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Drainage Mana ement ... .. ...... . ..... . ........ ......... Plan Homer, Alaska GB AUGUST 1979 CH2MIIIHILL 991 A4 D73 1979 -* 1) DRAINAGE MANAGEMENT PLAN HOMER, ALASKA "Ne N Prepared by: CH2M HILL US ]Department of Commerce 4%. _-nR Services Cente:r L"o-Ty NCAA C .-, @' " @ C, , I i-'outh Hobson Aven:-0 L , -' Ckj&rjeston, SC 29405-2423 August 1979 The preparation of this report was financed in part by funds from the Office of Coastal Zone Management, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, Department of Community and Regional Affairs. 2*4 VIN SUMMARY This study of surface water drainage in Homer analyzes the existing drainage system and proposes a drainage management plan to cope with existing and future drainage problems. Design criteria and methods are presented so that the city and developers will have a standardized approach to con- struction of drainage facilities. No immediate capital improvements to the existing drainage system are required. Rather, a phased evolution of the system as development occurs and as priority remedial projects a re recommended. PLANNING CRITERIA The study area characteristics, population, and land use information presented in this drainage plan are a thorough update of the planning analysis presented in the,Compre- hensive Sewer Plan and the Comprehens@ve Water Plan prepared in May of 1977 by CH2M HILL. The population of Homer in 1990 is estimated to be between 4,500 and 6,500, projecting 7- and 10-percent average annual growth rates. The 1978 population was 2,050. Current and expected future land use maps were prepared to update those presented in the previous plans. The future land use map is consistent with the city's new comprehensive plan. A detailed review of the Soil Conservation Service soils reports was performed to determine what effect soil types and ground slopes have on patterns of development and expected runoff rates. EXISTING DRAINAGE SYSTEM The existing surface water drainage system for the City of Homer is a combination of natural creeks and manmade drain- ageways. The natural creeks have either year-round or intermittent flow and have steep or flat gradients. Creeks with steep gradients normally have adequate channel capacity for most floods; whereas those with flatter slopes do not. Manmade modifications to the natural drainageways are usually associated with roads. Roadside ditches collect and concen- trate the runoff, and culvert crossings restrict the channel capacity of the natural creeks. An inventory of the existing major culverts is presented in appendix A. These culverts are shown in figures 5, 6, 7, and 8 in the main part of the report. Current drainage management includes maintenance by city and state Department of Transportation crews within their respec- tive jurisdictions. Most existing culverts are corrugated metal types with no headwalls, inlets, or thaw wire protec- tion. The major culverts for the Homer bypass (now under construction) will include headwalls and thaw wires. The minimal drainage design considerations contained in the Homer city code and the borough subdivision ordinance are not adequate to ensure proper construction of additions to the city's drainage system. Runoff Determination A standardized method of determining the peak rate of surface water runoff in Homer was developed. Rainfall at Homer is relatively light compared to other cities in Alaska. However, heavy rainfall is likely to occur in late fall when snow is on the ground. The peak rate of runoff, including a reason- able amount of snowmelt, was determined for the range of drainage areas between 10 and 500 acres and for the 5-, 10-, 25-, 50-, and 100-year storms. These rates are shown in figure 9. It is recommended that the 25-year storm be used to design drainage facilities for drainage areas less than 200 acres. Because of the extra hazard associated with larger drainage- ways, the 50-year storm is recommended for design of drain- age facilities for drainage areas larger than 200 acres. Proposed Drainage System A complete drainage system for the City of Homer is proposed and shown in figures 5, 6, 7, and 8. The drainage system is made up of trunk drainageways and local drainageways. The trunk drainageways are a combination of natural creeks and manmade ditches which collect and convey runoff to Kachemak Bay or Beluga Lake. The local drainageways are the roadside ditches and culverts which convey water from small drainage subareas to the nearest trunk drainageway. Because of icing and sediment blockage problems, open ditches and natural creeks are preferred drainage system components. Buried storm drainage systems and storage detention ponds are not suggested because of high capital and maintenance cost as compared to the open drain concept. Buried storm drainage systems could become part of the city's system if the city believes they are especially desirable and worth the additional cost in certain areas. Drainage and erosion control guidelines have been developed to provide a common basis for the construction of drainage ii I facilities and for the control of erosion during construc- tion. These guidelines are presented in appendix C and were developed from the standard specifications of the State of Alaska Department of Transportation and erosion control methods developed by the Soil Conservation Service. Drainage Plan Implementation Several legal means of implementing the drainage management plan were investigated. The drainage control ordinance presented in appendix D is the recommended legal means to implement the drainage management plan. An intergovern- mental agreement with the Kenai Peninsula Borough is recom- mended to ensure that areas in the borough that drain into the city meet the design requirements of the city. In order to effectively administer the drainage management plan, the city should identify staff persons responsible for reviewing plans for proposed system expansion. At a mini- mum, the public works director should review and approve all drainage system improvements. It is recommended that the city require drainage plans be designed and field certified by a civil engineer registered in the State of Alaska. The city needs to adopt a set of standard design criteria which incorporate sound engineering practice and meet local requirements. The drainage and erosion control guidelines presented in appendix C should be modified by the city, as required, and made available to developers and others who would construct portions of the drainage system. The rate at which capital improvements to the drainage system are implemented is limited by the budget available. Therefore, it is recommended that improvements to the exist- ing drainage system be made in accordance with a priority list developed and maintained by the public works director. Easements should be obtained for all drainage system compon- ents not within city rights-of-way. Drainage improvements should then be scheduled, designed, financed, and constructed through the public works department. Recommendations The major recommendations contained in the drainage manage- ment plan are listed below: 1. A drainage ordinance similar to the model ordinance in appendix D should be enacted by the city to implement the drainage management plan. 2. The city should establish an intergovernmental agree- ment with the Kenai Peninsula Borough giving the city review authority over activities affecting drainage management, including subdivision design, road construc- tion, and drainage improvments. 3. The drainage management plan should be coordinated with the city's master road plan and the comprehensive sewer and water plans. 4. The public works director should review all improve- ments and proposed additions to the existing drainage system. The capability of the city's current staff to carry out this function should be reviewed, and any additional staff needs identified. 5. Improvements to the existing drainage system should be made in accordance with a priority list developed and maintained by the public works director. As funds become available, system upgrading should occur. 6. A capital improvement program should be developed, approved by the city council, and administered by the public works department to coordinate drainage system improvement and expansion with road construction proj- ects. Acquisition of drainage easements should be included as part of the capital improvement program. 7. Drainage system components should be designed using the runoff design curve, figure A-1, which is based on using the 25-year design event for drainage areas less than 200 acres, and the 50-year design storm for drain- age areas 200 acres and larger. 8. The city's public works department should modify, as required, the drainage and erosion control guidelines in appendix C and make them available to developers and others who would construct portions of the drainage system. 9. The city should require that drainage plans prepared by developers be designed, inspected, and field certified by a civil engineer registered in the State of Alaska. iv CONTENTS 2,Laq e Summary Planning Criteria Existing Drainage System 1 Introduction Previous Studies Scope of Study 3 2 Planning Criteria 5 Study Period 5 Study Area Characteristics 5 Population 11 Land Use and Development 13 3 Existing Drainage System 23 Natural Drainage 23 Manmade Modifications 24 Current Drainage Management 33 4 Runoff Determination 37 Precipitation 37 Runoff Determination 38 Alternative Design Frequencies 39 5 Proposed Drainage System 43 Trunk Drainage System 43 Alternative Physical Systems 45 Local Drainage Systems 46 Drainage and Erosion Control Guidelines 47 6 Drainage Plan Implementation 49 Legal Implementation 49 Requirements for Implementation 55 General Principles of Implementation 57 Recommendations for Implementation 58 Appendix A. Culvert Inventory Appendix B. Drainage System Cost Estimates Appendix C. Drainage and Erosion Control Guidelines V Page TABLES 1 Population Growth 11 2 City of Homer Population Projections 12 3 Housing Units Authorized by Building Permits City, City of Homer, 1976-78 14 4 Estimated Housing and Land Requirements for Residential Growth, City of Homer, 7- Percent Growth Rate 17 5 Estimated Housing and Land Requirements for Residential Growth, City of Homer, 10- Percent Growth Rate 17 6 Rainfall Frequency Data, Homer Airport 38 7 25-Year, 24-Hour Rainfall at Selected Locations 38 FIGURES 1 Study Area 6 2 Average Montly Precipitation 7 3 Current Land Use 15 4 Future Land Use 19 5 Drainage System Map 25 6 Drainage System Map 27 7 Drainage System Map 29 8 Drainage System Map 31 9 Relatiopnship of Peak Discharge and Drainage Area for Average Recurrence Intevals 40 Vii Chapter 1 ME INTRODUCTION Recent rapid development and expected future growth have prompted local concern over storm water drainage control in Homer. Rain and snowmelt flooding, glaciation, and erosion have been identified as problems that are expected to increase in severity unless a comprehensive drainage management plan is developed and implemented. This study analyzes the existing drainage system for current problem areas and predicts future system requirements in light of expected land use changes and local hydrologic conditions. Alternative approaches to storm water drainage control are considered, and as a result of close interaction with city and borough officials a recommended drainage management plan is presented. PREVIOUS STUDIES Several studies, either recently completed or currently underway, provide the basis for this drainage management study. These studies were reviewed and their major findings considered in developing the drainage management plan. The following is a brief discussion of the studies as they relate to the drainage plan. City of Homer Comprehensive PZan, 1978 The City of Homer revised its Comprehensive Plan in 1978. The plan, officially adopted by the Kenai Borough Assembly in March 1979, recommends areas for future residential, industrial, and commercial development. The Comprehensive Plan also contains the following recommendations relating to drainage problems: 1. Prepare and adopt a drainage management plan. 2. Consider responsibility for erosion and sedimentation control before approval by the Planning Commission of any proposed subdivision. The proposed methods for alleviating erosion and sedimentation control problems should be reflected in the developmental design speci- fications, where applicable. 3. Include stringent control measures stipulating respon- sibility for erosion and sediment control during foun- dation excavations with the issuance of building permits. 4. Require that developers submit drawings including proposed drainage patterns during actual construction periods, as well as permanent drainage plans. Temporary structural measures for erosion and sediment control should be required as necessary (diversion berms, interceptor swales, energy dissipators, channel lining, crushed aggregate, mulching, etc.). 5. Require that developers and/or subdividers submit drawings indicating those areas most likely to be subject to glaciation as a result of construction, development, or interruption of natural drainage pat- terns, together with proposed methods for elimination, amelioration, or control of same. Such regulations should be applicable to any adjoining properties or other areas sub*ject to such effects, as well as the subject property itself. City of Homer Zoning Ordinance, September 1979 The city is substantially revising its zoning ordinance, with an expected completion date of September 1979. The revisions will include new zoning district boundaries and regulations governing permitted uses. PotentiaZ FZoodinq, City of Homer, Kenai PeninsuZa Borough, U.S. Department of Agriculture, Soil Conservation Service (SCS), Anchorage, Alaska, June 1978 This study provides a technical assessment of flooding problems in Homer. It includes a description of the Homer area and its historical flooding problems. Reduced flow capacity of the natural drainageways by either manmade or natural obstructions is identified as the most common cause of flooding. The study concludes that, with the expected development, future flooding problems will be similar to, but more numerous than, current problems. Several recommen- dations were included, the most important of which was that the City of Homer should develop a drainage management plan. Homer, AZaska, History of FLooding, Aufeis (GLaciation) :Erosion and Sedimentation. Sandra Stringer, The Scotia Group, Fairbanks, Alaska, November 1976 A detailed study of flooding and related problems in Homer prepared for the Anchorage office of the SCS. The study was based on a literature search and numerous interviews with knowledgeable Homer residents. Glaciation was frequently mentioned as a local problem, but extensive or damaging floods seem to be infrequent. The most serious flood events were two outbreak floods in Palmer Creek. In 1937 and again in 1952, landslides blocked Bear Canyon during rain and snowmelt floods that occurred in late fall. Floodwaters backed up behind the slides and then broke out, sending a wall of water and debris down Palmer Creek. Seventeen historical flood and glaciation areas were described and mapped in the study. 2 Soil Surveys, Homer, Alaska, and Homer-Ninilchik Area, Alaska. U.S. Department of Agriculture, Soil Conservation Service, Anchorage, Alaska, July 1971 This publication is a result of two separate soil surveys, one (Homer-Ninilchik area) a more general survey; the other (Homer) a detailed survey. Other than the difference in level of detail, both surveys map and catalog various soil types and list their agricultural and engineering properties. The detailed survey of Homer was of particular value in projecting likely areas of future development and determining the amount of runoff expected from different soil types. Comprehensive Water PZan, Homer, AZaska, and Comprehensive Sewer PZan, Homer, AZaska, CH2M HILL, May 1977 Both studies present current and expected future utility service for water and sewerage. Detailed population and land use projections were included, as well as recommended system improvements. Annual reviews and updates of the plans were recommended to keep pace with actual population growth and development. Much of the population and land use data was incorporated into the drainage management study with appropriate modifications to reflect recent trends. Master Roads and Street PZan, SiZvers Engineeri7ig, 1979 A master roads and streets plan for the City of Homer was completed in June 1979. The plan contains a summary of existing traffic conditions and an analysis of trip genera- tion characteristics. The study recommends a plan for major arterials and establishes a set of operating design standards for future roads, including surface widths, grades, and traffic volumes. SCOPE OF STUDY The purpose of this study is to develop enough data for the city to make management decisions on storm water drainage controls. The following tasks were accomplished with that purpose in mind: 1. A collection and review of all available reports and data. 2. An update of population and land use data in light of recent developments. 3. An examination of the existing drainage system and a rating of its flow capacity. 3 4. A review of historical drainage-related problems. 5. The development of appropriate drainage planning criteria. 6. An estimate of the expected change in rate of runoff due to future development. 7. The development of a drainage management plan to deal with expected problems. 8. An assessment of alternative means of implementing the drainage plan and the development ofmodel ordinances, regulations, and guidelines. 4 Chapter 2 PLANNING CRITERIA This chapter discusses the general planning criteria that were considered in preparing the drainage management plan for the City of Homer. It provides information on the physical and economic characteristics of the study area, population trends, and land use. The information presented is limited to those items that are pertinent to planning for storm water drainage control. STUDY PERIOD This drainage management plan is prepared for ultimate development within the city and the larger drainage area around the city. In addition, specific improvements are to be recommended for both a short- and a long-range time frame. The city will review and update this plan on a regular basis. STUDY AREA CHARACTERISTICS Boundaries and Topography The boundaries of the study area are shown in figure 1. They encompass all the area within the city and the adjacent area in the borough that drains to Kachemak Bay, Beluga Slough, Beluga Lake, and the lowlands northeast of the Homer Airport to Millers Landing. The areas near the airport and on either side of Ocean and Kachemak Bay Drives, as well as all of Homer Spit, were not studied, but drainage management measures developed for the city would be generally applicable to all areas within the city limits. The area within the boundaries of the City of Homer is approximately 6,400 acres. The total drainage area that was studied is about 6,500 acres, which include approximately 4,500 acres within the city and 2,000 acres of borough land north of the city. The topography of the area rises moderately from sea level at Kachemak Bay to the steep bluff that runs along the northern boundary of the city. At the top of the bluff, at about elevation 1200 in the northeast section of the study area and 900 in the southwest, the topography gradually slopes down and out of the study area into the Diamond and Bridge Creek drainage basins. Climate Homer has a maritime climate that is influenced by airflow from the Gulf of Alaska and modified by the intervening Kenai Mountains. The mountains are located about 20 miles 5 ------------- - - - - - - - - - - O.s, ,n an' Os' Ridge n T,@ ell 2% 5 4 @4 2 3, . - % C ree 0 X, d, 00 -Cabin, 9 0 12 1 7 8 71 Ei6chemak . 11, o Radioi-r._;@ 074 'llers @Millers Rid 'A 'n4jn ge I CITY LIMITS I -- La _,0e RAN M-1 Alx_LJNLJ@@ NILIL I - - - - - - - - - - - - - - - - - - - - - @39 Cree 0 15 Quarry 4" sw JL= J! :0=4 17 141 16 15 V a 9 z G fig Homer lool FAA J % 41 Range' A. _457 3: Beluga L..p+t 23/ 4:, ZJ.,. 24 21 Lak@p j'i Homer Lake 19 jj. I j )0 ili-:: U111Qpd -Homer Ai@p t .. . ......... mi FAA SRA ....... .. .. sta ... ....... STUDY AREA BOUNDARY 27 o/ @N KACHEMAK SAY J- @P: T 7 Figure 1 H Study Area il" i I I Im low I'm as 00 Sn, ist from Homer and have a northeast-southwest orientation with elevations between 4,000 and 6,000 feet. The average annual precipitation is approximately 23 inches; whereas, other areas along the gulf coast experience normal precipitation as high as 60 inches. The average precipitation amounts on a monthly basis are shown in figure 2. 4 - W LX3 Z 0 2 Uj 11 7L@LIII I LI, oL 1 IiI IN I I @Ij' 11111111i'l .111!11 '1 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC MONTHS Figure 2 Average Monthly Precipitation The normal annual snowfall of approximately 50 inches occurs mainly from November through March. Winter temperatures seldom drop below zero degree F. January is normally the coldest month of the year and July and August are normally the warmest. Soil Conditions The types of soil and the depth to groundwater in the study area were catalogued and mapped in two 1971 soil survey reports by the U.S. Department of Agriculture, Soil Conser- vation Service. The data in those reports were condensed for planning purposes to guide the delineation of expected development areas and to determine the expected rate of storm water runoff for this study. 7 The total area within the city limits, plus the drainage area tributary to the city, was divided into three geotech- nical categories: I Moderately good soil and drainage conditions II Marginal soil and drainage conditions III Poor soil and drainage conditions Of the total area, about 10 percent falls in category 1, 30 percent falls in category II, and 60 percent falls in cate- gory III. Category I This category includes the soil and groundwater conditions best suited for development. The soil types generally include CL, ML, SP, GM, GW, and GP (unified classification). The soils are predominantly fine grained. The slopes are generally 3 to 12 percent, and the land is moderately well drained. The permeability of the soil is about .63 to 2.0 inches per hour. The water table is generally more than 5 feet below the ground surface. Category 11 This category includes fine-grained soil types of the Beluga series (CL, ML, MH, SM). It also includes soils from the Kachemak, Spenark, Beluga-Mutnala, and Moose River series. Slopes range from zero to 12 percent generally, and the land is moderately well drained to poorly drained. The water table is generally within 5 feet of the ground surface. Erosion and stability of the steeper slopes are more of a hazard than with category I soils. Category This category is relatively poorly suited for development in general. The soil is fine grained in most areas. Soil types include CL, ML, MH, SM, SW, SP, GM, GP, GW, OL, and pt (unified classification). Slopes range from level to greater than 45 percent. Water tables are at the ground surface in many areas and it is poorly drained. Other areas are very steep and erosion and stability of slopes are a significant concern. Some of the major limiting factors that inhibit development, especially in category III, and to some extent in category II, are as follows. 8 1. Shallow, slowly permeable substratum 2. High water table or seepage conditions 3. Susceptibility to flooding or to inundation by high tides 4. Steep slopes or rough topography 5. Clayey material at shallow depths (groundwater problems) 6. Higher-than-average susceptibility to frost action 7. Erosion hazard 8. organic material 9. Possibility of contaminating groundwater As indicated above, 60 percent of the land area falls in category III. Much of this land is very steep (bluffs near the ocean and in back of town) or is swampy and peaty. Drainage in many of the swampy areas is limited because of the terrain. Much of the present development is in category III areas which contain soils of the Beluga series. Where construction has occurred in these areas, drainage and control of the groundwater have usually been a primary consideration and will continue to be an important concern. Because it is prime view property, development on the steep bluffs has occurred in some areas. Constraints to develop- ment are severe, especially in the case of higher density development. Erosion, slope stability, road construction, and difficulty in providing utilities all tend to severely inhibit growth in these areas. Many areas in category III can be developed, but special measures must be taken. Category II or category I areas are not generally as limited, but many category II areas also need special care in develop- ment. A work map was prepared showing the areal extent of the three geotechnical categories. This work map was used.as a guide in determining future land use patterns. Economy Commercial fishing, fish processing, retail services and trades, and tourism all make a strong contribution to Homer's economy. Twenty-four percent of the city's employed adults are service workers, 21 percent are in the professional- 9 technical occupational category, and another 20 percent work as fishermen and laborers. Homer's average family income is about $22,000. Unemployment and seasonal employment fluc- tuations are still a problem in Homer despite rapid growth. The industries causing the greatest seasonal fluctuations are fishing, food processing, and tourism-related retail trades and services. Commercial fishing for salmon, crab, halibut, shrimp, and herring will continue to play an important role in the economy. Two large and two small processing plants are located on Homer Spit. Expansion of the fish processing industry to include bottomfish is expected as a result of the extension of the 200-mile limit. The city is under- taking a port study to assess the probability and facility requirements of bottomfish-related development. A federal oil and gas lease sale, held in October 1977, has resulted in offshore exploration activity near Homer. The Homer city dock is located approximately 40 miles from the central area of the lease sale and the city will experience economic and population impacts if oil and gas are discovered and developed. As of spring 1979, two drilling rigs were operating in Lower Cook Inlet, with no reported discoveries. During the explora- tion phase, Homer will provide water and fuel for supply boats, and the Homer Airport will serve as a transfer point for drilling rig crews. If major discoveries are made, there will be an increasing demand for onshore facilities, staging areas, and dock space in the Homer area. In addition to the economic potential of both bottomfish and oil development, the retail services and trades are growing employment sectors. Between 1976 and 1978, a total of 46 commercial building permits were issued. These included construction of a new shopping mall, office space, and a bank branch. Tourism and recreation are also increasing with most tourist-related commercial activity located on Pioneer Avenue and on Homer Spit. Homer's highway, air, and water-based transportation facili- ties enhance the city's potential for economic development. Homer's port facilities include a 410-foot, city-owned dock that serves the U.S. Coast Guard, the state ferry, and the Standard Oil tanker. The city's small boat harbor has a long waiting list, but expansion is planned. The State of Alaska owns and maintains an airport at Homer with a 7,400- foot runway. Expansion and upgrading of airport support facilities are also planned within the next 5 years. 10 POPULATION Population Trends The City of Homer was incorporated in 1964, with an estimated population of 800. Population figures through 1978, along with annual percentage growth rates, are shown in table 1. The annual growth rate for the period from 1964 to 1968 was 5.1 percent per year. This growth rate increased to 7.8 percent per year for the period from 1972 to 1975, and to 11 percent a year from 1975 to 1978. TabZe 1. POPULATION GROWTH Average Annual Year Population Percent Increase 1964 a 800 1968 b 975 5.1 1970 c 1,083 5.4 1972 d 1,243 5.7 1975 e 1,583 7.8 1978 f 2,050 11.0 a City incorporated with present boundaries. Population estimated by city personnel. b Estimate by Alaska State Housing Authority. c U.S. Census, April. d official City Census, October. e Special U.S. Census, August. f Special U.S. Census, September. Growth rates in other Kenai Peninsula Borough cities have varied from an average annual rate of 4 percent for Seward, 5 percent for Seldovia and Kenai, to 8 percent for Soldotna. The Kenai Borough as a whole has grown at an average annual rate of about 6.5 percent. Future Population Growth Although not always accurate, population projections serve as a guide for predicting future land use and development trends. The factors most likely to affect future population growth in Homer are (1) the development of bottomfishing and fish processing, (2) oil and gas development activity in Lower Cook Inlet, (3) tourism, and (4) the general attrac- tiveness of Homer as a place to live for both permanent and seasonal residence. Table 2 shows estimated population growth for the City of Homer at both a 7- and 10-percent average annual rate of growth. These rates correspond to the city's growth rates for the period from 1972-1978. A continuation of the 10- percent rate to 1990 assumes some development of either oil or bottomfish or both. The 7-percent growth rate assumes a more moderate level of development in these industries. Using these rates of growth, Homer's population could increase by 2,500 to 4,500 residents by the year 1990. This, in turn, increases the amount of land devoted to residential and commercial uses both within and just outside the city boundaries. Table 2. CITY OF HOMER POPULATION PROJECTIONS 7-percent Growth Rate 10-percent Growth Rate Number of Number of a Year Population Households Population Households 1978 2,050 640 2,050 640 1980 2,350 765 2,480 810 1985 3,200 1,055 3,995 1,315 1990 4,490 1,490 6,435 2,140 a The U.S. Census Bureau projects that average household size will drop'for the country as a whole. These estimates assume a decreasing average household size as follows: 1978-3.2; 1980-3.07; 1985-3.04; 1990-3.01. Major oil or gas development would probably result in popu- lation increases over and above those indicated by the 10-percent growth rate. Estimates of population growth related to outer continental shelf development are contained in Offshore Oil DeveZopment In Lower Cook Inlet (CH2M HILL, 1978). The high case projection (which has a 5-percent probability of occurring) shows a possible 1,700 people added to the Homer population by 1990 due to oil and gas development alone. The use of a 7- or 10-percent average annual rate of growth can be somewhat misleading since this "straight-line" method of projection does not show the variations in the rate that are likely to occur from year to year. The method is intended to give a general indication of future population levels. The estimates should be revised when more information is available on the likelihood of new or expanded industrial activity. Future population is estimated to the year 1990 only; it is nearly impossible to foresee all the factors that could influence population growth beyond this date. 12 LAND USE AND DEVELOPMENT Knowledge of current and future land use patterns is generally required to determine the magnitude of storm water runoff. Existing and future land use within the city's boundaries and drainage area was estimated based on the inventory contained in the city's water and sewer plan, building permit data, the new comprehensive plan, and anticipated zoning ordinance revisions. Current Land Use Current land use in the study area is shown-in figure 3. The majority of new residential construction has been occur- ring in the central part of the city in areas currently served by water and sewer. The extension of water and sewer service out East Hill Road has stimulated new residential construction in that area. Some building is also occurring along West Hill Road, an area not served by water or sewer. The central commercial area is fairly well established along Pioneer Avenue between Olsen Lane and Lake Streets, and it is continuing to grow. The construction of stores and offices within this area and the new shopping mall on the east side of Lake Street are examples of recent additions to Homer's emerging central business district. When the Homer bypass opens, additional commercial establishments can be expected there. Many subdivisions have been approved in the area just above the northern city boundary over the last several years. A number of these subdivisions are located within the city's drainage boundaries. Lot sizes within the subdivisions vary, ranging from 1/3 acre to 5 acres. The number of housing units and commercial establishments authorized by building permit for the City of Homer is shown in table 3. There were 117 housing units authorized in 1977 and 90 units authorized in 1978. No data exist to indicate how many of these units might be for seasonal use only. 13 TabZe 3. HOUSING UNITS AUTHORIZED BY BUILDING PERMITS CITY OF HOMER, 1976-78 1976 1977 1978 Number Percent Number Percent Number Percent Single-family 33 55 68 58 42 46 Multifamily 27 45 36 31 29 31 2-4 units (17) 5+ units (12) Mobile Homes Not available 13 11 21 23 Total 100 117 100 92 100 Commercia 1 12 15 19 Source: Staff Economist, U.S. Department of Housing and Urban Development, Anchorage. Future Land Use The population projections presented earlier can be used to estimate future housing and land use requirements. These estimates, in conjunction with the land use recommendations in the city's comprehensive plan, indicate future land use. Tables 4 and 5 estimate the housing and land requirements that could result from the 7- and 10-percent population growth rates. The number of new units needed for a given period is an estimate based on the existing housing stock, the expected growth in population and households from table 2, and the number of additional units required to sustain a reasonable vacancy rate. In each table, the average annual housing requirement for the period is further broken down by housing type (single- family, multifamily, and mobile home). This breakdown is an estimate of future trends based on percentages observed over the last several years in Homer. The amount of land that will be required to accommodate this growth in housing units is estimated using an expected density of about 4 units per acre for single-family units, 12 units per acre for multifamily units, and 8 units per acre for mobile homes. At a 7-percent rate of growth, a total of about 154 acres would be required for residences from 1978 to 1990. At a 10-percent growth rate, about 263 residential acres would be required. These estimates are for population growth within the city limits only. 14 ...... .... ..... ....... .... RESERVOIR TF ---- - 7-- - WATER IRE-AIMEENT PLANT CITY LIMITS ..... ...... ... ..... ..... . _j144, 'r, CITY LIMITS =?AAA CAMPGROUND 'sc I OUNDS -iAIRGROUNDS T-5 PELEAGA LAKz LEGEND FAA RANGE SITE @A-'A Rural Residential SEWAGE TREATMENT I- Urban Residential PLANT MUD SA Y Commercial with Residential Industrial and Transportation KACH!FAIAK SAY Undeveloped Community Facilities Generally Unsuitable for Development SMALL BOAT HARBOR, INDUSTRIAL AND COMMERCIAL CITY DOCK PUBLIC CAMPGROUND TabZe 4. ESTIMATED HOUSING AND LAND REQUIREMENTS FOR RESIDENTIAL GROWTH, CITY OF HOMER 7-PERCENT GROWTH RATE 1978-80 1980-85 1985-90 1. Housing Stock (beginning of 740 770 1,070 period) 2. Anticipated Household Growth 125 290 435 3. Requirements for 3.5-percent 4 10 15 Vacancy Rate 4. New Units Needed 50% single-family 64 150 225 30% multifamily 40 90 135 20% mobile home 26 60 90 Total 130 300 450 5. Land Requirements (acres) Single-family (4/acre) 16 38 56 multifamily (12/acre) 3 8 11 Mobile home (8/acre) 3 8 11 Total 22 54 78 NOTE: Total additional residential land required = 154 acres. TabZe 5. ESTIMATED HOUSING AND LAND REQUIREMENTS FOR RESIDENTIAL GROWTH, CITY OF HOMER 10-PERCENT GROWTH RATE 1978-80 1980-85 1985-90 1. Housing Stock (beginning of 640 815 1,340 period) 2. Anticipated Household Growth 170 505 820 3. Requirements for 3.5-percent 6 18 29 Vacancy Rate 4. New Units Needed 50% single-family 88 260 425 30% multifamily 52 160 255 20% mobile home 36 103 170 Total 176 523 850 5. Land Requirements (acres) Single-family (4/acre) 22 65 102 Multifamily (12/acre) 4 13 20 Mobile home (8/acre) 4 13 20 Total 30 91 142 NOTE: Total additional residential land required = 263 acres. 17 Although future requirements for commercial land are diffi- cult to estimate, a rough estimate can be obtained by applying a ratio of land to population, as reported in current planning studies. If about 0.2 acre of commercial land is required for each 100 new residents, then an additional 5 to 10 acres of land in commercial use could be required by 1990. It should be noted that the demand for commercial acreage is tied to increases in tourism and population growth outside the city limits, as well as to increases in permanent resi- dents within the city. Industrial land use needs are more difficult to estimate. They will be influenced, to a large extent, by oil and gas development and growth in the demand for fish processing plants. When these land use needs are compared with the amount of land proposed for residential, commercial, and industrial uses in the city's comprehensive plan, it appears that these needs can be easily accommodated within the city limits. The comprehensive plan recommends that about 14 percent of the city's land be designated industrial (880 acres), 9 percent as commercial (530 acres), and 56 percent as residential (3,380 acres). Another 6 percent would be reserved for recreation and open space and about 15 percent as government reserve land. A future land use map is shown in figure 4. The map is based on the city's comprehensive plan (adopted March 1979) with some modifications made to distinguish between low- and medium-density residential areas and between the central and highway-oriented commercial uses. The location and density of future development in the City of Homer will be influenced by the following factors. 1. Proposed zoning district boundaries and lot size regu- lations. 2. The location and capacity of water and sewer lines. Development is most likely to occur where water and sewer are available. Ultimate densities of 4 single- family to 12 multifamily units can be expected in the areas served by water and sewer. This would result in a population density of 12 to 36 persons per acre. 3. Development is likely to occur at a density of .5 to 1 unit per acre in areas not served by public water and sewer. This includes areas both within and outside the city limits. The resulting population density would be about 1 to 3 persons per acre. 18 - - --------- - WATER RESERVOIR WATER TREATMENT PLANT . . . . ... .... CITY LIMITS 77 12 . ........ ... T- . .... .. ....... .. CITY LIMITS HOE PITAL 1K 1 0 f"MI I q AMP GROUND -FAIRGROUNDS Aj ;jVF Ile-.1-w- a Ep@' W, I @- . - - , - i , J@: _k' T"Li P, HOMER HIGH SCH004 P, I- .___2j LEGEND FAA RANGE SITE Rural Residential SEWA E TREA EN Urban Residential PLANT ------- Central Commercial with Residential j<ACHFAf4K6AY Industrial Water Oriented Industry Open Space Recreation SMALL BOAT HARBOR, Highway Commercial INDUSTRIAL AND COMMERCIAL FF, Community Facilities -CITY DOCK Generally Unsuitable for Development PUBLIC CAMPGROUND NOTE: LAND OUTSIDE CITY LIMITS EXPECTED TO DEVELOP AT THE RURAL DENSITY 4. Some multifamily residential development is likely to occur in the central commercial area. 5. A demand for residential development on prime view property can be expected to continue. Even without any further development controls, densities will be restricted in those areas by topography and soils, especially as these limit the approval of septic systems. Densities in some subdivisions will also be restricted by special covenants established by the developer. 21 Chapter 3 EXISTING DRAINAGE SYSTEM The components of the existing surface water drainage system in the City of Homer are presented in this chapter. Excerpts from and references to previous reports will be used to provide detail. NATURAL DRAINAGE The natural drainageways in the City of Homer are of two types. The first type is the large drainageways that have flow in them for most of the year (perennial) and usually have larger drainage areas. Bidarki Creek, Woodward Canyon, and Palmer Creek are three such drainageways and are the only ones in Homer that have been named. They have total drainage areas of approximately 280, 400, and 830 acres, respectively. The larger drainageways are generally identi- fied by their deep, steep-sided channels, which under natural conditions extend down from the bluffs all the way to Kachemak Bay or the lowlands around Beluga Lake. These larger drain- ageways have channel lengths of approximately 1 mile, with Palmer Creek the longest with a length of 2.3 miles. The second type of natural drainages is the smaller drainages with drainage areas less than 50 acres. The areas near and just east of West Hill Road are typical of this type of natural drainage. Drainage water collects in small, steep ravines on the bluff and appears as streamflow in the bottoms of the ravines only during rainy periods (intermittent). When the flow from the ravines reaches the flatter grassed slopes below the bluffs, it fans out, infiltrates the soil, and enters the groundwater. As a result, no defined channels are apparent in the field or on aerial photographs. Under natural conditions most of the drainageways with 10 percent gradient or steeper have adequate channel capacity to contain even a 100-year flood. If the channel slope remains steep all the way to the discharge point, as in the case of Bidarki Creek, no flooding would be likely to occur outside the channel banks. However, if the slope of the channel becomes flatter than 10 percent before reaching its discharge point, an alluvial fan develops. An alluvial fan is a broad topographic feature caused by the natural outwash of debris from a steep canyon. Drainage channels on alluvial fans are generally intermittent and can change course during floods. For example, the Palmer Creek alluvial fan dominates the topography in the northeast part of Homer and can be recog- nized on a contour map by the fan-shaped concentric contour 23 lines. The Palmer Creek fan is made up of all the material which has naturally washed off the bluffs above to form Bear Canyon. The process of building the Palmer Creek fan was furthered by the outbreak floods in 1937 and the early 1950's, as described by Stringer (1976). The drainageways that have alluvial fans and ill-defined channels in their lower reaches are subject to overflow during even minor floods. The natural drainageways in Homer can therefore be cate- gorized as either perennial or intermittent streams, which are either flood-prone or not based on their natural channel geometry and slopes. The topography and natural drainage- ways in Homer and the tributary drainage areas in the borough can be seen in figures 5, 6, 7, and 8. MANMADE MODIFICATIONS The development of the City of Homer has imposed numerous structural changes to the natural drainageways. Generally, the changes have modified the natural channel capacity and/or alignment. The existing drainage system is comprised of roadside ditches and cross culverts tied into the natural drains. In areas where no natural drains exist, manmade ditches have been constructed. Roads and highways have had three main impacts on the natural drainageways. The first and most obvious is the necessary crossing of the drainageways. Road fills block the natural drainageways and force all the flow through the culvert that is provided. If the flow in the drainageway exceeds the culvert capacity, flow backs up behind the road embankment and overtops the roadway, which in some cases can lead to flooding of nearby properties and possible loss of the road embankment due to erosion. Culvert capacity is often reduced by blockage from debris, sediment, or ice. The second, less obvious, impact of roads on the natural drainage is the tendency for roadside ditches to collect and redirect drainage water from its natural course into a route paralleling the road. Runoff is often diverted out of the subbasin from which it originated. This impact is common,- especially in areas where no well-defined drainage channels exist. The construction of roads in Homer has, in several cases, redefined the alignment of the drainageways and redirected additional runoff to compound drainage problems. The third impact is associated not only with the roads but with the land development that comes with them. The intro- duction of impervious surfaces and drainage ditches normally 24 .... ..... . 7- CITY LIMITS - - - - - - - - - - - CITY LIMITS 7 ;,Z IN tK_ Tj _X2 6N 'i @T -pl, V\ k AI lk - ----- :::2 zklk@ ... .. ... . sti@ -t@' @N2-@ r 7- 1Y 3, MA A-C ok Rj i T,.!-,. 7,@Z@ 0 4 al '700 wo A. 1, 'V 'A Zt @4 % ,Q--)) @j g-W) ll@ Ci 64r Z, @LP - Vv) Al PE @,; I i t I q, f07 6 4 eo 6 50 9 60- Of Ij Ip, ,ee sill "Nal, 'l,' 1, ly) iK kf!@ @j All 77 A'o I TT, 71 W04 f, @J 90 ------------------- Iv s j ie . . .... .. ---- 4ot, 3@r A REEK LAI,, -J"I fRjTzCREEKDRIIE J II ki . . ..... ... . ...... . ... ... .I- p/ mmn tiK 4A cu Z L 3 CD CO CO r (D C) r c 0 M Cl) CD M M IM (D CL ... ...... ID CL 0 10 increases the rate and amount of runoff from a drainage area by providing a more hydraulically efficient flow path and by reducing the amount of pervious area that can accept infil- tration. The impact of road construction on the drainage system in Homer is shown in figures 5, 6, 7, and 8. The maps show all existing roads and those that are currently under construc- tion or platted on approved subdivisions. Roads planned for the Master Roads Plan being prepared by Silvers Engineering were also included in this report. The major drainageways are shown on the maps, as well as the location of the existing culvert crossings. Each culvert crossing is assigned an index number that is shown on the maps and cross-referenced to a culvert inventory in appen- dix A. The inventory shows the culvert number, existing size, cumulative tributary drainage area, existing flow capacity, and expected design flood flow. Existing flow capacity is based on the assumption that the culvert is not blocked with sediment, ice, or debris, which under present conditions is not always a valid assumption. CURRENT DRAINAGE MANAGEMENT Current drainage management in the City of Homer falls into the categories of system maintenance and control regulations. The drainage system maintenance includes the maintenance of ditches and culverts as provided by the City Public Works Department and the State of Alaska Department of Transpor- tation, within their respective jurisdictional rights-of-way. The management philosophy to date has been to clean and maintain culverts on a priority basis and to replace cul- verts which are damaged or washed out. The state has two electrical thaw wire installations in Homer to prevent ice from blocking the culverts during the winter months. Four such installations are planned for the Homer bypass now under construction. These systems replace the steam-thaw pipe systems which are becoming outdated due to the high labor cost associated with the steam trucks. The Municipality of Anchorage, for example, is phasing out all the old steam-thaw pipe systems and anticipates over 6,000 thaw wire installations. Most of the culverts in Homer are corrugated metal type made of either galvanized steel or aluminum. Some have prefabri- cated metal inlet and outlet sections. Few have concrete headwalls. Most culverts protrude from the road embankment with no special inlet or outlet treatment. 33 The existing regulations regarding road construction and drainage are contained in the city code and the borough subdivision ordinances. City code requirements related to drainage are contained in Articles 4 and 5. Article 4, concerning driveway and right-of-way construction permits (Section 14-400g), requires that permit applications be accompanied by a plan showing complete details on drainage. The code requirements contain the following language: All driveways and buffer areas should be constructed so as not to impair the drainage within the street or road right-of-way nor alter the stability of the roadway subgrade and at the same time not impair or materially alter drainage of the adjacent areas. All culverts, catch basins, drainage channels, and other drainage structures required within the buffer area and under driveways as the result of the property being developed, shall be installed in accordance with the standards set by the city, said standard being available at City Hall. Article 5 of the code contains the following standards for street construction (Section 14-500.4.): A. Cross Culverts 1. Shall be sized for stream flow based on a 25-year flood. 2. Shall be 18-inch minimum inside diameter. B. Driveway Culverts 1. Shall be 18-inch minimum diameter. 2. Minimum length shall be 21 feet - maximum length 35 feet. a. Special conditions requiring longer culvert lengths will be subject to the approval of the Public Works Director. 3. Driveway elevation at road ditch line shall be 0.1 foot below the elevation of the edge of shoulder. 4. Driveway ditches shall be constructed in such a manner so that no scour will occur to road ditch. 34 The borough has a subdivision ordinance which is administered by the Borough Planning Commission for areas both within and outside the Homer boundaries. Applications for subdivision approval are submitted to the Plat Committee of the Borough Planning Commission. Subdivision applications for areas within the city are referred by the Plat Committee to the City's Advisory Planning Commission for review and comment. Decisions of the Plat Committee can be appealed to the Planning Commission as a whole, with subsequent appeal to the Borough Assembly. The subdivision ordinance requires that only limited infor- mation on topography, soil conditions, or drainage patterns be submitted with the plat application. These information requirements are listed below (from Subdivision Ordinance, Section 20.12.060). 1. A vicinity map showing natural and manmade features, such as shorelines and streams. 2c Approximate locations of areas subject to inunda- tion, flooding or stormwater overflow; when adjacent to lakes or nontidal streams, the line of ordinary high water; wetlands. 3. Contours at suitable intervals when any roads are to be dedicated, unless the Planning Director or Commission finds evidence that road grades will not exceed 6 percent on arterial streets, 10 percent on other streets. 4. Approximate locations of slopes over 20 percent in grade. The subdivision ordinance (Section 20.20.070) also limits grades on roads within subdivisions to 6 percent on arterial streets and 10 percent on other streets. 35 Chapter 4 RUNOFF DETERMINATION The work done by the Soil Conservation Service in their study, "Potential Flooding, City of Homer," provided a starting point for the determination of runoff. The speci- fic methods used to determine the expected runoff for the purpose of drainage management planning are presented in this chapter. PRECIPITATION The average annual and monthly precipitation were presented in chapter 2 of this report. The design of drainage systems requires determination of specific runoff events usually tied to an estimated probability of occurrence. A specific design event may contain more precipitation in one day than is normally expected for a whole month. Meteorological data are collected at the Homer Airport weather station and published by the National Oceanic and Atmospheric Administration (NOAA). The maximum daily pre- cipitation amount for each year during the period 1932 to 1978 was determined using the published records. Records completed after 1951 included both daily rain and snow amounts and, for some years, the maximum daily precipitation was in the form of snowfall. Several maximum precipitation events started as snow and changed to rain. A precipitation frequency analysis was performed on the available data under the assumption that all annual maximum daily precipitation values were rainfall events. The data were ranked and plotted on log probability paper in accor- dance with the Weibull plotting position formula. The maximum daily rainfall of record, which fell in November 1952, was 3.02 inches. That data point was a high outlier on the frequency plot at the 48-year recurrence interval, and was therefore subjectively assigned a 100-year recur- rence interval to give a less positive skew to the distri- bution. The frequency data based on daily rainfall records were increased by 13 percent in accordance with accepted practice to determine the maximum 24-hour rainfall for the various recurrence intervals. Table 6 lists the rainfall frequency data developed from this analysis. 37 Table 6. RAINFALL FREQUENCY DATA, HOMER AIRPORT Recurrence Interval 24-Hour Precipitation (years) (inches) 2 1.42 5 1.85 10 2.06 25 2.41 50 2.80 100 3.39 Adjustment of the rainfall frequency data due to orographic effects of the steep bluffs at the north end of Homer was not considered necessary for development of runoff criteria. Comparison of the 25-year, 24-hour precipitation at Homer with totals for several other Alaskan cities is shown in table 7. Table 7. 25-YEAR, 24-HOUR RAINFALL AT SELECTED LOCATIONS City Inches Homer 2.4 Fairbanks 2.5 Anchorage 2.9 Kenai 3.1 Juneau 5.0 Seward 7.0 RUNOFF DETERMINATION There are several accepted methods of determining the ex- pected rate of runoff resulting from a specific design rainfall event. Because of the previous work done by the SCS on potential flooding in the City of Homer, the SCS method of runoff determination was chosen for use in develop- ing the drainage management plan for Homer. The SCS method is based on extensive empirical studies of the relationships between rainfall, soil types, land use, and runoff. Both peak rates and volumes of runoff can be determined by the SCS method. Only the peak rates of runoff were determined for this study. More than half of the annual maximum rainfall events in Homer occur in the late fall, when very wet or frozen ground is common. Individual extreme runoff events have occurred as a result of rain falling on snow-covered frozen ground. These conditions are common enough to justify their inclusion in the runoff determination. 38 A reasonable amount of snowmelt was added to the previously determined rainfall amounts to be representative of the expected conditions. U.S. Army Corps of Engineers snowmelt equations were used to calculate that approximately 0.1 inch of water would result from melting of the snowpack during the maximum hour of the extreme rainfall events. An equiva- lent 24-hour amount of snowmelt water was added to the 24-hour rainfall amount to give a total 24-hour precipita- tion for each event. A 24-hour melt of 0.6 inch was used for all recurrence intervals. This results in 25- and 50-year, 24-hour.rainfall plus snowmelt totals of 3.01 inches and 3.40 inches, respectively. The SCS type IA storm was chosen as appropriate for the Homer area. A curve number of 95 was used to represent the expected frozen ground condition. The SCS Standard Drawing Number ES 1029, sheet 24 of 24, dated 15 March 1971, was used to determine the peak rates of runoff for drainage areas comprising 5 and 1,000 acres. The results of this analysis are shown in figure 9. ALTERNATIVE DESIGN FREQUENCIES The recurrence interval chosen for the design of storm drainage facilities is rarely based on detailed cost/benefit analyses. more commonly, it is established by local prac- tice. For example, the 5-year recurrence interval is used for design of drainage systems for most residential areas and 10- to 25-year design events are commonly used in com- mercial areas. Major stream and river crossings are usually designed for 50- or 100-year events. The design frequency is chosen with consideration of the consequences of having an event occur that is even bigger than the design event. Minor street flooding in a residential area is much more tolerable than the washout of a major arterial highway. Thus, different design frequencies may be selected for different areas. The runoff versus drainage area curves presented in figure 9 were used to compute runoff flows for various design fre- quencies in order to assess the existing capacity of parts of the present drainage systems. Two drainage subbasins, each discharging to Kachemak Bay, were analyzed. The Wood- ward Canyon subbasin drains an area of about 370 acres in a steep, natural channel that has a number of road crossings at the lower end. The second subbasin drains about 111 acres through a series of both natural drainageways and manmade ditches that are crossed at several points by roads and driveways. The general alignment of this drainage is along Svedlund Street. 39 300- i 250- tt::- . . . . . . . . . . . . . ....... 200- TYPE 1A STORM DISTRIBUTION SOIL CONSERVATION SERVICE ...... ...... STEEP SLOPES FROZEN GROUND (RCN=95) 150-- I M HIM I e I I I (IiIIIIIIIHIM11111 I HIII JX I K 11 IIIIII IIIII I I I I I I I I 1 (111 fli !I III III t III I II It 1 111, flillill 9111 Ill, I II I if fill Ill I lif I yl I yo 90.-- - ---------- 70- zz z ---- --------- 0 50- LU En 40- LU --- CL LU LU U- 30,-- ------ I I . . . . . . . . . . . 25 D LU I T. I I I I I I I I IT cc - - - 0 I T I I I I I I I (n - - - oI 01 1 f I I I I yo I I I I I I jo 16,1 "1 1 1 11 I I I I 11f I orl I,I I I III H I LU I I X1 I I H Y I I Ill if 0- 00 e --.I .I Io"I I L/11 A I- I111 1 10__ X LAHIV Ill Ao I i I f 01 9 8 10 7 ------- + __z 6 if 4 3 1b 1,5 2'0 25 30 40 50 60 70 80 90 100 150 200 250 300 400 500 DRAINAGE AREA (ACRES) Figure 9 rielationship of Peak Discharge and Drainage Area For Average Recurrence Intervals The analysis showed that 40 percent of the existing culverts in the two subbasins are inadequate to convey 10-year runoff flows. An additional 20 percent are undersized for passing 100-year flows. Lack of field data makes it difficult to assess the adequacy of channels and ditches. However, because most such drainageways flow on steep gradients, their channels have been cut to depths that provide ample capacity to pass anticipated design flows. Planning level cost estimates were made to determine the costs for upgrading the existing systems to the 25-, 50- and 100-year level of protection. It was found that designing for the 50-year event would increase costs about 20 percent above those for the 25-year design, while 100-year costs would be approximately 70 percent higher than those for the 25-year design period. In light of expected operational problems such as culvert blockage with sediment, ice, or debris, it is recommended that the 25-year design event be used for the design of most drainage system components. Extra protection should be provided, however, at major culvert crossings. At those points where the tributary drainage is 200 acres or more, a 50-y'ear design event is recommended. The Homer city code currently requires that culverts be designed for the 25-year flood with an 18-inch minimum diameter. 41 Chapter 5 PROPOSED DRAINAGE SYSTEM A complete definition of the proposed drainage system for the City of Homer is provided in this chapter. Methods of determining the size and location of drainage system com- ponents, the expected cost of upgrading portions of the existing system, and suggested sediment control,measures are given. The proposed system is designed to reduce drainage, flooding, and erosion problems in Homer. These problems are generally described in the SCS study of potential flooding in Homer and are described in detail in the 1976 report on flooding by the Scotia Group. A discussion of the site- specific flooding problems will not be repeated in this report. TRUNK DRAINAGE SYSTEM The physical description of the Homer drainage system in- cludes delineation of a trunk drainageway system and its tributary subdrainage areas. The existing drainage fa- cilities, as described in chapter 3, form the basis of a complete drainage system. Reliance on these natural drain- ageways and pre-existing manmade drainage ditches is the most cost-effective way to develop the complete drainage system. Although it would be possible to redefine the course of an existing drainageway or to put the entire flow in pipes, the cost of those alternatives would always be higher than the cost of improving the existing system. Figures 5, 6, 7, and 8 show the proposed trunk drainage system for the City of Homer. The trunk drainage system is that portion of the city's drainage network that conveys runoff collected from small land areas (subareas) to a logical disposal point such as Kachemak Bay or Beluga Lake. The total drainage area tributary to an individual drainage trunk can be subdivided into subareas. Generally, each subarea has a culvert at its lower end. The cumulative drainage area and the drainage area versus discharge curves are used to calculate the design flow capacity required for each segment of a trunk drainageway, and for the outlet culvert. The channel of the trunk drainageway should have sufficient capacity throughout the reach to carry the flow calculated for the lower end of the subarea. Some of the trunk drainageways shown on the maps already exist and have adequate channel capacity to carry the design flow. Others currently exist but are estimated to be too small to carry the expected flow. Still others do not yet 43 exist and must be constructed to meet future needs. Several of the existing trunk drainageways have adequate channel capacity but are restricted by undersized or plugged cross culverts. Figure 6 will be used as an example of how the trunk drain- ageways and subareas were determined. There are three major natural drainageways on this figure: Woodward Canyon in the west and two unnamed drainages in the east. The intervening areas are served by manmade ditches and minor natural drain- ageways. The locations of the trunk drainageways were determined from the available topographic maps, recent aerial photographs, and field inspections. Subdrainage areas are.generally determined by the location and orienta- tion of the existing and planned roads. Locations of future roads were taken from subdivision plats that to date have been approved by the city. Drainage from all land within a given subarea should be conveyed through roadside ditches to the trunk drainageway serving that area. In areas where road plans were not available, the trunk drainageways were laid out along the natural low spots in the topography. If these alignments prove to be incon- sistent with future development plans for those areas, the alignment of the drainageway may be changed in the future if a properly designed alternative is constructed. A field inventory of existing culverts was performed, and the hydraulic capacity of each existing culvert in the trunk drainage system was determined. In areas where the trunk drainageways cross proposed roads, assumptions as to the depth of the roadfill were made in order to size the appro- priate culvert. Each existing and proposed new culvert was given a four-digit identification number, the first digit being the same as the number of the figure on which the culvert is shown. The selection of recommended design storms used to size components of the trunk drainage system is discussed in the preceding chapter. Portions of the system that drain areas 200 acres and larger are sized to convey 50-year flows, while the remainder of the system is designed for the 25- year event. Hydraulic analyses of existing trunk system culverts indicate that a significant percentage is under- sized for the appropriate design storm. Most trunk channels have adequate capacity, although insufficient data are available to do detailed hydraulic analyses. Two subbasins were selected for which data for upgrading the trunk drainage system were developed. The Woodward Canyon subbasin encompasses an area of 370 acres and is drained by a natural channel. The Svedlund Street drainage serves an 44 area of 111 acres with a series of natural channels and manmade roadside ditches. Need for improvements was based on a preliminary engineering analysis of existing capacities and estimated flow requirements, and used available data. No detailed design of improvement work was undertaken. Cost figures are planning level estimates, in 1979 dollars, and were developed by extrapolating the bid tabulation data from the Homer bypass project and local construction costs. The estimated cost to upgrade the Woodward Canyon trunk drainage system is $111,000 and the estimated cost to upgrade Sved- lund Street trunk drainage is $11,000. Methods for implemen- tation of these improvements are presented in the next chapter. Recommended improvements and associated costs for these two,subbasins are tabulated in appendix B, and are meant to serve as an example only. Detailed reconnaissance and engineering design effort are required prior to actual construction of the improvement projects. ALTERNATIVE PHYSICAL SYSTEMS Buried storm drains and storm water detention ponds were eliminated from consideration as components of the Homer drainage system for several reasons. Piped storm drainage systems typically cost from $50 to $100 per linear foot; whereas, a comparable roadside ditch, when included in the original road construction, costs $5 to $10 per linear foot. open ditches are subject to blockage by glaciation, although modern design techniques can alleviate some of these.problems. Piped systems can also fail as a result of ice blockage, and the economic consequences can be extreme. Other advantages of open ditches and natural drainageways are associated with water quality and groundwater recharge. Well-maintained ditches and natural streams tend to filter out sediments and pollutants, especially if the ditches are grass lined. Evapotranspiration is also enhanced by natural drains and open ditches. Groundwater control is enhanced by open ditches because they act as drains and lower the ground- water table during low flow periods and store water, thus reducing peak runoff during high flow periods. Storm water detention ponds are used in many areas in the Lower 48 states where peak flow reduction is desirable. Peak flow reduction by detention ponds reduces the size and therefore the cost of the downstream trunk drainage system. These types of systems were considered impractical for Homer for the following reasons. 0 In Homer the distance and time of travel from the upper end of any subbasin to its discharge point are relatively short. 45 0 A certain amount of peak flow reduction can be achieved by utilizing open ditches that provide for infiltration and channel routing. 0 The steady and relatively light rainfall/snowmelt events in Homer are not well suited for peak flow reduction. 0 Operation of such ponds in cold environments is very difficult. In the case of Homer, if the pond is glaciated during breakup, it would be of no value. Most importantly, the construction, operation, and main- tenance of storage detention ponds are extremely difficult to administrate. Jurisdictions that have successfully implemented such programs employ large professional staffs to oversee the proper functions of the facilities. A good example of the difficulties associated with implementing such a program is the experience of the Municipality of Anchorage. The Public Works Department has not found stor- age detention ponds very useful, except where they are installed and maintained exclusively by the municipality for the purpose of water quality improvement prior to discharge to sensitive receiving waters. Limited success has been achieved in Anchorage in requiring large commercial devel- opets to provide detention storage to reduce downstream peak flows. For the above-mentioned reasons, the drainage management plan for the City of Homer is based on the maintenance and expansion of the existing open drainage system without the use of storage detention ponds. LOCAL DRAINAGE SYSTEMS The Homer trunk drainage system is defined as a combination of natural drains and open ditches. Local drainage systems serve areas tributary to the trunk system and should be provided with roadside ditches and appropriately sized driveway and cross culverts. The areas tributary to local drainage systems are generally small and system components are therefore sized for the 25-year event. Local drainage systems were not specifically laid out in this report, but the following general guidelines apply. Drainage water should be conveyed via the local drainage system to the designated trunk drainageway serving the specific subarea of concern. Conveyance should be by way of approved ditches and culverts. The tributary drainage area for each local drainage ditch should be determined and the associated design flow calculated using the appropriate 46 runoff design curve. Discharge of local drainage waters into the trunk drainageway should be done in such a way as to minimize erosion potential at the discharge point. DRAINAGE AND EROSION CONTROL GUIDELINES The combination of the trunk and local drainage systems makes up the city's entire drainage system. The design of the various components of the system should be based on sound engineering principles which are presented in the form of design guidelines. The intent of these criteria is to allow for a planned, logical expansion of the city's exist- ing drainage system to meet future needs and solve current problems. The recommended design guidelines are presented in appen- dix C. The material in this appendix was compiled from design references currently being used by the Alaska Depart- ment of Transportation, the Federal Highway Administration, and the U.S. Department of Agriculture Soil Conservation Service, as well as hydrologic data developed specifically for Homer and explained in chapter 4. These design stan- dards should be used by anyone who plans to construct any drainage system components in the city. Appendix C includes recommended procedures for the control of erosion and sedimentation that are related to the expan- sion of the drainage system. Erosion and the subsequent deposition of sediment are natural processes that can be greatly aggravated by the activities of man. In many areas of the country, sediment control is practiced to preserve valuable topsoil for agricultural uses. In other areas, especially those that are rapidly urbanizing, sediment control is practiced to reduce water quality degradation caused by the presence in surface runoff of soil particles and the pollutants associated with them. Although incidences of soil erosion in Homer are not directly linked to operation of the drainage system, such erosion can have a major impact on the maintenance of system components. Many of the existing culverts in the city are partially blocked with sediment; therefore, a major concern in Homer is the reduction of sediment to ensure that the capacity of the drainage system is not reduced. Water quality impacts due to erosion are generally not significant in Homer. In summary, the recommended drainage system for the City of Homer consists of a series of natural and manmade drainage components. The system utilizes existing facilities as much as possible and includes improvements to upgrade the present system capacity. System layout is based on topography and proposed land development plans. Under the recommended plan 47 the city area has been divided into a number of drainage subareas, each served by a trunk drainage system consisting of a combination.of natural channels, open ditches, and appropriately sized culverts. Local drainage systems convey flow to the designated trunk drainageway via open ditches and cross culverts. It is recommended that the design of drainage system compo- nents be in accordance with the criteria and guidelines presented in appendix C. The purpose of these design criteria and standard specifications is to direct the development of the city's drainage system according to a logical expansion plan which incorporates accepted engineering methods. 48 Chapter 6 DRAINAGE PLAN IMPLEMENTATION The proposed drainage management plan, as presented in the previous chapter, can be implemented in several ways. Al- though maintenance of the status quo is an alternative, it will not be considered a desirable one because of an expected continuation of drainage problems in Homer. This chapter contains several legal, administrative, and financial options which could be used to implement the drainage management plan. LEGAL IMPLEMENTATION The basic need for a legal mechanism to implement the plan lies in the fact that much of the city's drainage system will be designed and constructed by developers. If all drain- age system components were to be constructed and maintained by the city, the city could use the drainage management plan as an internal document for the design of the system. How- ever, as the city grows, road, sewer, water, and drainage services will have to be provided. Connection of all these utilities to the existing city systems should be accomplished by the developers in accordance with standard design specifi- cations. The various alternative legal mechanisms that are available to implement the Drainage Management Plan are de- scribed below. Ado2tion by Resolution At a minimum the City Council could adopt this report by resolution and use its recommendations as general guidelines. This approach would be the easiest form of implementation but it would not be very effective in guiding the development of the drainage system. Drainage Control Ordinance The next level of implementation is to develop a new ordinance that would require that certain drainage control measures be accomplished. Ideally, the ordinance would provide for the orderly development of the city's drainage system and provide for control powers to be extended to areas in the borough which physically drain into the city. The intent of a drainage ordinance is to document the city's policy and procedures for maintaining and expanding the drain- age system. For the most part, the ordinance is designed to provide guidelines for future development. The city will have to pursue a parallel course of obtaining easements for 49 the portions of the drainage system which go through developed private property and of initiating a capital improvement program to upgrade the existing system. In September 1978 the Washington State Chapter of the American Public Works Association developed a draft model comprehen- sive drainage ordinance. This model'ordinance contains several parts which are applicable to Homer with regard to the content and structure of a drainage control ordinance. The model ordinance, as amended to suit the needs of the City of Homer, is presented in appendix B. Further revisions to the drain- age ordinance may be required to ensure that it meets the needs of Homer and is acceptable to city officials and legal counsel. The model ordinance would require developers to submit a drainage plan as part of their application for a subdivision approval, building permit, zone change, conditional use, and other such applications (see Section 7D, appendix D.) Con- struction work would not be permitted until the drainage plan is approved. The ordinance would allow certain excep- tions to the drainage plan requirement if the public works director makes certain findings. Section 9 of the ordinance specifies the contents of the drainage plan. The plan would contain: 1. A depiction of the drainage area with topography and other site features. 2. Description of the peak discharge and surface water currently entering or leaving the property. 3. Proposed facilities for handling the runoff. Guidelines to aid developers in preparing a proper drainage plan would be available as a handout from the Department of Public Works (see appendix C). The ordinance would also establish performance standards to minimize downstream damage and erosion, to guide construction practices, and to protect water quality (Section 11). Sections 12 through 14 describe the review, approval, and appeals process and standards for granting a variance. The proposed ordinance would give the public works director a key role in drainage plan review. He would make a finding as to the adequacy of the technical data and would recommend to the planning commission that they approve, approve with conditions, or reject the application. The review by the public works department should include an assessment of the relationship between the proposed drainage system and pro- posed roaddesign and construction. After receiving the 50 public works department recommendation, the planning commis- sion would act on the application as a whole (subdivision, rezone, etc.), considering all aspects of the proposed develop- ment, including drainage. Under Section 15, easements would be required for all drain- age system components as is required for other utilities such as sanitary sewers. The size and location of particular easements for existing developed property have not been deter- mined as part of this study, but these would be similar to those required of new developments, as shown in the model ordinance. In some instances, it may be necessary to grant a variance from the requirement that a local drainage system connect to the trunk drainage system. As implied in Section 15, a developer is normally required to provide a physical con- nection to the city drainage system and to provide an ease- ment for these connections. A variance might be appropriate when a development is isolated by undeveloped land downhill from its site. In such a case, there would be no logical point at which the discharge from the site could be connected to the city system. The public works director would then have to decide if a connection to the nearest component of the city system would be required or if another discharge method would be appropriate. Whichever method is selected, written permission from the owner and/or easements on or through neighboring property must be obtained. Sections 16 through 21 of the model ordinance cover bonds and liability insurance that could be required of developers to ensure that drainage system improvements are constructed and maintained. These sections also set forth a possible city policy on maintenance and enforcement. Modifications to Model Ordinance Several revisions could be made to the model drainage ordi- nance if city officials find that it is too restrictive in its present form. These possible changes are described below. 1. omit the requirement that drainage plans be submitted with building permit applications and conditional use requests. Retain the drainage plan requirement for subdivisions, rezonings, contract zonings, and planned unit developments. If this option if chosen, the city should make informa- tion about drainage concerns available to building permit applicants, especially relating to the location of the trunk drainage systems and any easement requirements. 51 2. Omit the requirement that the drainage plan be prepared, inspected, and field certified by a civil engineer. If this requirement is deleted, the city staff and plan- ning commission will have to assume greater responsibil- ity for reviewing the drainage plans. The city would also need to expand its budget to pay for additional staff involvement. 3. Modify the section that requires bonding and 2-year maintenance of drainage improvements by the developer. Modifications to Existing Ordinances A possible alternative to a new city drainage ordinance is to includedrainage and erosion control requirements in exist- ing ordinances. Whether there is a new ordinance or controls are added to existing ordinances, the primary objective is to ensure that basic data are available to assess how well proposed developments will meet drainage and erosion control criteria. Both the subdivision ordinance and zoning ordi- nance could be revised to include drainage requirements. Borough Subdivision Ordinance The proposed subdivision ordinance (draft March 1979) re- quires that only limited information on topography, soil conditions, or drainage patterns be submitted with the plat application. The ordinance does not require runoff calcu- lations, a drainage system plan, or drainage easements. As currently written, the subdivision ordinance offers few tools for evaluating or solving drainage problems. making changes to the borough subdivision ordinance may be more difficult than passing a citywide drainage ordinance since it requires approval by both the borough planning com- mission and assembly. However, it may be worthwhile to recom- mend such changes since the subdivision ordinance is the only mechanism currently available to address drainage prob- lems related to development outside the city's boundaries. The major area of concern with regard to drainage control outside the city limits is that of the adequate construction of cross culverts. Although erosion control and proper local drainage are generally recommended for areas outside the city, construction of,cross culverts is the primary concern. The city should, at a minimum, ensure that crossings of the trunk drainage system, as shown in figures 5, 6, 7, and 8, be in accordance with the recommended guidelines regardless of whether the subject crossing is within the city or the borough. 52 Possible additions to the subdivision ordinance are listed below. 1. More specific requirements for information on drainage, topography, and soils to be included with the prelimi- nary plat application. (Add to Section 20.12.060.) 2. Requirements for the dedication of drainageway ease- ments. (Add to Section 20.20.040.) 3. Setback and.other design standards for lots within a subdivision that abut or include a natural or manmade drainage channel. (Add to Section 20.20.230.) 4. Provisions for review of the subdivision plat by the borough engineer or another certified engineer. That review process would include an assessment of drainage data and recommendations to alleviate potential drain- age problems. (Add to Section 20.12.080.) 5. Procedural changes whereby the city advisory planning commission would be permitted to review and comment on applications for subdivisions in areas which are tribu- tary to the city. This procedure could be initiated through a change in the ordinance itself or possibly through an intergovernmental agreement between the city and the borough. These suggested revisions to the subdivision ordinance may be difficult to achieve. As an alternative, the city may be able to utilize Section 20.16.060 of the current subdivision ordinance to achieve its objectives. That section does not allow the borough to give final approval to a plat until there is compliance with all city-required improvements. The section reads as follows: Improvements--Installation agreement reguired. No final plat of a subdivision located within a first class or home rule city shall be recorded prior to compliance with any city ordinances concerning the installation of improvements. Evidence of such compliance shall be provided by the subdivider in the form of a written statement from the appropriate city official that im- provements required by city ordinance are or will be installed. Such evidence of compliance shall be a part of the final plat submission and the time for action by the Commission as required by 20.16.170 shall not com- mence until said evidence is submitted. If drainage improvements are required through a city ordi- nance, the city may then refuse to sign-off on the subdivi- sion until the developer posts a bond or otherwise guarantees 53 to the city that the drainage improvements will be constructed. Section 20.20.250 of the proposed subdivision ordinance gives the cities another opportunity to use the subdivision ordi- nance to enforce more stringent requirements for subdivisions within their boundaries. This section of the proposed ordi- nance is quoted below: Different Standards in Cities. Where cities have enacted by ordinance different design standards than those set forth in this chapter, the Planning Commission may apply such city standards in lieu of those set forth in this chapter. Drainage design standards for subdivisions within the city would have to be established through a city drainage ordi- nance as discussed earlier in this chapter before enforcement through Section 20.20.250 of the proposed subdivision ordi- nance would be possible. Even then, the application of these standards would be at the discretion of the borough planning commission. Zoning Ordinance Another opportunity for enacting drainage regulations is through the city's zoning ordinance. Possible options are listed below. 1. The zoning map could be revised to include a drainageway overlay zone. Within this zone, special regulations and design standards relating to drainage could be im- posed. 2. All critical drainageways could be included in the gov- ernment reserve district. This would involve purchasing the land outright, or acquiring easements. The city could then keep the land in its natural state or develop it as park land. 3. Drainage regulations and data requirements could be added to existing zoning district regulations (resi- dential, commercial, industrial). These requirements might include (a) a site plan showing drainage, topog- raphy, and proposed location of structures; (b) runoff data; and (c) a minimum setback for structures from drainage channels. These regulations could also be cross-referenced to the city drainage plan or ordinance if adopted. 54 REQUIREMENTS FOR IMPLEMENTATION In addition to legal implementation, the city will have to take several other steps to ensure proper management of the drainage system. Management and Administration The city currently does not have the staff to administer the requirements of the drainage management plan and ordinance. The actual staff.requirements to upgrade the existing system and to review plans for system expansion depend on the rate at which improvements to the existing system are required and the rate of new development. I At a minimum, the public works director should review all improvements to the existing drainage system and the pro- posed addition of any new drainage system components. In- spection of drainage-related construction activities would also be desirable and should be accomplished by a building (construction) inspector in conjunction with other construc- tion inspection duties. The success or failure of the drain- age management plan is directly related to the availability and quality of the staff assigned to the implementation. Standard Design Criteria In addition to staff requirements, an adequate set of stan- dard design criteria for drainage improvements needs to be developed. Much of the material presented in appendix C, Design Criteria and Standard Specifications, could be used for that purpose. Standard drawings and specifications should be adjusted by the public works director to meet the partic- ular requirements of the city. These design standards should be available to developers at the public works department and city hall. These would supplement and elaborate any standards referenced in a city drainage ordinance. Capital Improvements The rate of capital improvements to the existing drainage system is directly related to the budget available. It is recommended that improvements to the existing drainage sys- tem be made in accordance with a priority list developed and maintained by the public works director. Two separate bases should be used to set the priorities. The first is improvements to eliminate a current chronic drainage problem. For example, if the section of the Wood- ward Canyon drainage behind the Pratt Museum is a constant problem, then it should be entered on the priority list. The second basis for inclusion as a priority is any street 55 improvement project within the city's rights-of-way. For example, when Lucky Shot Street is improved, the ditch along the west side of the street is to be part of the trunk drain- age system and should be constructed to accommodate the appro- priate design flow. Before each project on the priority list comes up for fund- ing, it should be properly designed and an up-to-date cost estimate prepared, as is done for all capital improvement projects. Easements In order to maintain, repair, and replace drainage system components, easements for all such components not within city rights-of-way should be obtained. Acquisition of ease- ments for newly developed property is spelled out in Sec- tion 16 of the recommended model ordinance. For areas currently developed and subdivided, drainage ease- ments should be acquired as part of any capital improvement program and elsewhere on an as-needed basis. That is, ease- ments should be acquired as soon as the need arises to per- form capital improvement of the drainage system components. Ultimately, the city should acquire easements to all trunk drainageways. An average easement 40 feet in width would result in 4.8 acres per mile of drainage system trunk. Financing Requirements Implementation of the drainage plan will require the expen- diture of funds by the city. Financing will be required for capital improvements, maintenance, administration, and re- view of development proposals. Bonds for the required capital improvements can be sold by the city. As indicated in the drainage ordinance, private developers can also be required to bear some of these costs. Typical costs for drainageway improvements and other system requirements are presented in appendix B. The proposed drainage ordinance in appendix D provides the city with the option of taking over maintenance of drainage facilities located on private property that discharge into the trunk drainage system. The city would then have to deter- mine how best to finance the maintenance. Two basic financing options exist: (1) the general fund, supported by taxes, and (2) a service utility charge or assessment charge. One drawback of use of the general fund is that drainage system maintenance must compete with other city budget items for those funds. The service utility charge is, however, very difficult to administer equitably. For Homer, it is recom- mended that maintenance of drainage facilities be funded 56 from the general fund and included in the public works budget. Acquiring drainage easements would also be an additional cost if the-city chooses to obtain easements in existing developments. Easements may be acquired in new developments by requiring that they be dedicated as part of the subdivi- sion approval process. The city may wish to consider com- pensating the developer in certain circumstances, such as when a lot, or lots, becomes unbuildable, specifically be- cause of the drainage easement requirement. The cost of city staff time to implement the drainage plan is also an important consideration. As mentioned above, staff requirements and costs will increase as the rate of development increases. To minimize the time required by city staff, the city can require that the drainage plan be prepared and certified by a civil engineer registered in the State of Alaska, and that the same engineer provide for in- spection during construction and certify that the project was constructed in accordance with the drainage management plan. GENERAL PRINCIPLES OF IMPLEMENTATION Overall, the following general principles should be con- sidered in implementation of the drainage management plan: (D The upgrading and expansion of the physical drain- age system should be in accordance with the drain- age management plan. (D A priority list for upgrading the existing system components should be established by the City Coun- cil. As funds become available, system upgrading should occur. 0 As new system components are added, they should be designed and maintained in accordance with standard design criteria. � Whenever possible, the trunk drainage systems should be improved from downstream ends to upstream ends to avoid the transfer of problems along the trunk system. � Although the design recurrence interval suggested in this report is fairly high for a drainage sys- tem, it should be remembered that there is always the chance that a given storm event will overtax the system. 57 0 Buying drainage easements or buying the land out- right will make it easier to maintain the system, but it will not solve all the drainage problems. It may, in fact, open up the city to damage suits if a flood greater than the design flood occurs. 0 The drainage plan can be partially implemented through existing or new city and borough ordi- nances. The choice of a regulatory strategy should be guided by the ability of the city to administer and enforce the proposed regulations. RECOMMENDATIONS FOR IMPLEMENTATION Of the several ways presented in this chapter to implement the drainage management plan, the following are recommended as being most appropriate for the City of Homer. 0 Adopt a new drainage ordinance similar to the model presented in appendix D. Modification of existing city ordinances would have to be extensive to be comparable with a new ordinance. 0 Establish an interagency agreement with the Kenai Peninsula Borough to provide the city with the power to review and approve any construction and subdivision design that could affect the function- ing of the city's designated trunk drainage system, as shown in figures 5, 6, 7, and 8. 0 Review the city's current staff availability and determine whether there is adequate staff to imple- ment the drainage management plan. The amount of staff involvement will depend on how much is re- quired of the developer. 0 Modify, as required, the Design Criteria and Stan- dard Specifications as presented in appendix C, and make them available to developers and others who would construct portions of the city's drainage system. 0 A capital improvement program should be established to relieve chronic drainage problems and to provide for future drainage needs. Much of this work can be accomplished in conjunction with the capital improvements to the streets and roads. 0 Drainage easements should be required for new developments and should be acquired, on an as- needed basis, for existing developments. 58 Drainage improvements should be scheduled, designed, constructed, and financed through the public works department, as are street, road, water, and sewer improvements. Local improvement districts should be used to add drainage improvements. 59 @ I @ I -1 I @ I ,I I .I I I I I I I I I I Appendix A I Culvert Inventory I Appendix A CULVERT INVENTORY This appendix is an inventory of existing road culverts and those required in the future as roads currently planned are constructed. Data for existing culverts were compiled from field inspections and design drawings. The drainage area tributary to each culvert was planimetered from topographic maps, and the corresponding design flow determined using figure A-1. This inventory should be expanded to include a narrative description of the current condition of the culverts and any associated problems. Jurisdictional responsibility should also be indicated, such as city or state ownership. Inlet and outlet conditions and the presence or lack of thaw wires should also be noted. Channel sections could be added by designation of the numbers of the culverts located at the upstream and downstream reaches of the channel. The basic inventory plus the required additional data should be maintained by the public works director. A-1 300. 250 E@H@ SOIL CONSERVATION SERVICE 200. WPE 1A STORM DISTRIBUTION ............... STEEP SLOPES FROZEN GROUND (RCN 95 150.. 1T T t r T IT T 7111TT11 TIII I I IInIIIII Iit1!11 T 1 r iI I 'tt @h - - - - - - -f4 -.Lit 100__ 4== 80 70. 60.- 50.- LL 40.- LU H < 30.-- < 0-- IIT 15-- 'Z I 111111 1 tt II 10__ Oli 111,1jill 9-- 7 6 5 4- Eli I I II,A 3 10 15 20 25 io 40 @O 60 70 80 9'0 1'00 150 200 250 300 400 500 DRAINAGE AREA (ACRES) Figure A-1 Runoff Design Curve A-2 CULVERT INVENTORY Existing Culvert Head Contributing Culvert Design Culvert Size Culvert Water Drainage Capacity Capacity Number* (inches) Material (ft) Area (acres) (cfs) (cfs) 5100 36 CMP 7 10 80 5 5200 24 CMP 15 35 33 16 5300 36 CMP 20 39 90 19 5400 36 CMP 20 107 90 44 5500 48 CMP w/HW 20 269 210 ill 5800 two 50 x CMP 5 149 110 58 31, 5820 None Existing 75 -- 32 5830 None Existing 75 -- 32 5840 18 CMP 3 75 8 32 5850 None Existing 64 -- 28 5860 48 CMP 10 64 130 28 6000 48 CMP 9 370 125 141 6010 two 65 x CMP 6 368 220 140 40 6020 30 CMP 4 363 28 138 6030 36 x 24 Conc. 8 355 81 136 box wing walls 6040 24 CMP 3.5 355 16 136 6050 two 24 CMP 6 340 43 132 6060 24 CMP 13 320 30 125 6070 30 CMP 0 320 0 124 Pipe is uncovered 6080 None Existing 12 6 6085 None Existing 11 -- 6 6090 24 CMP 3 10 15 5 6095 18 CMP 5 8 10 4 6100 two 48 CMP 7 203 203 84 6105 two 48 CMP 8 200 206 83 6110 None Existing 31 -- 15 6115 24 CMP 4 31 18 15 6120 24 CMP 5 13 20 7 6130 36 x 18 CMP 4 153 24 60 6140 24 CMP 3.5 18 16 9 6150 24 CMP 12 130 30 52 6160 24 CMP 5 123 20 46 6162 None Existing 90 -- 38 6164 None Existing 80 35 6166 None Existing 75 -- 33 6170 18 CMP 5 68 10 30 6172 None Existing 24 -- 12 6180 24 CMP 5.5 12 21 6 6190 30 CMP 10 11 57 6 6200 30 CMP 10 39 45 19 First digit of culvert number corresponds to figure number of drainage map on which it is located. A-3 Existing Culvert Head Contributing Culvert Design Culvert Size Culvert Water Drainage Capacity Capacity Number (inches) Material (ft) Area (acres) (cfs) (cfs) 6220 30 x 48 CMP 4 11 46 6 6240 30 CMP 8 28 40 14 6260 30 x 18 CMP 4 16 15 8 6300 30 CMP 9 ill. 43 46 6305 None Existing 90 -- 38 6310 None Existing 85 36 6315 None Existing 80 34 6320 None Existing 75 -- 33 6330 30 x 18 CMP 6 67 18 30 6335 None Existing 60 -- 27 6340 None Existing 55 25 6345 None Existing 50 -- 23 6350 24 CMP 5 38 20 18 6360 None Existing 30 -- 15 6370 None Existing 27 -- 13 6400 30 CMP 4.5 116 30 47 6410 30 CMP 10 116 45 47 6412 None Existing 100 -- 42 6414 None Existing 95 40 6416 None Existing 90 38 6418 None Existing 25 -- 12 6420 30 x 18 CMP 6 20 18 10 6430 18 CMP 4 70 9 41 6440 30 x 18 CMP 5 66 17 30 6442 None Existing 60 -- 27 6444 None Existing 55 25 6446 None Existing 50 -- 23 6450 18 CMP 5 44 11 21 6452 None Existing 44 -- 21 6454 None Existing 40 19 6456 None Existing 35 18 6458 None Existing 30 15 6460 None Existing 25 12 6470 18 CMP 5 23 11 11 6500 65 x 40 CMP 7 296 65 117 6505 24 CMP 3 7 15 4 6510 30 CMP 4 250 28 100 6515 24 CMP 6 250 22 100 6520 48 CMP 8 250 103 100 6530 one 36 CMP 7 30 one 24 CMP 3.5 233 +16 46 96 6540 18 CMP 6 29 12 14 6550 24 CMP 3.5 29 16 14 6560 48 CMP 10 204 130 w/ 85 thaw wire 6570 None Existing 103 42 6580 None Existing 48 -- 23 6590 24 CMP 5 11 20 6 6600 24 CMP 5 27 20 13 A-4 Existing Culvert Head Contributing Culvert Design Culvert Size Culvert Water Drainage Capacity Capacity Number (inches) Material (ft) Area (acres) (cfs) (cfs) 6610 24 CMP 5 27 20 13 6620 24 CMP 5 30 20 15 6700 None Existing 155 -- 60 6702 None Existing 150 59 6704 None Existing 145 58 6706 None Existing 140 56 6708 None Existing 135 -- 54 6710 36 CMP 7 122 55 w/ 49 thaw wire 6720 two 24 CMP one 14 103 62 42 7000 24 CMP one 5 12 22 20 11 7050 24 CMP 5 33 20 16 7100 24 CMP 5 33 20 16 7150 24 CMP 6 109 22 45 7200 24 CMP 6 109 22 45 7250 24 CMP 4 39 18 19 7300 two 24 CMP one 7.0 193 47 73 one 7.5 7350 24 CMP 6 -- 3 7400 two 24 CMP 4 35 36 17 7450 24 CMP 5 29 20 14 7500 24 CMP 5 79 20 34 7550 24 CMP 6.5 34 22 16 7600 36 CMP 10 83 70 35 7650 24 CMP 6 24 22 11 7700 24 CMP 7.5 57 24 25 7750 24 CMP 5 13 20 6 7800 24 CMP 6 4 22 2 7850 24 CMP -- 54 24 7900 24 CMP 7 28 23 14 7910 24 CMP -- 9 -- 5 7920 24 CMP 9 5 7930 24 CMP -- 9 -- 5 7940 24 CMP 6 26 22 12 7950 24 CMP 7 5 23 3 8000 None Existing -- 12 -- 6 8050 None Existing -- 765 -- 245 8100 48 CMP 9 246 150 102 8125 None Existing -- 230 -- 94 8150 None Existing -- -- -- -- 8200 two 36 CMP one 7 507 117 190 one 8 8250 24 CMP -- -- -- -- 8300 24 CMP 8350 24 CMP 8400 36 CMP 8450 24 CMP 8500 24 CMP A-5 a I I I I I I I I I I I i I I i Appendix B i Drainage System Cost Estimates I I APPENDIX B DRAINAGE SYSTEM COST ESTIMATES This appendix presents an example of the process used to determine necessary drainage system improvements for the design storm. Two subbasins were selected for analysis: the Woodward Canyon drainage and the Svedlund Street drain- age, which can be seen on figure 6 in the main text. Assess- ment of existing culvert capacities was based on data from appendix A. Channel capacities were estimated using data from topographic maps. Channel cross section data were not available. The sequence of hydraulic structures was taken in an upstream to downstream order. The design flow for each hydraulic component was determined-from figure A-1 for the upstream tributary area. Required channel capacities were based on flows for the contributing area'at the downstream end of the reach. Improvements are recommended wherever design flows exceed the capacity of the existing system. The recommended im- provements are the result of a preliminary engineering effort only and do not constitute final design. Costs are planning level estimates based on actual bid costs for the Homer bypass project. Detailed design and cost estimating are necessary prior to implementation of any of the recommended drainage system improvements. B-1 Appendix B Drainage System Cost Estimates Existing Conditions Prop sed Improvements Culverts Channels Culverts Planning Level Costs Sequence of Size Capacity D.A. Slope Capacity Size Hydraulic Structures No. (in.) Type (cfs) (Ac) M (cfs) No. (in.) Type Channels Culverts Channels Total- Woodward Canyon Culvert 6070 1 30 CMP 0 Remove old culvert $ 200 $ 200 Culvert is broken Natural Channel: 320 '-5 deep 100 None 6070-6060, 700' Culvert 6060, 60' 1 24 CMP 30 1 42 CMP 5,200 6,400 Wend section 1,200 Natural Channel: 340 %7 deep 118 None 6060-6050, 700' Culvert 6050, 60' 2 24 CMP 60 2 36 CMP 14,700 15,900 w/headwall 1,200 Natural Channel: 355 1-6 deep 109 6050-6040, 700' NJ Culvert 6040 1 24 CMP 16 Upgrade by Owner Private Driveway Natural Channel: 355 7 deep 118 None 6040-6030, 200' Culvert 6030, 100' 1 3'x2' Conc. 81 1 48 CMP 11,700 12,900 box w/headwall 1,200 Natural Channel: 363 %4 89 Improve capacity $15,000 15,000 6030-6020, 500' to 144 cfs as part of street project Culvert 6020, 60' 1 30 CHP 28 1 58x36 CHP 21,800 24,200 1 50x3l CMP 2,400 v/headwall Natural Channel: 368 @-4 89 Improve capacity 23,500 239500 6020-6010, 800' to 145 cfs as part of street project Culvert 6010 2 65x4O CMP 220 Natural Channel: 370 @,5 100 None 6010-6000, 500' Culvert 6000, 601 1 48 CMP 125 1 54 Cie 11,700 129900 w/headvall 1,200 $111,000 Existing Conditions Proposed Improvements Culverts___ --- Channels Culverts Planning Level Costs Sequence of Size Capacity D.A. Slope Capacity Size Hydraulic Structures No. (in.) Type (cfs) (Ac) M (cfs) No. (in.) Type Channels Culverts Channels Total- Svedlund street Trunk Culvert 6370 None existing 18 CMP $ 2,100 $ 3,300 w/end section 1,200 Natural Channel: 30 IuB 100+ None 6370-6360, 300' Culvert 6360 None existing- 1 18 CMP 2,100 3,300 w/end section 1,200 Channel and Ditch 38 D, -,6 50+ None 6360-6350, 900' Ch, 'x8 100+ Culvert 6350 1 24 CMF 20 Natural Ditch: 67 5-10 70+ None 6350-6330, 2,300' Culvert 6330, 60' 1 30x18 CMP 18 1 24 CMP 3,200 4,400 w/end section 1,200 W Natural Ditch/Channel: ill 1,6 100+ None 6330-6300, 2,100' Culvert 6300 1 30 CMP 43 None $11,000 I I I .1 I I I I I j I I -1 I Appendix C Drainage and Erosion I Control Guidelines i - APPENDIX C DRAINAGE AND EROSION CONTROL GUIDELINES All developments being constructed within the City of Homer shall be protected from drainage problems through the use of proven engineering techniques, as described in these guide- lines. DRAINAGE BASIN AREAS The drainage basin area includes the total land area of the subject site in acres and all upstream tributary watersheds, and may encompass portions of the basin which lie outside the development. Determination of the drainage basin's areal extent should be accomplished by using the city's 5-foot contour interval maps. If part of a basin lies outside the area covered by these maps, a combination of USGS topographic maps and field inspection should be used to determine the extent of the drainage basin. RUNOFF Runoff determination should be made using figure C-1, Runoff Design Curves. HYDRAULIC DESIGN CRITERIA To provide the city with an efficient and uniform drainage system, the following criteria will be used for the hydraulic design of drainage system components, unless specific excep- tion is made by the public works director. Standard Ditch/Trunk Ditch Standard ditches shall be provided in combination with street and road improvements, and as required to upgrade the capacity of the natural drainage system. The standard ditch shall conform to that shown on the typical roadway cross section adopted by the city. Maximum flow velocity allowed in a ditch shall be such that no erosion or scour will take place to the sides or bottom of the ditch during normal flow or design storm flow. Where design flow velocities exceed 6 feet per second, the ditch shall be lined to prevent erosion. Typical lined ditch cross sections are shown in figure C-2. Ditch lining shall consist of a layer of well-graded Anchor Point gravel riprap with a minimum thickness of 4 inches and minimum particle size of 4 inches, or a 3-inch-thick layer of asphalt paving. Linings shall be underlain by a 4-inch layer of 4-inch minus subbase material. Ditch lining shall extend up the sides to the design flow depth. C-1 300- 250. SOIL CONSERVATION SERVICE 200.. TYPE 1A STORM DISTRIBUTION ==4 STEEP SLOPES FROZEN GROUND (RCN = 95) 150 i I I I T I T 1111 ITA 1 1 f I I I fIIIIll I I I I I I I II IIIIfitI I I I I 111 q I I I I IiIIiI11111 1 1 1 1 I I I ITI 11111t1:11 11 it H il" it I I It I ilill I it liiiiiii! 11 1 it i illf] Mil it it 11H ill I I i -4@ i MH 11 1 W hIM ill I I; 1 11 1 ill![ 1 7 itill 11 .7 1 171 1 11; 1. 100- 90 so 70- T-rtt 60--- 50- L) UJI 0 30- I q I I Ipp i iIIII1111 25-- 20-- < ill 1; 1 1 15-- H +4- it It 9- p 1. -.,1 7 6- 5 it 3 10 15 20 25 30 40 50 60 70 80 90 100 150 200 250 300 400 500 DRAINAGE AREA (ACRES) -, @i-77 InRunoff Dpa'ogn Curve C- 2 r-OA@V 17 L-7 4" 'SaC-710@4- ?4N@ED DkTC-@-A r-O AO ft -0 '2\" COMPAr-rF-D SUBBASE 4" 4"+ 4 -5055ASE lj?\C-A@- M T-5 Figure C-2 Typical Lined Ditch Sections C-3 HIGHWAY (H-20) LOADING -CORRUGATED STEEL PIPE, CORRUGATED .02 ALUMINUM PIPE AND CORRUGATED STRUCTURAL PLATE PIPE GENERAL NOTES- I. All material and workmanship shall be in occordrum with PIPE CONDUIT STRUCTURAL PLATE PIPE State of Alaska. Standard Specifications for Highway Construction, latest edition. CORRUGATED STEEL PIPE GAGE TABLE (2W. CORRUGATED STEEL PIPE GAGE TABLE (6* x Z'Co".) 2. The contractor Shall select conduit type meeting height of HEIGHT OF COVER IN FEET D- MIN IN FEET MIN ('ncn-) COVER HEIGHT OF COVER cover criteria shown on the plans or in the special provislons. COVER (Imhall 0510 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 (Imi,n)05 10 15 20 25 30 35 40 45 50 55 60 65 70 75 90 85 90 95 too 12 112 116116116 16 16116 1 16116 16 1 1 !4 110110110 to toItoII nduit type shall be used which exceeds maximum or @ 1 !4 1 :01 1 1: 1 60 12010 to .0 1 to 1 10 1 8 1 a 88 7 7 1 5 1 5 1 3. No 0 16 16 1 16 16 @ 1 1111 72 12110 10 10 to 101to110 10 -07 514 15 12 161 16116 16- 16 1@6 :1 21, 14 q !62 1 @+3 .......... um cover requirements shown In the tables. is 12 G116 16 16 16 16 16 16 16 14 0to 1 0 84 12110 to to to 10110110 to -To- 8 1 81 7 1 7 1 5 1 11 24 12 16116 16116 16 14 12 -12 108a 1 96 121to to to to to101to 10 10 30 12 16116 :6 @;6 16 14 108 24110 10 10 10 101101108-7 4. Only one type of metal or fabrication my be used on any 36 12 14114414 12 108 120 24110 10 10 10 101a1753 single or multiple installation. 42 12 14 14 14 12 108 F-LONG11 UDINAL SPOT ELDED 132 24110 10 to 10a7531 48 12 14 14 14 12 106 @D,* REOUIRED SPOT WELDS 144 241to to 10 10a7531 54 t2 12 12 12 10a @ 1-2 _ '. S' NGLE WELDED 4 A Per It 156 24110 10 10a7531 5. All structural plate pipes shall be placed on a pro-shaped 60 12 10 to IQ to8 142'50@IDOUSLE WELDED 9 168 24 10 1087531 foundation Conforming to the depth of the bottom plates 66 12 10 10 10 ISO 24 ;0 10 1067531 with Clearance for assembling to the adjacent plates LONGITUDINAL RIVETED 192 24 10 10 10a753 RIVETS 204 10a87 72 12 10 10a '@-- @@r53 allowed. 78 12 8 36 94 12 14. 1. @.SINGLE RIVETS 216 36aIaa1 -5-3 LONGITUDINAL BOLTED ED Fo, Coldtt.ols R.ght of Hnly L-, 5% Elongation of Pipo is RMi,M. NGLE RIVET 228 36aF-8-17531 USE 4 - W No. ASTM A325 Son. 240 3677@53 H of A -1-1 A 11 1, 252 361F ina. 5. I.n .1 P- s Reo,@7@od, SUBGRADE 20 12, CORRUGATED STEEL PIPE GAGE TABLE (3"xi") CORRUGATED ALUMINUM PIPE THICXNESS TABLE (9" x 21A") Witichne, Ins Di.. MIN HEIGHT OF COVER IN FEET DMIN HEIGHT OF COVER IN FEET 2' E'astiftit G'onnd (I.-) COVER "@ER 1ZL) "0' D - No, -I P." Di-duH PAY IMITS SIDEFILL (1@nsnj 0510 15 20 21 30 35 40 45 50 55 60 65 70 75 80 85 90 105 115 ..) 0510 15 20 25 30 35 40 45 50 55 60 1. 11=ILL I PAY LIMITS 36 12 1Ic, 16 16116 16116116 16 14 114 1Is 1 12 1 12:' 1:2. 1 @1 1 1.1 1 10 8 72 18 .15 1 151151@15515 .175 '175 .20 .225 25 DT'S* IN TRENCH 14 14114 14114 14 14 1:20 84a n.h 4-2 :2 2 15 15 (5 .15 '15 i7s 2 225 .2511 0 48 2 4_L4 14 12 1 12 1 21 1 1 96-2 _14 t4l 14 14114 14 14 14 12 12 081811 is i15 .15 15 '15 15 175 20 So 12 12 -12 12112 12112 12 (2 12 12 to a -8 24 '15 '15 '15 15 J75 20 225 60 12 10 10 to 10 10 @o210 10 109 24_15 15 15 175 _@O 25 CIRCULAR E,istinq C-nd 12 10W10 10 'a100 132 24 15 15 .175 .20 .225 25 Pont. T%i--. 4 in im- S.arfill .-"..d in V 'A,- 72 12 10 10 to- to 'a110 10 108 144 24 _i5 _L75 A75 20 225 25 to ftnsity swified for AdjAcent nstonitnent 10 10 to 10 to to to to 156 24 175 175 20 225 25 LONGITUDINAL BOLTED 910to to LONGITUDINAL SPOT WELDED .175 1755USE 5h - Is' D, ASTM A!", ""s 2- _20 225 -12- -12-1-LO- REQUIRED SPOT WELDS -LO- 20- 225 25 fl. .1 PAY LIMITS FOR STRUCTURE BACKIFILL 10 to 10 10 oilI I,t &I H,,.y - ,,, 5%.Elongotion of Pips I, Rog,nd -io- -19- -12- FLAO TED -i-O -Lo- -to- -LOL __ NGITUDITL RIV -io- -L0L 1 -12- 1. @GAGE RIVET@ '1 10 to "'IW. ALL 1 14, 16 1% DOUBLE RIVETS It, Cons'-, R'n, 11 Hso, 1----, 5, .i,.d IALL 18, 10, 12 I%eDOUBLE RIVETS --I. of H.nt: SUBGRADE SUBGRADE W D,. ASTM A325 B.", Toy -o-wd 11 -11-1 "Is", 2' E.,,I,,g ...d D _PAY LIMIT FOR E,isninq U"Will Mothn,kil E.11t,19 G,o.nd Is* D to" STRUCTURE EX AVAI, ION CORIRUGATED ALUOINUM PIPE GAGE TABLE (2-A' A Mit") CORRUGATED BANDS Fir D s' DW, MIN EIGHT OF COVER IN FEET CIRCUMFERENTIAL HELICAL IS" 0 10. STEEL 8 ALUMINUM I STEEL 5 ALUMINUM COVER 3D (nKhwj 0 510 15 20 ZS 30 35 .0 45 50 Dim I Sond Sine" -MAX D,-W- B.H."' of ..A-IsTrl" 12 0 161161IsIIS 16 16 1 16 116 11411 DIA. IInd S-] uIr-tInc. 'a to 16116116116 16 14 112 1111 R.- U -I.W. it.- 1) Sodding M.NRk0 24 Is 16116116114 12 $0 11111 of '"o" It E.c S,ddinii to C=f- .1 30 18 1112 V. 1, 205 -3 01 12" Min ond ZD Mo. - - ; 414 12 12 to I-IIII- 36 is -I TYPE 'D' -i-2- 1-6 212212 TYPE "A" TYPE "B" TYPE"C" ROCK OR UNYIELDING MATERIAL 7;F- 1-8 :1 FOUNDATION STABILIZATION .j @.l1:2 54 Is 0:.2 To b. u- -Iottl- di,.,I.d STATE OF ALASKA 60 Is saIa8 b, III. Engi.s., aaIa DEPARTMENT OF MIGHWAYS F,, Co"doi- Rght of Rea, L-, 5% EI.N.I.- of P,, Iknq@i,.d, REVISIONS LONGITUDINAL RIVE ED pfion @0-1 CULVERT PIPE D- :;D@.:iGAGE -1 - -ETS 3/17/72 Chonod qpw. MnAws RF I _- I.GLE RIVETS CNA :2'- [email protected] 1% SIN LT11LE STAL ATIONS MU' L 2- - 36-10,10,12 IV. SINGLE RIVETS Be ... Pips. R--onelool In, A ......I 1-1Y26 A,@nd 42' &0., 1 14, 6 -4 DOUBLE RIVE Is 0 0 b48 D.o 42"&@-LB, 0. -2 [email protected] 001JOL E_RIVF La D Ch,,f Rmd Dnn;- E@9,-os-, Dote C.-'. Figure C-3 14 14 14 08 1'0 I"2 14 14 14 144 '2 12 12 12 1 '2 0100 16. '2 000 1So 2 to to 10 S 8a @24 I F., Cono... Its @20 Tr Tl@ T T : IT F I @LSL _WS ' Inbs no . P. 84 2 0 90 2 0 111 24 96 12 Fo@ ConItlil,- R. 102 24 0 106 24 14 24 0 1 0 24 0 To 2 G E Ir 6' "M:Nw':.- Will HIGHWAY (H-20) LOADING -CORRUGATED STEEL PIPE ARCH, CORRUGATED GENERAL Lllt@ D-03.01 ALUMINUM PIPE ARCH AND CORRUGATED STRUCTURAL PLATE PIPE ARCH 1. All material and worhmanship shall be in accordance with State at At Standard Specifications for Highway PIPE ARCH CONDUIT STRUCTURAL PLATE PIPE ARCH construction"I. edition. CORRUGATED STEEL PIPE ARCHES GAGE TABLE FC@RRUGATED STEEL STRUCTURAL PLATE PIPE ARCHES 2. The contractor shall select conduit type meeting height of (2W' X l/ki"Corr.) GAGE TABLE (6" X 2.. Corr.) cover criteria shown on the pion$ or in the special provisions. P FE MIN MUM COVER MAXIMUM FILL -FPE SIZE-- MINNI- COVER T.o ol P- I MIN F 21 - -CORNER Too of PIP. 1. 2 T- C.- '5. No conduit type shall be used which exceeds maximum of Top f SI,bg,.d. 3AIE 9-,ng P ...... R, RADIUS Top I II,,groo, B--, P minimum cover requirements shown in the tables. GAGE SPANT SE' 18 '6 13 6 - I1. 15 SUWRADL Is 'IS 12 is 10 15 2D Z, -1 4. Only one type of metal W fabrication My be used an any 54_ Is IS 10 7 -11 5@ - 7" :0 ---- --- single or multiple installation. 2984-4 1 8 -L6 0 1 E.,sting G-d 36 225 is 14 9 !F- 9@ 6'- 1.. 11 24 0- to -18 -- - - i@@ -. --I---- -L /L!I !DEil L L S. Ali structural plate pipes shall be placed an a pro - shaped 43 27 14 7 124 10 9 Is, 16-11' T. 3.16 7 10 7 o,;t, foundation clartforming to the depth of the bottom plates 50 - 12 12' - 10" -4 18 24 10 6 with clearanco for assembling to the adjacent plates 58H1 18 10 w 65 41z 8----S 'a -_T ----- ---- 18 24 5 14'- " 8'-9. allowed. 12 a. S io _L3@_- 3" 9: - 4" 31 24 10 13 E.,,I.ng G-7- % 79 490 Is 14 - 2" 9 -,0" 31-- 24 io2 85 - 15'- 4" Id- 4" 31 24 10 11 S.d1ifl Compa-d,n 6" lay- --I 161 @ 3m 16-10" 31W10 1] ai-l, -.,fi.d to, ad,al ..b..k-I 17'- 2" 14' 3,68 10 PAY LIMITS FOR STRUCTURE BACKFILL FC-ORR-UGATED -STEEL PI-PE A-RCHES -GAGE TABLE I,--,o- 31 36a 9 (3" X I' Corr.) ?31 368 9 CORNER MINIA 31 P.PE SIZE IUM `6@EFF MAXIMUM FILL 2o - 7' 13'- 2" 361 7 %, .1 P,,. a -7 lo, I To S AN I RISE RADIUS Sa'. E,W,kma I I-I bofw. GAGE 1-IiIs Pr ...... 0 I-h (F..0 CORRUGATED ALUMINUM STRUCTURA PLATE PIPE ARCHES 2. 43 27 ?1 is 14 12 50 _-il- -9- 4---- 12 t2 GAGE TABLE WX 2 V. Corr.) 58 --m- cv. IS- 10 12 PIPE SIZE MINIMUM COVER MIN MAXIMUM FILL C-M '5 Cz IS a CORNER 72 4o .3 % is 10 12 RADIUS TT ,,I 1"I* PLATE F. 2 T- C.- SPAN RISE 0,.f 'Uail'.. T. .... (-..) I 'C-) C'.'. 73 55 18 'a .0 15 Foal) -61 59 Is Is a 15 6 - I I 5@ - 4" 28.8 is 0,15 15 Ell- 63 --t-S is to 14 6@ -W 5@ - 9" 28 aaOls 15 95 67 Is Is 10 12 6 - 0" G- 2" Is 015 15 R--1 U-.10bil -e-1 le, 205 (1) : 10-3 L 71 18 24 10 11 91-0. G-8" 28 824 -215 - ------- i5 ------ E.@ B.od,.g -.1.01 .. C00.1. 1'#1,*__@4 !! @05 Id - 0" 7,-1" 28,18 24N 5 1, 205- 301 51 1'. _ Z_ 6` 26 a24_ OAT5 TYPE 'A!I TYPE "B" !2. 1 1 0 12'- 2' 28.8 24 0175 FOUNDAT ION 'STAB IL IZAT ION IS- 1" 24 0,175 To W .$ad .1 Instabl. dir.ct.d by 14'- 3' 24 OJ75 CORRUGATED ALUMINUM PIPE ARCHES GAGE TABLE -15--3 24 0200 16.-0. 24 0.200 (2,/", X ./." Corr.) 24 0,225 fTtPE SIZE IMUM COVER MAXIMUM FILL CORNER Hl F" SPAN J"@FSE RADIUS lop of Pi" M 2 To,% C Z", N@ Tag, of Subgraeo, GAGE 8-ng P-- 5N..N.I Pip. A,.h SpaN SUBGRADE SUBGRADE @J (1-0 0.0.0 _ (F..I) 1814 8 IS IS '3 18 is 14 25 16 AV, is 16- 29 18 414 Is 14 361225--FB- 1-4 PIPE-ARCH 1431Z7 _1'_A is 12 15013116 Is 10 15813617_ 'a a 'a a So,,, Iltdding Maltallot Vil P., 1, at @.... .. V Pipa@l 12"MI, OW 3/4D At " STATE OF ALASKA TYPE 'C" TYPE V OEPARTHENT OF HIGHWAYS ROCK OR UNYIELDING MATERIAL REVISIONS CULVERT PIPE MULTIPLE INSTALLATIONS RCH --@P. -- _M-- ce 6-- Pjges- L. 24' JR-1--ad 11 A,p .... I App,mad: oa, a c,., V, S- of e ch or 3. -pip -a- -cheier Is less I . @ C-1 Road 8:1=4 25' A 2 9 [7 I F 4 4== :::1'0"12#=24 2,88 is Figure C-3 Cont. The minimum sideslope shall be 1:1. The invert width shall be determined using the Manning's equation. Roadside ditches shall be excavated at least 6 inches below the subgrade. All-ditches that are located above sanitary sewer routes shall be paved with impervious lining. Sideslopes of ditches shall be seeded from the top of the bank down to normal channel flow depth to help in preventing erosion. Species being seeded will be subject to approval by the public works director. Culverts Cross culverts may be reinforced concrete box type, corru- gated metal pipe, reinforced concrete pipe, or corrugated metal pipe arch. Culverts under driveway entrances shall be either corrugated metal pipe or reinforced concrete pipe. Culverts may be designed by using Federal Highway Adminis- tration Engineering Circular No. 5, "Hydraulic Charts for the Selection of Highway Culverts." Minimum inside diameter of culverts shall be 18 inches for driveways and 24 inches for crossing the trunk drainageways. Culverts shall be designed with adherence to depth of cover requirements for the size and type of pipe being used. See figure C-3. Design head of water above the upstream invert of the culvert shall not exceed three (3) culvert diameters. Culvert thaw wires shall be provided, as required by the public works director, to control icing development in the culverts. Installation shall be in accordance with standard specifications, and as shown in figure C-4. A painted 2-inch by 4-inch post, or approved equivalent, shall be installed at each end of all cross culverts and at the upstream end of all driveway culverts to serve as a main- tenance marker. End sections shall be provided on the upstream end of all cross culverts. Concrete headwalls shall be provided on all double- and multiple-barrel installations and on culverts 48 inches and larger. End section and headwall details are shown in figures C-5 and C-6, respectively. Trashracks and metal beam guardrails may be required where necessary. Where a standard ditch discharges into a trunk ditch, an energy dissipator of the type shown in figure C-7 shall be provided for protection against erosion. C-6 Closed Conduit Systems Pipe material used shall be either cast-in-place or precast reinforced concrete pipe or corrugated metal pipe of the proper class or grade. Storm drains shall be sized using the manning's formula. Hydraulic nomographs may be used. Minimum allowable flow velocity shall be 2.5 feet per second. Hydraulic gradient shall not be higher than 0.5 foot below the elevations of inlet grates and manhole covers. Manholes shall be located at major junctions, changes in vertical or horizontal alignment, and changes in pipe size or shape. Spacing of manholes shall be nearly equal wherever possible and shall not exceed 400 feet for pipes 48 inches or less in diameter. Inlets shall be spaced so that a single inlet does not inter- cept drainage from more than about 1,200 feet or curb line or so that gutter flows do not exceed gutter capacity. Where an inlet is placed in an unpaved area or on a gravel street, an asphalt and concrete pad shall be placed around the inlet. When the outfall is from a pipe to a natural, unprotected channel, an energy dissipator of an approved type shall be provided to protect against erosion. If the natural channel is subject to flooding, headwalls, gabions, or other suit- able means of protecting the outfall from damage shall be provided. The outfall invert of a drainage system should be a minimum of 2 feet above the water surface of the natural drainage feature in order to provide storage for icing accumulations. Ail outfalls shall have icing control devices placed in them in accordance with standard specifications. SEDIMENT CONTROL DURING CONSTRUCTION Development being constructed on any land area should include control measures to reduce erosion and sedimentation. Prin- ciples of erosion and sediment control include the following: 0 Plan the development to fit the particular topog- raphy, soils, waterways, and natural vegetation at a site. Where possible, steep slopes should be left undistrubed. Natural vegetation should be retained and protected wherever feasible. Q Expose the smallest practical area of land for the shortest possible time. Plan the phases of develop- ment so that only the areas that are actively being C-7 Section A-A Section B-B Piol ha.W Section C-C Section D-D D-13.01 NOTES cities to be itcoled P"- PIP. C.Pie to be iocal.d . Pop- The 6' @ 6" MOM Post to N iocated not civem, than 10' non, the Oft, of his .I . its d"lld b, the anpoiser Set- 2@ A.,:ork to be done ii, -donce wish the Nat-al Elitch,ital th e to 5" able Ca and const-tion asectice of the Rincl Electrification Adit-afthei. inam belo, dOch botton, NO AN hop. nd hisol- Hein cab* W be appno,, 6' 6*- --4 fin allaching abi. .0 alb- bottom of dfth The sat" how inster 1* be 1,-hd and -11"d 1, oll- DETAIL OF HEAT CABLE WHERE BURIED pipe to be gohmmiatid. LOCATION OF HEAT CABLE UPSTREAM UNDERGROUND SERVICE CABLE A" @Warinti '& WbblN --, 1. coinitlele the sell - sholl AND DOWNSTREAM OF CULVERT he -whepas other the contract .0 .1 net be pommired t. ppyinted. 5The hwW ischoi, " be pioc" md. 02' fectinKlind tiblinnuied pipe thro,gle the culve,t . The IW tiol-nized pipe shall him, bass ood Pines, c,bW be field forsted 1. the cooll.. of the illimilimi ittlemes c cib-, Lock it, pothock -PP east tiatead apeftemme end donsittresse the diplainto As A .,-Ifi*d As the tiltiers. Pd. 6See plAn Keeps NK Pests" .meeges. -sher & lingth of .0bles. ach nt,i 2;:Z@ 2- 6.6'.9'esn' fired" post. dess par tool at fisibled sechines. Pest orA profile ses thonn is FIZ wlwl M) two it- '6 b- coppe, '"wel in". Q,.,d 'enwasit 7Th. trarshents, so be fenithed One sentient bit 0"Nse uldiess a-- nolied As the plarst s"weed t-ve Pw lo.pe, A.1 mthirod .w cold lead. - Z,-VZ' 'U' Clasm, 6' Sleel 1. be &,N if 'w seed C oweel. diess, - is iftil". 9--1 only 2V w. 4F " -m itn" T STEEL RO; ISTAND P= USE cable to posmir TYPICAL PIPE MANGER DETAILS -V4" woswl rod. C) METER POST DETAIL I 00 t P- pole ..d is., d.1.1 120/240 Von or 240/490 V*ft -ime Type USE coble to Pose, ce. post C PO ridarg-0 r*. cable PON us plens fo, cable for C. mr. .4 -AK. v- c@- 77 I connection see ol... to, length I-- of cold Wed I No C -PAt sl@ Ild to bless, iv., conom- 14-ighs pes unwir C- z ii. Valt a, 480 so" cable vothotte 'zo nin Pew "bew @-fkraricli bleak- See phone lot as ame 4-14 Use 2 pales 81) olit az4post fw lao PLAN VIEW WRING DIAGRAM so Pbm Idpw POLE RISER DETAIL STATE OF ALASKA 30. mn -0 osposunern of bill new 4'C-C 4ic-c CULVERT THAW W,, too G" of 9.1-lied -DoWf __-_ m-ldi _.-dis- WIRE INSTALLATION r ,ma'sain " donin." cost Not! See Section A'A PROFILE VIEW -s- abw 77, c- of hins" L* C--r 64 c' """N" Figure C-4 O-Y E., D 14.11 4 -.1 GENERAL NOTES: 6 1. The heated section of the them, unne shell be stainless stesil dwollhad. mifwal Insulated. SECTION THRU CULVERT 2. The cold load stall be of the tWe and Bass recommended by the incin- I LOW FILL I ufachwer of the heated section bwq supplied or as 0 an the Plorm. RECEPTACLE DETAIL 0 the Wad i5 not the nald encosed tm. it shot be Inslolled In I-W TO BE SUPPLIED BY OTHERS A& metal conduit. R- Sm plan stmet for opemd" voliftes, As ft and Wqffi of cables, dm pv IS. tot of heated sections. s@ R@. 4-, ;7 P, alm, SECTION THRU CULVERT END VIEW (HIGH FILL) ."r pb. 4-T-I o c TYPICAL MANGER DETAIL RE a- 414 1-1 M-n I-KI 4,41 -w -P.--dd 1. AW-I T,: STATE OF ALASKA DEFARTMENT OF HI HWAYS GROUNDING AND FA NG REMOTE TMW WIRE DETAIL INSTALLATION TYPICAL PLAN c- - A--L Figure CA Cont. E. --'- 1. "1 Itpe eed ID-06.10 I MINIMUM DIMIENSIONS ROUND PIPE Pip' 1)E P", "I I G@. I.' D-_ I"h.. Di- A a C G-A '.' 1 .8 _77- 4 L - .. -I.- I. 1'@H _ L @T IISkill Apwo., Pipe D- - 314" 4'* .6 21" Me'.1" I ?"Tol 2"*T.1 12 T. SIQD* _78@ 9 6. 2 r 24- W1 PC 2 1/2 e 5o" 36" "1 060 IS 6" 247 9 1/2" 2 V2" 3d` 72" 48" 12" 3. 20@ W6or 15" 0.060 161a6 26" 30- 40- 1 PC 2 V At- 3. 3-6 15" 3 3/8" 55" 97" 72" is" 0.060 16 8. '0.. G" 31* 36" 46" 1 PC. 2 1/2 go" a. 4e 7 21' 0060 16912" 6. 36, 42" 52" D 48" 24 84" 1 PC 2 1/2 9" -------- 2e 0075 ifi to" 13" 6. 41* 4e 56" 1 PC 2 V2 12 54' 27 411, 11 99" 82" PIP. 8.8 30' 0 Or5 14 Iz S*a 51, 60- To- ( P'. 2112 B 36. 0.105 14WW9!* Go" 72" 94' 2 PC2V2 a 42" 0,105 12 66" 22* it* 69" a4" 106' 2 PC2V2 48' 0.105 12 18" 27' 12" 70' So" 112" 2 PC. 2 V4 54" 0.105 12 19' 30-1 12184* 102' 122' 2 P..2V4 L At- AWI 12 IS 33' 12 87' Ile, 34' 3 PC21/4 134- f2 Is. 36. :2 87' 120" l4f 3 PC 2] 12 IS. 972 67* 126' 146" 3 P.. A Jato PRECAST CONCRETE 12 _.!8j 21 12 87- 132' 152'3PC1114 P END SECTION 12 10" 1 45" 12 87' 3,m 11W3PC PLAN RitIld Need Pipe Alch I" ift 12 gold bold lith 11widold PIPE - ARCH 6'.@2" bold boll IN It @ be immid io liw of thloodod rod m pipts C,totf WC11 P,"-A,ch .Am elutiliv. Dilemsto, Thickeems. fe, DIMENSION 11 CHES IlIChit. I. Gd, Pip, - CwNCI. S.- I.A8 SIN, TIN.1'.11 1 1 1 L . J'W T.T F101 A S Meew TIN! le e T.1 slop. to" it" 0@060 16 r. IN. 6. 19* 30' 40' 1 IP. 12172 12" 22" 13, 0,060 16 7. 10`6 23' 36, 4e I I Pc. 1 2 V2 P'. @Rftnf,,Cad Ed,e 25, 06, 0060 IS ar 12' Ir 219" 42' _W 14 PC 12 L12* 0 RwI ft1d., Boo., Ri..I.d IS, 6.075 16 S' 14' 111 32" 48, 58, 1 PC 21/2 T ..d.d R.d Collect., L.g T- Rood 6. 36" 22' 0075 141to' 16, se 60b 70" 1 PC. 2 V2 EN Stocliw, EN S.cli.. Em Sachiii, 43' 27* 12' is" e W 75" 05" 1 PC. 21/2 0.105 141 GwIdlized Metal m 50* 31, 0.105 12 13" 21' 11' 511 85' 103' 1 P., 21,2 a 90* 114" 2 P. 21/2 IS. Alwe AN.V T.@ Fw 12" 111. 24" Rwild PIP, F. 30"S 36"IRPI"d Pwk F., 42", 1 W RoIld PiPe .4 r -.1 36* 0.105 12 to* 26 12' I '. _ P. E.Iw- t% All.l., C.,.gCl-. wd 18'. 11" 111 36 65'. 40" thl. W.54"PiPo A,ch --- whe"I Rwpi P_ @'h with ..IN Allidet, Citt"golth Am Oj 105 12 go. "' 12, 70, 102, 11.2 PC.2 L 7.90w. All H-CII, C-.Wftd Pips wid 1 135 Pi" Ati 44" C_@2 :1:8@: 33, le 77' 114' 144 1 3ft. 21/4 44' 0.135 12 IN* it" LoNe- A DESIGN A _!f 09135 12 10" 39" 12' W IJWIJ70't3 P, 12114 1 ELEVATION Genwal metee: Eld secle. - III " - eleedd de Me vilever, Rowid Pips lim, he Ised Mi wepw hiselat- 2, TeN pkft eel be loweeted QrJY tefteek ploeleftid 1. . ft Pk- "N"'. lopervid. the F,111 A No plarke .-- khmil be ponchad eith hidle' REVISIONS le .00 thile . Up f ked, WIN fitaftled thok 3/8 IN Slope -.d - cied withe old bell Afi-A, I" W,imm L. Afle, Etivelew, ft wid -ficet. 6n Rtilf...d Edge 3. Gwiwigei, Need III AIwe-.p,A,1.d, E.d Simc- t @Wobd SM, PsPe lld, m Ieted ii Wood Skilit OF ALASKA Pi" 4, All 3 plec. bmete "I le- 12 DE STATE L... IN, 30`@Dkwi@! 9wp C wwwhs whom ;::rwr- PARTMENT OF INGHWAYS O.w 30 oi_ I;, W, eewe ehich we to be tigh"y Wind by 3/0, silwift, Gwe Metal Pipe -------- ------- SIftd A, W liked 8 gal-litm! meas w will, Gol-moid Now It 12' Eepteld. LIN AlItl- To; P-.,.E: END SECTIONS AN., Pa" whel Req,i,,d L T SECTION AmA DESIGN Aw,lilil MI Eld Sectiol CiellieCted T, Net" Stelik PIP' CAa _ELEVATION Lo.A Pip. Aic. JC.IEF ROAD DESIGN ENGINE R COMMISSIONER OF NIG"WAYS Figure C-5 m I'm M MAN smAm'Im Mw MMMMM H -11 Ir-- 10 D-30.10 NOTE F,, d-0--, 'X a- 'Y' .d 8-1 8". S.. C.1-1 a ... 1. Pip a S 1, y; I f I -T--j _7 _l_r ri HOOK BOLT I T_@ r 3*111... . 11 -4- -4 0 -1, --\I - 12" %Sar 24 24"r T- -T -4- '4 Bi, 12" r -+ I L D -4 r T A- 4 1 2"14' 80,010d Kayway 12* T L -1 IL I L -i--- Ser 12' a Is a., 12' *AD., 5L 2R_ @t\ @Wh- H ..axid. '.. E Dia 90, bate Wi,ro,u, to 12'. w E ELEVATION SECTION 9-9 ELEVATION SECTION A-A HEADWALL U HOOK BOLT HEADWALL I GENERAL NOTES: 1. Class W Concrete Shall be used on all hoodivalliI. Z@ All exposed concrete carriers shall be chamfsrsd C -k IPW 3. If unsuitable foundation Material is Itruccumforod, it CORRUGATED METAL PIPE - USE HEAD*ALL 11 %@Ld CORRUGATED METAL PIPE ARCH - USE HEADWALL It No shall be removed and backfilled With suitable DIA. H B D I EIft SPAN RISE WH a D E to lot as directed by the anginser. I! 1;:S, V-1. -2.10 is' It. e-6" 3! - It' I' - 5 (y- V e@lo' 1.0 motor --Le -9. V-11. V-4'13 22" 13* - _n@@ - 4 - I" V-11, 1. 1 4. Furnishing and installing hook bolts in place shall Ito 0 7M 1'-** 0`- 11' 3@-5' 1,5 2e 7'- Cr 4!- 4" I@ - _1. y- 1, 1 6 2 Z24 _16" 1 @Qr a-er 9-Or I1_O` 9-81 2 1 29, -4-6. Or - )CP S-e1 3 incidental to cost low Contra%. 36" 12'- 0 6,- or 2'- e l'- 2' 4'- 1* 3.5 or - 0. 4'- IV I, -a. 0'- 11" 3'- 4'1. 5. Hook bolts and nuts shall be gaivanizGd. 4@-5- 4.1 43- 2?' 91- C, 6- 1' 1.- 0. V_-S, 1.6 1. !V-lo"Ia 6. Headwalle for Ghosted culverts to be parallel to 48' Is'- 0* 1`-0' 2'-G' 4N A'-.' 5.5 SO" 51, V- 0" 5!- 7' 2'- 1' 1- _4 4 2'- 11' -6 5-1 .7 507 - _O" S`- 0' 2'- 3' 1'- 4-f2 !01 I_L read CG"t*rll*G. Dimensions for openings In head- 4@' e- j _j lf 65 1; 4- - 27*131 1L I I T -1'- -1" walls for skerrod culverts require special design 1@ 14 7. All material and Workmanship shall be in accord- once with State of Alaska, Standard Specifications NEADWALL I for Highway Construction. STRUCTURAL PLATE PIPE - USE HEADWALL I C@ Yd STRUCTURAL PLATE PIPE ARCH - USE HEADIVALL I 111 0. Relitforcomwint shall be placed 2' clear from sur- DIA, %7 H 6 DI E SPANIRISE I VH e 01 Eink PIP. S-in, Pi. S.... + Go. 9,-0, f-C` e-e (Y-9' 20- 1. 4 W- 1'14* - 7' 1Id- 0** to" a'- It* V - 5'12.91 two of concrete unlaos othOrwItIc noted. G* U-10, V-21- t+o 6 - 4" 4'- S" 16- 4*_ 51-01 11 - 1101 (a- I S-5 5.0 0 72" 11'- 0' 4`@G` I.-a. O`_IO` V_ 2* 1.9 e - 9" V - I I- Hr- 9. 5-0. 1- - Iol W- it" 3 0 1 1 1 1 9. Reinforcement stool shall t* Of intermediate OrGdO. 70' 12'- 0' 4'- G' 1'-a' (Y-Hr 3V - 2, 2.1 7'- 0" 5- 1" 0" I-r, r -r 7 -T 10. 14ultiplo, Pipe or Pips Arch, Installation SpecirQ P7L- 0" 1- 0' 1' - Icf 0'- 11"1 3- 3'3 e-10' S'- 2'12+2 !1" V - 3* 1?,- 3, 5@- c' I' - lo" 0'- it,I S-5 W 13' OF IV-6' - a.- 0' - It*I S - a" 3.1 So- Iv - 0. 5-0. r -,0- jl@ 3,-5.2 aw W-5, 17, - 8* 5- 0" r - le r-T- nimum Space Between Plpoo So. IS'-O' w - 0* I'-ICr 0'- 11' 3'- 5- 2.9 5. 7* 4 - 0' 51-0" 1-10, o`- it" S-5, 3.2 F, Di a' S kil is - 3, 5@ - 0' __ ____ - __ -- - -+4.1 '@ - 4PO" 24' 102- ls@ - w 5-0- 1.-10, O@- Ll@_ V-5, 3 0 8, - z5,-9, 1w d- it' V-5, 3.3 1. V- 6' 2*-0' V- 0' V-8, 3 5 if- 7' 1 -Ir- -6* 5- 0' 1'- 10" 0'- It- V-5- 40' 8 Over I/j DID. or Spon of Pipe or Pipe Arch. !OS" !T'- 0' 'd 6* 3.3 L L + 7 7 1 1 it 14, r_G* 51-61 V-01 11 - O@ 3'- S".I 6-W 6,- 1* '9@ !V - C, 1-10 or - 11 V-5 0; -120* 4' W-3* 11 4' 5' - 0" 1'- 10* - 11' S - 5" or 3!- Of, whichaver is lose. - Is- 0' i@ 6'_ 2'- 0* r -1Y 3'- 8* @3 i -1-4 126' W-0, 5.-6. 2'- 0' 1'-0' N - a" 3.0 9.-6. 6- 5* vq@ @6 S' - 0" e - to" a! - it" 3.-S. HEADWALL 19 V-0, _6 W Y-8' 4. 2 91- 9' -7'_1 1'- 10" Of- I ' 3-5* 3 5 138* 21'-2L V@ 6w 24@0` I` -o" S-S" 4 m 4 ICY - 3' 6- 9* 2C`_7_9!_Ve, to. Or - It" S-5*13 5 144! !L-V ?*- 11-0. 4 6 to - 8' V -Ir _V - 0* V - a" V-S, 4 1 MULTIPLE INSTALLATION STATE 0 ALASKA _V:Lk' 2@ _L@07_ _47 6"_ __g@ - 0' 1- 0' 9 - a" 4 2 DEPARTME HIT OF HIGHWAYS O__ --r- a' 2'- 3'- 8'_ 4 9 1 V - 5@. 7,e 22'@ 5*_ S'- 6@ 0-_ 3 162 25-0 6-0 62'_ -2. A!- 1'6 1 !L -_!L --L- 1" 2V-_7" V - 6'_ 2@ - 0' r- 0* S @S`4 3 160' 26'- Or 6- 6:, 2.- V-3* W-5' 6-5 11'- 10' 7'- 7. 22'_ IOr 1- 6* 2'- 0* '1_0. 3.-a.4 4 REVISION$ 174, 26i! w 6,-6- V-6, r __ 7--V@23 --4' - 1 2@- 0* f - O'_ _Y- a" 4 4 6-6' 6' It- 6" i-ir 23!-6" 5-6" 1'- D' 3'- 8* 4.4 HEADWALLS _12@ ir- 1* 123!- 6, S!! 0 -V-5@ 12f Iz-.Cr a, - 4" 123-11ffi@- 6;f @-O: 10" 3-61' 4 .6 4 1., APP-1 byl@ AV-6@ "o APPROVED ,Y_ 5"18_ 24 5" 4 6 3' 91=1111/ I IGHWAYS DATE 1 Chief Rwd U-In E.@-_-- D- SOLT, 0100. L Figure C-6 Slope as Staked 12" 3' Sew Flow Line of Crook Hond-Loid Rock Embankment 61 STORM SEWER OUTLET DETAIL 0r P pe Figure C-7 Storm Sewer Outlet C-12 Energy Dissipator developed are exposed. Ground cover should be replaced as soon as practical in the development. Minimize grading of large or critical areas during the season of maximum erosion potential (October through March). 0 Apply soil erosion control practices to prevent excessive sediment from being produced. Keep soil covered as much as possible with temporary or perma- nent vegetation or with various mulch materials. Where possible, divert surface runoff away from exposed soils. 0 Apply sediment control practices to remove sediment from runoff waters to prevent off-site damage. Generally, sediment can be retained by two methods: filtering runoff as it flows through an area or impounding the sediment-laden runoff for a period of time so that the soi I particles settle out. Implement a thorough maintenance and followup operation. Make periodic checks to ensure that all erosion and sediment control practices are working effectively. The above principles should be integrated into a system of temporary and permanent vegetative and structural measuresi, along with management techniques to develop a plan for ero- sion and sediment control. The Soil Conservation Service publication, "Standards and Specifications for Soil Erosion and Sediment Control in Developing Areas," contains design guidelines for the application of standard erosion and sedi- ment control measures. The following publications referred to in the guidelines are to be used by all developers in adhering to the drainage system design procedures stated herein. 0 U.S. Department of Transportation, Federal Highway Administration, Hydraulic Engineering Circular No. 5, "Hydraulic Charts for the Selection of High- way Culverts," December 1965. This publication is for sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. (9 State of Alaska, Department of Highways, Standard Specifications for Highway Construction 1972, Supple- mental Specifications 1975 and Standard Plans. These are available for purchase through the Alaska Department of Highways, Box 1467, Juneau, Alaska 99801. C-13 U.S. Department of Agriculture, Soil Conservation Service, Standards and Specifications for Soil Erosion and Sedimentation Control in Developing Areas, July 1975. This document is available through the Anchorage office of the Soil Conserva- tion Service. C-14 I I I I I I I - I I I I I I I I I I Appendix D I Draft Drainage Ordinance I Appendix D DRAFT DRAINAGE ORDINANCE Adapted from: Washington State Chapter American Public Works Association, September 1978 Model Comprehensive Drainage Ordinance In September 1978 the Washington State Chapter of the American Public Works Association developed a draft model comprehen- sive drainage ordinance. This model ordinance contains several parts which are applicable to Homer with regard to the content and structure of a drainage control ordinance. Following is the model ordinance, as amended to suit the needs of the City of Homer. Further revisions to the drainage ordinance may be required to ensure that it meets the needs of Homer and is acceptable to city officials and legal counsel. D-1 CONTENTS section 1 Title and Authority Section 2 Need Section 3 Purpose Section 4 Definitions Section 5 Description of Trunk Drainage System Section 6 Statement of Authority Section 7 Applicability Section 8 Applicability to Governmental Entities Section 9 Contents of Drainage Plan Section 10 Standards Section 11 Fees and Charges Section 12 Review and Approval of the Plan Section 13 Variances Section 14 Appeals Section 15 Easements Section 16 Bonds and Liability Insurance Required Section 17 Inspection and Acceptance Section 18 Enforcement and Penalties Section 19 Maintenance Section 20 City Assumption of Maintenance Section 21 Retroactivity Relating to City Maintenance of Drainage Facilities Section 22 Expiration/Renewal Section 23 Effective Date Section 24 Severability D-2 ORDINANCE NO. AN ORDINANCE establishing a new chapter in the City code requiring a storm water drainage plan to be submitted in conjunction with certain permits, specifying the contents thereof, regulating access to the storm water facility of the City, providing for enforcement thereof and penalties, requiring surety and cash bonds, and authorizing City assump- tion of storm water drainage facilities. WHEREAS, the City Council finds that an expanding population and increased development of land has led to drainage and storm water runoff problems within the City, and to water quality degradation, that uncontrolled water runoff on streets and highways poses a safety hazard to both lives and property, and finally that continuation of present drainage planning and practices, to the extent that they exist, will lead to erosion, property damage, and endanger the health and safety of the inhabitants of the City, and WHEREAS, the City Council finds that future such problems and dangers will be reduced and avoided if developers, both private and public, provide for storm water drainage of their respective properties, NOW, THEREFORE, THE CITY COUNCIL of Homer DOES ORDAIN as follows: SECTION 1. TITLE AND AUTHORITY There is hereby created a new chapter in the City Code, Chapter with the short title, "Drainage Management Ordinance." This ordinance may be cited by its short title. D-3 SECTION 2. NEED The City Council finds that this chapter is necessary in order to minimize water quality degradation and prevent the sedimentation of the natural creeks, and city drainage- ways; to protect property owners adjacent to developing land from increased runoff and erosion of abutting property; to promote sound*development policies which respect and pre- serve the City's watercourses; to ensure the safety of city roads and rights-of-way; to decrease drainage-related damage to public and private property; and to protect the health, safety and welfare of the inhabitants of the City. SECTION 3. PURPOSE The purpose of the rules and regulations described herein is to guide and advise all who desire to make use of or alter the city drainage system. The rul es and regulations establish the minimum level of compliance which must be met to permit a property to drain to the city drainage system. The concept of the trunk drainage system is to make maximum use of the natural drainage system of streams, lakes, and wetlands and to allow the continued functioning of the natural hydrologic cycle. To accomplish this, the drainage system will only accept for service the drainage from those properties which meet discharge requirements for storm water runoff as de- scribed herein. No building permit will be issued or subdivision and road construction approved by the City until a drainage plan has been approved by the City. D-4 SECTION 4. DEFINITIONS (1) Applicant: The person making application for a drainage use permit. (2) City: Refers to City of Homer. (3) Drainage Management Plan: An analysis of each drainage basin which compares the capabilities and needs for runoff accommodation due to various combinations of develop- ment, land use, structural and nonstructural management alternatives. The plan recommends the form, location, and extent of drainage control measures which optimally would meet the City's community objectives as well as identifying the institutional and funding requirements for plan imple- mentation. The most recent version of the City's Drainage Management Plan is included in a report dated June 1979. (4) Runoff Design Curveg The design curve developed by the Public Works Department to relate the peak rate of runoff to drainage area. (5) Developer: The individual(s) or corporation(s) applying for the permit required by Section 7 of this chapter. (6) Developmental Coverageg All developed surface areas within the subject property including, but not limited to, rooftops, driveways, carports, accessory buildings, and parking areas. During construction developmental coverage shall include the above in addition to the full extent of any alteration of previously occurring soils, slope, or vegeta- tion due to grading, temporary storage, access areas, or any other short-term causes. D-5 (7) Drainage Area: The subject property together with the watershed (acreage) contributing water runoff to and receiving water runoff from the subject property. (8) Drainage Basin: Those lands draining to a common watercourse or outlet including the headwaters of said watercourse. (9) Drainage Facilities: Any facilities installed or constructed in conjunction with a drainage plan for the purpose of conveying runoff. (10) Drainage Plan: A plan for collection, transport, and discharge of water within the subject property. (11) Drainage System: The system of conveying storm water runoff as described in Exhibit 1 and as may be further defined by the drainage management plan. (12) Flood Plain: The low lying lands adjacent to watercourses onto which excessive water flows during periods of prolonged and intense precipitation. The flood plain for a particular watercourse is a geographic area flooded by a storm of specified intensity. The flood plain usually includes all adjacent wetlands and may include other lands not normally classified as wetlands. (13) Natural Location: The location of those channels, swales, and other non-manmade conveyance systems as defined by the first documented topographic contours existing for the subject property from either maps or photographs. (14) Peak Dischar2e: The maximum water runoff rate in cubic feet per second (cfs) determined from the runoff design curve. D-6 (15) Project: Any construction, grading, clearing, covering, or other act which directly involves the water- courses, wetlands, lakes, or exposed ground surfaces. (16) Project Area: The actual ground area affected by the project. The project area may be equal to or less than the project site. (17) Project Site: The lot or lots upon which a project is to be undertaken. (18) Receiving Bodies of Water: Creeks, streams, lakes, and other bodies of water to which waters are directed, whether naturally, in manmade ditches, or closed conduit systems. (19) Sedimentation: Disposition of erosional debris- soil sediment displaced by erosion and transported by water from a high elevation to an area of lower gradient where sediments are deposited as a result of slack water. (20) Subject Propertyg The tract of land which is the subject of the permit or approval action, as defined by the full legal description of all parcels involved in the pro- posed development. (21) Trunk Drainage Systemz The trunk drainage system is that portion of the drainage system of the City which receives waters from an adjacent land area. The trunk drainage system may consist of watercourses or manmade facilities such as pipes, ditches, and culverts. The trunk drainage system is the primary conveyance system for drain- age waters and is illustrated in figures 5, 6, 7, and 8 of the drainage management plan. D-7 (22) Watercourse: The course or route followed by waters draining from the land generally formed by nature and consisting of a channel with a bed, banks, sides, and asso- ciated wetlands and headwaters. A watercourse shall receive surface and subsurface drainage waters and shall flow with some regularity but not necessarily continuously, naturally, and normally, in draining from higher to lower lands. The watercourse shall terminate at the point of discharge into a larger receiving body such as a lake. Watercourses shall include, without limitation, sloughs, streams, creeks, and wetlands. (23) Wetlands: Those lands adjacent to watercourses or isolated therefrom which may normally or periodically be inundated by the waters from the watercourse or the drainage waters from the drainage basin in which it was located. These include swamps, bogs, sinks, marshes, and lakes, all of which are considered to be part of the watercourse and drainage system of the City, and shall include the headwater areas where the watercourse first surfaces. They may be but are not necessarily characterized by special soils such as peat, muck, and mud. SECTION 5. DESCRIPTION OF THE TRUNK DRAINAGE SYSTEM The City of Homer has a trunk drainage system consist- ing of watercourses, sloughs, streams, ponds, lakes, swamps,, streets, ditches, conduit, culverts, bridges, and catch basins, among others. The extent of this trunk drainage system is indicated in figures 5, 6, 7, and 8 of the drain- age management plan. The City controls this system either through fee ownership, through formal easements, or by its prescriptive rights to pass storm and surface waters over private or public lands. D-8 SECTION 6. STATEMENT OF AUTHORITY The Director of Public Works, or the Director's desig- nated representative, is charged with the administration of and compliance with the rules and regulations. SECTION 7. APPLICABILITY In addition to other requirements for compliance with the drainage rules and regulations, the following conditions shall also apply: A. Area of Applicability. These rules and regulations shall apply to all property within Homer as indicated on the map of the drainage area and system, Exhibit 1, and may also apply to the full extent provided by law to those lands which are outside the city limits which discharge storm and surface waters into, from, and through the City. Jurisdic- tion in those areas not within the city limits shall be subject to the provisions of intergovernmental agreements as they now exist or shall be later entered into or modified between the City and the Kenai Peninsula Borough. The City Council further finds that construction or development of the following projects requires such regulation: 1. Subdivisions of land 2. Projects which include the construction of industrial, commercial, and single- or multi- family dwellings 3. All projects in areas identified as hazardous and subject to flooding or erosion by the D-9 comprehensive drainage management plan. No such areas have been identified to date. B. Alteration of the Existing Drainage System. As designated in Exhibit 1, a considerable portion of the drainage system of the City presently exists as natural watercourses and wetlands. No person shall undertake a project which would encroach upon, modify, realign, or change in any manner any of the existing drainage system as shown in figures 5, 6, 7, and 8 of the drainage management plan except for normal maintenance to keep property access- ible as provided for by the rules and regulations and with prior approval of the City. C. Degradation of Water Quality. No person, or property owner within or without the City shall cause or permit the discharge of storm water runoff from property under their control into the city drainage system, which discharge does not meet the minimum water quality standards, as described in Section 11. D. Relationship to Other Permits. All persons apply- ing for any of the following permits or approvals shall submit for approval a drainage plan with their application or request: 1. Subdivision approval 2. Rezones 3. Conditional use permits 4. Contract zonings D-10 5. Planned unit development 6. Road construction (if instituted) 7. Building permits Final subdivision design or commencement of construc- tion work under any of the above permits or applications shall not begin until such time as final approval of the drainage plan is obtained. Failure to comply with this provision shall result in revocation of all permits for the proposed development. Final plat approval shall be denied if it does not comply with the drainage plan. E@ Exceptions. The plan requirement established in this section will apply except when the developer demon- strates to the satisfaction of the Department of Public Works that the proposed permit or activity: 1. Will neither seriously nor adversely impact the water quality conditions of any affected receiving bodies of water, and 2. Will not alter the drainage patterns or peak discharge, or cause any other adverse effects in the drainage area. SECTION 8. APPLICABILITY TO GOVERNMENTAL ENTITIES To the extent not prohibited, or as permitted or pro- vided by law, all municipal corporations and governmental entities shall be required to submit a drainage plan and comply with the terms of this chapter when undertaking such projects or applying for such permits as stated in Section 7. This shall include road building and widening within the D-11 areas of the City. No state or municipal government shall permit a project which does not comply with this ordinance. It is recognized that many other city, borough, state, and federal permit conditions may be applied to the proposed action and that compliance with the provisions of this chapter does not constitute compliance with other such requirements. SECTION 9. CONTENTS OF A DRAINAGE PLAN All person applying for any of the permits listed in Section 7 shall provide a drainage plan, prepared by a civil engineer registered for practice in the State of Alaska, for surface and pertinent subsurface water flows entering, flowing within, and leaving the subject property. The contents of the drainage plan shall include the following information: a. Background computations for sizing drainage fa- cilities: i. Depiction of the drainage area on a topo- graphical map of scale 1 inch equals 200 feet and 5-foot contours, with acreage of the site, and developmental coverage indicated as well as the total area tributary to the site ii. Indication of the peak discharge of surface water currently entering and leaving the subject property as determined by the runoff design curves. b. Proposed drainage management system, including facilities for handling the design runoff. D-12 C. Arrangements by the developer to provide for continuing maintenance of the drainage management system and facilities. d. The requirements of this section may be modified if, in the City Public Works Director's profes- sional opinion, such additional or reduced amount of information is necessary or appropriate to carry out the expressed purpose and intent of the ordinance. SECTION 10. STANDARDS The following standards shall app ly to all projects subject to these rules and regulations. Additionally, the water quality standards shall apply to all properties dis- charging storm and surface water runoff into the drainage system. Except where specifically described, it shall be the applicant's responsibility to determine the method by which he will comply with the standards. A. Design The following design requirements shall apply to all projects and are intended to be consistent with the drainage management plan. 1. Mandatory Requirements a. Surface water entering the subject property shall be received at the naturally occurring location and surface water exiting the subject property shall be discharged at the natural location with adequate energy dissipators within the subject property to minimize D-13 downstream damage and with no diversion at any of these points b. Where open-ditch construction is used to handle drainage within the tract, a minimum of fifteen (15) feet will be provided between any structures and the top of the bank of the defined channel. i. In open-channel work the water surface elevation will be indicated on the plan and profile drawings. The configuration of the finished grades constituting the banks of the open channel will also be shown on the drawings. ii. Proposed cross sections of the channel will be shown with stable sideslopes as approved by the Public Works Director. iii. The water surface elevation of the flow for the design storm will be indicated on the cross section. C. When a closed system is used to handle drain- age within the tract, all structures will be a minimum of ten (10) feet from the closed system. 2. Construction Construction materials and methods shall be in ac- cordance with "Standards and Specifications" as developed by the Public Works Department. Copies of this publication are available for the public at the office of the Public Works Director. D-14 3. Erosion Control Where drainage facilities discharge to natural drainage ways or watercourses, energy dissipation facilities shall be provided to prevent erosion and deterioration of the stream- bed or banks. Energy dissipation facilities shall be con- structed of natural materials or materials fabricated solely for that purpose. Material such as broken concrete slabs, pipe, tires, scrap metal, or debris is prohibited. No person shall discharge drainage waters from their project to any point or in any manner not approved by the City. 4. Watercourses and Streams Except on bridges or over culverts, or immediate ap- proaches to them, no building, fences, construction, or obstructions shall be permitted within 25 horizontal feet of any stream or watercourse except as may be necessary to improve or stabilize the existing drainage. All construc- tion within 50 feet of a watercourse shall be subject to careful control of filling and grading to assure that no erosion products are permitted to enter the natural drainage system. B. Performance The performance standards are set as the minimum level of compliance. 1. Runoff Quality No one shall introduce into the drainage waters any liquid or solid foreign substances of biodegradable or other nature which shall cause the water quality to degrade from applicable state standards. Products of erosion shall be prevented from entering the natural drainage system at D-15 all times, during both the construction on the property and the subsequent operation of the facilities provided. All trash and debris shall be prohibited from entering the drainage system at any point within the property. It shall be prohibited and in violation of this ordi- nance for any person to: a. Cause or permit litter, trash, rubbish, or debris to enter the drainage system of the City. b. Cause or permit liquid or water-carried pollutants to enter the drainage system of the City including but not limited to oils and petroleum products, pesticides, fertili- zersp soaps, detergents, and washing wastes. C. Cause or permit horses, cattle, or other domestic animals other than dogs or cats to enter any watercourses or wetlands that are part of the drainage system of the City. Stables, pastures, or other animal enclosures shall be drained so as to prevent polluted drainage waters from entering the drainage system of the City. d. Cause or permit grading, clearing, filling, or other land surface changes to take place in such a way as to allow drainage from the property to carry any suspended or dissolved matter into the drainage system of the City. e. Cause or permit to take place in the streams, watercourses, or wetlands that are part of D-16 the drainage system any work that would result in the transmission of silt, pollu- tional materials, or other foreign substances from one part of the system to another. 2@ Runoff Rate The storm water runoff discharging from a project or property which directly or indirectly enters the drainage system of the City shall be released in such a manner as to be compatible with the drainage management plan or such other consideration as the City may deem appropriate. 3. Vegetation Removal When a project involves clearing of land, operations shall be conducted so as to expose the smallest practical area of soil to erosion for the least possible time during construction. Erosion control measures shall be undertaken from the time of beginning of clearing. Vegetation shall be restored or control measures instituted at the earliest possible date. On-site drainage shall be handled in such a way as to control erosion and to return waters to the natural drainage course free of sedimentation or other pollution. Drainage from areas above the developed site shall be temporarily diverted from the construction area to preclude erosion and sedimentation. The following are considered erosion and sediment control measures: a. Vegetation b. Mulch D-17 C. Natural or synthetic matting d. Riffles e. Impervious linings, including polyethylene and asphalt concrete f. Terraces, grassed waterways 9- Drop structures h. Storm drains i. Energy dissipation devices j. Debris basins k. Sedimentation ponds 1. Filters SECTION 11. FEES AND CHARGES A. Permit Fee The City shall levy such fees as are necessary to review and administer the drainage permit for the specific improvement and the basic permit fee shall be $ The permit fee for projects requiring additional ser- vices by the City shall be on the basis of the minimum fee plus all direct costs incurred by the City including, but not limited to, the following: 1. Costs of engineering - review time 2. Costs for inspection time 3. Costs for testing completed facilities B. Cost of Facilities on Private Property All costs of providing drainage facilities on private property to meet the requirements of these rules and regula- tions shall be borne by the owner. D-18 C. Cost of Future Public Facilities It is intended that funds for future trunk drainage system construction will be provided from the general fund or special assessments. SECTION 12. REVIEW AND APPROVAL OF THE PLAN Upon filing of the completed drainage plan and all supporting data as required by the City and upon payment of all applicable fees, the Public Works Director shall expedi- tiously review the plan in accordance with the procedures established by the City. The Public Works Director will review the drainage plan for technical accuracy and will recommend to the Planning Commission that the drainage plan be accepted, accepted with conditions, or disapproved. The City will then act upon the application of which the drainage plan is a part. Final approval and acceptance of the drainage facilities provided will only be made upon the completion of the project following necessary inspection and testing. The same plan submitted during one permit/approval process may be subsequently submitted with further required applications. The plan shall be supplemented with such additional information that is requested by the Department of Public Works. SECTION 13. VARIANCES variances from any of the foregoing requirements may be permitted only after a determination by the Planning Commis- sion that the proposed variance is in accord with the intent of the drainage management plan. D-19 SECTION 14. APPEALS In the event of disapproval of a drainage plan, the Planning Commission shall state the reasons for the denial and measures necessary to attain approval. The applicant shall have the right to have the denial reviewed by the full City Council or to make corrective measures to the project as necessary to obtain approval. Denial by full City Council shall leave the applicant with the choice of correcting the project or permit as suggested by the City or appeal through the judicial process. SECTION 15. EASEMENTS Easements for maintenance access to all drainage system components on private property must be provided. The ease- ment shall be 15 feet back from the top of each bank on any natural or manmade open channel and 10 feet on either side of the centerline of any closed conduit. In addition to the appropriate easements for drainage ways within the subject property, an applicant must obtain easements required to pass drainage water from his property to an approved point of discharge to the City's drainage system. These easements shall be obtained by the applicant at his sole cost and expense. A true copy of such easement shall be delivered to the City prior to final plat approval and prior to the time the applicant commences work on his project. Upon completion of the project and prior to acceptance of said project by the City in accordance with the provisions hereof, the original easement and easement releases shall be delivered to the City. Said easement shall provide for the perpetual access of the City for maintenance, repair, and replacement of drainage-related facilities. D-20 SECTION 16. BONDS AND LIABILITY INSURANCE REQUIRED The Department of Public Works is authorized to require all persons constructing drainage facilities to post surety and cash bonds. The City shall not authorize approval of a final subdivision plat until such bonds are prese nted. Where such persons have previously posted, or are required to post, other such bonds on the facility itself or on other construction relating to the facility, such person may, with the permission of the Director of Public Works and to the extent allowable by law, combine all such bonds into a single bond, provided that at no time shall the amount thus bonded be less than the total amount which would have been required in the form of separate bonds, and provided further that such a bond shall on its face clearly delineate those separate bonds which it is intended to replace. A. Construction Bond Prior to commencing construction, the person construc- ting the facility shall post a construction bond in an amount sufficient to cover the cost of conforming said construction with the approved drainage plans. B. Maintenance Bond After satisfactory completion of the facilities and release of the construction bond by the City, the person constructing the facility shall commence a two (2)-year period of satisfactory maintenance of the facility. A cash bond to be used at the discretion of the Public Works Direc- tor to correct deficiencies in said maintenance affecting public health, safety, and welfare must be posted and main- tained throughout the two-year maintenance period. The D-21 amount of the cash bond shall be determined by the Public Works Director but shall not be in excess of ten percent nor less.than five percent of the estimated construction cost of the drainage facilities. In addition, a surety bond or cash bond to cover the cost of design defects or failures in workmanship of the facilities shall also be posted and maintained throughout the two-year maintenance period. Alternatively, an equivalent cash deposit to an escrow account administered by a local bank designated by the City could be required at the City's option. C. Liability Policy The person constructing the facility shall maintain a liability policy in the amount of one hundred thousand dollars per individual, three hundred thousand dollars per occurrence, and fifty thousand dollars property damage, which shall name the City as an additional insured and which shall protect the City from any liability up to those amounts for any accident, negligence, failure of the facility, or any other liability whatsoever relating to the construction or maintenance of the facility. Said liability policy shall be maintained for the duration of the facility by the owner of the facility, provided that, in the case of facilities assumed by the City for maintenance pursuant to Section 20 of this ordinance, said liability policy shall be terminated when said City maintenance responsibility commences. SECTION 17. INSPECTION AND ACCEPTANCE After approval of the initial drainage plan the City shall be notified at the time any construction or alteration affecting drainage on the site shall begin and shall have the right to make periodic inspections during the construc- tion or alteration to ensure that the requirements D-22 stated in the permit and elsewhere in this ordinance are met. It will be the responsibility of the property owner to see that the construction inspections are performed and "as- built" drawings are prepared for the project and certified by a professional civil engineer registered to practice in the State of Alaska. SECTION 18. ENFORCEMENT AND PENALTIES The City reserves the right to enter the subject prop- erty from time to time to ascertain that all drainage facili- ties are functioning. In the event deficiencies are found, the property owner shall make such corrections as are neces- sary within 15 days of the date of notice by the City. In the event the property owner shall fail to make such correc- tions, the City may revoke the right to occupancy of the subject property, may charge the property owner with a misdemeanor punishable by fines, and may enter on to the subject property and take such corrective action as may be required by the drainage permit. All costs for corrective measures and enforcement actions shall be borne by the property owner. Any person causing material to be discharged to or enter the drainage system of the City shall be liable for all costs incurred by the City 6r others in cleaning up or correcting said action and may be charged with a misdemeanor punishable by fines. The City Council may institute a suit for a mandatory injunction directing a person to remove a structure or facility erected in violation of the provisions of this ordinance, or make the same comply with its terms. If the D-23 City Council is successful in its suit, the respondent shall bear the costs of the action, including reasonable attorney fees. The failure or refusal o f the City to enforce any provision of this ordinance, and as hereafter amended, shall not constitute a waiver or bar to prevent enforcement thereof against any person for a subsequent violation hereof, or for any other violation by any other person. SECTION 19. MAINTENANCE maintenance of the trunk drainage system on public or private property shall be the responsibility of the City, provided maintenance easements are granted in favor of the City where necessary by the private and public owners. Where such easements are not granted, the private or public owner shall be responsible and liable for maintenance. Maintenance of drainage facilities on private property discharging into the City's trunk discharge system (Exhibit 1) shall be the responsibility of the owner thereof unless otherwise provided herein. SECTION 20. CITY ASSUMPTION OF MAINTENANCE The City may assume the maintenance of any drainage facilities after the expiration of the two (2)-year main- tenance period in connection with the subdivision of land if: a. All of the requirements of Section 17 of this ordinance have been fully complied with. D-24 b. The facilities have been inspected and approved by the Public Works Department after two (2) years of operations. C. All necessary easements entitling the City to properly maintain the facility have been conveyed to the City and recorded with the City Auditor. d. The surety bond required in Section 17B has been .extended for one year, covering the City's first year of maintenance. e. The developer has supplied to the City an account- ing of capital, construction, and maintenance expenses or other items for the drainage facili- ties up to the end of the two-year period, for the purpose of establishing the basis for future bonding requirements for other developments. In the event that the City elects not to assume the maintenance responsibility for the facilities, it will be the responsibility of the developer to make arrangements with the occupants or owners of the subject property for assumption of maintenance in a manner subject to the approval of the Department of Public Works. Such arrangements shall be reported as part of the drainage plan required in Sec- tion 9. SECTION 21. RETROACTIVITY RELATING TO CITY MAINTENANCE OF DRAINAGE FACILITIES If any person has constructed any drainage facilities, or has received approval of drainage plans prior to the effective date of this ordinance, the City may assume main- tenance of the facilities if the facility so constructed or D-25 the plan so approved is re-evaluated according to the re- quirements of this ordinance and is found in compliance to the Public Works Director's satisfaction and all bonds specified in Section 17 are inspected, posted, acknowledged, and approved. In cases in which all or part of the drainage facili- ties are not accessible for maintenance purposes due to overlying structures or other causes, the City shall be held harmless for damages which might occur due to failure of design or workmanship of those segments and, further, will not be responsible for their maintenance. SECTION 22. EXPIRATION/RENEWAL Every permit issued under the provisions of this ordi- nance shall expire at the end of the period of time set out in the permit. If the permittee shall be unable to complete the work within the specified time, he shall, prior to expiration of the permit, present in writing to the City a request for an extension of time, setting forth therein the reasons for an extension of time. If in the opinion of the Public Works Director such an extension is necessary, he may grant additional time for the completion of the work. SECTION 23. EFFECTIVE DATE The requirements of this chapter shall apply to all plats receiving preliminary approval subsequent to . In the case of all additional actions enumerated in Section 7 of this ordinance, the terms of this chapter shall apply where final action by the City has not been taken prior to the effective date of this ordinance. D-26 SECTION 24. SEVERABILITY If any provision of this chapter or its application to any person or property is amended or held invalid, the remainder of the chapter or the application of the provision to other persons or circumstances shall not be affected. D-27 NOAA 0 SIAL SERVICES CIR 3 66:33 14110917 C A i