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pv WA 90961 Z861 88V DI @w or 4@1 I p"p-11Iqp@ Ul. %OW sp 0 lj@ Wit now a Sod m .... .. . .... .... .. . .... .. ....... . . .. .. .. TABLE OF CONTENTS Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . i Editors' Note . . . . . . . . . ... . . . . . . . . . . . . . . . ii Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . iv Chapter I. Introduction . . . . . . . . . . . . . . . . . . . . . 1-1 A. Purpose of the Study . . . . . . . . . . . . . . 1-1 B. Contents of this Report . . . . . . . . . . . . 1-1 C. The Results . . . . . . . . . . . . . . . . . . 1-3 D. The Conclusions . . . . . . . . . . . . . . . . 1-5 Chapter II. Evaluation of Erosion-Control Structures. . . . . . 2-1 A. Introduction. . . . * ' * * ' * * ' * ' * * ' 2-1 B. Case along the Lower Eastern Shore . . . . . . . 2-7 .C. Cases along the Lower Western Shore ' * * * * * 2-40 D. Cases along the Calvert County and Lower Anne Arundel County shoreline . . . . . . . . . 2-48 E. Cases along the Upper Western Shore . . . . ... 2-78 F. Cases along the Upper Eastern Shore . . . . . . 2-100 G. Cases along the Kent Island and Talbot County shoreline . . . . . . . . . . . 2-110 H. Summary . . . . . . . . . . . . . . . . . . . . 2-130 Chapter III. Designing Future Structures . . . . . . . . . . . . 3-1 A. Introduction . . . . . . . 3-1 B. Selecting the proper crest elevation for vertical protective structures . . . . . . 3-2 C. Selecting the proper stone armor weight for revetments * ' * . * ' ' ' * ' * ' ' * 3-7 D. Use of filter cloth in construction . . . . . . 3-19 E. Toe protection. 3-20 F. Provision of return walls to prevent structure flanking . . . . . . . . . . 3-20 G. Maintenance of structures . . @ . . . . . . . . . 3-22 Chapter IV. Discussion . . . . . . . . . . . . . . . . . . . . . . 4-1 A. Summary of observations 4-1 B. General design recommendations . . . . . . . . . 4-3 C. Selection of shoreline protection type . . . . . 4-3 D. Consideration of groins . . . . . . . . . . . . 4-4 E . Alternate Approaches - - Vegetative Control of Shore Erosion . . . . . 4-6 F. Alternate Approaches - Beach Nourishment . . . . . . . . . . . . . . 4-7 AN ASSESSMENT OF SHORE EROSION IN NORTHERN CHESAPEAKE BAY ,I- AND OF THE PERFORMANCE OF EROSION CONTROL STRUCTURES Chris Zabawa and Chris Ostrom, editors Prepared by Hsiang Wang, Robert Dean Robert Dalrymple, Robert Biggs Marc Perlin, and Vic Klemas Coastal and Offshore Engineering and Research, Inc. Newark, Delaware 19711 and Randall K. Spoeri United States Naval Academy Annapolis, Maryland 21401 Physical Descriptions of the Chesapeake Bay Shoreline Prepared by CIO Deborah Blades, Tina Dietz, Charles Griswold, Rhonda Howell, Rafael Perez, and Michael Perry Anne Arundel Community College C-7 Arnold, Maryland 21012 and Michael Thomas Lebanon Valley College Anneville, Pennsylvania 17003 Prepared for Coastal Resources Division Dr. Sarah J. Taylor, Director Tidewater Administration Maryland Department of Natural Resources Tawes State Office Building Annapolis, Maryland 21401. September 1, 1982 Preparation of this document was funded in part by NOAA, Office of Coastal rone.Management, and by the Maryland Department of Natural Resources Chapter V. Relationship o coastal processes to historic erosion rates . . . . . . . . . . . . . . . . . 5-1 A. Introduction . . ............................... 5-1 B. Historic erosion rates . . . . . . . . . . . . . . 5-2 C. Highly-eroding reaches . . . . . . . . . . . . . . 5-4 D. Relations of shoreline terrain and geology to coastal retreat 5-7 E. Relation of tide to coastal retreat . . . . . . . . 5-12 F. Relation of storm surges to coastal retreat . . . . . . . . . . . . . . . . . 5-17 G. Relation of wave climate to coastal retreat 5-24 H. Relation of littoral drift to coastal retreat . . . . . . . . . . . . . . . . . 5-37 I. Relation of rainfall to coastal retreat . . . . . . 5-46 J. Characteristics of highly-eroding reaches . . . . . 5-48 K. Classification of coastal characteristics . . . . . 5-59 Chapter VI. Statistical Modelling of Historical Shore Erosion Pattern . . . . . . . . . . . . . . . . . 6-1 A. Introduction . . . 6-1 B. Descriptive Statistical Analysis . . . . . . . . . 6-3 C. Regression Analysis . . . . . . . . . . . . . . . . 6-4 D. Discriminant Analysis . . . .. . . . . . . . . . . . 6-9 E. Summary . . . . . . . . . . . . . . . . . . . .. 6-11 Chapter VII. Land use and shore erosion . . . . . .. . . . . . . . . . 7-1 A. Introduction . . . . . . . . . . . . . . . . . . . 7-1 B. Methods . . . . . . . . . . . . . . . . . . . . . . 7-1 C. Results . . . . . . . . . . . . . . . . . . . . . . 7-5 Chapter VIII. References Cited . . . . . . . . . . . . . . . . . . . 8-1 Appendix A. Shoreline Sediments along the Chesapeake Bay in Maryland . . . . . . . . . . . . . . . . A-1 Appendix B. Examples of New Atlas Maps . . . . . . . . . . . . . B-l Appendix C. Glossary of Terms . . . . . . . . . . . . . . . . . . C-1 ACKNOWLEDGEMENTS We thank Lee Zeni, Moe Ringenbach, and Suzanne Bayley for reading the manuscript and providing valuable criticisms. The design of the study benefited from valuable discussions with Len Laresse-Casanova and Tom Morris of the DNR Shore Erosion Control Program, Randy Kerhin of the Maryland Geological Survey, and Paul Massicot of the Maryland Power Plant Siting Program. Abbie Ringenbach assisted in reviewing proposals and selec ting a contractor to perform the study. Harley Weiner of COER, Inc*. assisted in various field operations. Most of the illustrations were prepared by Dean Pendleton, Marsha Miller, Ruth Nuhn, Darryl Gurley, and Robin Checkla of the Johns Hopkins University, Illustrations Division. The maps and cover were drawn by Karen Mooring and Peter Lampell respectively, who also provided valuable assistance in producing the final report. We also thank Donna Klein and Kim Davidson for preparing the manuscript. The photographs were taken by Robert Dean, Robert Dalrymple, Marc Perlin, and Chris Zabawa. Special thanks go to the property owners at the shoreline sites for allowing ready access to DNR and COER, Inc. personnel, and for cheerfully participating in the study. We also thank Scott Zimmerman of the Maryland Natural Resources Police Force for piloting the airplane used to take aerial photos of the shoreline sites. Preparation of this report was funded in part by NOAA, Office of Coastal Zone Management, and by the Maryland Department of Natural Resources. EDITORS' NOTE For over Fifty years, erosion-control structures have been built in the northern Chesapeake Bay, either alone or in networks that stretch continuously along the shoreline. A recent study by the U.S. Army Corns of Engineers, The Chesapeake Bay Future Conditions Report (l977), finds that some areas with structural protection have persist- ent erosion problems, and other areas have aged or failing structures which are in need of improvement. The State of Maryland funds a program in the Department of Natural Resources with the purpose of providing the financial aid and engineering expertise that is needed to build erosion-control structures in problem areas. Decisions on maintaining the existing network of erosion-control structures, and on the public funding of new erosion-control projects in the northern Bay need to be made with some understanding of the performance of existing structures, and of the coastal processes and shoreline characteristics for which new structures need to be designed. This doctument describes selected shoreline structures in Mary- land's portion of the Chesapeake Bay, and discusses the physical processes of coastal erosion which affect their performance. The information that has been collected as part of this study was used to answer some important questions about shore erosion: 1. What are examples of success and failure of erosion- control structures? ii 2. What qeologic and hydrologic factors affect erosion and the performance of structures along the different types of Bay shoreline, in Maryland? 3. Do different types of land use cause different amounts of. shore erosion? This study report contains engineering evaluations of forty cases of structures which protect shoreline sites ranging from high bluffs to low banks, beaches, and marshes. The types of structures include: bulkheads, qroins, revetments, gabions, and well-rinqs. Each struc- ture is presented to illustrate its effectiveness in controlling fast- land loss, and soecific recommendations are provided to imorove the siting and.desiqn of similar structures in future shoreline situa- tions. The report also discusses the coastal processes along the main Bay shoreline, and illustrates their relationshit) to the historic rates of coastal retreat in different shorefront areas. Finally, the report describes land-use patterns along substantial portions of the northern Chesapeake Bay in Maryland, and discusses how the changing natterns of land iise in shorefront areas can be related to historic erosion rates. The data and analysis contained in this report provide answers to the questions above which should be useful to engineers, managers, decision-makers, and other persons who participate with interest in oublic forums and related discussions where the orotection of the Chesapeake Bay shoreline against further erosion is reqarded as a significant management issue. Chris Zabawa' Chris Ostrom- September 1, 1982 iii EXECUTIVE SUMMARY This report describes a study undertaken by the Maryland Department of Natural Resources to evaluate different types of erosion-control struc- tures, as well as several environmental factors which control rates of shore erosion, such as waves, tides, storms, and littoral sediment trans- port. A portion of the report contains forty "case studies" of shore erosion-control structures built around Maryland's Chesapeake Bay shoreline. Each "case study" included a site visit by a coastal engineering consultant to make important observations on the condition and performance of the structure in its shoreline environment. Another portion of this report describes the coastal processes that are responsible for erosion, and a statistical analysis which examined all the factors for their relationship to the historic erosion rate around the Bay margins. The major result of the study was that well-designed and constructed erosion-control structures are effective in stopping local shoreline erosion in the northern Chesapeake Bay, regardless of local geology, coastal morphology, wave energy, or other environmental parameters. Structures are successful in the northern Bay partially because of the relatively mild wave climate compared to the open ocean coastline. Several relatively low cost ($150.00 per foot) designs for structures can be effective along the northern Bay shoreline, but the individual character- istics of each structure (such as seawall elevation or revetment stone size) must depend on the particular physical setting. The results of the field evaluations by the independent engineering consultant showed most of the structures were successfully controlling erosion, even at the sites which had historic erosion rates exceeding ten feet per year before the structures were built. In a few cases the consul- tant suggested an alternative design which might perform better at a parti- cular shoreline site. These suggestions are included in this report, along with the consultant's observations on the condition and performance of the structures, and with photographs which illustrate the effectiveness of each structure in controlling the shoreline loss. Where available, informa- tion was also included in each "case study" about the initial cost of the structure and about the preconstruction engineering cross-section. Five of the forty "case studies" showed substantial deterioration which was judged to have been preventable through a different design, more effective maintenance program, or better understanding of the coastal processes. The deficiencies which were noted most of the time during the site visits were: 0 overtopping of structures by waves 0 lack of periodic maintenance and repair of damage to structures from storms or winter ice. iv After reviewing the modes of failure of some of the structures, the consultants recommended sloping revetments ("rip-rap") as their preferred strategy for many more shoreline situations on Maryland's Bay. This is because the materials used (stone) do not degrade with time; this type of strategy is less likely to fail catastrophically during a storm; there is less scour of sediment on the seaward sides of these structures; and the $trip-rap" generally provides a better habitat for biota than the treated wood or concrete used in other types of shore protection. Besides recommending sloping revetments for wider application on Maryland's Bay shorelines, the consultants also recommended using filter material in erosion-control structures under all circumstances, and more frequent maintenance of many erosion control structures. In designing and maintaining structures, serious consideration needs to be given to the combination of maximum tides and waves (run-up) which can be expected in the lifetimes of structures on the northern Chesapeake Bay. The height of structures necessary to prevent overtop- ping by waves depends on both the normal water depth at any shoreline site, and the maximum potential wave height. All structures as a minimum, should be designed for top elevations greater than the "annual" storm run-up to avoid serious damage due to wave overtopping. A simple procedure for determining the adequate heights of structures anywhere on Maryland's Bay shoreline is presented in Chapter III. The initial results of the statistical analysis seem to indicate that modelling the pattern of historic erosion rates around the e 'dges of the main Chesapeake Bay in Maryland cannot be suitably done by using traditional regression of discriminant analysis procedures. Areas with low, medium, or high.rates of coastal retreat were found to possess many similar characteristics of wave energy, tide, littoral sediment movement or other factors. But, there were no characteristics (such as high levels of wave energy, or high levels of- littoral sediment movement) which were found to be unique to areas of high erosion rates. V CHAPTER I INTRODUCTION Hsiang Wang, Robert Dean, Robert Dalrymple, Robert Biggs, and Randall K. Spoeri A. Purpose of the Study The shorelines of Chesapeake Bay are experiencing an erosion trend averaging approximately 2-3 feet per year. Since 1968, the State of Maryland through the Department of Natural Resources has maintained a program for technical and financial assistance to Bay-front property owners to mitigate erosion and, as of 1979, a total of $6.8 million in public funds had been appropriated for this purpose. The magnitude of this proqram and the importance of proper shore- line management are such that there is considerable interest in en- suring that the best designs for erosion control structures are de- veloped. This study evaluates the present design basis for existing structures and contains design recommendations for future erosion control structures which are based on environmental information that was synthesized from many sources to describe the wave, current, and wind forces acting on the northern Chesapeake Bay shoreline. B. Contents of this Report .Chapter II contains descriptions of forty case studies of shore erosion structures along the northern Chesapeake Bay shoreline which were selected for 4valuation to provide a variety of types and shoreline conditions. Each case study presents a hrief description of the type of materials and installation at the particular shoreline site, and assesses the performance of each structure relative to the 1-1 wave and storm conditions which can he expected. For the structures which had major flaws in design or construction, a corrective method is presented. Otherwise, the structures are rated on their present condition and comments are provided which are intended to help improve the performance of the different structural types when they are installed at new shoreline sites. Chapters III.and IV summarize the results of the field observa- tions of the forty "case studies", and develop recommendations for a future erosion control strategy in the northern Chesapeake Bay. Chapter V contains descriptions of the geologic and hydrologic charac- teristics along the Chesapeake Bay shoreline in Maryland, developed from field data and computer models. Each factor (shoreline type, tide range, storm surge, littoral drift, wave energy, and rainfall) is analyzed in a qualitative manner for its relationship to the pattern of historic erosion rates around the edges of the Chesapeake Bay in Maryland. Chapter VI describes an objective statistical analysis of the shoreline, which was undertaken with the data on individual reaches developed in Chapter V, in an effort to mathematically model the historic erosion patterns. The historic erosion rate was studied as a function of five explanatory variables: * dominant shoreline type * mean tide range e "100-year" storm surge * wave energy littoral drift. Three statistical methodologies were employed: * descriptive statistical analysis 9 regression analysis * discriminant analysis The statistical analyses which were performed to mathematically 'model the erosion rates used computer program packages and the actual reach data. Finally, Chapter VII examines the changes in land-use patterns which have occurred over the last few decades along substantial portions of the northern Chesapeake Say shoreline, and discusses the relation of these different land uses to the patterns of shore erosion on the same shoreline reaches. C. Results The major result of the study was that well-designed and con- structed erosion control structures are effective for stooping local shoreline recession in the northern Chesapeake Bay, regardless of the coastal morphology, wave energy, or other environmental parameters. Many of the forty "case studies" were judged to be satisfactorily controlling the shoreline loss in areas where the historic rate of coastal retreat had been as high as ten feet per year, or more before the structures were installed. Structures are successful in the northern Chesapeake Bay partially because of the relatively mild wave climate compared to the open ocean coastline. Another result of the study was that there is no strong relationship between any single cause of erosion and the historic pattern of coastal retreat around the edges of the northern Chesapeake Bay. The initial results of the statistical analysis seem to indicate that modelling the pattern of historic erosion rates around the edges of the main Chesapeake Bay in Maryland cannot be suitably done by using traditional regression of discriminant analysis procedures. The analysis is necessarily preliminary in nature, and further statistical tests may provide more conclusive results. There are many known characteristics which influence shoreline erosion rates: 0 waves, currents, and storm conditions, 1-3 0 type of material being eroded, 0 presence of vegetation along the shore, 0 height of bluff being eroded, 0 sheltering i)rovided by offshore islands or offshore bars 0 length of shoreline, * runoff or rainfall, seepage from bluff faces, 0 the freeze/thaw cycle, effects of nearby shoreline structures, 0 sea level rise. At any one shoreline location the erosion rate may be,due to a combi- nation of the above factors. Areas with low, medium, or high rates of coastal retreat were found to possess many similar characteristics of wave energy, tide, littoral sediment movement or other,factors; but, there were no characteristics (such as high levels of wave energy, or high levels of littoral sediment movement) which were found to be unique to areas of high erosion rates. After reviewing the modes of failure of some of the structures in the northern Chesapeake Bay, Coastal and Offshore Engineering and Research Inc. (COER) recommended sloping revetments as their preferred strategy for many more shoreline situations. This method for erosion control offers the fol,lowing advantages: (1) The materials used to build revetments do not degrade with time. 1-4 (2) Sloping revetments are unlikely to fail catastrophical- ly. (If design conditions should be exceeded slightly during a storm, inevitably some stones may become dislodged and can be replaced afterwards.) (3) Wave reflection from slopinq revetments is usually low; thus, less disturbance and less scour of sediments results at the toe of the structure. (4) Rubble generally provides a better habitat for biota than the materials which are used in most other types of shore protection. Another recommendation is for serious consideration to be given to the combination of maximum tides and waves (run-up) which can be expected in the lifetimes of structures on the northern Chesapeake Bay shoreline. Chapter III explains a simple method for determining the proper wall height of revetments, and the proper weight of the stone armor suggested for structures at any shoreline site. These recommen- dations will result in the cost of revetments exceeding the cost of timber bulkheads by approximately 30%, (timber bulkheads, as Dresently designed in the northern Chesapeake Bay, cost approximately 30% more than stone revetments as presently designed.) 0. Conclusions Based on the forty case studies of erosion control structures, it is concluded that: 1-5 (1) Relatively low cost (= ,150/ft) erosion control structures can he effective in controlling shore erosion around the northern Chesapeake Bay. (2) Revetments need to be strongly considered for future erosion situations due to their inherent durability. (3) Filter material needs to he used in erosion control structures under all circumstances. (4) Field demonstrations are needed to assess the effectiveness of innovative structures. Two examples are: (a) a groin compartment filled with sand selected to be sufficiently coarse that it will not move offshore during storms, and (b) the possible use of gabions only as a top stabilizing layer with the interior formed of smaller anqular rock fragments. (5) Most structures in the northern Chesapeake Bay do not cause substantial beach erosion alongshore. In part, this is because erosion of the fastland does not introduce large amounts of suitably-sized sand into the beach system. Thus, there are not substantial quantities of sand in littoral drift which can be intercepted by groins with subsequent sand starvation on adjacent "down-drift" beaches. 1-6 (6) Erosion control structures need to he monitored followinq extreme events, such as hurricanes or severe winter storms. The information obtained will aid in future selection and design of structures. (7) The procedure developed in Chapter III for establishing the crest elevations of protective vertical walls should be systematically incorporated into the design of new structures. (8) There needs to be frequent monitoring and maintenance of coastal structures. Protective coatings need to be maintained on hardware, sheeting, and Pile tops. Splits@ in wood need to be mended on aging bulkheads, and any backfill which has washed out behind vertical orotective structures needs to be replaced. Flanking erosion at the ends of any structure needs to be stooDed. Dislodged stones in revetments need to be repositioned. (9) Under some circumstances, man's activities such as land use could have an effect on shore erosion, but an attempt to quantify the effect of land use on erosion rates was not successful because it is not possible to locate an area where the land use had remained stable over a time span of several years for which there is a known erosion rate. How- ever, based on coastal engineering and geological consider- ations different types of land use (agriculture, woodlands, urban) are not expected to be a dominant factor influencing erosion. (10) The existinq data on rainfall distribution were also compiled as part of this study to be used to assess the effect on erosion of bluff shorelines in different areas, but the existing data were found to be insufficient for this nurpose. 1-8 CHAPTER II EVALUATION OF EROSION CONTROL STRUCTURES Robert Dean, Hsianh Wang, Robert Biggs, and Robert Dalrymple A. Introduction Many different kinds of engineering structures have been installed alon the northern Chesapeake Bay shoreline (Figure 2.1) to protect sites ranging from high bluffs to low banks, beaches, and marshes. The shoreline sediments which are armored by the structures range from gravelly sands to stiff clays. The structures themselves must endure a wide range of differ- ent wave, tide, longshore current, and storm conditions. This chapter presents "case studies" of forty different sites where structures have been installed for erosion protection. Each structure is presented to illus- trate its effectiveness in controllin fastland loss, and COER, Inc., was asked to make specific recommendations which would improve the siting and design of similar structures in future shoreline situations. The forty case studies include: 0 14 sites with timber bulkheads 0 4 sites with concrete bulkheads 0 3 sites with aluminum bulkheads 0 1 site with asbestos cement bulkhead 0 16 sites with stone revetments 0 4 sites with gabions 0 15 sites with groins Next Pages: Figure 2.1. Schematic drawings showing types of erosion control structures installed along northern Chesapeake Bay shoreline. 2-1 Figure 2.1 COAMISM WALL 0 0 0 HEM% lZR CONTwdOU* TAW-ME SO ow joo goo 60"', 0, 00 . c- :9 . 0 so * Glee op. .0 1 !40 0 Go :.0 0 whow I to, 06; w age & _0 .0@ 0 d6 .0. to 00 :Exls WIRE BA607 CU4010) F i LO MMMAR 0 00 a 0 a .00, 0 a 00, 0 00 off 0 Of so so 00" OL 0 d A ISIO foosee 00 610 0 too a klek 00 o 51EEL 6"EET g =UA)D BACX PIL 0 a V140 0 00 goo a *0 g6400 It 0 tpq WALE cgs a 0 0,00160 0 0000 cc', - 00 .4-0: jo 00 0 0. 0 0 00 0 0 0 @5MEL bU"LKH 00 0 90 0 0 0 !9-. 11 1100 000 2-2 Figure 2.1 "OK A?P-M -Colt lnt6TEcrl 0#4 15E-DDIN)C\ -6-TomE )AVER MW 10 A X C\UA)D 06*00 f4bo4.1:00, SrON E R 1,7 ONO Soo o -db- EXifnAjc\ 41WND so Le .0:00.2,03 too .90 1 090 & 00 * TMEER 15ULOE4 - 2-3 0 1 site with well-rings 0 1 site with concrete pipes The following pages discuss the evaluations on a case-by-case basis, for different portions of the Chesapeake Ray shoreline in Maryland. Each "case study" contains photohraphs along with descriptions of engineering criteria, hydrologic conditions, and nearshore characteristics. Where available, information is also included about the cost of the structure at the date of construction, about the historic erosion rate at the site before the structure was built, and about the pre-construction engineering cross-section. The results of the field evaluations show most of the structures are successfully controlling coastal retreat, even at the study sites which had historical erosion rates exceeding ten feet per year or more before the structures were installed. In a few cases, COER, Inc. suggested an alter- native design which might perform better at a particular shoreline site. Five of the forty case studies showed substantial deterioration which was judged to have been preventable through a different design, more effective maintenance program, or better understanding of the coastal processes. This investigation of a number of successful and unsuccessful shore erosion-control structures shows the need for property owners to use competent engineering expertise and top-of-the-line construction methods when planning and building a new shore protection project. There is a real potential for resources to he wasted through a combination of quick designs and improper construction methods. This report is not intended to address the economic considerations involved in projects requiring the least ex- penditure, and therefore, a smaller and more compact structure. Rather, the "case studies" were selected to illustrate the performance of struc- 2-4 tures along different types of shoreline on the Chesaneake '@av in 11arvland, and to show instances of success and failure of structures. It is important to note in the case studies that construction costs per linear foot are stated for the year of expenditure. These costs can be adjusted to 1980 levels through a published method of cost indexing contained in the weekly engineering magazine Engineering News Record. The method for determining approximate costs for construction is contained on the following page in Table 2.1. This method may not tndicate the true inflation rate for marine construction, but is included for illustration purposes only. The costs of structures are also reflected in actual 1980 bid prices for shore erosion-control projects built by the Department of Natural Resources Shore Erosion Control Program. Number if Average Cost Range of Costs Type of Structure Structures Per Foot Per Foot stone revetments 18 $124.24 $101-00 - $219.18 aluminum bulkhead 2 $141.19 $135.47 - $199.89 timber bulkhead 15 $211.54 $161.33 - $328.47 Total Cost $2,213,183.60 $143.87 average cost per foot. Total Footage 15,383.4 L Tabl e 2. 1 f rom: Engineering flews Record BUILDING COST INDEX HISTORY 1913-1990 How ENR builds the Index: 68.38 hours of skilled labor at a 20-cities average of bricklayers', carpenters' and structural ironworkers' rates, plus 25 cwt of standard structural steel shapes at the mill price, plus 22.56 cwt (1.128 tons) of Portland cement at a 20-cities average orice, nlus 1,038 feet of 2 x 4 lumber at a 20-cities average price. BUILDING COST INDEXES: 1913 = 100 1954 = 446 1963 = 594 1972 = 1048 1955 = 469 1964 = 612 1973 = 1138 1956 = 491 1965 = 627 1q74 = 1204 1957 = 509 1966 = 650 1975 = 1306 1958 = 525 1967 = 672 1976 = 1425 1959 = 548 1968 = 721 1977 = 1545 1960 = 559 1969 = 790 1978 = 1674 1961 = 568 1970 = 836 1979 = 1819 1962 = 580 1971 = 948 1980 = 1943 EXAMPLE: TO COMPUTE A CONSTRUCTION COST INCREASE FROM 1974 TO 1980: (a) Divide 1980 index by 1974 index: 1943 4 1204 = 1.61 (b) Mul ti ply to adjust 1974 cost to 1980 level 1974 cost x 1.61 = 19RO cost Adjusted costs determined by this method will be below changes.in the CPI (Consumer Price Index) as published by the U.S. Department of Labor, and may not indicate the true inflation rate for marine construction. This is intluded for illustration purposes only. B. Cases along the Lower Eastern Shore of the Delmarva Peninsula This area of the northern Chesapeake Bay contains portions of the shoreline in Dorchester County, Wicomico County, and Somerset County (Figure 2.2). The sections below present a brief physical description of the shorelines and coastal Drocesses, followed by a discussion of the case studies which were selected from this area. SHORELINE DESCRIPTION Dorchester County The Chesapeake Bay shoreline in Dorchester Count1v runs from the mouth of the Choptank River to Hooper Island. Shorefront areas contain heavily-wooded lands, agricultural fields, and some scattered residential development with shoreline structures at different noints. The shoreline along most of Trippe and Brannock Bays and Taylors Island is composed of exposed eroding banks which generally range from 3-6 feet high. The width of the beach at the base of these banks is extremely variable. At some sites, a beach is absent in front of the banks and trees growing along the land's edge are falling off the banks into the water. In other areas, a beach is present which extends landward into wooded areas, or onto farmlands. This is evidence of active beach erosion and coastal retreat. Next Pages: Figure 2.2. Shoreline along the lower eastern shore of the Delmarva Peninsula in Maryland. Figure 2.3. Some representative shoreline nrofiles collected in the summer of 1980 along the lower eastern shore of the Delmarva Peninsula in Marvland. 2-7 TAL50T COUNTY CHOFrrANKI. ASKYAM al, muls vr. 110M45 urr@O=Pjkw JAows r%. ..-* IWAAMP VIEAWA DoRcHESTER 'MYLO" IgtA%s3 couArry I WICOMICO V%W WJAA Lm ?Tl COUNTY 5ALISBURY Is AAWX k OCRWD - W45 RiN ur@ ASQojTA t5- ZWO MR NWMCOk-. t - apvl"g SIVOL&fff -WIMATU W%rrci4Av" I -r'AIV7rlcbvg ------------- $ IMOVAIT 1161WOM 50MERSET VAftell QUARTaiz L CRAMM 79MESS, 44.wc CHESAMM BAY do. V"L WEAVANVA %6 urPeR FAWvoov 6.#)A*W 11. 70=0KE J. AMomosex 4R. WEL@- 0 /a L 2 -.q Figure 2.3 SHORELINE PROFILES Dorchester County-Cook Point LOWER EASTERN SHORE 10 OF THE 5 - DELMARVA PENINSULA 0 U- SUMMER1980 -5 100 5 0 Feet 0 Dorchester County Taylors Island beach ........... 5 0 -5 ------ IF 200 150 foo 50 0 Feet Somerset County-Hazard Point beach 5 . . . . . . . . . . . . . . . . . . .......... 0 LL -5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 150 100 50 0 Feet Somerset County-Noah Ridge beach .10 5 LL 200 150 loo 50 0 Feet 2-9 On Hooper Island, the shoreline contains many erosion structures protectinq residential development. The lower r)ortion of HooDer Island is larqely undeveloped, and marshes along the shoreline are interrupted hv beaches of varying lengths. Some of these beaches contain berms or small vegetated dunes. Behind Hooper Island, the shoreline on the Honqa River and in Fishinq Bay is composed principally of marsh which ends abruntlY at the water's edge in most spots. Some small pocket beaches are present for distances of 200-2000 feet along the shore. A few of these beaches stretch for longer distances and are backed by isolated banks between 3 and 8 feet high. Shorefront development in this lower portion of Dorchester County is largely restricted to the areas shown on the map. 1wicomico countyl_ A small part of the Wicomico County shoreline which was included in the study runs along the lower reaches of the Nanticoke River estua ry below Long Point. Between Lonq Point and the Town of Nanticoke, the shoreline is comoosed of vegetated banks fronted either by sandy beaches or marsh. In some areas, the beach profile extends landward into wooded shorefront areas, and trees next to the beach are dyinq or falling into the water. There is enough sand present at most points to form berms on the-shor.eline orofiles, and the beach sediments are stabilized by shrubs and beach grasses. Shorefront homes have been built all along this reach, both on low sandy flats next to the beach, or on higher qround which slopes gently down to the water's edge. At the Towns of Rivalve, Tyaskin, and Nanticoke, many structures have been installed to protect shorefront development. 2-10 A-long arcuate beach extends along the shore south from the Town of Nanticoke to Roaring Point. This beach protects a heavily wooded area, and enouqh sand is present in the shoreline system at this point to form wide vegetated berms and small dunes in front of the trees. A large sand spit extends out from the land at Roaring Point almost to the main channel of the Nanticoke River. Relow Roaring Point, the shoreline is composed largely of beaches backed by sandy banks ranging from 3 to 10 feet. Most shorefro'nt homes are separated from the water by@ a buffer strip of lawn qrass, beach and berms. Where woodlands are present next to the shore, the beaches may be interrupted by stands of trees or small marshes which-extend down to the water's edge. !Somerset countyl Much of the Somerset County shoreline is composed of marsh with pocket beaches extending from 500-2000 feet alonq the shore. In the Big Annemessex River and Manokin River estuaries, marsh sediments form the northern shores, and long arcuate beaches form the southern shores. Small vegetated dunes are observed landward of these beaches in some areas. The remaining shorefront areas on Janes Island, on Cedar Island, and along Pocomoke Sound are also composed of marsh and intermittent beaches of variable length which often have small vegetated dunes. The Smith-Island shoreline contains marsh interlaced with many tidal creeks. Along Tangier Sound, the Smith Island shoreline contains marsh which ends abruptly at the wate'r's edge in most spots. On the Chesapeake Bay side of Smith Island, the shoreline contains some small sandy beaches and dunes. In many spots, these sand deposits are located only between 2-11 marsh and the waterline. Immediately seaward, the underlying marsh sediments are once again exposed in the nearshore zone of breaking waves. The shoreline on Deal Island and Dames Quarter is markedly different than in the lower portions of Somerset County. Here, most of the shoreline contains exposed sandy banks at least 6 feet high with beaches of varying widths at the waterline. There is also a large remnant sand dune in the middle portion of Deal Island. Coastal residential development extends along much of the shoreline of Deal Island and Dames Quarter together with many groins and bulkheads. Shorefront development and bulkheading are also present on the Somerset County shoreline at the towns of Ewell and Tylerton on Smith Island, around Crisfield, and at several smaller towns along the Big Annemessex and Manokin Rivers. Coastal Processes Many of the historical erosion rates for the lower Eastern Shore are greater than 8 feet/year (see Chapter V). The shoreline sediments which are eroded include the fine-grained sands of the Quarternary and Kent Island Formations, and younger marsh and alluvial deposits (Appendix A). The mean tide range varies in the area from 1.3 to 2.1 feet, dependinq on the shoreline location. The storm surges from "annual" storms are between 2-3 feet at all locations, and the surges from "100-year" storms can be greater than 4 feet above mean low water. Waves during these severe storms can be as high as 4 feet on top of the storm surqes. Waves in the area approach from the northwest and southwest with the longest fetches. But the waves travel across large shoals offshore in many 2-12 spots, and the wave energy can dissipate somewhat before reaching the beach. Thus, wave conditions on windy days and during "annual" storms are not exceptionally severe. The wave and storm conditions are discussed in greater detail along with the other coastal processes in Chanter V. I case Studies The structure case studies selected in this area include: Case No. Structure 0 1 A stone revetment on Taylors Island (598 feet long). 0 2 stone revetment on Taylors Island (206 feet long). 0 3 A stone revetment on Taylors Island (990 feet long) with 2 stone groins each 60 feet long. 0 4 A stone revetment in front of a timber bulkhead on upper Hoober Island (95 feet long). 0 5 A stone revetment (295 feet long) with 2 stone groins (104 feet total length) in Tar Bay. 0 6 A stone revetment on upper Honga Island (686 feet long). 7 An aluminum bulkhead at Parks Neck on the Honga River (502 feet long). 2-13 Case No. Structure 0 8 A timber bulkhead on Asquith Island in the Honga River (827.5 feet long). 0 9 A timber bulkhead in Trippe Bay (727 feet long). 0 10 A timber bulkhead (266 feet long) on the south shore of the Choptank River with 2 stone groins, each approx. 50 feet long. 0 11 A segmented stone revetment, in Brannock Bay (727 feet long). 0 12 A stone revetment (i069 feet long) on the south shore of the Choptank River. The following pages present brief descriptions of each structure, and near- shore bottom nrofiles collected at the sites. Most of the cases assiqned for the lower Eastern Shore were in gd'nerally fair condition. Some struc- tures were flanked by erosion at noints alongshore, and almost all of the structures showed evidence of wave splashover. A few of the structures do not have adequate height to orevent wave overtoppinq durinq severe storms as shown on the cross sections on the following pages. For Case No. 7, a redesign is suggested here to correct a serious deficiency due to the short return walls or the failure to extend these walls sufficiently landward as erosion continued. The historical erosion 2-14 rate is about 5 feet/year and the return walls with their 600 angles have an effective landward extent of only 12.6 feet. Theoretically this short wall at a site whose historical erosion rate is 5 feet/vear requires remedial efforts at least every 2.5 years, since in this amount of time, the flanking erosion reaches the end of the wall. Over.5 years have elapsed since construction with no additional wall extension , and a considerable amount of fastland loss has occurred. 'An appropriate design would be 900 angled flanked walls (i.e. perpendicular to the beach front), thus providing the greatest landward distance. These walls should be over 25 ft. in length, thus providing a minimum of 5 years flanking protection. At the end of 3 to 5 years, an additional- wall extension would have to be driven. Periodi-c extensions of the flank wall would have to be made in the future as well as on an as-needed basis. More discussion on the design of return walls to prevent flanking of new structures is contained in Chapter III. A reliable method for selecting the proper wal I elevation for revetments and vertical walls is also described in Chapter III. 2-15 CASE 1 A STONE REVETMENT ON TAYLORS ISLAND Structure was completed in 1978 at a cost of $84.56/ft. The historical rate of erosion at the site was 10.5 ft./yr. from 1848-1942. Stone revetment, on a 2:1 slope, consists of 400-1200 lbs. stone in a 3 ft.-thick armor layer. A bedding layer 8 in. thick was placed below the armor layer. Bedding layer con- sists of 3-8 in. stone. Filter material was used below beddinq layer. This structure is in generally good condition. Severe erosion and failed structures can be observed directly adjacent to this case. 2-16 IN ML Ali, tiff I KA; CASE 1 A STONE REVETMENT ON TAYLORS ISLAND 2-17 CASE 2 A STONE REVETMENT ON TAYLORS ISLAND Structure was completed in 1977 at a cost of $72.82/ft. The historical rate of erosion at the site was 10.5 ft./yr. from 1848-1942. Stone revetment, on a 2:1 slope, consists of 400-1000 lbs. stone in a 3 ft.-thick armor layer, with 8 in.-thick bedding layer. Revetment has m-shaped well-ring structure on sea- ward side, and connects to a well-ring structure alongshore in one direction. There is flanking erosion alongshore in the other direction. Sand has not been impounded in the lobes of the well-ring wall. This structure is in generally fair to good condition, but is constructed of smaller stone than other revetments along the same shoreline reach. 2-18 4 ,*41 j A wed, al sp@ 0, CASE 2 A STONE REVETMENT Oil TAYLORS ISLAND 2-19 CASE 3 A STONE REVETMENT WITH STONE GROINS ON TAYLORS ISLAND Structures were completed in 1975 at a cost of $44.80/ft. for the revet- ment, and $50.00/ft. for the groins. The historical rate of erosion at the site was 10.5 ft./yr. from 1848-1942. Stone revetment on a 2:1 slope, consists of 450-1200 lbs. stone in a 2.5 ft.-thick armor layer. A bedding layer 6 in. thick, composed of small stone, was placed below the armor layer. Filter material was used below bedding layer. Additional splash apron, 13 ft. wide, was installed. Two stone groins appear to be serving no useful purpose, as no beach was observed in the summer of 1980. This structure is in generally good condition. Owners report the revetment sustained no damage during Tropical Storm David (Sept. 1979). The presence of submerged tree stumps offshore is evidence of hiah erosion rates prior to installation of structure. 2-20 MN, iiA6 MIN ph =-,p Au CASE 3 A STONE REVETMENT WITH STONE GROINS ON TAYLORS ISLAND 2-21 CASE 4 A ST0NE REVETMENT IN FRONT OF A TIMBER BULKHEAD ON UPPER HOOPER ISLAND Structure was completed in 1977 at a cost of $67.55/ft. The historical rate of erosion at the site was 1-2 ft./yr. from 1848-1942. Stone revetment, on a 2:1 slope, consists of 400-1000 lbs. stone. Revetment fronts a timber bulkhead. Splashover apron, composed of 3-8 in. stone, is installed behind the timber bulkhead. Filter cloth was used under both the revetment and the stone apron. This structure is in generally good condition. 2-22 JOL .440 CASE 4 A STONE REVETMENT IN FRONT OF A TIMBER BULKHEAD ON UPPER HOOPER ISLAND 2 L- 2 3 CASE 5 A STONE REVETMENT WITH TWO STONE GROINS IN TAR BAY Structure was completed in 1977 at an approximate cost of $67.47/ft. for the revetment, and $50.00/ft. for the stone groins. The historical rate of erosion at the site was less than 2 ft./yr. from 1848-1942. Stone revet- ment, on a 2:1 slope, consists of 400-1000 lbs. stone in a 3 ft.-thick armor layer. A bedding layer, 8 in. thick, composed of 3-8 in. quarry stone, was placed beneath the armor layer. Filter material was used below the bedding layer. The revetment has a 10 ft.-wide splash apron. Two stone groins are 62 ft. and 42 ft. long. A sand beach has accumulated and covered the toe of the revetment in the summer of 1980. These structures are in generally good condition. 2-24 'low A 0 777::711,, vUi M N 7r 3.0,1 400 LB. TO 1000 LB. ARMOR STONE :,@,END OF FILTER CLOTH 10 END OF FILTER CLOTH APPROX. EXISTING GROUND EXISTING GROUND END OF FILTER CLOTH -5 STONE GROIN NO. 2 m m 0 EXCAVATE BOTTOM TO 0 MLW PRIOR TO PLACING FILTER CLOTH FOR STONE GROIN - - -5 55 50 45 40 35 30 25 20 15 10 5 0 -5 FEE7 CASE 5 A STONE REVETMENT WITH TWO ST014E GROINS IN TAR BAY 2-25 CASE 6 A STONE REVETMENT ON UPPER HOOPER ISLAND Structure was completed in 1977 at a cost of $66.15/ft. The historical rate of erosion at the site was 1-2 ft./yr. from 1848-1942. Stone revetment, on approximately 2:1 slope, is in good condition. This structure fronts several properties, and is doubly-reveted in some portions. Revetment also extends onto the fastland to different heights up to 7.5 feet above MLW, in front of different properties. 2-26 NNW 1.1% 1 '@, @ "k, @ X6 IMAM IML0,116 CASE 6 A STONE REVETMENT ON UPPER HOOPER ISLAND 2-27 CASE 7 Ail ALUMINUM BULKHEAD AT PARKS NECK ON THE HONGA RIVER Structure was completed in 1975 at a cost of $42.50/ft. The historical rate of erosion at the site was 5 ft./yr. from 1848-1942. Bulkhead consists of 103 aluminum corrugated panels, each 4.8 ft. wide, 0.10 in. thick, 8.5 ft. long. Short return walls of at least 14.6 ft. each used at each end have been lost due to flanking. About 50 feet of recession has occurred since emplacement of the structure. Overtopping occurs during storms, and material is being lost through the wall. An inspection report prepared in 1978 indicated (1) failure is due partly to one year delay in backfilling the structure; (2) structure exhibits lack of maintenance; (3) structure may have been partly damaged initially by heavy equipment used durinq backfill operation. 2-28 o"W oil CASE 7 AN ALUMINUM BULKHEAD AT PARKS NECK ON THE HONGA RIVER 2-29 CASE 8 A TIMBER BULKHEAD ON ASQUITH ISLAND IN THE HONGA RIVER Structure was completed in 1976 at a labor cost of $38.92/ft. All materials were provided by the property owner at an unknown cost. The historical rate of erosion at the site was 3.5 ft./yr. from 1848-1932. Bulkhead consists of 10-12 inch diameter pile, 12 ft. in length, on 9.5 ft. centers; 2X1O in. tongue-in-groove sheet pile, 10 ft. long; and dead- men with 3/4 in. galvanized tie rods on the landward side. Asphalt coat- ing on top of piling is in poor condition. No filter material was used. At least one patch has been applied to prevent loss of material through the wall. The structure is bordered by an eroding headland on one side and an eroding shoreline on the other. 2-30 [E-Z @RId V9NOH 3HI NI ONVISI HlInosv NO GV30ino @39V!Ii V 2 3SVO WOO 4- 4w 0 OIA -AIL 4 IOW rrm EMIR", In CASE 9 A TIMBER BULKHEAD IN TRIPPE BAY Structure was completed in 1975 at a cost of $65.43/ft. The historical rate of erosion at the site was 1-2 ft./yr. from 1847-1942. Structure consists of 16 ft. pile; 3 in. x 10 in. tongue-in-groove sheeting, 12 ft. long; and 14 ft. long deadmen, 10 ft. back, tied to the wall with 3/4 in. galvanized rod. Copper caps are installed on tops of piles. Some evidence of overtopping by waves was noticed at this site. Dead grass near bulkhead is evidence of salt damage to vegetation. Significant flanking erosion was observed at ends of the structure in the summer of 1980. 2-32 LJL Ali IM CASE 9 A TIMBER BULKHEAD IN TRIPPE BAY 2-33 CASE 10 A TIMBER BULKHEAD ON THE SOUTH SHORE OF THE CHOPTANK RIVER WITH 2 STONE GROINS Structure was completed in 1978 at a cost of $92.15/ft. for the bulkhead and $22.72/ft. for the groins. The historical rate of erosion at the site was 1 ft./ yr. from 1847-1942. Bulkhead consists of 10-12 in. diameter pile, 18 ft. long; 3 in. x 10 in. x 12 ft. tongue-in-groove creosoted sheetpile; and 2 wales. Deadmen are 16 ft. long. Piles are covered with 16 oz. sheet copper cap. Two stone groins are approximately 50 ft. long. Fillet had formed on the left sides in the summer of 198O. Natural grass is growing on the beach to the left of the groins. There is evidence of splashover at this site. 2-34 SNIOH 3MOiS Z HiIM @DM VlVidOHO Ri JO DOHS iiinOS 3HI NO GVPNino @39V!Ii V OL 3SV3 133J 99 09 99 09 9t, ot, 92 02 9z oz 91 01 9 0 H10-10 83 1-11:1 @NnOW@ .DNIISIX@ X .OkIddV -10 h131-liz.I :io H 1.0 m,lv4.0'E+ M-lv, g e + -9 m OV3H)nna 83ena Lol H1013 k131114 11 Z/1 I ZAI NIMIS IS- "P @Q2 I 'L " ' @@ - ..@@Rs@ CASE 11 A STONE REVETMENT IN BRANNOCK BAY Structure was completed in 1975 at a cost of $25.00/ft. The historical rate of erosion at the site was 4 ft./yr. from 1847-1942. Stone revetment, on a 2.5:1 slope, consists of 250-1000 lbs. stone in a 2-3.5 ft.-thick armor layer. A 3 ft.-wide splash apron was also installed. This structure is in generally good condition; but, there is active flanking erosion alongshore, as evidenced by a 4.3 ft. scarp in the adjoining exposed clay bank. 2-36 AVq 'A3ONNVH NI IN3Wi3A3d 3NOIS V LL 3SV) AM @q@@@MtIk@10 OPR@ V6. d,000 4 .0 i @ ; 00 - -i@, N7 Im - W CASE 12 A STONE REVETMENT ON THE SOUTH SHORE OF THE CHOPTANK RIVER Structure was completed in 1977 at a cost of $61.00/ft. The historical rate of erosion at the site was less than 1-2 ft./yr. from 1847-1932. Stone revetment, on a 2:1 slope, consists of 400-1000 lbs. stone in a 3 ft.-thick armor layer. Bddding layer is 8 in. thick, composed of 3-8 in. stone. Filter cloth was used below the bedding layer. This structure is in generally good condition. The ties located offshore appear to have been used in a breakwater consisting of regularly-spaced pilings which held the tires. Automobiles and an old cement truck were also placed in the nearshore to control erosion. 2-38 '4 FPI K 4&0 AL jb op . ILI. -MEL. '40 Not- maKsmor-21@ CASE 12 A STONE REVETMENT ON THE SOUTH SHORE OF THE CHOPTANK RIVER 2-39 C . Cases along the Lower @4estern Shore This area includes portions of St. Mary's County along the Chesaneake Ray and lower Potomac River (Figures 2.4, 2.5). The sections below oresent a brief physical descrintion of the shoreline and coastal nrocessps, followed by discussion of the case studies. I St. Mary's Countyl The Chesapeake Bay shoreline in St. Mary's County runs from the Patuxent River mouth to Point Lookout. 'The northern portion of this reach contains the Patuxent Naval Air Station, and the shoreline at the southern end is within the houndarIv of Point Lookout State Park. Shorefront areas in between contain heavily-wooded lands, fields, and scattered residential develooment protected at different points by erosion- control structures. There are exoosed eroding banks in many areas which range in height from 3-8.feet. The beaches on the shoreline profiles are of varying widths; in a few cases, there are well-develoned berms on the summer beach profiles with grasses or small shrubs stabilizing the sand. A portion of the shoreline included in the stiviv alonn the lower Potomac River contains wide beaches composed of coarse sand and gravel. Near Point Lookout and Piney Point, shorefront homes are separated from the water by a wide vegetated buffer strij) of beach and berms. Elsewhere wood- lands and fields are nerched on exposed eroding banks next to the beach. !lCoastal, Processesl Many of the historical erosion rates for the lower Western Shore are less than 4 feet/year (see Chanter V). The,mean tide range in the area is about 1.0 feet. The storm surqes.from "annual" storms 2-40 are about 3 feet, and the surqes from "100-year" storms can be qreater than 4.5 feet above mean low water. Waves during these severe storms can he as high as 3-5 feet on top of the storm surges, denendinq on the tvne of storm and its orientation relative to the fetches in the area. Waves in the area approach from the west, south, and northeast with the longest fetches. The annual wave energy on the shoreline is higher in this area than in many other areas farther north on the Chesapeake Ray. Shorefront areas exnosed to the long fetch from the south are particularly susceptible to wave attack from tropical storms. The wave and storm conditions are discussed in greater detail along with the other coastal orocesses in Chapter V. T tudies for structures selected in this area ICase Studies he case s include: Case No. Structure 0 13 Stone revetment near Point Lookout (1564 feet in length). 0 14 A timber bulkhead at Tall Timbers on the Dotomac River (1204 feet in length). The following Daqes present brief descriptions of each structure, and nearshore bottom profiles collected at the sites. Next Pages: Figure 2.4. Shoreline along the lower western shore of the Chesapeake Ray in Maryland. Figure 2.5. Some renresentative shoreline nrofiles collected in the summer of 1980 alonq the lower western shore of the Chesapeake Ray in Mar@yland. 2-41 Figure 2.4 cowm ClItSAPEAKE BAY CHARLES comy SUM STMARYS COUNTY @mv -mwtj pot @..o (-*PAR 9r. All *se4vvl)e awrok) Uy CXTOAJ *T.#%Ws it. IN SaVA WTOMAclk. 44 Cny VAMEIKOA) pow me, .57. If owla % poon jo ,41 4,re Figure 2.5 St. Mary's County SHORELINE PROFILES 15. Turkey Neck beach LOWER WESTERN SHORE 10. SUMMER1980 5. ------------ U_ 0. fff -5 0 50 100 Feet St. Mary's County-Point Look-In 5. 0 0. -5 0 50 100 Feet St. Mary's County - Comf i eld Point beach 10 .5 --------------- .......... -- ----- ------------ Lj W ---------------- AAAAAVWV .0 @,-pgg -5 150 loo, 50 0 Feet St. Mary s County-McKay Beach,( 5 . . . . . . . . . . . 0 - --- ------ - U_ -5 . . . . . . . . . . . 150 100 50 0 Feet 2-43 CASE 13 A STONE REVET14ENT NEAR POINT LOOKOUT Structure was completed in 1974 at a cost of $132.96/ft. The historical rate of erosion at the site was 5-14 ft./yr. from 1849-1942. Stone revetment on a 2:1 slope consists of 1400-2800 lbs. stone in a 4 ft.-thick armor layer. A bedding layer, 1 ft. thick, of smaller stone was placed below the armor layer. Filter material was used below the bedding layer. The revetment has a 20 ft.-wide splashover apron. This structure is in generally good condition. There is a -recedingl shoreline alongshore to the north of the structure. Eighty-five feet of shoreline recession has occurred there since the structure completion date. Nearshore profile I[= 15 :1 vertical exaggeration) .1 7 Case 13 100-year Survey Date: 7/12 /80 Run- up (11 .7') 10 - y e a r 5 PROFILE I P PROFILE 2 4 A nnuol Uj 3 Run-up U- z Tide z Range__ DISTANCE OFFSHORE (FT) 0* > UJ -1 50 100 150 200 Uj -2 -3 5 3 321 50 100 160 201 -41 2-44 ANN.- Mip, .14 lie ir Akg% oft@ ego! kMbt IN: CASE 13 A STONE REVETMENT NEAR POINT LOOKOUT 2-45 CASE 14 A TIMBER BULKHEAD AT TALL TIMBERS ON THE POTOMAC RIVER Structure was completed in 1976 at a cost of $112.19/ft. The historical rate of erosion at the site was 1.5 ft./yr. from 1868-1968. Bulkhead consists of a wooden sheetpile with an offshore batter pile. Two stone groins (not part of this project) are trapping small amounts of sand, but no beach exists in front of the bulkhead. One of these groins, 80 ft.-long, was added in 1979 at a cost of $156.00/ft. to act as a breakwater intended to reduce splashover. The bulkhead is in generally good condition. There is evidence of splashover at the site, and the bulkhead has flanking erosion alongshore at one end. 2-46 fniip 4L 40 71*4- WL. 7Z@ CASE 14 A TIMBER BULKHEAD AT TALL TIMBERS ON THE POTOMAC RIVER 2-47 D. Cases alon the Calvert County and Lower Anne Arundel County shorelines This area contains the shoreline between the Patuxent River mouth and the Chesapeake Bay Rridge (Fiures 2.6 and 2.7). The sections below pres- ent a brief physical description of the shoreline and coastal processes, followed by a discussion of the case studies which were selected from this area. SHORELINE DESCRIPTIONS Calvert County The Calvert County shoreline along the Chesapeake Bay is composed mainly of large bluffs, hiher than 5O feet in many areas, which extend for several thousand feet at a stretch along the water's ede. The bluff faces are mostly exposed and eroding, hut they are covered with vines and shrubs in a few places. Sections of the bluffs are senarated by ravines and stream valleys which contain either woodlands or marsh. The beaches at the base of these bluffs are of varying widths and may contain small berms on the summer shoreline nrofiles. At Cove Point and near Long Beach, the beach is separated from the bluffs by a wide flat terrace which contains trees and open grassy areas. Most of the shorefront bluffs adjacent to the main Chesaneake Bay in Calvert County are heavily-wooded, with scattered residential develonment in among the trees. More concentrated residential development protected by shoreline structures can he found at the communities shown on the man. Houses in these areas are located both along the bluffs, and on the low berm that extends landward immediately adjacent to the beach. 2-48 Above the Town of Chesapeake Beach in Calvert County, the shoreline is composed of low banks ranging in height from 3-12 feet. Much shorefront residential development is nresent, and erosion-control structures form a nearly continuous network along the water's edge in some spots. The few tinprotected areas contain beaches at the base of the shoreline banks, and marshes. ILower Anne Arundel County] The lower Anne Arundel County shoreline extends from Herring Bay to the Chesapeake Ray Bridoe. This area is characterized by gently rolling hills between 15 and 80 feet high. In Herring Ray, and in the lower reaches of the West, Rhode, and Severn Rivers, the hillsides end at the shoreline in steen, exposed, eroding bluffs and high banks. The beach at the base of these hillsides is narrow or absent, and trees growing along the land's edge are often falling off the shoreline banks into the water. In most other shorefront areas of lower Anne Ariindel County, the steeQ hillsides are covered with trees and shrubs, or they slope gently down to the waterline. On isolated points of land, the beach may he separated from higher ground hv a wide low terrace containing trees, grassv areas, or marsh. Pocket marshes are also present in protected coves. Elsewhere, a beach of varying width is nresent on the shoreline profile, and the beach sands are stabilized by shrubs and qrasses in many locations. Next Fiqure 2.6. Shoreline along Calvert and lower Anne Arundel Pages: Coijntv on the Chesaneake Ray in Maryland. Figure 2.7. Some representative shoreline profiles collected in the summers of 198n and 1981,along the Calvert and lower Anne Arundel Countv shoreline. 2-49 Figure 2.6 ,"pu3wp lb 74 ZAY WM%Q A -rAll ZVA -49vefw R. kwcou- ItivIc I i a Rt&%AtAOUDS9rAtH COLLIN6014 AfUOWL- OA) -T*s BA V JKALW"-fkl& , IMOIA" ". SAY SOMA. 09YF-IZL-4 OCACH Weems. r Aw .sHft.4 :slue Avnf.@- CDUkM "AL ASRAM4 Rose J(AVlZN WIMM AQNLbDRO CALVMT C&WTY VD-T CAESAMKE IDAV.05 PoSVA RAY MTCUArr R. rkoVear,)0% likVA) $RCOA41-1. 15. ST UZY-5 6T. CXAMY SOLOJ"Ais calm W. Figure 2.7 Anne Arundel County- SHORELINE PROFILES Beverley-Triton Beach CALVERT COUNTY ANDLOWER ANNE 10 ---------- --- --------- --- 5 - ARUNDEL COUNTY SUMMER 1980 U- 0 - - - - - - - - - - - - - - - - - - - - - - ----------------- ............ ------------ -5- ................. 0 50 100 Feet Calvert County- Randle Cliff 80- FEET --- -- - ------- ------------------------ 5. --------------- -- - -------- ------------------ 10- 5- U. 0- --------- . . . . . . . . . . . -5- ------------ 0 50 100 Calvert County-_ ove Point Feet Sill -------------- 0 -5 6 50 160, 150 200 Feet 2-51 Most communities contain concentrated residential shorefront develon- ment. Some houses have landscaped hillsides leading down to the water. Ilanv houses are Drotected by erosion-control striictures which often form a nearly-continuoits network along the water's edqe. Retween Annapolis and the Ray Rridqe, the terrain in shorefront areas on the Bay is noticeably flatter, and shoreline banks are generally less than 10 feet hiqh. The banks are covered with trees and hedqerows in some areas, and contain structures in other areas. Shorefront residential development is found orincipally in protected coves. Most houses in these areas are separated from the water by a wide vegetated buffer strip. Icoastal Processes Many of the shoreline reaches in Calvert and lower Anne Arundel County possess historic erosion rates between 2 and .11 feet per year. There are a few sites where the shoreline is stable or accretinq. The shoreline sediments which are eroded include (Iravels and a wide variety of sandy deposits in the Wicomico, St. Mary's, Chontank, Calvert, Nan-iemolv, Aquia, and Maqothy Formations (Annendix 4). The mean tide range in this area varies from 0.9 and 1.2 feet. Storm surqes from "annual" storms are around 2 feet, and the surqes from "100-year', storms can be 'qreater than 5-6 feet above I'lean Low '4ater. Waves during these severe storms can be as hiqh as 3-4 feet on top of the stor surge. 14aves in the area approach from the northeast and southeast with the longest fetches. The shallow nearshore zone is very narrow all along the Ray shoreline in Calvert County, and few reaches are sheltered from waves. However, in lower Anne Arundel County, some shorefront areas are sheltered from the longest wave fetches due to irreqularities in the shoreline. 2-52 Other shorefront areas which are exnosed to the longest fetches also possess broad shallow nearshore zones over which wave energies dissinate before reachinn the beach. The wave and storm conditions are discussed in more detail along with other coastal processes in Chapter V. The structure case studies selected in this area include: Case No. Structure 0 15 Timber bulkhead at the U.S. Naval Research Laboratories at Randl e Cl i f f (4297 f eet I ong) . 0 16 Timber bulkhead at Dares Beach (86 feet long). 0 17 Gabions and wood groins at Scientists Cliffs. 0 Is Stone revetment at the Westinghouse Laboratories on Broad Neck, below the Bay Bridge (2100 feet long). 0 19 Gabions at Thomas Point Park in the mouth of the South River. 0 20 Aluminum bulkhead at Hillsmere Reach on the lower South River. 0 21 Concrete bulkhead on the south shore of the Severn River near Tolly Point. 0 22 Asbestos cement bulkhead on the south shore of the South River near Hillsmere Reach. 0 23 Timber bulkhead (230 feet long) at Turkey Point on the lower South River, with rubble qroins. 9 24 Lonq Point The following pages oresent brief descriptions of each striicture, and nearshore bottom profiles collected at the sites. Some of the structures 2-53 assiqned as cases were in qood condition, but some have exnerienced nartial failure. A few of the structures evaluated do not have adequate heiqht to Drevent wave overtonninq dijrlnq storms, as shown on the nearshore bottom Drofiles. Continued erosion of the fastland was also noticeable in some cases. The paragraphs below contain suggestions for maintenance, redesigns and improvements for several of the structures to correct serious desiqn deficiencies. case 16. A timber bulkhead at Dares Beach The timber bulkhead at this pronerty is too low to adegiiately nrotect the upland property from solash-over and cliff base erosion. From infor- mation develoned in the next chanter, a wall height of 8 ft. above the bottom would be recommended at this site to accomodate wave run-up from the If Annual Storm". This is almost 2 ft. higher than at present, and this new elevation will still not orevent bank erosion. The weathering of the cliffs will continue until a vegetated equilibrium slope is achieved. This slope could he artifically maintained by slope stahility measures similar to those used by hiqhwa,v engineers, such as smal,l stone and/or venetative measures. Case 17. Gabions and wood groins at Scientists Cliff Scientists Cliffs (+60 feet) seem to be recedinn at a slow rate nartlY because their sediments are verv durable. Cliff damage is largely the result of the eros,ion of the cliff base hv waves and weatherinn. The present qroin system at the I)ase of the cliffs is not sufficient to main- tain a beach which is adequatelv wide to nrovide cliff nrotection as well 2-54 as to limit the transport of weathering products away from the area. There are several alternate means to stabilize the beach and cliffs in this area. These are described below: Alternative #1 The Randle Cliff anDroach - A sijhstantial bulkhead seaward from the base of the cliffs. This bulkhead will not permit a beach to form; however, it will prohibit shoreline retreat. The rate of cliff erosion will slow, since only weathering of the upper cliff face will continue to dislodge the fastland sediments. A groin system which would be filled with sand at the time of construction, and then periodically checked and nourished, could maintain a beach in this case. Alternative #2 Stone revetment - This will work in the same manner as Alternative #1, hut a natural beach may form in front of the revetment. Groins may be necessary to hold the beach, since there is a siqnificant net littoral trans- nort of sediment to the south. If a revetment is hOlt sliahtlv seaward from the nresent base of the cliffs, the initial cost of the protection will be higher, hut weathering of the cliff face should he slowed somewhat due to the structural protection against wave action. This could reduce the hazard to shorefront homes; hijt, erosion of the exposed cliff face will still continue. 2-55 Alternative #3 Groins and beachfill - The existing qroin field has not trapped a significant volume of sand. 9y ensur- inq that the qroins are sand-tiqht and bv usinq beach nourishment, a significantly-wide (say 20 ft.) beach may be constructed. This beach will serve as a buffer to storms, but will require maintenance. Otherwise, after a few years, the beach will be gone. All the above approaches would work to forestall erosion; however, they are all expensive and would require a concerted community-wide action alonq the entire shoreline reach. Case AA-2 Gabions at Thomas Pt. Park in the mouth of South River The initial design of this system appears to be adequate for wave and storm conditions. It is important, however, that a nroper maintenance orogram be instituted. As the qabions fail and the stones wash out, the structural integrity hegins to deteriorate. A renlacement Dronram for failed gabions must be instituted now and a biennial effort should be made to replace new failing nabions. 2-56 2-57 CASE 15 A TIMBER BULKHEAD AT RANDLE CLIFF This structure was completed in 1969 at an unknown cost. The historical rate of erosion at the site was 2 ft./yr. from 1847-1934. Structure consists of creosoted sheetpile, 4 in. x 12 in. x 15 ft. long. Batter piles were installed on the seaward side, except where prohibited due to remnants of a previous 40 year-old steel sheetpile wall. The new structure was placed within 100 feet of the bluffs. This structure is in generally good condition. Weep holes and drainage pipes were installed to keep earth pressures low behind the wall, as well as to accomodate runoff from the bluff face. Erosion of the cliff is continuing at sites alongshore where no structures are present. But at this case study site, the cliff is stabilized, as evidenced by the vegetation on the bluff face. Nearshore profile 15:1 vertical exaggeration) 7 Case 15 10 0-year R un-up 13.0') 6/5/80 10-year Run-up ( 8.7') Survey Date: 6 "A n nual 5 Run-up W 3 W LA_ ..:: '. *.2 Z Tide Range 0 DISTANCE OFFSHORE (FT) 0 W 50 100 150 200 _j W -2 -3 -4 2-58 WPM 't -J66 -11W WWI, n@7 6y A A&ANAL 11A CASE 15 A TIMBER BULKHEAD AT RANDLE CLIFF 2-59 CASE 16 A TIMBER BUCKHEAD AT DARES BEACH Structure was completed in 1975 at a cost of $122.21/ft. The historical rate of erosion at the site was 3 ft./yr. from 1848-1934. The timber bulkhead is composed of 18 ft.-long pile, and 12 ft.-long sheetpile. Several 16 ft.-long batter piles were installed on the seaward side to bolster the structure. Some stone groins are also present in the vicinity of the structure. A small amount of sand has been impounded in the fillets at the base of the groins. But elsewhere, a beach is absent. This structure is in generally good condition. The structure extends along- shore in front of several separate properties. There is significant overwash during strong wave conditions and there is evidence of continued bluff erosion. To the south, a neighboring property has a seawall installed which is approximately 18 in . higher, and evidence of wave overtopping at that site is noticeably less severe. To the north, the case structure does not quite connect with another bulkhead, and severe erosion and removal of the bluff face has taken place in the gap. "100-year" Run-up (12 -0 7 - Nearshore profile M 5:1 vertical exaggeration Case 16 "10-year" Run-up (8.91 Survey Date:'7/12/80 Annual" 5- PROFILE I Run-up - PROFILE 2 * -- 4 W. (70' north of Profile 1. W U_ .3- Just north of 90' long z 2 stone groin Tide z - Range 0 DISTANCE OFFSHORE (FT) > 0. _j 50 100 150 200 W -1 2. 4 2-60 JAW P-m Ja imp- + 'MOW 0 14 I 4' ilkpoow- CASE 16 A TIMBER BUCKHEAD AT DARES BEACH 2-61 CASE 17 GABIONS AND WOOD GROINS AT SCIENTISTS CLIFFS The historical rate of erosion at the site was about I ft./yr. from 1848- 1943. The groins are approximately 20-30 years old. The gabions have been installed in more recent times. The cost,of these structures is not known. .The structures were installed to prevent sand transport away from the base of the bluffs, and thus provide a beach to dissipate wave energy. These groins are of a unique construction. Well-rings were used to stabilize the substrate, and piles which hold the wooden groin panels in place were augered into the bottom. Later, gabions were used to extend the landward ends of the groins. These structures are in generally fair condition. However, the groins have not stopped the wave attack on the cliffs. Nearshore profile 15:1 vertical exaggeration) 7 17 "100-year Run-up 10. 7') Case Survey Date: 7/12 /80 10-year" Run-up (7.9') 6 - 5 "Annual Run-up 4 3 W. U_ Z Tide Z Range 0 DISTANCE OFFSHORE FT) 0. T. H > W - N.-Ij 50 100 150 200 W -2 *:o o -3 fo 4 2-62 CASE 17 GABIONS AND WOOD GROINS AT SCIENTISTS CLIFFS 2-63 CASE 18 A STONE REVETMENT NEAR THE BAY BRIDGE The structure was completed in 1969 at an unknown cost. The historical rate of erosion at the site was about 3 ft./yr. from 1845-1942. Revetment, on a 2:1 slope, consists of 30-300 lbs. stone in a 2 ft.-thick armor layer. A bedding layer of gravel 1 ft.-thick was placed below the armor layer. There was no filter material installed below the bedding layer. The revetment also has a concrete cap 1 ft. x 1.5 ft.-thick installed along the top. This structure is in generally fair to poor condition. Parts of the structure failed during Tropical Storm David in early September 1979. The wall still provides some protection to the property though. 2-64 44 -A go's .1 4@0 44 CASE 18 A STONE REVETMENT NEAR THE BAY BRIDGE 2-65 CASE 19 GABIONS AT THOMAS POINT PARK The historical rate of erosion at the site was less than 3 ft./yr. from 1847-1970. The structure is composed of stones in plastic covered wire baskets. The gabions are stacked in 3 levels, 4 baskets-wide at the base; 2 baskets-wide in the next layer; and 1 basket on top. On the landward side, filter material was used. Behind the filter material, a 10 ft.-wide rubble apron has been installed to protect the upland from further overwash. This structure is in generally good condition. However, a number of the gabions in the base layer are failing. The baskets corrode when the plastic coating is abraded; and, as holes form, the wave action washes out the stones. The baskets have no structural strength without the stone. "100 - year Nearshore profile (= 17:1 vertical exaggeration) 7 Run-up ( 13.3') Case 19 "10-yeor" Survey Dote: 9/4/80 6 R -up ( 9. 0') un 4 M r-n 3< "Annual" > Run-up 20 Tide z Range 2 DISTANCE OFFSHORE (FT.) A _T1 0M rn 200 150 100 50 f* 4 M rn 3< 20 PZ I Z @@@l 5 O@@@@@5 0. '00 -3 1-4 2-66 AF 7" 41 CASE 19 GABIONS AT THOMAS POINT PARK 2-67 CASE 20 AN ALUMINUM BULKHEAD AT HILLSMERE SHORES The historical rate of erosion at the site was about 1 ft./yr. from 1847- 1970. The bulkheads at this stte form "headlands" that extend out into the water at both ends of the beach, to prevent the beach sand from washing out. The bulkhead at one end of the beach is composed of "Shoreall" aluminum bulkheading fronted by rip-rap in an 8 ft.-wide revetment. At the other end of the park, a timber bulkhead is installed. These structures are in generally good condit(ion. At both structures, grass is growing offshore, and is stabilizing the*nearshore bottom. 7 Nearsh ore prof i I e (= 15: 1 vertical exaggeration) "100-year Case 20 Run-up (7.5') 6- Survey Date: 9/4/80 "10-year"-- 47 Run-up LLJ LLJ LL_ 3 Annual"-- 2 Run-up Z T ide Range RE (FT) > DISTANCE OFFSHO 141 0." T _j . - 50 100 150 200 -2 -4 2-68 WA-0 WAN AL -mom 54 J@Z@N-fS, V@@ w p jj 00 p'' Ir CASE 20 AN ALUMINUM BULKHEAD AT HILLSMERE SHORES 2-69 CASE 21 A CONCRETE BULKHEAD NEAR TOLLEY POINT This structure protects a site composed of high vegetated bank with a failed patio. The date and cost of the structure are not known. Structure was composed of a concrete wall , apparently @about 5 feet high, which failed several years ago, judging from the condition of the remaining rubble on the beach. Continuing erosion has resulted in the loss of a house apparently located on top of the bank. "100 - year" 7 - Nearshore profile (=15:1 vertical exaggeration) Case 21 Run-up (11.4') 6 - Survey Dote: 9/4/80 10- year" 5 - R u n- up (7. 3') Concrete 4 - wall "Annual Which Run-up 3 - Failed U_ 2 - Z* Tide Range 0 . DISTANCE OFFSHORE (FT) 0 W @O 100 150 260 _J -2 .00 1.50 21 50 2-70 PM@ 4, or, -d=W op -4-6; AwO 1'C@4@ AN --mmozzlommomm- CASE 21 A CONCRETE BULKHEAD NEAR TOLLEY POINT 2-71 CASE 22 AN ASBESTOS CEMENT BULKHEAD NEAR HILLSMERE BEACH This structure protects a site composed of a low grassy bank. The date and cost of the structure are not known. The structure is composed of asbestos concrete sheet pile panels. Filter materials were used behind the wall. Stone groins flank the structure at both ends alongshore. The groins are very low, and are about 65 feet long. This structure is in generally fair to good condition. It was damaged during Tropical Storm David in early September 1979. At present, a crack extends across several of the sheet pile panels, but filter cloth behind the wall helps to keep the fastland from washing out. Although the groins are very low on the shoreline profile, there is a beach present in the vicinity of the site. Offshore is composed of very fine gray muddy sand. 7- Neorshore profile (=15:1 vertical exaggeration) 100-year Case 22 Surge (7.6') Survey Date: 9/4/80 "10 - year"-- 4 Surge UJ W U_ An nuo I z -2 Surge Tide Range DISTANCE OFFSHORE (FT.) T 0 100 150 200 Uj -2- 1.00 1 iO@ 21 50. -4 2-72 dft Nfr.@ 4 T "@' CASE 22 AN ABESTOS CEMENT BULKHEAD NEAR HILLSMERE BEACH 2-73 CASE 23 A TIMBER BULKHEAD WITH RUBBLE GROINS ON THE LOWER SOUTH RIVER Structure was completed in 1970 at a cost of $48.70/ft. The historical rate of erosion at the site was 1.5 ft./yr. from 1847-1970. Structure consists of timber bulkhead which is angular in planform. To the south alongshore, the neighboring property has installed several 8 ft.-long concrete pipes laid out perpendicular from the shoreline to act as groins. To the north alongshore., 3 concrete rubble groins are present. The bulkhead is in generally good condition. The rubble groins are extremely effective in trapping littoral sediments, and pocket beaches are present between the groins. The concrete pipe groins have trapped some sediments to form a smaller beach, but these structures are not sand-tight. 2-74 41 .. GEM INMI A'o CASE 23 A TIMBER BULKHEAD WITH RUBBLE GROINS ON THE LOWER SOUTH RIVER 2-75 CASE 24 LONG POINT There.are no structures presently at this site, though remains of a smal,l.bulkhead are evident. The historical rate of erosion at the site A was-up to a maximum of 2.5 feet per year (at the middle of this shoreline reach) from 1847-19,70. Mayo Point to Long Point is a stretch of shoreline containing bluffs ranging from -15 to 30 feet in height, and a beach approximately 10 feet wide at high tide. Mayo Point appears to be accreting. However, the remaining portioh of the shoreline reach is experiencing erosion. Relics of the*bulkhead structure. provide evidence that the bulkheading utilized 4 inch piles with 2 inch x 12 inch, and 2 inch x 7 inch planking, 2 to 5 planks high. Presently this structure is having no beneficial effect on the shoreline. "100 -year" 7 Neo rshore prof iie 17:1 verl icai exaggeration Surge (7.0 Case 24 6 Survey Dote : 5/1 /81 5 PROFILE I - PROFILE 2 4- '10-year"- PROFILE 3 Surge PROFILE 4 Uj 3- Uj NOTE:NO STRUCTURES PRESENT Z 2- "Annual" Surge Z. Tide 0 Range DISTANCE OFFSHORE (FT.) TT 0 51@ 190 150 200 Uj _j Uj -2 -41 2-76 INIOd ONOI V@ 3SVO i@F ;jtmkl imtsml 'N VC o 15, t lp, NO E. Cases on the Upner Western Shore of Chesaneake Rlav This area of the northern Chesapeake Ray shoreline (Figures 2.R and contains nortions of Anne Arundel County, Baltimore and Harford Counties, and Cecil Countly. The sections below present a brief ohysical description of the shorelines and coastal processes, followed by a discussion of case studies which were selected from this area. SHORELINE DESCRIPTIONS upper Anne Arundel County sho The upner Anne Arundel Countv shoreline extends from the RaY Rridqe to Baltimore Harbor. This area is characterized hy gently rolling hills between 1@ and 70 feet hiqh. Alonn the Patapsco River shoreline, these hills end in exnosed eroding shoreline banks about 20 feet hiah in many soots, but farther south along Gibson Island and Broad Neck, the hillsides more often slone (jentlv down to the water's edge, or are covered by trees and shrubs. The beaches at the base of these hillsides are of varvinq widths, with considerable gravel present in some spots on the shoreline profile. At Sandy Point, the beach is separated from higher qround by a wide flat terrace containing trees, qrassy areas, and parking lots of the Sandy Point State Park. Shorefront development is concentrated at the many communities shown on the riaD. Houses are oresent both in amonq trees on the hillsides or in on en qrassY areas. Erosion control strtictures are nresent in different 2-7R spots, and a beach mav or may not he nresent alonq with bulkheadinq or revetment strtictures. Some houses have landscaped hillsides leadinq down to the water. jRaltimore7c7o:u@nt@y The portion of the Raltimore County shoreline included in the study extends from the mouth of the Patapsco River to the mouth of the Gunpowder River. Along the Patansco River, shorefront areas contain concentrated industrial development and many shore-erosion control structures. Some marshes are found in protected coves and at the heads of creeks. At North Point, the shorefront contains trees and qrassy slopes on the grounds of the Fort Howard Veterans Hospital. Immediately north along this shoreline reach is Black Marsh, which is fronted by a wide shallow nearshore area of sandy mud. Hart and Miller Islands are composed of marsh and woodlands on low banks, fronted by a heach and wide sandy herm. The beach on Hart Island extends into the woodlands, and trees along the shore are dying or fallina off the banks into the water. This is evidence of active erosion and shoreline retreat. r_xcept for Bayliqht Reach, directly across the inlet from Hart Island, shorefront communities are located hehind Hart and Miller Islands, and farther inland alonq the shores of Back and Middle Rivers. Homes on these reaches are either on the tops of low banks, on hillsides which slope Next Pages: Figure 2.8. Shoreline along upper Anne Arundel, Baltimore, Harford and Cecil Counties Figure 2.9. Some representative shoreline profiles collected in the summer of 1981 along the upper Western Shore of Chesapeake Bay. 2-79 Figure 2.8 i MARPOWD CECIL CDUOTY COUAPTY CoAjotow(. VAM CAVL657bWAl HAVUr ve AWRXEN BAunmow WVAITV a L CAMP 5 lRaveR Tuft"l 0" WAIAC JOPPATOWA TW5C;A) JlRooftAVA OAMATO BAL-nmoim 24cm it, ZVa WOO 4"&Wq(- ?AlVSCO DtWPALK rs ?r gf,*N"R IS YA) f'qA*T A % COV. SAW A WE BAY H MY 51DE 3FACH SOV14A) FFT. J` AANE LAkC-4HORC- VlAfEHvee,,r AIWOML CDOMIry CA PC 07. o LAtab $Amoy Tr. 14Y somAr 2-80 Figure 2.9 L Cecil County- 20 SHORELINE PROFILES Red Point UPPER WESTERN SHORE 15 OF THE .10 CHESAPEAKE BAY 5 LL SUMMER 1980 0 ............................ -5 150 100 50 0 Feet Harford County- Oak ngton bluffs 15 10. 5- ------------ 0. .......... . ... ..... -5- so 100 Feet Baltimore County-Hart Island 15 10- 5- LL ........... - --- ------- 0- .............. .......... 0 50 100 150 Feet 10 Anne Arundel County -Sandy Point 5- - -------- - ------------ --- ------ . . . . . . . . . . . . . . . . 00. ----- -- --- /VVVVV%AA ............ . . . . . . . . . . . . . . . . . . . . . . . . . -5 0 50 100 150 200 Feet 2-81 (iently down to the water, or in low-lvin(i areas protected hv networks of erosion control structures. Above Middle River, the Baltimore County shoreline contains few homes or other types of buildinqs, and shorefront areas consist orincipallv of marsh interrupted by beaches which extend for 500-2000 feet along the shore. At the mouth of the Gunpowder River, the beaches on Carroll Island are very wide and are separated from the marsh by vegetated diines. Upstream on the Gunpowder River, exposed erodinq hanks again appear along the water. These contain woodlands, and the open grassy areas of Gunpowder State Park. Farther upstream, residentialdevelopment it located along the shoreline overlooking the Gunpowder River delta. H a r f o r d c7o7u_n7ty] The.Chesapeake ;ay shoreline in Harford County is largely within the boundaries of the Aberdeen Proving Ground (Edgewood Arsenal) to which public access is restricted. This shoreline contains low exposed erodinq banks with beaches of varyinn width. Marshes are nresent in sheltered areas, and on isolated noints of land. Shorefront areas overlooking the Bay contain woodlands and open grassy areas, but few h0l di n(is. There are broad shallow areas upstream in the Rush River estuary which are often exposed at times of low tide. Shorefront residential Hevelooment is oresent along the upper reaches of the Rtish River, and erosion-control structures are stabilizing the low banks in some soots. Between Aberdeen and the Town'of Havre de Grace, the shoreline consists of hiqh veqetated hanks or hillsides fronted hv beaches containinq some.gravel and cobbles. Below Havre de Grace, most shorefront areas are heavily wooded and a few houses are visible on the hillsides in amonq the 2-82 trees. Concentrated residential and commercial develonment is oresent along with many erosion control structures on the shoreline at Havre de Grace. Farther upstream on the Susquehanna River, the shoreline, contains wooded areas and exposed rn.ck walls which are fronted @y narrow sandy heaches in most spots. Cecil Cotinty Along the Susquehanna River above the Town of Perry- ville, the shoreline consists of heavily-wooded land and rock walls. Large boulders and coarse gravels are the most common type of beach material on this shoreline reach. Some c6ncentrated shorefront development protected by erosion-control structures is present at the Town of Port Deposit. From Perryville to Charlestown, shorefront areas contain municinal development, recreational facilities, and homes, on banks ranqinq from S to 20 feet in height. The upper reaches of the Northeast River contain marsh and broad tidal flats, backed by fields and woodlands. At the Town of Northeast, the shoreline consists of qently rolling hills ranninq from 20 to 40 feet in height. In some snots, the hillsides end along the shore in exposed eroding banks, and in other nlaces the land slopes qently down to the water's edge. Homes are oresent all along the shore from the Town of Northeast to Red Point. Beaches along this shore- line reach are widest in nrotected coves. Elsewhere, the hillsides have small beaches or erosion-control structures at their bases. Relow Red Point, the shoreline consists of high wooded hills which are protected by wide qravel beaches. A few homes and recreational facilities are nresent along the shore, but much of the area is within the houndary of Elk Meck State Park. The hills form a series of headlands which extend out from the land into the Northeast River. @etween the headlands are a series 2-83 of sheltered embavments which contain marshes or wide qravelly beaches. The bluffs bordering the Shoreline are covered with trees, vines, and shrubs; but, Steen erodinq bluff faces are exnosed in some areas, narticii- larly along lower Elk Neck around Turkey Point. Homes and vacation cottages are present both along the bluffs and in low-lying areas next to the beach in the sheltered embayments. ICoastal Processesl Many of the historical erosion rates for the upper western shore are less than 4 feet Der year. But some ex.nosed noints of land have historic rates of erosion up to 8 feet per year. The shoreline sediments which are eroded include fine-grained silts, clav beds, sand, and gravel deposits of the Potomac Group, Upland Denosits, and other qeoloqic formations listed in Annendix A. The mean tide range in the area varies from 0.9 to 1.6 feet dependinn on the shoreline location. The storm surqes from "annual" storms are between 1 and 2 feet, and the surges from "100-year" storms can he qreater than R feet above Mean Low Water. Waves durinq these severe storms can be as hiqh as 4 feet on too of the storm surge. Waves in the area approach from the southeast and northeast with the lonqest fetches. Portions of the shoreline along the lower reaches.of rivers also receive wave enerqy from the northwest winds blowing down the river channels. Shallow offshore areas ranqe in width with different shoreline orientations, and much of the wave energy can dissipate before reachinq the beach. The nresence of substantial oravel and boulder denosits on the beach nrofile in some locations also helps to armor the beach aqainst wave -@rosion. 2-84 The wave and storm conditions are discussed in nreater detail along with the other coastal processes in Chanter V. The structure case studies selected for this area include: Case No. Structure 0 25 A buttressed concrete seawall, bulkhead, and timber groins north of Gibson Island. 0 26 A timber bulkhead/stone revetment on Middle River (381 feet long). 0 27 Gabions on Gibson Island, with groins. 0 28 Aluminum bulkhead on Back River (175 feet lonq) 0 29 Concrete bulkhead north of Gibson Island (aonrox. 2600 feet long). 0 30 Concrete bulkhead and concrete aroins near Hawkins Point. 0 31 A well-rinq bulkhead on Broad Neck. The following pages present a brief description of each structure and nearshore bottom profiles collected at the sites. Plany of the case structures appeared to be in good condition and will Drotect the fastland against adverse wave conditions. There were no serious nroblems which could not he prevented with routine maintenance. There were no redesigns suggested for this area. CASE 25 TI14BER BULKHEAD, GROINS, AND BUTTRESSED CONCRETE SEAWALL NEAR GIBSON ISLAND These structures protect a site composed of vegetated bluff. The date and cost of the structures are not known. The historical rate of erosion at the site was less than 1 ft./yr. from 1845-1970. A variety of structures are present at the site. These include an L-shaped concrete seawall, buttressed with triangular concrete sections. A splashover apron 8 feet wide has also been installed on the landward side. This concrete seawall is separated from a timber bulkhead alongshore at one end. Approximate- ly 9 feet of shoreline separating the two structures is filled with rip-rap. The timber bulkhead is fronted with both rip-rap and timber groins approximately 20 feet long. These structures are in fairly good condition. Some maintenance work could improve the wall in some locations. The groins have not trapped substantial amounts of sand to form a beach. 100-year Nearshore profile (=17:1 vertical exaggeration) -7 Run-up(13.1') Case 25 Survey Date: 8 /29/80 -6 to- year Run-up (8.5') "Annual" -4 rn Run-up r-I rn *3- < 2 C) Tide z ,Ra nge DISTANCE OFFSHORE (FT.) 200 150 100 50 M TT @4 rn r 3 rn o 2 0 z I z 0 1 -3 -4 2-86 vow vlow, pow 9i @W' Oil -mml@ Ag Afilat.- CASE 25 TIMBER BULKHEAD, GROINS, AND BUTTRESSED CONCRETE SEAWALL NEAR GIBSON ISLAND 2-87 CASE 26 A TIMBER BULKHEAD AND STONE REVETMENT 0N MIDDLE RIVER Structure was completed in 1978 at a cost of $115,60/ft. The historical rate of erosion at the site was about 2.5 ft./yr. from 1847-1936. Timber bulkhead consists of 3 in. x 10 in. tongue-in-groove sheetpile, and walers 6 in. x 8 in. The planform of the wall is S-shaped. A 10 ft.-wide rip rap toe has also been installed at the base of the structure on the seaward side. This structure is in generally excellent condition. The wall is constructed to extend very high up the bank face and limits splashover from the worst wave conditions. The rip rap at the toe of the structure provides added protection against wave scour and erosion of finer-grained sands and silts of the natural bottom. 2-88 ir AIL "- 4V rc X a. .40 4W CASE 26 A TI14BER BULKHEAD AND STONE REVETMENT ON MIDDLE RIVER 2-89 CASE 27 GABIONS ON GIBSON ISLA14D WITH GROINS These structures protect a site composed of a low bank that is eroding in some spots, and covered with trees, shrubs, and grass in others. The historical rate of erosion at the site was about 2-3 ft./yr. from 1845-1970. The groins were completed in 1970 at an unknown cost. Gabion structures have recently been installed to form a revetment at the base of the bank. Two groins, also composed of gabions, are in place offshore. This structure is new and had not experienced severe conditions at the time of the site visit. The gabions extend far up the bank face to protect against waves and tidal flooding from all but the worst conditions for this shoreline reach. too- year Nearshore profile I= 17:1 vertical exaggeration) Run-up 01.61 Case 27 1110- .1 Survey Date: 8/29/80 6 year Run up (7.4') "Annual 5 Run-up 4 rn r- M > '2 0 Tide Range DISTANCE OFFSHORE (FT) 0 -n M rn 200 150 100 0 -2 0 50 7 1 '00 50*** 2-90 OP % ..................... CASE 27 GABIONS ON GIBSON ISLAND WITH GROINS 2-91 CASE 28 ALUMINUM BULKHEAD ON BACK RIVER Structure was completed in 1974 at a cost of $70.00/ft. The historical rate of erosion at the site was about 2.5 ft./yr. from 1846-1944. Structure consists of corrugated aluminum sheetpile 0.125 in. thick and 10.1 ft. lonq. A deadman anchoring system is connected to the wall by tie rods 3/4 in. in diameter and 14 ft. long. This structure is in generally good condition. There is evidence of splashover at the site, but there are no problems with flanking erosion alongshore since the wall connects with other vertical structures on both ends. 2-92 Amp--- - 00, 70-0.", All am's", AS AK- CASE 28 ALUMINUM BULKHEAD ON BACK RIVER 2-93 CASE 29 A CONCRETE BULKHEAD NEAR GIBSON ISLAND This structure protects a site composed of eroding bluff. The historical rate of erosion at the site was less than 1 ft./yr. from 1845-1970. The structure was completed in 1929-1931 at an unknown cost. Structure consists of concrete seawall approximately 7 feet high. At least two differ- ent pours of concrete were used to build the wall, and the different sections are joined by rebars. Stone groins have been implaced at a few locations in front of the seawall. This structure is in poor condition. The rebars have failed in several places, and this failure has contributed to general wall failure. The groins have accumulated some sand to form a beach offshore, but the amounts of sand in each groin pocket are very small. 100- year" Nearshore profile (= 17: 1 vertical exaggeration) Run-up ( 13. 1') Case 29 6 Survey Date: 8/29/80 10- year PROFILE 1 5 un- up PROFILE 2 '*.*.a Annual M r- Run - up M 3 < r2 0 Tide Z Range 0 z DISTANCE OFFSHORE (FT) *?j0_-4;1 *0_11 M q C.0 . rn 200 150 100 50 -3 2-94 7 WWI A&A. rA NINO J% pool CASE 29 A CONCRETE BULKHEAD NEAR GIBSON ISLAND 2-95 CASE 30 CONCRETE BULKHEAD AND GROINS NEAR HAWKINS POINT These structures protect a site composed of a high terraced bank. The historical rate of erosion at the site was less than 2 ft./yr. from 1845- 1970. The date and cost of the structures is not known. Structures consist of reinforced concrete seawall with a concrete splash- over apron. Three tiers of concrete walls are stacked up the slope of the shoreline bank. The last tier is about 20 feet above the water level. A masonry dock and groin system has also been installed at the base of the wall. The groins are spaced about 30 feet apart. These structures are in generally good to fair condition. The structure evidently suffered some damage (which has been repaired) from a 1956 hurricane. Presently, there is freeze/thaw damage requiring the owner to periodically repoint the masonry walls. The groins have not trapped any amounts of sand from the natural littoral drift to form a beach. 16 14 Nearshore profile P 8 :1 vertical exaggeration) Case 30 Survey Date: 8/29/80 "100- year 12 Run-up 10- W W. LUL- 8 10-year Z Run- up 6-1 Groin 0 4r@ a Annual"--- -A . . Run- up >o 'C W 7 C; Tide Range W DISTANCE OFFSHORE (FT.) 0 00 150 200 61 -2 -4- 2-96 uj CASE 30 C014CRETE BULKHEAD AND GROINS 14EAR HAWKINS POINT 2-97 CASE 31 A WELL-RI14G BULKHEAD ON BROAD NECK This structure protects a site composed of high sloping bank. The historical rate of erosion at the site was about 2 ft./yr. from 1845-1970. The structure was completed in 1968 at an unknown cost. The concrete well-rings have an inside diameter of 3 'feet. They are placed 3-high, and are filled with stone. Only the top well-ring projects out of the sand. Two well-ring groins are also installed, with the well-ring bulkhead holding the fastland. The groins were filled with a substantial amount of beach sand at the time of the site visit. The.well-ring bulkhead is in generally good condition. The owners report no problems, and they appear to be quite pleased with the performance of the structure. There is no evidence of splashover or of washing out of the fast- land behind the well-ring structure. Nearshore profile (=14:1 vertical exaggeration) 7..: or. 0Case 31 100-year" Run-up(I 1.8') Survey Date: 8/29/80 6 10 eor up .3') Run 5 A n n u a I Run-up 4 W W 3 U_ -Z 2 Tide z Range 0 1 DISTANCE OFFSHORE (FT) < 0 > UJ _J 50 100 150 200 W -2- 7-7 7@1 too 150 200 50 -3 -4 2-98 4V x AZ7_ ON/ 8 4 "poll 0 Tom CASE 31 A WELL-RING BULKHEAD ON BROAD NECK 2-99 F. Cases along the Upper Eastern Shore of Chesapeake Bay This area of the northern Chesapeake Bay shoreline (Figure 2.10) contains portions of Cecil County and Kent County. The sections below present a brief physical description of the shoreline and coastal processes, followed by a discussion of the case studies which were selected from this area. SHORELINE DESCRIPTIONS Eastern Cecil County The Cecil County shoreline along the Elk River is composed of rollinq hills up to 80 feet in height. At most spots, the land slopes gently down to the water, but some hillsides end in exposed vertical walls of erodinq sediments. The beaches in this area are of varying width, and contain some gravel. Enough sand is present in some areas of the shoreline system to form wide sandy berms on the summer beach profiles. Marshes are found in protected coves, and in the headwaters of the Flk River. Most shorefront areas on the western side of the Elk River contain farmlands or woodlands. Houses are located in among the trees on hillsides next to the shore, on low hanks Drotected by erosion-control structures, or in open grassy areas behind a wide vegetated buffer zone. On the eastern side of the Elk River, the terrain is generally flatter, and shorefront areas contain banks ranging from 5 to 15 feet in height. Areas near the entrance to the C&D Canal contain concentrated residential shorefront development and networks of erosion-control 2-100 structfires which stretch nearly continuously alonq the shore. Other areas contain farmlands or woodlands perched on exnosed erodinn hanks. A beach is present along most of this shoreline, with small pocket marshes found in protected coves and at the heads of the inflowinq rivers. The beach profile is aidest on isolated points of land. South of the entrance to the C&D Canal there are few structures and few areas of shorefront development. Only woodlands and farmlands are found on the Bohemia and Sassafras Rivers, except at the towns shown on the map. Further south along the Elk River, there is shorefront residential development at different spots from Crystal Beach to Grove Point. Some houses and vacation cottages are located on rolling hills which slonp nently down to the water, and others are found in among stands of trees, next to the edges of exposed bluffs. IKent County] The Kent CountY shoreline along the Chesapeake Ray consists of bluffs and hiqh banks between 10 and 50 feet in height which overlook the water. From Retterton to Worton Point, the blijffs are exnospd and eroding in many areas. A sand and qravel beach of var@yinq width is found at the water's edqe. Landward of the beach, there are broad accumu- lations of eroded slumped material (talus slopes) which make the bluff faces a hit less steep than at other points in the northern Chesaneake Ray. A few isolated points of land have low grassy terraces extending out into the water from the higher ground. Next Pages: Figure 2.10. Shoreline along Eastern Cecil County and Kent County. Figure 2.11. Some representative shoreline profiles collected in the summer of 1981 along the upper reaches of the Eastern Shore. 2-101 Figure 2.10 &K NaK 'ruR=vrr. fSay - GP.Nr, VF C C-1 L -m*m*s @ ". couy-ry a cz Alrourm KF-mT coLwT New -rouw CR. Quim.14 4RATiTuot COURry ..Iwo jeftex ar 2-102 Figure 2.11 SHORELINE PROFILES Cecil County-Welch Point --15 %G .10 UPPER EASTERN SHORE ---------------- --------------- OF THE -- -------- - - - 5 ---------- -- -------------------- ------------- CHESAPEAKE BAY ..AL 0 . . . . . . . . . . . . .. L SUMMER 1980 5 150 100 56 6 Feet Cecil County- --- Grove Point 45 LA- 0 100 50 0 Feet Kent County-Worton Point 15 Kent County- .10 Eastern Neck beach 10 .5 5 - ------------- -------------- 0 0 LL --- - -- - - --------- -5 150 100 Feet 5b 6 150 100 Feet 50 0 2-103 At Worton Point, the shoreline banks are very steen and end ahruntly at the water's edge. The sediments exposed along the shoreline in this area contain considerable clay and the nParshore zone contains a shallow wave-cut shelf of hard slionery clay covered in some snots bY a thin layer of sand. Beaches in this area are found only inside protected coves. From Worton Creek south to Swan Point, the shoreline consists of high banks fronted in most areas by a beach containing both sand and gravel. Most shorefront areas south of Tolchester contain farmlands and woodlands, but from Tolchester north to Betterton, homes are found along the ednes of the bluffs and high banks in many spots. At Rock Hall, the shoreline contains banks of varying height, and there is a wide shallow nearshore area that is sometimes exposed at times of low tide. The shoreline frontinq the Chesapeake Ray below Pock Hall is composed of low rolling hills fronted by beaches which stretch nearly contintiously along the shore. In some spots the beach is backed h.v low dunes stabilized by grasses and shrubs. lCoastal Processesi The historical erosion rates for this portion of the northern Chesapeake Bay shoreline ranqe from 2-8 ft./year. There are a few sites where the shoreline is stable or accretinq. The shoreline sedi- ments which are eroded are sandy deposits of the Monmouth, Matawan, and Raritan Formations (Appendix A). The sediments in littoral drift are movino in both directions.along the shoreline, and the notential rates of littoral drift are variable denending on the different shoreline orientations. Waves in this area approach from the northwest and southwest with the lonqest fetches. Only arotected coves are sheltered from wave enernY by 2-104 CASE 32 GROINS AT BETTERTON BEACH These structures protect a site composed of sandy beach fronting a low sandy berm and vegetated bank on the Betterton waterfront. The historical rate of erosion at the site was less than 3 ft./yr. from 1845-1947. The cost and date of the structures are not known. The pocket beach is held between a groin to the west alongshore and a crib jetty/pier, 250 feet long, to the east. Groins are constructed of both stone and timber. The structures are in generally fair condition. The beach is largely fill material, and erosion is occurring to the west alongshore from the beach. But the existing pocket beach between the two structures appears to be held reasonably well, despite the deteriorated nature of the structures. 100- year Nearshore profile (= 17:1 vertical exaggeration) 7 Run- up ( 13.2') Case 32 "10-year" Survey Date: 7/19/80 - 6 Run-up ( 7.1 1) PROFILE I - South of beach PROFILE 2 South end of beach - 5 PROFILE 3 North end of beach PROFILE 4 North of beach - "Annual" M Run-up Note: Structures Include a Crib r- M Groin, a Pier and 3 < Fallen Trees. 2 0 de z Range DISTANCE OFFSHORE (FT.) z M M 200 150 100 50 -3 7": -4 2-106 irregularities in the shoreline, and the shallow offshore bottom runs in a very narrow zone between the beach and the navigation channel along the Eastern shore. As a result, wave ener(iies are medium to high for this entire shoreline reach. The mean tide range is above 1 foot in most areas. The storm surge from "annual storms" is about 1 foot, and the surges from "100 year" storms can he greater than 8 feet in many coastal segments., The wave and storm conditions are discussed in more detail along with the other coastal processes in Chapter V. The structure case studies selected in this area include: Case No. Structure a 32 Groins at Betterton Beach. 0 33 Stone revetment at Mitchell Rluffs (372.5 feet long). The following pages present a brief description of each strijcture and nearshore bottom profiles collected at the sites. Both cases are in qener- ally fair condition. There is a beach at both sites, and the revetment at Mitchell 9luffs should protect against wave snlashover from all hut the worst wave conditions. A redesign of the structure at Betterton Beach is discussed below. Redesign of Betterton Beach The continued existence of a pocket beach at Betterton renuires the nearly complete retention of sand within the beach "compartment" formed bY the groin near t-he' beach club building to the west and the crib pier to the east. The groin should be more sand-tiqht and extended up higher to nrevent westerly sand transnort. The beach can then be maintained in nood condition. To the west there is active erosion and means to curtail it shoul@ be exT)l ored. 2-105 .woo 41 CASE 32 GROINS AT BETTERTON BEACH 2-107 CASE 33 A STONE REVETMENT AT MITCHELL BLUFFS This structure protects a site composed of high eroding bank, alongshore from high bluffs. The historical rate of erosion at the site was about I ft./yr. from 1845-1953. The structure was completed in 1975 at a cost of $60.48 per foot. Revet- ment is in two sections, separated by a gap. Armor layer is composed of 350-1200 lbs. stone, 2 feet-thick, overlying a 6 inch-thick bedding layer of quarry stone. Filter cloth was used below the bedding layer. The revetment has a maximum elevation of 7 feet above MLW. This structure is in generally fair to good condition. A sandy beach exists along the shoreline reach, and the offshore bottom is covered with stones. There is significant shoreline retreat and active erosion presently alongshore to the nurth of this site. This adjacent eroding shoreline was once protected by a timber bulkhead which has since failed. "100- year Neo rshore profile (= 17:1 vert icai exaggeration) 7 R -up (14 Case 33 un .8 Survey Dote: 6 11/ 80 6 5 10-year" Run-up (9 0') 4 rn r- rn A nnu a I Run-up 0 z Tide onge ORE FT.) DISTANCE OFFSH rn M 200 150 100 50.*.*.. 5 @4 -n r rn @-3 -4 2-108 Of If -OW Or CASE 33 A STONE REVETMENT AT MITCHELL BLUFFS 2-109 G. Cases along Kent Island and Talbot County Shorelines This area of the northern Chesapeake Bay (Figures 2.12 and 2.13) contains portions of the shoreline in Queen Anne's and Talbot Counties. The sections below present a brief physical description of the shorelines and coastal processes, followed by a discussion of the case studies which were selected from this area. Kent Island] The Queen Anne's County shoreline on Kent Island contains farmland, a few heavily wooded areas, and many clusters of shorefront homes protected by erosion-control structures. North of the Bay Bridge, the Kent Island shoreline is composed of low rolling hills which usuallv end at the water's edge in exposed hanks from 3 to 15 feet in height. An exception is at Love Point, where the high around slones gently down to the water's edge. Shorefront areas on this reach contain mostly farmland, and the few houses that are present are separated from the water by a wide vegetated buffer strip. Below the Bay Bridge, many of the shoreline banks support residential development, and shorefront areas are often landscaped, covered with lawn grass and shrubbery, and protected hv erosion-control structures. Clusters of homes are interspersed with tidal creeks surrounded by marsh. Farther south, the shoreline contains farmlands and woodlands at the edges of eroding hanks, and the beach is nearly uninterrunted by erosion-control structures. The few groin fields that are present were filled with sand in the summer of 198O. 2-110 The southern most portion of Kent Island is a low wooded terrace extending out from higher ground, and fronted by marsh and small nocket @eaches. A few homes are present alonq the shore, nrotected by erosion- control structures. ITalbot Countyl From Tilghman Point south to Wades Point, the shoreline consists mostly of exposed eroding banks between 3 and 19 feet high. There is a beach at the base of the banks in most spots, and the trees perched on heavily-wooded Tilghman Point are falling off the banks onto the beach. Farther south along this shoreline reach, shorefront areas contain farmlands, and low-lying terraces containing qrass, shrubs, and Mars@, that extend out into the water from higher ground. Concentrated shorefront development and erosion-control structures are present on the shore at Claiborne, and at many different locations south along the shore to Lowes Point. From Lowes Ooint south to Tilghman Island, shorefront areas contain mostly woodlands, farmlands, and marsh. Where a marsh is absent, the shoreline banks are usually exposed and eroding, and end abruptly at the water's edge. Residential and commercial shorefront development is concentrated on the shoreline around Knapps Narrows, and some structures have been in- stalled to halt erosion. Along the Bay shoreline soiith of Knanps Marrows, shorefront areas contain exposed eroding banks which end at the water's Next Pages.: Figure 2.12. Shoreline fronting the Chesapeake Bay along Kent Island and Talbot County. Figure 2.13. Some representative shoreline profiles collected in the summers of 1980 and 1981 from Kent Island and Talbot County. 2-111 Figure 2.12 KENT cou'ry QulEEN ANNE'S C-bum"ry CftSATOKE BAY q0AXZZNW.K L",VW4 60pa C-F-;JTr-QV I LLA vat /* STVW-4v I l.,Lc CWSWR KFw teo - 0 WfJT0AI it - Tr- CLkl TALisoT IA'MDA04J COUNTY IMAR OJEASTOA) do cmtowme CaJMTY Mwvu V"7 MA nwt A@Wq aP"W*Lwy?r- -mv Avw A. C%MWWK WOK W. 2-112 Figure 2.13 Queen Anne's County northern Kent Island beach --- ------ .15 SHORELINE PROFILES .10 KENTISLAND AND 5 TALBOT COUNTY, 0 U- SUMMER 1980 -5 150 100 5b 0 Feet Queen Anne's County southern Kent island beach 15 .10 5 ;......@ . . . . . . . . . . . . . . . . .7: o ........... . . . . . . . . . . . . . . @-5 150 100 50 0 Feet Talbot County Rich Neck cornfield beach 20 .15 .10 Talbot County-Lowes Point beach 5 - --- -- --- -- 10 0 .......... ............... . . . . . . . . -5 5 100 50 0 o U- Feet 1 . . . . . - - - r-5 150 100 50 0 Feet 2-113 edge in most spots. In a few places, the hiqher qround is separated from the water hv patches of marsh, and small pocket beaches. Shorefront areas contain farmlands and clusters of houses in open qrassv areas. Along the shore at the sotithern end of Tilghman Island, and on Poplar and roaches Island, a beach is narrow or absent, and-dead trees arp lit- tered in the nearshore zone of breaking waves. This is evidence of ranid shoreline retreat. Most homes on the southern end of Tilqhman Island are separated from the water on the Bay side by a narrow buffer strip of roa.ds, and fields or trees, but these same buildings are immediately adjacent to the water on 81 ackwal nut Cove. .lCoastal Processes I The historical rates of erosion for this portion of the northern Chesapeake Bay shoreline range from less than 2 ft./vr. to greater than 8 ft./yr. in some areas. The shoreline sediments which are eroded are sand.v sediments of several different qeoloqic formations. Sedi- ments in littoral drift are moving in both directions along the shoreline, and the potential rates of littoral drift are variable with different shoreline orientations. Waves in this area annroach with the longest fetches from the north- west and southwest. Shallow offshore areas vary in width along the different coastal segments. Few of these reaches are sheltered from wave energy by irregularities in the shoreline. The wave energies (Table 5.5) are uniformly medium in strength along these reaches. The mean tide range is about 1.5 feet. Storm surqes from "annual storms" are around 3 feet, and the surnes from "100 Year" storms can he greater than 5-6 feet in many area's. The structure case studies selected in this area include: Case Ho. Structure 0 34 A stone revetment, timber bulkheads, and stone groins at the south end of Tilghman Island. 0 39 Timber bulkhead on Kent Island (650.5 feet long) with 4 stone groins. 0 36 Stone revetment (360 feet long) with stone groins (160 feet total length) placed seaward of an existing timber bulkhead on Kent Island. 0 37 An experimental site on Tilghman Island. 0 38 Gabions on Kent Island. 0 39 Stone revetment (475 feet long) at Wades Point. 0 4n Concrete pipe on Tilghman Island. The following pages present a brief descrintion of each structure and nearshore bottom profiles collected at the sites. Most of thp case struc- tures assiqned in this area were in good condition. A sand beach was noticed in front of some of the structures during the site visits in the summer of 1980. But few of the structures will protect the fastland against wave overtopping durinq severe conditions. The following paragraphs discuss some design deficiencies at one of the sites. Case 5R-73 Timber bulkhead (308 ft.) with stone-revetment on Kent Island. The nonding of water behind the bulkhead and the obvious attendent erosion is evidence of a wall which was too low. Based on an R val ue of 1 (see Section 9 in Chapter III), the wall would have to he 1.8 ft. higher to achieve reasonable orotection against overwash and splashover. Other asoects of the design appear to he satisfactorv. 2-115 CASE 34 A STONE REVETMENT, TIMBER BULKHEADS, AND STONE GROINS AT THE SOUTH END OF TILGHMAN ISLAND In 1976, the following work was accomplished: 3 new groins (40 ft., 53 ft., and 63 ft. long) were installed at a cost of $106.17/ft.; timber bulkhead was replaced at a cost of $163.64/ft.; and repairs to stone revetment cost $77.88 /ft. The historical rate of erosion at the site was 8 ft./yr. from 1847-1942. The timber bulkheads replaced sheetpile bulkheads at this site. Stone revet- ment was installed along with filter cloth. These structures are in generally good condition. The offshore profile is very deep at the base of the seawall, and no beach existed at the time of the site visit in summer of 1980. There is evidence of wave overtopping at locations along the timber bulkheads. 9 COPPER CAP WALE -6 BATTEN BOARD GRADE OF FILL, LEVEL AT + 4.0 8"x 8" WALES, BOLTED TO 20x7/8 GALV TIE ROD, W/ GALV.OGEE NUTS ACH EN -3 ASHERS a AT EACH EN PILE W/ 7/8" GALV. SOLT 8'3"X 1/4"GALV. WASHER 0PPOSITE SIDE. GALV OGEE WASHER & NUT APPROX. EXISTING THIS SIDE GROUND LLJ EX. STEEL SHEET PILING TREATED TIMBER PILES 8" MIN. TIP. ILL. O"-12" BUTT TREATED TIMBER PILES 3"x 10"x 14' T &G SHEETING 18' IN LENGTH, 5'-6"O/C 12 0 BUTT,8"MIN.TIP, FASTENED TO WALES W/ 60 d GALV. SPIKES 25'IN LENGTH, 5-6"O/C EXIS 6 3 0 -3 -6 -9 -12 -15 -18 -21 -24 -27 30 FEET "loo-year Run-up (12.1) Nearshore profile (=18:1 vertical exageration) "10- year " Case 34 Run-up (8.4') Survey Date:6/22/80 7 6 5 4 3 2 1 Annual" Run-up M 71 Tide q0 RAnge DISTANCE OFFSHORE (FT) 200 150 100 5O 4 2-116 14 @ @-W or i"IBBIG, xn @.4 lw Ni @11' EXISTING DETERIORATED TIMBER GROIN PROPOSED STONE GROIN NO, 3 10- EX "STING F@ILTEC@Tm APPROX STONE REVETMENT REMAINS OF EXISTING DETERIORATED TIMBER EXISTING GROIN CUT I ol To 1.5' BELOW TOP OF STONE 5- GROUND TOP OF GROIN CUTOFF LINE STONE GROIN NO. 3 11100 TO 1200 LB. LLI ARMOR STONE ON FILTER CLOTH LLJ ILL. 0 - END OF FILTER CLOTH END OF FILTER. CLO;. EXCAVATE EX BOTTOM 'T@ 0 MLW PRIOR TO PLACING E:-SIING BOY IC FILTER CLOTH -5 0 5 10 15 20 25 30 35 40 45 50 55 FEET CASE 34 A STONE REVETMENT, TIMBER BULKHEADS, AND STONE GROINS CUTOFF Ll.@E 0 OP OF GROIN DUN" T AT THE SOUTH END OF TILGHMAN ISLAND 2-117 CASE 35 A TIMBER BULKHEAD ON KENT ISLAND WITH ST0NE GROINS One stone groin existed prior to the construction of the rest of the structures. The original timber bulkhead and one groin were constructed in 1973 at a cost of $63.29/ft. and $35.80/ft., respectively. In 1976, 493 ft. of timber bulkhead and two stone groins were added at a cost of $79.35/ft. and $54.91/ft., respectively, and the two existing groins were refurbished and extended at a cost of $39.92/ft. Timber bulkheads consist of tongue-in-groove sheeting. and piles are spaced on 7.5 ft. centers. Groins were constructed of 400-800 lbs. stone on a 1.5:1 slope with a 3 ft.-wide crest. These structures are in generally good condition. No beach sand was observed at the site in thesummer of 1980. There is strong wave activity in this area, and the wave crests were observed to reflect against the vertical bulkhead. Bulkheads to the north alongshore are being forced landward by waves, and backfill is being lost through the bulkhead wall. There is also evidence of wave overtopping and splashover at this site. 10- 8 6 4 2 0 TREATED CAPBOARD COPPER CAP TOP OF WHALE 6"X6" WALES BOLTED TO PILE WITH 3/4" GALV. BOLTS A 3"X1/4 GALV. FLAT WASHER OPPOSITE SIDE. GALV OGEE WASHERS A NUTS THIS SIDE BATTEN BOARD 15 3/4" GALV TIE ROD WITH GALV OGEE WASHER & NUT EACH END APPROX. EXISTING GROUND 10"X 12" & TREATED TIMBER PILES 8"6 MIN TIP 14' IN LENGTH AT EACH WALL PILE 3"X 10"X12' T & G SHTG FASTENED TO WALES WITH 60 & GALV. SPIKES 10"-12 & TREATED TIMBER PILES 5"6 MIN TIP, 20'IN LENGTH AT 7'6 O/C -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 nearshore profile ( 18:1 vertical exaggeration Case 35 Survey Date: 6/11/80 PROFILE1 (Between Groins) PROFILE 2 (Between Groins- south alongshore) "100-year" Run-up (13.1) "10-year" Run-up (8.5) "Annual" Run-up 5 4 3 2 1 0 50 100 150 200 -1 -2 -3 CAPBOARD 2-118 f 15- CASE 35 A TIMBER BULKHEAD WITH STONE dkOINS ON,KEN:T,.jSLAND 3. 0' 10- 400- 800 LB. ARMOR STONE I BER BULKHEAD :'.!-;IL;E; C. 5- L07TH LLJ Lid Lj- 0- 'APPROXIMATE EXISTINI IROUND/ FILTER CLOTH -5 -5 5 10 15 @O 25 iO i5, 4'0 @O @O iO 0 9'0 1 0 FEET 60 F-4 T IMBER UlKHEAD IL;E; OT 1@. R 1. STIN ROUND MATE XI A PP OXI CASE 35 A TIMBER BULKHEAD ON KENT ISLAND WITH STONE GROINS 2-119 CASE 36 TIMBER BULKHEAD WITH STONE REVETMENT ON KENT ISLAND This structure protects a site composed of high sloping bank. The historical rate of erosion at the site was 8.5 ft./yr. from 1846-1942. Structure was completed in 1974 at a cost of $56.33 per foot for the revetment placed in front of an existing timber bulkhead. At the same time, groins were completed at a cost of $53.57 per foot. Timber bulkhead is fronted by revetment on filter cloth with 2 stone groins each 68 feet long. The rip-rap section is composed of 360-1200 lbs. stone on a 1:1.5 slope. A splashover apron consisting of boards placed on end was added 4 feet behind the bulkheading at some time after the revetment project and groins were completed. These structures are in generally good condition. No beach has accumulated except for a small pocket of sand at the base of each groin. Profiles taken alongshore from the site show the nearshore bottom in front of the structure is relatively shallow. This suggests that the addition of rip-rap and groins reduced wave reflections off the bulkheading, and has resulted in some accumu- lation of sand offshore at the time of the site visit. Ponded water on the fastland behind the bulkheading is a problem which needs correction. According to talks with local residents, the primary cause of damage to the structure has been winter ice, which displaces the stones in the rip-rap section. "100-year" Nears hore prof i I e I= 15:1 ver t ical exaggerat ion)7 Run-up (11.0 Case 36 6 Survey Dote: 6/11/80 10-yeor Run-up (7.1 PROFILE I - "Annual" PROFILE 2 Run- up 4 rn 3 ..rn 2 Tide .0 Range z DISTANCE OFFSHORE (FT) 0 z 260 150 100 50 rn .1 rn -2 .-3 -4 7 6 5 2-120 le t-z ONVISI AD NO INIWAA9d INOIS HIM GV3Wno 0WI K 3SVO 4Z SIR- 46W "MOM ask. CASE 37 EXPERIME14TAL STRUCTURE ON TILGHMAN ISLAND This site is composed of low fastland fronting a road. The historical rate of erosion at the site was 10.5 ft./yr. from 1847-1942. Several experimental erosion-control structures have been installed at the site. In 1965, a sloping (2:1) wall composed of interlocking concrete block was installed along with rip-rap, and a fabriform section. These eventually failed. Presently, there is an old timber bulkhead fronted by rip-rap and a new stone revetment. A 20 foot-wide splashover apron was also installed at the site containing the stone revetment. These structures are in good condition. There is a very small amount of sand in front of both structures. Along the shoreline to the north, the banks are severely eroding, and many fallen trees are laying in the water. Nearshore profile (=17:1 vertical exaggeration) Case 37 100-year" Run-up ( 11. 5') Survey Date: 6/22/80 7 j-"10-year" Run-up (8.2') PROFILE I - PROFILE 2--- 6 A n n u a I Run-up :4.. M* M .31 < Tide 2. o z Range I DISTANCE OFFSHORE (FT.) z 0- M M 200 150 100 50 @O 100 @O 0 4* 2-122 'Air oh 7q CASE 37 EXPERIMENTAL STRUCTURE ON TILGHMAN ISLAND 2-123 CASE 38 GABIONS ON KENT ISLAND This site is composed of low sloping bank fronted by a sandy beach and berm. A small headland exists alongshore to the north. The historical rate of erosion at the site was 2 ft./yr. from 1844-1942. The date and cost of the structure are not known. Gabion structure consists of a shore-parallel section and a hooked groin-breakwater section at the north end alongshore. The structure is about 5 years old. The gabions are stacked two-high. This structure is in generally good condition. At the time of the site visit, the structure was holding a nice sandy beach @extremely well. However, there is some evidence that the baskets holding the stones are d@teriorating due perhaps to abrasion and corrosion. I Do- year" Nearshore profile (=16:1 vertical exaggeration) - 7 Run-up (13.1') Co se 38 10 -6 -year Survey Date: 6/ 11 80 Ru n- up (8.5 "Annual Run-up 74 M :. *r- , M -3 < Tide 2 0 onge DISTANCE OFFSHORE (FT.) 0 M M 200 150 100 50 6 4 m r** 3 m< 2 z z .01 1 -3 -4 2-124 szl-z ONVISI iND NO SNOIM 8C 3SVO Ow, Ai rN"" 'o K@6 "Now ..,oow Mr, ir 77 4004P CASE 39 CONCRETE BULKHEAD/STONE REVETMENT AT WADES POINT Stone revetment was completed in 1975 at a cost of $40.22/ft. The historic rate of erosion at the site was about 3 ft./yr. from 1847-1942. Stone revet- ment consists of an armor layer of 250-1200 lbs. stone in a 2 ft.-thick layer. A 10 in.-thick bedding layer was installed under the armor layer. Filter mater- ial was used below the bedding layer. A 3 ft.-wide splash apron was also built. This structure is holding up quite well. Alongshore, an unprotected section of shoreline is eroding rapidly. Offshore, there are 8 groins which are submerged. These are approximately 45 years old and were once attached to the shore. They presently serve no useful purpose. 15 -12 9 250 TO 1200 LB ARM0R STONE CHINKED 800 TO 1200 A ARMOR STONE PLACED AT TOE 20' MIN. 6 10"-12" 3 NO I TO NO 2 BEDD1NG STONE END OF FILTER CLOTH COMPACTED FILL FILTER CLOTH UNDER ENTIRE STRUCTURE -03 3 6 9 12 15 9 6 3 0 -3 -6 FEET 100-year" Run-up (12.0) Nearshore profile(17:1 vertical exaggeration) 10-yeor Case 39 6 Run- up ( 8.0) Survey Date 6/22/80 PROFILE 1 5 "Annual PROFILE 2 ---- < 0 1 2 3 4 5 6 7 DISTANCE OFFSHORE (FT.) 200 150 100 50 150 100 ELEVATION IN FEET 2-126 aims",- N MM MI" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 40 CASE 39 CONCRETE BULKHEAD/STONE REVETMENT AT WADES POINT 2-127 CASE 40 CONCRETE PIPES ON TILGHMAN ISLAND This site is composed of a low grassy bank. The historical rate of erosion at the site was about 10 ft./yr. from 1847-1942. The date and cost of the structure are not known. Short sections of concrete pipe are laid horizontally parallel to the shore. Recently, a sloping smooth concrete revetment has been placed against the fastland, and above the pipe. Alongshore, concrete pipes have also been placed seaward of a timber bulkhead. A pier constructed of concrete pipe also extends offshore. This structure is in generally good condition. At the time of the site visit, there was a sand beach present. Alongshore to the south, trees are falling off the eroding bank. Alongshore in the other direction, the concrete pipes are installed in front of the bulkhead, and seem to be working fairly well in preventing erosion. 7- Nearshore profile (=16:1 vertical exaggeration) 100 -year Run up (12.0') Case 40 1110- 6- Survey Date: 6/22/80 year R un- u p (8 . 3,) 5- "Annual 1-4 Run-up Ui U_ z 2 Tide Range Z 0 DISTANCE OFFSHORE (FT) 0 150 21 0 _j 50 100 150 200 Ui -2 - 4 - 2-128 Ct I6AAkJAFA,1A" JWF@ L CASE 40 C014CRETE PIPES ON TILGHMAN ISLAND 2-129 H. Summary It is clear from this assortment of case studies that the different tvnps of shorelines on the northern Chesapeake Ray in general can be well- protected hy erosion-control structures. But, the individual characteris- tics of each structure will depend on the particular Dhvsical setting. These design features are discussed in greater detail in the next chapter. From the examples which were included in the case stiMies, it is evident that qroins were not trapping substantial quantities of sand in some areas to form beaches; but, most of the cases of revetments and bulk- heads were providing reasonable protection against wave attack for low- level storm conditions. The major deficiencies which were noted most of the time during the site visits were: (1) overtopping of structures by waves, with minor but bothersome erosion of the fastland, and salt damage to vegetation behind.the structures. (2) lack of periodic maintenance and renair of damage to structures from storms or winter ice. The types of maintenance which need to he nerformed on structures is discussed in the next chanter. It needs to he nointed out that for cases where an erosion-control structure is nerforming satisfactorily but where no a0ditio nal vegetative measures have heen eMDloved on Muffs or-hinh banks, .there can be continuing bank instability and bluff collapse due to normal weathering and (iroundwater seenaqe (Palmer, 11)73). For either design or maintenance of any erosion-control structure, serious consideration should he qiven to the combination of maximum tides 2-130 and waves (run-up) which can be expected in the lifetime of structures on the northern Chesapeake Ray shoreline. The drawings of the nearshore profile at each case studv site show either the approximate storm sijrqe or wave run-up conditions (storm surge plus wave height) which are predicted for storms with different recurrence intervals. The methods which were used to derive these predictecl storm conditions are explained in Chanter V. It is important to note that these elevations for either "annual" and "100-vear" surge or wave run-up will not occur exactly once every year, or once Pvery 100 years, resnectivelv. If a storm surae (or storm wave) is considered to have a return period of "TR" years, where "TR" is 100 for the "100-year" storm surge, then the probability that this surge, or a hinher one, wnuld occur in any one year is (I/TR). The prohahility that it does not occitr is (1 - I/TR)- (Mote that the sum of the nrobahilities must equal one; that is, the surge either does or does'not occur.) The probability that it does not occur for "n" successive year is 1/TR). Finally, the probability that the storm surqe will occur in "N" years is 1 (1 - 1/TR)N Table (2.2) shows the probabilities that the "TR" surqe elevation will he enualled or exceeded for various "N" years. 2-131 TABLE 2.2 Table of Exceedance Probabilities STORM RETURM PERIOD "N - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - T 1 5 10 20 50 100 200 10 0.10 0.4095 0.6513 0.8784 0.9948 .99997 1.000 20 0.05 0.2262 0.4012 0.6415 0.9231 .9941 1.000 so 0.02 0.0961 0.1829 0.33-24 0.6358 .8674 .9824 100 0.01 0.0490 0.0956 0.1821 0.3qS0 .6340 .8660 As an example, for a structure which has a desian life of 10Years, the probability that the "100-year" surge will occur during a 10 year period is 9.56%. A recommendation is offered in the next chapter that all stri,ictures, at a minimum, should be designed for ton elevations greater than the 11annual" run-up to avoid serious overtopping damage. ?-132 CHAPTER III DESIGNING FUTURE STRUCTURES Robert Dean, Robert Dal rvmple, Hsiang Wang, and Robert Biggs A. Introduction Different types of shorelines can be well-protected by erosion control structures, as long as the individual components of each structure, such as seawall elevation or stone size, are adjusted to the narticular physical setting at each individual shoreline site. Several recommendations for design features and maintenance are presented in this chapter to improve the performance of erosion control strategies along the northern Chesapeake Bay shoreline. These recommendations are derived from analysis of the forty case studies described in the previous chapter. These recommendations include: 1) selecting the proper crest elevation of any vertical structure 2) selecting the proper stone armor weight for revetments 3) using filter material 4) providing toe protection for vertical bulkheads 5) preventing flanking of structures due to erosion alongshore The following Chapter IV presents some reasons for selecting from among the different structure types and two alternative "non-struc- tural" strategies for erosion control are discussed: (1) beach nourishment; and (2) vegetative planting. 3-1 B Selecting the Proper Crest Elevation for Vertical Protective Structures Several of the case studies described in the previous chapter showed evidence of wave splashover or overtopping of the structure. It is strongly recommended that all structures, as a minimum, should be designed for top elevations equal to or greater than the wave runup from an "annual" storm to avoid serious damage to the fastland from overtopping. The correct combination of storm-tide and wave condi- tions which will result in overtopping at different locations on the northern Chesapeake Bay shoreline can be derived from mathematical engineering equations and from the observations of erosion and vegetation damage at the forty case studies. The wave run-up for vertical walls can be computed from mathe- matical equations which are based on small amplitude wave theory (Shore Protection Manual, 1977; Saville, 19W. The definition sketch in Figure 3.1 shows that overtopping will occur when the combination of tide plus wave run-up on the structure exceeds the maximum structure elevation. Onshore winds, of course, will often be present and will serve to transport a portion of the water exceeding the maxi-@- mum elevation of the structure onto the upland properties as spray. The correct combination of storm-tide and wave characteristics to be considered for any design to prevent overtopping depends on the amount and frequency of overtopping considered "tolerable". Opposite: Fiqure 3.1. Schematic diagram showing wave run-up ele- vation and overtopping of structures due to storm tides and waves. 3-2 Figure 3.1 OVERTOPPING OF A STRUCTURE DUE TO STORM TIDES AND WAVES -wind Maximum Run-up S pray Its ----------- R ------------ ----------- - .... ... H . ...... .... ----------- ... ---------- - - ----------- ....... ......... . ............ . ... ------------- n ... ---------- ........... T ...... ----------- . ..... .... .. ---------- ----------- - . . . . . . . . . . . .. ............................ Mean Sea Level (MSL):'. .......... ............. ---------- ------ ....................... ............. ............ .......... ....... - - - - - - - - - - - ............... - - - - - - - .............. :........... ............. ............. ............ ............ - - - - - - - - - - - -- - ............. ............. - - - - - - - - - - - ........ .............. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .. .... - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - --- - -- Wave Run-up Annual r I Wa ve Fr om Storm For Vertical Heig ht Annual It Storm L Surge Walls . . R n + r x H ............ T 3-3 Some idea of the heights of storm tides associated with storms of different return intervals is shown by plots in Figure 3.2 of height- frequency distributions from historic tidal records at the stations of Baltimore, Annapolis, and Solomons Island. These stations roughly represent three regions--upper, middle, and lower - in the northern Chesapeake Bay. To use these data for surge predictions, the statistical signifi- cance of these data first needs to be understood. As can be seen in the graphs of Figure 3.2, the maximum storm surges with annual fre- quency smaller than say, 0.1 (with return period longer than 10 years), are produced by tropical storms, whereas those of return periods less than 10 years (more than 0.1) are due mainly to extra- tropical storms. The difference between these two types of storms is explained in Chapter V, where storm surges are discussed. Because the extratronical storms are far more frequent, the surge data associated with these storms are expected to be far more statistically mean- ingful. Table 3.1 shows the heights "B" of 13 bulkheads included in the case studies in Chapter II, together with the predicted water depth "D" during "annual" storm conditions. This depth is equivalent to the total storm water depth plus the storm wave height. Also included in Table 3.1 is a listing of the field observations of overtopping at each site. Whenever overtopping was actuallv observed, a "Y" was Opposite: Figure 3.2. Graphs of historic tidal data showing storm- surge heights above Mean Sea Level for storms with different return levels at three gauging stations in the northern Chesapeake Bay (from Boon et. al., 1978). 3-4 Figure 3.2 1903-1976 BALTIMORE 6- EXTRATROPICAL STORMS TROPICAL STORMS/ 5 HURRICANES 1929-1976 U.1 ANNAPOLIS Uj U- 6 5 Lj 4 3 w 1938-1976 SOLOMONS IS. 4 3 FREQUENCY OF OCCURRENCE =t = t = + =+ m 2 ct 2 cr cr 2 < ct < Q@ < = < < cr Z) 0 o wowc Uj 0 Z z (n 0 cn 0 0 @- 41,J FT- 3-5 entered in the fourth column. Table 3.1 shows that only four of the 13 case studies were designed with elevations greater than the expected "annual" overtoppinq elevation "D". Of these four, two did not show evidence of overtopping. Fiqure 3.3 shows the same results from the case studies plotted in a graphic format. For structures desiqned with a top elevation equal to the expected wave run-up from "annual" storms (i.e. "0" "B"), a line was drawn (denoted 1:1) on the qraph. With the exception of the Cases No. 8 and No. 351, all structures where overtopping was actually observed (i.e. where "B" was less than "D") lie below the 1:1 line, while all structures where overtopping was not noticed lie above it. Thus, a calculation of "0", which characterizes "annual" storm conditions, provided a reasonable method for deriving a design requirement wh ich seemed to avoid overtopping at two of the structures which were among the case studies. The equation given below for calculating "D" utilizes Mean Low Water as a datum elevation, and the terms used are different than those in the definition sketch shown in Figure 3.1. This predicted overtopping elevation "D from "annual" storms can be computed as: 0 = h + R. 3.1 Where: "h" total stormwater depth at the toe of the structure. This is determined by measuring the depth below MLW at the toe of any structure, and adding the mean tide level (which can be approximated by one-half the tidal range) plus a storm surge for an "annual" storm which can be read from the graphs in Figure 3.2. 3-6 "R" the wave height associated with 30 mph winds (H30). This can he derived from a series of atlas maps pre- pared for this study. (See Figure 5.12). For a rough approximation, 80% of the total storm water depth (h) can be used; however, this approximation may prove to be very conservative for sites fronted by deep water. All structures, as a minimum, should he designed for top eleva- tions greater than the "annual" run-up to avoid serious overtopping damage. The wave climate around the Bay is one of the most evident factors for causing shoreline erosion and for potentially damaging shoreline structures, particularly vertical protective walls. Serious consideration must be given to the combination of waves and tides (run-up) which can be expected for storms of different intensities in the lifetimes of structures on the Northern Bay. The use of predictive methods (such as Equation 3.1), together with a series of maps prepared as part of the study (see Chapter V and Appendix B) can aid in the fore- cast of future storm tides and wave conditions at sites of new shoreline structures. C. Selecting the Proper Stone Armor Weight for Revetments After reviewing the modes of failure of some of the structures, MER, Inc. recommends sloping revetments as the preferred strategy for Next Two Pages: Table 3.1. Calculations of wave overtopping for vertical protective structures at se- lected case studies of structures along the northern Chesapeake Bay. Figure 3.3. Comparison of predicted annual overtop- ping of waves with field evidence of overtopping at structures along the northern rhesapeake gay shoreline. V 3-7 Table 3.1 CALCULATIONS OF WAVE OVERTOPPING FOR VERTICAL PROTECTIVE STRUCTURES Toto I I Case Depth Bulkhead Potential Field Study at Structure Height Overtopping Observed 01D III B2 D<H Overtopping (f t.) (f t.) 15 Randle Cliffs bulkhead 9.6 6 .2 Y ? 16 Dares Beach bulkhead 8.7 6.2 Y Y 34 Tilghman island bulkhead 8 revetment 12.6 It .21 Y Y 14 Tall Timbers bulkhead 8.7 8.2 Y Y 8 Honga River bulkhead 2.4 3.8 N Y 26 Middle River bulkhead arevetment 2.5 6.4 N N 9 TrIppe Bay bulkhead 6.5 5.8 Y Y 10 Choptank River bulkhead 6.2 5 1 Y Y 35 Kent Island bulkhead 8.3 8.7 N Y 36 Kent Island bulkhead revetment 9.4 7.5 Y Y 20 Hillsmere Beach bulkhead 2.5 3.6 N N 26 Back River bulkhead 6.0 2.5 Y Y 7 Hongo River bulkhead 8.6 6.2 Y Y ITotal depth at structure total storm water depth+ wave height ("H"30) water depth ( MLW) at toe of structure + mean tide level + annual storm surge + 30 mph wove height or 0.8 of the total storm water depth whichever Is smaller 2 Toto Ielevation above bottom. 3-8 Figure 3.13 COMPARISON OF PREDICTED "ANNUAL" OVERTOPPING WITH FIELD EVIDENCE OF OVERTOPPING 0 1:1.5 0 m 10- Uj > y 0 y m y 8 z y 0 N y 6. y > y Uj I y Uj 4- N Uj y r 2- _%t: _j 0 2 4 6 8 10 12 14 11D(f 1.) ANNUAL" RUN-UP ELEVATION ABOVE BOTTOM 3-9 many more shoreline situations in the northern Chesapeake lay. This method for erosion control offers the following advantages: (1) The materials used to build revetments do not degrade with time. (2) Sloping revetments are unlikely to experience catastrophic failure. (If design conditions should be exceeded slightly during a storm, inevitably some stones may become dis- lodged and these can be replaced afterwards.) (3) Wave reflection from sloping revetments is usually low; thus, less disturbance and less scour of sediments results at the toe of the structure. (4) Rubble generally provides a better habitat for biota than the materials which are used in most other types of shore protection. This section develops and presents recommendations related to the establishment of reasonable stone weiqhts for structures along various portions of Chesapeake Bay. The design median armor stone weight "W50" for a narticular structure is usually determined in accordance with the following equation taken from the U.S. Army Corps Shore Protection Manual (1973): 3-10 W50 YrH 3 3.2 KD(Ss cot a where: H = the design wave height. cot oL = where cL is the angle that the structure makes with the bottom. Yr the specific weight of the armor stone. Ss the specific gravity of the stone relative to the water in which it is placed. Generally, although not always, the specific weight of stone varies over only a narrow range, and can be approximated by Ss = 2.6. KD the stability coefficient depending on the interlocki ng or frictional characteristics of the armor stones. Kr) for reasonably angular rock is usually taken as 2.0 to 3.0, and for purposes here a value of 2.0 will be adopted. In order to develop a general guideline for stone weight selection, Equation 3.2 was simplified as follows: W50 = 20.2 H3/cot (1 3.3 where: W50 = the armor stone weight in pounds, H = the design wave height in feet. 3-11 Of forty case studies described in the Previous chapter, thirteen were revetment structures whose actual designs can he compared with the desiqn that would be aasociated with storms of various return periods. The stone weights for these thirteen structures are presented in Table 3.2. Based on a "W50" stone weight, and the bathymetry at the time the profiles were collected in conjunction with this study, the design conditions are such that five of the thirteen structures have design return periods of less than one year, which means they have probably experienced the maximum wave for which they are designed more frequently than once a year. This is quite unexpected, since only one of the structures has failed and the average in-service life is four years for the four that showed no visible signs of failure. There are two other possibilities for this apparent discrepancy: (1) the calculated wave heights are too large or the actual wave heights did not persist long enough to accomplish failure, and/or (2) the defi- nition of damage associated with the breakwater stabil.ity equation is so strict that such damage would not he evident in the field. The damage criterion relates to a displacement of 5%,of the stones. Pre- sumably, the movement would occur first among the smaller stones. If Equation 3.2 is used with the upper limit of stone weight contained in each revetment, then only the structure in Case No. 34 (stone revet- ment on Tilghman Island) is in a class with a return period of less than one year. This structure has been in service for approximately four years at the time of the site visits, and there was no record nor Opposite: Table 3.2. Characteristics of revetment structures dis- cussed in Chapter II. 3-12 Table 3.2 Characteristics of Revetment.Structures Included in Assessment Case Apparent Wave Heights (ft) Identification Stone Weight* W50 Design Wave Heights of One-Year No. Range (lbs) (lbs) cot (x Return Design Return Period For Erosion, e, of Period (yrs) e = 0 e = 01 e = V e 2' 36 350-1200 650 1.5 < I yr 3.6 4.0 4.0 4.0 4 400-1000 630 2.0 8 yrs 4.0 3.5 4.2 5.0 33 350-1200 650 2.0 > 5yrs 4.0 0.6 1.4 2.1 13 1400-2800 1980 2.0 50 yrs 5.8 3.9 4.6 5.4 3 450-1200 735 2.0 < I yr 4.2 4.4 4.6 4.6 2 350-1200 650 2.0 20 yrs 4.0 2.6 3.4 4.2 1 400-1200 690 2.0 < I yr 4.1 4.6 4.6 4.6 6 400-120& 690 2.0 8yrs 4.1 3.7 4.5 5.3 11 250-1000 500 2.5 8yrs 4.0 3.4 4.2 5.0 12 400-1000 630 2.0 6yrs 4.0 3.0 3.0 3.0 18 30-300 95 2.0 < Iyr 2.1 2.5 3.3 3.3 34 400-1200 690 2.0 < Iyr 4.1 4.9 4.9 4.9 5 400-1000 630 2.0 12 yrs 4.0 3.2 4.0 4.8 *Obtained from pre-construction engineering cross-sections. **W50 was obtained from the stone weight range by W50 = 1-85 WMIN + wMAX/1.85. This formula is empirically based. visual indication of revetment failure. Thus, the only possible conclusion is that the calculated wave heights are larger than occurred in nature or their duration was too short to allow failure to develop. If additional erosion takes place at the toe of sloping revetments such that the offshore water depth increases, then larger waves may be able to travel onto the shore without breaking. In this case, the revetment may sustain damage from storms which will occur more frequently than the design storm. To illustrate the effect of future erosion frontinq a revetment structure, detailed plots have been developed for the three followinq structures: No. 11, No. 10 and No. 34 (Fiqure 3.4). Figure 3.4 shows that the structure No. 11, with no add itional depth increase, is desiqned for a storm with a return period of approximately eiqht years. If an erosion of even one foot should occur, the indicated return period would be less than one year. It is informative to examine the "W50" requirements for various erosion considerations and for a particular storm return period. For example, for a return period of 20 years, the "W50" values are presented in Table 3.3. It is clear that the depths fronting the Case No. 11 structure reduce substantially the wave heights that can impinge on the revetment. If sufficient erosion would occur such that all waves would not break prior to impinging on the structure, the required stone weights would increase six-fold over that associated with "no additional erosion"., The site for case #10 is relatively sheltered and thus the maximum waves are much smaller than at the site of case #11 . Thus, opposite: Friqure 3.4. Renuired armor weiqht for storms oF varying return period at three shoreline sites in northern Chesapeake Bay. 3-14 Figure 3.4 REQUIRED STONE WEIGHT VS. RETURN PERIOD 'o-CASE 11 -Choptank River 8 - (Brannock Boy) WAVES NOT DEPTH LIMITED 6- 4- DEPTH INCREASE=2 FT. . ......... DEPTH INCREASE= I FT. Lf) 2- --NO FUTURE DEPTH INCREASE 0 a @ ns DESIGN UPPER LIMIT z .... .. .............. ARMOR STONE WT. D ....... 7'@@ACTUAL .1 W50"USED %-J0 CL 0 10 20 30 40 50 IN DESIGN LL- RETURN PERIOD OF DESIGN WAVES ( YEARS) 0 4- CASE 10 WAVES NOT DEPTH LIMITE (n ,,---ALSO DEPTH INCREASE OF2DF-T--'4, c - Choptank DEPTH INCREASE=I FT. wo- - z River MI;-wz-NO FUTURE DEPTH INCREASE < 2 ,,-DESIGN UPPER LIMIT V) ome@10618 OF ARMOR STONE WT. 7....................... ............ ACTUAL'45@'USED 0 0 -1 -o@IN DESIGN 0 10 20 30 40 50 RETURN PERIOD OF DESIGN WAVES (YEARS z -10- CASE 34 0 - (Tilghman Is.) 08- 31. - z 6- NOTE WAVES WILL NOT BE DEPTH LIMITED FOR ANY RETURN PERIOD 4 - DESIGN UPPER LIMIT 2- OFARMOR STONE WT. ACTUAL "W50"USED ............... .......................................................................... w'-IN DESIGN 0 1 '' 1- - 1 1--1 @rl 0 10 20 30 40 50 RETURN PERIOD OF DESIGN WAVES (YEARS) 3-15 Table 3.3 "W50" Requirements For Three Revetment Structures For Various Erosion Scenarios with a Twenty-Year Return Period Design Offshore Median Armor Stone Weight Obs.) "W50" for Structure at: Erosion Scenario rase No. 11 Case No. 10 Case No. 34 No Additional Erosion 1200 1600 6700 1 ft Additional Erosion 1600 1640 6700 2 ft Additional Erosion 2400 1'640 6700 Waves Not Denth-Limited 7200 1640 6700 any additional offshore depth increases can cause only negligible increases in the required Nq()" values over the "no additional erosion" scenario. Finally, the No. 34 structure is fronted by water of substantial depth (= 6 ft MSL), and none of the waves (up to a return period of 50 years) are depth-limited. Therefore, the required weiqht NSO" is the same for all depth scenarios. A favorable factor relating to stone revetments is the nature of revetment failures. When rubblerevetments fail, generally they do not fail catastronhically, hut fail through dislodgement of several stones. Moreover, several hours may be required to reach a near- equilibrium damage level for a narticular desiqn storm. Of course if 3-16 wave heights occur that are much greater than the design wave height, there could be complete and rapid failure of the structure. Regardless of the degree of failure, the individual stones do not suffer damage and, if they can be recovered, they can be replaced in a partially damaged revetment or used in a structure designed for a larger wave height. The recovered stones could be augmented by larger stones to increase the "WS()" value or the "W5()" value could be kept the same and a milder revetment slope used. The engineering cross-sections for many of the revetments described in Chapter 11 have slopes of about 2:1. In summary, for the revetted structures, it has not been possible to determine the exact cause of the apparent discrepancy between the calculated return Periods associated with the various designs and the performance history. In view of the indicated effects associated with future depth increases, the following are recommended: (1) A continuing Program of monitoring revetment structures. Monitoring should occur periodically on an annual basis and after severe storms. (2) The wave height calculation procedure used in this study should be evaluated against high quality wave measurements in Chesapeake gay. At least five wave gauge installations at selected locations should be installed for a one-or two- year duration. (3) In thd design of revetment structures, it is recommended that consideration he given to designing for a larger wave height and storm tide combination. In particular, until improved procedures are developed, a design wave height 3-17 and storm tide equal to 1.5 times the "one-year" wave height "Hl" and. storm tide "nT" are recommended for consider- ation. Calculations show that this would result in an approximate average design return period of 10-11 years. (4) Minimum stone weiqht N50" of 650 lbs is recommended. (This implies a range of stone weights of 350-1200 lbs.) If the water depth fronting a 1)articular structure is still sufficiently shallow (after reasonable consideration for future erosion) so as to limit the wave height, the design wave can be reduced accordingly. To provide an indication of the effect of this recommendation for the thirteen structures examined, the required 11WS0" values would range from 450 to 8500 lbs. considering an erosion of 1 foot. The average ratib of recommended to actual stone weights for the individual structures is 1.0 to 12.3, with an overall average ratio of 3.54. Althouqh this represents a sub- stantial increase in the weights of the individual stone sizes, the corresponding increases in volumes in on the order of 50%, and the associated cost increase is expected to be 60% to 70%, which would be approximately 30% greater than the cost of timber bulkheads. Of the forty case studies, adequate cost data were available for thirty-three of the structures. If the cost figures are adjusted to 1980 levels by using the indexes and method presented from the Engineering News Record in Table 2.1, then the ratio of the most costly (stone revetment $214.57 per foot) to the least costly (stone groin $26.35 per foot) is 3-18 8:1. The average a djusted cost of stone revetment ($90.71 per foot) is 300/0' lower than the average adjusted cost of timber bulkhead ($127.89 per foot). The average adjusted cost of the two aluminum bulkheads in the case studies is $88-11 per foot and the average adjusted cost of the 8 timber and stone groins is $92.79 per foot. It is important to note that the indexes presented in Table 2.1 are for general building trades and may not indicate the true inflation rate for marine construction. The costs of structures are also reflected in actual 1980 bid prices for shore erosion-control projects built by the Department of Natural Resources Shore Erosion Control Program. Table 3.4 Average Cost Per Unit Length of Various Types of Structures (1980 Dollars) Number of Average Cost Range of Costs Type of Structure Structures Per Foot Per Foot stone revetments 18 $124.24 $101.00 - $219.18 aluminum bulkhead 2 $141.19 $135.47 - S199.89 timber bulkhead 15 $211.54 $161.33 - $328.47 Total Cost $2,213,183.60.= $143.87 average cost per foot. Total Footage 15,383.4 0. Use of Filter Cloth in Construction The design ourDose of filter cloth is to prevent the le-achling or washing out of sediment fines from behind or under the structure with the possible consequence of at least partial failure of the structure due to void creation and slumning. Although the life of filter clot@ 3-19 is not well established, its use is certainly recommended. In some vertical structures which were among the case studies, it was clear that leaching had occurred through the seams of adjacent sheetpile and this could have been prevented by use of high quality filter cloth. E. Toe Protection There are a number of qualitative advantaqes to be qained hv providing toe protection for vertical bulkheads. Toe protection, usually takes the form of rubble, and reduces run-up, overtoppinq, and toe scour during storms, as well as provides a better habitat for biota. The installation of rubble toe protection should include filter cloth and perhaps a bedding of small stone to reduce the oossibilitv of rupture of the filter cloth. Ideally, the rubble should extend to an elevation such that waves will break on the rubble during storms. In many places, the associated cost may approach a substantial percentage of that for a revetment, making both a vertical bulkhead and sloping revetment difficult to justify on economic terms. F. Provision of Return Walls to Prevent Structure Flankinq (Figure 3.5) If a section of shoreline is protected by continuous structures of high integrity and good design, then there will he no possibility for erosion of upland property and/or erosion than can adversely affect the structure. However, if only a short shoreline segment is protected hv a structure, then the effects of continued erosion of the Opposite: Fiqure 3.5. Role of return walls at,the ends of shoreline protection structures. 3-20 Figure 3.5 RETURN WALLS PREVENT FLANKING AT THE ENDS OF VERTICAL PROTECTIVE STRUCTURES SHORELINE SHORELINE IN EXISTING IN EXISTING 10 YEARS HORELINE 10 YEARS SHORELINE 4 4 4 4 0 .... .11 .... .... 4 4 4 4 ........... o, 4 4 4 4 4 4 411- 4 4 4 4 4 44 . ............. 4 4 4 4@4 4 44 4 41 RETURN! A A A A A A A 4 4POTENT AL 4 0 4 WALLS 44 4 4 4 44 4 4 *STRUCTURAL 4 4444 4 4 4 DAMAGE DUE 4 4 4 4 4 4 .4 4 4 4 4 4 4 0 4 4 4 4 TO EROSION 4 4 4 4 4 10 4 4 4 01 4 4 4 4 4 4. 44, 0 44 4 4 4 4 4 4 4 4' LAND LAND WATER WATER., 4 4 W1 THOU T W1 TH 7,o. -4* 4 44 RETURN WALLS RETURN WALLS 3-21 adjacent shoreline should be recognized. At several of the structures examined, this process had occurred to a degree that either flanking and damage of the structure had occurred or was reasonably imminent. To prevent flanking, return walls should be provided for a distance consistent with the erosion rate and design life of the structure (see Figure 3.5). G. Maintenance of Structures Periodic maintenance of structures is necessary due to annual stom and winter damage and the possible effects of flanking and off- shore Profile deepeninq. The maintenance varies with the structural type; but annu al inspections should be made by the property owners. For stone revetments, the replacement of stones which have been dis- lodged is necessary; timber bulkheads need to be backfilled if there has been a loss of upland material, and broken sheetDile should he re- placed as necessary. Gabion baskets should be inspected for corrosion failure of the wire (the plastic packet can fail due to improper handling during construction or abrasion by stones inside the baskets). Baskets should be replaced as necessary, as waves will empty failed baskets. Asbestos cement and aluminum bulkheads should he inspected for sheetvile failure due to active earth pressure or debris impact and for loss of backfill. For all structural types not, contiauous to other structures, lengtheninq of flankinq walls may be necessary every few years. Through periodic.monitoring and required maintenance, a substantially greater oercentaqe of coastal structures will perform effectively over their design life. 3-29 CHAPTER IV Discussion Robert Dean, Robert Dalrymple, Hsiang Wanq, and Robert Biggs A. Summary of Observations Although there are examples of structures along the Chesapeake Bay shoreline which definitely have not been effective in preventing beach erosion, it is very clear that structures can he designed and installed to prevent erosion of upland property without having an adverse effect on the adjacent shorelines. One of the main differ- ences between the Chesapeake Bay shorelines and oceanic shorelines is that the material eroded along the Chesapeake Bay shoreline is pre- dominantly very fine sediment (less than 50 microns). The later discussion of this chapter will show that the average percenta,ge of eroded material that is of beach sand size in the bluffs and banks on the northern Bay is on the order of 10%. Thus erosion of the cliffs and bluffs does not result in significant quantities of beach sand, and any benefit that can be ascribed to allowing shorelines to erode to maintain beaches is relatively small. In fact, rational arguments can he advanced that those unprotected shoreline segments bounded by stabilized property on both ends will experience a long-term reduction in erosion forces. The forty sites which were included in this study are protected by a variety of coastal structures: bulkheads (14 sites have timber bulkheads, 4-concrete, 3-aluminum, 1-asbestos cement), stone revet- ments at 16 sites, gabions at 4 sites, groins at 15 sites, well rings at 1 site, and concrete Pines at I site. The sites were located in 4-1 eight of the Bay counties: 12 sites are in Dorchester County, 11 in Anne Arundel, 4 in Queen Annes, 4 in Talbot, 3 in Calvert and 2 sites each in St. Marys, Baltimore anI Kent Counties. No sites were selected in Cecil, Harford or Somerset Counties. The purpose of the structures at the forty sites has heen to stop shoreline recession. In a majority of the cases, this has been achieved, despite the range of coa'stal types and structures that appear in the Bay. The use of well-designed and constructed timber bulkheads can be expected to prevent upland erosion due to wave attack regardless of the coastal features of the area. Even at Randle Cliff, where 100 ft.-hiqh cliffs are eroding, the exneri6nce of the U.S. Naval Research laboratory has shown that (with the exception of weathering due to rain and the freeze-thaw cycle) cliff erosion can he halted. Of the forty sites visited, five showed substantial deteriora- tion. This deterioration is believed to have been preventable through a more proper desiqn or maintenance and recognition of the dominant natural forces present along the shore. The effectiveness of the remaining structures is really quite remarkable when it is considered that certain portions of the shoreline of Chesapeake Bay are eroding historically at rates of 10 or more feet per year. However, in general, the wave climate is reasonably moderate and thus it is not necessary to design the structures for extremely large waves. This is reflected in the reasonable costs of the-structures.. Where available, the structure cost ner unit length has been determined and adjusted to 1990 levels (see Chapter III, p. 3-18 and 3-19). The unit cost was found to be on the order of $150/ft. 4-2 The only general deficiencies occurring in a substantial per- centage of the structures that were visited were: (1) the occurrence of structure overtopping with qenprally minor but bothersome erosion of the upland and salt damage to the vegetation behind the structure, and (2) lack of maintenance. Recognition of the combination of maxi- mum tides and waves occurring within the various portions of the bay would minimize this overtoppinq problem. As far as maintenance is concerned, structures require periodic monitoring and repair for damage from winter conditions or storms. 3. General Design Recommendations As a result of some design deficiencies noted in the field investiqations, several recornmendations related to desiqn features and maintenance were discussed in Chapter III. These include: (1) the crest elevation of the structure, (2) stone (armor) weight for revet- ments, (3) general recommendations associated with use of filter material, (4) orevention of structure flanking, and (5) maintenance of structures. All of these recommendations are discussed at length in 'Chapter III. C. Selection of Shoreline Protection Type Each of the following structures appears to perform its design function adequately: timber, concrete, aluminum and asbestos bulk- heads, stone revetments and gabions. At the stage when a shorefront property owner is selecting a structure type, the results of this study suqgest that serious consideration he given to sloping stone revetments for the reasons noted below. 4-3 Fir'st, there are relatively small cost differentials (per foot of shoreline) between the stone revetments and the least costly struc- tures. The recommended increases in design for the proper wave height and storn tide made in Chapter III should result in the costs of timber bulkheads and stone revetments being within 30% of each other. Second, all of the structural materials except rock have a limited life. In the case of well-treated timber, this life may be fairl.v long (say 20-30 years); however, it is still limited. In comparing sloping stone revetment structures with more rigid structural types (including interlocking revetment)i it is clear that the latter can fail catastrophicallv if the design conditions are exceeded or if other characteristics (such as bay bottom level) change. If such an event should occur and the rigid structure were to fail, there could be little of salvage value and, in fact, costs could he associated with the clearing of structural debris. Frinally, an erosional loss of upland property can occur, even during the same storm which causes the structural failure, and in the time span prior to the installation of a new structure. The sloping stone revetments included in this study form a sample which is too small to address the long-term performance of sloping re- vetments, at least under past design practices and future erosion scenarios. But the inherent advantages of this structural type merit the strong consideration of sloninq stone revetments for future installations. 0. Consideration of Groins Groins can affect nearshore sediment transport processes in a number of ways. Probably the most effective way to consider their 4-4 performance is that, properly designed, they serve as a template to the beach so that a single groin will collect sand on the up-drift side to a design elevation, and then the sand either flows over or around the groin. However, groins are only effective when there is a suitable amount of beach sand available in the shoreline system. An alternate approach is to fill the groin pockets initially with suitable-sized sand, and then replenish the fill as needed. . If groins are too "severe," that is too long and/or too high, they can actually be counter-i)roductive by inducing rip currents which can cause sand to be jetted offshore resulting in a down-drift area deficient of sediment. It should be noted that no groin-related rip currents were observed in Chesapeake Bay during this study and that the conditions under which groins will cause rip currents are not well understood. If two or more qroins are present, forming one or several groin compartments, the groins tend to collect sand until they reach their retention capacity. The sediment impounded is obtained from that moving along the shoreline, and this represents a loss of material to the adjacent shoreline. It follows that if one or a series of aroins is not to cause an erosion of the adjacent shoreline, the groins should be filled to their capacity with quality sand (beach sand size) when installed. Groins should be sandtiqht if they are to retain sand. The sand- tight property results from installation of a graded stone cross-sec- tion such that only small interstices occur within the groin matrix. Some groins are not necessarily designed to be sand-tight if they are designed as current deflectors. But the quantitative benefits of groins acting as current deflectors are not well known. 4-5 Groins should only be used where it is known there is sufficient longshore sand transport. This implies that the littoral drift potential is hirlh for the area, as well as the presence of a suffl- cient source of sand, in either the nearby eroding bluffs or on neiqhhoring beaches. A good example of groins effectively holding the beach is at Case No. 23 in Anne Arundel County. E. Alternate Approaches - Vegetative Control of Shore Erosion On the basis of field visits and investiqations by others, it appears that reliable vegetative means of erosion control are not available in areas where the erosive forces are substantial. This would include most portions of the main Chesapeake Bay shoreline which were described in this report. Althouqh this study did not include an extensive analysis of vegetative types native to Chesapeake Bay, vigorous qrowth of marsh-type qrass was found only at one location, the Hillsmere Reach site (Case No. 20), where it appeared that the vegetation could exert some mitigating effect on shoreline erosion. Dean (1978) has reviewed the erosion-related physical effects of vegetation in the nearshore zone. These include the reduction and diversion of nearshore currents, thereby enhancing deposition. Phillips (1980) has attempted to develop planting guidelines for sea- grasses and has noted the adverse effects of a high energy environment on seagrass survival. For example, tidal currents of 0.8 knots caused seagrass sprigs to be washed out in Great South Bay, New York. Plant- ings of "shoalgrass" appeared to he unable to resist the action of waves of 4 - 6 feet high at Port St. Joe, Florida. These wave heiqhts are in the range that occur at least annually in Chesapeake @ay. 4-6 Wherever shore stabilization is considered a present necessity along the main body of the Upper Bay, the simple initiation and main- tenance of a vigorous vegetative stand does not appear to he practical at present. The hydrodynamic forces acting on the Bay shoreline are increasing, narticularly at most locations which alreadv contain structures. This can be seen wherever flanking of an existing struc- ture forms a protruding feature relative to the adjacent shoreline. This general increase in forces is due, in part, to sea level rise. F. Alternative Approaches - Beach Nourishment When sandy sediment is placed on a beach by either natural or artificial nourishment, the fine material will wash out until some equilibrium sediment size-distribution is reached under wave action. The amount of new material which must be placed on a beach to create one cubic vard of beach sand is referred to as the overfill ratio "K". Dean (1974) (Frigure 4.1) shows calculations of overfill ratios for different size ponulations of native beach sand (n) and newly-emplaced material (b). The values for the x- and y- axis in Figure 4.1 are non-dimensional ratios of the mean qrain-size to the standard devia- tions for the sediment populations on a beach, and for new beach fill. For any program of beach nourishment along the Chesapeake lay shoreline, an abundant source of suitable-sized material must be located, excavated, and transported to an erosion site. Suhstantial costs could be added to any beach nourishment project if sand has to he hauled more than a few miles to the shoreline; thus, sediments in the Coastal Plain which are located relatively close to the Bay would he the most likelv terrestrial source for fill material. 4-7 To demonstrate the suitability of deposits which are exposed along the Bay shoreline for beach nourishment, four reaches were sampl el to determine the size composition of the fastl 3nd sediments and of the beaches during the summertime. The four reaches were: 0 bluffs in Calvert County between Cove Point and the BG&E Nuclear Power Plant, 0 banks in Dorchester County on Taylors Island, banks in St. Mary's County hetween Point No Point and Cedar Point, 0 bluffs in Kent County from Fairlee fl'.reek to Swan Point. Representative shoreline profiles from these sites are shown in 'Figure 4.2. Beach samples were collected in August 1980 from a trench dug across the beach and berm at each location. At the same time, materials from the adjacent bluff and banks were also sampled. Each bed of sand, or silt and clay, which could be discerned in outcrop was sampled at least ten times both vertically anti horizontally. In the laboratory, the samples were wet-sieved to separate the sand and the weight of the sand was compared to the weight of silt plus clay. The sand fraction was then sieved again to further separate the size intervals of se@iiment. Opposite: Figure 4.1. Plots of different overfill ratios 'T' for different size populations of native heach sand and new beach fill. 4-9 Figure 4.1 PLOTS OF OVERFILL RATIOS K 6 5 W W W UJ Z Z u- U- 4 A 00 w Z 0 z 5; 3 w Z -50 w z 2 ro .0 A. 0 .2 .4 .6 .8 1.0 2.0 3.0 MEAN GRAIN SIZE OF NATIVE SAND @Ln STANDARD DEVIATION OF NEW BEACH FILL 4-9 r Some of the results are shown in Fiqure 4.3, as plots of the mean grain size and the standard deviation (sorting) of the size distri- butions. The qreatest size ranqe in source sediment was found at the shoreline sites with the highest relief. More than one geologic for- mation (Apnendix A) may he exposed in these shoreline areas, and this may contribute sediments in more size classes. This greater diversity of sediment size is particularly important for beach formation because the bluff sands are in most cases finer-qrained than the beach sands along the same shoreline reach, and only a small r)ercentaqe of the material eroded from the shoreline is sufficiently coarse to remain on the beach under summer wave energy conditions. The finer-qrained sediments which do not remain on the beach are either transported offshore or alongshore to be deposited in spits or shoals in nearby coastal areas. A determination of the amount of bluff material from these areas which actually remains on the beach can be computed from methods which are used to determine overfill ratios. The size statistics for the four sites are presented in Table 4.1, together with the appropriate value of "V which can be read from the graph. The tahl e al so includes the historic rate of shore erosion at each site. The results show the summer beaches at all four reaches were composed of medium to coarse-grained sands, and the material erodinq from the adjacent shoreline is much finer-qrained. The "overfill Opnosite: Figure 4.2. Representative shoreline profiles in four areas which were samoled for sediment characteristics. The data from the samples is shown in '@'iqure 4.3. 4-11) Figure 4.2 Chesapeake Bay Shoreline beach and bank sediment analysis Kent County Mitchell Bluffs typical profiles from somplingoreas 15 Summer 1,980 -10 5 .0 - ------------- - ------ --------- --- --- ------ --5 Calvert County ----- Calvert Cliffs 150 100 50 0 Feet 80 ---- --------- ------------------- ------ --- ---- ------------ -- - 20 ------------ 10 ------------------ 5 A 0 --------------- -5 0 50 160 Feet St. Mary's County Turkey Neck beach 15- 10. Dorchester County-Taylors Is. bank V 10 -- ---------- 5- Uo 5 0 --------------- 0 LL -5 -5 o 20 6 60 100 100 50 0 Feet Feet 4-11 ratio" of eroding shoreline sediments to volumes of native beach sand ranges between 5 and 10,000. Thus, at Taylors Island, only 0.01% of the eroded fastland sediments are remaining to form a beach, while 20% of the fastland sediments at Point No Point and 'Calvert Cliffs remain on the beach. Table 4.1. Material Characteristics of the Four Test Reaches in Summer of 1980. Erosion Reach Bluff (b) Beach (n) K Rate* a % Silt p (I ft/yr Pt. No Point 2 1.5 56 .9 1.1 5 2.9 Swan Point 2.2 1.0 78 .6 .9 27 3.3 Taylors Is. 3.0 .8 99 .8 .5 10,000 8.2 Calvert Cliffs 2.2 1.0 37 1.1 1.0 5 2.7 p = mean qrain size unit) a = standard deviation of grain size nopulation unit K overfill ratio from Figure 4.1 from Historical Shorelines and Erosion Rates (1975) opposite: Fiqure 4.3. Grain-size statistics of beach and bluff sediments from shoreline areas shown in Figure 4.2. 4-12 Figure 4.3 3.5 CALVERT CLIFFS- FAIRLEE CREEK- 3.0- COVE POINT SWAN POINT Ze.- 2.5- 2 2.0- 1.5- *2 1.0- a. 40.5- Cr 0 -0.5 -VERY MODER- VERY -VERY MODER- VERY WELL ATELY POORLY WELL ATELY POORLY SORTED1 ISORTED1 POORLY SORTED SORTED SORTED1 ISA6 R7ED POORLY SORTED so _j 3.5-. POINT NO POINT TAYLORS ISLAND 3.0- 2.5- 4 2.0- Uj 1.5- 1.0- CL 02 KEY -d 0.5 a: *2 BEACH SAMPLES (9 0- BLUFF SAMPLES I- COMPOSITE SIZES1 -0.5 -VERY MODER- VERY -VERY MODER- vrR7-- WELL IA Sa@@ POORL W JATE@@ P RLY _I.O,SORTEDj POORLY iSORTED SORT .ED I SOFRLDI I SOR POORLYI SORTED I SOORO TED 1 0.5 1.0 1.5 2.0 2.5 0.5 1.0 1.5 2.0 2.5 INCLUSIVE GRAPHIC STANDARD DEVIATION (@ units) Grain Size Analyses of Shoreline Sediments from Reaches Shown in Figure 4.2 The phi unit (@) = - 1092 d, where "d" is the grain diameter in millimeters. 4-13 In summary, the fastland material which was sampled in the four shoreline areas is much too fine-grained to remain on the beaches, in-licatin-1 that the eroding shorelines in these test areas do not contribute much sand to develop protective beaches. There is a wide-variation in the actual overfill ratios from area to area; this result is due to small variations in the grain size statistics of the samples collected from outcrops right along the shoreline. More extensive sampling of the same strata in areas farther landward might disclose the presence of zones where coarser-grained sand is located. Finding the source of suitable sand which is availablefor excavation and transport to the beach at a reasonable cost is the first hurdle which must be surmounted in implementing a strategy of beach nourishment along the Chesapeake Bay shoreline. 4-14 Chapter V RELATIONSHIP OF COASTAL PROCESSES TO HISTORIC EROSION RATES Hsiang 1.4ang, Robert Biggs, Robert Dean, and Robert Dalrymple A. Introduction The information contained in this chapter and in Chapter VI describes the assessment of shore erosion on the northern Chesapeake Bay which was conducted as part of this study, along with the evaluation of erosion-control structures. Different sections of this chapter describe the coastal processes that are responsible for erosion, and the next chapter (Chapter VI) discusses a statistical analysis which examined all the factors for their relationship to the historic erosion rate. The purpose of the reach-by-reach description of coastal processes (contained in this chapter) and the statistical treat- ment (in Chapter VI) was to find those factors which could best explain the historic erosion rate, and thus produce a statistical model, or predictive equation, which planners could have used in assessing erosion on any portion of shoreline. Unfortunately, the results of the statistical analysis described in the next chapter indicate that modelling the pattern of historic erosion rates around the edges of the main Chesapeake Bay in Mar@yland cannot be suitably done by using traditional regression or discriminant analysis procedures. The factors which were examined for their relationship to historic erosion rates include: 0 shoreline terrain 0 littoral drift of sediment 0 tidal range 0 rainfall 0 stom surge 0 wave climate B. Historic Erosion Rates Several years ago the Maryland Geological Survey (MGS) compared U.S. Coast and Geodetic Survey Charts dating back as far as 1941 with the latest available charts to show the linear recession of the Chesapeake gay shoreline, and hence, the shoreline erosion rate. The original work was done by Singewald and Slaughter (1949). More recently, as part of Maryland's Coastal Zone Manaqement Program, the MGS has updated and supplemented the earlier work with more man comparisons and field measurements from over 200 sites in Tidewater Maryland (from 1969-74). The results of this work are published in a map atlas entitled Historical Shorelines and Erosion Rates W)75). An example of the atlas product is shown in Figure 5.1. The entire atlas consists of all the 7 1/2 minute topoqraohic quadranqle sheets for the Maryland portion of the Bay shoreline. In these map reports, the erosion rate categories are designated in accordance with the following scheme: Opposite: Fiqure 5.1. Example of atlas product showing historic shore erosion rates, derived from comparison of recent and historic charts maintained by U.S. Coast and Geodetic Survey, Rockville, Maryland (from fICZMP, 1975). 5-2 -Figure 5.1 USGS 7.5" topo sheet Example of Atlas Historical Shorelines and E ro 'si'o-n-R-aTe s L map A a 656 .6!.'* T I L G M M A S L N 0 Dgw N*@@ S 5-3 Slight (S) 0 2 ft/yr. Low (L) 2 4 ft/yr. Moderate N) 4 9 ft/yr. High (H) > 8 ft/yr. Fill (F) artificial fill Accretion (A) C. Highly-eroding reaches Figure 5.2 shows the northern Bay shoreline broken down into reaches where the historic rate of erosion is generally "low" (< 4 feet/year), "medium" (4-8 feet/year) or "high" ( > 8 feet/vear) in the atlas Historical Shorelines and Erosion Rates (1975). It should be noted that the classification of historic erosion rate which is illustrated in Figure 5.2 represents only the gross characteristics within each reach. Considerable variations can exist within each reach; that is, if a reach is classified as highly erosional, it may contain suh- regions where the erosion is slight or even accretional. The classification is particularly subjective wherever the shoreline is hiqhly irregular within the reach. Mine reaches are identified as experiencing "high" erosion with average rates larger than 9 ft./year. These nine reaches are listed in Table 5.1. In addition, there are a few isolated points and small islands that are suffering severe erosion. There are also twenty- three reaches along the northern Bay margin that have experienced Opnosite: Figure 5.2. Map showing qeneralized erosion rates in the northern Chesapeake Bay. 5-4 Figure 5.2 760 30' 760 00' H i STOR IC PENNSYLVANIA 7- R- 7 -'- ' Z- * - -'- - -7 EROSION RATES -;;A Y A'N 0 ALONG NORTHERN CHESAPEAKE BAY HAVRE DE GRACE C 0 S H 0 R E L I N E cA NA I n-:T@ High erosion r o t e BALTIMO (>8 fl/yr) CHESTER - Medium TOWN R erosion rote (4-8 ft/yr) WASHINGTON to 39000 ANNA OLIS ZIM DENTON EASTON CAMBR@OGE 'AK 38030'- SA@@SBUQY 0 '09 "q 7X CR Sr E--- IZ) STATUTE MILES 10 0 10 20 FM 5-5 Table 5.1 Shoreline Reaches in Northern Chesapeake Bay Experiencing High Erosion ( > 8 ft/yr) County Location St. Marys (Western Shore) Pt. Lookout to St. Jerome Creek Anne Arundel (Western Shore) Holland Point Anne Arundel (Western Shore) Thomas Point Queen Annes (Eastern Shore) Kent Island - Craney Creek to Kent Point Talbot (Eastern Shore) Lowes Point to Knapps Narrows Dorchester (Eastern Shore) Mills Pt. to Hills Pt. Dorchester (Eastern Shore) James Island Dorchester (Eastern Shore) Oyster Cove to Punch Island Creek Dorchester (Eastern Shore) Barren Island 11medium" erosion ranging from 4-8 ft./year. Those reaches that are classified with either "high" or "medium" erosion total thirty- two reaches, or slightly more than a quarter of the entire shoreline in the northern Bay. The following sections of this chapter exnlore the different ways in which one can evaluate the relationship ),etween erosion parameters and the historic patterns of coastal retreat in the northern lay. 5-6 D. Relation of Shoreline Terrain and Geology to Coastal Retreat The shore zone classification that follows was developed origi- nally by Ahnert et al. (1974) for the Eastern Shore. For this study, the classification system was extended to the western shore of the Bay and its tributaries. The 1972 aerial r)hotos (1:12,000) on file in the Wetlands Section of DMR were used to classify the shorelines on the western shore according to the terrain. Ahnert's (1974) data were used for the classification on the eastern shore. The complete classification is renorted in a new atlas suhmitted to the Maryland Department of Natural Resources, which consists of transparent copies of all of the 7 1/2 minute topographic quadrangles of the tMaryland portion of the Bay. An example of the new atlas product is shown in Figure 5.3. The categories used by Ahnert are defined as: 1. Shoreline without @each or bluff 2. Reach greater than 20 ft. in width 3. Beach agaihst headland 0-20 ft. high 4. Beach against headland greater than 20 ft. high 5. Headland less than 20 ft. hiqh, no heach 6. Headland greater than 20 ft. high, no beach 7. Fringe marsh (width between 0 and 100 ft.) 8. Intermediate width marsh (width between 100 and 400 ft) 9. Extensive marsh (width greater than 400 ft.) 10. Deltaic inarsh (marsh containing mouth of tributary) 5-7 After the atlas Product was completed, the shoreline terrain was compared to the historic erosion rates to show the relationship between these two factors. Figure 5.4 (below) is a Graph which summarizes the historic erosion rates along all reaches of at least 0.5 kilometers in length which were also composed of only one type of shoreline terrain. The selection of 0.5 km. as a minimum length for study is arbitrary, but this is the smallest reach length which is regarded as suitable for analyzing variations in historical rates of coastal retreat. Figure 5.4 Above: Figure 5.4. Graph of relationship between the rate of coastal retreat anf the shoreline terrain for the norhern Chesapeake Bay. Opposite: Figure 5.3. Example of atlas product showing shoreline classification, derived from aerial photo- graphs. 5-8 Figure 5.3 USGS 7.5" topo sheet Example of Atlas Shoreline and Littoral Conditions or IL y to-1 QtA o.. t 000:- t 41 Qt& 44 S L A 0 UMW Shoreline Categories: Shoreline without beach or bluff -ALI Pont Beach. 20 ft. wide seach against headland 20 ft. high aeach against headland 20 ft. high Headland 20 ft. high, no beach Headland 20 ft. high, no beach spit Longshore transport direction air Photo) Fringing marsh Intermediate marsh Extensive marsh Littoral drift roses indicate potential longshore sediment movement from computer simulation not verified by field data. 5-9 Figure 5.4 shows reaches possessing the highest historical rates of erosion are principally banks less than 10 feet high and some marshes. Most of the high bluffs are eroding at rates oF 1-4 feet/year. Most of the marsh shoreline is also eroding at rates of 1-4 feet/year. Since there were a veny small number of beaches at least 0.5 kilometers long on reaches where the historic rate of erosion was relatively uniform, these features were not included in the graph for comparison. All the highly eroding reaches illustrated in Figure 5.2 can be compared with the distribution of bluffs and high banks which is shown in Figure 5.5, and with the broad categories of sediments which are exposed on different reaches. This figure shows all the highly- eroding reaches are located in regions of low relief, composed of either "Quaternary Lowland Deposits" or "Deposits Undivided" (see Appendix A). These materials are quite non-uniform and the textural characteristics of the exposures in some areas could be considered to have high resistance to erosion. Unfortunately, not all of the reaches composed of the same geo- logical formation are subject to "high" erosion rates. For instance, the hayside of Kent Island is highly erosional, yet the adjacent shoreline in @ueen Annes County (north of the Chester River) has ex- perienced only "low" shoreline retreat, although both regions have similar types of sediment exposed along the shore. The same relation- ship exists along many other shoreline reaches which have the same formations as those exposed in hiqh-erosion areas, but possess low historic erosion rates instead. Opposite: Figure 5.5. Map showing shoreline geology and shoreline terrain in the northern Chesapeake Ray. 5 -10 Figure 5._5 COASTAL PLAIN 760 130, 760 100' GEOLOGY AND .-PENNSYLVANIA TY L-A N* 0- S H 0 R E L I N E TERRAIN HAVRE DE GRACE 0 9 Lowland CANAL 1 Deposit %0 BALTIMO E Quaternary Im Deposits Undivided CHESTER- ===Shoreline Banks TOWN 10- 30 ft @High Bluffs over 30 ft. WASHINGTON ANNA OLIS 39000'- P OENTON EASTON Z_ CL bb tz CAM8R,,O E 3 8 30'- 0 SAL158URY 0 cW POCOMCKE, Z CRi F. E @_C STATUTE MILES 10 0 10 20 D 5-11 E. Relation of Tide to Coastal Retreat The astronomical tide in Chesapeake Bay is predominantly semi- diurnal with two high waters and two low waters per lunar day of 24.84 solar hours. Based upon tide records along Chesapeake Bay, Hicks (1964) constructed a mean range chart for the entire bay. Boon et al. (1978) have prepared a probabilistic model of the astronomical tide in Chesapeake Bay. Daily Mean Range and probability of occurrence of selected stations were computed for four classes shown in Table 5.2. Class 1 represents 12.5% of non-exceedance; Class 2 represents 37.5% of non- exceedance; Class 3 represents 62.5% of non-exceedance; and Class 4 represents 87.5% of non-exceedance. The Daily Mean Tide Range determined by Hicks is approximately equal to the average of values for Boon's Class 2 and Class 3 tides(see definition sketch on page 5-15). For this study, the tidal range in the Bay between the stations listed in Table 5.2 was computed by a three-point-interpolation procedure: 1 n(l) = v'4n(1)A(1) + n(2)A(21% + n(3)A(3)] A." where: is the tide range A =A(l) + A(2) + A(3), and A is the area shown in Figure 5.6 Based upon this procedure, the tidal elevations inside the Bay were computed and the resulting mean tide range and Class 4 tide range (about 87.5% non-exceedance) were compiled onto a set of maps submitted to DNR. A simplified version of the maps are contained in Appendix B. The results show the tide range is quite moderate in the entire upper Bay. Below the Bay Bridge, the mean tide range is about 1.15 feet along the 5-12 western shore and the Class 4 tide is about 0.25 feet higher. Along the lower Eastern Shore, the mean tide range increases to 1.5-1.6 feet. Above the Bay Bridge the differences in tide range between eastern and western shores diminish, and the tide range is generally less than in the lower Bay. Figure 5.6 st.3 .07 St. 2 (3) 0 St. Above: Figure 5.6. Interpolation scheme for computing tide range solely from tide gauge data at known points. Next Pages: Table 5.2. Class averages of Daily Mean Range and probability of I exceedance values at selected stations in northern Chesapeake Bay (from Boon et al.. 1978). 5-13 Table 5.2 Class Averages of Daily Mean Range (DMR) and Probability of Exceedance Values of Selected Stations in Chesapeake Bay From Boon et al. 1978) Probability of Station Class DMR (feet) Exceedance 1. Havre De Grace, MD 4 2.05 12.5% 3 1.78 37.5% 2 1.65 62.5% 1 1.50 87.5% 2. Betterton, MD 4 1.78 12.5% 3 1.59 37.5% 2 1.47 62.5% 1 1.30 87.5% 3. Tolchester, MD 4 1.37 12.5% 3 1.19 37.5% 2 1.06 62.5% 1 0.86 87.5% 4. Baltimore, MD 4 1.27 12.5% 3 1.07 37.5% 2 0.92 62.5% 1 0.72 87.5% 5. Love Point, MD 4 1.38 12.5% 3 1.18 37.5% 2 1.02 62.5% 1 0.78 87.5% 6. Matapeake, MD 4 1.21 12.5% 3 1.03 37.5% 2 0.92 62.5% 1 0.75 87.5% 7. Cambridge, MD 4 1.86 12.5% 3 1.63 37.5% 2 1.50 62.5% 1 1.27 87.5% 8. Annapolis, MD 4 0.98 12.5% 3 0.85 37.5% 2 0.74 62.5% 1 0.56 87.5% 9. Chesapeake Beach, MD 4 1.15 12.5% 3 1.00 37.5% 2 0.91 62.5% 1 0.77 87.5% 10. Cove Point, MD 4 1.56 12.5% 3 1.34 37.5% 2 1.20 62.5% 1 1.03 87.5% 5-14 Table 5.2 (Cont'd.) Probability of Station Class DMR (feet) Exceedance 11. Solomons Island, MD 4 1.35 12.5% 3 1.20 37.5% 2 1.10 62.5% 1 0.94 87.5% 12. Hoopers Island, MD 4 1.87 12.5% 3 1.56 37.5% 2 1.40 62.5% 1 1.18 87.5% 13. Chance, MD 4 2.46 12.5% 3 2.06 37.5% 2 1.83 62.5% 1 1.53 87.5% 14. Cornfield Harbor, MD 4 1.50 12.5% (Point Lookout), MD 3 1.28 37.5/*b' 2 1.13 62.5% 1 0.94 87.5% 15. Crisfield, MD 4 2.45 12.57. 3 2.03 37.5% 2 1.77 62.5% 1 1.33 87.5% Rn 1 v i Tnnr Md 4- w 0 ig z 2. z w 1. @7 1.07 0.72 0.92 0 0 10 20 30 40 50 60 TO 60 S0 [CC CUMULATIVE PROSABILITY (%) Definition sketch for Baltimore 5-15 After computing the expected variations in tides throughout the tipper Bay, the tidal range was compared to the historic erosion rate for all reaches at least 0.5 kilometers long which contained uniform erosion and tidal characteristics. The results are shown in Figure 5.7. Most of the reaches which were suitable for analysis possessed "low" rates of erosion. There are some slight differences in the curves shown in Figure 5.7, but there are no strong differences in the way tidal ranges are distributed between reaches with low, medium, or high historic erosion rates, Figure 5.7 HISTORICAL SHORELINE RETREAT (FT/YEAR) Above: Figure 5. 7. Graph of relationship between the rate of coastal retreat and Class 4 tides for the northern Chesapeake Bay. 5-16 F. Relation of Storm Surqes to Coastal Retreat 9ased on their origin, major storms along the Chesaneake Bay can be classified into three major categories: (1) Hurricanes and severe tropical storms, (2) Extratropical cyclones or frontal wave disturbances over the mid-Atlantic and southeast coastal states, (3) Wave developments along cold stationary fronts in the Gulf of Mexico west of 85OW longitude. Hurricanes and severe tropical storms are less frequent in the upper Chesapeake Bay but have the potential for producing higher surges because their great intensity can generate waves over the long- est fetches. Extratropical cyclones, mostly occurring during winter periods, are more frequent but their intensities are usually far less. Since most extratropical cyclones have strong "northeaster" winds, the resulting storm surge in the upper Bay is less severe but more uniform over a wide area. The frequency of occurrence and characteristics of different storms in the Chesapeake Bay region have been studied by many investi- gators. Brower et al. (1972) studied the distribution of tropical storms and hurricanes along the Atlantic coast from 1886-1957. Durinq this neriod, a total of seventy-two tropical storms were observed in the Chesapeake Bay area. Their predominant direction was from the southwest and their occurrences were concentrated from June to October with August to October as the most vulnerable period. Boon et al. Qq78) compiled a list of storms Pnterinq the Chesapeake lay area 5-17 between the years 1900 to 1977. A total of one hundred twenty-three tropical storns swept through this area over a record length of seventy-eight Years. Therefore, based upon Irower's account, the Chesapeake Bay area experiences approximately one tropical storm per year whereas Roon's tabulation yielded a higher frequency on the order of 1.5 per year. The discrepancies arise from the following sources: (1) Brower covered a period dating back to 1186 when the record was probably less than adequate. (2) Boon counted many storms (a total of thirteen) twice because these storms changed directions during the period entering the area. (3) Brower counted only observed storms, whereas Boon counted all the recorded storms. In summary, the storm frequency for the upper Bay would be around I to 1.5 peryear. Chen (1978) has studied hurricanes and severe tropical storms for the effect of storm track on the storm surge. Three types of tracks are found to he of great interest in the Chesapeake Bay. One is a track passing to the left of the Ray center; another is the track passing to the right of the Bay center, and the third type is a track passing to the south of the Ray from east to west. These are denoted as HT1, HT2 (or HT2'), and HT3 respectively in Figure 5.8 . Opposite: Fiqure 5.8 . Types of storm tracks in the Tlay region. Table 5.3. Some historical storm surges, comniled in the U.S. Army Corps Chesapeake @ay Future Con- ditions Report. 5-18 Figure 5.8 I 79000 w 760 00 W 740 00 W A 3T000N 370 00 N .......... ... . ....... .... HT3 alp 3400014 Table 5.3 RECENT CHESAPEAKE BAY STORMS STORM TIDAL ELEVATIONS ( Feet Above Mean Sea Level Norfolk Mid Bay Washington Baltimore August 1933 8.0 7.3 9.6 8.2 September 1936 7.5 - 3.0 2.3 October 1954 "Hazel" 3.3 4.8 7.3 6.0 August 1955 "Connie" 4.4 4.6 5.2 6.9 August 1955 "Diane" 4.4 4.5 5.6 5.0 April 1956' Northeaster" 6.5 2.8 4.0 3.3 March 1962 "Northeaster" 7.4 6.0 - 4.7 5-19 In the upper 9ay area, HT2-type storms occur rarely; thus, they are low frequency storms. But these types of storms are the most potent in creating high surges. The 1q33 storm and the 11)55 storm (Connie) which resulted in high storm surges in the upper Bay (Table 5.3) belong to this category. The difference in water heights from strong storm surges and those of extratropical cyclones (which are of higher frequency) can be seen by comparing the storm heights in Table 5.3 with the heights of surges compiled in Frigure 3.2 (Chapter III) from the tide records at Raltimore, Annapolis, and Solomons Island. Since the extratropical storms are far more frequent than the tropical storms, the surge data associated with extratropical storms are also expected to be far more statistically meaningful. Therefore, statistical interpretation of historical data can be used to produce meaningful information for storm surge with "annual" frequency, or with a frequency as high as 0.2 (with a return period of less than 5 years). On the other hand, the relatively small number of tropical storms that produced high surges of record at selected locations in the upper Bay is not sufficient to provide reliable statistical, samples to predict low frequency storm surge levels. Therefore, a computer simulation model was used. This model was developed by Chen (1978) and has been applied nreviously to the prediction of surge in the lower Chesapeake Bay. The basic procedures to produce low freqtiency surge height curves hy computer are as follows: (1) Create synthesized wind fields by a five parameter hurricane wind model. The five parameters are: (a) central pressure, N radius of maximum wind, (c) forward speed, (d) anqle of 5-20 approach, and (e) track. Each of these five parameters has an associated probability of occurrence which is combined to estimate the frequency of storms. (?) The synthesized wind field is next used to drive a finite element hydrodynamic model to compute the storm surge. The storm surge comDutations are repeated for storns with various parametric combinations but with the same joint probability of occurrence. (3) The maximun storm surge levels at selected locations are combined with a probabilistic astronomical tide model to produce the final computer projections of storm surge heights in the upper Bay. The results for a "100-year" storm surge are plotted in Figure 5.10. Predicted "100-year" storm surge heights were also compiled onto a set of atlas maps submitted to the Maryland Department of Natural Resources. A simplified version of the map is contained in Appendix B. As expected, the surge level increases progressively towards the head of the Chesapeake Bay. The predicted surge level is about 4.6 feet near the mouth of the Potomac River and increase to over 11 feet at Havre de Grace. After deriving these computer projections for the "100-year" storm surge, the surge levels were compare for all reaches at least 0.5 km. long where both the historic erosion rate and storm surge levels were 5-21 uniform. The results are plotted in Figure 5.9 . As in the case of the comparison based on tides (Figure 5.7), most of the reaches suitable for analysis possess "low" historic rates of coastal retreat, and there are no general differences in the way predicted "100-year" storm surge levels are distributed between reaches with low, medium, or high historic erosion rates. Figure 5.9 Above: Fiqure 5.9 Graph of relationship between the rate of coastal retreat and the predicted "100-year" storm surge height for northern Chesapeake Bay. opposite: Fiqure 5.10. Height-Frequency estimates of storm surges for the Maryland Bay shore. 5-22 Eastern Shore Western Shore 15 15 14 - 14 0 13 - 13 - X Cn CL 0) 0 Q) -)d Cn 12 - 0 -,id .,1 0 12 - M @4 0 Q) V) M 0 En a Q) 1-4 E .r4 Q) w .1 Q) C14 (U 0 0 -4.4 Q) CL E CL V) 0 M w 0 Q) U) CO cc 0 E I I -I > 0 M 0 0 0 0 0 10 10 R; 9 9 8 8 .002 .002 Lj 41 _r_ 7 x 7 00 .H 6 .01 6 .01 1110-year 4 4 .10 3 Frequency Years 3 Frequency (Years- I 2 2 /EO- 0 1 L 1 01 A A 60 80 100 120 140 80 100 120 140 if Distance from Bay Moutti (Nautical Miles) Distance from Bay Moutli (jNatjtj(-;jj @Iijes) Figure 5.10 Hei ght- Frequency Estimatesof Storm Surge, Maryland Bay Shore. G. Relation of Wave Climate to Coastal Retreat .Wave conditions near the shoreline-and the directions of wave energy flux are probably the most important factors which are needed to assess erosion potential. In northern Chesapeake Bay, only limited ship-observed wave data are available. They are visually-observed data reported by transiting ships. These data are inadequate for use in categorizing the wave climate on shorelines for a number of reasons: (1) The data are insufficient to be statistically meaningful. (2) Most of the observations are from t@e vicinity of main shipping channels whereas the main interests in applying the wave observations is along the shorelines. (3) Sporadic visual observations of wave heights tend to be biased to the median range waves; both high and low waves are often less than adequately recorded. Therefore, to establish wave statistics for erosion assessment a wave hindcast numerical model was used. This model is based on a shallow water wind-wave generation technique developed by Wilson (1965). For restricted and shallow fetches, it is necessary to compute wave heights using a computer model in order to include all important effects, such as bottom friction, irregular fetch areas, and wave breaking. The computer model developed by COER, Inc. is based on an empirical wave height and period formula of Wilson (lq65) and a procedure outlined @y St. Denis (1969). The basic equations are: and 5.1 5.2 Here "H" is the significant wave height (defined as the average height of the highest third of the waves) and "T" is the corresponding wave period; "g" and "U" are gravity and wind speed, respectively, and "F" is the fetch (the distance over which the wind blows). These equa- tions are based on North Sea wave data and are valid for an infinite depth. To incorporate depth effects, a reduction factor 'r' is introduced to reduce the wave height as a result of bottom friction. 5.3 and 5.4 where "k" wave number (2 /L) and "h" is the water depth. The factor "f" is a friction factor, which generally is taken as 0.01 for sandy areas. The x is the distance travelled by the wave over a shallow bottom of depth "h". For computational purposes, a given distance is broken down into numerous lengths " X" of assumed constant depth. The computational procedure consists of a number of steps. 1. The water surface is overlain by a fan of rays emanting from the shoreline point of interest. This fan is symmetrically 5-25 di,5tributed above the wind direction. Along each ray, the depth is determined at a number of points distributed at a distance A x 2. For a particular section along a ray, the wave height entering the section is taken as known. (It either is zero, at the upwind beginning of the ray, or it is known from the previous upwind section). The equivalent fetch length is determined for that wave height, by solving Equation 5.1 for "F". For the new section, a new "F" is computed by adding "A x". A deep water wave height and period are then obtained for the section using the two equations. 3. The wave height reduction factor is then calculated and used to reduce the wave height "H = r-4d"- 4. If the wave height exceeds the breaking wave height, the wave height is reduced to "H = h" where 0.8 and "h" is the average depth over the section. S. Move downwind to the next section and comnute wave heiqht and period there, etc., until the shoreline noint is reached. Repeat for all rays. 6. The significant wave height and period generated at a point is composed of the contribution from all the rays. Therefore IN 2 2 2 ij Hi cos a, Ti(Hi cos a i) H TS 2 2 5.5 cOs2 a, H. cos a .1 where "ot," is the angle the ray "i" makes with the wind direction, and "Hi" is the wave height at the shoreward most section. 5-26 Annual" Wave Statistics. - The distributions of "annual" wave height and direction were computed for the complete shoreline of the northern Chesapeake Bay. The wind input information was based on the long-term statistics at three stations--Baltimore, Annapolis, and Patuxent River which represent artificial divisions of the upper 3ay into three regions: in the upper northern-most region the Baltimore Airport wind data were used; in the middle re(iion the Annapolis data were used; and in the lower northern region the computations were based on the Patuxent River wind information. The complete "annual" wave statistics are presented graphically in atlas form as wave roses that plot the expected significant wave height versus direction. These atlas maps have been supplied to the Maryland Department of Natural Resources. The "annual" wave climate is composed principally of waves whose heights are on the order of 0.5 - 1 foot, and should he regarded with less imDortance than storm-wave conditions in assessing erosion and the performance of shoreline structures. Storm Wave Conditions - One of the important tasks in the present study which is discussed at some length here is the derivation of the storm wave conditions. The heights of these waves were plotted in the case studies in Chapter 11 at the sites of various kinds of structures on the Chesapeake BaY shoreline. Two kinds of storm-wave conditions were studied: the storm, waves due to tropical hurricanes, and the storm waves due to "northeasters". In the computations, the same wind-wave computer proqram was used for the annual wave climate, except that the input wind and initial hydrographic conditions are different. 5-27 Storm Waves Due to Extratropical Storms - As stated earlier, the extratropical storms are associated with low return periods of 10 years or less. For this type of storm waves, the following input conditions are used: Wind Speed : Uniformly over the water. Wind Direction : North, northeast, and east for the western shore and north, northwest and west for the eastern shore. Surge Elevation: Storm surge as obtained from historic tide records illustrated in Frigure 3.2 added to MSL. Storm Waves Due to Tropical Storms - For the case of low-frequency storm waves (here defined as storms of return period higher than 10 years), the input conditions are more difficult to define. This is because the hurricane wind model is not unique but is defined by five oarameters. In theory, by various combinations of these parameters, one can create an infinite number (or at least a large number) of synthesized wind conditions that are compatible to the "100-year" storm in a statistical sense. Foe a designated location, one of these storms will produce the most severe wave conditions. Thus, to de- termine the extreme wave condition for a "100-year" storm, one should test all the possible cases and then identify the most severe one among them. Such an approach is, of course, impractical. For the present study, only one synthesized storm was used. This synthesized "100-year" storm is selected to he compatible to the storms that have produced the highest surges in the upper bay. Based upon the histori- cal records, large storTi surges in the Chesapeake.Bay were usually produced by slow-moving landfall storms of type HT2 (Figure 5.8 ) with large wind radius. These types of storms which generate high surges are assumed to qenerate high waves in the same region also. 5-28 Based upon the above observations, the synthesized "100-year" storm, which was selected for the wave computations assumes the Following basic characteristics: 0 Wind direction South, southwest or southeast. 0 Wind radius "R" 40 nautical miles per hour. This is the mean value of a large radius storm compatible to historical storms causing high surges in the upper bay. 0 Forward speed "VF" - 12 knots, or stalling. 0 Wind strength Maximum wind speed "V pl' - 90 knots (104 mph) for 100-year storm. Maximum hourly wind speed (Vm) - 78 knots (90 mph) 0 Wind field - assumed to be an idealized Rankine vortex expressed as: V v = m r for r < R R (rotational core), and and v = VMR for r > R (irrotational outer region) r where "R" is the radial distance from the hurricane center. See Figure 5.11. 5-29 The wind strength in the above synthesi zed storm is determined in accordance with the procedure recommended by the U.S. National @-Ieather Service (1972). The maximum wind "VP is obtained by V p= 0.868 K (Pn - Po) 1/2 0.5 Rf 5.6 where: VP is the maximum wind speed in knots; Pn and Po are peripheral pressure and central pressure, respectively, in inches of mercury (H 9); R is the radius to maximum wind in nautical miles; f is the Coriolis parameter = 0.525 sin/hour with the latitude; and K is a constant approximately equal to 73. Based upon the design graphs prepared by the U.S. National Weather Service, "PO should be around 27.6 inches Hq for a "100-year" storm in the Chesapeake Say region. The correspondinq 11V should then be on the order of 90 knots. The maximum hourly 11 wind "V M can be estimated as: Vm = 0.865 VP 5.7 = 78 knots or 90 mph This value corresponds reasonably well with the value for extreme conditions extrapolated from the wind records from Baltimore Washington International Airport. Opposite: Figure 5.11. Wind field in idealized hurricane as a function of radius. Also shown is an example weather map for a hurricane. 5-30 Figure 5.11 .1 0 k .1 ITHEL I Soo -Po) SO DORA sot ZZ 30. 10 0. 29 to a SEPTEMBER 9,1964 1200 GMT Hurricane Dora Streamlines Figure 5.11 Wind Field in Idealized Hurricane > - Vrn Z 0 > F /2 F/2-0i' I R Eff ect ive fet ch F 5 0-31 With this hypothetical wind field, the storm waves at any location are generated by the following procedures: (1) The appropriate storm surge height is added to the astronomical tide plus MSL to determine the water depths under storm conditions. (2) Depending upon the location, the wind direction is selected from the three possible choices such that it coincides with the longest effective fetch. For instancet if a certain reach has effective fetches from the south, southeast and southwest of 25, 32 and 29 nautical miles respectivelv, then a wind direction from the southeast is selected. (3) Since the wind-wave generation model assumes a homo- geneous wind field, the mean wind strength over the effective fetch is estimated by the following equation: V R F V F + F V E dr Rdr m (1 + 2,R Xn (1 r- , 5_8 M F R r 2 _iR) M fR-1 R 2 The physical meaning of "V is shown in Figure 5.11. It represents the mean hourly velocity over a reqion that spans one-half the effective fetch length from either side of the peak velocity location. 5-32 (4) Since the strength of the wind over the qeneration area will gradually diminish due to either the storm moving out of the region or energy dissipation, one must check whether the wind-wave generation process is duration limited. To examine this possibility, the effective wind duration "tel' during which the wind velocity maintains "Vm", must he estimated. For a moving storm with forward speed "UF", the value for sit e" is obtained simply as: te F/UR 5.9 For a stalled storm, a storm histogram must he known or assumed. For the present study "UR" is taken as 12 knots as mentioned earlier. This effective wind. duration is now compared with the minimum wind duration "tmin" required to generate the fully risen sea. if "te" is greater than "tmin", the generation is duration-limited. (5) The above input information was fed into the computer model to obtain the storm wave conditions. The result- ing storm wave conditions were used with surge predictions to compute the levels of "Run-Up" for the 40 case studies in Chapter II. 5-33 The results of the storm wave computer forecasts are presented graphically together with the wave forecasts for "annual" storms in atlas form as wave roses that plot the expected significant wave height under storm wind conditions versus direction. These atlas maps have been supplied to the Maryland Department of Natural Resources. Some idea of the kind of wave energy distribution which is predicted around the upper Bay i s il I u strated i n the map i n f i gure 5.12 . The wave energy is arbitrarily categorized as "medium" if the maximum wave height during an "annual" storm is between 2.5 and 4.0 feet. The wave enerqy is considered "high" if the maximum wave height during an 11annual" storm is over 4.0 feet. All the highly-eroding reaches illustrated in Figure 5.2 can be compared with the distribution of wave energy in Figure 5.12. This comparison shows most of the highly-eroding,zones are situated in zones ,of "medium" to "high" wave energy. But the reverse is not true. The shoreline along Calvert County, for instance, is in "high" wave energy, but the historic rate of coastal retreat is generally low. After deriving the computer forecasts of wave climates, the general variations in wave energy were compared to the historic erosion rate for all reaches at least 0.5 km. long which contained uniform erosion and wave characteristics. The results are shown in Figure 5.13. As in the comparisons of storm surge and tide range, most of the reaches which again were of sufficient length to be included in the analysis have "low" historic rates of coastal retreat. Like the Opposite: Figure 5.12. Map showing distribution in wave energy in the Northern Chesapeake Bay. 5-34 Figure 5.12 WAVE ENERGY 760 130' 76D 00' DISTRIBUTI ON .-PENNSYLVANIA ALONG THE WYrA@D NORTHERN CHESAPEAKE BAY SHORELINE HAVRE DE GRACE C D CA IVA L. High "Annual' Maximum Wave BALTIM0 E > 4.0 ft. Medium CHESTER Annual TOWN Maximum Wove 1111N- 2.5-4.0 ft. WAS14INGTON ANNAPOLIS < 39000,- r- IX p so ZIM C) DENTON EASTON "Nor. QL CAMBRIDGE 38030, 00 SALISBURY POCOMOKE CITY CRISFIELD STATUTE MILES 10 0 10 20 D 5-35 graphs in Figures 5.7 and 5.9 the graph in Figure 5.13 reveals no general differences in the way wave climate is distributed between reaches with low, medium, or high historic erosion rates. The pattern emerging from this approach to evaluating erosion suggests that none of the factors necessary to explain erosion (waves, tides, storm surges) are by themselves sufficient to explain why any reach has had a "highil or "low" historic erosion rate. Figure 5.13 ae HISTORICAL SHORELINE RETREAT (FT./YEAR) 0 0 2 4 G 10 12 0 z A N LESS z W 30 THAN 2-5 2 Ix W 60 FT. X 0 W -4.0 > 0 2.5 N U- 30 7 1 FT. 0 >-- 60 z 0- W N OVER a 30- 3 4 4.0 FT W X L U. 601 SLIGHT.... LOW...... MODERATE ........ HIGH Above: Figure 5.13. Graph of relationship between the rate of coastal - zi retreat and the distribution of wave heights on the northern Chesapeake Bay. 5-36 14. Relation of Littoral Drift to Coastal Retreat Longshore sediment transport is the movement of sand more or less oarallel to the shoreline due to waves approaching the shoreline at an angle. The dominant effects of the waves breaking are to: (1) mobi- lize the bottom sediment, and (2) cause a weak lonqshore current in the "downcoast" direction, see Figure 5.1-4. In the Bay where long- shore currents may be due to other caiises, primarily tides, these currents also cause sediment transport. The direction of the long- shore sediment transport changes with time depending on the winds (which generate the waves) and possibly on tidal currents. In some places, there may be a seasonal variation in the longshore sediment transport, and the transport direction may he highly irregular, depending on individual, storms. If structures partially or completely impede the longshore sediment transport, the sand will deposit on the up-drift side of the structure, therebv leaving a siqnature of the direction of recent longshore sediment transport. It is useful to define an unambiguous direction for longshore sediment transport. For purposes here, the definition used in the Shore Protection Manual (1973) will he adopted; that is, the longshore sediment transport is positive if it moves to the right of a shore- based observer. Thus, in Chesapeake Bay on the eastern shore, Is positive" transport is to the north and on the western shore, to the south. This is a purely arbitrary notation. The capacity of the waves to cause longshore sediment transport, Qs, is qenerally,expressed as Q = K H 5/2 sin 2 5.TO S b 5-37 in which Qs = capacity for longshore sediment transport in cubic Yards per year if there is adequate sediment to be transported, K is an empirical constant, K = 3.5 x' 105, Hb is the breaking wave height in feet, and CL b is the breaking wave direction relative to a beach normal (see Figure 5.14). If only the longshore sediment transport is of importance, it is possible to relate changes in longshore sediment transport "Qs" to volumetric erosion rates. For example, referring to Figure 5.15, if the sediment transport rate "QB" out of a region of interest is greater than the sediment transport rate into the region of interest, volumetric erosion 'Y' will occur at a rate 5.11 '2A it B There are several measures of longshore sediment transport that are of interest. The net longshore sediment transport "QN" is either "positive" or "negative" and is given b@y QN = Q+ - Q- 5.12 where "Q+" and "Q-" are the magnitude of the "positive" and 11 negative" longshore transport rates, respectively. If a groin represents a complete littoral barrier installed on a uniform beach, the Opposite: Above: Figure 5-14. Longshore current resulting from waves breaking at an anqle to shoreline. Below: Fiqijre 5.15. Illustration of continuity equation 5.11 (after Dean, 1976). 5-38 Figure 5.14 SCHEMATIC DIAGRAMS OF LITTORAL DRIFT PLAN VIEW 4 4 LONGSHORE CURRENT- SHORE t 74 4 4! ,_p '*--BREAKER LINE Figure 5.15 3 -DIMENSIONAL VIEW 1-0 -MOBILIZED AX SAND 6 It seCTION B sscTjoh A . . .......... OF AREA L( RE 0T @_ @N MOBILIZED SAND_@: 7 5-39 .trapping effect of the groin is "Q@j" and there will be a deposit on the up-drift side of the groin and an erosion on the down-drift side of the groin. The rate at which sand is deposited on the up-drift side of the groin is "Q,4" and the rate at which sand is eroded on the down-drift side is "QN"- The second measure of longshore sediment transport is the gross sediment transport rate "QG": QG=Q++Q- 5.13 representing the total amount of sand being transported past a point on a straight and parallel shoreline. This measure would be of importance in evaluating the potential trapping hy an inlet. If the inlet trans all of the sediment moving toward it, the erosion of sediment on the left side is "Q-" and the erosion of sediment on the right side of the inlet is "Q+". 4 convenient representation, developed by Walton and Dean (11173) is the littoral drift rose (Figure 5.16), by which the potential for net littoral drift QN can be represented for arbitrary shoreline orientations given the wave information (wave direction, height, peri- od and percentage of occurrence; all of which are available from the wind-wave model). The littoral drift rose is computed by selecting a shoreline orientation and then, for each wind direction and the vari- ous wind speeds and associated percentages, computing the littoral drift(ie. the predicted rate of longshore sediment transport) for that shoreline. Then a different shoreline orientation is selected and the process is repeated. Once a sufficient number of opposite: Figure 5.16 Examole applications of the littoral drift rose for two different shoreline locations. Littoral drift roses indicate potential longshore sediment movement from computer simulation not verified by field data. 5-40 Figure 5.16' APPLICATIONS OF THE ROSE SHOWING POTENTIAL LITTORAL DRIFT RATES SHORELINE EXAMPLE 2 N DIRECTION OF NEGATIVE" DRIFT* DIRECTION OF POSITIVE DRIFT* 0 q X cn SHORELINE NORMAL EXAMPLE 2 N SHORELINE NORMAL EXAMPLE I 10 20 30 40 50 cu yd /yr (104) POSITIVE DRIFT-TO RIGHT OF OBSERVER FACING THE WATER --NEGATIVE DRIFT-TO LEFT OF OBSERVER FACING THE WATER r POSITIVE" AND "NEGATIVE" ARE ARBITRARY DI'RECTION DESIGNATIONS FOR REFERENCE USE ONLY 5-41 potential shoreline orientations is computed, the littoral drift rose may be drawn, which graphically represents the potential littoral drift versus shoreline orientation. [email protected])illustrates the use of a littoral drift rose for a hypothetical case for two different shoreline orientations. The solid lines of littoral drift represent "potential" transport (to the right as an observer faces the water) and the dashed lines represent "negative" transport (to the left). The potential annual rate of littoral drift is obtained by constructing a perpendicular to the shoreline and the value where it crosses either a solid or a dashed line represents the net annual littoral drift rate. In the case of a north-south shoreline (Example 1), the net annual littoral drift is approximately 47,000 cubic yards per year to the south. For Example 2, in which the shoreline is oriented north-northwest by south-southwest, the shoreline normal would be as shown and the net annual littoral drift would be 30,*000 cubic yards to the right. For this study, the potential rates of littoral drift were estimated from the computer models of wind and wave conditions which were described previously. The complete distribution of potential littoral drift roses in the northern Chesapeake Bay are plotted graphically in atlas form and have been supplied to the Maryland Department of Natural Resources. An example of the map atlas product is shown in Figure 5.3. Some idea of the kind of longshore movement of sediment which is predicted around the upper Bay is Opposite: Figure 5.17. Map showing potential littoral drift of shoreline sediments on northern Chesapeake Bay shoreline. 5-42 Figure 5.17 I lj@, I - - L- LITTORAL DRIFT 760 30' 760 00' > PENNSYLVANIA POTENTIAL ALONG --;;A - - - -- - RYLAND THE NORTHERN CHESAPEAKE BAY HAV ;ZE DE G RACE C S H 0 R E L I N E CANAL M BALTIMO 50,000-80,000 cubic yds./year C41ESTER@@ TOWN H I g h over 80,000 cubic ycls /year rm WASHINGTON % :01, 4 39 *DO'- ANNAPOLIS M DENTONi EASTON IL b. -1 @j Izz CAPABIQ OGE )K 3 8 3 0'- 0 SA, Q@ STATUTE M ILES 10 0 10 20 5-43 illustrated in the map in Figure 5.17. The littoral drift is catego- rized as "medium" if net littoral transport past a fixed point is estimated between 50,000-80,000 cubic yards/year, and as "high" if the net transport is estimated at greater than 80,000 cubic yards per year. It is important to note that these numerical estimates apply to the rates of longshore movement of all sediment which can he moved about by waves. This can be considered to include sediments at least out to around the nine foot bathymetric contour. All the highly-eroding reaches illustrated in Figure 5.2 can be compared with the distribution of potential, littoral drift rates in Figure 5.18 Above: Figure 5.18. Graph of relationship between the rate of coastal retreat and the distribution of potential littoral drift rates for northern Chesapeake Bay. 5-44 Figure 5.19. This comparison shows most of the highly-eroding areas are situated in zones with potentially high rates of longshore transport of sediments. This is to be expected, since longshore transport of sediments results from a predominance of waves approaching the shoreline from an angle, and the results will be movement of the eroded shoreline sediments away from erosion sites. However, there are reaches with "high" potential net littoral drift which are not highly eroding. After deriving the computer estimates of the distribution of littoral drift, the variations in predicted gross rates of littoral drift were compared to historic erosion rates for all reaches at least 0.5 km. long which contained a uniform prediction of littoral drift characteristics and a uniform historic erosion rate. The results are shown in Figure 5.18. As in the other comparisons discussed so far in this chapter, most of the reaches which were suitable for analysis have "low" rates of erosion. The similarities in the curves show there are no general differences in the way potential littoral drift rates are distributed between reaches with low, medium, or high historic erosion rates. 5-45 I. Relation of Rainfal-I to Coastal Retreat On an annual basis, or even on a monthly basis, the amount of rainfall is rather uniform over the entire upper Chesapeake Bay. Table 5,4 summarizes the normals for the studied area. The total annual amount of roughly 44 inches is more or less evenly distributed over the year with the highest rate of approximately 4i5 inches/month occuring in July and August on the high end and the lowest rate of 3 inches/month- occuring in the months of November and December. The spatial distribution of annual rainfall in the northern Chesapeake Bay region is shown in Figure 5.19. This map can be compared with the distribution of highly eroding areas in Figure 5.2 to show the relationship of rainfall to coastal retreat. But, there appears to be no substantial differences in the distribution of total annual rainfall which could help to explain the variation in shore erosion in the northern Chesapeake Bay over long periods of time. Opposite: Table 5.4. Monthly rainfall data betweeq 1931. and 1960 for Maryland. Figure 5.19 Spatial distribution for the average rainfall in Maryland, from Walker, 1970. 5-46 Table 5.4 Rainfall Data - Monthly Normals - Years 1931 - 1960 (inches) Station Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Annual Elkton, MD 3.46 2.99 4.19 3.60 4.25 3.96 4.35 5.02 3.56 3.23 3.55 3.19 45.35 Annapolis, MD 3.14 2.57 3.62 3.31 3.83 3.51 4.14 4.50 3.46 2.63 2.78 2.85 40.34 Crisfield, MD 3.56 3.15 4.01 3.66 3.69 3.31 5.05 5.05 3.83 3.37 3.24 2.92 44.89 Baltimore, MD 3.43 2.89 3.82 3.60 3.98 3.29 4.22 5.19 3.33 3.18 3.13 2.99 43.05 Coleman, MD 3.61 2.93 3.86 3.43 4.17 3.64 4.29 4.97 3.17 3.08 3.41 3.18 44.28 Solomons, MD 3.55 2.78 3.61 3.50 3.76 3.45 5.57 5.00 3.59 3.11 3.33 2.97 44.22 Washington, D.C. 3.03 2.47 3.21 3.15 4.14 3.21 4.15 4.90 3.83 3.07 2.84 2.78 40.78 Figure 5.19 MARYLAND RAINFALL DISTRIBUTION PENN SYLVAN I A LESS THAN 40 INCHES DELAWARE -40-45 INCHES 45-50INCHES OVER 50INCHES 5-47 J. Characteristics of Highly-Erodin2 Reaches The previous sections of this chapter have des.cribed the information on coastal processes which was compiled for this study, and have examined the relationship of each individual factor to the distribution of historic erosion rates found on different reaches in the northern Chesapeake Bay. Except for shoreline terrain, there were no clear differences which were able to be illustrated between any of the characteristics discussed (waves, tides, storm surges, potential littoral drift rates, or rainfall) and the historic erosion rates around the northern Bay. The relationship between shoreline terrain and historic erosion in Figure 5.4 shows that reaches with the highest historic erosion rates generally are composed of banks less than 10 feet high. A few reaches with high historic erosion rates were also found to consist of marsh. But Figure 5.4 also shows that reaches with marsh, or with higher shoreline banks or bluffs, generally possess low historic rates of coastal retreat. The same type of comparison between historic erosion rates and wave climate, tide range, storm surge, or littoral drift rates failed to illustrate any important differences in the ways each of these characteristics is individually related to the historic erosion of different reaches around the northern Chesapeake Bay. These are the results of one type of approach which can be taken towards evaluating shore erosion in the northern Chesapeake Bay i.e., by first producing maps of predicted wave climate, tide range, or storm surge characteristics around the Ray margins, then next select- ing reaches at least 0.5 km. in length where both the historic erosion rate, and any particular prediction, are uniform and both are able to 5-48 be characterized by a single value, and finally assessing whether reaches with different erosion rates are distributed any differently for one class (for instance, of wave climate or shoreline terrain) than for any other. The results of this approach to evaluating shore erosion were not presented along with any measure of statistical significance, since the statistical meaning would he difficult to interpret. This is because the classifications used in the previous sections represented only the gross characteristics of the shoreline within any reach, and considerable variations can and do exist within each reach. There- fore, the type of evaluation contained in the previous sections is somewhat subjective at places where the shoreline variations are irregular within a reach. 'The res0ts of the analysis in the previous sections simply illustrate that qualitatively, none of the factors which are part of the erosion process are individually sufficient to explain why some shoreline reaches have eroded at high rates,, while others.have retreated more slowly. An alternate approach to evaluating shore erosion in the northern 3ay consists of defining fixed reaches (see Figure 5.20) and catego- rizing shoreline characteristics within each reach. Again, this approach is somewhat subjective, since shoreline variations are irregular within each reach. In particular, it seems important to point out that no generalizations about the shore erosion process in the northern Chesapeake Bay should probably be applied to specific shoreline lengths any less than 0.5 km. long. But within this broad definition, some generalizations can he made about the 32 highly- eroding reaches mentioned on pages 5-4 and 5-6. The generalizations 5-49 listed below are drawn from the information on the maps presented in the previous sections, and from the reach categorizations in Table 5.6 at the end of this chapter. 1. All of the thirty-two highly-eroding reaches are located in regions of either Lowland Deposits or Quarternary Deposits Undivided. The material represented by these geological classifications is, however, quite non-uniform and some formations in outcrop should actually have high resistance to erosion. Furthermore, not all of the shore- line reaches composed of these geological formations are subject to high-erosion rates. For instance, the bayside of Kent Island (reaches 75 to 77) is highly erosional yet the adjacent shoreline in Queen Annes County north of the Chester River experiences only slight shoreline retreat although both regions have similar geological and environ- mental conditions. 2. All the thir ty-two reaches are in areas of low shoreline relief. All the nine high-erosion reaches are points, islands or tips of lowland. 3. Most of the thirty-two reaches, except one (reach 80) on the eastern shore, are situated in medium-to-high wave- energy zones. Again, the reverse is not true. The shore- Opposite: Figure 5.20. Map of northern Chesapeake Bay shoreline reach designations. General characteristics of each reach are presented in Table 5.6. 5-50 Figure 5.20 Illustration of Northern Chesapeake Bay Reach Designations Shown in Table 5.6 HAVRE DE GRACE BALTIMO E CHESTERTOWN WASHINGTON ANNAPOLIS OEASTON ly CAMBRIDGE C> SALISBURY '91 0 *6d 5-51 line along Calvert County, for instance, is in the high wave-energy zone. Yet, the historic rate of shoreline retreat is small. 4. The correlation between "net littoral drift" and "historical erosion" is less coherent. Reaches 64, 71, 72 and 73 do not currently have high erosion, although the net drift values for these reaches are hiqh. Thus, the maximum value in the littoral drift rose derived for any particular reach provides a better indication of erosion potential than the net drift for a certain shore orientation within any reach. A more detailed investigation was performed for the nine hiqh-erosion reaches to see whether common factors could be identified. Reach 14 - Pt. Lookout to Saint Jerome Creek, St. Mary's County This reach is about 5 miles long at the southern tip of St. Mary's County where the Potomac River meets the Chesapeake Bay. According to a historical map from 1849-1942, the shoreline retreat has been quite significant. There are three sub-reaches (about 1/3 of the total length) where the erosion can be classified as high (see Fiqure 5.21 ). Recent surveys at the control line "qIM7", however, seemed to indicate that the erosion has decreased considerably in this vicinity to less than 1 ft/yr. These survey results could he tilislead- ing as they were taken at the updrift end of coastal protection struc- tures emplaced at Scotland Beach. opposite: Fiqure 5.21. Shoreline retreat at Reach 14. 5-52 Fiqure 5.21 1849 SHORELINE Shoreline Retreat at Reach #14 1942 St. Mary's County SHORELINE ROSE OF POTENTIAL LITTORAL DRIFT RATES positive drift direction negative drift direction N-.O 2'03.'01'4.05.0 -,cu. yd. /yr. 0 0 SCOTLAND \BEACH BM7 k 0 BM7 Uj -3- LL - -5 1 1 -4 1970 1971 1972 1973 0 1/2 MILE 0 POINT I KILOMETER LOOKOUT 5-53 Geologically, this area is completely in the Quaternary Lowland Deposits with low coastal relief. The sub-aerial material is non- uniform but is qenerally of high resistance to erosion. The offshore slope is mild with fine sand found in the center section of the reach (see Case No. 13 structure described in Chaoter 11). Also, there is no material supply from the south other than from offshore. The area is exposed to a long fetch from the south, and is thus susceptible to tropical storm attack. The annual wave energy as computed is classified as "high". The predicted annual littoral drift is predominantly toward the north at approximately 3 to 4 x 104 cuhicyards per year. This quantity is considered to be "medium". The fact that the drift is toward the north (with no material from the south), coupled with low sub-aerial relief, results in high shoreline retreat. Reaches 26 and 31, Holland Point and Thomas Point, Anne Arundel County The high erosion is a local effect near the points. Geologically t0e areas are in Lowland Deposits with low sub-aerial relief. The material has high resistance to erosion. This is a high wave energy zone and exposed to both tropical and extratropical storm attack. The orientation of the point also makes it vunerable to high erosion. The predictions of littoral drift indicate that material moves away from these points in both direction. Opposite: Figure b.22. Shoreline retreat at Reach 86. 5-54 Figure 5.22 Shoreline Retreat at Reach 86 ROSE OF POTENTIAL Talbot County LITTORAL DRIFT RATES TILGHMAN IN 01 1 S LAND -.0.0 positive drift direction drift direction - - - - 1847 0100, SHORELINE 1942 510 4@O 10 2b 1.0 SHORELINE \%CU. JjT (104). BIV12 0 _10- _20- -30- BM2 0 1/2 1 MILE 40- i I I I I U. 0 1 KILOME-('ER -50- _60- -70- -80 4 -4 1969 1970 1971 1972 1973 1974 5-55 Reach 77, Price Creek to Kent Point, Kent Island, Queen Annes County This reach is the southern part of Kent Island. The erosion rate is actually between medium-to high but becomes progressively more severe near the southern tip. Geologically, it is Quaternary Lowland Deposits with low relief. The sub-aerial material is non-uniform but generally can be classified as low-to-medium resistance to erosion. The wave energy level is high; the erosion potential is also high. In addition, the littoral drift direction is unfavorable in that there is no material supply from the adJacent land. In general, the combined conditions are conducive for causing a high erosion rate. Reach 86 - Lowes Point to Knapps Narrows, Talbot County This reach is the southern part of Tilghman Island. The area suffers high erosion except for a short sub-reach in the middle where the erosion is low (Figure 5.22). Based upon recent surveys, the erosion has not been slowing down; 80 linear feet have been lost during a recent five year period,(Figure 5.22). This area is also composed of Quarternary Lowland Deposits with low sub-aerial relief. The material is very non-uniform varying from low resistance to high resistance. Because the area is flanked by shallow shoals, the wave energy is only moderate, although the area is exposed. Based upon the littoral drift rose and the present shoreline Opposite: Table 5.5. Storm wave conditions at the nine high-erosion reaches. 5-56 Table 5.5 Storm Wave Conditions at the Nine High-Erosion Reaches Storm Wave Height (ft) Reach 1 year* 5 year* 10 year** 20 year 50 year 100 year 14 5.56 8.83 10.31 11.11 12.20 12.76 26 5.20 8.25 9.85 10.66 12.11 13.03 31 0.50 0.79 9.14 9.97 11.00 11.67 77 3.86 6.15 8.16 8.88 10.13 10.92 86 4.53 6.92 7.63 8.57 9.38 9.95 87 4.55 7.17 7.57 8.39 9.32 9.99 99 5.30 8.18 3.89 4.57 4.96 5.25 101 4.93 7.04 7.18 7.80 8.84 9.58 103 4.59 6.73 8.68 9.43 10.51 11.219 104 4.74 7.15 7.84 8.48 9.57 10.23 Based upon extra-tropical storm (Northeaster). Main direction from north, NE or NW. Based upon tropical storms. main direction from south, S11 or SE. 5-57 orientation, the littoral drift should be moderate; however it can account for the high shoreline retreat because of the low shoreline relief. Reaches 99, 101, 103 and 105 From Mills Point to Barren Island, Dorchester County All these reaches are in the Quaternary Deposits Undivided area, all with very low relief of only a few feet. The sub-aerial material is qenerally considered highly resistant to erosion. All the sub- reaches that experience high historical erosion are on the bayside. All of them are either islands or tips of lowland protruding into the hay. Because of shallow water conditions surrounding these reaches, the annual wave conditions are not exceptionally high compared with the rest of the bayshore. However, the storm waves could be just as severe as any exposed area because of high storm surge conditions. All the reaches except Reach 99 are susceptible to both extra- tropical and tropical storm waves. Reach 99, on the other hand, is sheltered from severe waves from the south, but is subject to higher waves from the north than the other reaches. Almost all of them are subject to high potential littoral drift but not necessarily high net drift with their present shoreline orientations. Table 5.5 summarizes the storm wave conditions at the nine high- erosion reaches. In this table, the "I-year" and "5-1year" storm waves are based u,pon extra-tropical storms with directions assumed to be from 111, ME or NW; abnormally low values (Reach 31) mean the reaches 5-58 are shielded from this type of storm. The storm waves with return period higher than 10 years are based upon: tropical storms with direction from S, SE or SW; aqain, exceptionally low values (Reach 91) result from reaches shielded from tropical storm waves. K. Classification of Coastal Characteristics For future assessment of erosion conditions in northern Chesapeake Bay, Table 5.6 was prepared. In this table, the shoreline is identified by reaches shown in Figure 5.20; within each reach, the historical erosion rate is listed along with many other important factors. The interpretations of each column are given here. Column 1: Reach Number - See Figure 5.20 for location Column 2: Historical Erosion Rate - Data from MCZMP atlas "Historical S ines and Erosion Rates." S (Slight) - less than 2 linear feet per year L (Light) - 2 to 4 linear feet per year M (Medium) - 4 to 8 linear feet per year H (High) - greater than 9 linear feet per year A (Accretion) - Accretion reach Column 3: Shoreline Characteristics Dominant Type: From page 5-7 Column 4: Mean Tide Range - In feet from Appendix B Column 5: 100-Year Storm Surge - In feet from Appendix B Column 6: Wave Energy: Based on maximum wave height in 30 moh wind. L - less than 2.5 ft. M - 2.5 ft. to 4 ft. H - higher than 4 ft. 5-59 Column 7: Net Drift Characteristics Drift Potential: (in 104 cy/yr.) Based on the net littoral drift rose and mean shoreline orientation as explained in Section H. + means drift direction towards right with observer facing the water. means drift direction towards left with observer facing the water. x means difficult to interpret. Double value means two major shoreline orientations in one reach. The drift directions analyzed from aerial photographs are included in Table 5.6 to a'id in the determination of the stability and direction of littoral drift as well as to compare with the prediction. As can be seen from the comparison, the agreement hetween the predicted and observed drift directions is quite good. It must he noted that the historic erosion rate classifications in Table 5.6 represent only the gross characteristics within each reach. Considerable variations could exist within each reach. That is, i'f a reach is classified as highly erosional, it may contain sub- regions where the erosion is slight or even accretional. Therefore, the classification is somewhat subjective at times when the shoreline variations are irregular within the reach. 5-60 TABLE 5..6 CHESAPEAKE BAY SHORELIl'E CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN "100-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM AERIAL PHOTOGRAPHS 7-0 i5-r 144 2 V 5 Io zoo 4t ly A 12- y 5 "@LI44Z@16 aqk,----k YA IVA-e- ys P//V,e-y 7@@wr Ig F- y ;PMIX,4c RIVF-R 2201,0-r- -5r7 R,q,-,5 InAPZ Y 5 YDS-lyll? Ys 5 I.IVR Inqz Y S TABLE 5.6 CHESAPEAKE BAY SHORELII'E CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN I 00-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM (ft.) (ft.) AERIAL PHOTOGRAPHS joxe@ ,077`5 141 m4a v ao,elt)FIce-LD ;-7@!)//07- M4e, V 5 Z"( Po//V 7- lk oo/zoo Dig H r :5 r CIO + ,PlAAf-- #16L RZt,,V 12 V,05 + AYR J"/ d a YP5 Ale- At-lb n5p,4p Lbll-07- TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN I 00-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE S19ORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM AERIAL PHOTOGRAPHS CIO. yn; I-YR 1,1mc-e- cot/,-- clu plq@olztlw ae6_12:51k Co. YP5 LAJ AM/V-1 7 4@,76 912thVj7EZ- gl-sw11z)Lj- 'w/v C41 TABLE 5.6 CHESAPEAKE BAY SHORELIl'E CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN I 00-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM AERIAL PHOTOGRAPHS Y,9' 5 /y/l? e2 &-Z@ - 7,@ eq oo Co. y'-%1y1e. (- D 90 -T)V,L7/-An4/t/ P-DIAl 7- - -9000e:> t V 7- -) 5, 001 yo@@/ +) YR 7;;"o Y05 (4-) AIVNC- 4AIlU C- I ne- 9A) D I/ P0 0.5 ''Y0,51ye o-) qz djv@@L- 41YNL-Z C0 TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN 11100-yr.11 WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM AERIAL PHOTOGRAPHS AV V_,@:7 141 dV - y17!@ /X/,@ AVIV Ul AIV n). //V s ??zm) 7- / 00 r3 9--z TA-BLE -5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN 1 00-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM AERIAL PHOTOGRAPHS A 0005--r PDI"v o h4,@@ /0- Y, paw-, - y" 50 -'5,41V D Y P0,lA,`-7 - ;Z@@IAJ -7- co, -/004on 1-7 V, i /p 51@ TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE MEAN 1 00-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM (ft.) AERIAL PHOTOGRAPHS E -?V55 )?ccletl -rL)1?1<C-11 4>04,V7- 1.5 7 A' ,@@,Rcl vie A---mllj -7- 4 Z Al 7-0A) - All oa yp:@Iye k4o hlow6a- 0u. VA51YR ze)/ L tic). TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN "100-yr." WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM (ft.) AERIAL PHOTOGRAPHS -70 06). yp5lyk -Z Z-/ AlEIV 7- C4, Ln 00 0 00 /3 14 14 ;@70 J2,d4V 75, 000 k@ L7 t W)dl,-&12(1 7A'(21Zte@ ;2- 9 TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE MEAN I 00-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM (ft.) (ft.) AERIAL PHOTOGRAPHS o0e) 7,6 _,7 04:51-07, IYR, @)V& A) 70, 06a 10 - y1pOw c- F 3-9 1-2 re.,), 0 le, 5- y 77, 3 d,@l yx Ae TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HIS ORIC SHORE MEAN "100-yr.11 WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM (ft.) (ft.) AERIAL PHOTOGRAPHS /@Z@2 5AP141 7@11V zlc- "VN6--r7- INA Y-1) *95 -1144,@wwo 0, 006 Alwpc-s 13 U'l 000 1-71 -4@ a e-) yz) 5/y/; klotoz---e 154f Ne@-111-1 ou. -77@-@AC) -d- bc@ upkIleg- 617c -2 o" 0 cyo 911V7 44 d oY 0 51YR (+ TABLE 5.6 CHESAPEAKE BAY SHORELI17E CATECORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN 11100-yr.1' WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM AERIAL PHOTOGRAPHS @1-wopr":@,VZ pl;i5R@ 5-0 1,44 -7ZR /:5 # (27Z C--@- K 114 99 11116Je V P,0,1,,V7e- 7- (2 0, ty-OR C+) ,46 ?@l 00. Ul jo re a 51YR Z)o X/ 61 ev Y, P 51 -DOE -zo ou. (+ TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN 11100-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM AERIAL PHOTOGRAPHS ono e 0 -4 - -70, rot) 20. VD 51YID #0 3 51 Inc 0y5-;:25R A4 U-1 e C4J A ea Y/9 Jr Al@ v , -!i, a. VP,- TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN "100-yr.". WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM (ft.) (ft.) AERIAL PHOTOGRAPHS D WAO ol" -DDR + 5XW.PV 1:54Avi) 3 0 31 c; -7Z<) /4@5- 1@3, r 61 - vpVy,1,e v P,51YR TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN I 00-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM AERIAL PHOTOGRAPHS 1701V&D Ll -?1Rl'117-? Polll/v -7 @7 + 2-- 'gwl@zo 2-9 -.7- coo 441-2-1 7447-6qP 5-3 2-9 5-2 2-7 "l-Y7,ge J'w'vp-) Al y/e '500,,& 0, AR TABLE 5.6 CHESAPEAKE BAY SHORELIVE CATEGORIZATION REACH NUMBER AND LOCATION HISTORIC SHORE 14EAN I 00-yr. WAVE COMPUTER PREDICTION OF COUNTY EROSION TYPE TIDE STORM ENERGY NET LITTORAL DRIFT RATE RATE RANGE SURGE AND DIRECTION ( ) FROM AERIAL PHOTOGRAPHS W J@17@1 7110q,pollv-7 - 17 + CHAPTER VI STATISTICAL MODELLING OF HISTORICAL SHORE EROSION PATTERNS Randall K. Spoeri A. Introduction In the previous chapter, variations were described in several coastal processes, and a subjective, qualitative analysis was performed to examine the relationship between the historical rate of coastal retreat and each environmental variable: terrain, tide range, storm conditions, wave climate, and littoral drift. A general classification of shoreline characteristics was also compiled in Table 5.6 for 128 separate reaches of Maryland's shoreline on the Chesapeake Bay and on the lower Potomac River. In this chapter, a more objective statistical approach is used to analyze the information presented in Table 5.6, and to illustrate the statistical utility of the different environmental variables to estimate the erosion rate on a general Bay-wide basis. For this portion of the study, six variables were suhiected to further analysis: 9 Historical Erosion Rate 0 Dominant Shoreline Type 6 Mean Tide Range 6 "100-Year" Storm Surge 0 Wave Energy 0 Littoral Drift These variables were defined in sections of the previous chapter. For those reaches having missing values for certain variables, estimated values were provided from the detailed maps furnished hy COER, Inc. to the 6-1 Tidewater Administration. Furthe@,,more, dominant shoreline type (Chapter V, Section D) contained a very large number of categories (20). For the sake of simplifying the analysis discussed in the following sections of this chapter, these detailed categories for shoreline terrain were synthesized into seven qeneral divisions: 0 Reach 0 Beach with Headland less than 20 feet hiqh 0 Beach with Headland greater than 20 feet high 0 Headland less than ?0 feet hiqh 0 Headland greater than 20 feet high 0 Shore 0 Marsh This determination was made for each reach, by relying on the detailed observations of the shoreline compiled by student interns from Anne Arundel Community College. A final correction which was applied to the information in Table 5.5 was to eliminate twenty-one reaches which were not considered to be necessarilY representative o-F the main Chesapeake lay shoreline in Maryland. These reaches were Numbers 1-0 (all along the lower Potomac River), Numbers 73-82 (back side of Kent Island and Eastern 9ay) and Numbers 108-110 (lower Eastern Shore). The remaining one hundred seven reaches, or units of analysis, served as the data base for subsequent statistical analysis. Historical erosion rates on each of these reaches is predicted (or modelled) as a function of the remaininq five variables listed on the previous page, by organizing the values from Table 5.5 (with changes noted above) into a computerized data file, and perfonning various analyses. 6-2 The statistical analyses performed for this data can be organized into three categories: 0 Descriptive Statistical Analysis 0 Regression Analysis 0 Discriminant Analysis For these analyses, three statistical computer program package sources were employed: 0 Statistical Package for the Social Sciences (SPSS) Nie et. al., (1975). 0 Minitab- Ryan, et. al., (1981) 0 Miscellaneous Special Purpose Programs B. Descriptive Statistical Analysis Descriptive statistical methods are useful in summarizing large amounts of data as well as for examining the characteristics, distribu- tional properties, and interrelationships for variables under analysis. In this study, a variety of summary statistics and graphical methods were used to carefully examine the data in an effort to reveal patterns, extremely large or small values, and, in general, simolv to explore the data struc- tures. Such summary measures as the mean, standard deviation, and correla- tion coefficient were calculated and examined for the variables described previously. In addition, a variety of graphical displays were produced and evaluated. These included the more traditional histograms, bar charts, and scatter plots, as well as some of the newer methods generally referred to as "Exploratorv Data Analvsis" (EDA) methods. A full description of the EDA methods is given by McNeil (1977). Such EDA displays as "Stem-and- Leaf", "Boxnlots", and "Smooths" were used. 6-3 The results of these descriptive analyses suqgested a number of rela- tionships and patterns which may he useful in subsequent studies, and also helped to exr)lain some results observed in the regression and discriminant analyses. In general however, no "bad" data were identified although several seeminqly nonlinear relationships were apparent. This fact will be noted in later discussion. C. Reqression Analysis For this study, it was desirable to describe the joint relationship between a single dependent variable Y, the historic erosion rate on any particular reach, and several independent variables Xi, the values for wave climate, tide range, storm cor.@Ntions,, littoral drift rates, and shoreline terrain listed in Table 5.5. As mentioned in Chapter V, the historic erosion rate classifications represent only the gross characteris- tics within each shoreline reach, and the classification is necessarily subjective at times when the shoreline variations are irregular within the reach. This needs to he kept in mind when considering the results presented below. In order to determine if histeric erosion rates could he nredicted confidently on the one hundred-seven reaches as a function of the five explanatory variables, a multiple linear regression model was hypothesized: Yi = @O + @Ixii + @2x2i + @3X 3i + @4X 4i _@- @5X 5i + E:i (6.1) where: i indexes the In7 reaches Yi = historic erosion rate of the ith reach X1i = dominant shore type of the ith reach 6-4 X2i = mean tide for the ith reach X3i = "100-year" storm surge for the ith reach X4i = wave energy of the ith reach X5i = littoral drift of the ith reach. The @i values indicate model parameters to be estimated from the data and Ei represents a random error term, indicating the "lack of fit" of the explanatory variables to Yi. A thorough treatment of regression analysis is provided in Draper and Smith (1968). Now, in order to properly use a multiple regression analysis, each of the variables must he numerical. Since Y, X1, and X4 were categorical, an additional steD was necessary prior to performing the regression analysis. This involved the creation of "indicator variables" to represent the categories defined by variables X1 and X4- Y was quantified by letting Y 0, if historic erosion rate was A (accretion) 1, If 11 11 11 S 2, It It L If If It 3, M L 4, It H Then for Xii, six indicator or "dummy" variables were introduced, where Dli =j1, if the ith reach was a beach 0, if other-wTse D2i 1, if the ith reach was a heach with headland less than 20 feet. 0, if otherwise D =11, if the ith reach was a hIeach with headland greater than 3i 20 feet 0, if otherwise 6-5 if the ith reach was a headland less than 20 feet if other wise if the ith reach was a headland greater than 20 feet if otherwise if the ith reach was a shore if otherwise Obviously, if then the reach is a marsh. The variable X4 in equation 6.1 was similarlv transformed into two indicator variables for the regression analysis. A thorough treatment of the use of indicator variables is given by Neter and Wasserman (1974). A computer proqram was then written to transform the previously structured data file into a completly numerical data file incorporating the transformed Y, the six indicator variables representing X1 and the two indicator variables for X4. Finallv, the multiple linear regression model fit to the erosion data file can he expressed as (omitting the reach subscript "i" for simplicity): Hence, the final model involved the use of 11 explanatory variables, for which 12 parameters were to he estimated. The resultant estimates and their standard errors(A measure of an estimate's. "stability"), are shown in Table 5.1. At the a 0.05 significance level, only variables (dominant shore type = heach with headland greater than 20 feet high) and ("100 -year" storm surge coefficients which were statistica11y siginificantly different from zero. Further more, the "R2" statisti was 0.3077 for this model. This statistic renresents the amount of variation 5-6 Tahl e 6.1 Parameter 'Estimates and Standarl Errors for the Linear Regression Model Regression Standard Variable Coefficient (bi) Error (S(bi)) intercept 3.402917 01 0.228297 0.266250 -0.029221 0.375726 02 D3 -1.008549 0.422220 D4 -0.702722 0.375946 D5 -0.977971 0.638387 D 6 -0.077129 0.303585 X2 -0.229369 0.396837 X3 -0.153162 0.049054 D7 -0.498455 0.485153 D8 -0.204231 0.221474 X 5 0.040058 1.031133 in historic erosion rates which was explained by or oredicted using the eleven independent variables. The largest which R2 can be is 1.0 if there is perfect fit of all the data to the predictive equation. Accordingly, only 30.77% of the variation in Y was predicted using the linear model (equation 6.2).. Consequently, this particular model does not provide an adequate tool for suitably predicting, or modelling, the historical pattern of erosion on a general Bay-wide basis for Maryland. As a further check, a stepwise regression analysis was performed to determine which of the 11 predictor candidates wotild be most useful. This 6-7 analysis identified only two variables: variable X3 ("100-year" storm surge), and variable D, (dominant shore type = beach) as being the only useful variables at the 0.05 level of significance. R2 for this two variable model was only ?').73% exr)lained variation. In summary, the results of the regression analysis indicate that a multiple linear regression model does not provide a useful tool to suitably predict erosion rate as a function of environmental variables for portions of the main Chesapeake By shoreline in Maryland. It is important to note, however, that various technical assumptions may well have been violated in performing the regression analysis described in this section. These assumptions include linearity of the data, independence of the observa- tions, and common variance of the Y's across the range of the Xi's. Based on the descriptive analysis reported in section B of this chapter, and on a post-reqression residual analysis, it is suspected that, at a minimum, nonlinearity exists in the data. This means that the statistical relationship between the pattern of historic erosion around the northern Bay shoreline and the environmental variables might be more accurately assessed by introducing polynomial, multiplicative, or possibly exponential functions of the variables@ into the regression model. However the physical meaning of these results, should they prove to be a closer predictive fit of the data, would have to be carefully interpreted. Other assumptions may also have been violated. Nevertheless, it was not considered within the scope or time frame of the present study to investiqate all potential statistical relationships in the data, or to seek remedial measures or alternative models. That is a subject for later study. 6-3 D Discriminant Analysis In an effort to confirm the conclusions reached based on the regression analysis, ;in alternative statistical method was ipplied to the erosion data file. This method is called discriminant analysis. A good overview of the technique is given by Kendall (1975), while a thorough treatment of the subject can be found in Lachenbruch (1975). The basic objective of a discriminant analysis is to decide, on the basis of measured variables, to which of two or more predefined groups a particular unit of analysis should be assigned or classified. In this case, the unit of analysis was a shoreline reach along the main Chesapeake lay shoreline in Maryland, and the variables were those described previously for use in the regression analysis. There were five predefined groups: (1) Reaches experiencing accretion (A) (2) Reaches exneriencing a slight hi storical erosion rate (S) (3) Reaches experiencing a low historical erosion rate M (4) Reaches exneriencing a moderate historical erosion rate N (5) Reaches experiencing a high historical erosion rate W. When performing discriminant analysis, one heqins with a set of units which have been classified and for which measured variables are available. The technique then involves using this information to create a classifica- tion scheme (statistical model) @y which future units, whose grouO affili- ation is not known, can be classified. In this process, it is frequently of interest to also determine which of the measured variables is most use- ful or "important" in distinq1lishing among was not groups, although th the purpose of this study. Here, the goal was to be able to develop a mathematical expression (model) by which "future" reaches could he 6-9 categorized into one of the above groups. In this analysis, the SPSS (see Nie, et. al., (1975)) discriminant analysis program was used. A variety of information is provided by this computer program. A portion of this infor- mation is given in Table 6.2. The principal result of interest was the "misclassification rate." This indicates the proportion of reaches which would be incorrectly classified if they were to be "reclassified" using the discriminant analysis methodology previously developed. The percentage of all "classified" reaches correctly "reclassified" was 47.66%, so that the overall "chances" of properly classifying a shoreline reach on the basis of Table 6.2 Prediction Results Based on Discriminant Analysis Actual Historical Number of Predicted Historical Erosion Rate Reaches Erosion Rate A S L M H A 1 0 0 0 0 100% 0% 0% 0% 0% S 39 2 16 12 4 5.1% 41.0% 30.8% 12.8% 10.3% L 38 3 4 19 4 8 7.9% 10.5% 50.0% 10.5% 21.1% M 21 1 0 4 9 7 4.8% 0% 19.0% 42.9% 33.3% H 8 0 0 0 2 6 0% 0% ft 25.0% 75.0% IDT Overall number correctly classified = 51 out of 107 Overall % correctly classified = 47.56% Overall % incorrectly classified = 52.34% 6-10 the measured variables is less than 50%. Therefore, this approach seems to confirm the conclusions reached from the regression analysis. As with the regression analysis, no attempt was made to examine adhere nce to the technical assumptions required by discriminant analysis. This would be an important next step in the modelling effort. E. Summary In conclusion, the initial results seem to indicate that modelling the pattern of historic erosion rates around the edges of the main 'Chesapeake Bay in Maryland cannot he suitably done by using traditional regression or discriminant analysis nrocedures. This could he due to several causes. Among them are: 6 Monlinearities in the data 0 Violations of other technical assumptions 6 Poor data quality 0 Relevant variables not included. The analysis presented in this chapter is necessarily preliminary in nature, due to lack of useful results from only standard statistical approaches. To achieve the goal of explaining in a mathematical manner the reasons why different shoreline reaches on the Chesapeake lay in Many- land experience varying rates of historic coastal retreat, further statis- tical analysis and research would be necessary. This research would include the use of nonlinear models, various other data transformations, and alternative statistical methods, such as time series analysis. Even if these procedures were performed and were found to yield useful and encour- aging results from a statistical point of view, the physical meaning and tisefulness of the results to Bay managers would have to he carefully assessed. 6-11 I 6-12 CHAPTER VII LAND USE AND SHORE EROSION Vic Klemas, 4siang Ilang Robert Riggs, Robert Dalrymple A. Introduction Land use is one factor which has been often cited as influencinq erosion of shoreline (Dolan, et al. 1980*, Pilkey, et al. 1978), but the evidence is less than conclusive. A portion of this study was allocated to an examination of land-use changes in four selected shorefront areas (Figure 7.1) for evidence of impact on the shore erosion rate. 8. Methods The land-use analysis was performed directly on aerial photo index sheets which are available from the Agricultural Stabilization and Conser- vation Service of the U.S. Department of Agriculture. Aerial photo mosaic index sheets at a scale of 1:40,000 were chosen, since the individual pho- tographs at a scale of 1:20,000 would have been much too costly to obtain and too time-consuming to analyze. LANDSAT satellite imagers is also available but does not have the required spatial resolution and is avail- able only from 1972 to the present time. The aerial photo index sheets were flown as follows: 1. Queen Annes County 1937, '52, '57, '64, '72 2. Talbot County 19379 '52, '57, '64, 172 3. Anne Arundel County 1938, '52, '57, 163, '70 4. Calvert County 193% '52, '57, '64, 171 Opposite: Figure 7.1. Shoreline reaches in four counties which were analvzed for land-use relationships to shore erosion between 1939-1971. 7-1. Figure 7.1 6 0130, 7 65 000' SHORELINE PENNSYLVANIA REACHES --`MAZEA@O -T IN FOUR COUNTIES HAVRE DE GRACE C D WHICH WERE CANAL ANALYZED FOR EFFECTS OF SALTIMO LAND USE ON SHORE EROSION CHESTER- TOWN R. w z z z WASHINGTON 4 -c . lp 39000,- ANNA OLIS z r Ili w w lp z w z OENTONi EASTON 0 lz ol 1.161 > lz CAMBRIDGE X 1 rn SALISBURY POCOMOKE CRISFIELD 1-y STATUTE MILES 10 0 10 20 ..oo 149.1 7-2 Land-use was mapped on these sheets by visual photo-interpretation for a 250 meter wide strip along the shoreline in each year. Table 7.1 summarizes the patterns of development in the four test areas. The land- use categories which were identified included the following: 0 Lightly Developed M. (One house per acre or lower density) 0 Heavily Developed (H) (One house per 1/2 acre or higher density; marinas; commercial development; etc.) 0 Agricultural Land (A) (Cultivated or uncultivated fields reaching shoreline) Agriculture with Protective Strip (S) (Fields separated from beach by protective strip of trees or shrubs) a Forest and Uplands Vegetation W (Forest, shrubs, and other uplands vegetation) 0 Salt or Brackish Estuarine Marsh M (Includes river marshes in Calvert County) The interpreted shoreline lengths may he smaller than the actual shoreline distances on a man because creek mouths, small bays, inlets and other curved shoreline stretches were approximated by short straight segments. The accuracy of the land-use interpretation for the 1952, 1963-64 and 1970-72 dates is estimated at about + 7.5% of the stated lengths. For the 1937-38 time period, it is expected that the relative errors on the land- use maps are less than + 15%. Since land-use changes between 1937-38 and Onposite: Table 7.1. Land-use data and erosion rates. 7-3 Table 7.1 w z > w 49 w cc cnJ >- 0. >- a. L) _j 0 0 W CL @- -j -j &n w - x w > W w 0 m z 0 cc > 4c > 4 wo 0 z 0 w W w W owwa U. 44 ANNE ARUNDEL COUNTY FROM ROCK Pr. TO SANDY PT 933 1952 t4 1963 1970 0 50 0 50 0 50 0 50 0 so 0 50 CALVER" COUNTY FROM CHESAPEAKE BEACH TO DRUM PT. 1938 1952 964 1971 0 50 0 50 o 56 0 5io 0 50 QUEEN AN NES COUNTY FROM LOVE PT. TO KENT PT. 1938 1952 1957 1964 1972 io 0 50 TALBOT COUNTY FROM TILGHMAN PT. TO TILGHMAN IS. 1938 1952 IS 1964 1972 ; ,I - .1 ,.1 1 1 1 1 1 - II, I t I i 0 50 0 50 0 50 -5 t 0 50 0 50 0 SHOREFRONT LAND USE CHANGES 7-4 1()52 were small when compared to later periods (Table 7.1), the exnected overall accuracy of the percentaqe land-tise change results is estimated to be within abolit + 10%. C. Results As expected, agricultural land-use has decreased and developed areas have increased along the shoreline in all four test areas. This is particularly evident at the eastern shore sites. The development of the western shore was much more rapid than that of the eastern shore sites. The marsh areas have also decreased with time at each study site. The loss of forested or uplands areas to development appears slow, primarily because in the analysis, a large forested lot (e.g. ten acres) with a house on it was classified as forest or uplands M and not lightly developed (L). Because the land-use patterns are constantly changing, it is not pos- sible to relate this factor to the trends in shore erosion which must be measured over time-scales of decades. It is not possible to identify reaches greater"than 0.5 kilometers in the four test areas which have had a single land-use classification since 1937, and reaches of sufficient length and stable land-use elsewhere along the Chesapeake Say are probably very rare. The selection of 0.5 kilometers as a minimum length for study is arbitrary, but this is the smallest reach length which is regarded as suit- able for analyzing variations in historical rates of shoreline erosion. In summary, the attempt to relate land-iise characteristics to rates of coastal retreat was not successful because it was not possible to identify reaches which have had a similar land-use classification for a sufficient period of time. But this does not mean land-use cannot he siqnificant in shore erosion. The DNR Major Facilities Siting Study (1977) "Environmental 7-5 Assessment Handbook" contains the following passage on page 55-56 concern- ing erosion effects due to land use: "Shoreline erosion is aggravated by new development occurring where the rate of erosion is hiqh. Shore- line development activities may weaken the structure of the hank, causing collapse and slumping. Alteration of runoff and groundwater flow over or through the bank increases its susceptibility to erosion. Impervious surfaces such as paved roads, parking lots, structures, and agricultural drainfields may adversely affect the structure of the bank and the surface runoff and ground- water flow processes. Removal of vegetation on banks also .increases the shoreline's susceptibility to erosion. With the loss of the knotting and binding effect of roots hanks are directly exposed to the adverse effects of erosi;n.0 This is an accurate appraisal of the situation, but there is simply no suitable data collecte4 so far to relate these effects to differences in shore erosion over sufficiently long periods of time. A priority for future investigations would be the classification of all benchmark erosion stations maintained by state, local and federal agencies as to historical land-use, geology, erosion rate and littoral drift. Within 20-30 years, this miqht provide a suitable data base for analysis of the effect of land use on shore erosion. 7-6 Chapter VIII REFERENCES CITED Ahnert, Frank, Sallie Ives, Kevin Kelley, Kerry McArtor, Laura Poracsky, and Bob Oudemans, 1974, Classification and Mapping of Shore Zone Features Eastern Shore of Chesapeake Bay in Maryland: Annapolis, Md., Chesapeake Research Consortium Publication No. 7, 3 op., 66 maps. Boon, J. D., C. S. Welch, H. S. Chen, R. J. Lukeus, C. S. Fang, and J. M. Ziegler, 1978, A Storm Surge Model Study - Vol. I: Storm Surqe Height - Frequency Analysis and Model Prediction for Chesapeake Bay: Gloucester Point, Va.: Virginia Institute of Marine Sciences, Special Report No. 189, 155 pp. Brower, W. A., D. D. Sisk, and R. G. Quayle, 1972, Environmental Guide for Seven U.S. Ports and Harbor Approaches: Asfieville-,-W.7@-., NOAA Environmental Data Service, 166 pp. Chen, H. S., 1978, A Storm Surge Model Study - Vol. II: A Finite Element Storm Surge An ysis and Its Application to a Bay-Ocean System: Gloucester Point, Va., Virginia Institute of Marine Scien s, Special Report No. 189, 155 pp. Cleaves, E. T., J. Edwards, Jr., and J. 0. Glaser, 1968, Geologic Man of Maryland: Baltimore, Md.: Maryland Geological Survey. Crowley, W. P., Juergen Reinharlt, and Emery T. Cleaves, 1976, Geoloqic Map of Baltimore County: Baltimore, Md., Maryland Geological Survey. Dean, R. G., 1974, Compatibility of Borrow Material for Beach Fill, in: Proceedings, 14th Coastal Engineering Conference, Copenhagen Denmark. Dean, R. G., 1976, Beach Erosion, Cause, Processes, and Remedial Measures: Critical Reviews in Environmental Control, p. 259-296. Dean, R. G., 1978, Effects of Vegetation on Shoreline Erosional Processes, in: Proceedings of the National Symposium on Wet lands: Mir@n-eapolis, Ill nesota, American wa-te-F-7-esources Ass-ocia- fi'on, n. 415-426. Dolan, Robert, Harry Lins, and John Stweart, 1980, Geogranhical Analy- sis of Fenwick Island, Maryland, a Middle Atlanfic Coast Barrier Island: U.S. Geoloqical Survey Professional.Oaper 1177-A, 24 op. Draper, N. R., and H. Smith$ 11)68, Applied Regression Analysis: New York, John Wiley and Sons, Inc. 3-1 Gernant, R. E., 1970, Paleoecology of the Choptank Formation (Miocene) of Maryland and Virginia: Baltimore, Md., Maryland Geological Survey, Report of Investigations No. 12, p. 64-77. Gernant R. E. , T. G. Gibson, and IF . C. Whitmore, Jr., 1971 Environmental History of the Maryland Miocene: Raltirmore, Md., Maryland Geological Survey Guidebook No. 3, 0. 49-58. Glaser, J. D., 1960, Petrology and Origin of Potomac and Magothy (Cretaceous) Sediments, Middle Atlantic Coastal Plain: Balti- more, Md.: Maryland Geological Survey, Report of sti- gations, No. 11, p. 43-49. Glaser, J. D., 1976, Geological Map of Anne Arundel County: Baltimore, Md., Maryland Geological Survey. Gumbel, E. J., 1958, Statistics of Extremes: New York: Columbia University Press. Hicks, S.D., 1964, Tidal Wave Characteristics of Chesapeake Bay: Chesapeake Science, Vol. 5, No. 3, op. 103-113. Kendall, M. G., 1975,Multivariate Analysis: New York, Hafner Press. Lachenbruch, P. A., 1975, qDiscriminant Analysis: New York, Hafner Press. McNeil, D. R., 1977, Interactive Data Analysis: New York, John Wiley and Sons Inc. Maryland Coastal Zone Management Program, 1975, Historical Shorelines and Erosion Rates: Annapolis, Md., Maryland department of Natural Resources, 4 vols. Maryland Coastal Zone Management Program, 1977, Maryland Major Facili- ties Study, vol 4: Environmental Assessment Handbook: Annapolis, Md., Department of Natural Resources, 264 pp. Maryland Geological Survey, 1902-1979, County Geological Maps (scale 1:62,500), includes maps of Calvert (1902), St. Mary's 1902), Kent (1915), Queen Anne's (1915), Talbot (1916), Harford (1968), Anne Arundel (1976), Baltimore (1976), Wicomico (1979): Balti- more, Maryland. Neter, J., and W. Wasserman, 1974, Applied Linear Statistical Models: Homewood, Illinois, Richard D. irwin, Inc. Nie, N. H., C. H. Hull, J. G. Jenkins, K. Steinbrenner, and D.H. 3ent,1975, Statistical Package for the Social Sciences (SPSS): New York, McGraw-Hill , Inc. 8-2 Owens, J.P. and C.S. Denny, 1979, Upper Cenozoic Deposits of the Central Delmarya Peninsula, Maryland and Delaware: Washington, D.C., U.S. Geological Survey Professional Paner 1067-A p. Al- A27 Palmer, Harold D. ,1973 Shoreline Erosion in Upper Chesapeake Bay: the Role of Groundwater: Shore and Beach, October 1973, vol .41 No. 2,p.1-5 Phillips, R.C. ,1980 planting Guidlines for Seagrasses: Ft. Belvoir, Virginia, U.S. Army Corps of Engineers, Coastal Engi- neering Research Center, Coastal Engineering Techinal Aid No. 80-2 Pilkey, Orrin H., Jr, William j. Neal, and Orrin H. Pilkey Sr. 1978 From Currituck to Calabash: Living with Norht Carolina's Barrier Islands: Research Triangle Park, North Carolina, North Carolina Science and Technology Research Center Press, 223 pp. Ryan, Thomas A., Jr., Brian L; Joiner, and Barbara F. Ryan, 1981, Minitah Reference Manual; University Park, Pa., The Pennsylvannia University Press. St. Denis M., 1969 On Wind Generated Waves; Generation in Restricted Waters of Shallow Depth, in: Bretschneider, C.L., ed., 1969 Topics in Ocean Engineering; Houston, Texas, Texas Gulf Publishing\ co. Saville, T., 1958, Wave Runup on Composite Slones, in: Proceedings of Sixth Conference on Coastal Engineering. Singewald, J.T., and T. and 4. Slaughter, 1949 Shore Erosion in Tide- water Maryland: Baltimore, Md., Maryland Department of Geology, Mines, and Water Resources, Bulletin No. 5, 141 pp. Tzou, K.T. S., 1972, Meteorological and Hydrological investigations, in: Clarke, Wiliam D., harold D. Palmer, and Lawrence C. Murdock, eds.m Chester River Study: Annanopolis, Md., Maryland Department of Natural Resourdes, Chapter 6. U.S. Army Corps of Engineers, 1973 Shore Protection Manual: Washing- ton, D.C., U.S. Government Printing office, 3 vols. U.S. Army Corps of Engineers, 1977, Chesapeake Bay Future Conditions Report, Vol. 8, Navigation Flood Control and Shoreline Erosion Baltimore, Md. , U.S. Army Corps Baltimore Districts. Vokes, H.E., 1957 Geography and Geology of Maryland; Baltimore, Md., Maryland Department of Geology, lines and Water Resources, Bulletin No. 9, p. 36-45 3-3 Walker, Patrick 4.,1970, Water in Maryland: A Review of the Free State's Liquid Assets: Baltimore, Md., Maryland Geological Survey Educational Series No.2, 52 pp. Walton, T.L., and R.G. Dean, 1973 Application of Littoral Drift Roses to Coastal Engineering Problems, in : Proceedings, Conference on Engineering Dynamics in the Surf Zone, Sydney, Australia, p. 221-227 Wilson, R.S., 1957 Hurricane Wave Statistics for the Gulf of Mexico: Ft. Belvoir, Va., U.S. Army Corps of Engineers, Coastal Engineer- ing Research Center, Technical Memorandum No. 98 Wilson. B.S., 1965 Numerical Prediction of Ocean Waves in the North Atlantic for December, 1959: Deutsche Zeithshrift, vol. 18, No.3. 8-4 APPENDIX A Shoreline Sediments Along the Chesapeake Bay in Maryland Robert Biggs, Robert Dean Hsiang Wang and Robert Dalrymole The table on the next page describes the nature of the geoloqical formations which are found along the Chesapeake Bay shoreline in Maryland. These sediments are part of the Atlantic Coastal Plain and are as old as the early Cretaceous Period (approx. 70 million years before present). The formations are largelv horizontal sedimentary beds of sand, silt, and clay. Recent alluvial and marsh deosits also occur in certain environments. The formations are essentially hori- zontal in outcrop and intersect the shoreline in a variety of terrains which range from the high cliffs of Calvert County to the marshy low- lands of the southeast. The major source of information for many if the geologic de- scriptions in the table is the Geological of Anne Arrudel Countv Glaser, l976), and the Geologic Map of Maryland (Cleaves, et al., 1968). Modifications and additions are from Geograqraphy and Geology of Maryland (Vokes, 1957), and Glaser's (1960) study of the Magothy and Potomac Gp. sediments, the most recent intensive study of anv of the formations in the county. The most recent manpping of the county was done by Glaser (1976) using a standard scale of 1:52,500. Overall, this map can he considered verv accurate and the modern standard For description of these sediments. The major source of information for the description of the Talbot, Formation is the Geologic Map of Baltimore County and City (Crowley, A-1 et al., 1976 ). Modifications are from Vokes (1957). Mapping is of standard scale of 1:62,500. The source of description of the combined Potomac Gp. sediments is the Geologic Map of Harford County (Owens, 1963) in standard 1:62,500 scale. Sources of geologic description for the lower western shore include the Geologic Man of St. Marys County (Clark, 1902), scale 1:52,500, the Geologic Map of Calvert County (Clark, 1902); and Environmental History of Maryland Miocene (Gernant, et al., 1971). Sources of geologic information on Kent, Queen Annes, and Talhot County are the maps of the three corunties (Clark, 1915, 1916). These are all standard 1:62,900 scale. Owens and Dennv (1979) have recently completed a new interpre- tation of the stratigraphy in some areas of the Delmarva Peninsula and have reclassified those sediments. The descriptions used in the table reflect their work. This involves renaming the Talbot, Pamlico and Princpss Anne lowland deposits as the Kent Island Formation. Other sources of information on the geology of the lower eastern shore include the Geologic Plan of Wicomico County (Owens and Denny, 1979) and a map, in U.S.G.S. Professional Paper #1067-A, of scale 1:1,267,200 (Owens and Denny, 1979). Next Pages: Table A.I. Shoreline sediments along the Chesapeake Bay in Maryland. A-2 Table A.1 Shoreline Sediments Along the Chesapeake Bay in Maryland Artificial Fill - Sand, gravel and clay. Construction debris and dredge spoil also common. In most countries this material is used as nourishment at beach sites and inlets and as foundation in nearshore construcion projects and landfills. Extensive areas of the City of Baltimore are comporised of this material. Tidal Marsh - Silty clay to fine sand with woody debris and organic matter abundant. Most abundant in Dorchester, Wicomico, and Somerset counties. Alluvium - Interhedded sand, salt-clay and gravel. Reach denosits are well sorted, fine-to-medium grained sands. Marsh deposits are dark, organic-rich mud. Present in all counties excent Dorchester, Wicomico, and Somerset. In Baltimore County, the natural distribution of alluvium has been heavily modified hy artificial fill oDerations. Talbot Fm. - Interhedded muddy sand, salt, and clay; lower nortions are typically pebbly sand or gravel. In all counties excent Cecil, Dorchester, Wicomico and Somerset. This formation typically underlies low flat areas bordering the Ray and shores of the larger estuaries. Parsonher Sand Fm. - Mostly moderately sorted, medium-to-coarse grained loose, vellow sand. Found only sparingly in the coastal areas of Wicomico County. Kent Island Fm. - Sand interstratified with thin beds of dark gray salt or salty fine-rained sand. Gravelly sands common at hase. Found along the shoreline in portions of Dorchester, Wicomico, and Somerset Counties. Lowland Deposits - Gravel, sand, silt, and clay, with cohbles and houlders near the base. Also contains reworked glauconitic sands. Found princinally in Cecil County. Terrace Deposits Medium-to-coarse grained pebbly sand, with suh- ordinate mud. Found in minor amotints along the shoreline in Anne Arundel County. Wiomico Fm. - Loam, clay, sand, gravel and houlders. Found between 90 and 200 feet elevation along the shoreline in Calvert and St. Mary's Counties. Upland Deposits-Typically cross-bedded, poorly-sorted, medium-to- coarse grained sand and gravel, with boulders near base and subordinate silts and clays. Found in Cecil County. A-3 Table A.I Shoreline Sediments Along the Chesapeake Bay in Maryland St. Mary's Fm. Bluish clay, sand clay and marl. Sand tends to be fine-grained. Found along Calvert and St. Mary's county shore- lines. Choptank Fri. - Yellow sandy clay and marl. Found along Calvert and St. Mary's County shorelines. Calvert Fri. - Fine-grained sand, silt and diatomaceous silt. Basal beds (Fairhaven Member) contain much poorly-sorted medium sand overlain by highly diatomaceous silt. Found along Anne Arundel, Calvert, St. Mary's, and Queen Anne's Count'y shorelines. Manjemov Fm. - Fine-to-medium grained, poorly-sorted clayey sand with subordinate silt and silty clay. Found along Anne Arundel County shoreline. Aquia Fm. - Well-sorted, medium-grained, clean-to-moderately clavev, glauconitic sand. Cemented in places, but typically soft and friable. Found along Anne Arundel County shoreline. Monmouth Fm. - Fine-grained, variably glauconitic sand and micaceous, clayey silt. Found along Anne Arundel & Kent County shorelines. Matawan Fm. - Dark gray, micaceous, and glauconitic, Fine-grained sand and silt. Found along Cecil and Kent County shorelines. Magothy Fm. - Fine-to-coarse grained sand interstratified with silt- clay and subordinate pebbly sand or gravel. Found along Anne Arundel and Cecil County shorelines. Potomac Gp - Found along Anne Arundel, Baltimore, Harford, and Cecil County shorelines. Sand-Gravel Facies - Interbedded quartz sand, pebbly sand, gravel and subordinate mud. Silt-Clay Facies - Clay, silt and subordinate fine-to-medium grained, muddy sand. Generally massive, compact and "tough" in nature. Raritan Fm. - Interbedded sand, sandy clay, and clay. The sands are at times indurated. Found along Kent County shoreline. Appendix B Examples of New Atlas Maps Several new sets of atlas maps were developed by COER Inc. as part of this study to aid in the planning for future shore erosion assessment and the siting of new erosion-control structures. The original copies of each atlas are are on file in the Coastal Resources Division of the Maryland Department of Natural Resources. The atlas maps include: 9 a shore zone classification, discussed in Chapter V ages 5-7 through 5-9). The *1972 aerial photos (1:12,000 scale on file in the Wetlands Section of the Maryland DNR were used to classify the shoreline according to terrain. The classification scheme used was previously developed by Ahnert (1974) and is listed on page 5-7. The complete classification of the Maryland Chesapeake Bay shoreline is contained in a new atlas which consists of transparent copies of all 7 112 minute topographic quadrangle sheets of the Maryland portion of the Bay. An example of the new atlas product is shown in Figure 5.3 (Chapter V). @ a set of maps showing tidal elevations-inside the Bay (mean tide range and Class 4 tide range). The method for computing the tide ranges was discussed in Chapter V (pages 5-12 through 5-16). The computer predictions of tide conditions were compiled onto a set of transparent Bay navigation charts (scale 1:80,000). The computer predictions were produced in metric units, and a simplified version of the charts is shown in Figure B.1 and Figure B.2. 9 a set of maps showing Class 4 tidal currents and "100-year" storm surge heights predicted from a computer model. The method for predicting the storm surge heights was discussed in Chapter V (pages 5-17 through 5-23). The results of the computer predictions were compiled onto a transparent set of Bay navigation charts (scale 1:80,000). The computer predictions were produced in metric units, and a simplified version of the charts is shown in Figure B.3. For the prediction of maximum Class 4 tidal currents, the maximum tidal currents associated with each class of tidal range were estimated using the same numerical-storm'surge model developed by Chen (1978) as for "100-year" storm surge predictions. The model was calibrated by comparing the calculations with results by Hicks (1964) and the U.S. Tide Tables and U.S. Tidal Current Tables. The hydrodynamic model was used to generate tidal currents at 4-minute intervals for a complete tidal cycle using Class 4 tide as input (see Table 5.2). The maximum values were then determined. The results are printed on a transparent set of Bay navigation charts (scale 1:80,000). B-1 Figure B.1 760 30, 76000' PENNSYLVANIA -7 MEAN TIDE NAVRE OE GRACE D (centimeters) 50" CANAL IN @5 T H E BALTIMO 50- ItA NORTHERN 4 CHESAPEAKE % 5 31 CHESTER - SAY TOWN 50 WASHINGTON % Mir AN" OLIS 3p 39000'- 1E ZIM J/ a-M J 36 40 DENTON 35 EASTON 14 N& 30 I % % 1135 %45 % cz 40 )K CAMOP-DGE 3p 1 38030'- ;5 $A,-SOUPY 0 40 35 55%, N 5 0 \59 1, % 5 POCOMCKE CR 40 STATUTE MILES 10 0 10 20 D B-2 Figure B.2 76. 130, 'r ro o00, TIDE RANGE PENNSYLVA141 -7 WD (centimeters --ZiY7A CLASS 4 (87.5% PROBABILITY HAVRE DE GRACE C o D OF NON-EXCEEDENCE) 6 C,4 #V A L IN THE NORTHERN BALTIMORE 55 CHESAPEAKE 50 BAY 55 HESTER- TOWN 5 0 045 r . a ! 11 WASHINGTON 39000,- ANNA 0 L 11 S z 4 DIENTONi EASTOw 35 ,dn 55 40 CAMBRIDGE 3 45 00 SALtSlUfty 4@ 5 7 60 0 65 POCOMOKE 55 CRISFIELD STATUTE MILES 10 0 10 20 rv:m--= 8-3 Figure B.3 76 * 30' 760 00' loo, PENNSYLVANIA M PREDICTED .-..";YEAND 100-YEAR" STORM SURGE HEIGHT HAVRE DE .GRACE C q D c e n t imeters 35 4 CANAL IN 30 T H E BALTIMORE 32 NORTHERN CHESAPEAKE 0 70 300 BAY 41 C04ESTER - 270 TOWN 6 25 24 3 WASHINGTON ANNA OLIS 39000'- Ilk 220 T', ZIM C) 10 DENTON 20 EASTON 190 17 1 0 b, 16 150 CAMBRIDGE 1-K I 1 0 160 Qo 180 SALISBURY 0 -f-4,r 1 0 qz- 1 0 19 150 170 170 140 1 0 kh 1z POCOMOKE 140 15 6% CRISF,ELC STATUTE MILES 10 0 10 20 1501, D B-4 a set of maps showing wave conditions near the Maryland Bay shoreline. To establish wave statistics for erosion assessment, a wave hindcast model was used based on the shallow water wind- wave generation technique developed by Wilson' (1965). It was further modified to account for the limited fetch width in the Bay. The procedures are discussed in Chapter V (pages 5-24 through 5-35). The complete annual wave predictions are presented graphically in the form of wave roses on a transparent set of Bay navigation charts (scale 1:80,000) for each of the 128 reaches listed in Table 5.6 (Chapter V). The range of highest predicted waves for each reach on Maryland's Bay shoreline are shown in the map in Figure 5.12. a set of maps showing potential rates of longshore movement of sediments (littoral drift). The method for computing the littoral drift rates, and for producing littoral drift roses was discussed in Chapter V (pages 5-37 through 5-45). The results of the computer predictions were compiled onto trans- parent copies of all 7 1/2 minute topographic quadrangle sheets of the Maryland portion of the Bay. An example of the new atlas product is shown in Figure 5.3 (Chapter V). The range of predicted littoral drift rates for each reacn"on Maryland's Bay shoreli m are shown in the map in Figure 5.17, and in Table 5.6 (Chapter V). To convert centimeters to feet, multiply by 0.0328. Example: 45 centimeters x 0.0328 = 1.48 feet To convert feet to centimeters, multiply by 30.48. Example: I foot x 30.48 30.48 centimeters B-5 Appendix C Glossary of Terms These definitions are taken from a list compiled by the U.S. Army Corps of Engineers Coastal Engineering Research Center (1973). ALONGSHORE - Parallel to and near the shoreline; same as LONGSHORE. BANK - (1) The rising ground bordering a lake, river, or sea; of a river or channel, designated as right or left as it would appear facing downstream. (2) In its secondary sense, a shallow area consisting of shifting forms of silt, sand, mud, and gravel, but in this case it is only used with a qualifying word such as "sandbank" or "gravelbank." BACKSHORE -That zone of the shore or beach lying between the foreshore and the coastline and acted upon by waves only during severe storms, especially when combined with exceptionally high water. It comprises the BERM or BERMS. BEACH - The zone of unconsolidated material that extends landward from the low water line to the place where there is marked change in material or physiographic form, or to the line of permanent vegetation (usually the effective limit of storm waves). The seaward limit of a beach - unless otherwise specified - is the mean low water line. A beach includes FORESHORE and BACK- SHORE. BEACH PROFILE - A side view of the zone along the shoreline that extends landward from the water's edge to the toe of a dune or bluff. BERM - A nearly horizontal part of the beach or backshore formed by the deposit of material by wave action. Some beaches have no berms, others have one or several. BLUFF - High, steep bank at the water's edge. In common usage, a bank composed primarily of soil. See CLIFF. BREAKER ZONE - Area offshore where waves break. BREAKWATER - A structure protecting a shore area, harbor, anchorage, or basin from waves. BULKHEAD - A structure or partition to retain or prevent sliding of the land. A secondary purpose is to protect the upland against damage from wave action. CLAY - Extremely fine-grained soil with individual particles less than 0.00015 inch in diameter. C-1 CLIFF - High steep bank at the water's edge. In common usage, a bank composed primarily of rock. See BLUFF. COBBLES - Rounded stones with diameters ranging from 3 to 10 inches. Cobbles are intermediate between GRAVEL and BOULDERS. COAST - A strip of land of indefinite width (may be several miles) that extends from the shoreline inland to the first major change in terrain features. COASTAL PLAIN - The plain composed of horizontal or gently sloping strata of clastic materials fronting the coast, and generally representing a strip of sea bottom that has emerged from the sea in recent geologic time. COASTLINE - (1) Technically, the line that forms the boundary between the COAST and the SHORE. (2) Commonly, the line that forms the boundary between the land and the water. COVE - A small, sheltered recess in a coast, often inside a larger embayment. CREST - Upper edge or limit of a shore protection structure. CREST OF BERM - The seaward limit of a berm. CROSS SECTION - A vertical section (profile) of the surface, the ground, and/or underlying material, which provides a side view of the structure or beach (see beach profile). CURRENT - A flow of water. CURRENT, EBB The tidal current away from shore or down a tidal stream. Usually associated with the decrease in the height of the tide. CURRENT, FLOOD The tidal current toward shore or up a tidal stream. Usually associated with the increase in the height of the tide. CURRENT, LITTORAL Any current in the littoral zone caused primarily by wave action, e.g., longshore current, rip current. CURRENT, LONGSHORE The littoral current in the breaker zone moving essentially parallel to the shore, usually generated by waves breaking at an angle to the shoreline. CURRENT, TIDAL - The alternating-horizontal movement of water associated with the rise and fall of the tide caused by the astronomical tide-producing forces. DATUM, PLANE - The horizontal plane to which soundings, ground elevations, or water surface elevations are referred. C-2 DEEP WATER - Area where surface waves are not influenced by the bottom. Generally, a point where the depth is greater than one-half the surface wavelength. DEEPWATER WAVE - Waves which develop in water of sufficient depth that are not influenced by the friction of the bottom. DEPTH - The vertical distance from a specified tidal datum to the sea floor. DIFFRACTION (of water waves) - The phenomenon by which energy is transmitted laterally along a wave crest, when a part of a train of waves is interrupted by a barrier, such as a break- water, the effect of diffraction is manifested by propagation of waves into the sheltered region within the barrier's geometric shadow. DIURNAL - Having a period or cycle of approximately one TIDAL DAY. DOWNDRIFT - The direction of predominant movement of littoral materials. DRIFT.Anoun) - (1) Sometimes used as a short form for LITTORAL DRIFT (2) The speed at which a current runs. (3) Also floating material deposited on a beach (driftwood). DUNES (1) Ridges or mounds of loose, wind-blown material, usually sand. (2) BED FORMS smaller than bars but larger than ripples that are out of phase with any water-surface gravity waves associated with them. DURATION - In wave forecasting, the length of time the wind blows in nearly the same direction over the FETCH (generating area). EBB CURRENT - The tidal current away from shore or down a tidal stream; usually associated with the decrease in the height of the tide. EBB TIDE - The period of tide between high water and the succeeding low water; a falling tide. EMBANKMENT - An artificial bank such as a mound or dike, generally built to hold back water or to carry a roadway. EMBAYED - Formed into a bay or bays, as an embayed shore. EMBAYMENT - An indentation in the shoreline forming an open bay. EQUILIBRIUM - A state of balance or equality of opposing forces. EROSION - The wearing away of land by the action of natural forces. On a beach, the carrying away of beach material by wave action, tidal currents, littoral currents, or by deflation. C-3 ESCARPMENT - A more or less continuous line of cliffs or steep slopes facing in one general direction which are caused by erosion or faulting. ESTUARY - (1) The part of a river that is affected by tides. (2) The region near a river mouth in which the fresh water of the river mixes with the salt water of the sea. FEEDER BEACH - An artificially widened beach serving to nourish downdrift beaches by natural littoral currents or forces. FETCH - Area where waves are generated by wind which has steady direction and speed. Sometimes called FETCH LENGTH. FETCH LENGTH - Horizontal direction (in the wind direction) over which a wind generates waves. In sheltered waters, often the maximum distance that wind can blow across water. FILTER CLOTH - Synthetic textile with openings for water to escape, but which prevents passage of soil particles. FLOOD CURRENT - The tidal current toward shore or up a tidal stream, usually associated with the increase in the height of the tide. FLOOD TIDE - The period of tide between low water and the succeeding high water; a rising tide. FOREDUNE The front dune immediately behind the backshore. FORESHORE The part of the shore lying between the crest of the seaward berm (or upper limit of wave wash at high tide) and the ordinary low water mark, that is ordinarily traversed by the uprush and backrush of the waves as the tides rise and fall. FREEBOARD The additional height of a structure above design high water level to prevent overflow. Also, at a given time, the vertical distance between the water level and the top of the structure. On a ship, the distance from the water- line to main deck or gunwale. FUNCTIONAL LIFE The period of time the structure performs as intended. Performance can be expressed in terms of benefits obtained versus the cost of maintenance. GRADIENT (GRADE) See SLOPE. With reference to winds or currents, the rate of increase or decrease in speed, usually in the vertical; or the curve that represents this rate. GRAVEL Small, rounded granules of rock with individual diameters ranging from 3.0 to 0.18 inches. Gravels are intermediate between SAND and COBBLES. C-4 GROIN - Shore protection structure built perpendicular to shore to trap sediment and retard shore erosion. GROIN FIELD Series of groins acting together to protect a section of beach. Also called a groin system. GROUND WATER Subsurface water occupying the zone of saturation. In a strict sense, the term is applied only to water below the WATER TABLE. HEADLAND (HEAD) - A high steep-faced promontory extending into the sea. HIGHER HIGH WATER (HHW) The higher of the two high waters of any tidal day. The single high water occurring daily during periods when the tide is diurnal is considered to be a higher high water. HIGHER LOW WATER (HLW) The higher of two low waters of any tidal day. HIGH TIDE, HIGH WATER (HW) - The maximum elevation reached by each rising tide. See TIDE. HIGH WATER LINE - In strictness, the intersection of the plane of mean high water with the shore. The shoreline delineated on the nautical charts of the U.S. Coast and Geodetic Survey is an approximation of the high water line. For specific occurrences, the highest elevation on the shore reached during a storm or rising tide, including meteorological effects. IMPERMEABLE - Not permitting passage of water. IMPERMEABLE GROIN - A groin through which sand cannot pass. INLET - (1) A short, narrow waterway connecting a bay, lagoon, or similar body of water with a large parent body of water. (2) An arm of the sea (or other body of water), that is long compared to its width, and may extend a considerable distance inland. INTERTIDAL ZONE - Land area alternately inundated and uncovered in tides. Usually considered to extend from MEAN LOW WATER to MEAN HIGH WATER. JETTY (1) (U.S. usage) On open seacoasts, a structure extending into a body of water, and designed to prevent shoaling of a channel by littoral materials, and to direct and confine the stream or tidal flow. Jetties are built at the mouth of a river or tidal inlet to help deepen and stabilize a channel. (2) (British usage) Jetty is synonymous with "wharf" or "pier." LITTORAL - Of or pertaining to a shore. LITTORAL DRIFT - The sedimentary material moved in the littoral zone under the influence of waves and currents. C-5 LITTORAL TRANSPORT - The movement of littoral drift in the littoral zone by waves and currents. Includes movement parallel (longshore transport) and perpendicualr (on-offshore transport) to the shore. LITTORAL TRANSPORT RATE - Rate of transport of sedimentary material parallel to or perpendicular to the shore in the littoral zone. Usually expressed in cubic yards (meters) per year. Commonly used as synonymous with LONGSHORE TRANSPORT RATE. LITTORAL ZONE - In beach terminology, an indefinite zone extending seaward from the shoreline to just beyond the breaker zone. LONGSHORE - Parallel to and near the shoreline. LONGSHORE TRANSPORT RATE - Rate of transport of sedimentary material parallel to the shore. Usually expressed in cubic yards (meters) per year. Commonly used as synonymous with LITTORAL TRANSPORT RATE. LOWER HIGH WATER (LHW) The lower of the two high waters of any tidal day. LOWER LOW WATER (LLW) The lower of the two low waters of any tidal day. The single low water occurring daily during periods when the tide is diurnal is considered to be a lower low water. LOW TIDE (LOW WATER, LW) - The minimum elevation reached by each falling tide. LOW WATER LINE - The intersection of any standard low tide datum plane with the shore. MARSH - An area of soft, wet, or periodically inundated land, generally treeless and usually characterized by grasses and other low growth. MARSHj SALT - A marsh periodically flooded by salt water. MEAN HIGHER HIGH WATER (MHHW) - The average height of the higher high waters over a 19-year period. For shorter periods of observation, corrections are applied to eliminate known variations and reduce the result to the equivalent of a mean 19-year value. C-6 MEAN HIGH WATER (MHW) - The average height of the high waters over a 19-year period. For shorter periods of observations, corrections are applied to eliminate known variations and reduce the results to the equivalent of a mean 19-year value. All high water heights are included in the average where the type of tide is either semidiurnal or mixed. Only the higher high water heights are included in the average where the type of tide is diurnal. So determined, mean high water in the latter case is the same as mean higher high water. MEAN LOWER LOW WATER (MLLW) - The average height of the lower low waters over a 19-year period. For shorter periods of observations, corrections are applied to eliminate known variations and reduce the results to the equivalent of a mean 19-year value. Frequently abbreviated to LOWER LOW WATER. MEAN LOW WATER (MLW) The average height of the low waters over a 19-year period. For shorter periods of observations, corrections are applied to elliminate known variations and reduce the results to the equivalent of a mean 19-year value. All low water heights are included in the average where the type of tide is either semidiurnal or mixed. Only lower low water heights are included in the average where the type of tide is diurnal. So determined, mean low water in the latter case is the same as mean lower low water. MEAN LOW WATER SPRINGS - The average height of low waters occurring at the time of the spring tides. It is usually derived by taking a plane depressed below the half-tide level by an amount equal to one-half the spring range of tide, necessary corrections being applied to reduce the result to a mean value. This plane is used to a considerable extent for hydrographic work outside of the United States and is the plane of reference for the Pacific approaches to the Panama Canal. Frequently abbreviated to LOW WATER SPRINGS. MEAN SEA LEVEL The average height of the surface of the sea for all stages of the tide over a 19-year period, usually determined from hourly height readings. Not necessarily equal to MEAN TIDE LEVEL. C-7 MEAN TIDE LEVEL A plane mideway between MEAN HIGH WATER AND MEAN LOW WATER. Not necessarily equal to MEAN SEA LEVEL. Also called HALF-TIDE LEVEL. MIXED TIDE - A tide in which there is a distinct difference in height between successive high and successive low waters. For mixed tides there are generally two high and two low waters each tidal day. Mixed tides may be described as intermediate between semidiurnal and diurnal tides. MUD A fluid-to-plastic mixture of finely divided particles of solid material and water. NAUTICAL MILE The length of a minute of arc, 1/21,600 of an average great circle of the earth. Generally one minute of latitude is considered equal to one nautical mile. The accepted United States value as of 1 July 1959.is 6,076.115 feet or 1,852 meters, approximately 1.15 times as long as the statute mile of 5,280 feet. Also geographical mile. NEAP TIDE - A tide occurring near the time of quadrature of the moon with the sun. The neap tidal range is usually 10 to 30 percent less than the mean tidal range. NEARSHORE (ZONE) In beach terminology an indefinite zone extending seaward from the shoreline well beyond the breaker zone. It defines the area of NEARSHORE CURRENTS. NEARSHORE CURRENT SYSTEM - The current system caused primarily by wave action in and near the breaker zone, and which consists of four parts: The shore- ward mass transport of water; longshore currents; seaward return flow, including rip currents; and the longshore movement of the expanding heads of rip currents. NEAT LINES - Lines on drawings which establish tolerances for construction. NODAL ZONE - An area in which the predominant direction of the LONGSHORE TRANSPORT changes. NOURISHMENT - The process of replenishing a beach. It may be brought about naturally, by longshore transport, or artificially by the deposition of dredged materials. OFFSHORE - (1) In beach terminology, the comparatively flat zone of variable width, extending from the breaker zone to the seaward edge of the Continental Shelf. (2) A direction seaward from the shore. OFFSHORE CURRENT (1) Any current in the offshore zone. (2) Any current flowing away from shore. C-8 OVERTOPPING - Passing of water over the top of a structure as a result of wave runup or surge action. OVERWASH - That portion of the uprush that carries over the crest of a berm or of a structure. PERCOLATION - The process by which water flows through the interstices of a sediment. Specifically, in wave phenomena, the process by which wave action forces water through the interstices of the bottom sediment. Tends to reduce wave heights. PERMEABLE- Having openings large enough to permit free passage of appreciable quantities of sand or water. PERMEABLE GROIN - A groin with openings large enough to permit passage of appreciable quantities of littoral drift. PIER - A structure, usually of open construction, extending out into the water from the shore, to serve as a landing place, a recrea- tional facility, etc., rather than to afford coastal protection. In the Great Lakes, a term sometimes improperly applied to jetties. PILE - A long, heavy timber of section of concrete or metal to be driven or jetted into the earth or seabed to serve as a support or protection. PILE, SHEET - A pile with a generally slender flat cross section to be driven into the ground or seabed and meshed or interlocked with like members to form a diaphragm, wall, or bulkhead. PILING - A group of piles. PLANFORM - The outline or shape of a body of water as determined by the stillwater line. PROFILE, BEACH - Intersection of the ground surface with a vertical plane that may extend from the top of the dune line to the seaward limit of sand movement. RECESSION (of a beach) - (1) A continuing landward movement of the shoreline. (2) A net landward movement of the shoreline over a specified time. REFERENCE STATION - A place for which tidal constants have previously been determined and which is used as a standard for the comparison of simultaneous observations at a second station; also a station for which independent daily predictions are given in the tide or current tables from which corresponding predictions are obtained for other stations by means of differences or factors. C-9 REFLECTED WAVE That part of an incident wave that is returned seaward when a wave impinges on a steep beach, barrier, or other reflecting surface. REFRACTION (OF WATER WAVES) - (1) The process by which the direction of a wave moving in shallow water at an angle to the contours is changed. The part of the wave advancing in shallower water moves more slowly than that part still advancing in deeper water, causing the wave crest to bend toward alignment with the under- water contours. (2) The bending of wave crests by currents. REVETMENT A facing of stone, concrete, etc., built to protect a scarp, enbankment, or shore structure against erosion by wave action or currents. RIPRAP - A layer, facing, or protective mound of stones randomly placed to prevent 'erosion, scour, or sloughing of a structure or embankment; also the stone so used. RUBBLE - (1) Loose angular waterworn stones along a beach. (2) Rough, irregular fragments of broken rock. RUBBLE-MOUND STRUCTURE - A mound of random-shaped and random-placed stones Protected with a cover layer of selected stones or specially shaped concrete armor units. (_Armor units in primary cover layer may be placed in orderly manner or dumped at random.) SAND Generally, coarse-grained soils having particle diameters between 0.18 and approximately 0.003 inches. Sands are intermediate between SILT and GRAVELS. SAND FILLET Accretion trapped by a groin or other protrusion in the Iittoral zone. SCARP, BEACH An almost vertical slope along the beach caused by erosion by wave action. It may vary in height from a few inches to several feet, depending on wave action and the nature and composition of the beach. SCOUR Removal of underwater material by waves and currents, especially at the base or toe of a shore structure. SEA14ALL - A structure separating land and water areas, primarily designed to prevent erosion and other damage due to wave action. See also BULKHEAD. SEMMIURNAL TIDE - A tide with two high and two low waters in a tidal day with comparatively little diurnal inequality. C-10 SHALLOW WATER - (1) Commonly, water of such a depth that surface waves are noticeably affected by bottom topography. It is customary to consider water of depths less than one-half the surface wavelength as shallow water. (2) More strictly, in hydrodynamics with regard to progressive gravity waves, water in which the depth in less than 1/25 the wavelength. Also called VERY SHALLOW WATER. SHINGLE - (1) Loosely and commonly', any beach material coarser than ordinary gravel, especially any having flat or flattish pebbles. (2) Strictly and accurately, beach material of smooth, well-rounded pebbles that are roughly the same size. The spaces between pebbles are not filled with finer materials. Shingle often gives out a musical sound when stepped on. SHOAL - (noun) Rise of the sea bottom from an accumulation of sand or other sediments. (verb) - (1) to become shallow gradually. (2) To cause to become shallow. 03T -to proceed from a greater to a lesser depth of water. SHORE - Narrow strip of land in immediate contact with the sea, including the zone between high and low water lines. A shore of uncon- solidated material is usually called a beach. SHOREFACE - The narrow zone seaward from the low tide SHORELINE covered by water over which the beach sands and gravels actively oscillate with changing wave conditions. SHORELINE - The intersection of a specified plane of water with the shore or beach. (e.g., the highwater shoreline would be the intersection of the plane of mean high water with the shore or beach.) The line delineating the shoreline on U.S. Coast and Geodetic Survey nautical charts and surveys approximates the mean high water line. SILT Generally refers to fine-grained soils having particle diameters between 0.003 and 0,00015 inches. Imtermediate between CLAY and SAND. SLOPE Degree of inclination to the horizontal. Usually expressed as a ratio, such as 1:25 or 1 on 25, indicating I unit vertical rise in 25 units of horizontal distance; or in degrees from horizontal. SPECIFICATIONS - Detailed description of particulars, such as size of stone, quality of materials, contractor performance, terms, and quality control. STILLWATER LEVEL - The elevation that the surface of the water would assume if all wave action were absent. STORM SURGE - A rise above normal water level on the open coast due to the action of wind stress on the water surface. Storm surge resulting from a hurricane also includes that rise in level due to atmospheric pressure reduction as well as that due to wind stress. C-11 SURF - The wave activity in the area between the shoreline and the outer- most limit of breakers. SURF ZONE - The area between the outermost breaker and the limit of wave uprush. SURGE - (1) The name applied to wave motion with a period intermediate between that of the ordinary wind wave and that of the tide, say from 1/2 to 60 minutes. It is of low height; usually less than 0.3 foot. See also SEICHE. (2) In fluid flow, long interval variations in velocity and pressure, not necessarily periodic, perhaps even transient in nature. SWASH - The rush of water up onto the beach face following the breaking of a wave. TIDAL PERIOD The interval of time between two consecutive like phases of the tide. TIDAL RANGE Difference in height between consecutive high and low (or higher and lower low) waters. The mean range is the difference in height between mean.high water and mean low water. The diurnal range is' the difference in height between mean higher high water and mean lower low water. For diurnal tides, the mean and diurnal range are identical. For semidiurnal and mixed tides, the spring range is the difference in height between the high and low waters during the time of spring tides. TIDE The periodic rising and falling of the water that results from gravitational attraction of the moon and sun and other astronomi- cal bodies acting upon the rotating earth. Although the accompanying horizontal movement of the water resulting from the same cause is also sometimes called the tide, it is preferable tc designate the latter as TIDAL CURRENT, reserving the-name TIDE for the vertical movement. TIDE, DIURNAL A tide with one high water and one low water in a tidal day. TIDE STATION A place at which tide observations are being taken. It is called a primary tide station when continuous observations are to be taken over a number-of years to obtain basic tidal data for the locality. A secondary tide station is one operated over a short period of time to obtain data for a specific purpose. TIE ROD - Steel rod used to tie back the top of'a bulkhead or seawall. WAVE PERIOD - The time for a wave crest to traverse a distance equal to one wavelength. The time for two successive wave crests to pass a fixed point. WAVE, REFLECTED - That part of an incident wave that is returned seaward when a wave impinges on a steep beach, barrier, or other reflecting surface. C-12 WAVE SPECTRUM - In ocean wave studies, a graph, table, or mathematical equation showing the distribution of wave energy as a function of wave frequency. The spectrum may be based on observations or theoretical considerations. Several forms of graphical display are widely used. WAVE STEEPNESS - The ratio of the wave height to the wavelength. WAVE TRAIN Ase'ries of waves from the same direction. WAVE TROUGH Lowest part of a wave form between successive crests. Also, that part of a wave below the stillwater level, WEEP HOLE Hole through a solid revetment, bulkhead, or seawall for relieving pore pressure. WEIR JETTY An updrift jetty with a low section or weir over which littoral drift moves into a predredged deposition basin which is dredged periodically. WHITECAP - On the crest of a wave, the white froth caused by wind. WIND SETUP - The vertical rise in the stillwater level on the leeward side of a body of water caused by wind stresses on the surface of the water. WINDWARD - The direction from which the wind is blowing. WIND WAVES (1) Waves being formed and built up by the wind. (2) Loosely, any wave generated by wind. C-13 111011111111111111 3 6668 14102 3657 1