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TORM WATER M N EMENT -1 rl _T SEVENMILE CREEK VOLUME 12 ERIE COUNTY DEPARTMENT OF PLANNING COMMONWEALTH OF PENNSYLVANIA .7. Ju(, ft TD j6- 665 S76 1981 f 71 V12 it C 1 oL 5@ @_51 PLAN -41 OCTOBER 1981 PREPARED BY NORTHWEST INSTITUTE OF RESEARCH WOODRUFf, INC. A C A ED TI I I&& WATERSHED ADVISORY COMMITTEE Member Representing Joyce Andrews Lake City Borough Delores Bendig Lawrence Park Township Gerald Blanchfield Harborcreek Township Harold Crane, Jr. Elk Creek Township Frank Fenton North East Township John Gresch Platea Borough LeRoy Gross Erie County Conservation Dist. Ted Guzzy Girard Township Richard P. Hessinger Summit Township John Klier Fairview Township Earl Koon Washington Township Roger C. Latimer Fairview Borough Rose Little McKean Township Jacob Luke Greenfield Township Kenneth Maas North East Borough Paul Martin Millcreek Township Wasinder Mokha Erie City Jeanne O'Brien McKean Borough Wilbur Osborn Waterford Township Lawrence Pieper Franklin Township Norman H. Rabell Conneaut Township Mary B. Ripley Wesleyville Borough Robert Smith Greene Township Ronald VanTassell Springfield Township Larry Wygant Girard Borough ERIE COUNTY DEPARTMENT OF PLANNING David Skellie Acting Director Thomas DeBello Senior Planner Jeffrey Spaulding Transportation Planner Gilbert Rocco Project Planner A. Latif Panhwar Planning Analyst Dolores Oblinski Draftsman 11 Lori Prody Executive Secretary Kathleen Anderson Secretary This study was financed through a planning assistance grant from the National Oceanic and Atmospheric Administration as administered through the Pennsylvania Department of Environmental Resources Coastal Zone Management Office (Office of Resources Management), and the Erie County Department of Planning. STORM WATER MANAGEMENT PLAN SEVENMILE CREEK WATERSHED Volume 12 V! Prepared For -9 Commonwealth of Pennsylvania Department of Environmental Resources and Erie County Department of Planning Prepared By Northwest Institute of Research - Woodruff, Inc. As a Consortium October 1981 TABLE OF CONTENTS Page Section I SUMMARY AND RECOMMENDATIONS 1-1 Section 2 BACKGROUND 2-1 Section 3 DESCRIPTION OF THE SEVENMILE CREEK WATERSHED 3-1 3.1 Local Input Data 3-1 3.1.1 Significant obstructions 3-1 3.1.2 Existing drainage problem areas 3-2 3.1.3 Existing storm sewers 3-2 3.1.4 Proposed storm sewers 3-2 3.1.5 Existing and proposed flood control projects 3-2 3.2 Present and Projected Land Use 3-3 3.3 Soil Types 3-3 3.4 The National Flood Insurance 100-Year Flood Plain 3-3 Section 4 STANDARDS AND CRITERIA FOR STORM WATER MANAGEMENT 4-1 4.1 Definition of Design Storm 4-1 4.2 Definition of Type I and Type 2 Channels 4-1 4.3 Criteria for Type I Channels (Main Stream) 4-2 4.4 Criteria for Type 2 Channels (Branch Streams) 4-2 Section 5 IMPLEMENTATION 5-1 5.1 Introduction 5-1 5.2 Special Considerations 5-1 5.3 Building Permit Process 5-2 5.4 Subdivision Review Process 5-3 5.5 Conclusions 5-3 Section 6 THE SEVENMILE CREEK COMPUTER MODEL 6-1 6.1 Existing Stream Characteristics 6-1 6.2 Post-Development Stream Characteristics 6-1 TABLE OF CONTENTS (Continued) Appendix A Tables and Plates Table 12-1 Significant Obstructions Table 12-2 Storm Drainage Problems Table 12-3 Proposed Storm Water Collection Systems Table 12-4 Storm Water Collection and Control Facilities Table 12-5 Project Development and Construction Schedule and Costs Table 12-6 Existing Flood Control Projects Table 12-7 Proposed Flood Control Projects Table 12-8 Watershed Runoff Data Table 12-9 Various On-Site Storm Water Control Methods Table 12-10 Advantages and Disadvantages of Various On-Site Storm Water Control Measures Plate 12-1 Sevenmile Creek Watershed Base Map Plate 12-2 Sevenmile Creek Watershed Significant Obstructions Map - Plate 12-3 Sevenmile Creek Watershed Drainage Problem Areas Plate 12-4 Sevenmile Creek Storm Sewer Systems Plate 12-5 Sevenmile Creek Watershed Flood Control Projects Plate 12-6 Sevenmile Creek Watershed Existing Land Use Plate 12-7 Sevenmile Creek Watershed Ultimate Land Use Plate 12-8 Sevenmile Creek Watershed Soil Map Plate 12-9 Sevenmile Creek Watershed 100-Year Flood Plain Plate 12-10 Sevenmile Creek Watershed Subwatershed Map Appendix B Calculations to Determine Increased Runoff and Examples of Specific On-Site Storage Section I SUMMARY AND RECOMMENDATIONS This document has been prepared in accordance with the provisions of the Pennsylvania Storm Water Management Act, P.L. 864, Act 167, October 4, 1978 and is a pilot study under that Act. The Northwest Institute of Research of Erie, Pennsylvania and Woodruff Incorporated, Consulting Engineers of Cleveland, Ohio have formed a consortium for the purpose of developing a pilot storm water management plan for the Lake Erie and Elk Creek Watersheds. This study has been prepared under the direction of the Pennsylvania Department of Environmental Resources, Bureau of Dams and Waterway Management, Division of Storm Water Management and the Erie County Department of Planning. This report is Volume 12 in a series of 14 volumes prepared for the Erie County Department of Planning. The purposes of this report are: 1. To establish as base conditions the existing land use and the existing storm water runoff in the Sevenmile Creek Watershed against which future conditions can be compared. 2. To calculate the runoff from a projected land use to indicate how much more flow the main stream and its branches would be required to carry. 3. To present a set of criteria and standards for storm water management in this watershed. 4. To recommend the one or more alternative storm water management methods best suited to the needs of the Sevenmile Creek Watershed. The standards and criteria which are to be applied to storm water runoff have been summarized in Section 4 and are described in complete detail in Volume 1. It is recommended that these standards and criteria be adopted by the committee in the Sevenmile Creek Watershed Area. The various means of implementing these standards and criteria are discussed in Section 5. It is recommended that the on-site approach to storm water management as described in Section 5 be adopted immediately and included in all future development plans. Immediate steps are to be taken so that the Sevenmile Creek Watershed Area will be prepared for the tremendous growth that will occur should the U.S. Steel proposal for Springfield Township come to fruition. It should be emphasized that this storm water management plan is intended solely to minimize the creation of new flood problem areas as a result of increased runoff due to development. Also, existing problem areas will not be aggravated by increased runoff. In this way, the municipalities will be able to concentrate on solutions for those flooding problems that presently trouble local property owners. 1-1 Section 2 BACKGROUND The basic approach to storm water management in the past has been to achieve maximum convenience at an individual site by getting rid of any excess surface water after a rainfall as quickly as possible. This removal is accomplished typically by disposal of the water through a storm sewer or other closed system. As the land in a given area becomes more and more developed, this policy has led to the following problems: 1. Flooding due to overland flow. 2. Increasingly frequent downstream flooding. 3. Diminished groundwater supplies. 4. Erosion of stream banks. 5. Siltation and pollution of streams. As land development continues, the percentage of impervious land surface increases as paved roads, sidewalks, parking lots, and other structures are built. The result of this change is to further aggravate the problem. Areas that previously had no flooding begin experiencing problems and areas which might have been prone to flooding earlier now experience an even more severe problem. The solution of passing one's own water problems downstream is no longer acceptable. The potential damage created by such an approach cannot be tolerated as developments continue to move into once rural areas. Clearly, a new approach to handling storm water runoff is needed. A storm water management plan is necessary that protects our land and streams as well as permits reasonable development. The new approach must strike a balance between local convenience and protection against the hazard of flooding. One significant feature of the approach presented in this document will be the planned detention of water on-site in various types of storage facilities. Such structures will hold the water and release it slowly over time, after the danger of flooding is past. In the process, downstream areas will be protected. This concept will be discussed more fully in the following pages and will be applied to the specific requirements of the Sevenmile Creek Watershed. 2-1 Section 3 DESCRIPTION OF THE SEVENMILE CREEK WATERSHED, On Plate No. 12-10) the base map for the Sevenmile Creek Watershed Area is presented. On this map, major topographic features of the watershed are shown. The Sevenmile Creek Watershed is located in the townships of Harborcreek and Greenfield. It covers an area of approximately 5,600 acres. 3.1 Local Input Data There are five types of local data which have been considered in the description of the Sevenmile Creek Watershed Area. These include: 1. Signif icant obstructions 2. Existing drainage problems 3. Location of existing storm sewers 4. Proposed storm sewers - 5. Existing and proposed flood control projects Each of these types of data are discussed in the following paragraphs. This information is as complete as possible at the time of writing. Additional information may be added as it becomes available. 3. 1.1 Significant obstructions A significant obstruction is defined as any structure or assembly of materials which might impede, retard or change the flow of storm water runoff. Significant obstructions in the Sevenmile Creek Watershed were located both by surveys conducted by the consultant and by local input from municipal and county officials as well as the Advisory Committee composed of representatives from the affected municipalities. Those obstructions which were identified are described on Table 12-1 and located on the map presented on Plate No. 12-2. A total of 16 obstructions were mapped. These include many bridge abutments and piers or culverts through which the main stream or side branches pass as they flow under highways, driveways and railroads. While many of these structures do not obstruct normal flow, all may be considered potentially obstructive during severe storms if debris is allowed to collect in culvert openings or around bridge piers. They also serve as potential entrapments for ice floes. MFor the convenience of the reader and to facilitate locating of tables and maps, all of these illustrations are placed in order in Appendix A at the end of this report. 3-1 The importance of these obstructions is obvious since anything which interferes with the natural flow of the stream can contribute to local flooding under storm conditions. The control of increased runoff due to development that would result from the implementation of this storm water management plan will insure that these structures will operate hydraulically at their present levels. Thus, if a particular structure has no recurrent problems in passing stream flows at the present time, no problems would be expected in the future under the plan as development proceeds. Flooding problems due to structures of insufficient hydraulic capacity will not get worse in the future, nor will they be eliminated by the institution of these storm water management policies. The intent of this plan is to maintain the status quo regarding stream flow. 3.1.2 Existing drainage problem areas There were no drainage problems identified in the Sevenmile Creek Watershed. Table 12-2 and shown on Plate No. 12-3, are provided to locate and to describe problems as they are identified in the future. 3.1.3 Existing storm sewers The third type of local input- involved the location of all existing storm sewers in the Sevenmile Creek Watershed Area. This information is shown on Plate No. 12-4. These data can be obtained by consulting the Comprehensive Plan for Harborcreek Township. At the present time, barring evidence to the contrary, the assumption is made that none of these storm sewers has a significant impact on the management of storm water in this area. 3.1.4 Proposed storm sewers Tables 12-3, 12-4 and 12-5 are provided for the purpose of listing and locating all. proposed storm sewers in the Sevenmile Creek Watershed Area. At the time of writing this report, no new storm sewers are known to have been proposed for the Sevenmile Creek area. The tables are provided so that information can be added to them and Plate No. 12-4 as it becomes available. Further information on storm sewers can be obtained by consulting the Comprehensive Plan for Harborcreek Township. 3.1.5 Existing and proposed flood control projects Plate No. 12-5 and Tables 12-6 and 12-7 are provided for the purpose of entering the location and description of all existing and proposed flood control projects. No known existing or proposed flood control projects were identified at the time of writing. Additional information can be added to these maps as it becomes available. 3-2 3.2 Present and Projected Land Use Present land use is shown on Plate No. 12-6. Existing land use data was taken f rom the Erie County Land Use Plan Update (June, 1978). It can be seen from the existing land use map that the area is at present largely undeveloped with many open areas and small widely spaced residential areas. Projected land use was derived from various Erie County projections. This is shown on Plate No. 12-7. As can be seen, the Sevenmile Creek Watershed Area is seen as an area of extremely high potential growth. This would be most evident if the proposed U.S. Steel plant is built in Springfield Township. Existing development has brought about the institution of a sewage disposal system in portions of the watershed area. The presence of a public sewer system often has a strong influence on area growth. 33 Soil Types The various soil types found within the Sevenmile Creek Watershed Area are shown on Plate No. 12-8. These soils include the following: 1. Gravelly and sandy soils of the beach ridges (Conotton-Ottawa- Fredon). 2. Silty and clayey soils, chiefly on the lake plain (Wallington-Birdsall- Williamson and Collamer). 3. Deep, medium-textured soils in moderately limy till of the glaciated upland (Erie-Ellery and Alden-Langford). 4. Deep, medium-textured soils in slightly limy till of the glaciated upland (Volusia-Mardin). '5. Shallow, medium-textured soils of the glaciated upland and the lake plain (Allis-Ellery and Alden). 3.4 The National Flood Insurance 100-Year Flood Plain The 100-year flood is defined as the highest level of flooding that is likely to occur on the average, every 100 years. The fact that an area has not flooded recently does not mean it will not do so in the future. The probability of such an occurrence is I percent in any given year. The Flood Plain Management Act, Act 166, October 4, 1978, prohibits development within designated flood plains. No development is allowed in any areas 50 feet or less from the boundaries of designated flood plains. This is intended to reduce flood damage and accumulation of debris due to the 100 year flood and is consistent with the intent of the Storm Water Management Act. On Plate No. 12-9, the flood plain for the basic or 100-year flood is shown. The information was taken from the National Flood Insurance Program Maps (Available for reference at the Erie County Planning Department office). 3-3 Section 4 STANDARDS AND CRITERIA FOR STORM WATER MANAGE MENT The following are the recommended standards and criteria for storm water Lnagement in the Sevenmile Creek Watershed Area. A complete derivation and justification of these standards are to be found in Volume I of this study report. m @` The recommended standards and criteria may be completely satisfied by use of the on--site approach discussed in Section 5 of this volume. The most fundamental standard of this study is that the amount of flow along Sevenmile Creek must not be allowed to increase at the data points labeled "All through IIPII on Plate No. 12-10 above those existing flows indicated on Table 12-8 for, each of these points. These flows were obtained from a computer model developed expressly for Sevenmile Creek using the design storm described below. Flows at positions between the given points must not exceed a straight line interpolation of flow values at adjacent points. This will insure that the flow characteristics of Sevenmile Creek will remain at their 1981 level for storms equal to or less than the design storm. The objective is to maintain the existing level of flow in the main stream channel for the design storm and to maintain bank-full capacity for the side branches. A policy such as this will not only effectively manage increased runoff as desired, but will help to maintain the sensitive ecological balance of the stream. 4.1 Definition of Design Storm The design storm for this study has been determined to be the 10-year, 24- hour storm. The choice of this storm is justified in Volume I of this study. The 10- year, 24-hour storm is that theoretical storm of 24-hour duration that statistically will occur once in 10 years. On the average such a storm would produce 4.8 inches of rain in a 24-hour period. As previously mentioned, this is the storm used to derive the magnitude of flow at the data points described above. 4.2 Definition of Type I and Type 2 Channels Because some of the channels that make up the Sevenmile Creek drainage systems are more able to carry increased flows than are others, two sets of criteria and standards have been devised for two types of channels. The first, or Type I Channels, are characterized as main stream channels. They have a well-defined flood plain and can handle increased flows very easily. These are the shaded portions of the Sevenmile Creek drainage system shown on Plate No. 12-9, "The One-Hundred-Year Flood Plain." The second are referred to as Type 2 channels. These consist of all the other portions of the Sevenmile Creek drainage system that are not shaded on Plate No. 12-9. They are characterized as branch stream channels. Plate No. 12-10, the Subwatershed Map for Sevenmile Creek, indicates those portions of the watershed area whose runoff is initially discharged into Type I Channels and those whose runoff is initially discharged into Type 2 Channels. 4-1 4.3 Criteria for Type 1 Channels (Main Stream) For those sites which are to discharge their runoff into a Type I Channel, it will be required that the increased runoff after development (due to the design storm) be managed by any of the recommended on-site methods discussed in Section 5. That is to say, the runoff due to the 10-year, 24-hour storm is to be calculated again for the same storm taking into account the specific proposed development. The difference between these two runoffs is that which must be managed. 4.4 Criteria for Type 2 Channels (Branch Streams) For those sites which are to discharge their runoff into a Type 2 Channel, a more stringent standard is to be applied. This is necessary because these channels typically are too small to accommodate increased runoff. They have no flood plain to act as a cushion. In this situation, the amount of storm water that must be stored is the difference in runoff between that due to proposed land use for the 10-year, 24-hour storm and that due to the mean annual storm for existing land use conditions. As defined previously, the mean annual storm (1) is calculated by taking the largest storm for each year on record and averaging them together. Statistically, the mean annual storm is equivalent to a storm with a return frequency of 2.33 years. Whereas side branches are naturally formed to handle the more frequent mean annual storm, this more stringent criterion would now protect them against flooding for all storms up to and including the 10-year, 24-hour storm. G)The concept of a mean annual storm was developed by L. Leopold and referenced in Storm Water Management,. 4-2 Section 5 IMPLEMENTATION 5.1 Introduction Every parcel of land has unique storm water runoff characteristics which inevitably change when the parcel is developed, usually resulting in an increase in storm water runoff from the site. When development takes place the increase in storm water runoff is magnified and serious problems can result. Prior to the development of this Plan there was no established method through which a municipality could require developers to take precautions against causing storm water runoff problems. The purpose of this Plan is to help correct the situation by establishing standards for storm water management and an administrative procedure whereby those standards can be applied by local governments to development within their jurisdiction. The Storm Water Management Plan will be implemented by individual municipalities through the adoption of a storm water management ordinance or through amendments to existing subdivision or zoning regulations. Administration of the storm water management program will be accomplished through a combination of enforcement actions undertaken through the building permit process and through the subdivision review process, both of which are detailed later in this Section. 5.2 Special Considerations Prior to discussing the specifics of the Building Permit Process and the Subdivision Review Process, two subjects which fall outside of the scope of this Plan's evaluation procedures will be discussed. The Building Permit and Subdivision Review evaluation procedures for storm water management apply to all forms of development and land use except development in areas with an existing storm sewer infrastructure and with respect to agricultural land. In situations where development or redevelopment occurs in an area where direct access to an established storm sewer infrastructure is possible, the development or redevelopment is considered sufficient to manage its storm water runoff if its on-site storm drainage network is incorporated into the existing storm water infrastructure. By connecting with the existing storm sewer system, the development would be relieved of further obligations to manage storm water runoff in accordance with this Plan unless the municipal governing body perceives a pctential storm water drainage problem or if the governing body wishes to correct an. existing storm drainage problem. In these cases where the governing body desires a more stringent application of storm water management controls they may require that a detention/ retention plan be developed which would alleviate the storm water drainage problem. 5-1 Evaluating agricultural land for compliance with storm water management controls is the second topic which falls outside of the scope of the Building Permit and Subdivision Review procedures. With respect to agricultural land, the recommended method of storm water management is to have a Soil Erosion and Sedimentation Control plan and/or permit prepared in accordance with existing State law and reviewed by the Erie County Soil Conservation Service. This applies only to cultivated land; agricultural accessory structures and residential structures should be evaluated by the municipality through the applicable method as outlined in the following sections. 5.3 Building Permit Process If a proposed subdivision is defined by the host municipality's subdivision regulations as a minor subdivision (usually 10 lots or less) or if development is proposed involving no subdivision of property, then storm water management standards and criteria should be evaluated at the time when development is formally proposed via an application for a building permit. This system is designed so that smaller developments may occur without incurring added engineering expense and so that municipalities can implement storm water management requirements without incurring substantial administrative overhead expense. The recommended technique to be followed when evaluating a minor SUbdivision or a development on an existing lot of record is presented here. First, all developments which fall into the above categories must meet each of the following: Standard Controls 1. Roof drains are not to be connected to streets, sanitary sewers or roadside ditches. 2. Runoff from the impervious areas must be drained to the pervious areas of the property. 3. Runoff is not to be collected or concentrated into an artificial conveyance and discharged onto adjacent property. Next, the zoning officer must calculate the percentage of the parcel which will be covered by impervious surfaces after development is concluded. In this context impervious surfaces mean all land covered by a house, barn, garage, patio, driveway, etc. Information needed to calculate the percentage of impervious area should be readily available on the building permit application. Once the calculation is made the zoning officer should refer to the following table to determine how many storm water controls in addition to those listed above will be needed to comply with the standards of the Storm Water Management Plan. The additional controls can be found in Table 12-9. 5-2 Determination of Controls Less than 15% impervious Standard controls only 15% - 19.99% impervious Standard controls only plus one additional control 20% - 24.99% impervious Standard controls plus 2 additional controls 25% - 30% impervious Standard controls plus 3 additional controls The methodology outlined above is designed to be used f or a proposed development which covers 30% or less of the parcel with an impervious surface. Under such circumstances the zoning officer can show the potential developer what storm water management controls are needed in order to receive this building permit. If the proposed development will cover greater than 30% of the parcel wi-rh an impervious surface or if the total impervious area exceeds one acre, then a licensed professional must be consulted to prepare a detention/ retention plan which meets the approval of the governing body. An additional fee is recommended to be added to the existing building permit fee to cover the expense of administering the program. 5.4 Subdivision Review Process If a development is defined by the host municipality's subdivision regulations as a major subdivision (usually more than 10 lots), the storm water management standards and criteria should be evaluated during the subdivision review process. This use of the subdivision review process is designed to ensure that large scale developments employ proper techniques to control storm water runoff and that these controls are firmly established prior to municipal or county approval of the subdivision plat. When a preliminary major subdivision plan is submitted for municipal review it shall be accompanied by detailed storm water detention/ retention specifications which meet the criteria of the Plan and which have been prepared by a professional licensed to perform such work in this Commonwealth. The proposed storm water detention/retention specifications shall be reviewed by the municipality and/or its engineer and shall satisfy the municipality before the major subdivision plan is approved. The municipality may require controls which are more stringent than those which meet the Storm Water Plan's criteria if circumstances dictate that such measures are needed to alleviate a current drainage problem or a suspected future drainage problem. 5.5 Conclusion The Lake Erie and Elk Creek Storm Water Management Plan has been developed in accordance with Act 167 of 1978, the Pennsylvania Storm Water Management Act. Under the provisions of this Act, municipalities are granted certain powers and must assume certain responsibilities. One of the responsibilities which has been assigned to local governments by the Act is the responsibility to adopt implementing ordinances such as those described in this section. Another responsibility assigned to the municipality is that of properly enforcing the storm water management ordinances and regulations. Because of the responsibilities awarded to municipalities under Act 167, each municipality affected by this Plan should consult their municipal solicitor for a briefing about the extent of their obligations under the provisions of Act 167. 5-3 Section 6 THE SEVENMILE CREEK COMPUTER MODEL As has been discussed previously, a computer model of the Sevenmile Creek drainage system was developed for the purpose of this study. A complete description of the background and development of this computer model is given in Volume I of this report. The following is a summary of the data used as input for the model and a description of the data it yielded as output. 6.1 Existing Stream Characteristics The existing land use for the Sevenmile Creek Watershed Area is shown on Plate No. 12-6. This is a base land use against which future development is to be compared upon adoption of this storm water management plan. It can be seen that the area is generally rural with some residential and commercial development. The runoff due to this land use was entered into the computer model. A soil factor derived from the various types of soils found in the Sevenmile Creek Watershed Area, as shown on Plate No. 12-8, was also taken into account. The results of the computer output are summarized on Table 12-8. The f low characteristics of Sevenmile Creek due to the runoff from existing land use are shown in the first columns labeled "Existing Runoff" for various data points. These da-ta points are located on Plate No. 12-10. These are the flow characteristics of the stream which must not be altered due to the development of land in the watershed area. 6.2 Post-Development Stream Characteristics A projected ultimate land use for the Sevenmile Creek Watershed Area was taken from the Erie County Land Use Plan Update (June, 1978). It is shown on Plate No. 12-7. This projection assumed that all of Erie County would develop to its maxmum potential, as it would if U.S. Steel were to build the large steel producing facility it has proposed for Springfield Township. The area is at present primarily a rural area. Projections indicate major growth in residential- agricultural usage. The runoff due to this projected land use was entered into the computer model. Again, a soil factor was taken into account. The resultant flow characteristics at the data points are shown in the column labeled "Ultimate Runoff" in Table 12-8. It can be seen that the peak flow of the ultimate runoff is considerably higher at all points than is that of the existing runoff. For example, at outlet to Lake Erie, the peak flow is calculated to be 5,060 cubic feet per second (cfs) for existing runoff and 6,181 cfs for ultimate runoff. 6-1 The depth of the ultimate flow is substantially higher at all data points. The increased depth becomes more critical in upstream reaches of the watershed. This implies a great risk of flooding in portions of the channel which have a naturally smaller cross section. These are generally the branch or Type 2 Channels. The velocity of the flow can also be seen to be much higher for ultimate runoff than for existing runoff. This is an undesirable situation that could result in excessive erosion of the stream bed. The stream channels would eventually widen and deepen beyond their present limits and possibly interfere with development along their banks. Foundations for bridges, culverts or retaining walls might be undermined due to a process known as scour. Scour is the washing away of earth around the footings of piers, bridge abutments retaining walls or the like, and in the process, exposing them. This reduces their structural stability. Water quality would decline due to the inordinant amount of soil particles being carried along by the current. Development would decrease the absorption of rainfall due to the amount of impervious cover it would probably bring with it. This could lower the groundwater table to unacceptable levels. The COWAMP Study Area 7 Report, prepared by the Department of Environmental Resources of the Commonwealth of Pennsylvania does not reveal any of the above to be current problems for the Fourmile Creek Watershed Area. This makes it very important to maintain existing water quality standards related to storm water runoff. In addition, the Clean Streams Law of Pennsylvania regulates activities that affect any stream in the Commonwealth in order to preserve and improve the purity of their water. The Storm Water Management Act will aid in the attainment of these objectives. All work done to manage storm water must be done in compliance with these rules and regulations. 6-2 I I I I I I I I APPENDIX A TABLES AND PLATES I I I I I I I I I I I DI A M 1,10_ SIGNIFICANT 013STRUCTIONS DRAINACIE ARLA %It Nit H'A[ ITY @PL Ok SIRUCR Rk So. MI,s CIPACITY I CIF S I DATF BUILT OWNI It AND ADI)Rfss " . t, QCO 6 '.4, 'or ip t-, 1 OWP6*@5, A-lb.-,eek rowsb,p-- 4 AObrborcr*ek lownih x le. 5' 15 5.1 "t-;, -c wll,@ 'c.,41 6 7o-krA,.p Culvert Ellipolical C-AfRI-i@, a' eave". a htborc,-k Bridg., Co@,.** i . B'idge, cb-"" 0 7 Morb-crook 7b@sh,,o 21-'a _q,, ll@b@Croeh rownj*iv S/O-e F3;1 -/j 13 At,b-,.,.ek ro w,,s h,p 14 ro-^sh", Wi" cb@,,,,, 48 6' 13 8,,dg,, 0.1 /6 c... A 700D tUFF, INC. . ........ SWM 2s S"emmill.r. CREEK TA8LE 12-1 &N NQ@ STORM DRAIN.A09 PROBLEMS NO LOCATION UUMMALITY PROBLEM PROPOSED SOLUTION F f e!@ swm 25:23 SEVEIAMILE CREEK TAILE 124 PROPOSED STORM WATER COLLECTION SYSTEMS 'AND FINAL OWN91tSHIll NO. LOCATION AI4D MUNICIPAL11Y CONML DATE EQ 14AINTENANCE IRESPON'SIBILITY. AdAP ITEM lFFE2ENFF NIJURJL_ I N lit, VA N A2 WOODRUFF, 1.@C s ESNWMMI L 2ES 2C& It E E X ev TABLE 13-1 SHEET I OF I PLAN b10- STORM WATER COLLECTION AND CONTROL FACILITIES PROjECI NO LOCATION TYPE OF FACILITY METHODS Of FINANCING t ALL PHASES i FINAN(IAL LiABILITY K o e@- e-' DRUFF, C. SWM 25;21 IRV ENMILE CREEX TABLE 134 PLON NO SHEET I OF I PROJECT'DEVELOPMENT AND CONSTRUCTION SCHEDULE AND COSTS SCIIEDU EST[ p COSTS MAINTENANCE Pit(JEL I NO@ DESIGN G START DESIGN --ALQULQLWAX.- CONSTRUCTION FINANCE CHARGES ---------------------- woof)RUFF, 1@c. swM 25 .. ..... IEVZNMILE TABLE 12-5 PLAN NO' EXIST114G FLOOD CONTROL PROJECTS NO PROIECT I OCATION AND MUNICI nATm BUILT p rAPACITY I IFF FXPECTAMCV@ YlLs le V, WOODRUFF, IN SWM 2s..28 F, BVBNMILE CRIZE TAKE 124 N N a PROPOSED FLOOD CONTROL PROJECTS NO PROJECT LOCATION AND MUNICIPALITY TE BUILDER OWNER CAPACITY C FmS I 01 )h ILA 2 WOODRUFF, INC. swm 25:28 SEVENMILE CILE TAKE 12.7 WATERSHED RUNOFF DATA EXISTING RUNOFF ULTIMATE RUNOFF ULTIMATE RUNOFF WITH STORAGE LOCATION PEAK FLOW TI to LUMI hilL. PEAK FLOW TIME OF LUME MW PEAK FL W TIME OF LUME MIL. C.F.S. a DEPTH FT CU. FF. C.F.S. PEAK MR. CU. FT. CFS. 0 CU. FIT. PEAMK HF. VELOCITY F.F.S. Vo DIPTH FT. VELOCITY F.P.S. Vo PEAK HR. DEFrH FT., VELOCITY F.P.S. Vo 2,43 &39 A 77 zo 2-36 12, ZO 40, .0 680 71 a04 13.04- 730 zi -0.29 ----397 U 706 70 1046 -fl85 zo 8.27 54? 5,92 -72 lomt-l- 1225 Z2 -14A9 71 Dowast-- 1774 Z2. AV ---AC7 f9" .4 4,40 f7.23 -7 Ela-@lh 3431 72 515 -72 2254 73 -'6fg i3 2583 617 f3-08 D--t'e- -@3 42.4 N0,9 --?.g -8.73 F, B-0, 2244 74 -- 26Y7 -73 -- V t1f.- 7.3 R4 2686, 74 3263 49,70 Z4 5 69 12.1v 5900 7.3 12.89 6, 8-h t24 70 i6o 70 uj4i'e- 4927 74 sviz 74 0-mi- 4979 74 t2.70 --8007 -7.3 -8-97 *41 &'a'ch 166 zi _ZM- zi@ 4978 Z4 -M5 -7.4 "9 74 652 14.26 7S :@060 Z4 6yof ".Doovsyr 109, 70 149 -9-Z2 f22 70 157 0.0/ J. D.-M- 28? zi 2.12 11.62 30 zi e2. 14 599 74 3.3? cm- 2f -346 15 Z 401 71 413 766 72 72 R41 -12 A63 --/fflg Z2 1.2 At D-xl-.@- 1320 72 1.4f 9.27 -13e3 -22 -A49 QJS N, B-ch 862 -7.3 120 Z2 pke- M03 '24 7-4-- D-slie- 2253 7.3 777 i87 2651 73 906 0 266 70 2.84 9w as 70 947 _Downil'"m - --2.72 589 ?1 3.71 gaz -613 71 Az? io-63 SWI4 25;28 SEVENMILE CREEK TAKE 12-9 Table 12-9 VARIOUS ON-SITE STORM WATER CONTROL METHODS AREA REDUCING RUNOFF DELAYING RUNOFF Large Flat Roof 1. Cistern storage 1. Ponding on roof by 2. Rooftop gardens constricted 3. Pool storage or fountain downspouts storage 2. Increasing roof roughness a. Rippled roof b. Gravelled roof Parking Lots 1. Porous pavement 1. Grassy strips on a. Gravel parking lots parking lots b. Porous or punctured 2. Grassed waterways asphalt draining parking lot 2. Concrete vaults and 3. Ponding and cisterns beneath parking detention measures lots in high value areas for impervious areas 3. Vegetated ponding areas a. Rippled pavement around parking lots b. Depressions 4. Gravel trenches c. Basins Residential 1. Cisterns for individual I .Reservoir of homes or groups of homes detention basin 2. Gravel driveways (porous) 2. Planting a high 3. Contoured landscape delaying grass (high 4. Ground-water recharge roughness) a. Perforated pipe 3. Gravel driveways b. Gravel (sand) 4. Grassy gutters or c. Trench channels d. Porous pipe 5. Increased length of e. Dry wells travel of runoff by 5. Vegetated depressions means of gutters, diversions, etc. General 1. Gravel alleys 1. Gravel alleys 2. Porous sidewalks 3. Mulched planters Source: Urban Hydrology for Small Watersheds. Technical Release No. 55 Table 12-10 ADVANTAGES AND DISADVANTAGES OF VARIOUS ON-SITE STORM WATER CONTROL METHODS MEASURE ADVANTAGES DISADVANTAGES A. Cisterns and 1. Water may be used for: 1. Expensive to install Covered Ponds a. Fire Protection 2. Cost required may b. Watering lawns be restrictive if the c. Industrial processes cistern must accept d. Cooling purposes water from large 2. Reduce runoff while only drainage areas occupying small area 3. Requires slight 3. Land or space above maintenance cistern may be used for 4. Restricted access other purposes 5. Reduces available space in basements f or other uses B. Roof top 1. Esthetically pleasing I . Higher structural Gardens 2. Runoff reduction loadings on roof and 3. Reduce noise levels building 4. Wildlife enhancement 2. Expensive to install and maintain C. Surface Pond 1. Controls large drainage 1. Requires large areas Storage (usually areas with low release 2. Possible pollution residential 2. Esthetically pleasing from storm water areas) 3. Possible recreation and siltation benef its 3. Possible mosquito a. Boating breeding areas b. Ice skating 4. May have adverse c. Fishing algal blooms as a d. Swimming result of 4. Aquatic life habitat eutrophication 5. Increases land value of 5. Possible drowning adjoining property 6. Maintenance problems Table 12-10 (Continued) D. Ponding on 1. Runoff delay 1. Higher structural Roof by 2. Cooling effect loadings Constricted for building 2. Clogging of con- Downspouts a. Water on roof stricted inlet re- b. Circulation through quiring maintenance 3. Roof ponding provides fire 3. Freezing during protection for building winter (expansion) (roof water may be trapped 4. Waves and wave in case of fire) loading 5. Leakage of roof water into building (water damage) E. Increased Roof 1. Runoff delay and some 1. Somewhat higher Roughness reduction (detention in structural loadings a. Rippled roof ripples or gravel) b. Gravel on roof F. Porous 1. Runoff reduction (a and b) 1 . Clogging of holes or pavement 2. Potential groundwater gravel pores (a and (parking lots recharge (a and b) b) and alleys) 3. Gravel pavements may be 2. Compaction of a. Gravel cheaper than asphalt or earth below parking lot concrete (a) pavement or gravel b. Holes in decreases impervious permeability of soil pavements N, (a and b) in. diam.) 3. Ground-water filled with pollution from salt sand in winter (a and b) 4. Frost heaving for impervious pavement with holes (b) 5. Difficult to maintain 6. Grass or weeds could grow in porous pavement (a and b) G. Grassed 1. Runoff delay 1. Sacrifice some land channels and 2. Some runoff reduction area for vegetated vegetated Qnf iltration recharge strips strips 3. Esthetically pleasing 2. Grassed areas must a. Flowers be mowed or cut b. Trees periodically (maintenance costs) Table 12-IO(Continued) H. Ponding and 1. Runoff delay (a, b, and c) 1. Somewhat detention 2. Runoff reduction (a and b) restricted measures on movement of impervious vehicle (a) pavement 2. Interferes with a. Rippled normal use (a and c) pavement 3. Damage to rippled b. Basins pavement during c. Constructed snow removal (a) inlets 4. Depressions collect dirt and debris (a, b, and c) I. Reservoir or 1. Runoff delay 1. Considerable detention basin 2. Recreation benef its amount of land is a. Ice Skating necessary b. Baseball, football, etc. 2. Maintenance costs if land is provided a. Mowing grass 3. Esthetically pleasing b. Herbicides 4. Could control large c. Cleaning drainage areas with low periodically (silt release removal) 3. Mosquito breeding area 4. Siltation in basin J. Converted 1. Low installation costs 1. Requires periodic septic tank for 2. Runoff reduction maintenance (silt storage and (infiltration and storage) removal) ground-water 3. Water may be used for: 2. Possible health recharge a. Fire protection hazard b. Watering lawns and 3. Sometimes requires gardens a pump for c. Ground-water recharge emptying after storm K. Ground-water 1. Runoff reduction 1. Clogging of pores or recharge Onf iltration) perforated pipe a. Perforated 2. Ground-water recharge 2. Initial expense of pipe or hose with relatively clean water installation b. French drain 3. May supply water to (materials) c. Porous pipe garden or dry areas d. Dry well 4. Little evaporation loss L. High delay 1. Runoff delay 1. Possible erosion or grass (high 2. Increased infiltration scour roughness) 2. Standing water on lawn in depressions Source: Urban Hydrology for Small Watershed Technical Release No. 55 30 HARBORCREEK NORTH EAST + GREENFIELDi 2000 mom mm WOO mom WOODRUFF, INC. .. .. ........ v 0 16 > Is 4 el 14 OL ART BRID 9 10 11 12 6 -0 6 V RD, HARBORCREEK 5 BACKU 3 2 PR A b . . . ........................ NORTH EAST + GREENFIELDI 20M a 20M 4wo 6000 so" WOODRUFF, INC. --:x" FERT HARBOR@REEK f NORTH EAST + -,.--GREENFI ELDi WOODRUFF, INC. a 20= 40M 4000 sooo VXIT m m m m m m m m m m m m m m m 0 EXISTING SEWE 00 ARBO REEK IST EWER 0 NFI WOODRUFF, INC. ::Z= ... ......... UNA a PICT HARBORCREEK t NORTH EAST GREENFIELDi Im a 20M 40M 6000 Sam WOODRUFF, INC. ........... ......... WAII PUT WEIGHYED C& SUBWArERSHW FOR EXaTmL4ww 77 JS V4 4 74.02 78.01 .0 7 75.4e 7765 69.72 /0 75.61 7Z. 75 u /Z 78.01 f5_ 7-5, 48 14 76.24 fs 7752 D 78.6Z 7Z.97 70.06 19 68.49- 75.80 0 HARBORCREEK Q@ z/ 72.2-9 zz 75.79 - t zi 73.Z5 Z4 7Z47 Z5 74. W NORTH EAST EXISTING LAND USE LEGENI OPEN WOODED CULTIVATED GREENFIELDI RESIDENTIAL + COMMERCIAL INDUSTRIAL swM 23:22 0 2m W@ oom *am SEVENMILE CREEK WATERSHEL EXISTINP LAND USE WOODRUFF, INC. wc7/GWFi CA, SUBWATERSNSD FOR ExisrAfG LAND ......................... 79.90 i8 55 77. 4Z 4 70..94 5 7039 6 7168 7 79.24 79-91 8z. 07 84.8? /Z 7St 90 /3 7821 14 80.99 /5 81.14 -as 81 17 79.75 -/a 75.8Z 7189 HARBORCREEK zo 79.50 Z/ 79.50 22 83.99 + + zi 60.36 Z4 d5.z9 Z5 80.465 NORTH EAST ULTIMATE LAND USE LEGEND RESIDENTIAL - AGRICULTURAl = WOODED GREENFIELDI :2-RESIDENTIAL C COMMERCIAL INDUSTRAL SWM 25;2S a 2000 *am wm Woo C. WOODRUFF, IN SEVENMILE CREEK WATERSHEI, ...... ...... W FtXT ULTIMATE LAND USE . ..... . . . r KBORCREEK i A 30if U-berf NORTH EAST soilvum Soil Alumber ENFI ELD@ Soil Alilmb4r 6 Soil Mu-ber 9 20M a 2000 46M ww so= WOODRUFF, INC. 111T too It Is jo 1 HARBORCREEK t NORTH EAST GREENFI ELDI LgafAV Mf NArIO&ot FLOW 2000 0 2000 40M 60M woo WOODRUFF, INC. m m m = = m m m m m m m = m m = m = m AV7F THE SYMSM BELOW 13 USED TO THE DATA POINTS L93TED ON THE WATER@ED MIXFF DATA ONART (TABLE -4. ?3 24 22 z If S118WATERSHED AREA OF ?'o CONCENTR4RON NUMBER ACRES MINurfs 7 1 95.40 2240 18 2 155 /Y 24.7? /0 3- 2705,9 JO-81 19 4 18039 9 5 354.77 40.47 -s -49121 92-V 7 -13132 41.49 8 213.04 ?3.a? f 8 5 % 9 382.01 92. to /0 30733 4946 16 it X.43 -6 94 14 HARBORCREEK Q@ 12 2Z 00 26-56 13 &5.84 1W.50 17 14 3979 // Y? 15 298451 32.39 11 /s ff 160610 & 38 17 48 7 62 48.35 13 18 616Y. 14 AFZ610 19 444.15 4745 20 X/ j/ 71 2 21 lv,6y 15.1;9 NORTH EAST A? 104,69 29-51 2-3 S704 26. 37 3S.05 24 12 05 80.81 X [--TOr,41- WAURSHED AREA IN ACRES 5604-54 GREENFIELDI + Am" rmr av*w wro rym cmwwLs CM Aw.4s rm4r auwwm r rpe * cmAwas swm 25:28 INC. 2000 a 2000- 4000 6000 woo SEVENMILE CREEK WATERSHU i,,WOODRUFF, SUDWATERSHED ...... JICALK 1. 199T (-@ATGK IVWA6EMC@37 PL -- AA1 fA - E & j ,7CYtKM i L-Cf- t fC E--L-7K'- V(-) Z- U f 0 -u I 0 -- 6-kic OU@J-JRI J)CPT, C)F PLAIJM(@J@ - I tkIE: eO, I fA I I I I I I I I A.PPENDIX B Calculations To Determine Increased Runoff I And I Examples f Specific On-Site Storage I I I I I I I I I APPENDIX B CALCULATIONS TO DETERMINE INCREASED RUNOFF AND EXAMPLES OF SPECIFIC ON-SITE STORAGE The procedures presented in this appendix are applicable to all unit developments which contain between 2500 square feet and 43,560 square feet of impervious surface area. Those exempt cases discussed in the text need not make the, following calculations. Developments with more than 43,560 square feet of impervious surface area must consult a qualified professional person to aid in determining their excess storm water runoff volume. By following these methods, the non-technical individual can easily determine the amount of excess storm water runoff which he is required to manage. The methods of control presented in this study, or any other approved innovative methods, may be used to manage this calculated runoff volume. Excess Storm Water Runoff Calculation Procedure Step I Determine dimensions of proposed buildings, drives, patios or other impervious areas. These can usually be found on building site plans. Step 2 Calculate impervious area. The more common shapes that will be encountered are rectangles, triangles or circles. Equations to calculate the areas of these shapes are as follows: (all dimensions are assumed to be in f eet) i) Rectangle: area (sq. ft.) = length (ft.) x width (ft.) ii) Triangle: area (sq. ft.) = 1/2 x base (ft.) x height (ft.) iii) Circle: area (sq. ft.) = 0.785 x diameter2 (ft.) Step 3 Refer to Section 4.2 and plate of volume describing the watershed in which construction is to take place. If construction is found to be along a Type I channel, then use Type I criteria. All others use Type 2 criteria. Step 4 Use Figure B-1 to find excess runoff volume to be managed. Example: Figure B-2 shows a typical site plan for proposed residential lot located along a Type I Channel. Determine the amount of excess runoff volume required to be managed. (1) Dimensions as shown on Figure B-2. B-1 (2) Impervious Area: (a) Drive: 14' x 701 = 980 sq. ft. (b) House: 40' x 801 = 3200 sq. ft. (c) Patio: 1/21 x 201 x 201 = 400 sq. ft. Total Impervious Area 6180 sq. ft. (3.) Type 1 criteria as given. (4.) From Figure B-1, excess runoff volume to be managed is 1150 cubic feet. Note: One acre contains 43,560 sq. ft. One cubic foot contains 7.48 gallons of water. B-2 FIGURE B -1 RUNOFF VOL :--FROM IMPEC?VIOUSAR 4 14 12 ZZ 77:-@ 'r Ypec r V UAf6(A'rj) =a /d r IMPFRI110W AREA 01 4/p ro 4,1,45roocr @1:1 to 7-7 7-- ARE4 _,frA _.UP rO 43,560 2 Oct.; IM1,0@W1110ZIS ARV -6190 Ll UAE Vol U AIRE 7z 2- E're'rs's RUVOA7 VOZ UME x foo 0 .r j FIGURE B-2 TYPICAL RESIDENTIAL SITE PLAN 40' x --Z House 60, R1W R1W /00, FIGURE X 3 ON-SITE STORM WATER MANAGEMENT ALTERNATE NO. I SURFACE STORAGE 75 A 1'oeep Area A Sec -tion A -A 40' zoA7,7* Houce do' 19/w /010, RIW FIGURE B-4 ON-SITE STORM WATER MANAGEMENT ALTERNATE NO-2 OVERSIZED STORM SEWER PIPE 40' House 80' Ape ReStriC7ed OU741ell- RIW Rlw FIGURE B-5 ON-SITE STORM WATER MANAGEMENT ALTERNATE NO.3 POND STORAGE 24 24 z0btio lZl Houce 60' Rlw /00, Rlw FIGURE B@-6 ON-SITE STORM WATER MANAGEMENT ALTERNATE NO. 4 UNDERGROUND TANK STORAGE N, 2,51 -5, Deep /0, 404 Houce 60' Rlw loo, Rlw I I 'I I I I I I I I I I I. I I I I IIllollum 1 3 6668 14101 1868