (fig. 7B) is marked by rising the southwestward decrease in vegetational stability of tides (forerunners) and increased wind velocities. When barrier islands and fore-island dunes. A total of 137 the storm strikes the coast, the storm surge and washover channel sites have been recognized and are associated waves erode the normal beach and asociaed waes eofr roade lt he nrmcal beach an shown on the Natural Hazards Maps. The location of foredunes to form a broad, flat hurricane beach. these sites is based on interpretation of aerial photo- Storm-surge flooding often scours washover channels low-level aerial reconnaissance, and field work across barrier islands and peninsulas. Sediment is trans- graphs, low-level aerial reconnaissance, and field work undertakenaspartoth "Envionmeported through the storm channels and is deposited on undertaken as part of the "Environmental Geologic Atlas of the Texas Coastal Zon e." Construction within barrier flats and along bay margins as washover fans. Atlas of the Texas Coastal Zone." Construction within Miln hrlnsrciemdysdmn hti Mainland shorelines receive muddy sediment that is or immediately adjacent to hurricane breach or surge deive fm th a i derived from the bay bottom and carried ashore by channels may lead to property damage in the event of rie foosStom-re d are y a hurricane landfall. storm-surge floods. Storm-surge tides are commonly higher in the bays than on the Gulf beaches, although Rainfall the flooding and the effects of the accompanying waves are pronounced in both areas. Some of the greatest rainfalls recorded in Texas have resulted from hurricanes. Upon striking a land- Landfall mass and moving inland, the forward movement of a hurricane is reduced, and the rate of rainfall increases. At landfall (fig. 7C), when the storm passes over Maximum rainfall occurs in front of and along the the shoreline, the direction of current movement and right side of slowly moving tropical storms. Rainfall is wave approach shifts into compliance with the change equally distributed in the front and rear halves of in wind direction. Highest intensity winds are felt as storms whose forward motion has stalled. the storm comes ashore. On the left side of the storm, water and sediment are moved from the bays back Wind into the Gulf through inlets and breaches in the island, while water and sediment are still being pushed into Hurricane winds rank third behind waves and the bays on the right side. Waves strike the Gulf rainfall flooding in destructive potential. Width of the h e a o the side the shoreline at a low angle as the back side of the storm area of destructive winds may range from about 14 to area of cile s (Duny andlefr, 194Wd v itisof passes, creating currents that transport sediment north- 300 miles (Dunn and Miller, 1964). Wind velocities of eastward alongshore in the same manner that the 100 to 135 mph are common. Severe storms have velocities of 135 to160mph;front-edge winds and currents had moved materials velocities of 135 to 160 mph; the most violent toward the southwest. toward the southwest. hurricanes have wind velocities of 200 mph or greater. Damage to structures results from sudden pressure A changes associated with gusts. Damage begins when pressure reaches approximately 15 to 20 pounds per square foot (wind velocity of about 60 mph). The highest velocity winds associated with hurri- canes are contained in tornadoes having estimated velocities of 400 to 500 mph. Tornadoes may occur at any time during and immediately following hurricane passage; their most frequent occurrence is in the ....... forward half of the storm. GENERALIZED HURRICANE MODEL PHYSICAL FRAMEWORK, TEXAS COAST Historical records indicate that successive hurri- .. canes may differ markedly (table 4). One hurricane .......... bo may generate a large storm surge, another may be < ... characterized by torrential rainfall, while exceptionally high wind velocities may define a third type. From these records and from previous studies, a general hurricane model (fig. 7) was developed (Price, 1956; Hayes, 1967; McGowen and others, 1970). The following is a description of a model hurricane as it approaches the Texas Coast,. makes landfall, and moves inland. / HURRICANE APP H ITT- TYPES OF HURRICANES During the past 70 years, most coastal areas in z/ _ = - . Texas have experienced severe weather resulting from direct impact or nearby passage of a hurricane. No area, however, has experienced each of the hurricane , : < =t_;:' < I *types which can strike during the hurricane season. Using meteorological and hurricane data accumulated over the past several decades, it is possible to rec- .= . C..- ·so ......... cC (x ognize at least three general kinds of hurricanes and to predict their impact on different parts of the Texas Coast (table 4). Predictability of hurricane effects is based on (1) bay-estuary shape, (2) Gulf shoreline configuration, (3) track of the hurricane relative to the HURRICANE LANDFALL coastline, (4) nature and distribution of physical and biological environments, and (5) population density. D Three recent, well-documented hurricanes, Carla, Beulah, and Celia, illustrate the nature of hurricane variations (table 5; fig. 8). The reader should be aware // __ DD that observations such as storm-surge elevation, hurri- cane wind velocity, and pressure values, may vary among observers. For this reason, the sources of the data are noted in this atlas; any inconsistencies in wind velocity or storm surge, for example, result from the use of several data sources. d T n A;]orI' nnl................... Hurricane Carla Hurricane Carla was spawned in the western HURRICANE AFTERMATH Caribbean on or about 3 September 1961. She became a hurricane on 5 September and moved into the Gulf Figure 7. Schematic model of hurricane effects on the Texas of Mexico between Cuba and the Yucatan Peninsula coastline. (A) Physical features characterizing the Texas Coast, on 7 September (Hayes, 1967). Carla moved toward (B) Effect of approaching hurricanes, (C) Effect of hurricanes the Texas Coast at about 9 mph, making landfall (fig. upon impact with coast, (D) Aftermath effects of hurricanes. 8) near Port O'Connor on 11 September (Port Lavaca After McGowen and others (1970). map). Her travel time over the warm waters of the Caribbean and Gulf of Mexico was about nine days. Hurricane Aftermath Maximum sustained winds at landfall were about 175 mph, and pressure in the eye was about 931 millibars Hurricane aftermath (fig. 7D) is the period following passage of the storm inland from the coastal Table 5. The characteristics of basic types of hurricanes area. As the storm moves inland, it becomes weaker striking the Texas Coastal Zone. After McGowen and others and more diffuse, and commonly spawns numerous (1970). tornadoes. Excessive water in the bays drains gulfward through storm breach channels and passes, depositing Variables Beeuah type Carl type Cea type sediment within the channels and in the nearshore Wind Moderote Moderate High Gulf. Heavy rains that commonly accompany hurri- Storm-surge canes produce runoff of flood proportion, inundating Stormsure Moderate Hgh Low low-lying areas along stream courses and bay margins. Rainfall High Moderate Low The influence of strong winds and heavy rains may accompany the storm inland for considerable destructive Medium Large Small destructive Medium Large Small distances. core Length of Longshore currents begin to build bars that even- aftermath Extended Intermediate Brief tually close off the mouths of hurricane channels, and effects waves begin to restore the normal beach profile. Character of Port Mansfield: Port O'Connor: Port Aransas: Hurricane deposits are reworked by subsequent rains coastline poorly vegetated, well vegetated, moderate vegetation, and wind. Some of the sand that is exposed in breach affected low relief, broad local relief to local relief to 30 feet, channels is blown landward onto the barrier flal, and unrestricted bay 30 feet, funnel-like funnel-like Nueces Bay washover fans are reworked by bay and lagoon waves Lavaca Bay and currents. II-9 .,,s. \,,,4CAL ....................WsSTR / ILA \ EA s 'SEAUM 75 8RA S.F Nfl l NS S25 SCA AjILE <IN M ILES IT 8 <' r - ' - I_1k , 'O t t \ 4/TW;-wt z 1 75MP ' CA RLA5 CELLA WNSV LLE NSVILLE -.2' '- . -- . .. '-4'.RRNS A T ORNADOES The trc , f t es . -i'vA an Ce a the area covere by YTGt Nwn s ICANE IN DS END T RNA i- S p - C . ,:i "i"( , 7 r s:: SCmE N MIS,)AES 25SAEIsMS A,(FAR, ° i' 175 MPH !.. t [..¥.rI.,TORNADOES NNVILLE Figure 8. The track of the eyes of Hurricanes Carta, Beulah, and Celia, and the area covered by hurricane-level winds, Texas Coastal Zone. Based on data from Cooperman and Sumner (1961), Orton and Condon (1970), Orton (1970), and U. S. Army Corps of Engineers (1968). After Texas Coastal and Marine Council (1974). (mb). The Galveston weather station was under effects Carla's track across the Gulf of Mexico was of gale-force winds for 49 hours (Colo'n, 1966). northwestward. After landfall, her course curved to Corpus Christi, only 50 to 60 miles from the storm the northeast, and she crossed the United States and center, experienced peak gusts of 85 mph and pressure entered Canada in the Great Lakes area. of 977 mb. Hurricane wind diameter was approx- imately 300 miles (fig. 8). Carla was probably the Hurricane Beulah largest Atlantic hurricane for which there are reliable data (Colon, 1966). Hurricane Beulah was spawned in the Atlantic, becoming a hurricane on 7 September 1967 (Scott and Carla was characterized by extensive storm-surge others, 1969). She moved west-northwestward into the flooding (fig. 9) and severe shoreline erosion. Surge Caribbean, lost considerable energy in the mountains height in the Port O'Connor area was in excess of 10 of Haiti, re-formed and assumed a more westerly feet above mean sea level (MSL), and at Port Lavaca, course crossing the Yucatan Peninsula on 17 Sep- the surge reached a maximum of 22 feet above MSL tember. She made landfall (fig. 8) in Mexico, just (U. S. Army Corps of Engineers, 1962). Parts of south of Brownsville, on 20 September (Brownsville- Matagorda Peninsula were breached by storm channels, Harlingen map). After becoming a hurricane, her travel anedshorelines were eroded as much as 800 feet time over the Caribbean Sea and Gulf of Mexico was (She pard n Be, 1973; McGowen and Brewton, 1975). Dunes 13 days. Maximum wind velocity at landfall was 125 on Mustang Island were eroded landward as much as to 160 mph. In Texas, winds of hurricane force 150 feet (Hayes, 1967). extended from the Rio Grande northward approx- the eye decreased in size by about 40 percent, and wind velocity increased from 90 to 130 mph with 20-" gusts of 160 to 180 mph. The width of Celia's /iX S BAY destructive path was about 15 miles, and her hurricane Om=OPEN GULF winds had a diameter of about 80 miles (fig. 8). w / x Celia's inland path was west-northwest to Del Rio -' / IXx where her progress became irregular. The storm X RIGHT SIDE expired in the mountains near Chihuahua, Mexico. 0 a: - / x XX 0 1o-/ Celia was accompanied by high-velocity winds 0 XOO0 and a few tornadoes. Rainfall was minimal and storm LEFT SIDE 0 surge was restricted to a very narrow zone. Maximum :D x / I surge (determined from debris lines and, therefore, not X < )p indicative of stillwater level) was about 9 feet along X the Gulf shore near the Aransas Pass jetties, 12 to 14 *- 0 feet along the bay shore at Aransas Pass, and up to 9 0 I/ 27 i i feet at Corpus Christi. Surge height in the North Pass PORT ISABEL EYE GALVESTON MISSISSIPPI RIVER and Corpus Christi Pass areas was Qnly 4 feet. Hurri- oF HURRICANE cane Celia was characterized by her destructive winds; storm-surge flooding and rainfall were relatively SW COASTLINE > NE insignificant. Figure 9. Maximum storm surge that occurred during Hurricane Carla, 1961, at 14 bay and 10 open Gulf localities FACTORS INFLUENCING SEVERITY along the northwest Gulf of Mexico. Note that the right side of OF HURRICANE IMPACT Carla generated greater storm surge than the left side of the storm. Based on tide data collected by the U. S. Army Corps of Engineers, Galveston and New Orleans Districts, and presented by The severity of hurricanes can be expressed in Cooperman and Sumner (1961) and Harris (1963). After Hayes various terms, such as damage to man-made structures, (1967). monetary losses, and loss of human life. The nature of the storm, population density, and shoreline charac- teristics determine the number of lives lost, the extent imately 250 miles (fig. 8). Storm surge was about 10 * feet above MSL at Brazos Santiago, and tides were 6 of shoreline erosion, and damage to or destruction of to 7 feet between Port Mansfield and Port Aransas and man-made structures. The nature of the storm dictates 5 feet near Cedar Bayou (Behrens, 1969; Scott and whether storm surge, fresh-water flooding, or wind will others, 1969). be the dominant destructive element. The loss of human life and the amount of property damage is After making landfall, Beulah traveled north- directly affected by population density. Shoreline northwestward inland into Duval County, changed her characteristics will either amplify or diminish some of course to the southwest, and moved back into Mexico. the hurricane processes. The long path overland slowed the storm, resulting in heavy rainfall and the generation of at least 115 tornadoes (fig. 8). Beulah was characterized by excep- tionally heavy rainfall; in some areas, rainfall was in hree destructive potential, exces of 0 inhes urin the our r fie das of hurricanes. In order of decreasing destructive potential, excess of 30 inches during the four or five days of te eae()somsreadatnatbekn aftermath storms, these are (1) storm surge and attendant breaking waves, (2) fresh-water flooding, and (3) wind. Assuming a common point of landfall, Carla-type Hurricane Celia hurricanes have the greatest destructive potential of the three basic hurricane types, Beulah-type storms Hurricane Celia was spawned in the Caribbean rank second, and Celia-type storms are the least de- Sea near Cuba. A tropical squall struck the western structive. A Celia-type storm, nevertheless, can become part of Cuba on 31 July 1970. On the morning of i highly destructive when it strikes a highly developed August, the disturbance became a tropical storm, and area (table 4). on the afternoon of 1 August, Celia became a hurri- cane (McGowen and others, 1970). Celia's course was Large, intense hurricanes, which create high west-northwest toward the Texas Coast, and her rate storm-surge flooding with attendant wave erosion, can of forward movement was 10 to 15 mph. She made be expected when a storm moves slowly across the landfall at Port Aransas on 3 August (Corpus Christi ocean without being impeded by landmasses en route map); her travel time over the Gulf of Mexico was to the Texas shoreline (Carla-type hurricane). The path only three days. At about the time she made landfall, that a hurricane takes after making landfall, the rate II-ll of forward movement, and the topography of the landmass over which it moves have an effect on rainfall rate, which dictates the magnitude of fresh- E AM water flooding. A long route over the ocean by a SALT slowly moving storm significantly increases the mois-A ture content of the storm clouds. Slow forward move- ment overland, coupled with considerable topographic relief, is conducive to high rainfall rates (Beulah-type VEGETATED FLATMAS hurricane). A hurricane that is spawned in the Gulf of ;BAR A Mexico and travels rapidly across the open Gulf willB most likely be accompanied by high-velocity wind, SHOREFACE FOREISLAND DUNES minimal rainfall, and minimal storm surge. These BC storms are generally small, but intense (Celia-type BESEACHED FLAT DUNESI hurricane). Shoreline Characteristics SHOREFACE Figure 10. Generalized profiles of types of Texas Gulf Coast The Texas Coast is characterized by an outer shorelines. (A) Headlands, (B) Peninsulas, (C) Barrier islands. Gulf shoreline and an inner bay shoreline (fig. 7A). Gulf shorelines exhibit -three principal morphological Peninsulas, which resemble offshore islands, are types: (1) deltaic headlands, (2) peninsulas, and (3) elongate strips of sand and shell that are attached to barrier islands. Bay shores consist of a variety of headlands and extend in the direction of longshore shoreline types; among these are (1) relatively high drift. Three peninsulas on the Texas Coast are Bolivar cliffs, (2) low-lying marshes, (3) bayhead deltas and Peninsula, Matagorda Peninsula, and south Padre river valleys, and (4) areally restricted sand and shell Island. A generalized profile across a peninsula is beaches. The shoreline type determines, in many in- illustrated in figure 10. stances, the extent of storm-surge flooding and wave erosion. Bolivar Peninsula (Galveston-Houston map) is Deltic hadlads ocurbetwen SbinePassandabout 23 miles long, is densely vegetated, and consists BoiaDensltaic h letIsandlands Bocubewen CaiedPass Cut, chiefly of fine-grained sand. It is characterized by Boiand thenRinuaFot Islande and BraoswSntig Peass CThe well-developed ridge-and-swale topography, and there twasendos theRoGandelands (BeaumosSnti-Por PAss.thuran is no evidence of recent storm erosion or breaching of Bay eastyreprnot heaplns) areaumontPrprholgcal siiar. Boilvar Peninsula by storm washover channels. Max- BaysCity-Freeportubdivisionsmorphhesgicwolheadmilar imum elevation along the seaward edge of Bolivar Pyincludehic surbdivi 2)ersional oftescapentwo hedands Peninsula is about 10 feet above MSL. Several storm- (3) shell apron or ramp (fig. 10). A shell ramp, which surgetatioon hasvprevented the peiscuring but chanselan is about 5 to 7 feet above MSL, is commonly backed dvegeltonhspreenteof ative wscoverin ofcannes.an by marshes with attendant lakes and tidal creeks. d vlpeto ciewsoe as These low-relief shoreline features are readily breached Matagorda Peninsula (Bay City-Freeport map) is by storm surge and adjacent marshes are commonly about 51 miles long. The eastemnmost three miles of flooded. With the exception of part of the Modern the peninsula is separated from the western segment Brazos delta, the Texas coastal headlands erode rapidly by Brown Cedar Cut, a tidal pass created by a under normal sea conditions and erode excessively hurricane breach channel. Greens Bayou, similar to during storms. Incipient dunes occur along the Brown Cedar Cut, is open only during and shortly headlands; most dunes are destroyed by storm surge following the passage of hurricanes. and breaking waves. The elevation of Matagorda Peninsula averages 5 The Rio Grande deltaic headland (Brownsville- to 7 feet above MSL. Continuous low dunes, 8 to 12 Harlingen map) is characterized by sand beaches and feet above MSL, extend from the mouth of the fore-island dunes. The vegetated dunes locally are 30 Colorado River eastward for about 8 miles, and from feet high. Breaks in the fore-island dune ridge may be Greens Bayou westward to within a mile or two of a few hundred feet to a mile wide. The storm-tidal Pass Cavallo. Storm washover channels are common surge commonly breaches and scours the low areas along the peninsula. Spring high tides and forerunner between dunes and floods the Rio Grande delta plain tides associated with distant storms frequently over- and adjacent lowlands. Shoreline erosion is excessive wash beaches adjacent to storm channels. Most of even under normal sea conditions, but under storm Matagorda Peninsula is overwashed by 5- to 7-foot conditions, shorelines may retreat a few hundred feet storm surges. Continuous dunes with heights greater within a few hours. Post-storm processes may accrete than about 10 feet afford some protection from storm the shoreline to its approximate prestorm position. surge. 11-12 During major storms such as Hurricane Carla feet with some peaks up to 30 feet above MSL. In (1961), two types of washover deposits are developed historical times, hurricanes have not scoured washover along Matagorda Peninsula: shell ramps and washover channels across the island, but because of the devel- fans. Shell ramps are long berms that parallel the opment of several blowouts during the past few elongate peninsula. Individual ramps are a few miles decades, breaching may occur in the near future. long and 180 to 2,180 feet wide. Washover fans are lobate sand-shell bodies that accumulate at the bay St. Joseph Island (Corpus Christi map) also dis- terminus of storm channels that transect the peninsula. plays prominent ridge-and-swale topography. Veg- Small storm surges reactivate the channels and some- etation on the island is less dense, and blowouts are times construct a washover fan along the bay margin. more numerous than on islands to the east. Average Large storms with 10 to 11 feet of storm surge cut elevation of St. Joseph Island is slightly more than 5 the peninsula into numerous small islands separated by feet above MSL. Vegetated fore-island dunes average channels up to 1,700 feet wide. These same storms about 15 feet above MSL; there are some dunes that also may erode the shoreline as much as 800 feet extend to 35 feet above MSL. Active washover (Shepard, 1973). channels occur at the extreme northeastern and south- western ends of the island (Price, 1956; Andrews, In South Texas, the gulfward part of the Rio 1970; Nordquist, 1972). North Pass was formed by a Grande delta grades northward into south Padre Island major hurricane in 1919 (Price, 1956; Nordquist, (Brownsville-Harlingen map). South Padre Island, 1972). Approximately 9.3 million cubic yards of sedi- which originated as a peninsula, is now separated from ment accumulated along the bayward terminus of the the deltaic headland of the Rio Grande by Brazos washover channel as a consequence of hurricane Santiago Pass. South Padre Island is characterized by activity, beginning with the 1919 hurricane and sand and shell beaches, sparse vegetation, and poorly continuing through 1971. developed fore-island dunes. Its morphology is the product of combined wind and storm activity. There is Mustang Island (Corpus Christi map) is a broad little natural defense to prevent breaching of south barrier which has an average elevation of about 7 feet. Padre Island by storms of the magnitude of Carla It does not display ridge-and-swale topography. Veg- (1961) and Beulah (1967). Flow across the island is etated fore-island dunes have an average elevation of virtually unconfined during principal hurricanes; for about 15 feet above MSL and a maximum elevation of example, south Padre Island was highly segmented by about 50 feet above MSL. Vegetation is less dense on washover channels during Hurricane Beulah. Active Mustang than on islands to the northeast; conse- dunes on south Padre Island range in height from 5 to quently, blowouts, hurricane breaches, and washover 25 feet above MSL, but they present little resistance channels are more numerous. Two factors contribute to tidal flow once a storm breach has been opened. to the increased frequency of storm channel breaching Width of storm breach channels ranges from about 0.2 on southern Mustang Island. First, there is a south- to 1.0 mile. westward decrease in vegetation along the Texas Gulf Coast, and consequently, fore-island dunes are more Barrier islands are elongate, detached sand bodies susceptible to blowouts by wind erosion. Second, a that are separated from the mainland by bays or major tidal pass existed in the southern Mustang Island lagoons and from each other by tidal passes. The five area until the early 1900's. Hurricanes tend to readily barrier islands of the Texas Coast are Galveston, breach those barrier segments that are adjacent to, and Matagorda, St. Joseph, Mustang, and Padre. A gen- on the upcurrent (longshore current) side of, tidal eralized profile combining the features of Mustang inlets such as North Pass on St. Joseph Island and Island is shown on figure 10. southern Mustang Island (Price, 1952, 1956). Galveston Island (Galveston-Houston map) is wide Padre Island (Corpus Christi and Kingsville maps) and densely vegetated and is characterized by is distinctively different from barrier islands of the numerous sand ridges and swales. Average elevation is central and upper Texas Coast. Vegetation on Padre about 5 feet above MSL; maximum elevation of Island is less dense, but fore-island dunes are generally poorly developed fore-island dunes is about 15 feet well developed southward along north Padre Island above MSL. Hurricane erosion on Galveston Island is almost to Mansfield Channel. Average dune elevation is confined primarily to beaches and dunes. about 15 feet above MSL; maximum elevations reach about 50 feet above MSL. Near Mansfield Channel, Matagorda Island (Port Lavaca map) like fore-island dunes are low and discontinuous; hence, Galveston Island is a broad, sandy island with well- along central Padre Island, storm-surge flooding is defined ridge-and-swale topography and more or less virtually unimpeded and many breach or washover continuous fore-island dunes (Wilkinson, 1974). channels are concentrated in the area. Northern Padre Average elevation is about 5 feet above MSL. Fore- Island beaches are generally low and broad and consist island dunes on Matagorda Island average about 10 of terrigenous sand. Southward, beaches become II-13 shelly, narrow, and high. The height of back beaches man-made structures in the populated Corpus Christi increases to about 7 feet above MSL, thereby region. In monetary terms, Celia was a severe storm. providing some protection to fore-island dunes during Had Celia made landfall on deserted central Padre storms. Island and moved westward over the sparsely popu- lated eolian sandplain, there would have been very Bay shoreline and in land areas are severely little loss of life or damage to man-made structures. In affected by storm-surge flooding, wave erosion, and such a setting, Celia would not have been a severe fresh-water flooding from hurricanes. Severity of storm. storm-surge flooding and destruction of man-made and natural features by waves is chiefly a function of bay PREDICTION OF SEVERE HURRICANE DAMAGE size and configuration, presence or absence of cliffs, and location of hurricane landfall. Severity of fresh- The most severe storm damage can be expected water flooding is determined by local topography and when large hurricanes of the Carla type make landfall storm characteristics. (1) where barrier islands or peninsulas are of low relief (fore-island dunes are poorly developed or absent), (2) Storm-surge flooding and wave damage are where sands constituting barrier islands or peninsulas greatest along the shores of large, funnel-shaped bays are relatively thin, (3) where elongate bays lie to the with relatively high cliffs at the bayhead, which lie to right of the hurricane track, and (4) where the landfall the right of the landfall area. As onshore winds within area is densely populated. Examples of situations (1) the right side of the hurricane strike the Coastal Zone, and (2) are Matagorda Peninsula and south Padre storm-surge height increases toward the heads of bays Island. Funnel-shaped or elongate bays that may be as the surface area of the bay decreases and cliff the sites of extreme storm-surge flooding (situation 3) height increases. Flooding along Matagorda Bay and are Trinity, Galveston, Lavaca, San Antonio, Corpus Lavaca Bay shores during Hurricane Carla, 1961, is an Christi, and Nueces Bays. Densely populated areas and example of hurricane impact within funnel-shaped areas that are currently experiencing rapid devel- Texas bays (Bay City-Freeport and Port Lavaca maps). opment (situation 4), which can be expected to be severely damaged by a Carla-type hurricane, are the Bays that lie to the left of the storm track are south Padre Island area, the Corpus Christi area (in- not as severely flooded by storm surge as those lying cluding the smaller cities adjacent to the bays), the to the right because storm tides and waves are driven Port Lavaca area, the Galveston-Houston area, and the toward the Gulf of Mexico on the left side of the Beaumont-Port Arthur area. counterclockwise wind systems. In this situation, most of the surge and wave attack is directed toward the The Beulah-type hurricane causes extensive flood- back side of peninsulas and barrier islands. ing. Man-made structures (i.e., residences, farm build- ings, recreational facilities) situated on floodplains and Low-lying areas, such as marshes, delta plains, adjacent to creeks and rivers can be expected to be and river floodplains, are commonly flooded by storm damaged or destroyed. A storm such as Beulah in surge. River floodplains and flat upland areas also may 1967, or Carmen in 1974, does not necessarily have to be extensively flooded by rainfall associated with a make landfall along the Texas Coast to cause flooding hurricane that moves slowly inland. Unless these areas along Texas creeks and rivers. For example, Carmen are inhabited, little damage occurs; salt to brackish struck the Louisiana coastline during the first week of marshes are temporarily freshened. Floodplains may September in 1974. She was still influencing weather pond water for months. in Texas as late as the second week in September, triggering excessively heavy rainfall in the Coastal Population Density Zone between Port Lavaca and Sinton. During the early morning of 13 September 1974, up to 17 inches Storm-surge flooding, breaking waves, wind, and of rain fell on the Papalote Creek drainage, a tributary fresh-water flooding may cause considerable destruc- to Aransas River. Flooding of Papalote Creek from tion in areas that are sparsely populated, but because this heavy rainfall was greater than the flooding of the low population density, this kind of natural experienced during the earlier Hurricane Beulah rains. damage does not significantly affect man. Perhaps the severity of a hurricane should, therefore, be measured MITIGATION OF HURRICANE IMPACT in terms of its impact on man and man-made struc- tures or developments-according to this viewpoint, Hurricanes cost the people of Texas millions of the greater the population density, obviously the dollars (table 6). Several methods have been employed greater the severity of the storm. to reduce the destructive potential of hurricanes. Miti- gation of the hurricane hazard is in part accomplished Hurricane Celia was a small hurricane with high- by (1) reliable forecasting and prediction, (2) formu- velocity winds, which damaged or destroyed many lating evacuation procedures, (3) strengthening natural 11-14 defenses such as fore-island dunes, and (4) erecting B. HURRICANE BEULAH rigid structures to withstand wave attack or to retard waves and prevent storm-surge flooding. Another Tidal Win ad Stream faooding possible method of reducing the destructive potential Type of loss flooding wind-driven and pnndng of a storm lies in altering the storm itself. Finally, the rain most certain means of reducing storm damage is Agriculture 0 6,835 31,019 37,854 avoidance. Need for mitigation throughout the Commercial 2.241 1192 6,370 9,803 Atlantic and Gulf coasts becomes progressively more Residential 615 21,457 25,463 47,535 urgent since there was a 40-percent increase in beach Services 2,097 12,781 35,474 50,352 residents between 1960 and 1970 (Frank, 1974). Total 4,953 42,265 98.326 145,544 Although numerous problems arise from such rapid Lives lost: 15 persons in Texas growth in the Coastal Zone, perhaps the most critical problem is the lack of hurricane experience of many of the new coastal residents. C. HURRICANE CELIA Forecasting and prediction are now very sophis- Type of loss Wind damages Tidal flooding Total ticated. Hurricanes are carefully monitored by elec- tronic methods, by air surveillance, and by weather Agriculture 19220 13 19,233 satellite. Residents in the vicinity of predicted landfall Residential 199,652 3,523 203,175 generally have sufficient time to evacuate the area. On Commercial 44,375 917 45,292 the other hand, the time may be approaching when it Industrial 75,980 8.705 84,685 will be impossible to entirely evacuate some coastal Public 33,633 150 33.783 areas, e.g., barrier islands. A mass exodus of hundreds Transportation 540 1,186 1.726 of thousands of people by automobile across con- Utilities21 2 2 8 7210 Utilities 21,922 187 22,109 Marine 3,100 7,029 10,129 gested causeways may not be physically possible. Two Automobiles 18,944 620 19,564 alternatives may be considered in order to reduce the Services 22,372 5,243 27,615 number of people that would be required to flee the Total 439,738 27,573 467,311 islands. First, with better forecasting, it may become Lives lost: 13 persons possible to determine with even greater accuracy the "direct hit" and "fringe" areas. Evacuation of resi- Estimated losses from hurricanes since 1900: $1,271,983,000 dents in the direct hit areas would be required; those _ in fringe areas would remain. A second alternative to vegetation cover. Many dunes have been weakened or evacuation would be the utilization of specially struc- destroyed through devegetation. This occurs naturally tured high rises (hotels, motels, condominiums, and during droughts and as a result of man's activities. apartments) as vertical refuges (Frank, 1974). Attempts have been made to strengthen dunes through Fore-island dunes if present form the first line of artificial stabilization by increasing the vegetation natural defense against storm surge and breaking density. Most notable of these ventures has been on waves. The ability of dunes to withstand hurricane the barrier islands of North Carolina (Dolan and attack is dependent upon the density of stabilizing Godfrey, 1973; Dolan and Odum, 1973). Artificial dune stabilization in North Carolina, however, has Table 6. Losses from recent hurricanes. (A) Hurricane aggravated shoreline erosion. Carla, (B) Hurricane Beulah, (C) Hurricane Celia. Values in thousands of dollars. Data from U. S. Army Corps of Engineers (1962, 1968, 1971a). Note that data do not necessarily agree The Galveston seawall is an example of an engi- with that provided by National Oceanic and Atmospheric neering approach to retard hurricane damage, but as a Administration (1900-1974). result of stabilizing the shoreline, the beach has been A. HURRICANE CARLA lost. The seawall was erected specifically to protect Type of loss Tidal flooding Wind and Rain Total the city against overflows from the sea (Davis, 1961). Sand, excavated from western Galveston Island, was Agriculture 19,544 41,314 60,858 used to fill part of the low area behind the seawall. Residential 105,779 66,441 172,220 Bulkheads and revetments are also commonly used to * Commercial buildings 39,148 25,658 64,806 protect some bay shores from hurricane wave attack. and contents Other proposed methods to alleviate potential storm Industrial plants 11,683 3,349 15,032 surge and wave damage to bay-shore property include Transportation 9,207 3,141 12,348 Transportatility 1,27 3 ,11 2,3485 the use of breakwaters constructed within the bays Utility 1,198 8,787 9,985 Miscellaneous 13,636 6,801 20,437 specifically to reduce wave action, and the construc- Services - 52,604 tion of a system of locks which, in the event of a Total 200,195 155,491 408,290 hurricane, could close off the tidal and navigation Lives lost: 32 persons channels. 11-15 Two other means of lessening damage potential 0 FLOODING 0 are to avoid those areas that are prone to storm-surge and fresh-water flooding and to enact appropriate GENERAL STATEMENT building codes; areas that have been flooded by storm surge and fresh water are shown on Natural Hazards Two principal types of flood hazards exist in the Maps. Buildings can be constructed to withstand the Texas Coastal Zone: storm-surge tidal flooding and high-velocity winds and sudden pressure changes asso- fresh-water flooding. During the passage of hurricanes ciated with hurricanes. Elevation of buildings by and tropical storms, storm-surge tides may flood low- utilizing pilings can eliminate most of the damage lying coastal areas up to elevations above 20 feet (fig. from storm-surge flooding, but will not eliminate 7). Fresh-water flooding, on the other hand, results damage or destruction from breaking waves. from hurricane-aftermath rainfall, as well as from severe thunderstorms and frontal-related storms. Fresh- Attempts have been made to alter the hurricane water flooding may occur as stream flooding of flood- itself, and research is being conducted to determine plains or as rainfall flooding of broad areas of the the feasibility of altering tropical storms (Dunn and coastal plain. On the flat coastal plain, the runoff is Miller, 1964; Simpson, 1966). The object of hurricane ponded in natural depressions or dammed behind modification is to decrease the steep pressure profile highways, railroads, and other man-made structures. (hence decrease the wind velocity) and to convert the hurricane to a tropical storm. Profiles through hurr- Shoreline erosion and land subsidence, both canes and tropical storms (fig. 11) show that wind natural factors that can be accelerated by human velocity and pressure gradient are greatest near the eye impact, are increasing the hazard of storm-surge and of a hurricane. The tropical storm, which has no eye, fresh-water flooding in the Coastal Zone. As shorelines has a much lower wind velocity than hurricanes. At retreat, or as lands subside, greater areas of the Coastal present, cloud seeding appears to be a promising Zone are exposed to storm-surge tides. Similarly, land method to reduce wind speed and eliminate the eye. subsidence, whether due to natural compaction and The seeding method may never lead directly to useful subsidence or to ground-water withdrawal, produces modification, however, because hurricanes are so large broad irregular depressions that can pond substantial and their energy is so enormnous (Simpson, 1966). A volumes of rainfall on the impermeable muddy sub- hurricane with moderate strength releases as much strates of much of the lower coastal plain. Ship condensation heat energy in a day as the nuclear channels, irrigation ditches, and extensive dikes, re- fusion energy of four hundred 29-megaton hydrogen lated both to agriculture and industrial/commercial bombs. Significant modification of hurricanes may be development, may also serve to aggravate the impact impossible. It also may prove to be undesirable to of the storm-surge tide and to impede rainfall runoff. destroy a hurricane or to alter its course, since these storms supply a quarter to a third of the rainfall in Those areas actually flooded by the storm-surge critical areas of the world. tides that accompanied Hurricanes Carla and/or Beulah (3,164 square miles) are shown on the Natural Hazards 80 - Maps. Likewise, areas flooded by Hurricane Beulah aftermath rainfall (2,187 square miles) define the extent of fresh-water flooding (stream flooding, ponding, and dammi-ng) in the Texas Coastal Zone 70 4between Bay City and Brownsville. Data on Hurricanes (3 Carla and Beulah were obtained from the U. S. Army Corps of Engineers (1962, 1968) and are based on - v6,- -HURRICANE aerial photographs, drift-line observations, and a >. variety of recording gages. The reader is referred to t the above reports, as well as to a report on Hurricane 050 Celia (U. S. Army Corps of Engineers, 1971a) and a J report on hurricane-surge frequency estimated for the W 0\ >40 - N, Texas Coastal Zone (Bodine, 1969). Maps and text which were distributed as part of the Texas Hurricane 30- - Awareness Program by the Texas Coastal and Marine 20- TRPCL- a'-- - ._Council (1974) also provide information on flooding. 20- STORM 306 9 0 IS 8 In the northeastemn part of the Coastal Zone, RADIUS (N. M.) where adequate hurricane-aftermath flood data are Figure 11. Velocity profiles characteristic of hurricanes and generally unavailable, areas of possible stream flooding tropical storms. After Simpson (1966). (2,073 square miles) shown on the Natural Hazards Maps are based upon the distribution of floodplain 11-16 sediments and upon the geomorphic character of the plain (fig. 9). The frequency of storm-tidal surge stream systems. Areas that will be flooded by ponding greater than 10 feet is consistently and substantially of excessive rainfall were not delineated for the north- greater for bays than for open Gulf beaches (fig. 12). eastern part of the Texas Coastal Zone because the necessary mapping of subtle topographic variations is Rainfall Flooding beyond the resolution of regionally available topo- graphic maps. In addition, the degree of ponding is Rains may precede the landfall of a hurricane, also related to the efficiency of highway and railroad but as the storm center moves inland, heavy rainfall, drainage systems, which may be blocked by driftwood often accompanied by tornadoes, generally strikes the and other debris. coastal plain (fig. 7). If the hurricane moves directly inland, the period of heavy rainfall may be limited to The flood-prone areas shown on the Natural three or four hours. If the storm moves parallel to the Hazards Maps are, therefore, based principally upon coastline or repeatedly changes its forward direction, historical or geologic evidence and not upon excessive rains may continue for many hours or even theoretical prediction and extrapolation methods. several days. For example, in 1967 Hurricane Beulah remained in the South Texas area for almost three FLOODING PROCESSES days; up to 32 inches of rain fell in the region during the five or six days following landfall (fig. 8). Stream Hurricanes and Tropical Storms flooding and ponding inundated 1.4 million acres of land while only 630,000 acres were flooded by storm- As previously described, the most destructive surge tides (U. S. Army Corps of Engineers, 1968). aspect of hurricanes that have struck the Texas Coast (table 4) is the impact of the storm-tidal surge; Hurricane-aftermath rainfall is generally so exces- widespread forerunner tides of lesser magnitude may sive that coastal streams inundate floodplains. Flood- precede the storm-surge tides. Storm surge, which is waters are discharged into the various Texas bays, generated within the storm by the low barometric which are already experiencing high tides. As a result, pressure and the intense, counterclockwise winds, combined storm-surge tides and overbank stream strikes the coast as the storm makes landfall and flooding may devastate vast areas of the flat, lower spreads across the low coastal plain with lethal results. coastal plains. As the hurricane moves inland, rainfall Most property damage and, more critically, most runoff continues to flood drainage systems; streams deaths result from the surge of ocean water across may discharge floodwaters into bays for many days exposed, low-lying barrier islands and mainland shore- following storm passage. lines (table 6). Nine out of ten deaths as a result of hurricanes are caused by drownings (Texas Coastal and Ponding of rainfall on the coastal plain may Marine Council, 1974). As the hurricane moves ashore, inundate more area than stream flooding. Most of the floating debris propelled by the storm surge adds to lower 50 miles of the coastal plain is underlain by the damage inflicted by the rising water and pounding flat-lying, poorly drained, moderately to highly imper- waves. The greatest property losses result both from meable sediments (refer to "Environmental Geologic flooding and from the battering effect of water-carried Atlas of the Texas Coastal Zone," Fisher and others, debris. The devastation imposed upon Mississippi in 1972, 1973; also Fisher, 1973); rainfall runoff is high 1969 by Hurricane Camille was caused principally by a because of this relatively impervious substrate. storm surge of nearly 25 feet above MSL. Most seawalls and hurricane protection dikes along the Although lives may be lost in hurricane-aftermath Texas Coast are less than 20 feet above sea level. flooding, more commonly the principal loss is to property such as bridges, highways, and homes. Storm-Surge Tides Thousands of persons may be left temporarily homeless by the stream flooding and ponding; trans- A general model that illustrates the nature of portation systems may be destroyed or blocked. storm-surge tidal flooding along the Texas coastline Flooding also damages water and sewerage facilities, during approach and passage of a hurricane has been leading to the threat of epidemic diseases. previously described (fig. 7). The elevation of the storm-surge tide generated by a hurricane is generally less on the Gulf shoreline (barrier islands, peninsulas, Frontal-Related Storms headlands) than along the shorelines of constricted bays and estuaries where storm-tidal surge may be Storms associated with more normal meteorologic significantly elevated. A storm surge greater than 10 circulation also produce flood hazards in the Coastal feet above MSL, therefore, may occur within con- Zone. Although thunderstorms are generated during stricted bays because of superelevation of the tide on the summer months in the coastal region by con- the gently sloping bottoms and on the adjacent coastal vection, most severe weather, excluding hurricanes and 11-1 7 tropical storms, is related to frontal systems that move MSL possible on the Gulf beaches and with more than eastward and southeastward across the North 20 feet of storm tide possible within restricted bays American continent. In the winter, polar fronts may (fig. 12), the potential flood-prone area of the Texas move rapidly into the coastal area suddenly bringing Coast may be significantly greater than the net area low temperatures, rain, and strong northerly winds. reported for Carla and Beulah flooding. These storms may last for two or three days, during which time some locally heavy rainfall can occur. The A total of 5,787 square miles of Texas coastal northerly winds may generate flood tides that in- plain ties below an elevation of 20 feet above MSL undate wind-tidal flats and other low areas, especially (table 1). Much of this land below an elevation of 20 along the southern margins of the bays and the back feet may be flooded locally when maximum storm- sides of barrier islands. Wind-tidal flooding is slow, and surge conditions are focused on the specific section of it does not present a serious hazard. the Texas shoreline. During spring and fall, when polar fronts diminish In the Beaumont-Port Arthur map area, Carla in strength, the cooler air mass of the frontal system is floodwaters moved inland from the Gulf beaches for unable to maintain its momentum against warmer Gulf 15 to 20 miles and reached up the Neches River valley air; stationary fronts (sometimes called warm fronts) to the vicinity of Beaumont. Tidal levels ranged from result. These broad fronts, which lift warm Gulf air 6.8 feet above MSL at Orangefield to 10.5 feet above aloft, may remain in the coastal region for many days MSL northwest of High Island. Flood levels reached while generating widely distributed rainfall. Serious 8.5 feet above MSL at the mouth of the Neches River, flooding of coastal streams may occur but rarely to 7.9 feet near Port Neches, 5.0 feet near Port Acres, the degree experienced during hurricanes and tropical 7.6 feet at Port Arthur, 9.4 feet along the northern storms. shore of Sabine Pass, 8.6 feet near Big Hill, and 8.9 feet at High Island. FLOOD-PRONE AREAS A total of 583 square miles of coastal lands in Storm-Surge Tidal Flooding the Beaumont-Port Arthur map area were flooded by Hurricane Carla. If the center of a Carla-level storm Between 1900 and 1972, 27 hurricanes (winds struck the Sabine Lake area, tidal flooding might greater than 74 mph) and many less severe tropical inundate areas up to elevations of 15 to 20 feet, hence storms (winds greater than 39 mph and less than 74 covering 20 to 30 percent more land than indicated on mph) struck the Texas Coast (table 4), generally in the Natural Hazards Map. Although only two hurri- August or September (fig. 3). This constitutes a rate cane washover channels have been recognized near of one hurricane every 2.5 years. Very few areas of High Island, Hurricane Carla floodwaters apparently the Texas Coast have escaped hurricane impact during crossed the low-lying shoreline at many points to this century. Each hurricane is a rather unique storm flood the broad marshlands along the Intracoastal in terms of the nature and degree of winds, storm Canal. surge, and aftermath rainfall. Every bay, barrier island, peninsula, and headland exhibits some unique physical In the Galveston-Houston map area, Carla variations which can serve to modify the impact of flooding extended inland for 15 miles in the Angleton storm-surge tides. area, covered most of Galveston Island and Bolivar Peninsula, most of Smith Point area, and extended up Two recent well-documented hurricanes (Carla, the Trinity and San ,Jacinto river valleys. Flooding 1961 and Beulah, 1967) have been used in this atlas along the western side of Galveston Bay extended up to define known limits of storm-surge flooding and Dickinson Bayou and Clear Creek to Interstate 45. On aftermath-rainfall flooding (table 5). Flood-surge eleva- the Gulf beaches, maximum tidal levels of 9.6 and tions and area of flooding are based on studies by the 12.1 feet above MSL were recorded on Bolivar U. S. Army Corps of Engineers (1962, 1968); flood Peninsula and central Galveston Island, respectively. elevations are based on drift line and various gage Tide levels reached 14.0 feet above MSL at Wallisville, measurements. Although Carla and Beulah flooded 13.4 feet at Anahuac, 9.8 feet at Smith Point, 14.1 3,164 square miles, they probably do not represent feet at Baytown, 15.0 feet at Morgan Point, 14.2 feet ultimate hurricanes. One must assume, nevertheless, at the mouth of Clear Creek, 12.7 feet at Dickinson, thatstors sch a Cara o Beuah my eentully 11.0 feet at Texas City, and 14.7 feet at Chocolate strike other parts of the coast. For instance, should a Byu Carla-type storm directly strike the Galveston area (such as the 1900 storm, table 4), the area of tidal Hurricane Carla tidal waters flooded 694 square flooding could be much greater than the actual miles of the Galveston-Houston map area. If tidal flooding that occurred when Carla struck Port flooding were to approach 15 to 20 feet in the O'Connor. With storm flood tides of 15 feet above Galveston Bay vicinity as a result of the direct impact of the center of a Carla-level storm, perhaps 10 to 20 west side of Carancahua Bay, 20.1 feet at the State percent more land area would be flooded than indi- Highway 35 bridge over the upper part of Carancahua cated on the Natural Hazards Map. Seven potential Bay, 16.3 feet in Keller Bay, 17.3 feet at Point washover channels occur on Galveston and Follets Comfort, 22.0 feet at Port Lavaca, 15.4 feet near Port Islands; other channels may develop during severe O'Connor, 10.3 feet at the ship channel on Matagorda hurricanes. Peninsula, 12.3 feet along the west side of Pass Cavallo, 12.1 feet at Matagorda Island Air Force Base, Continued land subsidence centered in the 11.2 feet at Seadrift, 10.3 feet on the west side of San Baytown region is yearly subjecting greater areas to Antonio Bay, and 7.3 feet at the State Highway 35 potential tidal flooding. If the flood levels that oc- bridge over Copano Bay. Hurricane Carla tidal surge curred in Galveston Bay during Hurricane Carla, in flooded 495 square miles in the Port Lavaca map area. 1961, were to strike Galveston Bay today, it is Tidal-flood levels generally coincided with the 20-foot- estimated that approximately 70 additional square elevation contour line along and to the right of Carla's miles would be subjected to flooding because of land landfall. Had Carla made landfall at St. Joseph Island, subsidence (Texas Coastal and Marine Council, 1974). perhaps an additional 5 to 10 percent of the western part of the Port Lavaca area would have been inun- In the Bay City-Freeport map area, tidal flooding dated by tidal floodwaters. Two hurricane washover by Hurricane Carla extended inland approximately 10 channels have been recognized near the western end of miles from the Gulf beach. Most of Matagorda Matagorda Peninsula; Vinson Slough on St. Joseph Peninsula and the Colorado River delta were inundated Island is a major washover channel. and flood tides moved from 3 to 8 miles inland from the shoreline of east and west Matagorda Bay. Flood- In the Corpus Christi map area, land inundated tidal levels were measured at 10.9 feet above MSL at by tidal flooding by Hurricane Carla in 1961 slightly the mouth of the Brazos River and 5.2 feet above exceeded the area flooded by Hurricane Beulah, which MSL at the Freeport channel; other levels include 13.8 made landfall near the Rio Grande in 1967. Carla's feet above MSL at a site on the Brazos River about 7 tidal surge flooded most of southern St. Joseph Island, miles inland, 11.0 feet near the mouth of the San Mustang Island, and northern Padre Island, except for Bernard River, 13.7 feet about 10 miles inland along elevated areas comprising fore-island dunes and stabi- the San Bernard River, 14.1 feet on Lake Austin, 13.7 lized blowout dunes. Tidal flooding extended for 10 feet along the Intracoastal Canal on the north side of miles up the Mission, Aransas, and Nueces river East Matagorda Bay, 15.3 feet near the town of valleys. Low-lying areas surrounding Port Bay were Matagorda, and 15.4 feet at Palacios. similarly inundated. Minor tidal flooding occurred along the landward sides of Corpus Christi Bay and Hurricane Carla tidal surge flooded 564 square northern Laguna Madre. Measured Carla tidal-flood miles of coastal lands in the Bay City-Freeport map area. The Bay City-Freeport map area was situated to levels include 7.3 feet above MSL at the mouth of the area. The Bay City-Freeport map area was situated to Aransas River, 7.9 feet on the east side of Port Bay, the right of Carla's center when the hurricane made landfall. This location, relative to the hurricane's eye 7.5 feet n ear Key Allegro, 9.3 feet at Port Aransas, received some of the most intense winds and storm and 5.9 feet at the southeast end of Lve Oak tides experienced along the entire coast. If tidal-flood Peninsula near Ingleside. Measured reulah tidal-flood levels were to approach 15 to 20 feet in the area, elevations in the Corpus Christi map area include 8.0 levels were to approach 15 to 20 feet in the area, perhaps 10 percent more land area would be flooded feet above MSL on northern Mustang beach, 7.3 feet at Portland, 7.3 feet near the bay bridge at Corpus than indicated on the Natural Hazards Map. Numerous y g hurricane washover sites occur along Matagorda Christi, 8.2 feet at the Corpus Christi Naval Air Peninsula. Station, 6.8 feet at the Flour Bluff bridge, and 8.8 feet in upper Oso Bay. The eye of Hurricane Carla crossed the Texas coastline at Pass Cavallo, located in the Port Lavaca The elevation of Carla's tidal surge significantly map area. Flood tides were highly elevated in diminished southwestward across the Corpus Christi Carancahua Bay, Keller Bay, and Lavaca Bay. Tidal map area; this region was located on the left or waters moved from 10 to 18 miles up Garcitas Creek low-intensity side of Carla's storm center (fig. 9). and the Lavaca River, respectively. Most of the land Hurricane Carla's tidal flooding inundated 203 square area between Seadrift and Port Lavaca was flooded; miles in the Corpus Christi map area; Hurricane Beulah very little of Matagorda Island remained emergent. flooded only slightly less area. If the center of a Extensive flooding occurred in the Green Lake- Carla-level storm made landfall at Port Aransas, tidal Guadalupe delta area, along Blackjack Peninsula, and levels might reach 15 to 20 feet above MSL and an in the vicinity of St. Charles Bay. additional 10 to 15 percent of the land area would be flooded by the surge, particularly in the Port Bay and Measured Carla tidal-flood levels in the Port Laguna Larga-Oso Bay areas. Broad hurricane washover Lavaca map area include 18.4 feet above MSL on the channels occur at the southeastern end of St. Joseph II-19 Island and in the Packery-Newport-Corpus Christi Stream Flooding and Ponding channel area on southern Mustang and northern Padre Islands. On the Natural Hazards Maps, flood-prone areas resulting from rainfall associated with tropical storms, hurricanes, and frontal systems are based on two Storm-surge tides generated by Hurricane Beulah sources: (1) data on Hurricane Beulah flooding (U. S. in the Kingsville map area far exceeded Carla's tidal Army Corps of Engineers, 1968) served as a guide to flooding in the area. Hurricane Beulah storm tides flood-prone areas in South Texas between the Rio inundated much of Padre Island, all tidal flats and Grande and the Lavaca/Navidad River system; and (2) low-lying areas along the landward side of Laguna aerial photographs, topographic maps, and field obser- Madre, large areas adjacent to Baffin Bay, and the vations were used to delineate flood-prone areas (based lower reaches of Olmos Creek, San Fernando Creek on eologc/eomorhc evidence the and Petronilla Creek. Hurricane Beulah tidal flooding the Lavaca/Navidad River system and the Sabine River inundated 288 square miles in the Kingsville map area. Measured Beulah flood-tide elevations include 8.7 feet where regional rainfall flood data are unavailable. The above MSL at Malaquite Beach (Padre Island National use of Beulah stream floodig and pondig data Seashore), 5.6 feet at Penascal Point at the mouth of provides an actual historical example of flooded areas. Baffin Bay, 8.8 feet near Loyola Beach, and 10.9 feet It should be realized, however, that the fresh-water along the lower reaches of San Fernando Creek. flood area shown on the Natural Hazards Maps is probably a conservative estimate below the maximum flood levels which can occur in the region. Northeast If the center of a Beulah- or Carla-level storm of the Lavaca/Navidad River basin, flood-prone areas were to make landfall along north-central Padre Island, are underlain by floodplain sediments, which are 10 to 15 percent more land would probably be geologic evidence of flooding. inundated by tidal flooding, especially in the Baffin Bay region, on Padre Island, and within low areas In the south coastalareas, Hurricane Beulah associated with the extensive sand dune fields. Much delivered approximately 30 inches of rainfall in less of Padre Island near the land-cut area was breached by than one week. It is one of the best documented flood hurricane washover channels. events in the region. Although Beulah-related rainfall was general in the region, certain areas received anom- alous quantities of precipitation. For this reason, one In the Brownsville-fIarlingen map area, Hurricane must recognize that the fresh-water flood limits on the Beulah tidal flooding inundated most of southern Natural Hazards Maps are not based upon uniform Padre Island and all of the extensive tidal flats, rainfall within each stream system. particularly in the Arroyo Colorado area and in the vicinity of the Brownsville ship channel. Hurricane Every stream between the Rio Grande and the Beulah did not strike the south Texas Coast head-on, Lavaca/Navidad Rivers experienced flooding; the but moved into the region from Mexico, almost par- general limits of flooding are shown on the Natural allel to the coastline. For this reason, the Brownsville Hazards Maps. Flooding inundated 2,187 square miles region may have experienced lower storm tides than it (table 1). Extensive ponding occurred between Baffin would if the hurricane had moved directly westward Bay and the North Floodway/Arroyo Colorado area, out of the Gulf of Mexico. where stream drainage is essentially nonexistent within the broad fields of sand dunes. Impervious substrates, Measured Beulah tidal elevations include 6.9 feet which occur locally beneath the dunes, coupled with above MSL at Port Mansfield, 3.5 feet on the Gulf the hummocky sand ridges and blowout depressions, beach south of Mansfield jetty, 5.3 feet along the ponded the rainfall and inhibited its runoff to the Intracoastal Canal at the mouth of Arroyo Colorado, Gulf of Mexico. Earthen embankments along State 3.9 to 7.4 feet on southernmost Padre Island, 7.5 feet Highway 77 and the Missouri Pacific Railroad locally on the Gulf beach at Boca Chica, 6.3 feet near Port retarded runoff. Ponded water remained for months Isabel, and 8.5 feet along State Highway 48, halfway before evaporation and slow percolation combined to between Boca Chica and Brownsville. Sugg and Pelissia lower water levels. (1968) reported a high-water mark of 12 feet above MSL in a house at south Port Isabel. Hurricane Beulah In the northeast coastal area between the tidal surge flooded 336 square miles in the Lavaca/Navidad Rivers and the Sabine River, Beulah Brownsville-Harlingen map area; much of this flooded rainfall was insufficient to produce stream flooding area consists of low tidal flats. If the center of a and ponding. Because of the absence of regional Beulah- or Carla-level storm were to strike the south historic rainfall data for the upper region of the Texas Texas Coast while moving westward or southwestward, Coastal Zone, flood-prone areas on the Natural a significantly greater land area than indicated on the Hazards Maps are based on geologic and geomorphic Natural Hazards Maps might be flooded. evidence. On the Natural Hazards Maps, these areas, II-20 which cover 2,073 square miles (table 1), are called complex and variable bays. The variety of bathymetry, " potential areas of fresh-water flooding by hurricane shoreline configuration, and other factors make rainfall." The areas are underlain by floodplain sedi- accurate prediction of surge within bays much more ments, which verify their flood potential. This flood difficult. Estimates of the frequency of surge heights category is comprised chiefly of river or stream valleys on the Gulf shore at Freeport and within Galveston and adjacent depressed, poorly drained areas that Bay at Baytown are shown on figures 12A and 12B3; occasionally may be flooded by overbank discharge of figure 12C shows predicted Gulf beach tidal elevations the stream, as well as by intensive hurricane rainfall. along the entire Texas Gulf Coast. Such flood-prone areas can be delineated with rea- sonable accuracy, but they do not represent flooding Hurricane-tidal levels will be predicted with in- by a single, observed flood event similar to that caused creasing accuracy, especially along the Gulf beaches, by Beulah rainfall. Because of the variability of the Gulf hurricane, its path, and its interaction with the highly variable Delineation of potential areas of ponding are not configuration of Texas bays, precise prediction of included for the northeastern part of the Coastal maximum flood levels will take many years to perfect. Zone. Ponding results from a complex interplay of In the meantime, the charting of observed flood events subtle topographic depressions, water-table elevations, provides a valuable guide to flood-prone areas. man-made structures, and available drainage systems. For this reason, the precise limits of ponding can best be determined by actual experience. Ponding rarely MITIGATION AND AGGRAVATION OF FLOODING leaves a distinctive geologic deposit that can be used to determine its limits. Before man settled the Texas Coastal Zone, hurri- cane processes, along with all coastal and marine Predicting Flood-Prone Areas processes, were generally in equilibrium with the natural coastal environments. Hurricanes are but one Meteorologists and engineers have correctly of a large number of natural phenomena that probably placed a high priority on learning to predict the level have operated for tens of thousands of years in the of tidal surge caused by hurricanes. When enough is Texas coastal region. Before man arrived, the storms known about tidal levels, wind direction and intensity, expended much of their great energy in the coastal atmospheric pressure, and other factors, it may be system and brought about, in a natural way, certain possible to construct reasonably accurate hurricane physical and biologic changes. The slow evolution of prediction models. Hurricanes strike Texas an average the Texas Gulf Coastal Zone has been affected by the of once every 2.5 years. Meager quantitative data are tropical cyclone. available on most of these storms, especially data at many sites along the Gulf beaches and within the Tropical storms and hurricanes have effected bays. For this reason, insufficient data exist at this certain changes in the region; barrier islands were time to develop a truly accurate and statistically valid modified and, perhaps, even their origin was, in part, model (Bodine, 1969). A dense network of tidal gages controlled by such storms. Bays were flushed and and other recorders are needed throughout the region. supplied with marine nutrients; sediment was eroded Even if such a data system were now available, it and redistributed. When man became part of the would take many years to sample a sufficient number coastal system, however, hurricanes became disastrous of hurricanes to generate highly reliable prediction because man does not necessarily live in equilibrium models. with the natural environment. Hurricanes have become severe problems today because they strike man's habi- By using a combination of observational informa- tation and development. It is important during this tion and logic, some progress has been made in period of growing population and development in the predicting the level of storm-tidal surge. One such coastal region that man strive to live in harmony with method (Bodine, 1969) is based on a hypothetical the hurricane, while at the same time developing hurricane with a central pressure index frequency safeguards to prevent loss of life and to minimize loss probability of once in 100 years (fig. 12). This of property. * hypothetical hurricane is the Standard Project Hurri- cane of the U. S. Army Corps of Engineers, if it Many natural features of the coastal area tend to generates maximum surge at a specific, selected mitigate the impact of hurricane flooding on man- location. made structures and developments. In addition, man has attempted to alleviate the danger and destruction Because the Gulf beaches are relatively straight caused by the hurricane floods in a variety of ways, and offshore bathymetry generally uniform, estimates most of which involve protective structures. It is of surge elevations are probably significantly more probable that man can significantly improve his safety accurate on the Gulf shoreline than within the highly and can reduce storm damage by careful development I11-21 of building codes and construction methods. In some areas, nevertheless, it may prove to be thoroughly impractical for man to try to control the impact of storm surge. In these flood-prone areas, it may be more profitable to avoid a potential disaster by ......... utilizing the areas for more compatible uses than 5 - habitation. 5 3 / .. : :- : : iiiiiiiiiiiiiiiiil l.......... Natural Flood Protection In the coastal region, the first natural defense against hurricane surge is the barrier island, which EXCEEDENCE FREoUENCYt ion :::-:::::-: :.: .. constitutes a barrier to waves generated on the inner EXCEEDENCE FREQUENCY PER 100 YEARS element which allows the barrier island to block A effectively some of the storm-surge energy. The barrier islands, however, are effective in absorbing some of the storm's energy only if they are well stabilized by vegetation. Along the shoreline of the bays, extensive 20 - marshes and shallow grassflats provide a buffer or 20 _ baffle which dampens some of the erosive power and .. 15- Hi....:: ...wave energy generated by tropical storms. Marshes, lO ....:.... .... . lihke vegetated barrier islands, are resistant to storm -{ :::?:?::::erosion. Elongate oyster reefs, which grow upward from the bay bottom to within 1 to 3 feet of the 5-......... water surface, provide a natural baffling system that aids in reducing tidal surge and that reduces the effective fetch of waves within the bays. Land Use and Coastal Flooding I............. - .....................;.;.;. 99 95 90 80 60 40 20 10 5 1.0.5 0.1 0.01 A number of man's activities may aggravate the EXCEEDENCE FREQUENCY PER 100 YEARS destructive power of the storm-tidal surge and fresh- water flooding. Any activity that destroys stabilizing B vegetation will weaken and subject a barrier island or a bay shoreline to increased storm-tidal erosion. Addi- tional hurricane washover channels may develop if 20- a z fore-island dunes are destroyed. Navigation passes con- 18- z structed through barrier islands provide additional F 16- < -o > routes by which storm-surge tides may enter the ,I4- z restricted bays. Construction of channels, dikes, or any , o b other modification which can serve to divert or focus 12- o00 YEARS _ storm tides may lead to acceleration of natural shore- OYEAR YEARS line erosion. Land subsidence resulting from use of w 8 ·----------... ground water exposes greater areas of the coast to the I 6- 0 YEARS impact of tidal surge and flooding. Modification of -4 5 YEARS - - -stream courses to provide better drainage can also lead to accelerated erosion and, perhaps, even expose new v) 2- areas to stream flooding and ponding. Structures that O .. .cross stream courses may impede the flow of flood- 50 100 150 200 250 300 350 400 waters; similarly, ponding may develop because runoff DISTANCE A LONG THE TEXAS COAST (MI) is impeded by man-made structures. C Flood Prevention Structures Figlre 12. Estimation of storm-surge height and frequency, Texas Gulf Coast. Based on mathematical methods. After Bodine (1969). (A) Gulf beaches at Freeport, (B) Bay shoreline at Under the pressure of growing population and Baytown, Galveston Bay, (C) Predicted tidal elevations (in terms industrialization, man has impinged upon more and of exceedence frequency) along entire open Gulf Coast. more flood-prone areas; for example, homes and busi- nesses are constructed within areas that have histor- II-22 ically flooded. Dikes, berms, levees, seawalls, groins, The first effort in this shoreline monitoring and bulkheads have been constructed to protect life program was an investigation of Matagorda Peninsula and property in flood-prone coastal areas. and the adjacent Matagorda Bay area, a cooperative study by the Bureau of Economic Geology and the Every reasonable effort should be made to General Land Office of Texas. In this study, basic protect life and property from the threat of hurricane techniques of historical monitoring were developed flooding. Maximum use of premium coastal lands will (McGowen and Brewton, 1975). require that more extensive flood protection structures be engineered and built. New and innovative methods In 1973, the Texas Legislature appropriated funds of construction, along with improved building codes, for the Bureau of Economic Geology to conduct should be an effective means of diminishing flood historical monitoring of the entire 367 miles of Texas damage. It is important, nevertheless, to consider the Gulf shoreline during the 1973-1975 biennium. Results rational limits on coastal construction aimed at flood of tile project will be published ultimately in the form prevention. More importantly, at some point, man of detailed, cartographically precise shoreline maps. must decide how far he can afford to go to eliminate Work versions of these maps (scale 1:24,000) will be flooding in low-lying coastal areas. Areas that are on open file at the Bureau of Economic Geology until repeatedly and severely flooded might best be utilized publication. In advance of the final report and maps, a for activities that preclude extensive property damage series of preliminary interim reports (e.g., Morton, and safety hazards. 1974; Morton and Pieper, 1975) is being published. GENERAL METHODS AND PROCEDURES * SHORELINE EROSION 0 Definition GENERAL STATEMENT Historical Shoreline Monitoring is the documenta- Shorelines are in a state of erosion, accretion, or tion of direction and magnitude of shoreline change equilibrium, either naturally or artificially. Erosion through specific time periods using accurate vintage produces a net loss in land, accretion produces a net charts, maps, and aerial photographs. gain in land, and equilibrium conditions produce no net change. Shoreline changes are the response of the Sources of Data beach to a hierarchy of natural cyclic phenomena including (from lower to higher order) tides, storms, Basic data used to determine changes in shoreline sediment supply, and relative sea-level changes. Time position are near-vertical aerial photographs and mosaics periods for these cycles range from one day to several and topographic charts. Accurate topographic charts thousand years. Most beach segments undergo both dating from 1850, available through the Department of erosion and accretion in response to lower order Commerce, National Oceanic and Atmospheric Admin- events no matter what their long-term trends may be. istration (NOAA), were mapped by the U. S. Coast Furthermore, long-term trends can be unidirectional or Survey using plane table procedures. Reproductions of cyclic; that is, shoreline changes may persist in one originals are used to establish shoreline position (mean direction, either accretion or erosion, or the shoreline high water) prior to the early 1930's. Aerial pho- may undergo repetitive periods of erosion and accre- tography supplemented and later replaced regional tion. Shoreline erosion assumes importance along the topographic surveys in the early 1930's; therefore, Texas Coast because of active loss of land, as well as subsequent shoreline positions are mapped on individual the potential damage or destruction of piers, dwellings, stereographic photographs and aerial photographic highways, and other structures. mosaics representing a diversity of scales and vintages. These photographs show shoreline position based on the SHORELINE MONITORING PROGRAM sediment-water interface at the time the photographs were taken. In 1972, the Bureau of Economic Geology initiated a program in historical monitoring for the Procedure purpose of determining, on a quantitative basis, long- term shoreline changes in the Texas Coastal Zone. The The key to comparison of various data needed to recent acceleration in Gulf-front real estate and indus- monitor shoreline variations is agreement in scale and trial development has provided the incentive for adjustment of the data to the projection of the selected adequate evaluation of shoreline characteristics. Of map base; U. S. Geological Survey 7.5-minute quad- special concern has been the documentation of those rangle topographic maps (1:24,000 or 1 inch = 2,000 shorelines undergoing erosion and accretion, as well as feet) are used for this purpose. Topographic charts and those that are in equilibrium. aerial photographs are either enlarged or reduced to the II-23 precise scale of the topographic maps. Shorelines shown factors, much less attempt to quantify the error they on topographic charts and sediment-water interface represent,'in general the accuracy of a particular survey mapped directly on sequential aerial photographs are is related to its date; recent surveys are more accurate transferred from the topographic charts and aerial than older surveys. Error can also be introduced by photographs onto the common base map mechanically physical changes in material on which the original data with a reducing pantograph or optically with a Saltzman appear. Distortions, such as scale changes from ex- projector. Lines transferred to the common base map pansion and contraction of the base material, caused by are compared directly and measurements are made to reproduction and changes in atmospheric conditions, quantify any changes in position with time. can be corrected by cartographic techniques. Location of mean high water is also subject to error. Shalowitz Factors Affecting Accuracy of Data (1964, p. 175) states ". . . location of the high-water line on the early surveys is within a maximum error of Documentation of long-term changes from avail- 10 meters and may possibly be much more accurate able records, referred to in this report as historical than this." monitoring, involves repetitive sequential mapping of shoreline position using coastal charts (topographic Aerial photographs.-Error introduced by use of surveys) and aerial photographs. This is in contrast to aerial photographs is related to variation in scale and short-term monitoring which employs beach profile resolution, and to optical aberrations. measurements and/or the mapping of shoreline position on recent aerial photographs only. There are advantages Use of aerial photographs of various scales intro- and disadvantages inherent in both techniques. duces variations in resolution with concomitant varia- tions in mapping precision. The sediment-water inter- Long-term historical monitoring reveals trends face can be mapped with greater precision on larger which provide the basis for projection of future changes, scale photographs, whereas the same boundary can be but the incorporation of coastal charts dating from the delineated with less precision on smaller scale photo- 1850's introduces some uncertainty as to the precision graphs. Stated another way, the line delineating the of the data. In contrast, short-term monitoring can be sediment-water interface represents less horizontal extremely precise. However, the inability to recognize distance on larger scale photographs than a line of and differentiate long-term trends from short-term equal width delineating the same boundary on smaller changes is a decided disadvantage. Short-term moni- scale photographs. Aerial photographs of a scale less toring also requires a network of stationary, permanent than that of the topographic base map used for markers which are periodically reoccupied because they compilation create an added problem of imprecision serve as a common point from which future beach because the mapped line increases in width when a profiles are made. Such a network of permanent photograph is enlarged optically to match the scale of markers and measurements has not been established the base map. In contrast, the mapped line decreases along the Texas Coast and even if a network was in width when a photograph is reduced optically to established, it would take considerable time (20 to 30 match the scale of the base map. Furthermore, shore- years) before sufficient data were available for lines mechanically adjusted by pantograph methods to determination of long-term trends. match the scale of the base map do not change in width. Fortunately, photographs with a scale equal to Because the purpose of shoreline monitoring is to or larger than the topographic map base can generally document past changes in shoreline position and to be utilized. provide basis for the projection of future changes, the method of long-term historical monitoring is preferred. Optical aberration causes the margins of photo- graphs to be somewhat distorted and shorelines mapped Original Data on photographic margins may be a source of error in determining shoreline position. However, only the Topographic surveys.-Some inherent error central portion of the photographs are used for mapping probably exists in the original topographic surveys purposes, and distances between fixed points are conducted by the U. S. Coast Survey [U. S. Coast and adjusted to the 7.5-minute topographic base. Geodetic Survey, now called National Ocean Survey]. Shalowitz (1964, p. 81) states ". . .the degree of Meteorological conditions prior to and at the time accuracy of the early surveys depends on many factors, of photography also have a bearing on the accuvacy of among which are the purpose of the survey, the scale the documented shoreline changes. For example, devia- and date of the survey, the standards for survey work tions from normal astronomical tides caused by baro- then in use, the relative importance of the area metric pressure, wind velocity and direction, and surveyed, and the ability and care which the individual attendant wave activity may introduce errors, the surveyor brought to his task." Although it is neither significance of which depends on the magnitude of the possible nor practical to comment on all of these measured change. Most photographic flights are 11-24 executed during calm weather conditions, thus and reproduced chart, previously discussed, require eliminating most of the effect of abnormal adjustment; and (3) paucity of culture along the shore meteorological conditions. provides limited horizontal control. Interpretation of Photographs Aerial photographs.-Accui acy of aerial photo- Another factor that may contribute to error in graph mosaics is similar to topographic charts in that determining rates of shoreline change is the ability of quality is related to vintage; more recent mosaics are the scientist to interpret correctly what he sees on the more accurate. Photograph negative quality, optical photographs. The most qualified aerial photograph resolution, and techniques of compiling controlled mappers are those who have made the most observations mosaics have improved with time; thus, more on the ground. Some older aerial photographs may be of adjustments are necessary when working with older poor quality, especially along the shorelines. On a few photographs. photographs, both the beach and swash zone are bright white (albedo effect) and cannot be precisely differ- Cartographic procedures may introduce minor entiated; the shoreline is projected through these areas, errors associated with the transfer of shoreline position and therefore, some error may be introduced. In from aerial photographs and topographic charts to the general, these difficulties are resolved through an under- base map. Cartographic procedures do not increase the standing of coastal processes and a thorough knowledge accuracy of mapping; however, they tend to correct the of factors that may affect the appearance of shorelines photogrammetric errors inherent in the original on photographs. materials such as distortions and optical aberrations. Use of mean high-water line on topographic charts and the sediment-water interface on aerial photographs Measurements and Calculated Rates to define the same boundary is inconsistent because normally the sediment-water interface falls somewhere Actual measurements of linear distances on maps between high and low tide. Horizontal displacement of can be made to one-hundredth of an inch which the shoreline mapped using the sediment-water interface corresponds to 20 feet on maps with a scale of I inch = is almost always seaward of the mean high-water line. 2,000 feet (1:24,000). This is more precise than the This displacement is dependent on the tide cycle, slope significance of the data warrants. However, problems do of the beach, and wind direction when the photograph arise when rates of change are calculated because: (1) was taken. The combination of factors on the Gulf time intervals between photographic coverage are not shoreline which yield the greatest horizontal displace- equal; (2) erosion or accretion is assumed constant over ment of the sediment-water interface from mean high the entire time period; and (3) multiple rates water are low tide conditions, low beach profile, and (n 2_, where n represents the number of mapped strong northerly winds. Field measurements indicate shorelines) can be obtained at any given point using that along the Texas Gulf Coast, maximum horizontal various combinations of lines. displacement of a photographed shoreline from mean high-water level is approximately 125 feet under these The beach area is dynamic and changes of varying same conditions. Because the displacement of the magnitude occur continuously. Each photograph rep- photographed shoreline is almost always seaward of resents a sample in the continuum of shoreline changes mean high water, shoreline changes determined from and it follows that measurements of shoreline changes comparison of mean high-water line and sediment-water taken over short time intervals would more closely interface will slightly underestimate rates of erosion or approximate the continuum of changes because the slightly overestimate rates of accretion. procedure would approach continuous monitoring. Thus, the problems listed above are interrelated, and Cartographic Procedure solutions require the averaging of rates of change for discrete intervals. Numerical ranges and graphic displays Topographic charts.-The topographic charts are are used to present the calculated rates of shoreline replete with a 1-minute-interval grid; transfer of the change. shoreline position from topographic charts to the base map is accomplished by construction of a 1-minute- Where possible, dates when individual photographs interval grid on the 7.5-minute topographic base map actually were taken are used to determine the time and projection of the chart onto the base map. Routine interval needed to calculate rates, rather than the adjustments are made across the map with the aid of the general date printed on the mosaic. Particular attention 1-minute-interval latitude and longitude cells. This is is also paid to the month, as Well as year of pho- necessary because: (1) chart scale is larger than base tography; this eliminates an apparent age difference of map scale; (2) distortions (expansion and contraction) one year between photographs taken in December and in the medium (paper or cloth) of the original survey January of the following year. II- 25 Justification of Method and Limitations precise, -represents the best method available for investigating long-term trends in shoreline changes. The methods used in long-term historical moni- toring carry a degree of imprecision, and trends and rates of shoreline changes determined from these tech- Limitations of the method require that emphasis niques have limitations. Rates of change are to some be placed first on tr-end of shoreline changes with rates degree subordinate in accuracy to trends or direction of of change being secondary. Although rates of change change; however, there is no doubt about the signif- from map measurements can be calculated to a precision icance of the trends of shoreline change documented well beyond the limits of accuracy of the procedure, over more than 100 years. An important factor in they are most important as relative values; that is, do evaluating shoreline changes is the total length of time the data indicate that erosion is occurring at a few feet represented by observational data. Observations over a per year or at significantly higher rates. Because short period of time may produce erroneous conclusions sequential shoreline positions are seldom exactly par- about the long-term change in coastal morphology. For allel, in some instances it is best to provide a range of example, it is well established that landward retreat of values such as 10 to 15 feet per year. As long as users the shoreline during a storm is accompanied by sedi- realize and understand the limitations of the method of ment removal; the sediment is eroded, transported, and historical monitoring, results of sequential shoreline temporarily stored offshore. Shortly after storm mapping are significant and useful in coastal zone passage, the normal beach processes again become planning and development. operative and some of the sediment is returned to the beach. If the shoreline is monitored during this recovery RESULTS OF HISTORICAL MONITORING period, data would indicate beach accretion; however, if PROGRAM the beach does not accrete to its prestorm position, then net effect of the storm is beach erosion. Therefore, Gulf Shoreline Erosion long-term trends are superior to short-term observations. Establishment of long-term trends based on changes in Long-term erosion during the past 74 to 132 shoreline position necessitates the use of older and less years (table 1) has subjected 47 linear miles, or 13 precise topographic surveys. The applicability of topo- percent, of the Texas Gulf shoreline to severe erosion graphic surveys for these purposes is discussed by and shoreline retreat (greater than 10 ft per year); 154 Shalowitz (1964, p. 79) who stated: linear miles, representing 42 percent of the Texas Gulf shoreline, similarly has been affected by moderate "There is probably little doubt but that long-term erosion and shoreline retreat (up to 10 ft the earliest records of changes in our coastline per year). Long-term accretion has occurred along 35 that are on a large enough scale and in percent of the Texas Gulf shoreline; 10 percent of the sufficient detail to justify their use for quan-Gufcatiehsbninlg-rmqiiru. titative study are those made by the CoastGufcatiehsbninlg-rmqiiru. Survey. These surveys were executed by competent and careful engineers and were Short-term erosion during the past 7 to 23 years practically all based on a geodetic network has subjected 153 linear miles, or 42 percent, of the which minimized the possibility of large errors Texas Gulf shoreline to severe erosion and shoreline being introduced. They therefore represent the retreat (greater than 10 ft per year); similarly 101 best evidence available of the condition of ourliermesrpeenng2prctofheTxsGf coastline a hundred or more years ago, and theliermlsrpeenng2prctofheTxsGf courts have repeatedly recognized their shoreline, has been affected by moderate short-term competency in this respect ....erosion and shoreline retreat (up to 10 ft per year). Only 13 percent of the Texas Gulf shoreline is under- Because of the importance of documenting changes going short-term accretion, while 17 percent is in over a long time interval, topographic charts and aerial short-term equilibrium. photographs have been used to study beach erosion in TeGl hrlna rvosycasfei oHarri andJoeas. For 9eampl, Morga and Larimore (1968), composed of deltaic headlands, peninsulas, and barrier Branti and Mcones (1973), E-s and Wtanles (1973),h v islands. Areas undergoing shoreline erosion can be Bryat ad Mcann(197), nd Sapo (193) ave related to this physiographic classification on a successfully used techniques similar to those employed regional scale. Deltaic headlands are comprised pre- herein. Previous articles describing determinations of dominantly of mud with relatively low percentages of beach changes from aerial photographs were reviewed sand, a factor that contributes to high rates of severe by Stafford (1971) and Stafford and others (1973). shoreline erosion. Eroded mud is carried seaward where it is deposited and, hence, removed from the sediment supply system. Brazos Island and south Padre Simply stated, the method of using topographic Island of the Rio Grande delta (Brownsville-Harlingen charts and aerial photographs, though not absolutely map) and the beach between San Luis Pass and Brown 11-26 Cedar Cut of the Brazos-Colorado delta (Port Lavaca Bays (Corpus Christi map), and Baffin Bay (Kingsville map) are Holocene deltaic headlands. The Gulf shore map), as well as in Laguna Madre (Brownsville- from Sabine Pass to Rollover Pass (Beaumont-Port Harlingen map). Similarly, northerly winds generate Arthur map) is developed on a relict (Pleistocene) waves that strike and erode southern and southwestern deltaic headland overlain by Modern marsh and strand- shoreline segments in Galveston, Matagorda, San plain sediments. Bolivar Peninsula (Galveston-Houston Antonio, Corpus Christi, and Baffin Bays. Bay shore- map) and Matagorda Peninsula (Bay City-Freeport line erosion along Matagorda, St. Joseph, and Mustang map) are also undergoing erosion as a result of their Islands and Matagorda Peninsula is also caused by close association with the sand-deficient deltaic waves and currents generated by northerly winds. Sand headlands. eroded from bay shorelines is deposited within the bay; some mud derived from shorelines may reach the Barrier islands of the Texas Coast, which include Gulf, but much of it gradually fills the bay. Galveston, Matagorda, St. Joseph, Mustang, and north and central Padre Islands (Galveston-Houston, Bay City-Freeport, Port Lavaca, Corpus Christi, andFATRAFEINSHELECAGS Kingsville maps, respectively) are elongate bodies ofFATR AFE IN SH EL ECAGS fine-grained sand from 20 to 60 feet thick. Rates of Studies indicate that shoreline changes along the shoreline erosion along barrier islands are generally Texas Gulf Coast are largely the result of natural lower because of the increased availability of sand. processes, although in some instances the changes may Apparently, the shoreline along central Padre Island have been aggravated by human activities. Geologic (Kingsville map) is relatively stable because sand is processes and, more specifically, coastal processes are supp lied to this segment of the coast by longshore complex dynamic components of large-scale systems. currents that converge in the general vicinity of 27 Coastal processes are dependent upon the intricate degrees North latitude (Lohse, 1955). Although con- interaction of a large number of natural variables such siderable sand is removed from the beach by eolian as wind velocity and duration, fetch, rainfall, storm processes along central Padre Island, sufficient sedi- frequency and intensity, tidal range and characteristics, ment to replenish the losses is transported by net and littoral currents. It is difficult, therefore, if not longshore currents flowing northward from the impossible, to isolate at this time all the specific southern part of the coast and southwestward from factors causing shoreline changes. the upper part of the coast. Bay Shoreline Erosion Climate Of the 1,100 miles of bay and estuarine shore- Climatic changes during the 18,000 years since line, 408 linear miles or 37 percent of the total the end of the Pleistocene ice age have been docu- bay-estuarine shoreline is undergoing varying rates of mented by various methods. In general, air temper- shoreline erosion (table 1). At present, research on ature was lower and precipitation was greater at the precise rates of bay-shore erosion has not been com- end of the Pleistocene than at the present; the warmer pleted; bay shorelines undergoing erosion have been and drier conditions, which now prevail, affect other interpreted qualitatively. Bay shoreline erosion is factors such as vegetal cover, runoff, sediment concen- related principally to the dominant wind regimes of tration, and sediment yield. Observations based on the region, but hurricanes and tropical storms may geologic maps prepared by the Bureau of Economic inflict bay shores with severe erosion during brief Geology ("Environmental Geologic Atlas of the Texas periods of landfall. Coastal Zone") confirm that many rivers along the Texas coastal plain were larger and probably trans- ported greater volumes of sediment thousands of years Southeasterly winds persist throughout the spring, ago (early Holocene). This, in turn, affected the summer, and fall months, whereas northerly winds of sediment budget of the Texas Coast by supplying less duration but greater strength persist during the additional sediment to the littoral drift system. winter months. Wind strength and duration, fetch, depth of water, and orientation of bay shorelines are Severe droughts that occur periodically are a some of the important factors controlling bay shore- potential, though indirect, factor related to minor fine erosion. In areas where fetch is measured in miles, shoreline changes because of the adverse effect of low the southwesterly winds generate waves and currents rainfall on vegetation. Because dunes and beach sand that impinge and erode shoreline segments along are stabilized by vegetation, sparse vegetation resulting northwestern bay margins; examples occur in Trinity from droughts offers less resistance to wave attack. and Galveston Bays (Galveston-Houston map), Regional variations in rainfall and wind dominance Matagorda Bay (Bay City-Freeport map), San Antonio along the Texas Coast also must exert some Bay (Port Lavaca map), Aransas and Corpus Christi differential effect on shoreline stability. 11-27 Storm Frequency and Intensity Whether the beach returns to its prestorm position depends primarily on the amount of sand The frequency of tropical cyclones is dependent available. If net sand is lost, the beach profile will not on cyclic fluctuations in temperature; increased fre- reestablish itself at the prestorm position; thus, net quency of hurricanes occurs during warm cycles (Dunn shoreline erosion or retreat has occurred. The beach and Miller, 1964). Because of their frequent occur- profile readjusts to normal prestorm conditions much rence, devastating force, and catastrophic nature, more rapidly than does the vegetation line. Generally tropical cyclones have received considerable attention speaking, the sequence of events is as follows: (1) in recent years. The significance of hurricanes as return of sand to beach and profile adjustment (accre- geologic agents was emphasized by Hayes (1967) who tion), (2) development of low sand mounds (coppice concluded that most of the Texas coastline experi- mounds) seaward of the foredunes or vegetation line, enced the passage of at least one hurricane eye during (3) merging of coppice mounds with foredunes, and this century. The general nature of tropical storms and (4) migration of vegetation line to prestorm position. hurricanes, as well as their relationship to flood The first step is initiated within days after passage of hazard, has been described in this report. The specific the storm and adjustment is normally attained within relationship between these storms and shoreline several weeks or a few months. The remaining steps stability in Texas also is important in understanding require months or possibly years and, in some the nature of rapid changes in shorelines. instances, complete recovery is never attained. As previously described, high-velocity winds with attendant waves and currents of destructive force Local and Worldwide Sea-Level Conditions attendant waves and currents of destructive force scour and transport large quantities of sand during hurricane approach and landfall (fig. 7). The amount Two factors of major importance relevant to of damage suffered by the beach and adjoining areas land-sea relationships are sea-level changes and compac- of damage suffered by the beach and adjoining areastinlsbdec.Spad190)icuedHoee depends on a number of factors including angle of tional subsidence. Shepard (1960b) discussed Holocene storm approach, configuration of the shoreline, shape or post ice-age (Pleistocene) rise in sea level along the and slope of Gulf bottom, wind velocity, forward Texas Coast based on C14 age determinations. During speed of the storm, distance from the eye, stage of historical time, relative sea-level changes are deduced astronomical tide, decrease in atmospheric pressure, by geodetic engineers who monitor mean sea level and longevity of the storm. Beach profiles adjust using tide observations to develop trends based on themselves to changing conditions in an attempt to long-term measurements. This method, however, does maintain a profile of equilibrium; shorelines experience not distinguish between sea-level rise and land-surface their greatest short-term changes during and after subsidence. A minor vertical rise in sea level relative to storms. Storm surge and wave action commonly plane adjacent land in low-lying coastal areas causes a con- off preexisting topographic features and produce a siderable horizontal, landward displacement of the featureless, uniformly seaward-sloping beach. Eroded shoreline. dunes, wave-cut steps, and washover fans are common products of the surge; the sand removed by erosion is Shepard and Moore (1960) speculated that coast- (1) transported and stored temporarily in an offshore wise subsidence was probably an ongoing process bar, (2) transported in the direction of littoral drift, augmented by sediment compaction. More recent data and/or (3) washed across the barrier island through tend to support the idea that natural land subsidence hurricane channels. Sediment transported offshore and is occurring along the Texas Coast (Swanson and stored in the nearshore zone is eventually returned to Thurlow, 1973). the beach by bar migration under the influence of normal post-storm wave action. The processes involved in beach recovery are discussed by Hayes (1967) and Sediment Budget McGowen and others (1970). McGowen and others (1970). Sediment budget refers to the amount of sedi- Foredunes are an important line of defense ment in the coastal system and the balance among against wave attack and, thus, afford considerable quantity of material introduced, temporarily stored, or protection against hurricane surge and washover. removed from the system. Beaches are nourished and Dunes also serve as a reserve of sediment from which maintained by sand-size sediment contributed by the beach can recover after a storm. Sand that is major streams, updrift shoreline erosion, and onshore removed from the dunes and beach, transported off- movement of shelf sand by wave action. Sand losses shore, and returned to the beach, provides the material are attributed to (1) transportation offshore into deep from which small coppice mounds and eventually the water, (2) accretion along and against natural littoral large fore-island dunes rebuild. Dune removal, barriers and man-made structures, (3) deposition in therefore, eliminates sediment reserve, as well as a tidal deltas and hurricane washover fans, (4) natural defense mechanism established for beach excavation for construction purposes, and (5) eolian protection. processes. II-28 Sediment supplied by major streams is trans- (3) excavation of sand from barrier islands and ported along the shore by littoral currents. The Brazos peninsulas, (4) construction of dams on the Rio River, Colorado River, and Rio Grande are the only Grande and Brazos River, and (5) artificial main- major Texas rivers that debouch directly into the Gulf tenance of the current position of the Mississippi of Mexico, but discharge data indicate that these rivers River. currently contribute very little sediment to the littoral drift system. The Mississippi River was a possible LONG-TERM TRENDS IN SHORELINE POSITION source of beach sediment prior to its shift to the eastern part of the delta about 400 years ago. Shore erosion is not only a problem along United States coasts but also is a problem worldwide. Even Van Andel and Poole (1960) and Shepard though some local conditions may aggravate erosion, (1960a) suggested that sediments of the Texas Coast major factors affecting shoreline changes are sea-level are largely of local origin. Sands derived from pre- variation, including compactional subsidence, and a viously deposited sediment on the floor of the conti- deficit in sediment supply. A deficit in sand supply nental shelf were apparently reworked and transported may be related to climatic changes, human activities, shoreward by wave action during the post ice-age and the exhaustion of the shelf supply through sub- (Holocene) sea-level rise. McGowen and others (1972) sequent burial of shelf sand by finer sediments to a also concluded that the primary source of sediment depth below wave scour. for Modern sand-rich barrier islands, such as Galveston, Matagorda, and St. Joseph Islands, was local A logical conclusion that can be drawn from Pleistocene and early Holocene sources on the adjacent available information is that shoreline position will inner shelf. continue to change, and landward retreat (erosion) will be the long-term trend. The combined influence of FACTORS AGGRAVATING EROSION interrupted and decreased sediment supply, relative sea-level rise, and tropical cyclones is insurmountable Shoreline changes induced by man are difficult to except in very local areas such as river mouths. There quantify because human activities promote alterations is no evidence to suggest that a long-term reversal may and imbalances in the sediment budget of the Coastal occur in the foreseeable future to change the present Zone. Furthermore, ground-water withdrawal increases trends of shoreline change. land subsidence. Construction of dams, erection of seawalls, groins, and jetties, artificial stabilization of POTENTIAL MITIGATION the Mississippi River, and removal of sediment for OF SHORELINE EROSION building purposes all contribute to changes in quantity and type of beach material delivered to the Texas The best defense against the hazard of shoreline Coast. Even such minor activities as vehicular traffic erosion is recognition and subsequent adjustment in and beach scraping can contribute to the overall land use. Other alternatives include artificial beach changes, although they are in no way controlling nourishment or artificial stabilization by dune factors. Erection of impermeable structures and re- vegetation and structures. moval of sediment have an immediate, as well as a long-term effect, whereas a lag of several to many It should be noted, however, that dune stabiliza- years may be required to evaluate fully the effect of tion, while appearing to be environmentally sound, can other changes such as river control, dam construction, be counterproductive and may have a definite impact and subsurface fluid withdrawal. on beach steepness and erosion. This was demon- Jett costrutio alog te Teas oastwasstrated on the North Carolina coastline where veg- initiated in the late 1800's. These projects serve to etae ue eitdsomwv taks elta alter natural processes such as inlet siltation, beach the normal exchange of sand between the dunes and eroion an huricne urg. Teireffct n soreinebeach was eliminated; increased beach steepness and changes is subject to debate, but it is an obvious fact b ueac erosion resltd fromdhsefortosaiiey 1973) that impermeable structures interrupt littoral drift, and dns( oa n ofe,17) impoundment of sand occurs at the expense of beach The shoreline in Texas could be stabilized at nourishment downdrift of the structure. It appears enormous expense by a solid structure such as a reasonable to expect that any sand trapped by the seawall. Any beach seaward of such a structure would jetties is compensated for by removal of sand eventually be removed unless maintained artificially by downdrift, thus increasing local erosion problems. sand nourishment (a costly and sometimes ineffective practice). The U. S. Army Corps of Engineers (1971b, Factors which have contributed to the deficit in p. 33) stated: "While seawalls may protect the upland, sediment budget include: (1) removal of sand from the they do not hold or protect the beach which is the fore-island dunes, (2) dredging of sand from the Gulf, greatest asset of shorefront property." Moreover, con- II-29 struction of a single structure may trigger a chain The extent and amount of subsidence are well reaction that will require additional structures and defined and known through a series of elevation maintenance. benchmarks established and resurveyed or leveled at selected intervals by the National Geodetic Survey When development plans are being formulated, (formerly the U. S.'Coast and Geodetic Survey) of the careful consideration must be given to the evidence Department of Commerce. The first leveling program that shoreline erosion will continue into the fore- was a first-order line from Smithville to Galveston seeable future. While beach-front property may surveyed in 1905 and 1906. In 1918, a first-order line demand the highest prices, it may also carry with it was established from Sinton, Texas, to New Orleans, the greatest risks. Louisiana. During the period between 1932 and 1936, several other first- and second-order lines were estab- S LAND-SURFACE SUBSIDENCE 0 lished, and the two original lines were releveled. In 1942 and 1943, a large number of second-order lines GENERAL STATEMENT were established and most of the older lines were releveled. Following the leveling program of Land-surface subsidence, primarily a consequence 1942-1943, subsidence in the Houston area was first of ground-water pumping and withdrawal that began documented. Subsequently, releveling surveys were in the Texas Coastal Zone in the early part of this completed in 1951, 1953-54, 1958-59, 1964, and century, affects to varying degrees a substantial part of 1973. These surveys clearly establish the extent and the lower Texas coastal plain. Most serious subsidence amount of subsidence in the lower Texas coastal plain. is in the Greater Houston area, where some localities show recorded subsidence up to 8.5 feet (Galveston- Houston map). Significantly, both the rate of land Likewise, the cause of subsidence is well docu- subsidence, in terms of lost land elevation, and the mented, primarily through the extensive monitoring of area of impact are progressively increasing and have water-well levels, which was started in 1929 by the increased dramatically in the past two decades (fig. Water Resources Division of the U. S. Geological 13). Survey. Comparison of areas of water level and piezo- metric decline with areas of land-surface subsidence clearly shows that they are coextensive. Results of monitoring by the U. S. Geological Survey have been o reported in several papers; refer especially to those 0_ reports by Gabrysch (1969, 1972), Gabrysch and McAdoo (1972), and Gabrysch and Bonnet (1974) as well as to reports by Marshall (1973) and Turner, 0 Collie, and Braden, Inc. (1966). Portions of this section of the atlas have' been drawn from these previously published reports. _- o UJ Although the principal cause of subsidence is ground-water withdrawal, a minor amount of sub- 00 O_ sidence can be attributed to natural compactional subsidence, to tectonic subsidence, and locally, to the withdrawal of oil, salt, and sulfur. Subsidence resulting W O from mineral extraction has been restricted largely to < 0 areas of production on and adjacent to certain coastal salt domes. More than 3 feet of subsidence at the Goose Creek oil field was caused by oil production, resulting chiefly from poor production practice in the early history of the field (Pratt and Johnson, 1926). --I- I , , I While the extent, amount, and mechanisms of o') o o 0 0 0 0 land-surface subsidence are well documented, methods for mitigating the problem, short of massive curtail- ment of ground-water pumping, are not evident. Varia- Figure 13. Area in the Texas Coastal Zone impacted by tiof indte pumposition ot ev ident. as land-surface subsidence in excess of I foot between 1943 and tions in hydrologic behavior, s 1973. Values are cumulative. well as local difference in hydrologic behavior, suggest 1973. Values are cumulative. that certain areas are more prone to subsidence than are others. 11-30 CAUSE AND MECHANISMS OF LAND SUBSIDENCE The amount of subsidence that will occur is directly related to the decline in piezometric level, Most of the ground-water production in the which is a function of the volume of water withdrawn Texas coastal plain is from aquifers occurring from from the aquifer. The amount of subsidence, however, near the surface to depths as great as 3,000 feet. The will vary further depending upon the amount of clay geologic formations involved are composed of varying within the aquifer section, the vertical distribution of amounts of alternating sands (the aquifers) and inter- the clay, the compressibility of the clay, and finally, stratified clays. Significantly, the clays are water the degree of undercompaction of the clay in its saturated and undercompacted; clays nearer the sur- natural state. The amount of clay in the aquifer and face are commonly less compacted than those at the number of clay beds within the aquifer sands, as greater depths. The aquifer sands and interbedded clays dip gently toward the coast; they crop out in a general coastwise-trending belt extending from about eP . o P Susienh ,o,,10, Wner- ln crese in inter- S b ie cm 30 to 50 miles inland from the coastline. It is in the groruor pr...... grasuror pressure zone of outcrop that the aquifers are recharged by r .... infiltration of fresh water. Principal water production stages is from the Lagarto and Goliad Formations T/ ....... (Evangeline Aquifer), and from the Willis, Lissie, and s[ad Beaumont Formations (comprising the Chicot'.-- Aquifer). Earlier authors referred to these two aquifers simply as the Principal Aquifer. Similarly, in certain ( areas of the northeast part of the Coastal Zone, sands /, ---- o above the Principal Aquifer were referred to as the Alta Loma sands or the Alta Loma Aquifer. / __ Prior to 1900, before heavy pumping com- menced, water wells in the artesian aquifers flowed naturally; that is, the aquifers were under sufficient pressure to force water to the land surface within Figure 16. Effects of ground-water withdrawal on intergranular open wells. Subsequent pumping, especially in the past pressure, with consequent volume reductions and surface three decades, has resulted in a continuing decline in subsidence. After Turner, Collie, and Braden, Inc. (1966). artesian pressure or piezometric surface over wider and wider areas. Geologists and engineers of the U. S. Geological Survey, who started monitoring water levels well as the compressibility of the beds, vary areally; in coastal plain wells in 1929, have charted the certain areas are more prone to subsidence than long-term decline in the pressure levels. In 1943, others, even with the same amount of ground-water maximum decline of the water level was about 150 withdrawal and comparable levels of piezometric feet; by 1954, the piezometric level had dropped to decline. about 300 feet; by 1964, it had declined to about 350 feet; and in 1974, it locally has declined to 400 feet. Compaction of the clays and resulting subsidence Comparison of areas of pressure-level decline and areas are nearly 100 percent irreversible (a small rebound of subsidence show clearly their coextensive nature may be possible). Further, additional subsidence may (figs. 14, 15). occur even if ground-water withdrawal is reduced and the decline in piezometric levels is arrested. This is The water-saturated clays that occur inter- because of a lag between the addition of the load and stratified with the aquifer sands are compressible and ultimate compaction of the clays. Computations by become compacted when subjected to increased load. Marshall (1973) indicated that additional subsidence This reduction in volume of the compressible clays is after water-level decline ceases will be at least 50 translated to surface subsidence. Reduction in artesian percent and possibly as much as 150 percent of the pressure from pumping causes a loss of buoyant subsidence experienced prior to that time. Gabrysch support to the granular structure of the aquifer sands and Bonnet (1974) state that only 15 to 20 percent of (decreased pore pressure), and each layer is, therefore, additional subsidence will occur. R. 0. Kehle (personal subjected to a corresponding increase in effective communication, 1974), however, suggests that sub- vertical pressure. This decreased pore-pressure effect is sidence may stop immediately if piezometric decline is immediately transferred to the contact surface with arrested. Variation in the percentage of eventual sub- interbedded clays, but, because of the low perme- sidence, even after arrest of piezometric decline, is also ability of the clays, the clays drain more slowly (fig. a function of the amount and nature of clays occur- 16). The clay layers compress vertically and become ring within and associated with the aquifer. Eventual thinner; consequently, the overlying sediments and the subsidence, therefore, should be variable and will ground surface subside. depend on the geologic nature of the aquifer. 11-31 - DECLINE iNJ PRINCIPAL AQ1UIFERf \J --- DECLINE IN ALTA LOMA SAND ,j A i I .. . . / - 4. . "005.0CC V 7 - - 7 I ii a "j" 1" r·,·.·. - -- k' i C,-.· I IC N,.· r? C-C-- `· i a Ce $ * 1 Scale in RiPe C /In Scale in Miles \ 0C LAND SUBSIDENCE (FT I C *CiCCCCCC. Aa l I ZOMETRIC DECLINE (FT CSCCCO fC\C C a A9614 S NELN NPlCPLAIIE C - OCCCCCOCCCN I ---ECINEN TALM'>N i. ,,,.,,_,,,,,iF /d b: C ( C CCC 8\ \CQ <7CC,-i 4 I CC '0 1 'Ci ' s . Y·.·- P -i TB 5. 1906-195 t CC CC: COCO C . r CC i, 1 C NCCIN PRNIA /(UIE ··· 7 C/I···' · A /C." 7- O zV ,JC\ 9 > c i CC· LAD UBIENE C Scale in Mile ZMTI ELN F I OScCCC CC Mlp 'C C1906-1964 Figure 14. Land-surface subsidence and decline of piezometric (ground water) surface within Principal and Alta Loma Aquifers, 1906-1963, Greater Houston area, Modified after Marshall (1973). II 32 * '/ ' ,- I , ------ DECLINE IN CHICOT AQUIFER "I : ' ' ,' DECLINE IN EVANGELINE AQUIFER 4-A I ,,\ 4 /; > I ' - >',., 9'', - > ,,_ , " - (-. , -tb' 'K ,. .t :-. ,-:4'- / / ' i44 f,-,,/ ,-- ," 7 N-, -4 ... .... 'C> I'x,. . ?, .'/' II ' - ,. . , " .,-141 .............. I :-' .... ' ? . .......... "' EXETO AN U S D N C ByCtyFepr, avso-Hutn n (I -.4,44,44444,'. " 7 LAND SUBSIDENCE (FT I PIEZOMETRIC DECLINE (FT )SacMc 1943 1973 Figure 15. Land-surface subsidence and decline of piezomnetric (ground-water) surface within Evangeline and Chicot Aquifers, 1943-1973, Greater Houston area. After Gabrysch and Bonnet (1974). EXTENT OF LAND SUBSIDENCE (Bay City-Freeport, Galveston-Houston, and Beaumont-Port Arthur maps); this zone includes the Land subsidence, both in amount of land eleva- critically impacted Greater Houston area; (2) a large tion lost and in area affected, has been increasing part of Jackson County (Port Lavaca and Bay City- significantly during the past three decades. Coincident Freeport maps); and (3) an area in Nueces and San with accelerating subsidence have been increases in the Patricio Counties centered near the community of volume of water withdrawn and decline of artesian Odem (Corpus Christi map). Maximum subsidence in pressure levels. In 1943, when releveling recorded the the Corpus Christi area is in excess of I foot, with the first measurable subsidence, a little more than 140 distribution of subsidence showing a pattern square miles of land in the Houston region had remarkably similar to that of the Houston area in subsided I foot or more, with maximum subsidence of 1943. about 1.5 feet. By 1954, about 1,000 square miles of land had experienced subsidence in excess of I foot, with maximum subsidence up to 4 feet. In 1964, more Subsidence values shown on the Natural Hazards than 1,800 square miles of land had subsided more Maps were calculated with data derived from various than I foot, with maximum subsidence up to 6 feet. releveling surveys conducted by the National Geodetic By 1974, more than 3,000 square miles of land on the Survey. Periodic releveling data are limited; therefore, lower Texas coastal plain had undergone more than a the boundaries between subsidence zones are approx- foot of subsidence, and maximum subsidence had imate. Three subsidence zones, (1) 0.2 foot to I foot, reached 8.5 feet (Galveston-Houston map). The area of (2) 1 foot to 5 feet, and (3) greater than 5 feet, are lands impacted by subsidence of 1 foot or more has based on maximum recorded subsidence for any par- doubled approximately each decade for the past 30 ticular benchmark or level station. In some areas, the years. At the present time, about 230 square miles of "total" amount of subsidence has been determined land, centering on Pasadena, has subsided more than 5 from elevation differences recorded at a benchmark feet. for relatively short periods of time (for example, 1951 to 1973); in other areas with more data, the measured Measurable subsidence, defined herein as 0.2 foot subsidence includes elevation differences recorded for and greater, now impacts three areas of the lower longer periods of time (for example, 1905-1973). This Texas coastal plain: (1) an extensive area of the upper approach of using net or maximum elevation variation Texas coastal plain extending from Bay City north- at each benchmark provides a map that displays ward into Louisiana and inland as much as 60 miles maximum recorded subsidence. II-33 Land subsidence is minimal in the zone of 0.2-foot to 1.0-foot subsidence and has progressed substantially in the zone defined by subsidence in the range of 1 foot to 5 feet. Within the zone of maximum subsidence (greater than 5 feet and, cur- rently, less than 8.5 feet), land subsidence is a factor '963- 913 that requires careful consideration both in urban and 9 9-93 industrial development and in maintenance of public'9- facilities. The three zones provide a perspective of the land-subsidence problem consistent with the map scale and goals of the Natural Hazards Maps. The reader may wish to refer to specific studies on land sub- 3. sidence; e.g., Marshall (1973) and Gabrysch and Bonnet (1974).o 2 Figure 17. Correlation of active faults with sharp breaks in land-subsidence profiles. Elevation data from National Ocean PROBLEMS CAUSED BY LAND SUBSIDENCE Survey (formerly U. S. Coast and Geodetic Survey). Profile parallels State Highway 3 south of Dickinson, Texas, The most obvious consequences of land sub- Galveston-Houston map area. sidence in coastal areas are actual loss of lands in low-lying tidal areas and submergence of structures along these subsiding coastlines. Equally threatening is MITIGATION OF LAND SUBSIDENCE the loss of ground elevation and the potential subjec- AND ASSOCIATED PROBLEMS tion of more land to the natural hazard of flooding, either by hurricane surge or stream runoff. For Although the withdrawal of ground water in the example, assuming an ultimate subsidence of 10 to 12 lower Texas coastal plain is the principal cause of feet in the Greater Houston area, it is estimated that subsidence and associated problems, use of ground approximately 20,000 acres (about 31 square miles) of water has proved to be a significant economic benefit. land may be lost by the year 2000; substantially more At the present time, for example, about 650 million land could be lost if ultimate subsidence is greater. gallons per day are withdrawn from aquifers in the Furthermore, if storm tides with the same surge height Greater Houston area. The cost of ground water is as those generated by Hurricane Carla in 1961 were to significantly less than the cost involved in transporting strike upper Galveston Bay today (1974), an addi- and treating surface water. Ground water is, therefore, tional 70 square miles of subsiding lands, much of it an important natural resource in the coastal area of extensively developed, would be flooded by hurricane- the State and its use results in substantial savings to surge waters. the users. A recent report on the economics of subsidence (Warren and others, 1974) suggests that the Depending upon original topography, subsidence total cost of land loss and damage to structures may can result in change of land slopes, stream gradients, exceed the cost difference between surface water and and stream drainage patterns. Changes and reversals in ground water. The problems caused by subsidence and land slope can and have caused problems in such ground-water withdrawal must be evaluated in the gravity transport systems as water and sewerage lines. context of the economic alternatives. Although land subsidence is regic-.. in pattern Land subsidence that has occurred in the Coastal and is regionally expressed as "bowls" of subsidence, Zone is irreversible and, due to lag time in clay recent studies by the Bureau of Economic Geology compressibility, may continue to a substantial degree, indicate that, in detail, subsidence tends to occur in even if pressure-level declines are arrested. Mitigation blocks. Such movements are shown by abrupt changes of the impact already experienced and that which will in detailed land-subsidence profiles (fig. 17); a great inevitably be experienced in the future can only be number of the downward-subsiding blocks shown on accomplished either by vacating the impacted lands or these profiles are bounded by active faults. Such faults by constructing protective structures. Of principal are posing additional problems for areas of subsidence. concern is the maintenance of lands subject tc water encroachment, particularly those subject to flood inun- The particular hazard of . Surface faulting and dation. Construction of protective structures is the associated problems is discussed in the chapter, only means of mitigating the problems of flooding in Faulting. Subsidence of shoreline lands along the open areas already developed. Several dikes and levees have Gulf and bay shorelines, which can measurably in- already been built in critically impacted areas; the crease the already critical natural hazard of shoreline elevation of many of these will have to be raised and erosion, has been discussed under Shoreline Erosion. others constructed. The U. S. Army Corps of 11-34 Engineers has investigated the possibility of con- * FAULTING * structing an extensive hurricane barrier system across the southern end of Galveston Bay; the costs of GENERAL STATEMENT constructing and maintaining this system can be weighed against its benefits in protection from Active surface faults in the Texas Coastal Zone flooding and inundation. For other areas where sub- have become an important geologic hazard which daily sidence is occurring but where development has not affects the economic well-being of the people in this yet taken place, nonstructural methods such as zoning area. Active faults severely damage houses, apartment for certain uses might be more feasible. complexes, and industrial plants. Some city streets, farm-to-market roads, and interstate highways must be continually repaired because of fault damage; faults Finalythemodiicaionof te hstoicalpaternalso cross the runways of Hobby Airport and Ellington ofigond-ally, wthemdificaltion ofthe Texasoricsal platten Air Force Base. Active faults intersect the extensive can effectively mitigate subsidence and its associated randlroadbnetwor atndvra plcesreakeing raptnialso ftures problems. Such a plan will necessarily involve signif- anodbedanreatingamoentias. ftr icantly less withdrawal of ground water, but a variety drimns of other mitigating factors should be considered. Dif-EXNTOACIEFUIG ferent levels of subsidence arid associated problemsEX NTO ACIEFU IG may be tolerated; for example, subsidence is clearly a Active surface faults are relatively common in much greater problem in low-lying, developed areas parts of the Texas Coastal Zone. Most active faults than it is in less developed areas or in areas at higher that have been recognized occur in the Galveston- elevations. The aquifers, of course, are homogeneous Houston map area, where 95 linear miles of faulting neither in geologic nor in hydrologic character; are shown on the Natural Hazards Map. Many other aquifers with a minimum of intercalated muds can active faults exist inland from the map area. An active sustain more withdrawal than aquifers containing a surface fault about 4 miles long also occurs in the large number of undercompacted clay beds. Other Corpus Christi map area. There are 96 miles (table 1) mitigating factors include the extent to which asso- of known active faults in the entire area covered by ciated clays are compressible and the extent to which this report; locations of the faults have been compiled compesson ad cnsoldaton hve lreay tkenfrom studies by other workers (Weaver and Sheets, place, both naturally and as a result of ground-water 1962; Van Siclen, 1967; Sheets, 1971; Reid, 1973; production. Hydrologic variations indicate that certain Clanton and Amsbury, 1974) and as the result of aquifers can sustain greater ground-water production recent mapping in this region by the Bureau of with less severe declines in artesian pressure than can Economic Geology. More detailed mapping in the others. Accordingly, detailed analysis and mapping of future will undoubtedly locate more faults, and the eoloic ad th hydologc chractr ofthepossibly may discount some faults already mapped. In coastal aquifers might permit delineation of preferred addition, new faults may be generated in areas of production areas and pumpage levels (natural carrying land-surface subsidence. capacity). This approach could provide the necessary base for determining the maximum amount of with- drawal and the density of producing wells that can IDENTIFICATION OF ACTIVE FAULTS exist within prescribed acceptable levels of subsidence. Ultimately, acceptable levels of subsidence or nonsub- Active faults are defined as faults which have had sidence could be defined, depending on such factors as movement since the end of the Pleistocene (ice age) present state of development and original or present about 20,000 years ago. Most of the faults shown on topography or land elevation. the Natural Hazards Maps, however, have moved in the last 30 years. Ground water in the Texas coastal plain is and Four lines of evidence have been used in this should be considered a very valuable natural resource. atlas to identify active faults: (1) breaks in street Nevertheless, if subsidence and the several associated pavements, foundations, highways, airport runways, problems are to be mitigated, use of ground water, and swimming pools involving vertical displacement both in water volume and well density, must be (cover photograph); (2) topographic scarps defined by adjusted to the carrying capacity of the aquifers. This an abrupt steepening of land surface along uniform will require a modification of historical use patterns slopes or flat areas; (3) sharp breaks in rates of and most certainly some reduction in the amount of subsidence as determined from cumulative topographic ground water used in given areas, but it need not profiles; and (4) linear tonal anomalies on black-and- involve a complete curtailment of ground-water use white and on color-infrared aerial photographs. All and withdrawal. active faults shown on the Natural Hazards Maps have 11-35 been verified by ground observation; most of these are the Addicks fault in the Fairbanks oil field north- features have not been subjected to subsurface west of Houston (Van Siclen, 1967) and the analysis. Clarksville fault in the Saxet oil field west of Corpus Christi (Poole, 1940). Both of these faults can be The presence of cracks in highways and struc- traced to depths of 7,000 feet. The Saxet fault is tures, coupled with evidence of continual repaving of shown on the Natural Hazards Map of the Corpus highways or repairing of buildings, is an excellent Christi area. The Addicks fault occurs immediately guide for locating active faults. This type of evidence northwest of the Natural Hazards Map of the is considered the most reliable because it shows the Galveston-Houston area. precise location of the surface expression of the fault and indicates that the fault is presently active. A fault Several linear tonal anomalies, along which there crossing a parking lot at Ellington Air Force Base is has been no perceptible fault movement, also correlate shown on the cover of this atlas; this fault also with subsurface faults. Subsurface faults extrapolated extends across the runways, causing extensive, con- to the land surface in the Angleton oil field, the tinuing damage to the landing surfaces. Blessing oil field, and the West Columbia oil field generally coincide with both location and orientation Changes in the elevation of survey benchmarks of linear tonal anomalies. The lack of detailed well can also be used to delineate location and amount of control and seismic data, however, prevents a defin- movement along faults. Topographic profiles break itive conclusion that, in these cases, the surface linea- sharply across active faults. A subsidence profile, based tion and subsurface fault are in fact coincident. on cumulative, first-order topographic leveling data from Virginia Point to League City (along State The similarity in trend of surface and subsurface Highway 3 in Galveston County), is one of several faults indicates that most surface faults are probably such profiles that shows changes in topographic slope genetically related either to long-trending coastwise at the intersections of level lines and faults (fig. 17). fault systems extending upward from several thousand This technique is capable of pinpointing very slight feet below surface and/or to faults associated with the changes in differential subsidence; the only drawback numerous salt domes of the area. Faults radiating from to the method is that the benchmarks are generally salt domes may explain why some surface faults trend located a mile apart; this distance precludes a precise perpendicular to the common coastwise trend. Where location of the active fault with the level profile. verified, the association between surface and sub- surface faults indicates that some surface faults are Low topographic scarps may show the exact products of natural geologic processes. location of a fault, but it is difficult to determine if the fault is presently active or inactive. The continua- Faults of the Coastal Zone have been explained tion of such topographic scarps into a continually by a number of processes: (1) deposition of sediments cracking highway pavement nearby does confirm, (Carver, 1968); (2) upward movement of salt masses however, the recent activity of the fault, to form salt domes (Quarles, 1953); (3) gulfward creep of the coastal landmass (Cloos, 1968); and (4) bending The least confirmatory method for locating faults of the landmass due to regional tectonics. Sediment is the identification of linear tonal anomalies on loading, salt movement, and gulfward creep are black-and-white and on color-infrared photographs. probably the dominant causes for fault development in Nearly all active faults can be identified on aerial the Coastal Zone. Sediment accumulation in the photographs, but not all linear tonal anomalies are present-day Gulf Coastal Zone, however, is occurring active faults. Aerial photographs are a very important principally in the area of the Mississippi delta; there is tool, however, because they identify areas where more little evidence to document continued growth in the intensive ground study should be conducted. Several salt domes or a natural gulfward creep of of the active faults on the Galveston-Houston area unconsolidated sediments. map were initially identified by this technique and later substantiated by field work. METHODS OF FAULT ACTIVATION Faults in the Texas Coastal Zone are products of GEOLOGIC CONTROLS OF FAULTING natural geologic phenomena. Geologic evidence suggests that fault activity today should be a relatively Mapped surface faults and the surface trace of minor process. The frequency and activity of fault subsurface faults that are projected to the land surface movement, nonetheless, is increasing. There are clear exhibit a strong parallelism. At this time, however, indications that certain of man's activities, such as there are only a few cases for which sufficient data are ground-water withdrawal and oil and gas production, available to reliably connect the surface-expressed fault are causing this increase in fault activation. In the with a verified subsurface fault. Two such examples Houston-Galveston-Baytown area, where there has II-36 been heavy withdrawal of ground water, oil, and gas The amount of land subsidence at any particular and extensive concomitant subsidence, several faults point is also controlled by the amount of decline in have become active. Nearly all faulting has occurred in the potentiometric surface, as well as by the amount areas where the potentiometric surface (piezometric of mud within the aquifer system. If a fault acts as a surface) has dropped over 100 feet and where there hydrologic boundary and causes the potentiometric has been at least 1 foot of land-surface subsidence surface to be at different elevations on either side of (Galveston-Houston map). Of course, these areas of the fault, there will be different amounts of consolida- heavy ground-water usage are also the areas of greatest tion that may be expressed as fault movement at the land use and, hence, the presence of active surface land surface. faults and their effect is more likely to be noticed than in areas of less intense use. Vertical displacement on the Eureka Heights fault demonstrates fault activation by differential consolida- tion of sediment (fig. 18). The rebound of vertical The monitoring of movement on the Long Point displacement shown on the graph can be explained by fault and the Eureka Heights fault in western Houston shows a direct correlation between vertical fault dis- the slight expansion of elastic sand bodies within the placement and change in the potentiometric (piezo- aquifer on only one side of the fault. Rebound can metric) surface of the Chicot Aquifer (fig. 18). In occur if there is a hydrologic boundary or if there is a March of each year, when the potentiometric surface significant lateral change in the composition (facies) of begins to drop, movement along the Long Point fault the aquifer. becomes more rapid. In October, when ground-water pumpage decreases, the potentiometric surface rises Faults may also be activated by increasing the and the rate of fault movement decreases. Some overburden pressures (vertical effective stress), re- rebound even occurs on the Eureka Heights fault. suiting in a landslide-type failure. If the Gulf Coast sediments are treated as a large landslide, they are unstable with a factor of safety less than 1.0 (Reid, Faults are being activated by natural as well as 1973). The Coastal Zone theoretically should be man-induced phenomena. The Long Point fault in slowly sliding into the Gulf of Mexico. An increase in western Houston appears to be moving for normal effective overburden pressures (analogous to loading at geologic reasons and because of man-induced phe- the head of a landslide) should cause the unstable nomena. A topographic map with a 1-foot contour mass of sediments to move more rapidly toward the interval, surveyed before 1920, shows a topographic Gulf of Mexico and initiate an increase in active scarp coinciding with the location of the Long Point faulting. fault (Van Siclen, 1967). The curve of the fault displacement for the Long Point fault (fig. 18) at sectin .An increase in effective overburden pressure is section a-a shows movement even though there is accomplished by dropping the potentiometric surface decreased ground-water production and a rising poten- in an artesian aquifer. The downward flow of water tiometric surface, possibly indicating a natural method from a shallow, unconfined aquifer and overlying aquitards to the artesian aquifer transfers some of its energy to the sediments through frictional lag, causing Man-induced fault movement may occur by two an increase in the effective stress in the direction of different mechanisms: differential consolidation of ground-water flow. This increase in stress is known as sediments and landslide-type failure caused by vertical "seepage pressure." The effective overburden pressure seepage forces. Differential consolidation of sediments in a static system at any particular point in the can occur (1) if there is more mud on one side of a subsurface is approximately equal to the bouyant fault than on the other because of a facies change, or weight of the sediments. The additional seepage is (2) if the fault acts as a hydrologic barrier to fluid equal to the decline in the potentiometric surface migration. The amount of land-surface subsidence by times the unit weight of water (Lofgren, 1968). For consolidation of sediments depends, in part, on the example, at a depth of 400 feet, the effective over- amount of compressible clay associated with a sand burden pressure is equal to approximately 170 pounds aquifer. Many growth faults in the subsurface of the per square inch (psi). A drop in the potentiometric Gulf Coast area are located at major facies boundaries, surface of 200 feet will cause an additional effective separating, for example, prodelta muds from deltaic overburden pressure of 86 psi or a 50-percent increase sands. If growth faults were active during the Pleis- in the effective overburden pressures, which would be tocene, they may have caused appreciable facies varia- the same as depositing an additional 200 feet of tions in the Chicot Aquifer. An equal lowering of the saturated sediment over the Houston and Baytown potentiometric surface across a fault with different area. In some places in the Houston area, the poten- clay-sand ratios (facies) on either side will result in tiometric surface has dropped over 400 feet. This different amounts of consolidation and differential increase in overburden pressure may be enough to land subsidence. activate some faults in the Gulf Coast sediments. II-37 ........... .....o.. Vertical displacement Long Point Fault - 200 30 - rtico splacement Eureko Heights Foult 2-% .,,.I - 210 20- --., LU-.'A CL I'Drawdown /- -20 '0 LU -220 Completion interval 488 - 850 ft 0 I I I I I I I I I II I I I I I I I I[ I I I I I I I I I I I I 1971 1972 1973 1974 YEAR Figure 18. Vertical displacement on Long Point and Eureka Heights faults in western part of Houston compared to drawdown of piezometric surface of Chicot Aquifer. Displacement data for April 1971 to April 1972 from Reid (1973); displacement data for May 1972 to January 1974 and drawdown data for piezometric surface for federal observation well LJ-65-13-408 from R. Gabrysch (personal communication, 1974). Natural movement, differential consolidation, and where special care may be required in future develop- landslide-type failure are all important mechanisms for ment. It stands to reason that man-made structures fault activation; their relative importance in the Texas should be built with full knowledge of potential Coastal Zone has not yet been determined. Fault foundation problems. activation by oil and gas exploitation has also been documented in the Texas Coastal Zone. Pratt and Another related problem is the distance a struc- Johnson (1926) observed fault activation in the Goose ture should be built from a fault. Along some faults, Creek oil field. The Clarkwood fault west of Corpus the scarp (the topographic expression) is narrow, Christi, which exhibits a 4.5-foot scarp, was probably perhaps less than 30 feet wide, such as the fault in the caused by oil production from the Saxet oil and gas town of Hitchcock. Structures can be located safely in field. The extensive faulting over the Clear Lake oil close proximity to these kinds of faults, especially field also may have been caused by oil production. when special engineering techniques are applied. Other faults have relatively wide scarps. For example, the MITIGATION OF PROBLEMS topography in the area of the Long Point fault where ASSOCIATED WITH FAULTING it crosses Memorial Drive in western Houston appears to be altered up to 150 feet on either side of the fault One of the purposes of including the trace of (Reid, 1973). Construction of large, heavy structures active faults on the Natural Hazards Maps of this atlas should be carefully designed for or perhaps even is to help explain the reason for continual repair eliminated from this wide zone, whereas light struc- problems in particular areas (e.g., highways, city tures, such as houses, may not be adversely affected. streets, and train tracks) and to delineate those areas The width of these hazardous zones needs to be 11-38 evaluated for each fault. Because the coastal plain is so prone lands and in attempting to explain, with current flat, unlevel land adjacent to an active fault is knowledge, the processes leading to the hazard. probably an indication that the area is being affected Second, the present and projected use of hazard-prone by recurring fault movement. Subtle variations in lands needs to be determined and inventoried. Third, topography can best be determined by measuring the hazard impact, in terms of frequency, extent, and change in slope with surveying equipment. These slight severity, can be assessed in terms of the relation of variations can also be determined by detailed analysis costs to benefits. Special attention needs to be of benchmark-level data. directed to those natural hazards that may pose a threat to life or property. Cost-to-benefit analysis can also be applied to determine whether it is feasible to The rate of movement along a Coastal Zone fault undertake technological and engineering programs is another factor of importance to the people of the aimed at mitigation. For hazard-prone lands already region. The sudden movement along a California-type developed, the construction of hazard prevention fault produces earthquakes and does extensive damage structures is the only recourse in hazard mitigation; to areas not even close to the active fault. Fault for hazard-prone lands that have not been developed, a movement in the Texas Coastal Zone, however, is variety of alternative measures may prove to be both gradual, and earthquakes are not a hazard. The economical and appropriate. amount of surface displacement that can be recognized on the Coastal Zone surface faults ranges up to as In a recent study by the California Division of much as 40 feet at the Hockley scarp northwest of Mines and Geology (Alfors and others, 1973), the Houston. This accumulated displacement has, however, total projected loss to the State of California from occurred over a long period of time predating man's natural hazards over the period 1970 to 2000 is settlement of the Coastal Zone. Most fault scarps in estimated to be $55 billion. While California has some the Coastal Zone are no more than a few feet high. In hazards not common to Texas, such as earthquakes, Houston, the average rate of displacement has been Texas experiences some natural hazards that do not estimated to be 1.3 inches per year (Reid, 1973). It is occur in California. Importantly, the California report feasible to build structures across these faults as long estimates that $38 billion of the $55 billion loss, or as they are designed so that engineering techniques can about 70 percent, can be prevented by applying compensate for differential offset. current state-of-the-art loss reduction or hazard mitiga- tion measures. These measures include technological and engineering approaches, as well as methods Faults of the Texas Coastal Zone need not be a pr oblem. Future T constalcZon needlt cno be a involving zoning and preventative planning. Further, prolem Fuureconstruction on faults can be these hazard mitigation measures can be applied at a avoided, and where this is impossible, the awareness of cs $ iion e te ape cost of $6 billion over the 30-year period. A corn- faults will permit architects and engineers to design b l l over t eef rio om parable overall cost-to-benefit ratio generally would be structures that can accommodate the low rates of applicable in the Texas Coastal Zone. In addition to differential movement. Decreased ground-water usage aiin the ee o as l Zet an satisfying the need for increased public safety and may tend to deactivate many of the faults (fig. 18). Tehnically, this method of tefault mitigation is fulfilling the social and political requirements, natural Technically, this method of fault mitigation is hzr euto n iiaini ipygo possible. hazard reduction and mitigation is simply good possible.buies business. * CONCLUSIONS * A number of natural hazards affect the Texas Coastal Zone. Some of these hazards are actually increasing in magnitude, but the impact of all hazards obviously becomes more critical with increased devel- opment in the Coastal Zone. The degree of impact and the damage and loss resulting from natural hazards depends upon the particular use made of hazard-prone lands. Mitigation of the impact of natural hazards can lead to significant reduction of losses currently sustained or likely to be sustained in the future. Clearly, the first step in mitigating the effects of natural hazards is adequate and comprehensive delinea- tion of hazard-prone lands and of processes that give rise to the hazard. "Natural Hazards of the Texas Coastal Zone" is a first effort in delineating hazard- II-39 * SELECTED REFERENCES e Gabrysch, R. K., 1969, Land-surface subsidence in the Houston- Galveston region, Texas: Tokyo, Japan, InternaL Symposium on Land Subsidence, Proc. 1969, p. 43-54. 1972, Development of ground water in the Houston Alfors, J. T., Burnett, J. L., and Guy, T. E., Jr., 1973, Urban district, Texas, 1966-69: Texas Water Devel. Board Rept geology master plan for California: The nature, mag- , 24 p. __ , and Bonnet, C. W., 1974, Land-surface subsidence in nitude, and costs of geologic hazards in California and the Houston-Gaveston region, Texas: U. S. Geol. Survey recommendations for their mitigation: California Div. op en-file rept., 23 p open-file rept., 23 p. Mines and Geology, Bull. 198, 112 p. , and McAdoo, G. D., 1972, Development of ground- Andrews, P. B., 1970, Facies and genesis of a hurricane- water resources in the Orange County area, Texas and washover fan, St. Joseph Island, central Texas coast: Louisiana, 1963-71: Texas Water Devel. Board Rept. 156, Univ. Texas, Austin, Bur. Econ. Geology Rept. Inv. 67, 47 p. 147 p. Harris, D. L., 1963, Characteristics of the hurricane storm Behrens, E. W., 1969, Hurricane effects on a hypersaline bay, in surge: U. S. Weather Bur. Tech. Paper No. 48, 139 p. Castanares, A. A., and Phleger, F. B., eds., Lagunas Harris, W. D., and Jones, B. G., 1964, Repeat mapping for a Costeras, Un Simposio: Mexico, D. F., Universidad Nac. record of shore erosion: Shore and Beach, v. 32, no. 2, p. Autonoma de Mexico, UNAM-UNESCO, Mem. Simposio 31-34. Internat. Lagunas Costeras, p. 301-312. Hayes, M. O., 1967, Hurricanes as geological agents: Case Bodine, B. R., 1969, Hurricane surge frequency estimated for studies of Hurricanes Carla, 1961, and Cindy, 1963: Univ. the Gulf Coast of Texas: U. S. Army Corps Engineers, Texas, Austin, Bur. Econ. Geology Rept. Inv. 61, 56 p. Coastal Eng. Research Center Tech. Mem. 26, 32 p. Lofgren, B. E., 1968, Analysis of stresses causing land sub- Bryant, E. A., and McCann, S. B., 1973, Long and short term sidence: U. S. Geol. Survey Prof. Paper 600-B, p. changes in the barrier islands of Kouchibouguac Bay, B219-B225. southern Gulf of St. Lawrence: Canadian Jour. Earth Sci., Lohse, E. A., 1955, Dynamic geology of the modern coastal v. 10, no. 10, p. 1582-1590. region, northwest Gulf of Mexico, in Finding ancient Carr, J. T., Jr., 1967, Hurricanes affecting the Texas Gulf shorelines-a symposium: Soc. Econ. Paleontologists and Coast: Texas Water Devel. Board Rept. 49, 58 p. Mineralogists Spec. Pub. 3, p 99-105. Carver, R. F., 1968, Differential compaction as a cause of Marshall, A. F., Jr., 1973, How much more will Houston sink? regional contemporaneous faults: Am. Assoc. Petroleum The disturbing problem of land surface subsidence: Geologists Bull., v. 52, no. 3, p. 414-419. Houston Eng. & Sci Society, The Slide Rule, v. 33, no. Clanton, E. S., and Amsbury, D., 1974, Open fissures associated 2 6 p. with subsidence and active faulting in the Houston area, McGowen, J. H., and Brewton, J. L., 1975, Historical changes Texas (abs.): Geol. Soc. America, Abs. with Programs, v. and related coastal processes, Gulf and mainland shore- 6, no. 7, p. 688-689. lines, Matagorda Bay area, Texas: Univ. Texas, Austin, Cloos, E., 1968, Experimental analysis of Gulf Coast fracture Bur. Econ. Geology Rept Inv. 84 patterns: Am. Assoc. Petroleum Geologists Bull., v. 52, , Garner, L. E., and Wilkinson, B. H., 1972, Sig- no. 3, p. 420-444. nificance of changes in shoreline features along Texas Colon, J. A., 1966, Some aspects of Hurricane Carla (1961), in Gulf Coast (abs): Am Assoc. Petroleum Geologists Bull., Hurricane Symposium: Am. Soc. Oceanography Pub. No. v. 56, no. 9, p. 1900-1901. 1, Oct. 10-11, 1966, Houston, Texas, p. 1-33. , Groat, C. G., Brown, L. F., Jr., Fisher, W. L., and Cooperman, A. I., and Sumner, H. C., 1961, North Atlantic Scott, A. J., 1970, Effects of Hurricane Celia-a focus on tropical cyclones, September 1961: Climatological Data, environmental geologic problems of the Texas Coastal Natl. 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Texas Coastal and Marine Council, 1974, Hurricane awareness II-41 SECTION III HAZARD ZONE DELINEATION FOR STANDARDS AND CODES The principal purposes of the effort reported in this volume are to develop minimum performance criteria for structures located in high-hazard coastal areas and to draft a model building standard that can be readily incorporated into common existing building practices. From the beginning it was obvious that it would be necessary to define specific hazard zones on the basis of the degree of exposure to destructive processes, and to develop standard requirements for each zone.* The standards and model building code presented in the following section are designed to provide a reasonable chance for survival of buildings during the occurrence of a hurricane. Any structure built to the code is likely to survive, but an extra margin is provided for high-rise structures that could be used for safe refuge, i.e., vertical evacuation of residents. For high-rise buildings, specific requirements are given for the skin or cladding, since these are of utmost importance if the building is to be used for safe refuge. THE TEXAS DESIGN HURRICANE Before looking at the zone delineation process, it is necessary to determine what parameters are most likely to be associated with the occurrence of a "probable" hurricane. Many approaches exist for statistically estimating hurricanes of specific recurrence intervals, and for classifying them as minor, major, or great hurricanes. Section II, "Natural Hazards of the Texas Coast," contains a detailed discussion of these approaches. Some federal agencies have used the concept of standard, project or probable maximum hurricanes. These classifications differ among agencies, mostly because the different agencies have different missions and thus are concerned about different effects. For the purpose of this report--the development of model minimum building standards--a mixture of the likely forces taken from federal agencies' definitions of typical hurricanes, tempered Since this hazard zone delineation process is vital to correct application of the model standard, this entire section should be distributed with any copies of the model standard. by the judgment of a panel of experts, is combined to give the Texas Building Design Hurricane (TDH). This hurricane is severe enough to warrant consideration in building standards and occurs frequently enough to make the use of more rigid standards than those presently being used economically feasible. It is expected to generate the following sources of potential damage: * WIND: maximum windspeeds (fastest mile) up to 140 mph at a height of 30 feet, increasing with height in accordance with the one-seventh power law to a maximum about 300 feet above the surface for open coastal areas. Peak gust speeds will exceed the sustain'ed values by varying percentages as given in the wind load section of the code. (In general, gust percentages will decrease with height increase.) a HURRICANE TIDES (three sources of potential damage): 1. SCOUR due to currents and wave action, including washovers; 2. BATTERING due to waterborne debris; 3. FLOODING due to combinations of rises in sea level from storm surge and inland runoff from heavy rains and riverine discharges. HURRICANE HAZARD ZONES An analysis of the processes and forces associated with a hurricane; extensive examination of empirical damage data; and a thorough knowledge of the geological, hydrological, and topographical characteristics of the Texas coast leads to the identification of four distinct coastal hazard zones.* These are shown in Figure 111-1. Ranging from most to least severe, they are ZONE A: 1. 140 mph sustained winds; 2. scouring action affecting foundation design; 3. battering due to waterborne debris. For further discussion of specific daimage mechanisms, see Section II of this report; U.S. Army Corps of Engineers Hurricane Dcmiage Survey Reports; and NOAIA's damage assessments. 111-2 WIND Zones 14O MPF A. BATMERIN VD WIND FLO)DI NG WIND B TrnI 140 MPH BATT ...... . WINDE!N 140 MP14 FLooDING WIND WID -WIND FIGURE 111-1 (SAME AS FIGURE i-2) SCHEMATIC REPRESENTATION OF HAZARD ZONES A TO D IN TEXAS COASTAL AREAS, 111-3 4. flooding (still water levels from expected hurricane inundation more than one foot above building grade level). ZONE B: Same as Zone A except without scour. ZONE C: Same as Zone A except without scour and battering. ZONE D: 140 mph sustained winds at C-D boundary, diminishing inland as an inverse function of distance to 100 mph.* COMPUTATION OF HAZARD ZONES For regular coastlines without barrier islands, embay- ments or estuaries, the four hazard zones will comprise a family of narrow strips paralleling the coast. The inland extent of each is normally a function of the height of the storm tide hydrograph at the open coast, the topo- graphy of the coastal plain, and the rainfall runoff associated with the hurricane. When barrier islands and large estuaries are present the inland flooding and the disfiguration of otherwise uniform hazard zone strips is influenced by (1) barrier islands which impede volume transport of surge water inland, (2) the additional component of surge (wind setup) due to wind stresses on shallow water surfaces in estuaries which in turn is a function of (3) the bathymetry and geometry of the estuary, (4) the size and rate of movement of the hurricane, (5) the rainfall runoff and riverine discharges (fresh water), (6) the initial rise of salt water (1-3 feet) in the estuary (fore- runner tide), often arriving more than 24 hours ahead of the storm center, (7) the tendency for seiching action as the hurricane moves inland, and (8) the usually smaller incre- ments (on the Texas coast) contributed by astronomical tides and wave setup. There is no general two-dimensional model for use in bays or estuaries to compute numerically the total inundation 40 VD = 100 + 1+-d ' where VD = wind speed in Zone D d = distance inland from C-D boundary III-4 potential across inland bay shores.* Most models with enough physics incorporated to accomplish this are either adapted to the bathymetry of a single shallow estuary, or otherwise compute in one dimension the inundation along a single line or transect inland from the coast. To model, in two or more dimensions, the scope of inland flooding for a single bay area is a very expensive and time-consuming task, and the results apply only to that area. What is needed is a reasonable, conservative approximation procedure which can be used quickly and inexpensively by competent engineers, and which will always yield the same results. The method and alternative specific procedures described in Annex C meet these requirements. It is a general method, physically founded, that can be applied quickly and inexpensively by qualified engineers. It is sufficiently objective to yield repeatable results, and precise enough to use for determining the hazard zone of a particular structure and for establishing the appropriate building standard/code.** PRIMA FACIE FACTORS IDENTIFYING HAZARD ZONES*** Irrespective of the flood levels computed for a building site using the procedures described in Annex C, the following physical exposures will be overriding in determining in which zone a particular site is located. I. ZONE A. Areas of washover and scour: a. Narrow, low segments of barrier islands and peninsulas that are generally breached as a * A quasi-two-dimensional model has been applied to individual bays and estuaries of some portions of the Texas coast by the U.S. Army Corps of Engineers based upon work by Reid and Bodine (1970), and work is in progress on similar models elsewhere. However, each bay poses a separate modelling problem, and the output comprises only the surge component of tidal flooding, not the freshwater contributions or the initial rises, which on the Texas coast may be considerable. ** A technical paper by Drs. Simpson and Freeman, who developed the procedure, is available through the Texas Coastal and Marine Council for those wishing to explore the theory and mathematics of the procedure. ** As used herein, "prima facie conditions" refer to physical evidence--meteorological, geological, topographical, or hydrological--which may be in disagreement with the analytical results. In such cases, the specified prima facie evidence will govern. III-5 result of elevated water levels during hurricanes or tropical storms will be classified as Zone A. Such areas include much of Bolivar Peninsula in the vicinity of Bolivar Bay, Matagorda Peninsula east of Green's Bayou, the southern end of San Jose Island, and South Padre Island. Other coastal areas having experienced or presently holding a high potential for washover (breaching) during a hurricane will also be classified as Zone A. Sources for the identification of such areas include the Bureau of Economic Geology, the University of Texas at Austin. b. A zone extending between Gulf beaches and a line at least 300 feet inland from the maximum elevation immediately adjacent to the beach (e.g., dune crest or crest of sand and shell ramp) will be classified as Zone A. c. A zone along low-lying (less than 10 feet) unpro- tected (nonbulkheaded) bay shorelines, extending at least 200 feet inland from the highest elevation near the shoreline will be classified as Zone A. d. Areas within 200 feet of unprotected (non- bulkheaded) navigation channels on peninsulas and barrier islands will be classified as Zone A. e. Areas with a sand substrate subject to hurricane flooding greater than 3 feet in depth and with expected water current velocities greater than 3 feet per second for one hour or more during the rise or fall of the surge will be classified as Zone A. 1I. ZONE B. Battering: In the absence of washover channels and extensive scour, battering from waterborne debris will be expected to occur and will comprise the basis for defining Zone B under the following situations: a. On barrier islands and peninsulas a zone of flooding extending inland from the most landward foredune or ridge line to the boundary of Zone C, or on low-lying bay shorelines having primarily clay substrates, a zone extending inland from the shoreline at least 500 feet regardless of building density. III-6 b. In areas where hurricane flooding is expected to be greater than 4 feet, building density is not greater than one major structure per acre, and fetch is considered to be the distance a wind of constant direction travels without interruption or diversion over a water surface. III. ZONE C. Wetting: In the absence of the above conditions, but where still water hurricane flood levels are in excess of one foot, the area will be designated as Zone C. IV. ZONE D. Wind Only: Zone D is concerned only with wind forces on structures, primarily the dynamic loads. The problem in defining the inland extent of unusually severe hurricane winds and thus the width of Zone D is that the rate at which winds of design speed at the coast diminish is less a function of the roughness of the terrain than it is of the baroclinity* of the environment into which the hurricane moves as it passes inland. If a hurricane retains the barotropic** environment which attends it most of its life over ocean areas, the loss of energy flowing from sea to air will rob a hurricane of its hurricane force winds in a few hours after it crosses a coast. If, however, it encounters a baroclinic environment, especially one which accelerates the outflow at the top of the cloud system, it may retain winds of 75-100 mph great distances inland--e.g., in Hurricane Hazel, 1954, and to a lesser degree, Hurricane Agnes in 1972. However, there are no examples of hurricanes maintaining such extreme winds as 140 mph observed at ocean or bay shores more than a few tens of miles inland. Therefore, Zone D is arbitrarily defined as an area in which the wind at the C-D boundary is 140 mph, but diminishes to 100 mph as an inverse function of distance inland from the C-D boundary***, to a minimum of 100 mph. In this specification * Baroclinity - a property of the atmosphere characterized by large horizontal temperature variations. Energy from baroclinic sources sometimes succeeds in accelerating movement of air flowing out of the top of hurricanes, and thus the flow of air through the hurricane, keeping it strong after it loses its initial barotropic energy sources. ** Barotropic - a condition characterized by very small temperature gradients and one in which the sources for the development of storms depends primarily upon the release of heat from the growth of cumulus clouds. This condition is essential to the formation of hurricanes and for the growth which characterizes most of their life cycle. *** VD = 100 +-40 , where VD = wind speed in Zone D l+-T d = distance inland from C-D boundary 111-7 it is acknowledged that large variations around these figures will occur from hurricane to hurricane. In a few cases even small interior areas of barrier islands may be classified as Zone D where elevations are substantially above 20 feet MSL and the soil is stabilized from erosion. DOCUMENTATION OF HURRICANE-RELATED PROCESSES AND ATTENDANT DAMAGE IN ZONE A From the standpoint of coastal planning, Zone A is the most critical zone for building design. It is also the most readily identified hazard zone in the field and on aerial photographs because of the distinct alteration of the land- scape by strong currents and wave action. Extensive coverage of aerial photographs taken immediately following Hurricanes Carla, Beulah, and Celia provide sufficient information for the delineation of washover channels as defined above. The damage from Hurricanes Carla, Beulah, and Celia is well documented in other reports (U.S. Army Corps of Engineers, 1962, 1968, 1971; Brown and others, 1974; Hayes, 1967; McGowen and others, 1970), but the principal cause of damage from each storm (surge, aftermath rainfall, wind) exceeds the equivalent characteristics of the design storm used to determine the extent of hazard-prone areas. On the other hand, data on dune retreat and shoreline changes are available for other storms; for example, the 1949 hurricane (aerial photographs) and Hurricane Fern (beach profiles). From these and other field data we can determine the maximum and average beach scour and dune retreat. These figures can then be used with other physical parameters to determine the projected limits of areas affected by hurricane-related processes. Several storms have caused beach erosion and dune retreat of 50 feet or more. Maximum shoreline erosion documented on the Texas coast occurred during Hurricane Carla when a segment of Matagorda Peninsula retreated 600 feet (McGowen and Brewton, 1975). Dune retreat and shoreline erosion produced by surge from Carla were of extraordinary magnitude in the area affected by the right semicircle of the storm. Fortunately, there was no residential or commercial development near the site of landfall on Matagorda Peninsula, for many buildings would have been destroyed. Recently, a storm less intense than Carla (Hurricane Eloise, September 1975) struck the Florida coast and caused extensive damage. Building foundations were undermined and superstructures collapsed as a result of beach scour and dune retreat (Morton, 1976). I1I-8 The fixed distance (300 feet) representing the landward boundary of Zone A was selected primarily for a pragmatic reason: the constant distance facilitates the hazard zone identification process. Otherwise, it would be necessary to develop a complicated procedure whereby the probability of storm occurrence for a given time period and coastal segment would be used with an average value of dune retreat per storm to determine, in conjunction with dune characteristics, a theoretical dune erosion value which then would be used with a margin for indeterminants to define the landward boundary of Zone A. In essence, the value of 300 feet represents an estimate of dune retreat that might be expected over a long period with the probability of a hurricane every 11 years, and the probability of a great storm every 29 years. Historical records indicate that the cumulative effect for a long period would be about 200 feet with a margin of safety of 100 feet. This does not suggest that scour will not occur 300 feet inland from the dune crest, but rather that the probability of such an event is rather low. ALTERNATIVE BOUNDARY SELECTION--ZONE A In many respects, the beach and washover areas described in preceding sections are similar to Zone V (velocity) on the FIA flood maps.* There are, however, minor differences in the boundaries. For example, the FIA maps exhibit straight line boundaries which do not conform to the topography. In contrast, the boundaries proposed for the hurricane hazard zones are controlled largely by the topography; therefore, mapped boundaries for Zone A would not be straight lines but would be dependent on the configuration of the dunes and washover areas. Another difference in approach is that the FIA maps emphasize elevation whereas the hurricane hazard zones emphasize distances on the ground. PEAK STORM SURGES A major input to the zone determination is an estimate of the peak storm surge and flooding levels at the open coast and at bay shores. Too often it is assumed or concluded that the highest surges always occur at the open coast directly exposed to the sea. Factually, the ratio of surge heights at the open coast to those on bay shores depends upon the speed, size and direction of approach of a hurricane. A severe slow-moving hurricane can cause much higher flooding at bay shores many miles from the open coast than at the *Those maps issued by the Flood Insurance Administration that define their categories of floodplain. 111-9 coast itself. For example, in Hurricane Carla, 1961, the maximum surge height on the Gulf front of barrier islands was approximately 15 feet, but near Port Lavaca, 23 miles away, the surge exceeded 22 feet. On the other hand, a storm moving inland at moderate speeds may cause surges of equivalent height at both open beaches and bay shores far inland, and a rapidly moving hurricane will cause greater tides at the open coast. The selection of a design hurricane needs to provide an equitable balance between these possibilities, and the methodologies used to define the Texas Design Hurricane addressed this problem. The profile of peak open-coast surges for the Texas Design Hurricane is presented in Figure 11-2. The methods used and input parameters for computing this profile are contained in Annex A. The average surge level is 13.5 feet, with bimodal peaks of 15.4 feet and 17.7 feet at central Padre Island and near Orange, respectively. Minimum expected surges of 12.0 feet and 11.5 feet occur at Port Isabel and Rockport, respectively. To these surge heights must be added the initial rise and astronomical tide stage to obtain the total hurricane tide. As explained in Annex A, this increment totals 3 feet to which the freshwater accumulations must be added to compute the total flooding potential. PROCEDURES FOR COMPUTING INLAND FLOOD LEVELS AND FOR DESIGNATING HAZARD ZONES The flood levels caused by open coast storm tides, the additional surges which develop over bays and inland water, the tidal maxima at bay shores, and associated inland flooding, are presented in the Annexes to this section. Annexes A, B, and C present the procedures for com- puting flood levels and other characteristics which are necessary to identify the hazard zones for a proposed building site in order to select the appropriate model building code. Annex A contains the background and results of computations of open coast storm tides to be expected from the Texas Design Hurricane. Annex B describes the methodology and conceptual basis for computing surge maxima at bay shores and the inland flooding these cause. III-lo Houston LA. L ORER --_, , ALVESTON Texas Design Storm Surge 20 (Open Coast) PT. ISABEL P.AA S FEPR AVSO EA-A FIGURE C 1411-2 (See A-i f ormdetaieelationPons) III-11 Annex C details the procedures to be used in computing inland flooding profiles and the design flood level at a specific location. Alternative methods for applying these Procedures, with sample computations, are presented. They include (1) the use of a nomogram for computing the series of hydrographs needed to construct flood level profiles, and (2) a program for use with a hand-held programmable calculator to accomplish the same purpose more rapidly. A listing of the program for the latter procedure is included. The results using either method are equivalent. Not presented here, but currently being developed, is a FORTRAN IV program which can be used with almost any modern time-share facility which has a FORTRAN compiler to obtain the same results very quickly. The time required for determining the design flood level at one location, using the nomogram is nominally 6 hours; with the programmable calculator, 2 hours; and with the FORTRAN program, this can be done with a few minutes of man-time and then only a few seconds of computer-time. For references, see Appendices following Section IV. III-12 ANNEX A COMPUTATION OF HURRICANE TIDES AT THE OPEN COAST The hurricane tide at the open coast is a combination of several components, the principal one of which is storm surge. Other components include (1) the astro- nomical tide; (2) the "initial rise" or "forerunner tide" (occurring more than 24 hours prior to arrival of the hurricane with range of 1-3 feet); (3) wave setup, (rarely over 2 feet, but in some peculiar bathymetric configurations may be much larger; e.g., Eloise, 1975, where surge may have been only 9 feet, and wave setup 4-6 feet); (4) wave runup (usually small); and (5) rainfall runoff. At two Texas coast locations wave setup may be important: (a) central Padre Island and (b) the Rockport area. Within computational error the open coast hurricane tide on the Texas coast is primarily a function of the computed surge height. The computations of storm surge profiles for the open coast of Texas have been made for a severe hurricane whose damage potential, in terms of characteristic strength, size, movement, and recurrence frequency, can be effectively and economically mitigated by building design measures. The climatology upon which the computations were based is taken from a recent study by Ho, Schwerdt, and Goodyear (1975).* The characteristics used in this study, a function of latitude, are listed in Table A-1 and vary up the coast as follows: 1. Central pressure: 903mb at Port Isabel increasing to 937 at Orange. 2. Radius of maximum wind: 14 miles. 3. Hurricane movement at point of landfall: 14 kts. 4. Direction of hurricane approach: normal to the coastline. NOAA Tech. Report NWS 15 entitled, "Some Climatological Characteristics of Hurricanes and Tropical Storms, Gulf and East Coasts of the United States" (May, 1975). III-A-1 TABLE A-1 INPUT DATA FOR SPLASH II PROGRAM TO COMPUTE SURGE HEIGHTS FOR THE STATE OF TEXAS DESIGN HURRICANE Point Landfall Pmi SPma Rmax C Dir. of (mb) (m) ( mi) (kt) Storm Pt. Isabel: 30L 903 113 14 14 W 2 Pt. Isabel: 0 904 112 14 14 W 3 Pt. Isabel: 30R 910 106 14 14 W 4 Pt. Isabel: 60R 915 101 14 14 W 5 Pt. Isabel: 90R 920 96 14 14 W 6 Aransas Pass: 12R 925 91 14 14 WNW 7 Matagorda: 6L 928 88 14 14 NW 8 Matagorda: 23R 930 86 14 14 NW 9 Matagorda: 54R 931 85 14 14 NW 10 Galveston: 15L 934 82 14 14 NNW 11 Galveston: 15R 936 80 14 14 NNW 12 Galveston: 45R 937 79 14 14 NNW 13 Cameron, La.: 12L 937 79 14 14 N III-A-2 This climatology is statistically founded without explicit dynamical constraints and as such may tend to overemphasize the gradient characteristics from southern to northern coastal areas. This may result in a slight under- estimate of computed surge heights in the upper coastal reaches. However, the differences are believed to be within the probable errors in distributing the water inland. The selection of a relatively small radius of maximum wind and fast approach to the coast was adopted as a most equitable compromise in obtaining realistic flood levels at the open coast and for inland reaches of estuaries and bays. A slower-moving storm would provide lower surge values at the open coast and high values for bay shores. A larger radius of maximum wind would be inconsistent with the very low central pressure adopted. The central pressures are those which have an expected return period of 100 years. Realistic values of flooding at bay shores have been built into the procedures for computing inland flooding as a function of wind setup on the inland water bodies described in Annexes B and C. The model used for computation of the surge profiles, known as SPLASH II, was developed by Jelesnianski (1972). The decision to use this model is supported by the report of a Panel on Coastal Surges appointed by the Building Research Advisory Board of the National Academy of Science.* This report reviews a number of dynamic prediction models and concludes that the Jelesnianski model is the best presently available for computing surges at the open coast. Computations were made at 13 positions, 30 miles apart for a hurricane approaching normal to the coastline and having the characteristics listed in Table A-1. The results are presented in Figure A-i, where the profile represents the envelope of peak surge values for the 13 computations made. In the procedures for computing the inland flooding, Annex B, the convention adopted is to assume that a pre- liminary rise of two feet exists both at the coast and on inland water prior to the initiation of rises due to surge. Then an increment of one additional foot due to astronomical tide stage is added to the computed peak storm surge for the Design Hurricane as a basis for deriving the surge hydrograph. This combination is approximately equivalent to the arrival of peak surge at time of spring high tide. *National Academay of Science, Panel of Hurricane Surges, 1975, Washington, D.C. 111-A-3 100 200 300 TEXAS DESIGN STORM SURGE 20 2 (Onen Coas0 J 20 I--is U10 OPE Rv MAX - 14m i R lO AT 14K. 5se Dtie ine fmFiue15 Pt. Aransas FrTexas-La. if _-_ - S lBo rder 0 100 200 300 OPEN COAST DISTANCE FROM PT. ISABEL LIGHT (mi.) FIGURE A-1 SURGE ELEVATIONS AT OPEN COASTLINE (Detailed inset from Figure II-2) HURRICANE HYDROGRAPH The Design Hurricane characteristics from Table 1 run on the SPLASH II program produce a hydrograph whose shape is essentially that of Figure A-2. Hydrographs were computed for the lower, middle and upper Texas coasts. Since the shape and size is very nearly conserved for constant radius of maximum wind (R) and forward speed (c), a normalization is feasible in which surge values for the design hydrograph are expressed in terms of percentage of peak surge value. Figure A-2, the design hydrograph, shows the rate of rise (and fall) of surge heights at the open coast and is the basis for computing the distribution of surges inland. It should be noted that the rate of fall implied is not real, however, since the retreat of inundation is more complex than the advance and involves in many uses additional water volume accumulations (rain and riverine discharges) and much larger bottom or frictional stresses. Therefore, the ebb rate will be distorted, usually (but not always) being slower than the computed rate. Figure A-3 is a schematic showing spatial distribution along the coast and vertical rise prior to landfall. III-A-5 LANDFALL HOURI5 BEFORi'E LANDFALL TIME HOURS ARER LAND:FALL -10 -8 - -4 -2 T. 42 +4 +6 I jI I I \ I ioo - -so Io/ HURRICANE TI MACK ,8 ,/ Z 150- FIGURE A,2 TIME HISTORY OF OPEN COAST STORM SURGE HEIGHTS FOR DESIGN HURRICANE, (THIS IS A NORMALIZED HYDROGRAPH SURFACE EXPRESSED IN TERMS OF PERCENTAGES PEAK SURGE ENVELOPE GIVEN IN FIGURE A,1) III-A-6 f it bi 1J ,9 N FIGURE A-3 SCHEMATIC SHOWING RISE OF SURGE ALONG OPEN COASTLINE BEFORE LANDFALL AND SPATIAL DISTRIBUTION ALONG COAST. Ill-A-7 ANNEX B CONCEPTUAL BASIS FOR COMPUTING INLAND FLOODING The Texas coast comprises mainly a chain of barrier islands separated from the mainland by narrow shallow bays or lagoons, a few of which expand into larger, deeper bays or estuaries as in the Corpus Christi, Galveston and Matagorda areas. Tides from severe hurricanes will overtop portions, if not all, of-most barrier islands, combining with the wind-driven shoal waters of bays and estuaries to flood the lee shores. The routing of these floodwaters is accomplished by using a procedure designed by the Institute for Storm Research at Houston, Texas. This procedure requires as input: 1. a hydrograph or chronology of the storm tide stages at the open coast for the period 10 hours before through 6 hours after hurricane landfall (see Figure A-2); 2. the hurricane wind field corresponding to the hydrograph values for the line of computation. This line, which is parallel to and 14 miles to the right of the hurricane track, passes through the position of tidal maximum at the open coast (see Figures B-la and B-lb). 3. a topographic profile of ground (or bottom) levels, relative to mean sea level, extending inland normal to the open coast or bay shore (whichever is applicable) through the point (Q) for which the hazard zone is to be determined. The initialization selects the appropriate design surge maximum for the coastal point in question (Figure A-l). Hydrograph computations to complete Table B-1 are made in terms of a peak tidal value comprising the peak surge plus an astronomical tide of one foot MSL (2.1 feet MLW), considered to arrive at the coast or shoreline coincident with the surge maximum. To the computed hydrograph from Table B-1 is added an invariant value of initial rise, 2.0 feet, to obtain the total tidal stage for each time step in the compu- tation of inland flooding. For flood routings across land, or over inland water surfaces less than 5.5 feet deep (MSL), the line of computation is positioned to pass through (Q) and to cross the open coast (P) at right angles (see Figure B-2). III-B-1 / -- - 20 t 4 140 - t TEXAS DESIGN HURRICANE -1 Surface Wind and Inflow J s 120 Z < t {Q (uass-Stationary System ) 1 100 - | \--10 180 I -18 Z 160 1 166 UI 40 4 2 0 Ife 2 10 20 30 40 50 60 70 80 90 100 t11 RADIAL DISTANCE FROM CENTER R ( mi.) FIGURE B-1A COMPOSITE WIND FIELD FOR THE TEX AS DESI GN HURRICANE FOR A QUASI-STATIONARY SYSTEM BASED UPON SPLASH II COMPUTATIONS. The actuaZ wind field (Figure B-lb) accounts for the hurricane movement by addition of a component of movement nC, where C is the vector of U movement (down trfack)e Wind n is a ndt in the SPLAS model. III-B-2 -120- (Ouasi- Stationary System) - 01 0 L, 10-'10 -L.3 80' 60- 2 0 3 0 5 07 0 9 0 1 RAIAD I TNEFOCETR(m. FIGUEB1 CMOITWNDFEDFRTETXSDSGHURCEFR A QUAS I-TTNAYSSEBAEUPNSLSIICOPTIN, 40 cua id il F igr B-4bconsfrtehriaemvmn by add itino opnn fmvmn ,weeCi h etro moemn (on rck ndnisaemiilcofceninteSLH moe. I-- (mph) II · · - *+1' .....-' '3'1. · lomi. * .33 ' . . · · - ' * ' ......-:*. 39.... *-.. .80' .-- '42 l,· i 5 , . , i, Ioe .40 76. '. ,20' .' X , *-. *'. '. * .' . J 59 '. I 106 70 --...., .. 51 1 (mph) FIGURE B-lB COMPOSITE WIND FIELD FOR THE LINE OF COMPUTATION USED IN THE TEXAS DESIGN HURRICANE MOVING INLAND AT 14 KNOTS. III-B-3 4. & ........ . . ... *.d... ... ..+4 H." .... ....... ... ........... .. .......... .... .. ..... .... .. ............ ... ............ ...... .................... . ...... .. ....... . .... .... ...........2 ...... I ............ .......... ............ .......... ....... . ...L ..........14 mi. GULF... ........FGUR.B- ORENATONOFLIE F OMUTTIN ORDITRBUIN OE COAST. ...IAN TIE.NADADOE SOLILN AEWY Landfall11-8- For flood routings across bays or estuaries of greater depth, the tilting up of the water surfaces at lee shore due to wind setup may bring even larger inundations than at the open coast if severe hurricane winds operate on the water surface for 90 minutes or more. (In Carla inland flooding reached the 22 foot level, while tidal maxima at the coast were only about 15 feet.) Therefore, a special computation procedure is used for determining the surge maximum due to wind setupt. This surge maximum, physically determined, is a function of the water depth (MSL) and an optimal distance over which hurricane winds can operate on the shallow water basin. Procedures for these computations are contained in Annex C. A sample computation sheet is shown in Figure B-3. The computation procedure uses a chart similar to that in figure A-2. This is an x-t diagram where the x-axis is the line of computation directed landward. The t-axis extends from -10 hours (before landfall) to +6 hours. The initial input is based upon the expected peak surge value selected from Figure A-l, the computed hydrograph for the open coast (x=O, t=-10 to +6) from Table B-l, and the wind history accompanying the hydrograph (Table B-2). Hydro- graph points (for -10 H to +6H) are computed at 7.5, 15, or 30-minute intervals depending upon the length of spatial steps on the x-axis. The spatial computation intervals used are a function of the distance inland of point Q and range from 1 to 4 miles. ROUTING OF RAINFALL RUNOFF The design hurricane expects a rainfall of 8 inches uniformly distributed over a semicircular area 28 miles in diameter extending landward from point P and occurring at a uniform rate during the 4-hour period prior to the arrival of the peak storm tide at point Q. It is assumed that initially river and stream levels are normal, that prior to the beginning of heavy rains (4 hours before the hydrograph peak is reached), the rainfall saturates and is largely absorbed by the soil, and that normal drainage systems are functional. During the last 4 hours, the rapid hydrograph rise due to saltwater intrusions blocks the urban and natural drainage systems for fresh water accumulating at point Q. For purposes of this computation, the contributions of riverine flooding over the short period of hurricane approach are considered small and thus incorporated in the value of the initial rise. The rainfall runoff cannot be dismissed III-B-5 TABLE B-1 TEXAS DESIGN HURRICANE The wind field lies along a line parallel to the track and passing through the tidal maximum, from 10 hours before until 6 hours after landfall. If this line is defined as the x-axis increasing downtrack, 0 is the angle which a wind vector observed on this line makes with the line, positive when measured counterclockwise from the x-axis. (Based upon hydrograph and computed winds from SPLASH II program [Jelesnianski, 1972], using TEXAS DESIGN HURRICANE parameters.) LANDFALL SURFACE WIND OPEN COAST TIDE Distance Time Speed Track Fraction Hurricane D(mi) (Hours) W(mph) Crossing of Max Tide Angle e (deg) N(MSL) -140 -10.0 22 80.1 .00 -133 - 9.5 23 81.0 .005 -126 - 9.0 24 81.9 .01 -119 - 8.5 25 82.7 .015 -112 - 8.0 27 84.3 .02 -105 - 7.5 29 85.5 .023 - 98 - 7.0 31 86.5 .025 - 91 - 6.5 33 87.3 .027 - 84 - 6.0 36 88.4 .030 - 77 - 5.5 39 89.2 .040 - 70 - 5.0 42 89.7 .05 - 63 - 4.5 47 90.1 .075 - 56 - 4.0 51 90.5 .10 - 49 - 3.5 59 89.7 .16 - 42 - 3.0 66 88.2 .22 - 35 - 2.5 76 85.1 .26 - 28 - 2.0 85 79.1 .30 - 21 - 1.5 103 68.0 .45 - 14 - 1.0 123 50.2 .60 - 7 - .5 134 31.6 .85 0 0.0 137 2.2 1.00 7 0.5 134 -26.0 .85 14 1.0 124 -43.7 .60 21 1.5 106 -46.0 .40 28 2.0 89 -46.3 .20 35 2.5 81 -47.9 .12 42 3.0 70 -49.3 .05 49 3.5 63 -50.6 .025 56 4.0 56 -51.6 .00 63 4.5 51 -52.9 - .05 70 5.0 46 -53.6 - .10 77 5.5 43 -55.2 - .07 84 6.0 40 -54.8 - .03 III-B-6 TABLE B-2 WIND HISTORY FOR TEXAS DESIGN HURRICANE Based upon SPLASH II Stationary System Wind Field Corrected for Design Hurricane Movement. MOVING QUASI-STATIONARY SYSTEM SYSTEM R W 6 D t 6' W W (mi) (Kt) (deg) (mi) (hours) tan (deg) s s (deg) (Kt) -(deg) (tan + 6') Kt 4 78 0.44 -140 -10.0 85.1 13.3 98.4 22 80.1 22 8 119 1.18 -133 - 9.5 84.8 13.7 98.5 23 81.0 23 12 130 2.27 -126 - 9.0 84.6 14.2 98.7 24 81.9 24 16 124 4.04 -119 - 8.5 84.2 14.7 98.9 25 82.7 25 20 114 6.67 -112 - 8.0 83.9 15.3 99.2 27 84.3 27 24 103 11.21 -105 - 7.5 83.5 15.9 99.4 29 85.5 29 28 94 15.32 - 98 - 7.0 83.0 16.5 99.5 31 86.5 31 32 85 17.77 - 91 - 6.5 82.5 17.0 99.5 33 87.3 33 36 78 19.14 - 84 - 6.0 81.9 17.7 99.6 36 88.4 36 40 71 19.88 - 77 - 5.5 81.1 18.4 99.5 39 89.2 39 44 66 20.24 - 70 - 5.0 80.3 19.0 99.3 42 89.7 42 48 61 20.34 - 63 - 4.5 79.2 19.5 98.7 47 90.1 47 52 57 20.28 - 56 - 4.0 77.9 20.3 98.2 52 90.5 51 56 53 20.10 - 49 -3.5 76.2 20.3 96.5 59 89.7 59 60 50 19.87 - 42 - 3.0 74.1 20.2 94.3 66 88.2 66 64 47 19.57 - 35 - 2.5 71.1 19.3 90.4 76 85.1 76 68 44 19.22 - 28 - 2.0 66.8 17.0 83.8 84 79.1 85 72 42 18.86 - 21 - 1.5 60.5 11.4 71.7 101 68.0 103 76 40 18.46 - 14 - 1.0 49.4 3.4 52.8 119 50.2 123 80 38 18.11 - 7 -0.5 30.3 2.9 33.2 128 31.6 134 84 36 17.81 0 0 0 2.3 2.3 130 2.2 137 88 35 17.43 7 0.5 -30.3 2.9 -27.4 128 -26.0 134 92 33 17.07 14 1.0 -49.4 3.4 -46.0 119 -43.7 124 96 32 16.71 21 1.5 -60.3 11.4 -48.9 101 -46.0 106 100 31 16.36 28 2.0 -66.8 17.0 -49.8 84 -46.3 89 110 28 15.51 35 2.5 -71.1 19.3 -51.8 76 -47.9 81 120 25 14.73 42 3.0 -74.1 20.2 -53.9 66 -49.3 70 130 23 14.00 49 3.5 -76.2 20.3 -55.9 59 -50.6 63 140 22 13.32 56 4.0 -77.9 20.3 -57.6 52 -51.6 56 150 21 12.83 63 4.5 -79.2 19.5 -59.7 47 -52.9 51 70 5.0 -80.3 19.0 -61.3 42 -53.6 46 77 5.5 -61.1 18.5 -63.6 39 -55.2 43 84 6.0 -31.9 18.0 -63.9 36 -54.8 40 III-B-7 Hurricane Tidal Inundation Computation Sheet +61 ' . +2 * : : : * * * * * +1 · · · · · · · · * O * · · * 0 · e· 0 -1 * · · · · · · · · o ·* · · · · · · · · I -2 · · · · · · · · · w . . . . . . . . . -10 * * * · * * * · · DISTANCE (Miles) +20 4 8 12 16 20 24 28 32 36 40 +20 +20 +10 . . .- +10 -J U- 0 a- MSL MSL w 0 U) -10 -10 -20 4 8 12 16 20 24 28 32 36 40 FIGURE B-3 BASIC COMPUTATION SHEET AND VERTICAL SECTION FOR CONSTRUCTING PROFILES OF MAXIMUM FLOOD HEIGHTS INLAND FROM THE OPEN COAST III-B-8 so easily, however. While this contribution is acknowledged as likely to vary appreciably with topography, for purposes of this computation the freshwater contribution is considered to be 0.7 feet. This value is added directly to the maximum saltwater depth computed for point Q to determine total flooding levels. III-B-9 ANNEX C PROCEDURES FOR COMPUTING INLAND FLOODING Annex B explains the conceptual basis for computing the inland flooding due to storm surges. This annex sets forth the procedures which, if followed closely, will provide the computational results which are fundamental to the effectiveness of this program. These procedures draw upon many different sources of competence to compute flooding levels and identify in which hazard zone a proposed building site is located. The final determination of the hazard zone must combine the maximum computed flooding level at the building site (Q) with the prima facie factors identifying the hazard zones specified on pages III-5 through III-8. 1. FORMULATION SUMMARY. The procedure for routing storm tidewaters inland computes the flux from the equation for steady-state flow. This includes the forces due to (1) wind stress on the water surface, (2) gravity action due to the mean slope of the water surface, and (3) bottom stresses given by Mannings formula. A hydrograph is computed for successive space steps, xl to xn, along an x-axis extending inland from the point of maximum storm tide at the beach or shore (P), passing through Q, the site in questions. The procedure solves the equation NA = NB + K3 [P(C,R) - P(L,C)] (1) where the tidal flux for a given time step is NA - NB. This computation derives from the function P(l,r) = /Kl(h'-hg)lU"/3(Nr-N1) + K2W2cosO(h'-hg)7/3 (2) expressed relative to the grid array N1 Nr 0 0 hgl hgr The total water depth (h' - hg) = (Nr - hgr + N1 - hgl) 2 2 Symbols and constants are defined on page III-C-16. In (2) if the quantity under the radical is defined as B, the convention is that P(l,r) = /B if B is positive = -vC- if B is negative III-C-1 To simplify computations, it is assumed that all terrain is initially covered by 0.2' of water, so that for all time periods before surge waters have extended inland to a position xi, for which a hydrograph is being computed, the value of N (water level above MSL) is 0.2' greater than hg (terrain level MSL). The maximum storm tide at xi is obtained from the computed hydrograph for xi and plotted on a vertical cross section of Nmax vs. x to obtain the profile and inland extent of saltwater flooding. To the water depth at Q obtained from this profile is added the accumulation of fresh water from rain runoff, nominally 9.7 ft., to obtain the computed depth of flooding at Q. Finally, the design depth at Q is considered to be the computed depth if greater than that which would exist in terms of the floodplain level established by FIA. If lower, the design depth will be equal to that defined by the floodplain. 2. CLASSIFICATION AND INITIALIZATION. 2.1 Locate the building site Q on a coastal map. Select a map preferably with a scale of I" 2000 ft., but not smaller than l" = 1 mile. Contours of elevation (and for inland waters the bottom depths) should have a resolution of not less than 5 feet. 2.11 Draw a line through Q normal to the bay shore or coastline terminating at point P, tne water's edge at MSL. 2.12 Measure the distance S from point P to point Q in tenths of miles, and the elevation H' (MSL) for point Q. 2.2 Select the appropriate space and time increment (Ax, At) for making computations. 2.21 If S is 12 (statute) miles or more, use the following increments: Ax = 4 miles; At = 30 min. 2.22 If S is greater than 6 miles, but less than 12: Ax = 2 miles; At = 15 min. 2.23 If S is 6 miles or less: Ax = 1 mile; At = 7 1/2 min. 2.3 Construct and label an appropriate computation sheet following the example in Figure B-3. III-C-2 2.31 If P is located at a narrow barrier ridge or continuous line of dunes, the computation will begin with the time step at which the surge height N is just below the mean height of the ridge. Conceptually, the ridge is regarded as a sill over which surge waters upon reaching that height cross freely and quickly. For other circumstances the procedures in 2.32-2.34 apply. 2.32 If Ax = 4 miles the computation will nominally be conducted for x = 0 to nAx, where n is the integer (S/Ax) + 1, and from t = -10 to +6 hours (unless started later due to terrain conditions in 2.321). 2.321 If terrain rises rapidly at the shore to a height of hg 6 ft. MSL, the computations will begin at the hydrograph hour most nearly corresponding to a tidal stage equal to hgo - 0.5', where hgo is the mean height of terrain immediately adjacent to the shoreline. 2.33 If Ax = 2 miles, the computation will be conducted for the time interval: -5 to +3 hours, or t(hg) to +3 hours whichever is shortest. Here t(hg) is the time the hydrograph at P reaches the height N(t) = hgo - 0.5'. 2.34 If Ax = 1 mile, the computation will be conducted for the time interval: -3 to +1.5 hours, or t(hg) to +1.5 hours whichever is shorter. t(hg) is the time the hydrograph at P reaches a height of hgo - 0.5'. 2.35 When a computation begins at a new time step the value of N for x1 to xn should III-C-3 SAY SHO2EINUN DAT ION .%......... ..... * . .. ..... . ** . . .... .... .. . . .: .. .. ..... ...... * U FAA...P.. .. .......... CA5 ....S............G....... ..........IGUR ............................. ORIENTATION....... ... ......... ... COPUATO ... ROTIGCOSTLSUGE.NLN ACROSS LARGERBAYSJ....... COMPTIN BA .HR INNAIN...................... III-C-4.... .......... .. not be less than (a) hg + 0.2', or (b) 2 ft., MSL, or (c) half the value of N at x = 0 whichever is largest. 2.4 From Table B-2 record the appropriate values of 0 and W to the left of each time step on the computation chart, Figure B-3. 2.5 Compute the hydrograph for xo. If P is at an inland shore where mean water depths across the bay are at least 5.5 feet MSL, proceed to 2.53; if P is at the open coast, proceed as follows: 2.51 From figure A-1 determine the maximum surge height (feet and tenths) for the Texas Design Hurricane at the coastline position nearest to P. 2.52 To this surge height add 1.0 feet (astro- nomical tide increment). Using the sum as the peak open coast tide (MSL) compute the hydrograph values for each time step in Table B-1. Proceed to step 2.54. 2.53 Compute the equilibrium tilt of the water surface in the bay (see Figure B-2). 2.531 Select a point at the open coast, 0, which (1) maximizes the distance OP (this line need not be normal to the coastline), and (2) is centered in a major pass connecting the ocean with the inland waters, or alternatively is centered on an 8-mile stretch of coast where the barrier island, dunes or stable terrain, offers the lowest mean elevation to block movement of the open coast surge. 2.532 Compute the equilibrium height of water surface Nx at point P as a function of distance S' from 0 to P and of mean water depth (below MSL) H. III-C-5 Use the formula Nx(ft.) = l0.58S' + T H + h where h is the initial rise E 2 ft. MSL and T, the astronomical tide E 1.0 ft. MSL. H is taken as the mean depth MSL for a strip 2 miles wide extending from 0 to P. Nx is the peak storm tide at P. 2.533 Enter Table B-1 with the peak tide value, Nx; compute the hydrograph values for each time step. To this add the initial rise 2.0 ft. and enter the sum N(t) on the computation sheet. Proceed to step 2.6. 2.54 Add the height of initial rise (2.0 feet) to the hydrograph values computed in 2.52 and record the sum at each respective time step for x = 0 on the computation sheet. 2.6 Compute hg and N for each space step xj. 2.61 From the map contours (2.1) plot a profile of terrain heights (or shoal water depths) from P inland to a point at least one space step beyond point Q where hg must be more than 1 ft. above N at the previous space step; or for very flat, low terrain, at least 8 miles beyond Q. hg should be representative values for the area, nominally the mean hg's whose width extends one half mile to either side of the x-axis. 2.62 On the computation sheet at the initial time step, record the value of hg for each xj. 2.63 Above each hg value record the value of N, where N E hg + 0.2' except where hg + 0.2' is less than the initial rise (2.0' MSL). In the latter case N E 0.2'. 3. COMPUTATIONS OF HYDROGRAPHS FOR SUCCESSIVE SPACE STEPS INLAND. The computation sheet, similar to figure B-3, now has appropriate initial values of W, 0, and N for x = 0 (point P) at each time step, and values of hg, and for N at the initial time step for each space step, x1 to x,. The next step is to compute hydrograph values of N for each time step at xl, x2----xn. Each III-C-6 computation uses the graphic convention below: NA NL NC NR [tj, (W,O)j] a e e hgL hgc hgR 0 NB (xi) 3.1 Convention for computing NA from baseline data. The initial computation, made at (to, xl) uses values of NL, hgL, NC, hgc, NR, hgR already recorded in the initialization. For this baseline compu- tation NB is set equal to NC. Accordingly, the resulting value of N'A must be adjusted so the recorded value is: NA = (NC + N'A) 2 3.2 Convention for computing successive NA'S for a given time period. After computing NA for position xl, move to the right (inland) computing successive NA'S for the same time period, NR for the first computation becoming NC for the second. When a space step is reached where hgR is more than a foot higher than NC, then for the space step corresponding to this hgR set NA = NC and proceed to the next time step. 3.3 Compute NA using the HP-65 programmable calculator. 3.31 With the calculator "on" in the "RUN" position, insert the program chip for the appropriate space step: 1-, 2-, or 4- miles. 3.32 Key in the value of 0; STRIKE C. Key in the value of W; STRIKE R/S. 3.33 Key in NL and store in 2; Key in hgL and store in 3; III-C-7 Key in NC and store in 4; Key in hgC and store in 5. 3.34 STRIKE A. 3.35 If hgR is more than one foot greater than NC, STRIKE D, then STRIKE B. Proceed to 3.37. (This is considered by the program as a "cliff effect" and sets P(R) E 0.) However, if (hg9R - NC) 5 1.0', then 3.36 Key in NR and store in 4; Key in hgR and store in 5. STRIKE A (let it finish computing!) STRIKE B 3.37 Key in NB STRIKE R/S The displayed value is NA. 3.38 Compute the next NA to the right (inland). 3.381 Let NR and hgR in 3.36 become NC and hgC, then moving to the right for a new NR and hgR: 3.382 Key in NR and store in 4; Key in hgR and store in 5. STRIKE A (see 3.35 for exception) STRIKE B 3.383 Key in NB. STRIKE R/S The value displayed is the newNA. 3.384 Continue to the right until (hgR - NC) > 1.0 ft., then set NA = NC. III-C-8 3.39 Go to the next time step, key in new values of 0 and W, and proceed as in 3.32 and 3.33. 3.391 In order to maintain computational stability: 3.3911 For time steps following t = 0, when (NC - NA) becomes greater than 1 ft., then for all succeeding time steps the convention requires that NA 5 NC. 3.4 Compute the profile of saltwater flooding inland. 3.41 Identify the highest value of N computed for each space step inland. This will come at positive time values (following t = 0) and at successively later hours for each succeeding space step. 3.42 Plot values of Nmax for each space step on the N/x cross section at the bottom of the computation sheet (see Figure B-3) and draw the flood profile. 3.43 From the profile read the inundation depth at Q due to saltwater inundation. 3.44 To the above value add the design value of freshwater flooding, 0.7 ft. to obtain the total flood level D for point Q. 3.45 Determine the legal floodplain height established by the Flood Insurance Administration (HUD) for Q. 3.451 The flooding at Q due to F is defined as D' = F - hgQ. If D' > D, set D = D'. 3.452 D 0 design flooding at Q. 3.5 Compute NA using the ISR nomogram (figures C-2 and C-3). 3.51 Using the lower portion of the nomogram, locate the intersection of the horizontal line for 0 values and the vertical line for W; designate this A. III-C-9 100: 80- a j I 70- * I g II * I I ' -4 5 3 I I 60- 1 - I 50- I 5 11 a I I- 40- --> - 3- . 1 1 1- - 20- 16 I8 20I 3 0 - 50- - It*I 60 - '0 . either p s or k % N k- 'g,'A 'V". 'k ne.,a id- II \'uj cated 2b 3 4 0 5 607 010 6 6 0 I ' kot +go- Il S? I lc S C S) S OD m '(hR(-hL) feet 0 'S:v -: I I* I s :- I I I Ii I I *B 100- * L I , I I 100- 1 I II I * 3151 I I I - S I I 5 I II I I I 80- : a a , a a I u s 70- 1 I I * Urn , I 60- I I I a I I I I I 60- S I S' 5 I I 1 I I g I I I 40- , * I0 I UI Ilg I-- I I 30- * I I II a I I I - -I I I I Ii *I - I -I 20- I I I II I I I - I I - - 0 - a - L L 1 - I I II tI I I· - - I .4 1 I '. ' . 4( S . .4 .. .4 .4 ..... 4- . 10: S 1_ · ·; I - 3-_ . . .4' . I '5 .4 -5 I-. --1 i ;- -csP- S . 5- 2 0---3.- I 12 . '0 3- 1 I 1 .. .. I 6c - I W .\ S\\4- 5.xu -NMGA O FIGURE C-3 80- A - Angles can be ' \" " . either po.oIL 45 .a.. S 5 neg., as indi- " \ .' 55 'S '' S. I .4 cated 2 ' 2b 30 40 0 6'0 7080 10 10 0 0200 300 4'00 knots ±901 3.52 Following the slanting lines upward to the left from A to the horizontal line representing the base of the upper nomogram, mark the intersection B and construct the vertical line BC from bottom to top of the upper nomogram. 3.53 From the computation format in 3.0, compute: (a) (h' - hg)L = (NL - hgL) + (NC - hgc) 2 (b) (NL - NC) 3.54 On the vertical axis at the center of the upper nomogram, locate the value of (a). Mark this D. Draw a horizontal line DE to the intersection of BC. 3.55 From E follow the diagonal thin lines to point F on the prominent horizontal line located one third the distance from B to C. 3.56 At the top of the upper diagram locate the value of (NL - NC); mark this G. Drop vertically to the line DE (extended if necessary) and mark the point H. 3.57 From H move diagonally and parallel to the white stripes to the intersection of the vertical white stripe. Mark this point J. 3.58 Move horizontally from point J and vertically from point F to the intersection. Mark this P(L). Read the value of P(L) from its interpolated position between those hyperbolas which extend from left to right sloping downward to intersect the base of the upper nomogram where their values are recorded.* 3.59 From the computation format in 3.0, compute (a) (h - hg)R (b) NC - NR With these values repeat the computations in 3.54 and 3.58 to determine the value of P(R) If P(L) lies on the left side of the split nomogram (negative values) then interpolate its value between the hyperbolas which extend from right to left curving downward to intersect the baseline. III-C-12 3.60 Compute: NA = NB + K3(PR - PL) 3.61 Continue computing successive NA'S to the right (inland) for the same time step as in 3.2. 3.62 Complete the profile of saltwater flooding as in 3.4. 3.63 Add the freshwater accumulation to the salt- water flooding in 3.62 to determine the total flooding, D. Proceed as in 3.45 to obtain the design flood depth. 4. SAMPLE COMPUTATION OF NA. From the computation sheet values in figure B-3, the following is a sample computation of NA for the step t = -0.5 hours, x = 4 miles. 4.1 The array of known values (Figure B-2) is: NA = ? 0 = 31.6° NL = 11.04' NC = 5.26 NR = 8.7' W = 134 mph hgL = 2.0' hgc = 2.0' hgR = 8.5' NB = 4.18' (At 30 min.; Ax = 4 mi.) 4.2 Compute NA using the HP-65 program. 4.21 With HP-65 "on" and in "run" mode, insert the program chip for x = 4 mi. 4.22 Key in 6 = 31.6° STRIKE C--------(read 0.85) 4.23 Key in W = 134 STRIKE R/S-----(read 3.06) 4.24 Key in NL = 11.04, store in 2; Key in hgL = 2.0, store in 3; Key in NC = 5.26, store in 4; Key in hgC = 2.0, store in 5. III-C-13 STRIKE A-----.(read 2.00) 4.25 Since (NR - NC) > 1.0' (cliff effect) STRIKE D---.- (read 0.00) 4.26 Key in NB = 4.18 STRIKE R/S -----(read 7.17') This is the value of NA. 4.3 Compute NA using the nomogram. 4.31 From the computation format in 4.1, compute: (h' - hg)k = (NL - hgL) + (NC - hgC) 2 = 9.04 + 3.26 = 6.15' 2 (NL - NC) = 5.78' 4.32 Locate 0 = 31.60 on the vertical axis, lower nomogram. Draw a line horizontally to the right. Locate W = 134 on the horizontal axis, lower nomogram; draw a vertical line upward to intersect the 0 value at A. 4.33 Move diagonally to the left from A parallel to the slanting lines to B, the base of the upper nomogram. Draw a vertical line BC to the top of the upper nomogram. 4.34 Locate (h - hg)L = 6.15 on the vertical axis at center of the upper nomogram. Mark this D and draw the horizontal line DE to intersect BC. 4.35 Follow the diagonal thin lines downward to F, the intersection with the prominent horizontal line 1/3 the distance from B to C. 4.36 Locate NL - NC = 5.78' on the horizontal line at top of the upper nomogram. Mark this G, and draw GH vertically downward to the intersection of DE. 4.37 From H move diagonally to the right parallel to the white stripes to J, the intersection with the vertical white stripe. III-C-14 4.38 From J move horizontally and from F vertically to the intersection K. 4.39 Now following the family of hyperbolas enclosing K moving from left to right and sloping downward to the base of the upper nomogram; interpolate the value of K to be 17.5 P(L). 4.40 Since (hgR - NC) > 1.0 ft., P(L) 0. 4.41 (NA - NB) = K3(0 - 17.5) = -.17(-17.5) = +2.98 4.42 NA = NB + 2.98 = 4.18 + 2.98 = 7.16' III-C-15 DEFINITION OF SYMBOLS N: height of water above MSL hg: elevation of terrain above MSL (+), or bottom depth below MSL (-) Subscripts C, A, B, L, R, referred to N and hg, represent values centered, one step above, below, and to the left and right of a given time and space step, respectively. Subscripts 1, r refer to any left and right grid points later referred to as L, C, and R xi: a computation point on the x-axis from x = 0 to x = n 0: the angle which the wind vector makes with the x-axis measured counterclockwise from the axis (h' - hg): total water depth S: distance inland of the building site S': distance across an inland body of water from the open coast, point 0, to the bay shore, P H': elevation of point Q MSL H: mean depth of an inland body of water over a strip 8 miles wide along the line OP h: initial rise defined as 2.0 feet MSL T: astronomical tidal component at time of max surge, defined as 1.0 feet MSL, 2.1 ft. MLW CONSTANTS K1 = -.02 K2 = +.001 K3 = -.17 III-C-16 COMPUTATION OF HYDROGRAPH TIME STEPS NA WHERE At = 30 min.; Ax = 4 mi. Program listing for HP-65: STEP NO. KEYS STEP NO. KEYS LBL 26 (-) 2 A 27 RCL 3 3 RCL 8 28 (x) 4 STO 7 29 (.) 5 RCL 2 30 0 6 RCL 3 31 4 7 (-) 32 CHS 8 STO 6 33 (x) 9 RCL 4 34 STO 2 10 RCL 5 35 RCL 6 11 (-) 36 2 12 RCL 6 37 (.) 13 (+) 38 3 14 2 39 3 15 () 40 16 STO 6 41 5 17 3 42 RCL 1 18 (.) 43 X 19 3 44 RCL 2 20 3 45 (+) 21 [1 46 STO 3 22 5 47 [g- 23 STO 3 48 6 24 RCL 4 49 E 25 RCL 2 50 9 III-C-17 STEP NO. KEYS STEP NO. KEYS 51 STO 2 76 C 52 RCL 3 77 E 53 RCL 2 78 5 54 (.) 79 STO 1 55 STO 8 80 R/S 56 RCL 4 81 ENTER 57 STO 2 82 (x) 58 RCL 5 83 (.) 59 STO 3 84 0 60 RTN 85 0 61 LBL 86 0 62 B 87 2 63 RCL 8 88 (x) 64 RCL 7 89 RCL 1 65 (-) 90 (x) 66 (.) 91 STO 1 67 1 92 RTN 68 7 93 LBL 69 (x) 94 D 70 STO 6 95 RCL 8 71 R/S 96 STO 7 72 RCL 6 97 0 73 (-) 98 STO 8 74 RTN 99 RTN 75 LBL 100 il NOP III-C-18 SECTION IV - ?7, MODEL MINIMUM STANDARD S . CHAPTER 1 INTRODUCTION SECTION 1.1 PURPOSE 1.1.1 APPLICATION: This document is intended to serve as an amendment to the City Building Code in Hurricane Hazard Areas. The provisions contained herein, along with the legally adopted City Building Code shall constitute the minimum building standards and requirements. In case of conflict between the two documents, the most severe requirement, in the judgement of the building official, shall control. SECTION 1.2 OUTLINE 1.2.1 ADMINISTRATION AND DEFINITIONS: Chapters 2 and 3 define terms and describe implementation procedures including permits, inspection, notice of hurricane hazard, and classification and posting of buildings. Classification and posting of a building declares if the building is safe refuge. In applying for a permit for construction, the owner states the type of hurricane floodproofing desired (from completely floodproof to non-floodproof), and the completed building will be posted accordingly. Due to construction requirements, some of these buildings may be designated and used for safe refuge for vertical evacuation. 1.2.2 DEFINITION AND DELINEATION OF HURRICANE HAZARD ZONES: Chapter 4, along with Annexes A, B and C, defines the various hazard zones and sets out computational procedures for the determination of the zones. 1.2.3 DESIGN PARAMETERS: Chapters 5, 6, 7 and 8 set out the specific design requirements for each hazard zone. Chapter Item 5 Wave and Scour 6 Battering by Debris 7 Flooding 8 Wind 1.2.4 STRUCTURAL INTEGRITY: Chapters 9 through 15 set out specific requirements for various types of construction. Chapter Item 9 Foundation 10 Masonry 11 Steel and Iron IV-1 SUBJECT TO RK iIO' Chapter Item 12 Wood 13 Concrete 14 Cladding and Glazing 15 Roofing SECTION 1.3 USE: In summary, if one wanted to construct a building, the following steps would be required: 1.3.1 Refer to Chapters 2 and 3 for application information and legal procedures. 1.3.2 Refer to Chapter 4 to determine the hazard zone for the particular location. 1.3.3 Refer to Chapters 5, 6, 7 and 8 for design requirements depending upon hazard zone: Zone Design Requirements Chapter 5 6 7 8 A X X X X B X X X C X X D X 1.3.4 Refer to Chapters that cover specific construction materials: Type of Bldg. 9 10 11 12 13 14 15 Light-Gauge Metal Building X X X X X Frame House X X X X X Concrete Block Building X X X X X SECTION 1.4 CONTINUING UPDATE OF CODE: This document is not a perfect work. A continuing effort will be made to keep the requirements in line with new knowledge and actual experience. Therefore, the user is urged to continually update the provisions of this code as information is documented. CHAPTER 2 UJ ADM IN ISTRAT ION Ii SECTION 2.1 PURPOSE 2.1.1 APPLICATION: The provisions contained herein shall constitute the minimum building standards and requirements that are applicable to safeguard life or limb, health, property and public welfare by regulating and controlling design, construction, and quality of materials of all buildings and structures which are or will be located in all lands shown within the Hurricane Hazard Area(s). Hereinafter these provisions will be referred to as the "Hurricane Regulations" part of "The Building Code," or in short as "these Regulations." 2.1.2 REGULATORY FLOOD DATUM: For the purpose of these Regulations, the Regulatory Flood Datum, hereinafter referred to as the "RFD," is hereby declared and established for use as the reference datum for determining the elevation above mean sea level to which flood-proofing protection shall be provided. 2.1.3 HURRICANE HAZARD AREAS: For the purpose of these Regulations, the Hurricane Hazard Areas, as further described in Chapter Four, and the RFD are hereby declared and established for use in determining Building Code requirements. 2.1.4 HURRICANE PRECAUTIONS: During such periods as are designated by the National Weather Service as being a hurricane warning or alert, the owner, occupant or user of a property shall take precaution for the securing of buildings and equipment. Canvas awnings and swing signs shall be lashed to rigid construction, tents shall be taken down and stored or lashed to the ground, and such other precautions shall be taken for the securing of buildings or structures or equipment as may be reasonably required. SECTION 2.2 SCOPE 2.2.1 APPLICATION: These Regulations shall apply to the construction, alteration, and repair of any building or parts of a building or structure in the Hurricane Hazard Area(s) of the (city, town, village, etc.) . Additions, alterations, repairs, and changes of use or occupancy shall comply with all provisions for new buildings and structures as otherwise required in "The Building Code," except as specifically provided in these Regulations. 2.2.2 NONCONFORMING USE: A structure or the use of a structure or premises which was lawful before the passage or amendment of the ordinance but which is not in conformity with the provisions of these Regulations may be continued subject to the following conditions: (1) No such use shall be expanded, changed, enlarged IV- 3 or altered in a way which increases its nonconformity. (2) No structural alteration, addition, or repair to any conforming structure over the life of the structure shall exceed 50 per cent of its value at the time of its becoming a nonconforming use, unless the structure is permanently changed to a conforming use. (3) If such use is discontinued for 6 consecutive months, any future use of the building premises shall conform to these Regulations. The assessor shall notify the zoning administrator in writing of instances of nonconforming uses which have been discontinued for a period of 6 months. (4) If any nonconforming use or structure is destroyed by any means, including Hurricanes, to an extent of 50 per cent or more of its value, it shall not be reconstructed except in conformance with the provisions of these Regulations. (5) Uses or adjuncts thereof which are or become nuisances shall not be entitled to continue as nonconforming uses. (6) Except as provided in "The Building Code," any use which has been permitted as a special exception shall not be deemed a nonconforming use but shall be considered a conforming use. (7) Any alteration, addition, or repair to any nonconforming structure which would result in substantially increasing its hurricane damage or hurricane hazard potential shall be protected as required by these Regulations. (8) The Building Official shall maintain a list of conforming uses, including the date of becoming a nonconforming use and the nature and extent of nonconformity. This list shall be brought up to date annually. (9) The Building Official shall prepare a list of those nonconforming uses which have been hurricane-proofed or otherwise protected in conformance with these Regulations. He shall present such list to the Board of Adjustment, which may issue a certificate to the owner stating that such uses, as a result of these corrective measures, are in conformance with these Regulations. SECTION 2.3 ALTERNATE MATERIALS AND METHODS OF CONSTRUCTION 2.3.1 APPLICATION: These Regulations are not intended to prevent the use of any materials or methods of construction not specifically prescribed herein or by "The Building Code," provided any such alternate has been approved and its use authorized by the Building Official prior to its incorporation or use in the construction, in accordance with methods and procedures set forth in this code for approval of new materials and special systems of design or construction. 2.3.2 APPROVAL. The Building Official may approve any such alternate, provided he finds the proposed design is satisfactory and complies with the provisions of "The Building Code" and that the material, method, or work offered is, for the purpose intended, at least equivalent to that prescribed in "The Building Code" in quality, strength, effectiveness, fire resistance, durability, and safety. The Building Official shall-require that sufficient evidence or proof be submitted to substantiate any claim that may be made regarding its use. If, in the opinion of the Building I V-4 Official, the evidence and/or proof is not sufficient to justify approval, the owner or his agent may refer the entire matter to the Board of Appeals. SECTION 2.4 TESTS 2.4.1 PROOF OF COMPLIANCE: Whenever there is insufficient evidence or proof of compliance with the provisions of these Regulations, or evidence that any material or any construction does not conform to the requirements of these Regulations, or in order to substantiate claims for alternate materials or methods of construction, the Building Official may require tests or test reports as proof of compliance. Tests, if required, are to be made at the expense of the owner or his agent by an approved testing laboratory or other approved agency, and in accordance with approved rules or accepted standards as prescribed in "The Building Code." 2.4.2 ABSENCE OF APPROVED RULES: In the absence of approved rules or other accepted standards, the Building Official shall determine the test procedure or, at his election, shall accept duly authenticated reports from recognized testing authorities or agencies in respect to the quality and manner of use of new materials. 2.4.3 RECORDS: Copies of such tests, reports, certifications, or the result of such tests shall be kept on file in the office the Building Official for a period of not less than three years after the approval and acceptance of the completed structure for beneficial occupancy. SECTION 2.5 ORGANIZATION AND ENFORCEMENT 2.5.1 RULES AND REGULATIONS: The Building Official is hereby authorized and directed to enforce the provisions of these Regulations as part of "The Building Code." For such purpose he shall have the powers of a police officer. 2.5.2 DEPUTIES: The Building Official may appoint such number of officers, inspectors, and assistants as required. He may deputize such employees as needed to perform the functions of the Building Department. 2.5.3 OFFICIAL RECORDS: The Building Official shall establish and maintain an official record of all business and activities of the department relating to these Regulations, and all such records shall be open to public inspection. He shall keep a permanent, accurate account of all fees and other monies collected and received under these Regulations. The Building Official shall, at least once a year, submit a report to the proper city official covering the work of the Department during the preceding period. Said report shall include detailed information regarding the administration and enforcement of these regulations. I V,_ 5 SUBJEO A RO ISOM 2.5.4 RIGHT OF ENTRY: Whenever it may be necessary to make an inspection to enforce the provisions of these Regulations, the Building Official or his authorized representative may enter such building or premises at all reasonable times to inspect all parts that are or may be subject to flooding or where the potential for hurricane damage exists. 2.5.5 STOP WORK ORDER: Whenever any building work is found to be done contrary to these Regulations, the Building Official shall order the work stopped by notice in writing to the person doing the work. 2.5.6 BOARD OF APPEALS: In order to determine the suitability of alternate materials and methods of construction and to provide reasonable interpretations of the provisions herein, there shall be and is hereby created a Board of Appeals of ___members. Each member of the Board shall be a licensed professional architect or engineer, or a builder or superintendent of building construction, with at least ten years experience, for five years of which he shall have been in responsible charge of work. At no time shall there be more than two members from the same profession. At least one of the members shall be a licensed structural or civil engineer with architectural engineering experience. The Board shall adopt reasonable rules for its investigations and shall render written decisions to the Building Official. 2.5.7 VALIDITY: It shall be unlawful for any person, firm, or corporation to erect, construct, enlarge, alter, repair, move, improve, remove, convert, or demolish any building or structure in the Hurricane Hazard Area(s), or cause the same to be done, contrary to or in violation of any of the provisions of these Regulations and/or "The Building Code." 2.5.8 VIOLATIONS AND PENALTIES: Any person, firm, or corporation violating any of these provisions shall be deemed guilty of a misdemeanor, and upon conviction thereof shall be punished by a fine or by imprisonment as provided in the laws of the municipality for such misdemeanor, or as specified in "The Building Code." SECTION 2.6 PERMITS 2.6.1 STATEMENT OF INTENTION TO IMPROVE: The Owner or any registered architect or licensed professional engineer authorized to represent the Owner shall, before preparing final plans for any improvement in the Hurricane Hazard Area(s), file with the Building Official a Statement of Intention to Improve, including a brief description of the type of improvement being considered and giving its precise location, on a form provided by the Building Official. The Building Official shall note on two copies the Hurricane Hazard Zone and the elevation of the RFD at the location of the proposed improvement. One copy of the Statement of Intention to Improve shall be retained by the Building Official until a permit for IV-6 improvement on the site is approved or one year has elapsed;a second copy shall be returned to the Owner for his use in final siting and design of his improvement. Assignments of the Hurricane Hazard Zone and the RFD elevations at all locations shall be as described in Chapter Four. This information shall be open to public examination at all reasonable times. 2.6.2 PERMITS REQUIRED: No person, firm, or corporation shall erect, construct, enlarge, alter, repair, remove, convert, or demolish any building or structure or any .part thereof, or make any other improve- ment within the Hurricane Hazard Area(s), or cause same to be done, without first obtaining a separate building permit for any such improvement from the Building Official. Ordinary minor repairs may be made without the approval of the Building Official without a permit, provided that such repairs shall not violate any provision of these Regulations or of "The Building Code." 2.6.3 APPLICATIONS: To obtain a permit, the applicant shall first file an application therefore which shall consist of: (1) A descrip- tion of the work to be covered by the permit including a list of all spaces affected by these Regulations giving flood-proofing class, elevation of RFD, Hazard Zone, floor elevations), proposed uses and contents, and references to drawings and specifications which explain the flood-proofing measures that apply to each space. The description shall include an estimate of the total value of the improvement. This description shall be made on a form provided by the Building Official (Figure 1). (2) __ sets of complete plans and specifications, in addition to plans and specifications required by "The Building Code," except that plans and specifications for any and all proposed improvements in the Hurricane Hazard Area(s) shall be prepared by an engineer licensed by the State to practice as such. All drawings and specifications shall bear the name of the author thereof in his true name, followed by such title as he may be lawfully authorized to use. All plans and sections shall be noted with the proposed flood-proofing class of each space below the RFD including detail drawings of walls and wall openings. (3)___ copies of the Owner's Contingency Plan, which shall describe in detail all procedures for temporary placement and removal or contingent protection proposed for items in spaces affected by these Regulations including: a. Plans and schedules for items to be removed and locations of places above the RFD to which they will be removed if these contents violate restrictions associated with the flood-proofing class of the space in which they are placed temporarily, including specific organizational responsibilities for accomplishing this removal. b. Procedures, material and equipment for protecting items required to have protection by their flood-proofing class but for which this protection is proposed to be provided contingently, including specific organizational responsibilities for accomplishing this protection. Waivers of restrictions implicitly requested by submission of the Owner's Contingency Plan may be granted by the Building Official as provided by _____. (4) Any other information as reasonably may be required by the Building Official, including computations, stress diagrams, and other data sufficient to show the correctness of the plans. IV-7 SI-Et) ro, F!E I7 Supplementary BUILDING OR STRUCTURE IN FLOOD HAZARD AREA Application (To Accompany Application for Building Permit) City or Town County Location Intended Use Value Of Improvement S ____ Type of Construction No. of Stories__________ Owne r Address Exsit.Ground Elee. *...MSL; Fin.Ground Elso. MSL; Reg.Flood Datum Elev.at Sits MSL; RFD Veiocity..........Ft/See .....Fioor Elev. _ ML: Proposed Use g.......Floor Eiev. - SL, Pro posed Use -Floor Ely - dSL: P roposed Use ;Floor Elev. _ M...,..SL,, Proposed Use Maximuis Loading on Walls: Ilydrostatip (Uplift) Pressure on Floor Slabs(MaximumL_?...SF Non Flood Load PSF Foundation Type(s) Hydrostatic Load PSF Lowest Foaotr Elen. (Bottom) MSL Hydrodynamic Load psF Savage Disposal, ...Septic Tank,....Pub.Syst.,........ther(Explain) impact Load PSF Potable Ietsrt I...ndivldual Weill -..Pub.Syst.,-...Other(Explaln) Total Flood Load PSF Exterior Wall Construction Type(s): Floor Construction Type(s)-. Above ______Floior Floor Above Floor F l o o r ____ A bove Floor ______f loor Types of Waterproofing Type(s) of Joints; Wells_______ Floors f eeaos als(ye) als Floor_______ Sump Location Sump Typo All Tanks and/or Bouyont Equipment Are Are Not Anchored To Prevent Flotation Alternate Power Source Is 151.11t Provided For Emergency Operation Of Surcp Puimp Sanitary. Drainage & Water Supply Facilitlim Are....._........Are Not -___ Protected From Contamination & Back Flow by Flood Water Retaining Wall(s) Are Ara Not Used To Protect 801ilding/StrUCt lr intentional Flooding is Is Not Planned For This Bui IdIn2/S tructure Temporary And/Or Emergency Flood Proof ing is Is Not __________Planfefl For This Building/Structure Building Structure Is Is Not Protected Against Erosion By Flood Flows Sits Is Is Not Protected Against Erosion By Flood Flows Classification of Building/Structure: F........................,Primary . Secondary . F lood Hazard Arma SPACES: List below all spaces of the building or structure below the Regulatory Flood Datum Including their name, room num - bar, and proposed flood-proofing claastioiatlon (i.e. WI, 12 etc.). List 311 contents of each space (see Chapter 10 of the Flood-Proofing Regulations). Mark all Items whIch oer to be either protested contingently or removed to safe refuge upon receipt of a flood warning with an asterisk (0); all such items must be mentioned in the owner's Contingency Plan. Attach additional sheets if necessary. The applicant hereby certifies that the above information Is correct and that the plans submitted herewith conform to thais submitted for occupancy permit application. The applicant agrees to comply with the provisions of the Zoning Ordi- nance, the Building Code and all other laws and ordinances affecting the construction and occupancy of this proposed build- ing. Signature Of Architect/Engineer Address The undersigned will supervise the construction of the work above. Signature SEAL TItle. Address (signature) Clerk APPROVED FOR COMPLIANCE WIhi BUILDING CODE Date Figure I 2.6.4 ACTION ON PERMIT APPLICATION: The complete application filed by an applicant for a flood-proofing permit, including all of the above listed items, shall be checked by the Building Official. Such plans may be reviewed by other Departments of the (city) to check compliance with the laws and ordinances under their jurisdiction. The Building Official shall determine that the RFD elevation and Hazard Zone noted in the application are correct in accordance with the Statement of Intention to Improve and that all requirements for the flood-proofing classes selected by the Owner are met. If the Building Official determines that for any space affected by these Regulations, any requirement for particular flood-proofing class, Hazard Zone, or any other requirement of these Regulations has not been met, he shall so indicate on the drawings and a permit shall not be granted. If the Building Official is satisfied that the work described in all parts of the application conforms to the requirements of these Regulations and "The Building Code" and other pertinent laws and ordinances, and that the fees specified in "The Building Code" have been paid, he shall issue a permit therefore to the applicant. When the Building Official issues the permit, he shall endorse in writing or stamp on ___sets of descriptions, plans and specifications, and the Owner's Contingency Plan "APPROVED" (name and date) .___sets of the complete application as approved shall be retained by the Building Official for a period of not less than two years after the approval or issuance of a certificate of occupancy for the completed improvement. ___sets of the complete application as approved shall be returned to the applicant, of which one set shall be kept at the building site and available for review by the Building Official at all reasonable times. 2.6.5 ISSUANCE OF PERMIT: The Building Official shall not issue a permit for the partial execution of any improvement until the complete application for the entire improvement has been submitted and approved. The issuance or granting of a permit or approval of an application shall not be construed to be a permit for, or approval of, any violation of these Regulations or of "The Building Code." The issuance of a permit based upon an approved application shall not prevent the Building Official from thereafter requiring correction in such application or any part thereof or from preventing work related to the execution of any improvement from being carried on thereunder when in violation of these Regulations, "The Building Code" or of any other ordinance of the (city) 2.6.6 EXPIRATION: Every permit issued by the Building Official shall expire by limitation and shall become null and void if the work authorized by such permit is not commenced within 90 days after issuance date of such permit, or if the work authorized by such permit is suspended or abandoned at any time after the work is commenced for a period of 120 days. Before such work is re-commenced a new permit shall first be obtained, and the fee therefore shall be one-half the amount required for the original permit for such work; and provided, further, that such suspension or abandonment has IV-9 SUBJEU 10 REVISION not exceeded one year, after which, a new application for permit must be submitted and the permit fee shall be based on the total value of all construction work for which the permit is issued. 2.6.7 REVOCATION OF PERMIT: The Building Official may revoke a permit or approval issued under these Regulations in case of any false statement or misrepresentation of fact in the application or on the plans, whenever the permit is issued in error, or whenever the permit is issued in violation of any ordinance or regulation, "The Building Code," or these Regulations. 2.6.8 PERMIT FEES: Building permit fees shall be paid to the Building Official as required and set forth in "The Building Code," and in accordance with the determination of value or valuation under any provision of these Regulations that shall be made by the Building Official. 2.6.9 POSTING OF PERMIT: The building permit shall be posted at the site of operations in a conspicuous place open to public inspection during the entire time of prosecution of the work and until completion of the same. SECTION 2.7 INSPECTIONS 2.7.1 INSPECTIONS REQUIRED: All construction or work for which a permit is required shall be subject to inspection by the Building Official. 2.7.2 PERIODIC INSPECTIONS: Buildings or structures and parts thereof that contain or utilize contingent or emergency (temporary) type hurricane-proofing elements or devices shall be subject to inspection by the Building Official at intervals of three (3) years or less. The Owner or his agency shall be notified at least 10 days in advance of inspection date and shall be present at the inspection. He shall be responsible for demonstrating the availability, installation, and proper functioning, anchorage and support of all closure assemblies and other contingent or emergency (temporary) hurricane-proofing items. All necessary correction of deficiencies shall be performed within 90 calendar days of the inspection date and at the Owner's expense. Failure to perform the required work within the prescribed time shall be a violation of these Regulations and the applicable part(s) of "The Building Code." 2.7.3 MAN DATORY INSPECTIONS: (a) The Building Official, upon notification from the permit holder or his agent, shall make the *following inspections and shall either approve that portion of the work completed or shall notify the permit holder or his agent wherein the same fails to comply. 2.7.3.1 FOUNDATION INSPECTION: To be made after necessary excavations have been made, forms erected and reinforcing steel placed. IV-10 2.7.3.2 PILE INSPECTION: To be made during the driving of the piles and after all piles are driven and forms and reinforcing steel are in place and tied, and before placing any concrete. (Refer to 2.7.7 SPECIAL INSPECTOR.) 2.7.3.3 REINFORCING INSPECTION: To be made after any reinforcing steel is in place and before placing concrete. 2.7.3.4 FRAME INSPECTION: To be made at each floor level and after all framing, fire blocking, furring and bracing are in place, and plumbing and electrical work are roughed in. 2.7.3.5 ROOFING INSPECTION: To be made after anchor sheet or sheets have been tincapped and before cap sheet is mopped on. 2.7.3.6 CURTAIN WALL INSPECTION: To be made at each floor level after curtain walls are installed and before curtain-wall attachments are concealed. 2.7.3.7 STORE FRONT INSPECTION: To be made after store fronts are installed and before store front attachments are concealed. 2.7.3.8 WINDOW AND GLASS DOOR INSPECTION: To be made after windows and glass doors are installed and before attachments and connections to the building frame are concealed except that for one and two-story buildings this inspection shall not be required. 2.7.3.9 LATHING INSPECTION: To be made after lathing and before plastering, where plastering is a requirement for fire protection, or where suspended overhead. 2.7.3.10 PLUMBING INSPECTION: To be made of the ground work and at each floor. All plumbing work shall be left uncovered and convenient for examination until inspected and approved. Floors shall be left up in all bathrooms and elsewhere above all sanitary plumbing, water-supply and gas-supply piping and other plumbing work until it shall have been examined, tested and approved. 2.7.3.11 ELECTRICAL INSPECTION: To be made at each floor level; and no conduit boxes, panels or other electrical appurtenances shall be covered or concealed until approval shall have been received from the Building Official. 2.7.3.12 SPECIAL INSPECTIONS: To be made of all mechanical installations, signs and awnings immediately upon completion and at such intervals during the progress of the work as the Building Official or this Code may require. 2.7.3.13 OTHER INSPECTIONS: To be made as the owner or con- tractor or Building Official may reasonably request. IV-11 2.7.3.14 FINAL INSPECTION: To be made after thie work is completed and the structure ready for use or occupancy. 2.7.4 No work shall be done on any part of a building or structure or any plumbing, electrical or mechanical installation beyond the point indicated hereinabove for each successive inspection until such inspection has been made and the work approved and the inspector has so indicated on the approved plans or permit card at the job site. 2.7.5 No reinforcing steel or structural framework of any part of any building or structure shall be covered or concealed in any manner whatsoever without the approval of the Building Official. 2.7.6 Inspection requests shall be made to the office of the Building Official and shall provide reasonable time for such inspection to be made. Rejection or refusal to approve the work for reasons of incompleteness, Code violation or inadequacy shall nullify that request for inspection. This work shall be made to comply and the request for inspection repeated as outlined herein. It shall be assumed that the responsible individual or individuals in charge of the work shall have themselves inspected the work and found it to be in compliance with Code requirements before request for inspection is made. 2.7.7 SPECIAL INSPECTOR: (a) The Building Official may require the owner to employ a special inspector for the inspection of the structural framework, or any part thereof, as herein required: 1. Buildings or structures or parts thereof of unusual size, height, design or method of construction and critical structural connections. 2. Pile driving. 3. Windows, glass doors and curtain walls on buildings over two stories. (b) Such special inspector shall be an Architect or Professional Engineer or a duly accredited employee representing either. The special inspector shall be responsible for compliance with this Code and shall submit progress reports and inspection reports to the Building Official. (c) At the completion of the work or project, the special inspector shall submit a Certificate of Compliance to the Building Official, stating that the work was done in compliance with this Code and in accordance with the approved plan or plans; and his duties shall end with the submission of such certificate. Final inspection shall be made by the Building Official before a Certificate of Occupancy is issued. 2.7.8 INSPECTION REPORTS: The Building Official shall keep records of inspections, Certificates of Compliance, results of tests, plans, surveys and Certificates of Occupancy for a period of not less than seven years. Such records shall become a part of the public record and open to public inspection, except as may be elsewhere specifically stipulated. IV-12 2.7.9 SPECIAL HURRICANE INSPECTIONS: (a) During such periods of time as are designated by the National Weather Service as being a hurricane alert, all furniture, awnings, canopies, display racks, material and similar loose objects in exposed outdoor locations shall be lashed to rigid construction or stored in buildings. Orders shall be oral or written and shall be given to any person on the premises most logically responsible for maintenance and such orders shall be carried out before winds of hurricane velocity are anticipated. (b) After winds of hurricane velocity are experienced and have subsided, the Building Official shall investigate to determine if damage has occurred to buildings or other structures. (c) No building or other structure or assembly or part thereof which was damaged or collapsed or out of plumb or line shall be repaired or altered or otherwise returned to its original position without inspection and approval by the Building Official. SECTION 2.8 CERTIFICATE OF USE AND OCCUPANCY 2.8.1 NEW BUILDINGS AND STRUCTURES: No building or structure hereafter constructed in the Hurricane Hazard Area(s), or any portion thereof, shall be used or occupied until the Building Official shall have issued a certificate of use and occupancy. 2.8.2 BUILDINGS OR STRUCTURES HEREAFTER ALTERED: No building or structure in the Hurricane Hazard Area(s) hereafter enlarged, extended or altered, or any portion thereof, shall be used or occupied, and no change in use or occupancy shall have made, until the Building Official shall have issued the certificate of use and occupancy, except that the Building Official may permit lawful use or occupancy to continue upon the submission of evidence that the hurricane hazard or vulnerability of any occupied portions of the structure and its contents will not be increased during the execution of the improvements. 2.8.3 EXISTING BUILDINGS AND STRUCTURES: The Building Official shall issue a certificate of use and occupancy for an existing building or structure located in the Hurricane Hazard Area(s) upon receipt of a written request from the Owner, provided: (1) There are no violations of law or orders of the Building Official pending. (2) It is established after inspection and investigation that the alleged use or occupancy of the building or structure has heretofore existed. (3) There is a positive showing that the continued use or occupancy of a lawfully existing building or structure in the Hurricane Hazard Area(s), without requiring alterations, rehabilitation or reconstruction, does not endanger public safety and welfare. The Building Official shall refuse to issue a certificate of use or occupancy for any existing building or structure in the Hurricane Hazard Area(s) when- ever it is found that the building or structure, or any portion thereof or appurtenant thereto, is in an unsafe condition and/or would be potentially unsafe when subjected to floods up to the RFD. He shall, in writing, so notify the Owner, lessee, tenant, occupant IV-13 and/or agent thereof describing said condition and ordering abatement thereof within a reasonable length of time. Failure to comply with the order of the Building Official shall be a violation of these Regulations and the applicable part(s) of ".The Building Code." 2.8.4 CONTENTS OF CERTIFICATE: When a building or structure is entitled thereto, the Building Official shall issue a certificate of use and occupancy that shall certify compliance with the provisions of these Regulations and "The Building Code." Issuance Sl of a certificate does not assign liability to the community. SECTION 2.9 PUBLIC NOTICE OF HURRICANE HAZARD 2.9.1 PROCEDURE: On or about the first day of May, the Building Official shall alert the public of the existing Hurricane hazard of the (city) . He shall publish or cause to be published a public notice which shall indicate the recorded maximum wind velocity and the elevation of the flood of record together with depths and approximate area(s) of inundation (if known). Said public notice will also contain similar information about the RFD that is established for purposes of these Regulations. 2.9.2 OTHER INFORMATION: The public notice shall emphasize the necessity for maintenance and repair of all contingent hurricane- proofing measures and the probability of occurrence of a hurricane that would cause floods to reach elevations higher than the RFD. It shall advise owners and/or occupants to operate all mechanically and manually operated closure assemblies for doors, windows and utilities openings, emergency electrical generating units, sump pumps, etc., and to check the availability and condition of all temporary closure panels, gaskets and anchorage devices, etc. All organizational, volunteer or assistance groups having responsibilities to act at time of hurricane emergencies shall be advised to review their state of readiness for effective mobilization and implementation of the hurricane emergency plan. SECTION 2.10 CLASSIFICATION AND POSTING OF BUILDINGS AND STRUCTURES 2.10.1 GENERAL: For administrative purposes of coordination of zoning regulations, inspection of structures, and conduct of emergency public safety operations, all buildings or structures in the Hurricane Hazard Area(s), whether existing or hereafter erected, shall be classified and posted in accordance with this Section. Classification of buildings and structures (FPI, FP2, etc.) is shown in Table I and is based upon the flood-proofing classifications of the constituent spaces (WI, W2, etc.) of the structure below the RFD (see Chapter 4) and the means by which these classifications are achieved. Posting shall be accomplished by placards mounted on internal walls at building entrances. For public safety operations, an identification symbol, e.g., FP1, shall be placed on the outside of the building above the RFD so as to be readily visible. IV-14 TABLE 1I CLASSIFICATION OF BUILDINGS AND STRUCTURES Building or SPACE CLASSIFICATION Structure WI W2 I W3 1 W4 W5 Classifi- Completely Dry Essentially Dry Flooded with Flooded with Non-Flood- cation w/o HI* w/HI* w/o HI* w/HI* Potable Water Floodwater Proofed FP1 X X FP2 X X X X FP3 X X x x FP4 X X X X X X FP5 x Human Intervention 2.10.2 STRUCTURE DESIGNED FOR WIND AND COMPLETELY FLOOD- PROOFED (FP1, FP2): 2.10.2.1 FP1 -- Any building or structure located in Hurricane Hazard Area(s) designed in accordance with these Regulations and with no space below the RFD or in which all en- closed spaces below the RFD are classified WI or W2 without employing any contingent closure, removal, protection, or other measure which requires human intervention for effectiveness in a flood event to obtain those classifications shall be known as a Completely Flood-Proofed Structure and classified FP1. It shall be posted by the Owner with a Type 1 placard, which shall be fastened securely to the structure in a readily visible place. 2.10.2.2 FP2 -- Any building or structure located in a Hurricane Hazard Area designed in accordance with these Regula- tions and with any space below the RFD and in which all such spaces are classified WI or W2, but for which at least one or more of the spaces employs any contingent closure, removal, protection, or other measure which requires human intervention for effectiveness in a flood event to obtain those classifica- tions shall be classified FP2. It shall be posted by the Owner with a Type 2 placard, which shall be fastened securely to the structure in a readily visible place above the RFD. 2.10.3 STRUCTURES DESIGNED FOR WIND AND PARTIALLY FLOOD- PROOFED (FP3, FP4): 2.10.3.1 FP3 -- Any building or structure located in a Hurricane Hazard Areadesigned in accordance with these Regula- tions and which contains a combination of spaces below the RFD that are classified W1 or W2 which is achieved without human IV-15 TABLE 2 SPACE CLASSIFICATION CHART FLOOD-PROOFING CLASSIFICATION OF SPACES MINIMUM REQUIREMENTS Flood- Closure Internal Walls Proofing Water- Structural of Flooding & and Classes Proofing Loads Openings Drainage Flooring Ceilings Contents Electrical Mechanical W1 Completely Dry Type A Class 1 Type 1 Class 1 Class 1 Class 1 W2 Essentially Dry Type B Class 1 Type 1 Class 2 Class 2 Class 2 W3 o Flooded * with Pota- 4 4 able Water Type A Class 2 Type 3 V Class 3 Class 3 Class 3 W a) W4 a) Flooded with Flood Water Type C Class 3 Type 4 Class 4 Class 4 Class 4 W5 Non-Flood- Proofing -- -- Type 5 Class 5 Class 5 Class 5 IV-16 "'% F-177n "flT'' 7 intervention, and one or more spaces that will be flooded internally (W2 and/or W4), shall be known as a partially flood- proofed structure and be classified FP3. It shall be posted by the Owner with a Type 3 placard which shall be fastened securely to the structure in a readily visible place above the RFD. 2.10.3.2 FP4 -- Any building or structure located in the Hurricane Hazard Area designed in accordance with these Regulations and which contains a combination of spaces below the RFD that are classified WI or W2 which is achieved with human intervention, and/or one or more spaces that will be flooded internally (W3 and/or W4), shall be classified FP4. It shall be posted by the Owner with a Type 4 placard which shall be fastened securely to the structure in a readily visible place above the RFD. 2.10.4 STRUCTURES DESIGNED FOR WIND BUT NON-FLOOD-PROOFED (FP5): Any existing building or structure located in a Hurricane Hazard Area which contains one or more spaces below the RFD that are not flood-proofed (W5) shall be known as a Non-Flood-Proofed Structure and classified FP5. It shall be posted by the Owner with a Type 5 placard which shall be securely fastened to the structure in a readily visible place. 2.10.5 SAFE REFUGE AREAS: Buildings or structures located in the Hurricane Flood Hazard Area that are provided with area(s) of safe refuge shall have said area(s) posted by the Owner with a Type 6 placard, which shall be securely fastened to the structure in a readily visible place. 2.10.6 PLACARDS: All placards shall be furnished by the Building Official and installed by the owner and shall be replaced immediately if removed, or defaced. 2.10.7 PLACARD TYPES: Placards shall be white rigid plastic or other non-water-susceptible material, _ inches long and wide, and shall have printed thereon in black letters the in- formation shown in Figure 2. 2.10.8 VIOLATIONS: Failure to comply with the requirements of this section shall be a violation of these Regulations and the applicable part(s) of "The Building Code". IV-17 PLACARD TYPES " Ci'i,7 COMPLETELY FLOOD-PROOFED BUILDING This building is completely flood-proofed to withstand flooding to the expected high water level of feet MSL. Floor elevation at this point feet MSL. Type 1 FLOOD-RESISTIVE BUILDING This building contains areas below the expected high water level of feet MSL which require implementation of pumps or other devices to maintain the required degree of protection. Floor elevation at this point feet MSL. Type 2 PARTIALLY FLOOD-PROOFED BUILDING Structural integrity during floods to the expected high water level of feet MSL will be maintained by internal flooding of spaces when flood water reach feet MSL. Floor elevation at this point feet MSL. Type 3 PARTIALLY FLOOD-RESISTIVE BUILDING Structural integrity during floods to the expected high water level of feet MSL will be maintained by internal flooding of spaces when waters reach feet MSL. Some areas require implementation of pumps or other devices to maintain the required degree of protection. Floor elevation at this point feet MSL. Type 4 IV-18 NON-FLOOD-PROOFED BUILDING This building is not flood-proofed. Expected high water level is feet MSL. Floor elevation at this point feet MSL. Type 5 AREA OF SAFE REFUGE This space is above the expected high water level of feet MSL, and is authorized as an area of safe refuge for persons. Floor elevation at this point feet MSL. Type 6 CHAPTER 3vrI "r DEFINITIONS OF TERMS i " SECTION 3.1 SCOPE 3.1.1 PURPOSE: For the purpose of these Regulations, certain abbreviations, words, and their derivatives, shall be construed as set forth in this Chapter. SECTION 3.2 DEFINITIONS 3.2.1 GENERAL: The terms defined in this Chapter have been grouped in accordance with their main uses under the headings Administrative, Physical, and Regulatory. 3.2.2 ADMINISTRATIVE: 3.2.2.1 ACCESSORY USE OR STRUCTURE -- a use or structure on the same lot with, and of a nature customarily incidental and subordinate to, the principal use or structure. 3.2.2.2 BUILDING OFFICIAL -- the officer charged with the administration and enforcement of the Building Code and these Hurricane-proofing Regulations or his regularly authorized deputy. 3.2.2.3 HURRICANE HAZARD ZONES -- As defined in Chapter 4. 3.2.2.4 FREEBOARD -- a factor of safety usually expressed in feet above a design flood level for flood protective or control works. Freeboard tends to compensate for the many unknown factors that could contribute to flood heights greater than the height calculated for a selected size flood and floodway conditions such as wave action, bridge opening and floodway obstructions, and the hydrological effects of urbanization of the watershed. 3.2.2.5 HABITABLE ROOM -- a space used for living, sleeping, eating or cooking, or combination thereof, but not including bath- rooms, toilet compartments, closets, halls, storage rooms, laundry and utility rooms, basement recreation rooms and similar spaces. 3.2.2.6 NONCONFORMING USE -- a building or structure, or the use thereof, which was lawful before the passage or amendment of the (ordinance, resolution, act) but which is not in conformance with the provisions of these Regulations. 3.2.2.7 OWNER -- any person who has dominion over, control of, or title to an artificial or natural obstruction. 3.2.2.8 REGULATORY FLOOD -- a flood which is representative of large floods known to have occurred generally in the area or reasonably characteristic of what can be expected to occur in a particular hurricane. This hurricane is generally being recognized and accepted nationally by Federal and non-Federal interests as one with an average frequency of occurrence on the order of once in 100 years. IV-20 3.2.2.9 REGULATORY FLOOD DATUM (RFD) --established plane * of reference from which elevation and depth of flooding may be determined for specific locations of the floodplain. It is the Regulatory Flood plus a freeboard factor of safety established * for each particular area which tends to compensate for the many unknown and incalculable factors that could contribute to greater flood heights than that computed for a Regulatory Flood. 3.2.2.10 SUBDIVISION -- the partitioning or dividing of a parcel or tract of land. 3.2.3 PHYSICAL: 3.2.3.1 ARTIFICIAL OBSTRUCTION -- any obstruction whi ch is not a natural obstruction. 3.2.3.2 CHANNEL -- a natural or artificial watercourse of perceptible extent, with definite bed and banks to confine and conduct continuously or periodically flowing water. Channel flow thus is that water which is flowing within the limits of the defined channel. 3.2.3.3 FILL -- the placing, storing, or dumping of any material, such as (by way of illustration but not of limitation) earth, clay, sand, concrete, rubble, or waste of any kind upon the surface of the ground which results in increasing the natural ground surface elevation. 3.2.3.4 FLOOD -- an overflow of lands adjacent to a river, stream, ocean, lake, etc., not normally covered by water. Other- wise it is normally considered as any temporary rise in stream flow or stage that results in significant adverse effects in the vicinity. Adverse effects may include damages from overflow of land areas, backwater effects in sewers and local drainage channels, creation of unsanitary conditions, soil erosion, deposition of materials during flood recessions, rise of ground water coincident with increased stream flow, contamination of domestic water supplies, and other problems. 3.2.3.5 FLOOD CREST -- the maximum stage or elevation reached by the waters of a flood at a given location. 3.2.3.6 FLOODPLAIN -- the area, usually low lands, adjoining the channel of a river, stream or watercourse or ocean, lake, or other body of standing water which has been or may be covered by floodwater. 3.2.3.7 FLOOD-PROFILE -- a graph or a longitudinal profile showing the relationship of the water surface elevation of a flood to location along a stream or river. IV-21 3.2.3.8 FLOOD-PROOFING -- a combination of structural changes and/or adjustments incorporated in the design and/or construction and alteration of individual buildings, structures or properties subject to flooding primarily for the reduction or elimination of flood damages. 3.2.3.8.1 PERMANENT FLOOD-PROOFING -- permanent protection shall be provided against the flood which does not depend upon any judgment, flood forecast, or action to put flood protection measures into effect. 3.2.3.8.2 CONTINGENT (OR PARTIAL) FLOOD-PROOFING -- contingent measures shall not be effective unless, upon receipt of a warning or forecast, some minimal action shall be required to make the flood-proofing measures operational. 3.2.3.8.3 EMERGENCY (OR TEMPORARY) FLOOD-PROOFING -- emergency measures shall be, upon receipt of a warning or forecast, either improvised just prior to or during an actual flood or carried out according to an established emergency plan of action. 3.2.3.9 NATURAL OBSTRUCTION -- natural obstruction shall mean any rock, tree, gravel, or analogous natural matter that is an obstruction and has been located within the floodway by a nonhuman cause. 3.2.3.10 REACH -- a hydraulic engineering term to describe longitudinal segments of a stream or river. A reach will generally include the segment of the floodplain where flood heights are primarily controlled by man-made or natural floodplain obstructions or restrictions. In an urban area, the segment of a stream or river between two (2) physically identifiable points on the stream centerline would most likely be designated as a reach. 3.2.3.11 STRUCTURE -- anything constructed or erected on the ground, or attached to the ground, including but not limited to the following: docks, dams, fences, mobile homes, sheds and buildings. 3.2.3.12 UNDERCLEARANCE -- the lowest point of a bridge or other structure over or across a river, stream, or watercourse that limits the opening through which water flows. This is referred to as "low steel" in some regions. 3.2.3.13 WATERCOURSE -- any natural or man-made depression with a bed and well-defined banks two feet or more below the surrounding land serving to give direction to a current of water at least nine months of the year or having a drainage area of one square mile or more. 3.2.4 REGULATORY: 3.2.4.1 BUILDING CODE -- the regulations adopted by a local governing body setting forth standards for the construction, addition, modification and repair of buildings and other structures for the purpose of protecting the health, safety, and general welfare of the public. IV-22 3.2.4.2 SUBDIVISION REGULATIONS -- regulations and standards established by a local unit of government with authority granted under a state enabling law, for the subdivision of land in order to secure coordinated land development, including adequate building sites and land for vital community services and facilities such as streets, utilities, schools and parks. IV-23 CHAPTER 1 HURRICANE HAZARD ZONES SECTION 4.1 DEFINITION OF THREAT AND HAZARD ZONES: A severe hurricane will pose several classes of hazards along the Texas coastline and extending inland distances which vary with coastal configuration. 4.1.1 WIND: maximum windspeeds (fastest mile) up to 140 mph at a height of 30 feet, increasing with height in accordance with the one-seventh power law to a maximum several hundred feet above the surface. Peak gust speeds will exceed the sustained values by variable percentages. These gusts are considered in the tables in Chapter 8. 4.1.2 STORM SURGE: (three sources of damage potential) (1) Scour due to currents and wave action, including washovers; (2) Battering due to waterborne debris; and (3) Flooding due to combinations in rises in sea level from storm surge and inland runoff from heavy rains and riverine discharges. 4.1.3 In terms of these threat classes, the following coastal hazard zones are defined as the basis for the design of applicable model building codes: ZONE A: (1) 140 mph sustained winds (2) scouring action affecting foundation design (3) battering from floating debris (4) flooding (still water levels from expected hurricane inundation more than one foot above building grade level) ZONE B: Same as Zone A except without scour ZONE C: Same as Zone A except without scour and battering ZONE 0: 140 mph sustained winds at C-D boundary, diminishing as an exponential function of distance* to 100 mph at inland boundary SECTION 4.2 COMPUTATION OF REGULATORY FLOOD: The Regulatory Flood may be computed by adding the peak storm surge elevation and the inland rainfall backwater curve elevation as further described in this section. Refer to Annex A, B, and C. *VD = 100 + where VD = wind speed in Zone D I+-'T d = distance inland from C-D boundary IV-24 SECTION 4.3 GEOGRAPHICAL IDENTIFICATION OF HAZARD ZONES 4.3.1 ZONE A: Area of washover and scour. 4.3.1.1 Narrow, low segments of barrier islands and peninsulas that have been, are presently or have a high potential of being reached as a result of elevated water levels that generally exist during storms. (Ref: Bureau of Economic Geology, University of Texas.) 4.3.1.2 A zone extending between Gulf beaches and a line of at least 300 feet from the maximum elevation immediately adjacent to the beach (e.g., dune crest or crest of sand and shell ramp). 4.3.1.3 A zone along low-lying (less than 10 feet) unprotected (nonbulkheaded) bay shorelines extending at least 200 feet inland from the highest elevation from the shoreline. 4.3.1.4 Areas within 200 feet of unprotected (nonbulkheaded) navigation channels on peninsulas and barrier islands. 4.3.1.5 Areas with sand substrate subject to hurricane flooding of greater than 3 feet with current velocities greater than 3 feet per second for one hour or more during the rise and fall of the surge. 4.3.2 ZONE B: In the absence of washover channels and extensive scour, battering from waterborne debris will be expected to occur and will comprise the basis for defining Zone B. 4.3.2.1 On barrier islands and peninsulas, a zone extending inland from the most landward foredune line or line of highest elevation and on low-lying shorelines with primarily clay substrate, a zone extending inland from the shoreline at least 500 feet regardless of building density. 4.3.2.2 In areas where hurricane flooding is expected to be greater than 4 feet, building density is not greater than one major structure per acre, and effective wind fetch of greater than one mile. 4.3.3 ZONE C: In the absence of the above conditions but where "still water" hurricane flood levels are in excess of one foot. 4.3.4 ZONE D: This zone is concerned solely with wind forces on structures. Zone D is a strip beginning at the boundary with Zone C and extending inland to a point where the sustained hurricane winds are expected to reach 100 mph using the inverse relationship: VD = 100 + +-40, where VD = wind speed in Zone D d = distance inland from C-D boundary IVW25 CHAPTER5 WAVE AND SCOUR ACTION SECTION 5.1 GENERAL: Buildings and other structures shall not be constructed in Hazard Zone A unless positive provision is made either (a) to prevent movement or scour of underlying soil, or (b) to safeguard the structure in the event that such movement does occur. 5.1.1 PREVENTION OF SOIL MOVEMENT: Prevention of underlying soil movement may be accomplished by retaining structures or bulkheads adequately designed to resist, in addition to the vertical loads acting thereon, incident lateral earth pressures, surcharges and hydrostatic loadings corresponding to the maximum high-water level. 5.1.2 SAFEGUARDING STRUCTURE WHEN SOIL MOVEMENT OCCURS: In areas where scour and soil movement can occur if retaining structures or bulkheads are not provided, the structure shall be designed to be supported by properly designed pile foundations with due consideration being given to column action of piling in the event of scour, lateral loads on piling, and uplift capacity of piling when subjected to uplift loads by water or wind action. 5.1.3 SOIL INVESTIGATION: All plans for new structures shall bear a statement as to the nature and character of the soil under the structure. Where the capacities of the soil are not known, examinations of subsoil conditions by borings or other tests may be required and evaluation of such soil investigations shall be made by a Professional Engineer. (Ref: Sec. 9.2) 5.1.4 DESIGN OF FOUNDATIONS, RETAINING STRUCTURES, AND BULKHEADS All pile foundations, retaining structures and bulkheads in coastal areas subject to wind, wave and tidal action shall be designed by a Professional Engineer registered in the State of Texas. Records of penetration and bearing of all piles during installation shall be kept by the special inspector or Professional Engineer supervising the pile driving operations, bulkhead, or retaining structure installations. Copies of these records shall be submitted to the authority having jurisdiction. SECTION 5.2 STRUCTURAL REQUIREMENTS 5.2.1 GENERAL: All buildings and structures shall be designed and constructed to resist the erosive and corrosive effects of the elements and where applicable to withstand the horizontal and vertical forces or loads required by "The Building Code" and, in addition, all loads prescribed in this section, without exceeding the prescribed allowable stresses. IV- 26 5.2.2 LOADS: MiL'4 1 TO MGM ii 5.2.2.1 WATER: As specified in Section 7.3.3. 5.2.2.2 WAVES: The maximum wave force shall be calculated by using the maximum period. The most critical wave force, so determined, shall be used in the design. In case the natural period of vibration of the structure exceeds three seconds, dynamic analysis shall be performed to determine whether a resonance with the exciting wave forces is possible. 5.2.2.2.1 WAVE DESIGN INFORMATION: Wave force design assumptions and calculations shall be submitted to the Building Official. 5.2.2.3 BATTERING: As specified in Section 6.2. 5.2.2.4 WINDS: As specified in Chapter 8. 5.2.3 ALLOWABLE STRESSES: Allowable stresses for structural design shall be in accordance with the Building Code. 5.2.4 STRUCTURES - LOCATION, TYPE, GENERAL SPECIFICATIONS 5.2.4.1 LOCATION: Structure location must conform to other local, county, state and federal building and zoning regulations as well as these regulations. 5.2.4.2 GENERAL: If the proposed type (material and geometry) or method of construction does not have an experience record sufficient to justify approval, the Building Official may require special tests or demonstrations 'I-o prove the acceptability of the project. 5.2.4.3 BULKHEADS AND SEAWALLS 5.2.4.3.1 LOCATION: In order to obtain uniformity of the shoreline, bulkheads should be located so as not to interfere with the requirements of the Texas Open Beaches Act. Locations of bulkheads other than along the official bulkhead line may be approved to meet proper land use requirements and if it is shown that no detriment to adjoining property will result. In no case shall the actual bulkhead alignment differ more than two inches from the approved alignment. In no case shall a bulkhead project seaward beyond the official bulkhead line except within the above-stated tolerance. Bulkheads proposed between two properties where bulkheads already exist shall be designed' to connect such bulkheads. Bulkheads proposed adjacent to property not bulkheaded shall be designed to return along the side property line a distance sufficient to protect the backfill and prevent damage to adjacent property, but not less than 25 feet along the ocean and bay or 10 feet along canals, IV-27 rivers, and other water areas. The return wall shall be protected from erosion by riprap or slope pavement. 5.2.4.3.2 TYPE OF WALLS: The use of vertical face bulkheads will normally be limited to the bay front or inland waterways. Seawalls on the front and walls along sand beaches subject to wave action are to be an approved sloping high energy absorbing type, or vertical with energy-absorbing rubble mound on the face subject to wave action. The toe of the wall should be located sufficiently landward of the mean high-water line to prevent any immediate erosion of the foreshore area, and not less than 200 feet from the mean low-water shoreline on Gulf beaches subject to the Open Beaches Act; otherwise not less than 50 feet from same. Whenever the beach in front of an existing vertical wall has eroded to such extent that water reaches the bottom of the wall at mean high tide, a rubble mound shall be placed in front of the wall; and existing vertical walls along sand beaches, when in need of major repairs, shall not be replaced unless a rubble mound be constructed in front of them. 5.2.4.3.3 GENERAL SPECIFICATIONS: All bulkheads shall have a concrete cap designed to withstand the various loads placed upon it. The cap shall be large enough to provide no less than four inches of concrete cover between the piles, panels or masonry and nearest exterior face of cap. The elevation of the top of the cap shall be above the official flood criteria. (Such criteria provide for a minimum fill elevation, but not for storm wave heights.) Other cap elevations may be approved but only when land usage, proximity of buildings, and effect on adjacent property have been considered. Safety curbs or guardrails shall be provided for bulkheads adjacent to roadways. Handrails shall be provided for bulkheads adjacent to walkways. Cables or steel rods used in tiebacks must be protected by at least three inches of concrete encasement if the cable or rod is less than one inch in diameter. Tiebacks not encased in concrete are to be protected by coating and wrapping with bituminous or other corrosive-resistant material. Anchors for tiebacks, whether piles or other types, shall bear on undisturbed or well compacted soil and shall be designed to provide adequate horizontal support. Precast concrete panels of tee-pile and panel bulkheads shall have the foot of the panels placed in a manner that will prevent under- mining of the backfill material. Fill material placed on the water side of a bulkhead shall not be considered to offer any passive resistance when such fill is subject to erosion. Gravity type bulkheads of stone and concrete combination will be permitted, provided they are constructed of no less than 40 percent cast-in- place concrete by cross sectional area and volume. 5.2.4.4 PIERS AND DOCKS 5.2.4.4.1 LOCATION: Piers and docks at right angles to the shoreline, or nearly so, shall be located not closer to the side property line, or said line extended, than a distance equal to IV-28 the length of the pier or dock itself, provided however, no such distance shall be less than 10 feet. Where the zoning is residential or where the area is subdivided into tracts smaller than one acre each, piers and docks are to be located within the middle one-half of the water frontage. 5.2.4.4.2 TYPES: Structures such as piers which are to project beyond the bulkhead line, if allowed, shall be of an open type construction. Wharves, piers, or docks of solid fill construction will be approved only where such construction will not extend seaward of the approved bulkhead line. 5.2.4.4.3 GENERAL SPECIFICATIONS: In areas where the zoning is residential or in areas where no tract is larger than one acre, piers and docks shall be no more than 30 feet wide. In no case shall piers or docks obstruct navigation or interfere with drainage facilities. The projection of a pier or dock into a restricted waterway such as a canal, river, creek or basin shall be no greater than 10 feet or 20% of the waterway width, whichever is smaller, but shall comply with any other laws or regulations that may exist. Furthermore, the General Land Office's approval may be given for piers projecting into open water areas such as bays and sounds provided the projecting pier does not - obstruct navigation or encroach upon the rights of adjacent property owners. 5.2.4.5 GROINS 5.2.4.5.1 LOCATION: Groins are to be located so that the entire system of groins will provide the maximum benefit without adverse effects. Groins shall be anchored sufficiently landward to prevent flanking. 5.2.4.5.2 TYPES: Groins shall be either very low impermeable nonadjustable or impermeable adjustable, designed and maintained in adjustable condition for their entire life. The use of permeable groins shall be limited to special conditions. 5.2.4.5.3 GENERAL SPECIFICATIONS: Groins may be used to stabilize the beach if adjoining beaches are not adversely affected. Groins shall be impermeable, and adjustable to meet variations in natural conditions, and to produce the desired elevation of the beach. Adjustable groins shall be maintained at elevations in accord with actual beach needs and development of desirable changes of the beach profile, and so as to avoid damage to adjacent beaches. In no case shall the top of such groins be set higher than 2 feet above the beach profile. Impermeable, nonadjustable groins shall not extend seaward beyond the mean low water line, and their top elevation shall not be higher than 6 inches above the beach profile. Groins must be constructed or adjusted low enough to provide pedestrian access across them. Consideration of the degree of beach protection to be provided by proposed groins, and the acceptability of such installations, will IV-29 be based primarily on the following factors: Direction and Volume of Littoral Drift; Wave Force and Direction; Wind Force and Direction; Land Usage; Type of Bulkhead; Type of Groin; and Spacing and Length of Groins. A complete coastal engineering study may be required before approval is given to the number, type, and location of groins. 5.2.4.6 BEACH NOURISHMENT: Artificial nourishment of sand beaches or creation of new beach area are treated as construction projects. Typical profiles for such projects consist of a 50-foot level berm at elevation 6 ft. MSL; a I on 20 slope from there to MLW; and a I on 30 slope seaward to existing bottom. Special agreement between the upland owner proposing such a project and the building official may be required in order to adequately protect and permanently safeguard any public rights at the proposed site. 5.2.4.7 JETTIES AND BREAKWATERS: Jetties and breakwaters shall be designed in accordance with the latest issue of the U.S. Army Corps of Engineers' Technical Report No. 4 entitled "Shore Protection, Planning and Design." 5.2.4.8 MOORING PILES AND BUOYS: All mooring piles and buoys shall be placed within the limits of the owner's water frontage and shall be located in a manner not to interfere with navigation. Outer mooring piles and buoys shall not obstruct a navigable waterway except as permitted by the appropriate agency having jurisdiction over the waterway. 5.2.4.9 BOAT SLIPS AND BOATHOUSES: Boat slips and boathouses to be located on private property require approval and permit from the Building and Zoning Department. Bulkheads proposed to be constructed for retaining the banks of the boat slip shall meet the requirements of this section of the manual. The location of boat slips shall conform to the same requirements as for piers and docks. Boathouses may be constructed over boat slips or as a separate structure subject to the following conditions: (a) The boathouse is not used as a dwelling, guest house or servant's quarters unless specially constructed as such to the requirements of the Building and Zoning Department; (b) The boathouse does not extend into a water area a distance greater than that permitted for a dock or pier; and (c) The overall size of the boathouse does not exceed 25 feet in width, 45 feet in length, or 18 feet in height, except commercial marinas and drydocks may be permitted larger boathouses constructed in compliance with applicable zoning and building regulations. 5.2.5 INFORMATION REQUIRED ON AND FOR THE PREPARATION OF CONSTRUCTION PLANS: Construction plans must be prepared by an engineer registered in Texas. Plans shall be arranged and numbered as a set and contain all (or applicable portions) of the following: (1) Plan, elevation, and sections showing the complete structure; (2) Details of structural components including precast members, structural connections, steel reinforcement, and expansion joints; (3) Complete description of all materials to be used; (4) Design loading and minimum IV-30 penetration of piles; (5) Location control: a. Horizontal control referred to a section line, road, or permanent landmark, and including property lines and the Official Bulkhead Line. b. Vertical control referred to U.S. Coast and Geodetic Survey Datum (MSL) including elevations landward, soundings in water areas, and the mean high water line; and (6) Graphical representation of test borings or soil profile parallel to and within five feet of proposed structures. IV-31 CHAPTER6 W BATTERING BY DEBRIS SECTION 6.1 GENERAL: Buildings and other structures constructed in Hazard Zone B shall be designed in accordance with the provisions of this regulation and the "Building Code." 6.1.1 Buildings designated as "Safe Refuge" and constructed in Hazard Zone B shall be designated for special battering loads. All other structures, except as noted, in Hazard Zone B shall be designed for normal battering loads. SECTION 6.2 BATTERING LOADS 6.2.1 NORMAL BATTERING LOADS: Normal battering loads are those which relate to isolated occurrences of floatable objects of normally encountered sizes striking buildings or parts thereof. The normal battering load shall be considered as a concentrated load acting horizontally at the RFD or at any point below it, equal to the impact force produced by a 1,000 pound mass traveling at a velocity of 10 feet per second and acting on a one-square-foot surface of the structure. 6.2.2 SPECIAL BATTERING LOADS: Special battering loads are those which relate to large conglomerates of floatable objects, either striking or resting against a building, structure or parts thereof. Where special battering loads are likely to occur (as in Hazard Zone B), such loads shall be considered in the design of buildings designated "Safe Refuge." Unless a rational and detailed analysis is made and submitted for approval by the Building Official, the intensity of the load shall be taken as 500 pounds per foot acting horizontally over a one-foot-wide horizontal strip at the RFD or at any level below it. Where natural or artificial barriers exist which would effectively prevent these special battering loads from occurring, the loads may be ignored in the design. 6.1.3 EXTREME BATTERING LOADS: Extreme battering loads are those which relate to large floatable objects and masses such as runaway barges or collapsed buildings and structures, striking the building, structure, or component under consideration. It is considered impractical to design buildings having adequate strength for resisting extreme battering loads. Accordingly, except for special cases when exposure to these loads is highly probable and the resulting damages are severe, no allowances for these loads need be made in the design. IV-32 CHAPTER 7 L Lf Lj L IO FLOODING SECTION 7.1 FLOOD-PROOFING CLASSIFICATION OF SPACES BELOW THE REGULATORY FLOOD DATUM 7.1.1 SCOPE 7.1.1.1 GENERAL: The flood-proofing classification of a space is determined by the degree of protection required under these Regulations to permit its intended use. The flood-proofing class of a space for which temporary placement or contingent protection measures are approved assumes that these measures are in effect during a flood and defines the resulting relationship of protection to use. 7.1.1.2 ASSIGNMENT OF FLOOD-PROOFING CLASSES: Assignment is made by the Owner at the time of application for a permit and is subject to the approval of the Building Official. Every space of an improvement in a Flood Hazard Area which impinges in whole or part upon the RFD shall have a flood-proofing class assigned to it, and all requirements associated with a flood-proofing class shall be met by the space to which they apply in addition to all other requirements of these Regulations and the Building Code. 7.1.2 DESCRIPTIONS OF FLOOD-PROOFING CLASSES 7.1.2.1 CLASSIFICATIONS: The following descriptions of the five flood-proofing classes are approximate and general; more precise specification of the requirements associated with each class is given in Table 2 of the following section. 7.1.2.2 COMPLETELY DRY SPACES (WI): The spaces shall remain completely dry during flooding to the RFD; walls shall be impermeable to passage of water and water vapor. Permitted contents and interior finish materials are virtually unrestricted, except for high-hazard type uses or human habitation. No portion of the building or structure that is below the RFD, regardless of structure or space classification, shall be used for human occupancy or for storage of any property, material, or equipment that Might constitute a safety hazard when contacted by flood waters. Structural components shall have capability of resisting hydrostatic and hydrodynamic loads and the effects of buoyancy. 7.1.2.3 ESSENTIALLY DRY SPACES (W2): These spaces shall remain essentially dry during flooding to the RFD; walls shall be substantially impermeable to water, but may pass some water vapor or seep slightly. Contents and interior finish materials are restricted when hazardous or vulnerable under these conditions. Structural components shall have capability of resisting hydrostatic and hydrodynamic loads and the effects of buoyancy. IV-33 VV- I r ' 1.1.2.4 SPACES INTENTIONALLY FLOODED WITH POTABLE WATER (W3: These spaces will be flooded internally with potable water provided by the Owner in order to maintain the building's structural integrity by equalizing pressures on structural components during flooding to the RFD; walls shall be sufficiently impermeable to prevent the passage, infiltration, or seepage of contaminated floodwaters. Contents and interior finish materials are restricted when hazardous or vulnerable under intentional flooding conditions. 7.1.2.5 SPACES FLOODED WITH FLOODWATER (W4): These spaces will be flooded with floodwater (contaminated) by automatic means or are otherwise partially exposed to the unmitigated effects of the flood. Although there are minimal structural requirements for walls and other structural components, contents and interior finish materials are restricted to types which are neither hazardous nor vulnerable to loss under these flooding conditions. (Most spaces in existing buildings would have this classification if provided with a suitable automatic flooding system. Carports, loading platforms, open crawl spaces, porches and patios would generally fall into this classification.) 7.1.2.6 NON-FLOOD-PROOFED SPACES (W5): A non-flood-proofed space in an existing building or structure is defined as a space which fails to meet the requirements of any of the above-described classifications. 7.1.3 THE SPACE CLASSIFICATION CHART 7.1.3.1 GENERAL: Table 2 indicates the various degrees of protection required to permit uses of spaces for each flood-proofing class. Although spaces must meet the requirements shown for each element of flood-proofing, the chart in itself shall not be construed as being exhaustive with respect to all requirements imposed by these Regulations. In disputes arising over the interpretation of this chart, the written provisions of these Regulations shall be considered as definitive. 7.1.3.2 SEPARATION OF SPACES WITH DIFFERENT FLOOD-PROOFING CLASSIFICATIONS: Any two adjacent spaces below the RFD having different flood-proofing classes shall be separated by a barrier meeting the requirements for the space with the lower-numbered classification. In addition, any opening below the RFD between two adjoining spaces shall be provided with a closure meeting the requirements for the space with the lower-numbered classification. SECTION 7.2 WATERPROOFING 7.2.1 SCOPE 7.2.1.1 PURPOSE: This section shall govern the design, use and methods of construction and materials with respect to obtaining, IV-34 for a given space, the degree of protection against water, water vapor, and waterborne contamination determined by the vulnerability or hazard potential of the contents and interior finish materials to meet its flood-proofing classification. 7.2.1.2 PERFORMANCE STANDARDS: Three types of waterproofing are defined herein as to the degree to which they satisfy a standard of dryness. If any material or method of construction meets the functional performance standard defining a type of waterproofing construction it shall be considered as satisfying the requirements of the section. For the purpose of these Regulations, the detailed specification of Type A waterproofing construction, as contained in this section, shall be interpreted as a guide to measures which are reasonable prerequisites for attaining this standard of dryness. 7.2.2 TYPE A CONSTRUCTIONS 7.2.2.1 PERMEABILITY: Type A waterproofing constructions are completely impermeable to the passage of external water and water vapor under hydrostatic pressure of flooding to the RFD. Type A waterproofing construction shall consist of either a continuous membrane satisfying paragraph 7.2.2.2, integrally waterproofed concrete satisfying paragragh 7.2.2.3, or a continuous interior lining satisfying paragraph 7.2.2.4. 7.2.2.2 TYPE A MEMBRANE CONSTRUCTION: Type A membrane waterproofing forms a continuous external impervious lining to protect a structure with a concrete floor slab and concrete or reinforced concrete masonry unit walls. It shall comply with the following requirements for structural prerequisites, materials, and installation. 7.2.2.2.1 STRUCTURAL PREREQUISITES: 7.2.2.2.1.1 CONTINUITY OF STRUCTURE: Structural slabs below the grade shall be continuous under perimeter walls to prevent differential settlement and shall be designed to act monolithically with the walls; reinforced concrete masonry unit walls shall be connected rigidly to slabs with reinforcing steel. 7.2.2.2.1.2 PRO JECTION OF SLAB: Where a slab is continuous under perimeter walls, it shall project not less than six (6) inches beyond the outside of the wall in order to provide space for joining horizontal and vertical membranes. 7.2.2.2.1.3 COLUMNS: Where columns occur, there shall be no vertical discontinuity or abrupt change in slab cross sections. Where slab thicknesses change, they shall do so gradually, and the effects of pressure distribution on the thinner portions of the slab cross section shall be considered. IV-35 7.2.2.2.1.4 PROTECTION: All membranes shall be installed on exterior surfaces of perimeter walls. For floor slabs, the membrane shall be installed between the structural slab and wearing surface or otherwise placed on a nonstructural concrete sub-base at least two (2) inches in thickness to protect the membrane and insure its flatness; in the latter case (Figure 3) a two (2) inch thick sand-cement screed shall be placed over the membrane before laying reinforcing steel for the structural slab. If a floor membrane is sandwiched between two structural slabs, the membrane shall be positioned at a location that will not subject it to excessive overstress conditions. 7.2.2.2.1.5 PILE FOUNDATIONS: When spaces are supported on pile foundations, the pile shall be positively connected to the member which it supports (column, wall, beam, etc.) in order to prevent overturning or displacement of the building. The penetration required for this positive connection must be protected by keyways, asphaltic bitumen pocket, or other accepted engineering design. A reinforced concrete sub-slab of not less than four (4) inches thick shall be provided over the entire area in order to receive the membrane. If the weight of the structure is such as to prohibit overturning and displacement of the structure thereby permitting complete separation between the pile caps and the floor slab, the pile caps shall be inter- connected with stabilizing beams, cast monolithically with the sub-slab. 7.2.2.2.2 MATERIALS: For the purpose of these Regulations, a membrane shall be any layered sheet construction of tar/asphalt bitumen and felts, at least 3-ply in thickness neoprene-coated nylon fabric, other approved sheet material, or multiple applied hydrolithic coatings of asphaltic bitumens. All applicable ASTM standards shall apply to Type A membranes and their component parts. 7.2.2.2.2.1 PERMEABILITY: Type A membrane shall permit passage of no more than three (3) pounds of water per 1,000 square feet in 24 hours at 40 psi. 7.2.2.2.2.2 PLASTIC WATERPROOFING MATERIALS: Various plastic materials, including, among others, polyethylene, PVC, polyurethane, and polyisobutylene, shall be permitted in sufficient thicknesses in sheets or coatings. In certain cases the Building Official may require less protection beneath plastic than the concrete sub-base required in paragraph 7.2.2.2.1.4. 7.2.2.2.3 INSTALLATION: 7.2.2.2.3.1 APPLICATION: All Type A membrane waterproofing shall be applied by a certified roofing or water- proofing contractor. IV-36 7.2.2.2.3.2 TURNS: Turns at corners, both vertical and horizontal, shall be made with chamfers and fillets of not less than two (2) inches dimension on any side. 7.2.2.2.3.3 SEAMS: Membrane seams or overlaps, if any, shall be thoroughly interleaved and protected in accordance with accepted practice, but in no case shall seams or overlaps be less than two (2) inches in any direction. 7.2.2.2.3.4 PIPES: Points where pipes or ducts penetrate waterproofed construction shall be designed to be watertight in accordance with accepted engineering practice. 7.2.2.2.3.5 JOINTS: Membranes shall be continous across expansion, control, and construction joints, which shall have waterstops of rubber, copper, plastic, or other suitable materials. 7.2.2.2.3.6 PROTECTION: Membranes on walls shall extend at least three (3) inches above the RFD of the protected space and shall be attached with a reglet or covered with protective masonry at its upper termination. To protect all wall membranes during backfill operations, protection of not less than 1/2-inch thickness of cement parging, plastic sheets, or other rigid non-cellulose material, installed in a workmanlike manner, shall be provided; however, in large projects or where the protection required above may not be adequate, the Building Official may require protection by some other means. 7.2.2.2.3.7 EXCAVATION: Excavation preceding construction shall extend a minimum distance of 24 inches beyond the exterior wall lines to facilitate construction operations. In built-up areas where this requirement cannot be met, excavation limits will be as designated by the Building Official. 7.2.2.3 TYPE A INTEGRALLY WATERPROOFED CONCRETE CONSTRUCTION: Type A integrally waterproofed concrete construction shall comply with the following requirements for structural prerequisites, materials, and installation. 7.'2.2.3.1 STRUCTURAL PREREQUISITES: 7.2.2.3.1.1 CONTINUITY OF STRUCTURE: Structural slabs shall be continuous under perimeter walls. Slabs shall be designed to act monolithically with perimeter walls, or otherwise shall carry them non-rigidly in a recess with mastic V fillings and waterstops. (Figure 4.) 7.2.2.3.1.2 DEFLECTIONS: To prevent increases of permeability in tension zones, the maximum deflection of any structural slab or perimeter wall shall not exceed 1/500 of its shorter span. IV-37 7-L1b ,L , ]L ;' , , n - Reinforced Concrete Column Reinforced Concrete Structural Floor 1 " /-; * Membrane Waterproofing 2" Protective Sand ,. : .; - & Cement Screed -* . Concrete Sub-Base Angle Fillets TYPE "A" MEMBRANE WATERPROOFING IN FLOOR SLABS IV-38 (a) (b) NON-RIGID PERIMETER WALL AND FLOOR SLAB CONNECTIONS IV-39 SU % 10REVISION 7.2.2.3.1.3 COLUMNS: Where columns occur, there shall be no vertical discontinuity or abrupt change in slab cross section. Where slab cross sections change, they shall do so gradually, and the effects of pressure distribution on the thinner portions of the slab cross section shall be considered. 7.2.2.3.2 MATERIALS: 7.2.2.3.2.1 STRENGTH: All Type A integrally waterproofed concrete shall have a seven-day compressive strength of at least 3,000 psi and a 28-day compressive strength of 4,000 psi. 7.2.2.3.2.2 WATERPROOFING ADMIXTURES: If an approved waterproofing admixture is used, the cement content required to achieve the strength specifications may not be reduced by more than 10%. Approved admixtures shall not reduce the compressive strength of the concrete and shall act as a densifier and/or to increase workability. 7.2.2.3.2.3 JOINTS: Expansion joints shall be keyed and provided with waterstops. Construction joints shall be provided with waterstops and shall be thoroughly roughened and cleaned before continuation of concrete placement. 7.2.2.3.2.4 PROTECTION OF FRESH CONCRETE: When potentially aggressive groundwater conditions exist, the Building Official may require the protection of fresh concrete from contact with groundwater for a minimum of 14 calendar days. Protection shall be accomplished either by the removal of groundwater or by the application of a temporary membrane or surface coating (e.g., bitumen or tar emulsion) which, however, need not meet standards for permanent protection. 7.2.2.4 TYPE A INTERIOR LININGS: A Type A interior lining forms a continuous internal impervious barrier to protect a structure with a concrete floor slab and concrete or reinforced concrete masonry unit walls. All Type A interior linings shall conform to the following requirements for structural prerequisites, materials and installation. 7.2.2.4.1 STRUCTUAL PREREQUISITES: 7.2.2.4.1.1 CONTINUITY OF STRUCTURE: Structural slabs below grade shall be continuous under perimeter walls to prevent differential settlement and shall be designed to act monolithically with the walls; reinforced concrete masonry unit walls shall be connected rigidly to slabs with reinforcing steel. 7.2.2.4.1.2 COLUMNS: Where columns occur, there shall be no vertical discontinuity or abrupt change in slab cross sections. Where slab thicknesses change, they shall do so gradually, and the effects of-pressure distribution on the thinner portions of the slab cross section shall be considered. IV-40 7.2.2.4.1.3 DEFLECTIONS: To prevent cracking of the interior lining, the maximum deflection of any structural slab or perimeter wall to which the lining is applied shall not exceed 1/500 of its shorter span. 7.2.2.4.2 MATERIALS: For the purpose of these Regulations, an interior lining shall be any continuous coating, parging, or rendering of a cementious or other approved water- proofing material or compound with adequate structural strength and impermeability to serve its intended purpose. All relevant ASTM standards shall apply to Type A interior lining materials. 7.2.2.4.2.1 PERMEABILITY: Type A interior linings shall permit the passage of no more than three (3) pounds of water per 1,000 square feet in 24 hours at 40 psi. 7.2.2.4.3 INSTALLATION: 7.2.2.4.3.1 APPLICATION: All Type A interior lining waterproofing shall be applied by a certified roofing or waterproofing contractor. 7.2.2.4.3.2 TURNS: Turns at corners, both vertical and horizontal, shall be made with fillets of not less than two (2) inches dimension on any side. 7.2.2.4.3.3 PIPES: Points where pipes or ducts penetrate waterproofed construction shall be designed to be watertight in accordance with accepted engineering practice. 7.2.2.4.3.4 JOINTS: Interior linings shall be continuous across expansion, control and construction joints, which shall have waterstops of rubber, copper, plastic, or other suitable material. 7.2.2.4.3.5 VERTICAL EXTENT: Interior linings on walls shall extend at least 3 inches above the RFD of the protected space. 7.2.2.4 EXISTING SPACES: Spaces in existing buildings or structures which become subject to these Regulations may be approved as having Type A waterproofing upon submission by the Owner of plans and specifications for these spaces prepared by a licensed architect or engineer; however, the Building Official shall make a thorough inspection of actual site conditions and may require that tests be made to demonstrate the adequacy of the work before granting this approval. 7.2.3 TYPE B CONSTRUCTIONS 7.2.3.1 PERMEABILITY: Type B waterproofing constructions shall be substantially impermeable but may pass water vapor and seep IV-41 slightly during flooding to the RFD. Large cracks, openings, or other channels that could permit unobstructed passage of water shall not be permitted. In no case shall there be permitted the accumulation of more than four (4) inches of water depth in such a space during a 24-hour period if there were no devices provided for its removal. However, sump pumps shall be required to control this seepage. 7.2.3.2 UPGRADING EXISTING SPACES: Spaces with Type B water- proofing construction may be upgraded to Type A through the installation of a continuous exterior or interior lining or a combination of both, which the Building Official may approve as meeting the requirements for permeability of Type A waterproofing. 7.2.3.2.1 INSPECTIONS: The Building Official shall make inspections prior to and upon completion of this work before approving the completed work as meeting Type A waterproofing requirements. The Building Official may require that tests be made to demonstrate the adequacy of the work before granting this approval. 7.2.4 TYPE C CONSTRUCTIONS 7.2.4.1 NON-WATERPROOFED: Type C waterproofing constructions are any which do not satisfy the requirements for Type A or B in 7.2.2 and 7.2.3 respectively. 7.2.4.2 UPGRADING OF SPACES: Non-waterproofed spaces may be upgraded to Type A or B waterproofing when the Building Official shall approve such work as meeting the standard for Type A or B in 7.2.2 and 7.2.3. 7.2.4.2.1 INSPECTIONS: The Building Official shall make inspections prior to, during, and upon completion of this work before approving the improvement as Type A or B waterproofing, and may require tests be made to demonstrate the adequacy of the work before granting this approval. SECTION 7.3 STRUCTURAL REQUIREMENTS 7.3.1 SCOPE 7.3.1.1 GENERAL: All buildings and structures covered by these Regulations and all parts thereof shall be capable of resisting all loads required by "The Building Code" and, in addition, all loads prescribed in this section, without exceeding the prescribed allowable stresses. 7.3.2 CLASSES OF LOADS 7.3.2.1 CLASS I LOADS: Reflect the probable effects of flooding on structures which are waterproof (WI or W2). These loads IV-42 lie shall be calculated in complete accordance witn t I section and shall include all water, impact, and soil loads specified herein. 7.3.2.2 CLASS 2 LOADS: Reflect the probable effects of flooding on structures which include internal flooding as a means of structural protection and which shall be so flooded in accordance with Section 7.5. These loads shall be calculated in accordance with this section except that only hydrodynamic and impact loads must be considered when the interior and exterior water levels are equal. 7.3.2.3 CLASS 3 LOADS: Apply to buildings or structures which are to be flooded with floodwater either internally by automatic means or externally in partially exposed areas. For such internal flooding, Class 3 loads shall coincide with those of Class 2. For partially exposed spaces, however, any dependent or supporting structural components shall be designed for Class I or 2 loads if they are also structural components of any adjacent enclosed space, whichever is required; isolated or free-standing columns or walls shall meet all criteria of 7.3.9.2.3. 7.3.3 WATER LOADS 7.3.3.1 TYPES: Water loads, as defined herein, are loads or pressures on surfaces of the buildings or structures caused and induced by the presence of floodwaters. These loads are of two basic types: hydrostatic and hydrodynamic. 7.3.3.2 HYDROSTATIC LOADS: Hydrostatic loads are those caused by water either above or below the ground surface, free or confined, which is either stagnant or moves at very low velocities, or up to five (5) feet per second. These loads are equal to the product of the water pressure times the surface area on which the pressure acts. The pressure at any point is equal to the product of the unit weight of water (64 pounds per cubic foot) multiplied by the height of the water above the point or by the height to which confined water would rise if free to do so. Hydrostatic pressures at any point are equal in all directions and always act perpendicular to the surface in which they are applied. For the purpose of these Regulations, hydrostatic loads are subdivided into the following types: 7.3.3.2.1 VERTICAL LOADS: These are loads acting vertically downward on horizontal or inclined surfaces of buildings or structures, such as roofs, decks, or floors, and walls, caused by the weight of flood waters above them. 7.3.3.2.2 LATERAL LOADS: Lateral hydrostatic loads are those which act in a horizontal direction, against vertical or inclined surfaces both above and below the ground surface and tend to cause lateral displacement and overturning of the building, structure, or parts thereof. IV -43 Lid 7.3.3.2.3 UPLIFT: Uplift loads are those which act in a vertically upward direction on the underside of horizontal or sloping surfaces of buildings or structures, such as basement slabs, footings, floors, decks, roofs and overhangs. Hydrostatic loads acting on inclined, rounded or irregular surfaces may be resolved into vertical or uplift loads and lateral loads based on the geometry of the surfaces and the distribution of hydrostatic pressures. 7.3.3.3 HYDRODYNAMIC LOADS: Hydrodynamic loads, for the purpose of these Regulations, are those induced on buildings or structures by the flow of floodwater moving at moderate or high velocity around the buildings or structures or parts thereof above ground level. Such loads may occur below the ground level when openings or conduits exist which allow free flow of floodwaters. Hydrodynamic loads are basically of the lateral type and relate to direct impact loads by the moving mass of water, and to drag forces as the water flows around the obstruction. Where application of hydrodynamic loads is required, the loads shall be computed or estimated by recognized and authoritative methods. 7.3.3.3.1 CONVERSION TO EQUIVALENT HYDROSTATIC LOADS: For the purpose of these Regulations, and for cases when water velocities do not exceed 10 feet per second, dynamic effects of the moving water may be converted into equivalent hydrostatic loads by increasing the depth of water to the RFD by an amount dh, on the headwater side and above the ground level only, equal to: dh = a V2 Where 2' V is the average velocity of the water in feet per second; g is the acceleration of gravity, 32.2 feet per second per second; a is the coefficient of drag or shape factor. (The value of a, unless otherwise evaluated, shall not be less than 1.25.) The equivalent surcharge depth dh shall be added to the depth measured between the design level and the RFD and the resultant pressures applied to, and uniformly distributed across, the vertical projected area of the building or structure which is perpendicular to the flow. Surfaces parallel to the flow or surfaces wetted by the tailwater shall be considered subject to hydrostatic pressures for depths to the RFD only. 7.3.3.4 INTENSITY OF LOADS: 7.3.3.4.1 VERTICAL LOADS: Full intensity of hydrostatic pressures caused by a depth of water between the design level and the RFD applied on all surfaces involved. IV -44 7.3.3.4.2 LATERAL LOADS: Full intensity of hydrostatic pressures caused by a depth of water between the design elevations) and the RFD applied over all surfaces involved, both above and below ground level, except that for surfaces exposed to free water the design depth shall be increased by one foot. 7.3.3.4.3 UPLIFT: Full intensity of hydrostatic pressures caused by a depth of water between the design level and the RFD acting on all surfaces involved, unless provisions are made to reduce uplift intensities as permitted in 7.3.8. 7.3.3.4.4 HYDRODYNAMIC LOADS: Hydrodynamic loads, regardless of method of evaluation, shall be applied at full intensity over all above-ground surfaces between the ground level and the RFD. 7.3.3.5 APPLICABILITY: For the purpose of these Regulations, hydrostatic loads shall be used in the design of buildings and structures exposed to water loads from stagnant floodwaters for conditions when water velocities do not exceed five (5) feet per second, and for buildings and structures or parts thereof not exposed or subject to flowing water. For buildings and structures, or parts thereof, which are exposed and subject to flowing water having velocities greater than five (5) feet per second, hydrostatic and hydrodynamic loads shall apply. 7.3.5 ALLOWABLE SOIL PRESSURES 7.3.5.1 APPLICABILITY: Under flood conditions, the bearing capacity of submerged soils is affected and reduced by the buoyancy effect of the water on the soil. For foundations of buildings and structures covered by these Regulations, the bearing capacity of soils shall be evaluated by a recognized acceptable method. Expansive soils should be investigated with special care. Soils which lose all bearing capacity when saturated, or become "liquified," shall not be used for supporting foundations. If a detailed soils analysis and investigation is not made, and if bearing capacities of the soils are not evaluated as required above, allowable soil pressures permitted in "The Building Code" may be used, provided those values are reduced 50%. 7.3.6 STABILITY 7.3.6.1 OVERTURNING: All buildings and structures covered by these Regulations and all parts or elements thereof shall be proportioned to provide a minimum factor of safety of 1.50 against failure by sliding or overturning when subjected to flood-related loads or combined loads. The required stability shall be provided by the normal resistive loads allowed by "The Building Code," such as frictional resistance between the foundations and the soil, passive earth pressure, batter and vertical piles and permanent anchors which may be provided. For the purpose of providing stability, only IV-45 r,7-' the dead load shall be considered effective. No use shall be made of any resistance, either as weight or frictional or passive, from soils which could be removed or displaced by excavation, scour or other causes. Similarly, no use shall be made of frictional resistance between the foundation and the underlying soil in the case of structures supported on piles. 7.3.6.2 FLOTATION: The building or structure, and all appurtenances or components thereof not rigidly anchored to the structure, shall have enough weight (deadload) to resist the full or reduced hydrostatic pressures and uplift from flood- water at the RFD with a factor of safety of 1.33. For provisions governing reduced uplift intensities, see 7.3.7. In cases when it is not practical to provide the required factor of safety against flotation by weight alone, the difference shall be made up by providing dependable and permanent anchors that meet the approval of the Building Official. Elements which depend on anchorage to other portions of the structure shall be anchored to a portion or portions of the structure which have the required factor of safety against flotation from all contributing elements subject to uplift. Apportionment of uplift and resisting forces shall be made by a recognized method of structural analysis in accordance with accepted engineering practice. 7.3.6.3 ANCHORAGE: Any building and structure as a whole which lacks adequate weight and mass to provide the required factors of safety against overturning, sliding, and flotation shall be dependably and permanently anchored to the ground. In addition, all elements of a building or structure, such as wall, floor slabs, girders, beams, columns and other members, shall be dependably connected or anchored to form an adequate structural system to support the individual members and all the applied loads. Provision of adequate anchorage is also essential and required for all tanks and vessels, sealed conduits and pipes, lined pits and sumps and all similar structures which have negligible weight of their own. 7.3.7 REDUCTION OF UPLIFT PRESSURES 7.3.7.1 GENERAL: Uplift forces, in conjunction with lateral hydrostatic forces constitute the most adverse flood-related loading on buildings and structures and elements thereof. Their combined effect determines to a major extent the requirements for weight and anchorage of a structure as a whole to assure its stability against flotation, sliding and overturning. When uplift forces are applied to structural elements of a building or structure, such as footings, walls, and particularly basement slabs, they generally constitute the critical loading on such elements. In the interest of providing economical solutions to the basic problem of structurally flood-proofing buildings and structures, it is permissible under these Regulations to make provisions for effectively reducing uplift forces acting under the structure. The plans and design data submitted to the Building Official for approval shall show complete and detailed procedures, assumptions, IV-46 analyses and design information, and specific provisions to be incorporated in the work for accomplishing the proposed reduction in uplift. Data and design procedures shall be based on recognized and acceptable methods of foundation drainage and waterproofing. Such provisions shall include, but are not limited to, the following items, used alone or in combination, as conditions will dictate. 7.3.7.2 IMPERVIOUS CUTOFFS: Impervious cutoffs are barriers installed below the ground line and externally to the perimeter of the building or structure for the purpose of decreasing seepage quantities and/or reducing existing gradients. Such cutoffs must, in all cases where floodwaters will rise above the ground level, be connected by suitable impervious blankets or membranes to the walls of the building or structure. Cutoffs may consist of interlocking steel sheeting, compacted barrier of impervious soil, grouted or injected cutoffs, impervious wall of interconnected concrete piles or panels, and similar seepage barriers, used alone or in combination. 7.3.7.3 FOUNDATION DRAINAGE: Where impervious cutoffs are provided or where suitable foundation conditions exist, effective drainage and relief of uplift pressures under buildings and structures can be achieved. These foundation materials must be free- draining and have the desired degree of permeability. For the purpose of these Regulations, foundation drainage is intended to consist of the provision of drainage blankets, trenches, and, in all cases, drain tiles or perforated drainpipes adjacent to footings and under floor slabs. Other methods of foundation drainage, such as by means of sumps, well points, or deep wells can be used for special applications. Drainpipes shall discharge into a sump or suitable collection structure, where the water is collected and ejected by sump pumps. 7.3.7.4 SUMPS AND PUMPS: Spacing, sizing and determination of depth of sumps shall be consistent with and correlated to the intended drainage system, the estimated amount of seepage and drainage yield. 7.3.8 REQUIREMENTS FOR OTHER FLOOD-PROOFING METHODS 7.3.8.1 METHODS: A building shall be considered as being completely flood-proofed if the lowest elevation of all space(s) within the building perimeter is above the RFD as achieved by: (1) building on natural terrain beyond the RFD limit line on natural undisturbed ground, (2) building on fill, (3) building on stilts, and (4) protection by dikes, levees and/or floodwalls. These methods may be used alone or in combination to achieve the required degree of flood-proofing. Data and design procedures shall, in all cases, be based an recognized and acceptable methods of the applicable disciplines involved, and the following additional requirements. IV-47 U 11 7.3.8.2 FLOOD-PROOFING BY ELEVATING THE BUILDING 7.3.8.2.1 NATURAL TERRAIN: In addition to the requirements of "The Building Code," the building shall be located not less than 50 feet back from the line of incidence of the RFD on the ground, foundation design shall take into consideration the effects of soil saturation on the performance of the foundation, the effects of floodwaters on slope stability shall be investigated, normal access to the building shall be by direct connections with areas above the RFD and all utility service lines shall be designed and constructed as required to protect the building and/or its components from damage or failure during a flooding event to the RFD. 7.3.8.2.2 BUILDING ON FILL: The building and all parts thereof may be constructed above the RFD on an earth fill. Prior to placement of any fill or embankment materials, the area upon which fill is to be placed, including a five-foot strip measured horizontally beyond and contiguous to the toe line of the fill, shall be cleared of standing trees and snags, stumps, brush, down timber, logs and other growth, and all objects including structures on and above the ground surface or partially buried. The area shall be stripped of topsoil and all other material which is considered unsuitable by the Building Official as foundation material. All combustible and noncombustible materials and debris from the clearing, grubbing and stripping operations shall be removed from the proposed fill area and disposed of at locations above the RFD and/or in the manner approved by the Building Official. Fill material shall be of a selected type, preferably granular and free-graining, placed in compacted layers. Fill selection and placement shall recognize the effects of saturation from floodwaters on slope stability, uniform and differential settlement, and scour potential. The minimum elevation of the top of slope for the fill section shall be at the RFD. Minimum distance from any point of the building perimeter to the top of the fill slope shall be either 25 feet or twice the depth of fill at that point, whichever is the greater distance. This requirement does not apply to roadways, driveways, playgrounds, and other related features which are not part of the building proper. Fill slopes for granular materials shall be no steeper than one vertical on one and one-half horizontal, unless substantiating data justifying steeper slopes are submitted to the Building Official and approved. For slopes exposed to flood velocities of less than five (5) feet per second, grass or vine cover, weeds, bushes and similar vegetation undergrowth will be considered to provide adequate scour protection. For higher velocities, stone or rock slope protection shall be provided. 7.3.8.2.3 BUILDING ON "STILTS": The building may be constructed above the RFD by supporting it on "stilts" or other columnar type members, such as columns, piers, and in certain cases, walls. Clear spacing of support members, measured perpendicular to the general direction of flood flow, shall not be less than eight (8) feet apart at the closest point. The "stilts" shall, as far as practicable, be compact and free from unnecessary IV- 48 appendages which would tend to trap or restrict free passage of debris during a flood. Solid walls, or walled-in columns are permissible if oriented with the longest dimension of the member parallel to the flow. "Stilts" shall be capable of resisting all applied loads as required by "The Building Code" and all applicable flood related loads as required herein. Bracing, where used to provide lateral stability, shall be of a type that causes the least obstruction to the flow and the least potential for trapping floating debris. Foundation supports for the "stilts" may be of any approved type capable of resisting all applied loads, such as spread footings, mats, piles and similar types. In all cases, the effect of submergence of the soil and additional floodwater-related loads shall be recognized. The potential of surface scour around the stilts shall be recognized and protective measures provided, determined by a registered Professional Engineer. 7.3.8.3 PROTECTION BY DIKES, LEVEES, AND FLOODWALLS: The building shall be considered a floodproofed type when it is pro- tected from floodwaters to the RFD by means of dikes, levees, or floodwalls, either used alone or in combination, as necessary. This protection may extend all around the building where all surrounding ground is low, or on one or more sides where high ground (above the RFD) exists on the remaining sides. Regardless of type and method of construction, dikes, levees, and floodwalls shall be designed and constructed in accordance with recognized and accepted engineering practice and methods. They shall have adequate strength and stability to resist all applied loads and shall provide an effective watertight barrier up to the RFD. 7.3.8.3.1 DIKES AND LEVEES: Dikes and levees shall be constructed of suitable selected material, placed and compacted in layers to a section that has the required stability and imper- meability. Prior to start of placement operations, the area on which the dike or levee is to be constructed shall be prepared as required in 7.3.8.2.2. In cases where underlying materials are highly pervious, it may be necessary to provide impervious cutoffs. A filter blanket, drainage ditch and/or trench shall be provided along the interior toe of the construction to collect seepage through the dike or levee. All seepage and storm drainage shall be collected at a sump or sumps where it may be pumped out over the dike. Normal surface runoff within and into the diked area during nonflood periods may be discharged through appropriate drainage pipes and culverts through the dike. Such culverts shall have a dependable flap, slide gate, or backflow preventing device which would close either automatically or manually to prevent backflow during a flood. Scour protection measures for dikes and levees shall comply with the requirements of 7.3.8.2.2. Clearance from the toe of the dike or levee to the building shall be a minimum of 20 feet or twice the height of the dike or levee above the interior finished grade, whichever is greater. IV-49 7.3.8.3.2 FLOODWALLS: Floodwalls may be constructed of concrete, steel sheet piling, or other suitable structural materials. Regardless of type, the wall shall have adequate strength and stability to resist the applied loads. The provisions of 7.3.8.3.1 shall be followed, as applicable, regarding removal of unsuitable materials, provision of impervious cutoffs, provision of seepage and storm drains, drainage ditches, sumps and sump pumps, and the minimum clearances from the floodwall to the building. It shall be recognized in the drainage provisions that substantial amounts of leakage may occur through the interlock of a steel sheet piling wall. Adequate expansion and contraction joints shall be provided in the walls. Expansion joints will be provided for all changes in wall direction. Contraction and expansion joints in concrete walls shall be provided with waterstops and joint sealing material both in the stem and in the base. Steel sheet piling walls may be encased in concrete for corrosion protection or shall be coated with a coal tar epoxy coating system and periodically inspected and maintained. Steel sheet piling walls may be used as the impervious core of a dike. SECTION 7.4 CLOSURE OF OPENINGS 7.4.1 SCOPE 7.4.1.1 GENERAL: Openings in exterior and interior walls of buildings or structures in a Flood Hazard Area which are wholly or in part below the RFD shall be provided with waterproof closures meeting the requirements of this section. 7.4.2 TYPES OF CLOSURES 7.4.2.1 CLASSIFICATION: Closures shall be classified into five types according to their compatibility with the waterproofing standards of the various flood-proofing classes. 7.4.2.1.1 TYPE I CLOSURES: Shall form a complete sealed barrier over the opening that is impermeable to the passage of water at the full hydrostatic pressure of a flood to the RFD. 7.4.2.1.2 TYPE 2 CLOSURES: Shall form essentially dry barriers or seals, allowing only slight seepage during the hydrostatic pressure conditions of flooding to the RFD. 7.4.2.1.3 TYPE 3 CLOSURES: Shall form barriers or seals that are impermeable to the passage of waterborne contamination under equalized pressure conditions. 7.4.2.1.4 TYPE 4 CLOSURES: Shall form barriers to the passage of flood-carried debris and the loss of floating items from the interior, but are not required to form impermeable seals. 7.4.2.1.5 TYPE 5 CLOSURES: Are those of existing spaces which do not meet the requirements of any of the above described types, but are in use as required by "The Building Code." IV-so 7.4.3 REQUIREMENTS 7.4.3.1 DESIGN STANDARDS FOR CLOSURE ASSEMBLIES: The structural capacity of all closures shall be adequate to support all flood loads acting upon its surface. Closure assemblies may be fabricated of cast iron, steel, aluminum, or other adequate and durable structural material, provided with a continuous support around its perimeter, and shall be attached to the building or structure at its immediate location of use, i.e., hinged, or slides, or in a vertical recess. The closure device shall be capable of being set in place with minimal manual effort. Seals, where required, shall be gasketed pressure types permanently anchored or attached to the structure or to the closure assembly. Closures designed to lift into vertical recesses for storage when not in use, and/or located so that the open position of the assembly will not impede fire exit or the functioning of a fire closure assembly, shall be supported in the open position by auxiliary supports of safety latches that can be released at times of flooding. In the closed position the closure assembly shall engage fixed wedging blocks that will force the closure into a tight sealing position. The entire closure assembly should be inspected by the owner annually and suitably maintained to preserve its waterproof and structural quality, or be replaced as required. 7.4.3.2 FRAMES FOR OPENINGS: Each opening below the RFD shall have a metal frame suitable for providing an adequate sealing surface and for supporting the flood-proofing closure assembly. The frame shall be connected to the adjacent walls and floors and provide adequate bearing surface and anchorage to transfer the panel loading into the wall. It shall be supported upon adjacent walls and support shall be provided around the opening in the concrete or masonry wall to transfer the panel load to such inter- sections as required. 7.4.3.3 OPENINGS IN SHAFTS: All buildings or structures which have inclosing walls, decks, or shafts with horizontal or inclined openings at the top that are at or below the RFD and which would inundate WI or W2 spaces shall be provided with Type I closure assemblies that can be readily positioned and secured to prevent entrance of flood waters. Construction of such openings shall provide for permanently affixed doors, wall extensions, gates, panels, etc., that are either hinged or on slide tracks to facilitate prompt and positive sealing or openings with only minimal manual effort. Windows, grilles, vents, door openings, etc., in the side walls of a shaft and below the RFD shall be provided with flood-proofing closures meeting the requirements of 7.4.2. 7.4.3.4 FIRE RESISTIVITY OF CLOSURE ASSEMBLIES: All flood- proofing closure assemblies shall have a fire-resistive rating that conforms to the requirements of "The Building Code" and the particular fire protection requirements for the occupancy group and building type of the structure. IV-51 7.4.4 SPECIAL APPLICATIONS OF CLOSURE ASSEMBLIES 7.4.4.1 APPLICABILITY: Residences, firms, businesses or institutions with fewer than 10 permanent employees, or spaces which are or would be unoccupied and unattended in their foreseeable normal operation for periods of greater than 72 hours, shall not have any window, doorway, or other such opening any part of which is below the RFD unless at least one of the following conditions is met: (1) Type I and 2 closures are utilized and are fully automatic types, (2) Manually installed closure devices meeting requirements of the appropriate flood-proofing class are provided and are installed in their protective position by the Owner at any time in the season of high flood danger during which the space will be unoccupied and unattended for periods of longer than eight (8) hours. This requirement shall be considered in the Owner's Contingency Plan and noted by the Building Official on the permit and Certificate of Occupancy. (3) Watertight exterior walls, dikes, levees, or floodwalls of adequate design (Section 7.3) are constructed to prevent flood waters up to the RFD from entering the structure or space. SECTION 7.5 INTERNAL FLOODING AND DRAINAGE 7.5.1 SCOPE 7.5.1.1 GENERAL: The provisions of this section shall apply to the intentional flooding of buildings, structures, and spaces with water from potable or floodwater sources for the purpose of balancing internal and external pressures to protect a structure and/or its components from damage or failure during floods up to the RFD. 7.5.2 INTENTIONAL FLOODING WITH POTABLE WATER 7.5.2.1 APPLICABILITY: Spaces to be intentionally flooded (W3 spaces) to maintain a balanced internal and external pressure condition shall be filled automatically with potable water from a source provided by the Owner as required by 7.5.2.2 and approved by the Building Official. This level of filling shall be equal to that of the external flood surface unless a reduction in the internal flooding level is requested in writing by the Owner, and such approval is granted by the Building Official. The Owner shall, together with the written request, submit sufficient evidence that full internal flooding is unnecessary to protect the structure. The potable water flooding system shall activate and operate automatically and completely without human intervention and shall act independently of the emergency flooding system utilizing floodwaters as required for these spaces by 7.5.2.3. An automatic drainage system shall also be provided that will assure positive drainage of the space(s) at a rate comparable to the reduction of exterior flood height when floodwaters are receding. IV-52 7.5.2.2 POTABLE WATER SOURCES: At any location where disruption of water supply service from a public utility may occur or such service may be deemed inadequate, the Building Official shall require the Owner to provide an independent source of potable water that will be stored at the location of the improvement. 7.5.2.3 SAFEGUARD AGAINST FAILURE OF POTABLE WATER FLOODING SYSTEM: Where intentional flooding with a potable water flooding system is used for maintaining the structural integrity of buildings, structures, or spaces during flood events to the RFD. an emergency (backup) flooding system utilizing floodwaters shall be provided and maintained in a state of readiness for automatic implementation in event of failure of the primary potable water flooding system. The emergency flooding system shall comply with all requirements of 7.5.3. 7.5.3 AUTOMATIC FLOODING WITH FLOODWATER 7.5.3.1 APPLICABILITY: Spaces to be intentionally flooded with floodwater (W4) shall be provided with the necessary equipment, devices, piping, controls, etc., necessary for automatic flooding during the flood event and drainage of the space(s) when floodwaters recede. The automatic flooding and drainage system(s) shall utilize approved piping material and have sufficient capacity for raising or lowering the internal water level at a rate comparable to the anticipated rise and fall of a flood that would reach the RFD. These pipe systems shall be directly connected to the external floodwaters to maintain a balanced internal and external water pressure condition. Provisions shall be made for filling the lower portions of the structure first and for interconnections through or around all floors and partitions to prevent unbalanced filling of chambers or parts within the structures. All spaces below the RFD shall be provided with air vents extending to at least __feet above the elevation of the RFD to prevent the trapping of air by the rising water surface. All openings to the filling and drainage systems shall be protected by screens or grills to prevent the entry or nesting of rodents or birds in the system. 7.5.4 EMERGENCY FLOODING OF WATERPROOFED SPACES 7.5.4.1 APPLICABILITY: Spaces which have been waterproofed (WI or W2) to the RFD shall be provided with an automatic internal flooding system meeting all requirements of 7.5.3 to maintain structural integrity during floods which exceed the RFD elevation. Inverts shall be located at the RFD elevation unless an increase in invert elevation s) above the RFD is requested in writing by the Owner and approval is granted by the Building Official. Approvals shall not be granted by the Building Official until sufficient evidence has been furnished by the Owner that automatic internal flooding at the RFD elevation is not necessary to maintain structural integrity. Outlets for the drainage of water from IV-53 waterproofed spaces shall be located properly to drain the water from all parts of the spaces. To prevent the inflow of water at flood levels below the RFD each exterior drainage outlet shall be provided with a device for preventing backflow of water (flood) through the drainage system. Auxiliary outlets shall be provided as required to evacuate all water from upper floor levels before draining the lower spaces. All watertight walls shall be designed for an internal hydrostatic pressure equal to at least two (2) feet of differential head to provide for unknown factors that may cause malfunction of the required drains. SECTION 7.6 FLOORING 7.6.1 SCOPE 7.6.1.1 GENERAL: This section shall govern the design and use of floor systems and their constituent materials for buildings and structures located in a Flood Hazard Area. 7.6.1.2 BASIS FOR RESTRICTION: Floor systems and flooding materials are restricted according to their vulnerability to floodwater. For the purpose of these Regulations, vulnerability of a given floor or floor material may result from one or more of the following: (1) Normal suspended-floor adhesives specified for above grade use are water-soluble or are not resistant to alkali or acid in water, including ground seepage and vapor. (2) Flooring material contains wood or paper products. (3) Flooring material is not resistant to alkali or acid in water. (4) Sheet type floor coverings (linoleum, rubber, vinyl) restrict evaporation from non-WI slabs. (5) Flooring material is impervious but dimensionally unstable. 7.6.2 FLOORING CLASSIFICATIONS 7.6.2.1 CLASSES OF FLOORING: Floor systems and flooring materials are divided into five classes according to their degree of vulnerability. Class 1 floorings require conditions of dryness provided by WI spaces. Class 2 floors require essentially dry spaces which may be subject to water vapor and slight seepage that is characteristic of W2 spaces. Class 3 flooring may be submerged in clean water during periods of intentional flooding as provided by W3 spaces. Class 4 floorings may be exposed to and/ or submerged in floodwaters in interior spaces and do not require special waterproofing protection. Class 5 floors are permitted for semi-inclosed or outside uses with essentially unmitigated flood exposure. 7.6.2.1.1 Floors of a given class may be used in any application for which a lower-numbered class is permitted by these Regulations unless specifically restricted by notation in the following chart. For example, concrete (a Class 5 floor) may be used whenever floors of Classes 1, 2, 3, 4 or 5 are permitted. IV-54 -u A "'i o SiiaG 7.6.2.1.2 CLASSES OF TYPICAL FLOORING MATERIALS: The following chart is intended as an aid to the Owner, Architect/ Engineer and the Building Official in assessing the vulnerability of typical materials with respect to the criteria stated in 7.6.1.2. In disputes arising over the merits of particular materials or methods of construction, the Building Official shall be guided by and decide on the basis of those criteria. Class Asphalt tiles (A) 1 with asphaltic adhesives 3 Carpeting (glued-down types) 1 Cement/bituminous, formed-in-place 4 Cement/latex, formed-in-place 4 Ceramic tiles (a) 1 with acid and alkali-resistant grout 3 Chipboard 1 Clay tile 5 Concrete, precast or in situ 5 Concrete tile 5 Cork 1 Enamel felt-base floor coverings 1 Epoxy, formed-in-place 5 Linoleum 1 Magnesite (magnesium oxychloride) 1 Mastic felt-base floor coverings 1 Mastic flooring, formed-in-place 5 Polyurethane, formed-in-place 5 PVA emulsion cement 1 Rubber sheets (A) 1 with chemical-set adhesives (B) 5* Rubber tiles (A) 1 with chemical-set adhesives (B) 4 Silicone floors, formed-in-place 5 Terrazzo 4 Vinyl sheets (homogenous) (A) 1 with chemical-set adhesives (B) 5* Vinyl tile (homogeneous) (A) 1 with chemical-set adhesives (B) 4 Vinyl tile or sheets (coated on cork or wood product backings) 1 Vinyl-asbestos tiles (semi-flexible vinyl) (A) 1 with asphaltic adhesives 4 Wood flooring or underlayments 1 Wood composition blocks, laid in cement mortar 2 Wood composition blocks, dipped and laid in hot pitch or bitumen 2 * Not permitted as Class 2 flooring IV-55 Notes: (A) Using normally-specified suspended floor (i.e., above- grade) adhesives, including sulfite liquor (lignin or "linoleum paste"), rubber/Asphaltic dispersions, or "alcohol'" type resinous adhesives (cumar, oleoresin). (B) e.g., epoxy-polyamide adhesives or latex-hydraulic cement. SECTION 7.7 WALLS AND CEILINGS 7.7.1 SCOPE 7.7.1.1 GENERAL: This section shall govern the design and use of wall and ceiling systems and their constituent materials for buildings and structures located in a Flood Hazard Area. 7.7.1.2 BASIS FOR RESTRICTION: Materials treated in this section are those which constitute interior walls and ceilings including their finishes and structural constructions upon which they depend such as sheathing and insulation, and are restricted according to their susceptibility to flood damage. For the purpose of these Regulations, susceptibility of a given interior material or construction is dependent on one or more of the following: (1) Normal adhesives specified for above-grade use are water-soluble or are not resistant to alkali or acid in water, including ground seepage and vapor. (2) Wall or ceiling material contains wood, wood products, gypsum products, or other material which dissolves or deteriorates, loses structural integrity, or is adversely affected by water. (3) Wall or ceiling material is not resistant to alkali or acid in water. (4) Material is impervious but dimensionally unstable. (5) Materials absorb or retain water excessively after submergence. 7.7.2 WALL/CEILING CLASSIFICATIONS 7.7.2.1 CLASSES OF WALL/CEILING: Wall and ceiling systems and materials are divided into five classes according to the degree of vulnerability. Class I materials require conditions of dryness provided by Wl spaces. Class 2 materials require essentially dry spaces which may be subject to water vapor and slight seepage that is characteristic of W2 spaces. Class 3 wall and ceiling materials may be submerged in clean water during periods of intentional flooding as provided by W3 spaces. Class 4 materials ma y be exposed to and/or submerged in flood waters in interior spaces and do not require special waterproofing treatments or protection. Class 5 wall and ceiling materials are permitted for semi-inclosed or outside uses with essentially unmitigated flood exposure. 7.7.2.1.1 Materials of a given class may be used in any application for which a lower-numbered class is permitted by these Regulations. For example, concrete (a Class 5 wall/ceiling material) may be used whenever materials of Classes 1, 2, 3, 4 or 5 are permitted. IV-56 RAMU SON 7.7.2.2 CLASSES OF TYPICAL WALL/CEILING MATERIALS: The following chart is intended as an aid to the Owner, Architect/ Engineer and the Building Official in assessing the vulnerability of typical materials with respect to the criteria stated in 7.7.1.2. In disputes arising over the merits of particular products or of materials not listed below, the Building Official shall be guided by and decide on the basis of those criteria. Class Asbestos-cement board 5 Brick, face or glazed 5 Common 2 Cabinets, built in Wood 2 Metal 5 Cast stone (in waterproof mortar) 5 Cal kboards Slate, porcelain glass, lucite glass 5 Cement-asbestos 2 Composition, painted 2 Chi pboard I Exterior Sheathing Grade 2 Clay tile Structural glazed 5 Ceramic veneer, ceramic wall tile- mortar set 4 Ceramic veneer, organic adhesives 2 Concrete 5 Concrete block 5 Corkboard 2 Doors Wood, hollow 2 Wood, lightweight panel construction 2 Wood, solid 2 Metal, hollow 5 Metal , Kailamein 2 Fiberboard panels, Vegetable types Sheathing grade (asphalt-coated or -impregnated) 2 Other I Gypsum products Gypsum board 2 Keene's cement on plaster 2 Plaster, otherwise, including acoustical 2 Sheathing panels, exterior grade 2 Glass (sheets, colored tiles, panels) 4 Glass blocks 5 Hardboard Tempered, enamel or plastic-coated 2 All other types 2 IV-57 Cl ass Insulation Foam or closed cell types 4 Batt or blanket types 1 All other types 2 Metals, non-ferrous (aluminum, copper or zinc tiles) 3 Ferrous 5 Mineral fiberboard 1 Plastic wall tiles (polystyrene, urea formaldehyde, etc.) with waterproof adhesives, painted with waterproof grout 3 Set in water-soluble adhesives 2 Paint Polyester-epoxy and other waterproof types 4 All other types 1 Paperboard 1 Partitions, folding Metal 4 Wood 2 Fabric-covered types 1 Partitions, stationary Wood frame 4 Metal 5 Glass, unreinforced 4 reinforced 4 Gypsum, solid or block 1 Rubber, mouldings and trim with epoxy- polyamide adhesive or latex-hydraulic cement 4 All other applications 1 Steel, (panels, trim, tile) with waterproof applications 5 With non-waterproof adhesives 2 Stone, natural solid or veneer, waterproof grout 5 Stone, artificial nonabsorbent solid or veneer, waterproof grout 5 All other applications 2 Strawboard Exterior grade (asphalt-impregnated kraft paper) 2 All other types 1 Wall coverings Paper, burlap, cloth types 1 Wood Solid (boards, sheets, or trim) 2 Plywood Exterior grade 2 Otherwise 1 SECTION 7.8 ELECTRICAL 7.8.1 SCOPE 7.8.1.1 GENERAL: Where buildings or parts of buildings and structures extend below the RFD, the electrical materials, equipment and installation shall conform to the requirements of this section of the Regulations. 7.8.2 REQUIREMENTS AT LOCATIONS ABOVE AND BELOW THE RFD 7.8.2.1 MAIN POWER SERVICE: The incoming main commercial power service equipment, including all metering equipment, shall be located above the RFD. Whenever a building or structure is not accessible by a bridge, walkway or other connecting means except by boat during periods of flooding to the RFD, a disconnecting means for the incoming main commercial power service shall be provided at an accessible remote location above the RFD. 7.8.2.2 STATIONARY AND PORTABLE EQUIPMENT: Switchgear, control centers, transformers, distribution and main lighting panels in addition to all other stationary equipment shall be located above the RFD. Portable or movable electrical equipment may be located in any space below the RFD provided that equipment can be disconnected by a single plug and socket assembly of the submersible type and rated by the manufacturer as submersible for not less than 72 hours for the head of water above the assembly to the RFD. All disconnect assemblies shall be provided with submersible seals attached to the disconnect assembly by means of a corrosion resistant metal chain for immediate use when needed to insure safety to all personnel during a flood. All portable or movable equipment should be de-energized and/or moved out of potentially flooded spaces at time of flood warning and prior to floodwaters reaching floor levels where such equipment is located. 7.8.2.3 NORMAL AND EMERGENCY LIGHTING CIRCUITS: All circuits, except emergency lighting circuits, extending into areas below the RFD shall be energized from a common distribution panel located above the RFD. All emergency lighting circuits into areas below the RFD shall be energized from an independent distribution panel also located above the RFD. Each distribution panel shall have the capability of being de-energized by a separate single disconnecting device. 7.8.2.4 EMERGENCY LIGHTING REQUIREMENTS: All areas of the building or structure that are below the RFD, where personnel may be required to conduct emergency operations or work with water present on the floor of the area during a flood, shall be pro- vided with automatically operated emergency lighting facilities and automatically operated electrical disconnect equipment to insure that all electrical circuits into these areas, except emergency lighting circuits, are de-energized prior to personnel working in water. The electrical circuits shall be de-energized IV-59 prior to the presence of any water on the floor of the affected area. All components of emergency lighting systems installed below the RFD shall be so located that no component of the emergency lighting system is within reach of personnel working at floor level in the areas where emergency lighting systems are utilized unless the emergency lighting circuits are provided with ground-fault circuit interrupters having a maximum leakage current to ground sensitivity of five (5) milliamperes. The energy for emergency lighting may be furnished by a storage battery(s), prime mover-generator system, a separate commercial power supply system, the same commercial power system, or a combination thereof, subject to the following provisions of this section. 7.8.2.4.1 STORAGE BATTERY (including battery-operated lighting units): Battery-operated lighting units shall be completely self-contained and shall indicate the state of charge of the battery at all times. Lighting units shall automatically provide light when the normal source of lighting in the areas is de- energized. A sufficient number of emergency lighting units shall be provided to enable personnel to perform their assigned emergency tasks and to permit a safe exit to areas above the RFD. 7.8.2.4.2 SEPARATE COMMERCIAL POWER SUPPLY SYSTEM: This source of energy shall have a degree of reliability satisfactory to the Building Official. A system fed from a substation other than that used for the regular supply and not on the same poles (except service pole) as the regular supply is deemed to have the required degree of reliability. A secondary circuit fed from the same primary network circuit as the regular supply shall be regarded as a separate system. 7.8.2.4.3 SAME COMMERCIAL POWER SUPPLY SYSTEM: The system shall be an underground secondary network system and a separate service shall be connected on the line side of the service switch or breaker of the regular service. 7.8.2.5 LIGHTING CIRCUITS BELOW REGULATORY FLOOD DATUM: Lighting circuit switches, receptacles and lighting fixtures operating at a maximum voltage of 120 volts to ground may be installed below the RFD, provided that these circuits shall be de-energized as noted in 7.8.2.4. Should any switch, receptacle or lighting fixture be flooded, its particular circuit shall not be re-energized until such circuits and devices and/or any part thereof, have been disassembled and thoroughly checked, cleaned or replaced, and approved for use by qualified personnel. 7.8.2.6 SUBMERSIBLE EQUIPMENT: Except for the switches, receptacles and lighting fixtures noted herein, all other electrical equipment permanently installed below the RFD shall be of the submersible type rated by the manufacturer for submergence for not less than 72 hours for a head of water above equipment to the RFD. IV-60 7.8.2.7 SUBMERSIBLE WIRING REQUIREMENTS: All electrical wiring systems installed below the RFD shall be suitable for continuous submergence in water and shall contain no fibrous components. Only submersible type splices will be permitted in areas below the RFD. All conduits located below the RFD shall be so installed that they will be self-draining if subject to flooding conditions. 7.8.2.8 ELEVATORS: All electric power equipment and components of elevator systems shall be located above the RFD. Automatic type elevators shall be provided with a home station to which the elevator will automatically return after use, with home station located above the RFD. 7.8.2.9 ELECTRIC HEATING EQUIPMENT: Electric unit heaters installed below the RFD shall be capable of disconnection and removal in the manner described for portable electrical equipment in 7.8.2.2. Electric controls on gas and oil furnaces located below the RFD shall not exceed 120 volts to ground and the control circuits shall be automatically de-energized prior to the presence of any water on the floor of the affected area in accordance with 7.8.2.4. 7.8.2.10 SUMP PUMP INSTALLATION: Buildings and structures utilizing sump-pumping equipment of any type to keep areas within the structure free of water shall be provided with float- operated warning alarms that shall act independently of any other float- actuated devices used to start and stop pumping equipment. All buildings or structures utilizing sump-pumping equipment shall be provided with automatic starting standby electrical generating equipment located above the RFD. The standby generating equipment shall be capable of remaining in continuous operation for a period of 125% of the anticipated duration of the design flood. SECTION 7.9 MECHANICAL 7.9.1 SCOPE 7.9.1.1 GENERAL: All mechanical systems, including heating, air conditioning, ventilating, plumbing, sanitary, and water systems, in or serving buildings or structures in a Flood Hazard Area, shall be designed and installed to comply with the requirements of this section. 7.9.2 HEATING, AIR CONDITIONING AND VENTILATION SYSTEMS 7.9.2.1 APPLICABILITY: Heating, air conditioning, and ventilation systems, including all appurtenances, in buildings or structures in a Flood Hazard Area shall be designed and installed to comply with the requirements of these Regulations. 7.9.2.2 LOCATION: Heating, air conditioning, and ve ntilating Equipment should, to the maximum extent possible, be installed in areas and spaces of buildings that are above the RFD. When not IV-61 SUSIE feasible, said equipment shall be located in WI or W2 spaces (below the RFD) with direct access provided from a location above the RFD and shall conform to all requirements of this Section. 7.9.2.2.1 Heating systems utilizing gas- or oil-fired furnaces shall have a float operated automatic control valve installed in the fuel supply line which shall be set to operate when floodwaters reach an elevation equal to the floor level of the space where furnace equipment is installed. A manually operated gate valve that can be operated from a location above the RFD shall be provided in the fuel supply line to serve as a supplementary safety provision for fuel cutoff. The heating equipment and fuel storage tanks shall be mounted on and securely anchored to a foundation pad or pads of sufficient mass to overcome buoyancy and prevent movement that could damage the fuel supply line. As an alternate means of protection, elevation of heating equipment and fuel storage tanks above the RFD on platforms or by suspension from overhead structural systems will be permitted. All unfired pressure vessels will be accorded similar treatment. Fuel lines shall be attached to furnaces by means of flexible or swing-type couplings. All heating equipment and fuel storage tanks shall be vented to an elevation of at least 3 feet above the RFD. Air supply for combustion shall be furnished if required for systems installed in WI or W2 spaces, and piping or duct work for such purpose shall be terminated at least 3 feet above the RFD. 7.9.2.2.1.1 All duct work for warm air heating systems which is located below the RFD shall be provided with emergency openings for internal flooding and drainage of the ducts with all openings having covers with gravity operators for closure during normal operation. Where duct work must pass through a watertight wall or floor below the RFDJ, the duct work shall be protected by a mechanically operated closure assembly and shall be provided with the operator control position above the RFD. The closure assembly in its open position shall not impede the normal function of the heating system. 7.9.2.2.1.2 Steam or hot water heating pipes located below the RFD shall be provided with shutoff valves sufficient to isolate the piping system when warning of flooding to the RFD is received. 7.9.2.2.1.3 Electric heating systems, where utilized in Flood Hazard Areas, shall be installed in accordance with requirements of Section 7.8. 7.9.2.2.2 Air conditioning and ventilation systems that will be located below the RFD shall be installed in WI or W2 spaces only. All installation, piping, duct work, connections, and safety features shall conform to the same requirements stated for Heating Systems in paragraph 7.9.2.2.1. IV-62 7.9.2.2.3 Where heating, air conditioning, or ventilating systems (as defined in 7.9.2.2) are installed in other than WI or W2 spaces, all bearings, seals, shafts, gears, clutches, valves, or controls which are not capable of withstanding water or silt damage or hydrostatic or hydrodynamic loading shall be provided with suitable protective waterproofing enclosures as may be required by the Building Official, unless they are considered expendable. 7.9.2.2.4 All fuel supply lines that originate either outside of WI or W2 spaces or pass through areas that would be flooded shall be equipped with automatic shutoff valves to prevent loss of fuel in the event of a line breakage. The wall opening shall be made flood-proof by use of imbedded collars, sleeves, waterstops, or other means as may be approved by the Building Official. 7.9.2.2.5 Electrical connections to all mechanical systems covered by this section shall conform to the requirements of Section 7.8. 7.9.3 PLUMBING SYSTEMS 7.9.3.1 APPLICABILITY: For the purpose of the Regulations, plumbing systems shall include sanitary and storm drainage, sanitary facilities, water supply, storm water and sewage disposal systems. 7.9.3.1.1 Except as otherwise provided herein, nothing in these Regulations shall require the removal, alteration, or abandonment of, nor prevent the continued use of, an existing plumbing system. 7.9.3.1.2 No plumbing work shall be commenced until a permit for such work has been issued by the Building Official. Application for plumbing permits, denial of permit, time limitation on permits, and inspections shall be in accordance with requirements of the Building Code. 7.9.3.1.3 Plumbing materials shall be selected with due consideration given to the hydrostatic, hydrodynamic and chemical actions of floodwaters on the interior of piping systems, of the soil, fill or other materials on the exterior of piping systems, on joints, connections, valves, traps, seals (and caulking), and fixtures. 7.9.3.2 BELOW RFD: Sanitary sewer and storm drainage systems that have openings below the RFD shall be provided with automatic backwater valves or other automatic backflow devices that are installed in each discharge line passing through a building exterior wall. In WI spaces, manually operated shutoff valves that can be operated from a location above the RFD shall also be installed in IV-63 rf-i ' 8t such lines to serve as supplementary safety provisions for preventing backflow in case of automatic backflow device failure or line break between the space(s) and the device. 7.9.3.2.1 Spaces in buildings that are to be protected from floodwaters by implementation of the Owneris Contingency Plan may utilize standpipes attached to floor drains, cleanouts, and other openings below the RFD, and/or manually operated shutoff valves or closure devices. 7.9.3.2.2 Where the state of dryness of a space is dependent on a sump pump system, or where the stability of a structure during a flood event depends on the relief of uplift pressures on building components, all interior storm water drainage or seepage, appliance drainage, and underslab drain tile systems shall be directly connected to a sump (pump) and discharged at an elevation at least 2 feet above the RFD. 7.9.3.2.3 Sanitary sewer systems, including septic systems, that are required to remain in operation during a flood shall be provided with a sealed holding tank and the necessary isolation and diversion piping, pumps, ejectors and appurtenances required to prevent sewage discharge during the flood. The holding tank shall be sized for storage of at least 150% of the anticipated demand for the duration of a flood to the RFD. 7.9.3.2.3.1 All vents shall extend to an elevation of at least 3 feet above the RFD. 7.9.3.2.3.2 All pipe openings through walls below the RFD shall be flood-proofed to prevent floodwater backflow through spaces between pipes and wall construction materials. (See 7.9.2.2.4.) IV-64 CHAPTER8s a WIND SECTION 8.1 GENERAL: Buildings and structures and every part thereof shall be designed to withstand the forces of wind pressure assumed in any direction. No allowance shall be made for the effect of shielding by other structures. As further described in these Regulations, the floor, roof or other horizontal bracing system shall be designed and constructed to transfer horizontal forces to the parts of the structural frame designed to carry the forces to the ground. Where horizontal or vertical shear-resisting elements are used to transfer wind forces through diaphragm action, the analysis shallI include the design of chord members at or near the extremities of the diaphragm and the connections used to transfer the forces to the resisting elements. The total shear in any horizontal plane shall be distributed to the various elements of the lateral force-resisting system in proportion to their rigidities, taking into consideration the rigidity of the horizontal bracing system or diaphragm. Where roofs or floors are constructed of individual units and the transfer of forces to the building frame or foundation is totally or partially dependent on such units, the unit and attachment shall be capable of resisting applied loads in both vertical and horizontal directions. SECTION 8.2 VELOCITY PRESSURES: 8.2.1 WIND SPEED: The basic wind speeds to be used in design of buildings and structures shall be as follows: Basic Wind Speed in MPH at Hazard Zone 30 Feet Above Ground A 140 B 140 C 140 D 140 at C-D boundary, diminishing to 100 mph at inland boundary in accordance with the following: VD = 100 + I40 , where VD =wind speed in Zone D 1 +dY * d =distance inland from. C-D boundary 8.2.2 VELOCITY PRESSURES FOR ORDINARY BUILDINGS AND STRUCTURES: Velocity pressures for ordinary buildings and structures are given in Table 8-1. These velocity pressures are to be multiplied by the pressure coefficients as described in 8.3. The effective velocity pressures take into account the dynamic response to gusts M-'65 TABLE 8-1 Effective Velocity Pressure for Ordinary Buildings and Structures in Pounds Per Square Foot Wind Speed Elevation 100 110 120 130 140 Less than 30' 26 32 39 45 52 30 - 40 33 40 48 56 65 40 - 75 38 46 54 64 74 75 - 125 44 53 63 74 86 125 - 175 48 58 69 81 94 175 - 225 51 62 74 86 100 225 - 275 53 65 77 90 104 275 - 325 56 68 80 94 109 325 - 375 58 70 83 97 112 375 - 425 59 72 86 100 116 425 - 475 61 74 88 103 119 475 - 525 62 75 90 105 122 525 - 575 64 77 92 108 125 575 - 625 65 79 94 110 128 625 - 675 66 80 96 112 130 675 - 725 67 82 97 114 132 725 - 775 68 83 99 116 135 775 - 800 70 85 101 118 137 To find wind pressure at speed not shown in Table: Vn V2 where Pvn = pressure not shown in Table Vn = velocity not shown in Table Pv = pressure shown in Table Vn = velocity corresponding to Pv of ordinary buildings and structures in a direction parallel to the wind and should be considered as a minimum. They do not provide for the effects of vortex shedding or instability due to galloping or flutter. For buildings whose height exceeds five times the least horizontal dimension, and for buildings whose dynamic properties tend to make them wind-sensitive, a detailed analysis shall be required. 8.2.3 VELOCITY PRESSURES FOR PARTS AND PORTIONS: For parts and portions of structures, such as girts, purlins, windows, doors, curtain walls and cladding, etc., and tributary areas less than 200 sq. ft., the velocity pressures given in Table 8-2 shall be used. These values shall be multiplied by the pressure coefficients described in Tables 8-4, 8-5, or 8-6 and 8-7. For tributary areas from 200 to 1000 sq. ft., the values may be reduced linearly to the values in Table 8-1. 8.2.4 INTERNAL VELOCITY PRESSURES: Internal velocity pressures are given in Table 8-3. These are to be used with internal pressure coefficients listed in Table 8-8. The pressure is assumed to be uniform on all internal surfaces at a given building height. SECTION 8.3 PRESSURE COEFFICIENTS: 8.3.1 GENERAL: In the following sections, pressure coefficients are given for various building shapes and for various building element locations and configurations. These coefficients are to be multiplied by the appropriate velocity pressures given in Section 8.2. (Unit wind load = velocity pressure x pressure coefficient.) In the calculation of design wind loads on buildings and structures or elements thereof, the pressure difference between opposite faces shall be taken into account. Where more than one coefficient is specified, each shall be considered in determining the maximum stresses. The total design wind load on a building or structure may be obtained by calculating the vector sum of the resultant forces that act on its elements. SECTION 8.4 DESIGN OF BUILDINGS AND OTHER ENCLOSED STRUCTURES: 8.4.1 GENERAL: All buildings and other enclosed structures shall be designed to withstand the sliding and overturning effects of wind, allowing for the wind that is normal to any wall. The pressure distributions shall be determined by employing the * appropriate pressure coefficients specified below. 8.4.2 PRESSURE COEFFICIENTS: The pressure coefficients given in this section apply to typical rectangular buildings and other enclosed structures that have vertical walls which may have doors, openable windows, etc. The positive and negative coefficients indicate positive pressure and suction pressure, respectively. IV-"67 O bj'L &&i 'iff'i1 TABLE 8-2 Effective Velocity Pressure for Parts and Portions of Buildings and Structures in Pounds Per Square Foot Wind Speed Elevation 100 110 120 130 140 Less than 30' 38 46 55 64 74 30- 75 42 51 61 72 84 75- 125 49 59 70 82 95 125- 175 53 65 77 90 104 175- 225 57 69 82 96 111 225 - 275 59 72 86 101 117 275 - 325 61 74 88 104 121 325 - 375 64 77 92 108 125 375 - 425 66 80 95 111 129 425 - 475 67 81 96 113 131 475 - 525 69 84 99 117 136 525 - 575 70 85 101 119 138 575 - 625 72 87 104 122 142 625 - 675 72 88 104 123 143 675 - 725 74 90 107 126 146 725 - 775 76 91 109 128 148 775 - 800 76 92 110 129 150 11V8B SUb Ij jU a*2Eb TABLE 8-3 Effective Velocity Pressures for Calculating Internal Pressures in Pounds Per Square Foot Wind Speed Height 100 110 120 130 140 Less than 30' 26 31 37 43 50 30 - 75 30 36 43 50 58 75 - 125 36 44 52 61 71 125 - 175 40 49 58 68 79 175 - 225 44 53 63 74 86 225 - 275 47 57 67 79 92 275 - 325 49 60 71 83 96 325 - 375 51 62 74 87 101 375 - 425 54 65 77 90 104 425 - 475 55 67 80 93 108 475 - 525 57 69 82 96 111 525 - 575 59 71 84 99 115 575 - 625 60 73 87 102 118 625 - 675 61 74 88 104 121 675 - 725 63 76 91 106 123 725 - 775 64 77 92 108 125 775 - 800 65 79 94 110 128 IV-69 TABLE 8-4 vu External Pressure Coefficients for Walls Location of Wall Pressure Coefficient Windward wall 0.8 Leeward wall, both height- width and height-length ratios of building > 2.5 -0.6 Other buildings -0.5 Side walls -0.7 TABLE 8-5 External Pressure Coefficient for Arched Roofs Rise to Span Windward Center Leeward Ratio Quarter Half Quarter Roof on 0 < r < 0.2 -0.9 (-0.7 - r) -0.5 elevated 0.2 < r < 0.3 (1.5r - 0.3)* (-0.7 - r) -0.5 structure 0.3 < r < 0.6 (2.75r - 0.68) (-0.7 - r) -0.5 Roof 0 < r < 0.6 1.42r (-0.7 - r) -0.5 springing from ground level * When the rise-span ratio is (0.2 < r 0.3), alternate coefficients given by (6r - 2.1) shaZZll also be used for the windward quarter. IV-70 i r. 'I'!: ', '' r '6-, -.- : TABLE 8-6 External Pressure Coefficients for Windward Slope of Gabled Roofs h/w 10°-15° 200 250 30° 350 400 450 500 60° < 0.3 0.01 0* 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.01 e 0.5 -1.0 -0.75 -0.5 -0.2 0.05 0.3 0.45 0.5 0.01 0 1.0 -1.0 -1.0 -0.8 -0.55 -0.3 -0.05 0.2 0.45 0.01 a > 1.5 -1.0 -1.0 -0.9 -0.6 -0.35 -0.1 0.2 0.01 e * Except for roofs rising from ground level (h/w = U), a coefficient of -1.0 shall be used when 10° < 0 < 15°, 0 = slope in degree, from horizontal, h = wall height at eave, w = least width of building normal to ridge. IV-71 TABLE 8-7 Local Peak External Pressure Coefficients for Roofs Roof Slope Ridges and 6, Degrees* Eaves Corners 0- 30 -2.4 (0.1 e - 5.0) Greater than 30 -1.7 -2.0 * For arched roofs, 0 shall be taken as the angle between the horizontal and the tangent to the roof at the springing. TABLE 8-8 Internal Pressure Coefficients for Buildings Openings Mainly In = * Openings Uniformly Windward Leeward Side fl* Distributed Wall Wall Wall(s) 0 to 0.3 +± 0.3 (0.3 + 1.67n) (-0.3 - n) (-0.3 - n) Greater than 0.3 + 0.3 0.8 -0.6 -0.6 * n = ratio of open area to solid area of waZll having majority of openings IV-72 8.4.3 EXTERNAL PRESSURE COEFFICIENTS: The average pressure coefficients, listed in Table 8-4, shall be used for calculating pressures on external surfaces of buildings. 8.4.3.1 WALLS - LOCAL PRESSURE COEFFICIENTS: A pressure coefficient of -2.0 shall be used at the corners of all walls. The pressure shall be assumed to act on vertical strips of width 0.1 w, where w is the least width of the building, and the computed pressure shall be applied outward. These local pressures shall not be included with the net external pressure when computing overall loads. 8.4.3.2 ROOFS: 8.4.3.2.1 GENERAL: For buildings with a ratio of wall height to least width less than 2.5, an external suction coefficient of -0.7 shall be used for the roof and the computed pressure shall be assumed uniform over the entire roof area. For buildings in which the height-width ratio is 2.5 or greater, a value of -0.8 shall be used for the entire roof area. These coefficients allow for wind parallel to the surfaces of flat, arched, and sloped roofs. 8.4.3.2.2 ARCHED ROOFS: For wind perpendicular to the axis of the arch, the coefficients of Table 8-5 shall be used. 8.4.3.2.3 GABLED ROOFS: For wind perpendicular to the ridge of gabled roofs, a pressure coefficient of -0.7 shall be used for the leeward slope, together with a coefficient for the windward slope which depends on the roof slope and the height-width ratio of the building, as given in Table 8-6. These coefficients may also be used for shed and other sloped roofs of buildings. 8.4.3.2.4 LOCAL PRESSURE COEFFICIENTS: The pressure coefficients given in Table 8-7 shall be used at the ridges, eaves, cornices and 90-degree corners of roofs. The pressure shall be assumed to act on strips of 0.1 w and the computed pressure applied outward at these locations along the ridge, eaves and cornices; w = least width of building normal to ridge. These local pressures shall not be included with the net external pressure when computing overall loads. 8.4.3.2.5 OTHER LIVE LOADS ON ROOFS: In no case shall any roof be designed for less than 20 pounds per square foot live load. 8.4.4 INTERNAL PRESSURE COEFFICIENTS: Pressure acting on the interior surfaces of walls and roofs of buildings shall be computed by multiplying the velocity pressure obtained from Table 8-3 by the internal pressure coefficient obtained in Table 8-8. IV-73 Both positive and negative coeffients shall be considered in calculating the maximum stresses. SECTION 8.5 ROOFS OVER NON-ENCLOSED STRUCTURES: 8.5.1 NET PRESSURE COEFFICIENTS: The net pressure coefficients for horizontal or inclined flat roofs over non-enclosed structures, such as open-air parking garages, shelter areas, outdoor arenas, stadium and theaters, shall be as given in Table 8-9 in which "a" is the angle between the wind direction and the plane of the roof and `X" is the ratio of the length of the windward edge to the distance between the windward and the leeward edges (aspect ratio). 8.5.2 INWARD AND OUTWARD LOADS: The net pressure coefficients given in Table 8-9 are to be used in computing the resultant load normal to the surface. The resultant load may act either inward or outward. 8.5.3 ANGLE OF ATTACK: In computing the angle between the wind direction and the plane of the roof, the wind shall be assumed to deviate by plus or minus 10 degrees from the horizontal. 8.5.4 VARIATION OF PRESSURE: Pressures will be higher at the windward edge than at the leeward edge. To allow for this difference, the resultant load shall be assumed to act at the center of pressure X/C, as given in Table 8-10, where X is the distance to the center of pressure from the windward edge of the roof arnd C is the distance between the windward and leeward edges. SECTION 8.6 CHIMNEYS, TANKS, AND SIMILAR STRUCTURES: Net pressure coefficients for chimneys, tanks, and similar structures shall be as given in Table 8-11. These coefficients apply to the projected area of the structure on a vertical plane normal to the wind direction. For slender structures such as flagpoles, a minimum net pressure coefficient shall be used if dv'q- < 2.5. SECTION 8.7 SIGNS AND OUTDOOR DISPLAY STRUCTURES: 8.7.1 GENERAL: For the purpose of determining wind loads, all signs shall be classified as either open or solid. Signs with openings greater than 30% of the gross area shall be classified as "1open" signs. Those with openings less than 30% of the gross area shall be classified as "solid" signs. The effective velocity pressures of Table 8-2 shall be used in calculating design loads. 8.7.2 SOLID SIGNS: 8.7.2.1 HEIGHT ABOVE GROUND: Solid signs are classified as being at the ground when the ratio g/h is less than 0.25; otherwise, they are classified as being above ground (g = distance between the bottom of the sign and the ground, and h = the vertical dimension of the sign). IV -74 TABLE 8-9 i- Net Pressure Coefficients for Flat Plates a 1/5 1/3 1/2 1 2 3 5 100 0.2 0.25 0.3 0.45 0.55 0.70 0.75 150 0.35 0.45 0.5 0.68 0.83 0.88 0.83 200 0.5 0.6 0.75 0.92 1.0 0.96 0.9 250 0.7 0.8 0.95 1.14 1.1 1.04 0.95 30° 0.9 1.0 1.2 1.32 1.2 1.1 1.0 TABLE 8-10 Location of Center of Pressure, X/C, for Flat Plates a 1/5 to 1/2 1 2-5 100 0.35 0.30 0.30 15° 0.35 0.30 0.30 200 0.35 0.32 0.32 25° 0.35 0.36 0.40 30° 0.35 1 0.30 0.45 IV-75 TABLE 8-11 Net Pressure Coefficients for Chimneys and Tanks h/d Shape Type of Surface 1 7 25 Square (wind Smooth or rough 1.3 1.4 2.0 normal to a face) Square (wind Smooth or rough 1.0 1.1 1.5 along diagonal) Hexagonal or Smooth or rough 1.0 1.2 1.4 octagonal (dv > 2.5) Round Moderately smooth 0.5 0.6 0.7 (dVq > 2.5) Rough (d'/d 0.02) 0.7 0.8 0.9 Very Rough (d'/d 0.08) 0.8 1.0 1.2 NOTE: h = height of structure in feet d = diameter or least horizontal dimension in feet d'= depth in feet of protruding elements such as ribs and spoilers q = the effective velocity pressure in psf from Table 8-1 8.7.2.2 NET PRESSURE COEFFICIENTS: 8.7.2.2.1 NORMAL WIND INCIDENCE: The net pressure coefficients, Cf, for solid signs at ground level and above ground level, for wind normal to the surface, shall be as given in Table 8-12 in which H is the height-to-width ratio of the surface, a is the greater dimension, and b is the smaller dimension. The computed load shall be assumed to act uniformly over the entire sign area. 8.7.2.2.2 OBLIQUE WIND INCIDENCE: To allow for winds oblique to the surfaces of solid signs, the net pressure normal to the surfaces shall be assumed to vary linearly from a maximum of the windward edge to a minimum of the leeward edge, in accordance with the following equations: Max Cf = 1.6 K Cf Min Cf = 0.4 K Cf where Cf is the net pressure coefficient for normal incidence, and K is a factor depending upon the orientation of the sign relative to the wind. The values of K for signs at, and above, ground level shall be as follows: K = 1.0 for rectangular signs having the shorter edge upwind; K = 1.15 for rectangular signs having the longer edge upwind and for square signs. 8.7.3 OPEN SIGNS: For open signs the net pressure coefficients given in Table 8-13 shall be applied to the projected area normal to the wind of all exposed members and elements (excluding appurtenances and supports which shall be accounted for separately by using the appropriate net pressure coefficients for these individual elements). Table 8-13 gives net pressure coefficients for lattices that are comprised of flat-sided or rounded elements, where q is the ratio of the solid area to the gross area, d is the diameter in feet of a typical element, and "qi is the velocity pressure in psf. Weighted average coefficients may be used for signs with both flat-sided and rounded elements. 8.7.4 APPURTENANCES AND SUPPORTS: The wind loading on appurtenances and supports shall be accounted for separately by using the appropriate net pressure coefficients. Allowances may be made for the shielding effect of one element or another. SECTION 8.8 SQUARE - AND TRIANGULAR - SECTION TRUSSED TOWERS: 8.8.1 TOWERS WITH FLAT-SIDED MEMBERS: The net pressure coefficients to be applied to Table 8-1 for square- and triangular-section towers with similar faces comprised of structural angle or similar flat-sided members, and with the wind normal to a face, shall be as given in Table 8-14. Here, p is the ratio of the solid area to the gross area of the face and the net pressure coefficient applies to the solid area of the face. For square towers, the IV-77 TABLE 8-12 Net Pressure Coefficients for Signs At and Above Ground Level, Cf At Ground Level H < 3 5 8 10 20 30 2 40 Cf 1.2 1.3 1.42 1.52 1.75 1.84 2.0 Above Ground Level a/b 6 10 16 20 40 60 > 80 Cf 1.2 1.3 1.42 1.52 1.75 1.84 2.0 TABLE 8-13 Net Pressure Coefficients for Latticed Frameworks, Cf Flat-Sided Rounded Members cP¢ Members dVq < 2.5 d,/ > 2.5 Less than 0.1 2.0 1.2 0.8 0.1 to 0.3 1.8 1.3 0.9 0.3 to 0.7 1.6 1.5 1.1 IV48; coefficients do not allow for any unmasked (outstanding) lacing on the side faces; such lacing shall be accounted for separately by using the appropriate net pressure coefficients for these elements and by neglecting the interference effects of the other parts of the tower. 8.8.2 TOWERS WITH ROUNDED MEMBERS: For square- and triangular- section towers with round members, and with wind normal to a face, the net pressure coefficients shall be determined by multiplying the above coefficients for towers with flat-sided members by the factors in Table 8-15 for corresponding values of p. Weighted average coefficients may be used for towers with both flat-sided and rounded members. 8.8.3 OBLIQUE WIND INCIDENCE: 8.8.3.1 SQUARE-SECTION TOWERS: To allow for the maximum horizontal wind-load on square-section trussed towers, which occurs when the wind is oblique to the faces, the wind for normal wind incidence shall be multiplied by a factor of (1.0 + 0.75 cp) (for c < 0.5) and shall be assumed as acting along a diagonal. 8.8.3.2 TRIANGULAR-SECTION TOWERS: For oblique incidence, the wind force on triangular-section trussed towers (although lower than for normal wind incidence) shall be assumed to be the same as for normal incidence. 8.8.4 TOWER APPURTENANCES: The wind-loading on tower appurtenances, such as ladders, conduits, lights, elevators, etc., shall be as calculated by using the appropriate net pressure coefficient for these elements and the effective velocity pressures of Table 8-2. The contribution of these elements to the tower wind-loading shall be based on the effective velocity pressures of Table 8-2. Allowance may be made for shielding effects. 8.8.5 TOWER GUYS: The minimum net pressure coefficient for wind normal to the chord of tower guys shall be 1.2. For oblique wind incidence, the net pressure coefficients shall be as given in Table 8-16 in which B is the angle between the wind direction and the chord of the guy, CD is the drag coefficient which defines the horizontal component of the wind forces in the direction of the wind, and CL is a lift coefficient which defines that component acting normal to the wind and in the plane containing the angle B. The coefficients apply to the exposed area of the guys, Ld, L being their chord length and d their diameter. The coefficients shall be used in conjunction with the effective velocity pressures * of Table 8-1. 8.8.6 PATTERNS IN WIND LOADS: For guyed towers, a reduction of 25% * of the design pressure in guy span between guys, shall be made for the determination of maximum and minimum moments and shears. The cantilever portion shall be designed for 125% of the design pressure. IV-79 TABLE 8-14 Net Pressure Coefficients for Square - and Triangular - Section Towers, Cf Square Towers Triangular Towers Less than 0.025 4.0 3.6 0.025 to 0.45 4.13 - 5.18 3.71 - 4.47 p 0.45 to 0.7 1.8 1.7 0.7 to 1.0 1.33 + 0.67 p 1.0 + TABLE 8-15 Ratio of Drag on Towers with Rounded Members to Drag on Towers with Flat-Sided Members* Factor Less than 0.3 2/3 0.3 to 0.8 (0.66 p + 0.47) 0.8 to 1.0 1.0 * For drq < 2.5, where d = typicaZ member diameter in feet and q = velocity pressure in psf MIN-80 TABLE 8-16 - Wind-Loading Coefficients for CD and CL 100 200 300 40° 50° 600 700 800 900 CD 0.05 0.1 0.2 0.35 0.6 0.8 1.03 1.16 1.2 CL 0.04 0.15 0.27 0.36 0.45 0.43 0.33 0.18 0 IN s8 SECTION 8.9 OVERTURNING AND SLIDING: 8.9.1 OVERTURNING: The overturning moment due to the wind load shall not exceed 66-2/3% of the stabilizing moment of the building or other structure due to the dead load only, unless the building or other structure is anchored so as to resist the excess overturning moment without exceeding the allowable stresses for the materials used. The axis of rotation for computing the overturning moment and the moment of stability shall be taken as the intersection of the outside wall line on the leeward side and the plane representing the average elevation of the bottoms of the footings. The weight of the earth superimposed over footings may be used in computing the moment of stability due to dead load. 8.9.2 SLIDING: When the total resisting force due to friction is insufficient to prevent sliding, the building or other structure shall be anchored to withstand the excess sliding force without exceeding the allowable stresses for the materials used. Anchors provided to resist overturning moment may also be considered as providing resistance to sliding. IV,82 CHAPTER 9 ' FOUNDATI ONS SECTION 9.1 GENERAL: All buildings and structures constructed within Hurricane Hazard Zones A, B, C or D shall conform to these regulations (with special reference to Chapter 5) and the Building Code. SECTION 9.2 SOIL INVESTIGATION: 9.2.1 GENERAL: The classification of the soil at each building site shall be determined when required by the Building Official. This determination is to be made by a Professional Engineer registered in the State of Texas. 9.2.2 INVESTIGATION: The soil investigation shall be carried out in accordance with the recommendations of the Soil Mechanics and Foundation Section of the American Society of Civil Engineers. As a minimum requirement for a single family residence, or similar structure, one test hole to a depth of at least 25 feet shall be drilled and penetration tests (or other approved tests) shall be performed to determine the density and bearing capacity of the foundation material. In a residential subdivision planned by a Professional Engineer, adequate tests may be performed to indicate the condition of the foundation material for all of the lots without requiring one test hole per lot, if approved by the Building Official. 9.2.3 REPORTS: The soil classification and design-bearing capacity shall be shown on the plans. The Building Official may require submission of a written report of the investigation which shall include, but need not be limited to, the following information: (1) plot showing the location of all test borings and low excavations; (2) description and classification of the materials encountered; (3) elevation of the water table encountered; (4) recommendations for foundation type and design criteria including bearing capacity, provisions to minimize the effects of expansive soils, and the effects of adjacent loads; and (5) expected total and differential settlement. SECTION 9.3 DESIGN REQUIREMENTS: 9.3.1 GEN4ERAL: All foundations shall be designed in accordance with * the structural requirements of the Hazard Zone in which they are constructed. 9.3.2 HAZARD ZONE A: In Hazard Zone A the foundation of all buildings and structures will be designed to resist scour and soil movement, unless positive protection against scour and soil movement are provided. In addition, the foundation must be designed IV-83 to safely transfer to the underlying soil all loads due to wind, water, dead load, live load, and all other loads (including uplift due to wind and water). 9.3.3 HAZARD ZONE B: Same as Hazard Zone A except no requirement for scour or soil movement. 9.3.4 HAZARD ZONE C: Same as Hazard Zone B except no battering forces. 9.3.5 HAZARD ZONE 0: Same as Hazard Zone C except no flooding. 9.3.6 CONCRETE FOUNDATIONS: 9.3.6.1 PROTECTION OF REINFORCING STEEL: In Hazard Zones A, B, and C all concrete foundations shall be designed, detailed and constructed to provide a minimum of three inches (3") of concrete cover. 9.3.6.2 POSITIVE CONNECTIONS: All foundations shall be designed, detailed and constructed to provide positive connections between all members, pieces, and parts. These connections shall safely transmit all forces (compression, tension or shear) and moments required by the design. If reinforcing steel is to be welded, a test report must be submitted to prove that the steel is weldable. SECTION 9.4 CONSTRUCTION REQUIREMENTS: 9.4.1 GENERAL: All foundations constructed in Hazard Zones A, B, C, and D shall be built in accordance with good Engineering practice. When required by the Building Official, a Professional Engineer registered in the State of Texas shall supervise the construction of the building or structure and shall submit periodic construction reports to the Building Official. 9.4.2 INFORMATION REQUIRED DURING CONSTRUCTION: The design engineer may be required to furnish to the Building Official any portion of the following information during construction: (1) a complete pile-driving log; (2) a report on the manufacture of all precast members including the stressing operation of prestressed members; (3) test reports from a certified laboratory on all concrete used, including precast members; and (4) mill certificates for structural and reinforcing metals used. 9.4.3 INFORMATION REQUIRED BEFORE FINAL ACCEPTANCE: When the structure is complete, and prior to final acceptance, the design engineer shall furnish the Building Official a complete set of As-Built drawings, together with his certification that the structure has been built in accord with the approved plans and specifications. IV-84 CHAPTER 10 ' V u i41tuI MASONRY WALLS SECTION 10.1 GENERAL: All masonry walls of buildings and structures within Hazard Zones A, B, C, or D shall be designed, detailed, and constructed in accordance with the Building Code and these regulations. SECTION 10.2 STRUCTURAL INTEGRITY: 10.2.1 GENERAL: All masonry walls shall be designed to resist all loads or combination of loads which are applicable in the Hazard Zone in which the structure is located. The walls shall safely transfer these loads to the supporting structure without disintegration or other structural failure. 10.2.2 TIE COLUMNS: 10.2.2.1 TIE COLUMN SPACING: Concrete tie columns shall be required in exterior walls of unit masonry. Concrete tie columns shall be required at all corners, at intervals not to exceed 20 feet center-to-center of columns, adjacent to any corner opening exceeding four feet in width, adjacent to any wall opening exceeding nine feet in width, and at the ends of free- standing walls exceeding two feet in length. Structurally designed columns may substitute for the tie columns herein required. 10.2.2.2 TIE COLUMN DIMENSIONS: Tie columns shall be not less than 12 inches in width. Tie columns having an unbraced height not exceeding 15 feet shall not be less in thickness than the wall nor less than a nominal eight inches, and, where exceeding 15 feet in unbraced length, shall be not less in thickness than 12 inches. The unbraced height shall be taken at the point of positive lateral support in the direction of consideration or the column may be designed to resist applicable lateral loads based on rational analysis. 10.2.2.3 TIE COLUMN REINFORCING: Tie columns shall be reinforced with not less than four #5 vertical bars for 8" x 12" columns nor less than four #6 vertical bars for 12" x 12" columns nor less reinforcing steel than 0.01 of the cross sectional area * for columns of other dimensions nor less than may be required to resist axial loads or bending forces. Vertical reinforcing shall be doweled to the footing and splices shall be lapped 30 bar diameters. Columns shall be tied with #2 hoops spaced not more than 12 inches apart. IV-85 S A i 10.2.2.4 CASTING TIE COLUMNS: In load-bearing walls tie columns shall be cast only after masonry units are in place. Where masonry walls of skeleton frame construction are laid up after the frame has been erected, adequate anchorage designed by a Professional Engineer shall be provided. Where structural steel members are made fire-resistive with masonry units, the panel walls shall be bonded to the fire-resistive materials. 10.2.3 TIE BEAMS: 10.2.3.1 TIE BEAM LOCATION: A tie beam of reinforced concrete shall be placed in all walls of unit masonry, at each floor or roof level, and at such intermediate levels as may be required to limit the vertical heights of the masonry units to 16 feet. 10.2.3.2 TIE BEAM SIZE AND REINFORCEMENT: A tie beam shall be not less in dimension or reinforcing than required for the con- ditions of loading nor less than the following: A tie beam shall have a width of not less than a nominal eight inches, shall have a height of not less than 12 inches and shall be reinforced with not less than two #5 reinforcing bars in the top and two #5 reinforcing bars in the bottom of the beam. 10.2.3.3 CONTINUITY OF TIE BEAM: The tie beam shall be continuous. Continuity of the reinforcing in straight runs shall be provided by lapping splices not less than 18 inches or by adding two #5 bent bars which extend 18 inches each way from the corner. Continuity at columns shall be provided by continuing horizontal reinforcing in the columns or distance of 18 inches. 10.2.3.4 TIE BEAM AT GABLE END AND SHED END WALLS: A tie beam shall follow the rake of a gable or shed end. 10.2.3.5 TIE BEAM BOND: The concrete in tie beams shall be placed to bond to the masonry units immediately below and shall not be separated therefrom by wood, felt, or any other material which may prevent bond. Felt paper no wider than the width of the cells of the block may be used provided that it is depressed a minimum of 2 inches in one cell of each block. 10.2.3.6 PARAPET WALLS: Masonry parapet walls shall be not less than eight inches thick, shall be reinforced with minimum tie columns and shall be coped with a concrete beam not less than 64 square inches in cross section, reinforced with two #4 reinforcing bars. A parapet wall exceeding five feet in height above a tie beam or other point of lateral support shall be specifically designed to resist horizontal wind loads. IV -86 CHAPTER 11 i STEEL & IRON SECTION 11.1 GENERAL: Steel and iron members of buildings and structures constructed in a Hurricane Hazard Zone shall be designed, detailed, and constructed in accordance with the Building Code and these Regulations. SECTION 11.2 COLUMNS: Tubular columns and other primary compression members, excluding secondary posts and struts not subject to bending and whose design load does not exceed 2,000 pounds, shall have a minimum least dimension of 2-112 inches and a minimum wall thickness of 3/16 of an inch. SECTION 11.3 WELDING: Welding in the shop or field may be done only by persons who have been tested and certified by an approved testing laboratory for the welds to be performed, in accordance with the American Welding Society Standards. SECTION 11.4 INSPECTION: A special inspector shall inspect the welding and high-strength bolting on buildings exceeding 10,000 sq. ft. in area or 3 stories in height or as required by the Building Official because of special conditions. SECTION 11.5 OPEN-WEB STEEL JOISTS: 11.5.1 Where the net uplift force is equal to or greater than the load of construction, all web and bottom chord members shall have a minimum slenderness ratio of 200 and be proportioned to accommodate the maximum compression and tensile stresses. 11.5.2 The ends of every joist shall be bolted, welded or embedded at each bearing to provide not less resistance in any direction than 50 percent of the rated end reaction. SECTION 11.6 COLD-FORMED STEEL CONSTRUCTION: 11.6.1 GENERAL: All structural members and connections shall be designed, detailed, and constructed to resist the loads applicable to the Hazard Zone in which it is constructed. 11.6.2 CONNECTIONS: All connections shall be by welding, riveting, bolting or other approved fastening devices or methods providing positive attachment and resistance to loosening. Metal screws shall not be used without positive provision for resistance to loosening. * Fasteners shall be of compatible material, with consideration given to avoiding possible electrolysis. * 11.6.3 STRUCTURAL SHEETS: 11.6.3.1 Decks and panels properly supported by and attached to the building frame, including but not limited to those having IV-87 an approved fill material on their top surface, may be considered to act as diaphragms in resisting lateral forces where designed as such subject to the other limitations of the Building Code and these Regulations, except that metal without fill of less thickness than 22 gauge shall not be considered to have diaphragm value. 11.6.3.2 Poured fill on roof and floor decks shall not be assumed to have any structural value to support or resist vertical or lateral loads or to provide stability or diaphragm action unless so designed. 11.6.3.3 Positive attachment of sheets shall be provided to resist uplift and diaphragm forces. Attachment shall be as set forth in Paragraph 11.6.2 and not less frequently than the following maximum spacings or as required based on rational analysis and/or tests: (1) One fastener shall be placed near the corner of each sheet or at overlapping corners of the sheet; (2) Along each supporting member, the spacing of fasteners shall not exceed 8 inches on centers at ends of sheets nor 12 inches on centers at intermediate supports; (3) The spacing of edge fasteners between panels, and between panels and supporting members parallel to the direction of span, where continuous interlock is not other- wise provided, shall be not more than 12 inches on centers; and (4) Poured lightweight concrete fill will be acceptable as continuous interlock. 11.6.3.4 Wall panels shall be attached as set forth in sub-paragraphs 11.6.3.3(1), (2), and (3) preceding. 11.6.4 NONSTRUCTURAL SHEETS: Steel sheet sections not suitable by rational analysis for self-supporting structural sheets shall be termed roofing and siding. Roofing and siding shall be used only over solid wood sheathing or equivalent backing. Attachment shall be as set forth in Paragraph 11.6.3.3 except that connections shall not be more than 12 inches on center each way, and except that attachment may be by 8d nails or by No. 6 wood screws, in accordance with the standards of the National Forest Products Associ ati on. 11.6.5 PROTECTION OF METAL: Steel sheets used in Hurricane Hazard Zones shall be protected by being galvanized in accordance with ASTM A525 and have a minimum of 1.25 oz. class coating or be of an approved alloy or be otherwise coated to provide equal durability and protection. Abrasions or damages to the protective coating shall be spot-treated with a material and in a manner compatible to the shop protective coating. 11.6.6 WELDING: The fusion welding of structural members and structural sheets less than 22 gauge in thickness shall be through weld washers not less than 14 gauge in thickness and one inch in diameter, contoured if necessary to provide continuous contact, or through an equivalent device. IV-88 CHAPTER 12 WOOD SECTION 12.1 GENERAL: Wood members and their fastenings shall be designed by methods admitting of rational analysis according to established principles of mechanics. All members shall be framed, anchored, tied and braced to develop the strength and rigidity necessary for the purposes for which they are used and to resist the loads imposed as set forth in the Building Code and these regulations. SECTION 12.2 ALLOWABLE UNIT STRESSES: 12.2.1 Lumber used for joists, rafters, trusses, columns, beams, etc., shall be of a stress grade not less than 1000 psi nominal extreme fiber stress in bending. 12.2.2 Lumber used for studs in exterior walls and interior bearing walls shall be of a stress grade not less than 625 psi nominal extreme fiber stress in bending. 12.2.3 Lumber used for studs in interior non-bearing walls shall be of a stress grade not less than 225 psi nominal extreme fiber stress in bending. SECTION 12.3 ANCHORAGE: Anchorage shall be continuous from the foundation to the roof and shall satisfy the uplift requirements of the design wind and/or flood. 12.3.1 Sills and base plates, where provided in contact with masonry, shall be of an approved durable species or be treated with an approved preservative and shall be attached to the masonry with 1/2 inch diameter bolts spaced not over 4 feet apart and embedded not less than 7 inches in the masonry. 12.3.2 Columns and posts shall be framed to true end bearing and shall be securely anchored against lateral and vertical forces. The bottoms of columns and posts shall be protected against deteriora- tion. 12.3.3 Joists fire-cut into a masonry wall shall be anchored to * the concrete beam on which they bear. Such anchors shall be spaced not more than four feet apart and shall be placed at opposite ends across the building on the same run of joists. 12.3.4 Joists shall be nailed to bearing plates, where such plates occur, to each other where contiguous at a lap, and to the studs where such studs are contiguous; and ceiling joists shall be nailed to roof rafters where contiguous. IV-89 12.3.5 Every roof rafter and/or roof joist shall be anchored to the beam or studs on which they bear, and roof rafters opposing at a ridge shall be anchored across the ridge as set forth in subsection 12.3.7. 12.3.6 Anchors securing wood to concrete shall be not less than 1"t x 1/8" steel strap embedded in the concrete and nailed with three 16d nails to wood members. In lieu of such straps, anchorage may be as approved by the Building Official when designed by a Professional Engineer. 12.3.7 Anchors securing wood to wood shall be of I" x 1/8" steel strap, nailed to each member with three 16d nails, or shall be a commercial anchor approved by the Building Official anchoring each member. All anchors and relative nails exposed to the weather shall be galvanized. SECTION 12.4 STORM SHEATHING: Exterior stud walls shall be sheathed to resist the racking load of wind. Tightly fitted, diagonally placed, boards not less than 5/8 inch thickness, shall be nailed by three 8d common nails to each support for I" x 6" boards and four 8d common nails for I" x 8" boards. Plywood wall sheathing, 1/2 inch thickness, may be used in lieu of boards. SECTION 12.5 CANTILEVER ROOF JOISTS: Roof joists may cantilever over exterior walls as limited by the allowable stress, but the length of such cantilever shall not exceed the length of the portion of the joist inside the building, and where the cantilever of tail joists exceeds three feet, the roof joist acting as a header shall be doubled. IV-90 CHAPTER 13 . CONCRETE SECTION 13.1 GENERAL: All concrete members of buildings and structures constructed within Hazard Zones A, B, C, or D shall be designed, detailed, and constructed in accordance with the Building Code and these Regulations. SECTION 13.2 CONCRETE PROTECTION FOR REINFORCEMENT: 13.2.1 MEMBERS IN CONTACT WITH GROUND AND BELOW RFD: Concrete members which are constructed against the ground and members which are at or below the RFD shall have not less than three inches of concrete between the steel reinforcment and the concrete outer surface. 13.2.2 PRECAST UNITS: Concrete coverage of reinforcement in precast units shall be as set forth in the appropriate standard except that precast cement mortar units may have less cover than otherwise set forth, but not less than 1/8 inch providing: (1) The units are manufactured under the control, certification, * and supervision of a Professional Engineer. (2) Reinforcing shall be galvanized, stainless steel or approved equal. (3) To insure exact final location of the steel, positive and rigid devices for that purpose are employed in the manufacturing process. (4) Cement mortar density shall be not less than 155 pounds per cubic foot, including reinforcing, and the minimum strength shall not be less than 5000 psi in 28 days. (5) Cement mortar shall not contain less than I part cement, by volume, for each two parts of fine aggregate. (6) Fine aggregate shall have a maximum size of 4.76 mm. (7) No coarse aggregate shall be used. (8) Units shall be cast on vibrating forms. (9) Members shall not be in contact with the ground or standing water. (10) Where required, fire-resistivity concrete cover requirement will control. SECTION 13.3 PRECAST UNITS: 13.3.1 All precast structural items shall be designed by a Registered Professional Engineer. 13.3.2 Only the materials cast monolithically with the units at the time of manufacture shall be used in computing stresses unless * adequate and approved shear transfer is provided. 13.3.3 The Building Official may promulgate and set forth in writing such reasonable rules for requiring tests to be made by an * approved laboratory as he may consider necessary to insure compliance with this Regulation and the Building Code. 13.3.4 The Building Official or his representative shall have free access to the plant of any producer at all hours of normal operation, IV-91 ri, F and failure to permit such access shall be cause for revocation of approval. 13.3.5 All connections shall be designed, detailed and constructed to safely transfer all wind, live and dead loads to the supporting structure without disintegration or structural failure. I¥-92 CHAPTER 14 CLADDING AND GLAZING SECTION 14.1 GENERAL: All cladding and glazing of buildings and structures constructed within Hazard Zones A, B, C, and D shall be designed, detailed and constructed in accordance with the Building Code and these Regulations. All exterior cladding, wall covering, windows, doors, glass and glazing shall be designed to resist loads (including suction) due to the applicable wind speeds and to meet requirements of flooding if located below the RFD. Connections for these elements must be designed to safely transfer the design loads to the supporting structure without disintegration or structural failure. SECTION 14.2 LIMITS OF SIZE OF GLASS: Regular plate and sheet glass used in exterior walls shall not exceed the areas set forth in Table 14-1. The table applies for width-to-length ratios from 2:10 to 10:10. The allowable area of glass other than regular plate and sheet used in exterior walls shall not exceed the areas obtained by multiplying the areas in Table 14-1 by the following factors: Tempered Safety Glass 4.0 Insulating (double glazed) 1.5 Rough Rolled Plate 1.0 Lami nated 0.6 * Wire Glass 0.5 Sandblasted or Etched 0.4 SECTION 14.3 DOORS AND OPERATIVE WINDOWS IN EXTERIOR WALLS: The design and approval of operative windows, sliding doors and swinging doors, including their support members in exterior walls shall be based on the proposed-use height above grade in accordance with Chapter 8 of these Regulations. Maximum glass sizes shall comply with Table 14-1. IV-93 TABLE 14.1 . ,,iK ( [ , SILrL' T- \ , (:,jtUhf MAXIMUM AREA OF GLASS IN SQUARE FEET Wind Velocity Taken as 140 MPH at 30 Feet Above Grade Glass Thickness (Inches) Height Above 1/8 & 3/16 & Grade S.S. D.S. 13/64 7/32 1/4 5/16 3/8 1/2 5/8 3/4 0'-5' 7.3 11.4 22.0 27.2 33.8 47.0 60.1 88.2 119.8 150.6 5'-15' 6.0 9.2 17.6 22.0 27.2 38.2 49.2 72.0 97.7 124.2 15'-25' 5.0 7.6 15.4 17.6 22.8 31.6 41.1 60.0 80.8 101.4 25'-35' 4.3 6.8 13.2 16.2 19.8 27.9 36.0 52.9 71.3 89.6 35'-55' 3.9 6.1 11.8 14.0 17.6 25.0 32.3 47.0 63.9 81.6 55'-75' 3.5 5.4 10.7 12.9 16.1 22.8 28.7 41.9 57.3 72.7 75'-100' 3.2 4.9 9.7 11.8 14.7 20.6 26.4 38.9 52.9 66.9 100'-150' 3.0 4.6 8.8 10.8 13.2 19.1 24.2 35.3 48.5 61.0 150'-250' 2.6 4.0 7.7 9.4 11.8 16.2 21.3 30.9 41.9 52.9 250'-350' 2.3 3.5 6.8 8.3 10.4 14.0 19.1 27.2 37.5 47.0 350'-550' 2.1 3.1 6.1 7.4 9.2 12.9 16.9 24.2 33.1 41.9 550'-750' 1.8 2.8 5.4 6.6 8.3 11.6 15.4 22.0 30.1 38.9 750'-1000' 1.7 2.6 5.0 6.1 7.6 10.7 14.0 19.8 27.2 34.5 over 1000' 1.6 2.5 4.8 5.9 7.3 10.3 13.2 19.1 26.5 33.8 IVA14 CHAPTER 1 77 ROOF COVERING SECTION 15.1 GENERAL: All roof covering of buildings located within Hazard Zones A, B, C and D shall be designed, detailed, and constructed in accordance with the Building Code and these Regulations. The roof coverings and the connections to the supporting sheathing, deck, or structural roof member will be such as to provide for safe transfer of all applicable loads to the supporting structure without disintegration or structural failure. In general, all roof coverings shall resist the uplift forces given in these standards with at least a safety factor of 2. SECTION 15.2 PREPARED SHINGLE ROOF COVERINGS: 15.2.1 Wood roof decks to which prepared shingles are applied shall be solidly sheathed. Sheathing shall be well seasoned and dry. Sheathing boards shall be at least 1 inch nominal dimension boards not over 6 inches wide. Plywood sheathing shall be at least 5/8 of an inch thick. 15.2.2 Attic spaces shall be vented with vent openings so placed as to circulate air in all parts of the attic. 15.2.3 Nails shall be of sufficient length to extend through the roof deck (sheathing). 15.2.4 Thick-butt asphalt shingles shall be nailed in the thick portion of the shingle. 15.2.5 All butts or tabs of asphalt shingles shall be securely spotted or tabbed with a plastic, fibrous, asphaltic cement or anchored by clips or locks, and all edges at eaves and gables shall be set in such cement 3 inches back from the edge. 15.2.6 Metal drip edges shall be nailed to the roof deck with nails not less than 10 inches on centers. SECTION 15.3 BUILT-UP ROOF COVERINGS: 15.3.1 For built-up roof coverings cant strips shall be provided at the angle of roof and vertical surfaces. 15.3.2 Built-up roof coverings shall be carried at least 6 inches above the cant strip to a reglet in the parapet and covered with * flashing caulked into the reglet. The reglet may be omitted at parapet walls, provided two layers of felt or the equivalent are carried across the top of the parapet under coping and down the para- pet to the lower edge of the cant strip. The said layers are to run vertically, being properly lapped and cemented to the parapet. IV-95 15.3.3 All resinous places in the wood roof deck shall be covered with sheathing paper or unsaturated felt. 15.3.4 The first layer or anchor sheet shall be not less than 30-pound felt nailed 6 inches on center along a 2-inch lap and nailed 12 inches on center both ways, in the area between laps with tin caps and 1-inch nails; or shall be not less than two layers of 15-pound felt lapped 18 inches and nailed through both sheets on 6-inch centers along the lap and on 12-inch centers in the area between laps with tin caps and 1-inch nails; or, where the underside of the roof sheathing is to be exposed and its appearance considered, the first layer shall be not less than a 30-pound felt or two layers of 15 pound felt nailed 6 inches on centers along the rafters with tin caps and 1-1/4-inch nails, and nailed 12 inches on centers, both ways, between rafters, with tin caps and 3/4 inch nails. 15.3.5 Each additional sheet above the anchor sheet shall be thoroughly mopped between layers with a bituminous compound so that no layer touches an unmopped layer. Bituminous compound for mopping plys together shall be air-refined asphalt or coal tar pitch but shall not be any type of emulsion, cold or cutback liquid cement, oil or grease. 15.3.6 Gravel stop and drip strips, and eave and gable drips shall be not less than No. 26 guage galvanized metal, 16 ounce copper or 0.024 inch aluminum, with not less than 3-inch flange on roof and nailed with not less than 3/4 inch nails spaced not more than 6 inches apart. SECTION 15.4 ROLL ROOFING: 15.4.1 Roll roofing shall be applied only over a smooth surface. Roll roofing shall not be applied over shingle roofs. 15.4.2 Roll roofing applied in a single layer shall be spot mopped and applied by concealed nail method with a minimum 3-inch head lap and a minimum 6-inch end lap properly cemented. Nail spacing shall be not less than 4 inches on centers. 15.4.3 Nails that secure roll roofing to the roof deck shall be driven at least 3/4 of an inch from the edge of the sheet. SECTION 15.5 TILE ROOFING: 15.5.1 Tile roofing shall be laid over not less than one layer of 30-pound asphalt felt securely fastened by nailing with tin caps. 15.5.2 All tile shall be thoroughly watered with a hose before application. 15.5.3 Every tile shall be laid full length in portland cement mortar and, in addition, the first three horizontal courses shall be nailed. Under certain conditions additional nailing may be IV-96 required to prevent tile from slipping. Mortar shall be not less than one part cement and three parts sand and not more than twenty-five per cent lime by volume. 15.5.4 All nails for flashing and tiles shall be copper. SECTION 15.6 CORRUGATED METAL ROOFING, PROTECTED METAL ROOFING, CORRUGATED AND FLAT ASBESTOS CEMENT ROOFING: 15.6.1 When roofings of the above types are applied to wood roof decks they shall be secured with drive screws of sufficient length to extend through the roof deck. When applied directly to purlins and other roof members, they shall be secured with bolted strap fasteners, bolts or stud fasteners. Properly designed clip fasteners that are approved may be used in accordance with the conditions of such approval. Drive screws at least 4 inches in length may be used to secure these roofings directly to wood purlins. 15.6.2 Aluminum roofing when fastened to steel roof structure shall be insulated against electrogalvanic action. SECTION 15.7 INSULATED STEEL DECK ROOFING: Insulated steel deck shall be secured by spot welding of clips or spot welding the sheets to the steel purlins. IV-97 APPENDIX A iO SELECTED REFERENCES - HAZARD ZONE DELINEATION Bodine, B. R., "Storm Surge on the Open Coast: Fundamentals and Simplified Prediction." U.S. Army Corps of Engineers CERC Tech. Memo 35. 1971. Bretschneider, C. L. and J. I. Collins, "Prediction of Hurricane Surge: An Investigation of Corpus Christi and Vicinity." National Engineering Science Co., Tech Report SN-120: Pasadena, California. 1963. Cry, Geo. W., "Tropical Cyclones of the North Atlantic Ocean: Tracks and Frequencies of Hurricanes and Storms 1871-1963." Technical Paper No. 55, Weather Bureau, Department of Commerce; 148 pp. 1965. Frank, Neil L., "The Hard Facts About Hurricanes." NOAA Magazine, No. 4; Pages 4-9. 1974. Freeman, J.C., L. Baer, and G.H. Jung, "The Bathystrophic Storm Tide." Journal of Marine Research, Vol. 16; pp. 12-22. 1957. Ho, Francis P., R.W. Schwerdt, and H.V. Goodyear, "Some Climatological Characteristics of Hurricanes and Tropical Storms, Gulf and East Coasts of the United States." NOAA Tech. Report NWS 15. 1975. Hargis, Wm. J. et al., "Methodology for Estimati ng the Characteristics of Coastal Surges from Hurricanes," Technical Report of Panel on Coastal Surges from Hurricanes. National Academy of Sciences; 34 pp. 1975. Jelesnianski, C.P., "Bottom Stress Time-History in Linearized Equations of Motion for Storm Surges." Monthly Weather Review, Vol. 98, No. 6; pp. 462-478. 1970. Jelesnianski, C.P., "Numerical Computations of Storm Surges with Bottom Stresses." Monthly Weather Review, Vol. 95, No. 11; pp. 740-756. 1967. Jelesnianski, C.P., "SPLASH: Landfall Storms," NOAA Tech. Memo NWS TDL-46. 1972. Miller, B. I., "On the Filling of Tropical Cyclones Over Land." National Hurricane Research Project Report No. 66. Dept. of Commerce, Weather Bureau. 1963. Myers, V. A., "Joint Probability Method of Tide Frequency Analysis." ESSA Tech. Memorandum WBTM HYDRO--ll. 1970. Reid, Robert 0. and B.R. Bodine, "Numerical Computation of Tide and Storm Surges in Galveston Bay." ASCE Journal of the Waterways and Harbors SCIV. 1968. IV-98 Riehl, Herbert, Tropical Meteorology (New York, N.Y.: McGraw- Hill Book Co.; 392 pp.) 1954. Simpson, R.H., "Hurricane Prediction: Progress and Problems." Science, No. 181; pp. 899-907. 1973. Simpson, R.H., "Hurricane, Yes or No." NOAA Magazine, Vol. 1, No. 3. 1971. Simpson, R.H., et al, "Evacuation of Coastal Residents During Hurricanes." Report of Miami Federal Executive Board Hurricane Shelters Committee to Office of Management and Budget, Washington, D.C. 1973. Simpson, R.H. and John C. Freeman, "Coastal Hazard Potentials," Proceedings Technical Conference on Coastal Hazards, September 1976, American Meteorlogical Society, Boston, Massachusetts. 1976. Simpson, R.H. and Roger Pielke, "Hurricane Development and Movement: A Survey Paper." Applied Mechanics Reviews, May, 1976; pp. 601-609. 1976. Simpson', R.H. and J. Simpson, "Hurricanes: Structure, Development, Movement and Mitigation." Encyclopedia of Science, Vol. 6 (New York, N.Y.: McGraw Hill) 1976. Simpson, R.H. and J. Simpson, "Why Experiment on Hurricanes." Transactions N.Y. Academy of Sciences 28, No. 8; pp. 1045-1062. 1966. Thom, Herbert C.S., "New Distributions of Extreme Winds in the United States." Journal of the Structural Division, Proc. ASCE, Vol. 94: ST7; pp. 1787-1801. 1968. White, Gilbert F. and Eugene Haas, Assessment of Research on Natural Hazards (Cambridge, Mass.: MIT Press; 487 pp.) 1975. IV-99 Li! APPENDIX B J SELECTED REFERENCES - MODEL MINIMUM BUILDING STANDARDS ANSI A58.1 Building Code Requirements for Minimum Design Loads in Buildings and Other Structures (New York, N.Y.: American National Standards Institute) 1972. Bahamas Building Code (Nassau, Bahamas: Ministry of Works and Utilities). Basic Data for the Design of Buildings, Chapter V "Loading" (London, England: British Standards Institution). "Concrete Shore Protection" (Skokie, Illinois: Portland Cement Association). Coral Gables Bulkhead Ordinance (Coral Gables, Florida: City Commission of Coral Gables). "Floodproofing Regulations" (Washington, D.C.: Corps of Engineers) 1972. "Hurricane Camille Report, August 1969" (Mobile, Alabama: Corps of Engineers) May, 1970. Hurricane Carla (Denton, Texas: Office of Civil Defense) 1961. ICBO Code (Pasadena, California: International Conference of Building Officials) "Loads, External Forces, and Design Stresses," Japan Building Standard Law Enforcement Order; 1959. National Building Code (New York, N.Y.: American Insurance Association). Saffir, Herbert S., "Effects of High Wind on Glazing and Curtainwalls, and Rational Design Methods for Glazing and Curtainwalls," presented at USA-Japan Research Seminar on Wind Effects on Buildings; Kyoto, Japan. 1974. Saffir, Herbert S., "Glass and Curtainwall: Effects of High Winds, Required Design Criteria," presented at 4th International Conference on Wind Effects on Buildings; London, England. 1975. Saffir, Herbert S., "Housing Construction in Hurricane Prone Areas," for United Nations (New York, N.Y.: United Nations) 1971. Saffir, Herbert S., "Hurricane Camille - Data on Storm and Structural Damage," presented at 3rd International Conference on Wind Effects on Buildings; Tokyo, Japan. 1971. Saffir, Herbert S., "Hurricane Exposes Structural Flaws," Civil Engineering; February, 1971. IV-100 Saffir, Herbert S., "The Nature and Extent of Structural Damage Caused by Hurricane Camille," for NOAA (Washington, D.C.: NOAA) 1972. Saffir, Herbert S., "Report on Hurricane Eloise Damage," for Texas Coastal and Marine Council (Austin, Texas: Texas Coastal and Marine Council). "Some Climatological Characteristics of Hurricanes," NOAA Technical Report NWS 15 (Washington, D.C.: NOAA). South Florida Building Code (Miami, Florida: Board of County Commissioners). Southern Standard Building Code, Revised (Birmingham, Alabama: Southern Building Code Congress). Swiss Engineers and Architects Association Shape Factors, 1951, as revised by Herbert S. Saffir. IV-101 APPENDIX C The following Texas cities have adopted the Southern Standard Building Code (1) without modification: Beaumont League City Bridge City Orange Brownsville Nederland Clear Lake Shores Port Aransas Friendswood Port Arthur Groves Port Lavaca Hitchcock Port Neches Kemah Pear Ridge Lakeview Texas City La Marque Webster The City of Galveston has adopted the Southern Standard Building Code with increased wind pressures as follows: Height Wind Pressure Less than 30' 30 psf 31' - 50' 42 psf 51' - 99' 54 psf 100' - 199' 60 psf All elevations south 75 psf of seawall The City of Corpus Christi has adopted the Southern Standard Building Code with the following modifications: 1. Added paragraphs concerning "Hurricane Precautions" and "Special Hurricane Inspection." 2. Increased wind loads: Height Wind Pressure Less than 30' 30 psf 31' - 50' 40 psf 3. Established minimum lumber grade (1200 psi). IV-102 4. Added requirement for continuous anchorage in timber construction. 5. Established requirements for mobile homes. 6. Established more restrictive requirement for roof coverings. The town of South Padre Island has a "Building Requirement" which apparently requires: 1. A wind load of 45 pounds per square foot at 30 feet above existing grade. 2. 35-foot piles on the Gulf side, 25 foot piles on the Bay side, and pile penetration of 5' below mean high tide under concrete slabs (no required penetration otherwise). 3. Anchorage continuous from foundation to roof. Galveston County, in accordance with legislation concerning National Flood Insurance, has adopted the Southern Standard V Building Code as a part of its building regulations. This document defines flood hazard areas and requires the lowest floor level of all new construction to be above the 100 year flood or 18 inches above natural ground, whichever is higher. Part V of the regulation includes some requirements for structural design and material use. The City of Baytown requires compliance with the Southern Standard Building Code for commercial construction and FHA 300 Code (2) for residential construction. Rockport requires compliance only with electrial and plumbing codes. £ The above information is taken from a survey made by Dr. Charles Hix. This information is included only as a general reference, as in only one instance was the response to the survey provided * by a person familiar with building codes and construction practices. Only four of the respondents to the survey furnished copies of ordinances adopting the standard code. In one instance the written response indicated that the standard code was in use without modification and a telephone call to a building official indicated that important modifications had been made to the standard code. IV-103