[From the U.S. Government Printing Office, www.gpo.gov]
PHASE II STORM WATER MANAGEMENT PLAN FOR THE LAKE ERIE WATERSHED INTERIM REPORT FOR THE PERIOD OCTOBER 1, 1994 THROUGH SEPTEMBER 30, 1995 DER GRANT/CONTRACT NO. - CZ1:94.01PE GRANT TASK NO. CZ1:94.05PE ME NO. 94465 Co-ashl PENNSYLVANI-4 -- mmm@ A REPORT OF THE PENNSYLVANIA DEPARTMENT OF ENVIRONMENTAL RESOURCES TO THE NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION PURSUANT TO NOAA AWARD NO. - NA470ZO248 OA@wl, 94WINU6 TABLE OF CONTENTS Part 1: Project Status Report Part 2: Newsletters Part 3: Draft copies of Sections 3 through 6 of the Final Report - Section 3: Watershed Characteristics - Section 4: Watershed Technical Analysis - Modeling - Section 5: Development of Watershed Technical Standards and Criteria - Section 6: Stormwater Management Techniques QI I I I I I PART 1: PROJECT STATUS REPORT I I I I I I I --A 'A A I CHESTER ENVIRONMENTAL Ref. No. 4026-02 September 27, 1995 SEP 2 7 IM Mr. John, Mong Erie County Department of Planning Erie County Court House Erie, Pennsylvania 16501 Dear Mr. Mong: Re: Lake Erie Area Watershed Stormwater Management Plan 30-Month Project Status Report I am pleased to provide the following report on the status of the Lake Erie Area Watershed Stormwater Management Plan at this the 30-month point in the project. GENERAL On March 1, 1993, Erie County authorized Chester Environmental to complete a Phase II Pennsylvania Act 167 Watershed Stormwater Management Plan for the Lake Erie Watershed. According to the requirements of the Commonwealth of Pennsylvania's agreement with Erie County and the County's agreement with Chester Environmental, the plan is to be completed by June 30, 1996. The total budget for the project is $323,818 (Chester Environmental, $230,082; Erie County, $93,736). Pennsylvania will reimburse the County 75 percent of the total project cost. The County's agreement with the Commonwealth specifies the following payment schedule: Payment for Cumulative Cumulative Payment Period Period Payment (Percent of Total) 1/2/93 - 6/30/93 $ 8,550.00 $ 8,550.00 3.5 7/1/93 - 6/30194 80,000.00 88,550.00 36.5 7/1/94 - 6/30/95 80,000.00 168,550.00 .69.4 7/1/95 - 6/30/96 74,313.50 242,863.50 100.0 WORK PROGRESS AS OF SEPTEM[BER 1, 1994 The following paragraphs describe our work progress and status of our charges to the project as of September 1, 1995. 600 Clubhouse Orive Moon Township. Pennsylvania 15108 412-269-5700, Fax 412-269-5749 Mr. John Mong Page 2 September 27, 1994 Task I-Project Mitiation This task covers the administrative work required to initiate the agreements between the Pennsylvania Department of Environmental Protection (DEP), the County, and Chester Environmental. Task 1 was completed at the inception of the project. This included meetings and negotiations with DEP, preparation of the documents required to proceed to Phase 11, and execution of our contract with Erie County. No work remains to be completed under this task. Billings under this task total $3,536 or 99.75 percent of the budgeted total ($3,548). Task 2--Project Coordination/Public Participation This task consists of project coordination and reporting requirements as well as implementing a public participation program consisting of a project newsletter, meetings with the Watershed Plan Advisory Committee (WPAC), a training session, and public hearing. Task 2 will be ongoing throughout the project. Elements of this task completed to date include conducting three Phase II WPAC meetings and issuing twelve newsletters to the WPAC members and other interested parties. Work remaining to be completed under this task consists of the continued publication of the newsletter and conducting the remaining WPAC meetings, training session, and public hearing. Charges under this task total $23,324 or 79.7 percent of the budgeted total ($29,264). Task 3--Data Collection Review and Analysis Task 3 involves the efforts required to gather, review, and analyze the basic information required to complete the technical and institutional planning steps. The following work has been completed under this task: Collection, review, and compilation of flood problem information from Flood Information Studies completed throughout the watershed. Analysis of Flood Information Studies and the extraction of data describing stream flow and velocity relationships at various locations throughout the watershed. Mr. John Mong Page 3 September 27, 1994 Collection of rainfall data from the region and the analysis of this information to produce the determination of storm volume/duration/frequency relationships for the region. Compilation, review, and analysis of stream obstruction data contained in the prior plan. Identification, inspection, and measurement of additional obstructions as required to supplement the available information. Development of initial estimates of obstruction capacities. Collection of topographic mapping covering the area and the compilation of the hard copy topographic maps into a base map. Purchase of digital elevation models spanning the area. Preparation and distribution of municipal questionnaires. Compilation of the stormwater problem information contained in the municipal questionnaire responses. Compilation of the existing and proposed flood protection facilities information contained in the returned questionnaires. Contacting DEP to obtain information relative to existing and proposed flood protection facilities in the watershed. Compilation of the existing and proposed stormwater control facility information contained in the returned municipal questionnaires. Obtaining and incorporating TIGER file data into the project GIS database. Obtaining and incorporating the County street centerline data into the project GIS database. Obtaining and incorporating the Landsat Thematic Mapper Imagery into the project GIS database. Discussing municipal questionnaire responses at the WPAC meeting. Requesting streamflow monitoring records from the City of Erie. Collecting streamflow data from U.S.G.S records. Mr. John Mong Page 4 September 27, 1994 Obtaining projected future land use information from Erie County. Work under this task is essentially complete. Charges under this task total $30,632-50 or 100 percent of the budgeted total ($30,636). Task 4--Institutional Data Preparation This task involves the evalu ation of the municipal ordinances in order to prepare a municipal ordinance matrix. This matrix is intended to display the current stormwater management provisions contained in the various municipal ordinances. Work completed to date includes: Receipt of stormwater management ordinances currently in effect in the watershed. Preliminary review of the content of the ordinance. Providing the County with a sample municipal ordinance matrix to be used in compiling the matrix for the Lake Erie Area Watershed. Consulting with members of the staff of the Erie County Planning Department concerning procedures for the assembly of the municipal ordinance matrix. Receipt and analysis of the completed municipal ordinance matrix. Compilation of overall summary municipal stormwater management ordinance matrix. Work remaining under this task consists essentially of fuW editing of the ordinance matrix and incorporation of the matrix into the plan report. Charges under this task total $2,492 or 88.0 percent of the budgeted total ($2,832). Task 5-Data Preparation for Technical Analysis This task involves the engineering work necessary to transform the raw information collected in Task 3 into a form that can be@ directly used for the later technical tasks in the overall planning program. Work completed under this task includes the following: Initial classification of the satellite imagery to produce a preliminary land use classification. Mr. John Mong Page 5 September 27, 1994 Delineation of subwatersheds and subbasins. A total of 1,603 individual subareas have been delineated. Digitization of the delineated subareas and incorporation of the subarea boundaries into the project GIS. Digital elevation models have been incorporated into the project GIS for the purpose of calculating subarea slope area characteristics. Digitization of the hydrologic soil group boundaries is ongoing. Stream segment length information has been measured and assembled for each of the 1,600 delineated subareas. Locations of reported stormwater problem areas have been transferred to the base maps for subsequent digitization. Locations of existing and proposed flood control and stormwater management facilities have been transferred to the base maps for subsequent digitization. The existing land cover database and GIS coverage for use in the hydrologic model have been completed. Locations of reported stormwater problem areas have been digitized and included in the GIS. Locations of existing and proposed flood control and stormwater management facilities have been digitized and included in the GIS. Locations of significant obstructions have been digitized into the GIS. Strearnflow velocity information for various streams and locations throughout the watershed have been extracted from published flood information studies for use in -developing travel time estimates for modeling purposes. Dimensional statistics have been developed for each of the 1,600 subareas. Digitization of the hydrologic soil group boundaries has been completed. The geographic information system based analyses required to develop input parameters for use in the Penn State Runoff Model have been completed. Mr. John Mong Page 6 September 27, 1994 The County's land use projections have been incorporated into the project GIS and estimated future conditions model input parameters have been developed. Work under this task is essentially complete with the exception of finalizing the documentation of the completed activities in the final report and appendices. Charges under this task total $49,522.50 or 92.1 percent of the budgeted total ($53,748). Task 6--Model Selection and Setup Model selection and setup involve the selection and preparation of a hydrologic model appropriate for the analysis of the existing and projected land characteristics of the watershed. Work completed to date under this task includes the following: The Penn State Runoff Model has been selected for use on this project. Input data files containing the required topology and layout information have been prepared for all of the watersheds. The dimensions of the runoff model have been expanded to accommodate the size of the Elk Creek Watershed. Data describing the physical dimensions of the subareas have been, incorporated into the model files. Testing of the model input files has been completed.. Work regarding the determination of stream segment 'information and characteristics of small lakes in the watershed is completed. All input model files have been finalized. Work on this task is essentially complete. Charges to date under this task total $22,360 or 100 percent of the budgeted total ($22,368). Task 7 Task 7 consists of the completion of the hydrologic modeling runs and the documentation of the results. Work completed under this task includes the following: Mr. John Mong; Page 7 September 27, 1994 The hydrologic model has been successfully calibrated against measured stream flows. Hydrologic model runs have been completed for the 2-, 5-, 10-, 25-, 50-, and 100-year return frequency 3-, 6-, 12-, and 24-hour duration storms. This modeling was completed for each of 25 separate watersheds. This entailed the completion of 600 individual model runs. Work remaining under this task includes completion of 25-year return frequency, 24-hour duration storm model runs under future conditions. Charges under this task total $29,896.40 or 98.2 percent of the budgeted total ($30,452). Task 8 Task 8 consists of the analysis of the results of the modeling and data collection efforts and the development of recommended standards and criteria for the watershed. Work completed under this task includes the following: Selection of the design storm duration. Selection of the design storms return frequencies. Selection of the design storm temporal distribution. Calculation of peak discharge release rate percentages throughout the watershed. Identification of permissible computational techniques. Work remaining under this task consists of the finalization of the standards and criteria based upon input received from the WPAC and the County and completion of the necessary documentation in the plan report. Charges to. date total $5,499 or 66.3 percent of the budgeted amount ($8,288). Task 9 This task consists of the assembly of the model stormwater management ordinance. As of September 1, 1995, no work had been completed on this task. However, an initial draft of the model ordinance was completed in the middle of September. As of September 1, 1995, no charges were made to the task budget of $5,616. Mr. John Mong Page 8 September 27, 1994 Task 10-Plan Report Preparation This task consists of the preparation of a report documenting the investigations, findings, and recommendations of the planning process. To date, the following work has been completed under this task: Completion of draft Section 1 --Introduction. Completion of draft Section 2--Legal Framework for Stormwater Management. Completion of draft Section 3--Watershed Characteristics. Completion of draft Section 4--Modeling. Completion of draft Section 5--Development of Watershed Technical Standards and Criteria. Completion of draft Section 6--Stormwater Management Techniques. Work remaining und er this task consists of the preparation of the report as work progresses. Charges to date under this task total $8,126 or 39.2 percent of the total ($21.620). Task 11-Plan Adoption Work under this task involves work to be performed in conjunction with securing plan adoption. This work will be completed at the close of the project. No charges have been made to this task which has a total budget of $2,210. Direct Costs This category represents cost items for the purchase of data and.materials, travel, mail, telephone, printing costs, and miscellaneous expenses. Charges to date total $12,165.76 or 62.4 percent of the budgeted amount ($19,500). STATUS OF BUDGET AND SCBEDULE The status of our budget and progress relative to the schedule contained in our contract with the County is summarized in Figure 1. This graph compares our progress and total charges ' by work task to the schedule'. -As is indicated in Figure 1, we are essentially on schedule for all tasks through Task 8. We anticipate that we will be essentially complete with the remaining Mr. John Mong Page 9 September 27, 1994 tasks, including preparation of the draft report by December 31, 1995. This will be in general accordance with our schedule with Erie County and approximately six months ahead of the June 30, 1996, completion date in the County's agreement with the Commonwealth of Pennsylvania. We estimate that our work is approximately 85 percent complete versus a scheduled completion rate of 90 percent as of September 1, 1995. Billings to that date total $188,009.16. This represents 82 percent of our total budget. The project continues to be essentially on budget relative to progress and cost. Please contact me at 269-5828 if you have any questions. -Yery -truly yours ,16ii@ 14. ^Masl P. E. Technical Manager JMM/dJe/2 Enclosures Figure 1 Status 'of Schedule and.Budget 2 3 4 5 OWN 6 7 8 9 10 Tota I 0 .20 40 60 -80 100 Percent of Total Effort Scheduled 0 Completed El Billed. I I I I I I PART 2: NEWSLETTERS I I I I I I I I I I I I I a rie an ae**.* Volume 2 Issue 5 October 1994 LakeErie Watershed Eighteen Month Project Progress Report Project Has Reached 18 Month Point On N1.arch 1, 1993, Erie County authorized the initiation of an Act 167 Watershed Stormwater Management .Plan for the Lake Erie Area Watershed. September 1, 1994 marked the 18 month point in the project. According to the requirements of Erie County's agreement with the Commonwealth of Pennsylvania, the plan is to be completed by June 30, 1996. This issue of the newsletter presents a Mustration ofstreamr comprising the LakeErie Area Watershed (stream locations and general overview of the progress that municipal boundaries extractedfrom U.S. Census Bureau TIGER FUes. has been achieved on the Lake Erie Area Watershed Stormwater Data Collection Review and Analysis Management Plan during the initial 18 month period. Activities Data collection review and analysis activities involve efforts necessary to Public gather, review, and analyze the basic information required to prepare the Participation is watershed stormwater management plan. Work completed under this category of tasks includes the following: Ongoing 1. Collection, review and analysis of Flood Information Studies completed Elements of the public participation throughout the watershed. program completed to date include conducting two Watershed Plan 2. Collection and analysis of rainfall data and determination of storin Advisory Committee meetings and volume, duration, and frequency relationships for the region. issuing ten newsletters to members of the Watershed Plan Advisory 3. Compilation of stream obstruction information. Committee and other interested parties. Public participation elements 4. Assembly of digital and hard copy base mapping. will continue throughout the project and will include additional Watershed 5. Collection and compilation of municipal questionnaire information about Plan Advisory Committee meetings, stormwater problems and facilities. continued publication of this L ke E S[ormwaler M agemenl P d newsletter, and a public hearing at the 6. Acquisition of satellite imagery of the area. close of the projecL *2 Lake Erie Stormwate.r Management Update Data Preparation for Technical Analysis Summary Activities under this category involve the engineering work necessary to transform the raw data collected under the data collection phase into a form The project is currently on schedule that can be directly used for technical analysis. Work completed under this in terms of progress achieved. In the category of tasks includes the following: coming months, work will focus on the hydrologic modeling activities 1. A total of 1,600 individual watersheds and subwatersheds have been and the use of the model to develop delineated and their boundaries digitized. appropriate stormwater control standards. The results of these 2. Digital elevation models have been incorporated into the project efforts will be discussed in future geographic information system (GIS) to be used to estimate ground slopes Watershed Plan Advisory Committee throughout the planning area. meetings. This newsletter is published semi- 3. Classification of land cover classes for the purpose of estimating runoff monthly as a means of informing characteristics has been completed. interested parties of the progress 4. Locations of storinwater problems and facilities have been digitized into of the planning process and the project GIS. encouraging their input into the planning process. We encourage 5. Dimensional statistics for each of the delineated watersheds and you to direct any questions or subwatersheds have been calculated. comments to: Data Preparation for Technical Analysis Erie County Department of Plan- ning: Model selection and setup involve the selection and preparation of a hydrologic model to be used in developing the technical stormwater management Sharon L. Knoll standards. Work completed under this category of tasks includes the following: Eric County Court House Erie, PA 16501 1 .Ile Penn State Runoff Model has been selected for use on this project. (814) 451-6336 2. Input data files containing the required watershed and subwatcrshed or topology and layout information have been prepared for all of the watersheds. Chester Environmental 3. Testing of the model input files has begun. John M. Maslanik Chester Environmental 4. Data describing the physical dimensions of the watersheds has been P.O. Box 15851 assembled into the model input files. Erie County Department Of P1 9 Eric County Court House Eric, Pennsylvania 16501 a rie mwa ana 0*1+ Volume 2 Issue 6 December 1994 Overview of Hydrologic Modeling Activities Purpose of of runoff volumes and rates under a mathematical mpresentations of the range of conditions. physical factors that affect runoff Hydrologic rates. The hydrologic model The typical structure of hydrologic typically contains a set of algorithms Modeling computer models is illustrated in to convert rainfall on a subbasin to Figure 1. As is indicated in Figure runoff and another set of algorithms Hydrologic modeling plays two roles 1, the models generally consist of to route the runoff from the subarea in stormwater management planning three major components: downstream through the stream under Act 167. First, it provides A channel. The algorithms are linked means to describe hydrologic 1. input data . Output from one becomes input to conditions in the watershed and 2. the computer program another - so as to represent the quantify the impact of existing and 3. model output integrated behavior of the watershed potential future land development system. activities on stormwater runoff and Input data typically includes land stream flows. Second, hydrologic data, stream channel data, and 'Me third part of the computer modeling provides the technical meteorologic data. Land data model is the output or results of the basis for the selection of stormwater typically includes tributary area analysis. Typical output from control standards and criteria that measurements and layout, soil hydrologic models includes are appropriate for the watershed. characteristics, land cover, and estimates of peak flow rates, This is particularly true for the ground slope. Channel data includes discharge hydrographs, total runoff development of specific stormwater information describing factors that volumes, and the contribution of release rate percentages as discussed affect the capacity and time of travel flows from the each subbasins -to in the February 1994 issue of this of stormwater runoff through stream peak flow rates experienced at newsletter. channels. Meteorologic data downstream locations. This last includes total precipitation and output is particularly important to Definition of variations in rates of rainfall over the determination of release rate Hydrologic time. percentages that are an important. aspect of , the stormwater Modeling The computer program consists of management control standards. The amount of stormwater runoff that results from rainfall and the rate at Figure 1: Hydrologic Modeling Schematic which the runoff moves through a Physical Data Meteorological Data watershed are affected by a number of Drainage areas Rainfall volume physical factors. These factors Land cover Storm duration Soil characteristics Time 4istributioa include the volume 'and rate of Ground slopeii Area distribution Channel capacity rainfall and the physical features and Channel flow velocities characteristics of the ground upon which it falls. Hydrologic modeling refers to Hydrologic Model computerized computational metho;ds L ke E S[or ler M gemenl Updale ,mr that are used to mathematically describe the effects of the various Runoff rates and volumes Contributions to :,ts,soch tsubsro:t:ad ad downstream peak flow totes factors that affect rainfall - runoff thr hot the or robed by each sablissia relationships and produce estimates _J 2 Lake Erie Stormwater Management Update Model Selection Assembly of the files that describe the hydrologic conditions that waist in over 1,4W There are a number of hydrologic Penn State Runoff specific subareas that, together, form models available for use. Among the Model the Lake Eric Area watershed. models considered for use in this Current activities consist of final watershed were the US. Soil We are currently in the final stages data input file assemble and testin& Conservation Services' IR-20 model, of assembling and testing the Penn Once this is completed, hydrologic the US. Army Corps of Engineers! State Runoff Model representations modeling under a range of BEC-1 model, and the Penn State of the Lake Erie Area Watershed. precipitation conditions will begin. Runoff Model. Of the available This includes the assembly of the models, the Penn State Runoff Model following specific model input This newsletter is published semi- has been selected for use in the Lake information: monthly as a means of informing Eric Area watershed. The Penn State Runoff Model (PSRM) was selected for A_ Subbasin physical Features interested parties of the progress of a number of reasons, including: the planning process and encourag- 1. tributary land area ing their input into the planning 1. PSRM offers the ability to 2. land slopes process. We encourage you to di- analyze the timing of flow 3. overland flow widths rect any questions or comments to: contributions originating from Erie County Department of Plan- various locations throughout B. Subbasin Hydrologic Conditions ning: the watershed. This capability is particularly important in the 1. runoff curve numbers Sharon L. Knoll evaluation of the effects of 2. 'percentage impervious area Erie County Court House various stormwater control Erie, PA 16501 tech*niques; and the C. Drainage Channel Features (814) 451-6336 development of release rate percentage control standards. 1. strearn bankftdl capacity or 2. channel travel times 2. PSRM offers flexible data 3. overbank flow adjustments Chester Environmental input and output modes. D. Meteorological Inputs John M. Maslanik 3. PSRM is widely accepted for Chester Environmental use throughout Pennsylvania 1. rainfall volumes P.O. Box 15851 for the preparation of 2. rainfall distributions Pittsburgh, PA 15244 watershed wide stormwater (412) 269-5828 management plans under Act The information listed above has 167. been assembled into model input Erie County Department of Planning Erie County Court House Erie, Pennsylvania 16501 o a ,e* a rie Volume 3 Issue I Februuy 1995 Model Stormwater Mann:Fement Ordinance Role of Stormwater Form and Content of Stormwater Management Ordinances Ordinance - In general, stormwater management ordinance provisions can be implemented by The ultimate purpose of stormwater adopting them as a single purpose ordinance or by incorporating them as management is to control surface amendments to to existing development ordinances (zoning and subdivision/land water runoff resulting from land development ordinances). However, all stormwater management ordi 'nances development activities so as to avoid should include the following key provisions that are necessary in order to the occurrence of stormwater runoff implement the performance standards and criteria of the watershed plan. related problems such as flooding, APPLICABILITY stream erosion, and sedimentation. Under the provisions of Act 167, the The activities to which the provisions of the stormwater management ordinance means through which this is to be apply must be defined. accomplished is through the STORMWATER PLAN REQUIREMENTS enforcement of local municipal ordinances that contain specific stormwater management provisions The local ordinance should precisely describe stormwater management plan which must be satisfied by land submission requirements. This includes the requirement for preparation by developers. The responsibility for qualified experts and the specification of the content and the form of the the @ adoption and subsequent information that must be included in the plan. enforcement of the ordinances lies DESIGN STORM CHARACTERISTICS with the local municipalities. Consequently, the local stormwater The Stormwater Management Plan will recommend storm frequencies, rTianagement ordinance provisions durations, distributions, and associated rainfall volumes that should be used in represent the mechanism through the design of stormwater management measures (This topic was introduced in which the stormwater management goals are accomplished. the December 1993 issue of this Newsletter). These design storm criteria should be established by the municipalities as a provision of their stormwater For this reason, one of the major management ordinances. elements of the Lake Erie Area STORMWATER MANAGEMENT CONTROL STANDARDS Watershed Stormwater Management Plan will consist of the development of model ordinance provisions. The Stormwater Management Plan will recommend specific stormwater control These model ordinance provisions standards that should be met by land developers in order to adequately manage can be used by the local stormwater runoff from their activities (This topic was introduced in the municipalities as a guide for February 1994 issue of this Newsletter). The local stormwater management modifying or supplementing their ordinances must specify these stormwater control standards. existing ordinances so as to include METHOD OF STORMWATER CALCULATIONS provisions that are critical to the effective implementation of There are a wide number of methods for estimating stormwater runoff. In order stormwater management within their L ke E S[ormwa[er Ma agemen[ L P da specific municipalities and the to ensure that the appropriate methods are used, maintain consistency throughout watershed as a whole. the watershed, and facilitaie plan review, the ordinance should specify the use of a limited number of acceptable computational techniques. *2 Lake Erie Stormwater Management Update Form and Content of Stormwater This newsletter is published semi-monthly as a means of mfomung interested parties of the Ordinances (Continued) progress of the planning process and encouraging their input into the planning process. We encourage you to drect any CONTROL TECHNIQUES questions or comments to: Each developer must select the technique or combination of techniques that are Most Faie County Department of Planning: appropriate to the specific site. However, the stormwater management ordinance Shmn L. Knoll should identify general control techniques that are proven and appropriate for (Ise in Erie County Court House the watershed. The developers are to use his catalog of approved techniques to Erie, PA 16501 select their control methodologies. The ordinance should also encourage the use Of (814) 451-6336 stormwater volume reduction measures where feasible. It should also contain design or standards for the identified control techniques. Chester Envimninental PLAN REVIEW PROCEDURES John M. Maslanik Chester Environmental 600 Clubhouse Drive The ordinance should identify the specific procedures that will be followed during Moon Township, PA 15108 the review of developers' stormwater management plan submissions. (412) 269-5828 CONTINUING MAINTENANCE PROVISIONS The o 'rdinance should require the submission of a maintenance plan for all proposed stormwater management facilities. The ordinance should also provide for the provision of construction or performance bonds and maintenance bonds consistent with the Municipal Planning Code. The ordinance may also establish a system of financing public maintenance costs. FEES The municipal ordinance may provide for a fee schedule to cover the cost of reviewing developers' plan submissions. INSPECTIONS The ordinance should include a schedule for periodic inspections of stormwater facilities during the course of construction. ENFORCEMENT REMEDIES AND PENALTIES In order to enforce the provisions of the stormwater management ordinance, municipalities should incorporate into their ordinance remedies and penalties similar to those prescribed in the Municipalities Planning Code. Erie County Department of Planning Erie County Court House Erie, Pennsylvania 16501 rie a Volume 3 Issue 2 April 1995 Review of Existing Model Ordih ance Provisions Completed The February 1995 issue of this of the 25 municipalities: municipalities in the watershed newsletter contained a discussion of currently enforce one or more of these the vital role that the local municipal I .Subdivision and Land ordinances will facilitate plan ordinances will play in implementing Development Ordinances and implementation. stormwater management throughout Regulations the watershed. The local ordinances 2. Zoning Ordinances A matrix of stormwater management will be the vehicle through which land 3. Flood Damage Prevention Provisions is provided on the reverse developers are required to include Ordinances side of this newsletter. The effective stormwater controls into their 4. Stormwater Management information contained in the matrix development projects. The Lake Erie Ordinances indicates the extent to which the Area Watershed Stormwater required stormwater management Management Plan will present The ordinances were reviewed to elements are contained in the ordinance provisions which must be determine the manner in which the ordinances currently in force in each contained in the municipalities' following general categories of municipality. As the matrix indicates, ordinance packages in order to provisions related to stormwater several of the municipalities (the 6 accomplish effective stormwater management are addressed. with existing stormwater management management. ordinances) currently have provisions I .General land use planning in effect that directly relate to specific As an initial step in the development standards requirements for the control of and ultimate adoption of the required 2. Stormwater control requirements stormwater and the design of ordinance provisions, the Erie County 3. Specified runoff calculation stormwater management facilities. Department of Planning completed a methods However, in most cases the municipal review of ordinances currently in 4. Design standards for stormwater ordinances are essentially silent on effect in the 25 municipalities in the controls stormwater control issues. In all Lake Erie Area Watershed. The 5. Erosion and sedimentation control cases, amendments to the current review determined what types of requirements ordinance packages will be required stormwater management provisions 6. Formal plan review process to implement the stormwater are contained in the existing 7. Established basis for permitting fees management plan. ordinances and the general extent to 8. Specified facilities inspection which these provisions wiU have to be schedule modified in order to accommodate 9. Identified maintenance provisions This newsletter is published semi-monthly implementation of the Lake Erie Area. as a means of informing interested parties Watershed Stormwater Management Of the 25 municipalities that are of the progress; of the planning process and Plan. The findings of this review will located in the watershed, 24 - have encouraging their input into the planning process. We encourage you to direct any be presented in the Stormwater adopted individual subdivision/land questions or comments to: Management Plan document to assist development ordinances, 21 have Eric County Departmen.t of Planning: municipalities in evaluating their adopted zoning ordinances, and 6 have David Skellic existing ordinances in light of the plan adopted stormwater management Eric County Court House recommendations. ordinances. 'ne existing stormwater Eric, PA 16501 management ordinances and current (814) 451-6336 ne scope of the review of existing subdivision and land development or Chester Environmental Lake E Slormwaler M nagemen[ [ pdale ordinances consisted of reviewing the ordinances are the preferred locations John M. Maslanik following general types of ordinances for instituting stormwater management Chester Env ironmental and regulations as they exist for each requirements. The fact that most of the 600 Clubhouse Drive Moon Township, PA 15 109 +2 Lake Erie Stormwater Management Update Lake Eric Area Watershed Matrix ofStarmwater Ordinance Provisions Dtwa rim rim 1.11=7 calmildnes @.c'.-.: a Z. Facility D"i a s.b. Wide Review kiniswomm litepectiomi Ferimakiiis masicipality tuidards C im mediod Lands standards Requirvinests Procedures I- pro'sSioas Schedule Fees Consume I Ttivesibip 0 1 0 0 0 0 010- 0 0 lSlkCr"k T'..ip 0 0 0 0 0 (D 0 1 0 0 0 Bris City 0 0 0 0 1 0 0 (D 0 1 0 0 i Scroush 0 0 0 0 0 0 (D (D 0 Fauvism, Tovaship 0 0 0 0 0 1 0 (D 0 0 0 0 Fmkft To'catbip 0 0 0 0 0 0 Q a 0 0 Girard aciroagh 0 Q (D 0 0 Girard Tircuslkip 0 0 0 0 0 Gress 0 0 Tow:.hip 0 0 0 i 0 0 (D 0 1 0 1 0 Grecefield Township C) 0 0 0 0 C) 0 ! CD 1 0 0 1 Harbotereek Toessibip 0 0 0 CD 0 0 0 i 0 1 0 0 0 LI-11C.."... 0 0 0 0 0 (D+S i (D (D A Lzarence raft 0 Tow.esi 0 0 0-+0 (D 0 11 - 0 0 0 CD (D McKs" Borough 0 0 0 0 0 01 G) 0 0 0 0 To='- 0 1 0 1 MIJ)" 9 0 1 0 0 0 0 (D Tow ip CD I ?dot* EMI lko'odgb 0 0 (D Q 0 0 0 1 0 0 Mardi F.S. Ta.% kip 0 (D (D (D (D 1 0 0' 0 0 (D 0 0 0 0 1 0 0 Spilas am (D T,.,r .h" 0 0 0 (D 1 0 J 0 0 0 0 Toussbip (D 0 0 0 0 VeTs.,:.g 0 0 0 0 0 0 0 0 0 wathostos 0 To-kip (D 0 0 0 6 o T o 0 Waserford Towswirp 0 0 0 0 0 0 CD 0 Q 1 0 0 0 0 0 0 0 0 (1) 0 0 0 0 0 Topic iiat auctioned in ordinance - will r"u"a"incis Topic caucused to ordemeace but will be feq.xId [email protected] Erie County Department of Planning Erie County Court House Erie, Pennsylvania 16501 rie an Volume 3'Issue 3 June 1995 Overview of PENNVIEST Stormwater Project Loan Program Program sanitary sewer systems. Program Funding Overview (3) The Commonwealth's stormwater and Budget management program is enhanced by PAAU 11 of 1911 has been amended the availability of funding to resolve Funds for the loans are provided by to authorize the Pennsylvania existing flood problems identified in Act 16 of 1988. These loans for Infrastructure Investment Authority watershed stormwater management StOrmwater projects have been (PENNVEST) to provide low interest plans. available since November 10, 1993, loans to governmental units for the when the PENNVEST board approved construction or rehabilitation Of (4) Municipalities which do ' not the first two loan applications. stormwater projects and best regulate stormwater management for Currently, there are a total of fifteen management practices to address Point development activities in a manner approved loans with a cumulative loan or nonpoint source pollution associated consistent with the requirements of the amount of $15 million. Nine of these with stormwater. Examples of Stormwater Management Act of 1978 projects are currently . under stormwater projects eligible for are brought into compliance prior to construction. In addition, there are funding are construction of (1) new or loan approval. These municipalities eight pending PENNVEST stormwater updated storm sewer systems to must adopt implementing ordinances project loan applications which eliminate stormwater flooding' or to consistent with the Act. -request total funding of $2.3 million. separate stormwater from sanitary Several other municipalities have sewer systems, (2) detention basins to Pennsylvania DER's expressed their intent to submit their control stormwater runoff, and (3) loan applications for stormwater stormwater facilities to implement best Role projects in 1995. management practices that reduce non- The Pennsylvania Department of point source pollution. Environmental Resources' staff act as Application Process Program technical consultants to the and Deadlines PENNVEST administrative staff. The Importance Departments engineers serve as project The Pennsylvania Infrastructure managers for each stormwater project Investment Authority has developed an This PENNVEST loan program which is funded by PENNVEST, established procedure for making provides low interest loans for beginning at the planning stage and applications for PENWEST financial Pennsylvania's municipalities to continuing through the completion of assistance. This procedure is outlined develop and upgrade infrastructure for construction. Ile Department project on the reverse side of this newsletter. stormwater drainage. This program managers provide engmieermg services has the following benefits: which include conducting planning Pending cut-off dates for the submittal consultation meetings with of applications are September 27, (1) It has made it possible for municipalities, reviewing project plans 1995, for action at the November 29, municipalities to resolve storm and specifications, rating and 1995, PENNVEST Board meeting and drainage problems which are safety recommending . projects for January 24, 1996, for the March 20, ha7_q ds and to separate stormwater PENNVEST funding, conducting 1996, Board meeting. Questions drainage from combined sewer interim and final construction concerning the PENNVEST systems. inspections, participating in and Stormwater Program in Erie County representing the PENNVEST program can be addressed to: Lake E Slormwaler M agemenl lJpdale (2) This program supplements other at preconstruction conferences and Duria Lathia PENNVEST- programs which assist assisting PENNVEST in. conducting DER communities to upgrade water and educational programs. (717).772-5661 *2 Lake Erie Stormwater Management Update PENNSYLVANIA INFRASTRUCTURE INVESTMENT AUTHORITY FLOW CHART FOR APPLICATION FOR FINANCIAL ASSISTANCE STORMWATER PROJECTS APPLICANT JOINT ACTION Obtains application fo rm PENNVEST; This newsletter is published semi- arranges Planning Consultation meeting with Planning Consultation monthly as a means of informing DER Project Manager and submits stormwater Meeting interested parties of the progress of ordinance, if existing. the planning process and encourag- ing their input into the planning T process. We encourage you to di- DER PROJECT MANAGER JOINT ACTION rect any questions or comments to: Prepares Planning Consultation Report; sends Erie County Department of to applicant; if available, applicant sends III- Predesign or Planning: stormwater ordinance to DER for review, if preapplication meeting proposed. David Skellie Erie County Court House Erie, PA 16501 APPLICANT APPLICANT (814) 451-6336 If required, adopts ordinance in compliance Designs project and or with Act 167, and ensures compliance with W Watershed Itormwater Management Plan, if prepares documentation. appropriate. Chester Environmental John M. Maslanik T Chester Environmental APPLICANT PENNVEST P.O. Box 15851 Completes Application and sends to PENNVEST Board Pittsburgh, PA 15244 PENNVEST for processing, Action (412) 269-5828 1 -TP--PLICANT, DER, APPLICANT AND PENNVEST CONTRACTOR Loan Closing Preconstruct ion Meeting APPLICANT Start construction Erie County Department of Planning Erie County Court House Erie, Pennsylvania 16501 rie a Volume 3 Issue 4 August 1995 Preliminary Proposed Stormwater Control Criteria Introduction The following storm characteristics Storm Volumes have been developed for use in the Previous issues of this newsletter have Lake Erie Area Watershed: Storm volumes associated with the discussed the concept of stormwater 24 hour duration mean annual, 10, control standards and criteria and their Storm Duration 25, and 100 year return frequency application in the Lake Erie. Area storms were determined from Watershed. The hydrologic modeling The recommended storm duration for previous research to be as follows: z M in the watershed is the 24 hour work required to establish standards and use criteria appropriate for this watershed storm. This value was selected because Mean annual storm = 2.62 inches the hydrologic modeling indicated that, 10 year storm = 3.75 inches has been completed and recommended 0 for the great majority of the subbasins 25 vear storm = 4.61 inches stormwater management standards and . 0 criteria have been developed. This in the watershed, the 24 hour duration 100 year storm = 6.19 inches storm created the largest peak discharge newsletter presents these recominended standards and criteria. They will be of the candidate durations tested. As a Storm Distribution further discussed at a future Watershed result, the use of the 24 hour storm Plan Advisory Committee meetin1g. represents an appropriate and The U.S. Soil Conservation Service conservative criteria. Type 11 Synthetic Storm Distribution Storm has been selected for use in the Lake Storm Return Frequencies Erie Area Watershed. This storm Characteristics distribution is supported by extensive It is recommended that stormwater research and is the distribution most Criteria management facilities in the watershed frequently used in stormwater One element of the stormwater should be designed to control the mean management calculations. management standards and criteria annual, 1,0 year, 25 year, and 100 year deals with describin- the return frequency storms. The mean Runoff Control annual storm was included because this characteristics of the rainfall events to general.ly represents the threshold of Standards be used to develop the required storms producing overbank flooding controls. The critical rainfall event Runoff control standards refer to characteristics are as follows: The 100 year return frequency storm limits placed upon the peak rate of event was selected because a number . of discharge to be permitted following identified obstructions have capacities 1@ 1. An identified duration of the less than the flows from storms of this completion of land development particular rainfall event. activities (post development magnitude, and because control of the conditions). The basic runoff control 2. An identified frequency of 100 year storms will tend to preserve standard recommended for use in the occurrence of the storm event. the flood plain and floodway watershed is that the peak rate of boundaries as defined in completed dischar-e from a land development flood insurance studies. 3. An identified volume or total site should not exceed the rate that amount of rainfall that can be The intermediate 10 and 25 year return occurred prior to development (pre- expected from a particular storm. frequency storms were selected in order development). This minimum control verify that the performance of runoff standard may be waived if the 4. An identified distribution or control systems will generally parallel municipality determines that the Lake E Slormwaler M nagemen[ L P date pattern of precipitation falling discharge will be made to Lake Erie or during the storm. predevelopment conditions between the a properly designed regional upper and lower control boundary stormwater control facility through conditions. *2 Lake Erie Stormwater Management Update adeq uately designed and sized detention techniques in order to meet The application of the indicated release stormwater conveyance facilities. the basic runoff control standard. In rate percentages will serve to prevent these areas, the post development peak stormwater control efforts from The hydrologic analysis identified rate of discharge is limited to either inadvertently creating worse problems areas in the watershed where adequate 70%, 80%. or 90% of the pre- further downstream. They will also protection requires that further development peak dischar ge rate. introduce a factor of safety into the limitations to the allowable peak rate Areas of the watershed for which the regional slormwater management of discharge are appropriate if the use of these release rate percentages is program. developer intends to use stormwater recommended are illustrated below. I I Release Rate Percentage 70 80 90 100 -W T Ah- Proposed Stormwater Runoff Control Sta ndards Map Erie County Department of Planning Erie County Court House Erie, Pennsylvania 16501 PART 3: DRAFT COPIES OF SECTIONS 3 THROUGH 6 OF THE FINAL REPORT SECTION 3: WATERSHED CHARACTERISTICS SECTION 4: WATERSHED TECHNICAL ANALYSIS - MODELING SECTION 5: DEVELOPMENT OF WATERSHED TECHNICAL STANDARDS AND CRITERIA SECTION 6: STORMWATER MANAGEMENT TECHNIQUES LAKE ERIE AREA WATERSHED STORMWATER MANAGEMENT PLAN SECTION III WATERSHED CHARACTERISTICS GENERAL DESCRIPTION The designated Lake Erie Area watershed is located in Erie County in northwestern Pennsylvania. The watershed spans the northern part of the county 39 miles east to west and extends between 2.5 and 12.7 miles in a north to south direction, encompassing a total area of approximately 360 square miles along the shore of Lake Erie. The watershed includes all of the land in Erie County that drains to Lake Erie, excluding the Conneaut Creek watershed that empties into Lake Erie at Conneaut, Ohio. Portions of the watershed lie outside of Erie County in the states of New York and Ohio. A general watershed map is presented as Plate P(LITICAL:FE: T:UMS.'"..- ........... ...... ......... A total of 25 Pennsylvania municipalities are situated in whole or in part within this watershed. These municipalities are listed in Table III-1. Table III-1 Watershed Municipalities Conneaut Township McKean Borough Elk Creek Township McKean Township Erie City Milkreek Township Fairview Borough North East Borough Fairview Township North East Township Franklin Township Platea Borough Girard Borough Springfield Township Girard Township Summit Township Greene Township Venango Township Greenfield Township Washington Township Harborcreek Township Waterford Township Lake City Borough Wesleyville Borough Lawrence Park Township Lake Erie SWMP 4026-02 Lake Erie SWMP 111-2 4026-02 ............. . ................. ..........M .................. ............. ............. .. ................. TOPOGRAPHY The Lake Erie Area watershed lies within two physiographic provinces. The plain adjacent to Lake Erie is located in the Eastern Lake Section of the Central Lowland Province, while upland areas of the watershed are contained in the Glaciated Section of the Appalachian Plateaus Province. Each physiographic province and its respective section is separated from the other by an erosional scarp running from southwest to northeast through the County, approximately three to four miles inland from Lake Erie. The dominant topographic features of the watershed are the 47 miles of shoreline on Lake Erie and Presque Isle, which forms the bay and harbor for the City of Erie. Except for the relatively level western third of the watershed and the three to four mile wide lake plain, the remainder of the watershed is characterized by rolling hills. The watershed is split by numerous valleys formed by erosion and containing streams that empty into Lake Erie. Elevations range from the average Lake Erie elevation of 571 feet above mean sea level to 1,550 feet above mean sea level at the southern edge of the watershed in Greenfield Township. GEOLOGY The bedrock of the Lake Erie Area watershed was formed from sediments deposited on the floors of ancient seas. The sedimentary rock layers underlying the county are from 6,000 to 7,500 feet thick. Shale of the Upper Devonian age underlies most of the soils, developing from layers of silt and clay alternating with thin strata of sandstone. Sandstone that was formed from 'sandy sediments caps some of the higher hills. With the exception of Pleistocene age sands at Presque Isle, rocks of the Pennsylvanian system are exposed in the Lake Erie Area watershed. The Cattarugus Formation of the Pennsylvanian system consists primarily of red, gray, and brown shale and sandstone. The Conneaut Group of the Cattarugus Formation includes alternating gray, brown, greenish, and purplish shales and siltstones. Erie County was covered by at least three different glaciers, the last glaciation occurring approximately 10,000 to 15,000 years ago. As the glaciers melted and receded, they left the Lake Erie SWMP 111-3 4026-02 landscape covered, with debris or glacial till that was carried from the north by the ice. The glacial till consists of a mixture of former soils and some granite, limestone, quartzite, and sandstone. The till also contains various amounts of sandstone and acid shale bedrock that was ground into fine particles by the ice. This glacial material ranges in size from clay particles to boulders. SOILS Soils in the Lake Erie Area watershed can be divided into two broad groups based on as sociation with a specific parent material. These groups are soils formed in unconsolidated water sorted materials and soils formed in glacial till. The predominant soil associations in the Lake Erie Area Watershed include the following: 0 Conotton-Birdsall Association * Wayland-Chenango-Braceville Association 0 Canadice-Caneadea Association * Erie-Langford Association 0 Sheffield-Platea Association 0 Venango-Cambridge Association In addition, soils can be further categorized by hydrologic groups which are determined by. a soil's infiltration rate. Many factors influence infiltration rate, including physical composition, chemical composition, dominant slope, and depth of soil profile. The Soil Conservation Service (S.C.S.) has defined groups of soils having similar hydrologic properties which directly influence the volume and rate of stormwater runoff. These hydrologic soil groups are defined as follows. Group A: Soils having a high infiltration rate, even when thoroughly wetted, and consisting of deep, well to excessively drained sands or gravels. Group B: Soils having a moderate rate of infiltration when wetted and consisting chiefly of moderately deep to deep, moderately well to well drained soils with moderately fine to moderately coarse texture. Lake ae SWMP 111-4 4026-02 Group C: Soils having a slow rate of infiltration when thoroughly wetted, consisting chiefly of soils with a layer that impedes movement of water or soils with moderately fine to fine texture. Group D: Soils having a very slow rate of infiltration rate when wetted and consisting chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a claypan or clay layer at or near the surface, and shallow soils over nearly impervious material. As the soil descriptions imply, runoff potentials increase from a minimum for Group A soils o a maximum for Group D soils. Soils along the lake plain were formed in unconsolidated water sorted materials. These soils have substrata of sands, silts, and gravel and are t characterized by slow and very slow infiltration rates. Therefore, they fall in between the C and D hydrologic classes. Soils in upland areas in the central and northeastern portions of the watershed were primarily formed in glacial till. These somewhat poorly drained soils are in the C hydrologic class. For the purposes of classifying soil types for stormwater management, this investigation identified two additional classifications: water bodies and urban land. Water bodies represent areas covered by water, a condition which results in direct runoff of precipitation. Urban land consists of land which is so altered by earth moving or so obscured by buildings or other structures that the original soils cannot be identified. In some places, cuts have removed all or nearly all the natural soil horizons. In other places, fills have buried the original soils. Urban soils are generally assigned Group C hydrologic characteristic reflecting the characteristics of the predominant natural soils i ni the area. A map illustrating the distribution of soil groups throughout the watershed is provided in Plate IH-2. The distribution of soil groups throughout the watershed was determined based upon soil series information mapped on the S.C.S. soil survey for Erie County. The aggregation of individual soil series into appropriate hydrologic soils groups was performed using soil classification information from S.C.S. Technical Release 55. CLIMATE Climatic data are available from the Weather Bureau station at Erie.. The average annual temperature is about 47 degrees Fahrenheit. The mean annual freeze-free period is about Lake Erie SWMP 111-5 4026-02 195 days, being extended by about 45' days per year by the moderating effect that the lake waters exert on the temperature. The summer mean temperature is about 67 degrees Fahrenheit and the winter mean is about 27 degrees Fahrenheit. PRECIPITATION Long term precipitation data is available from the Erie airport weather station. Normal annual precipitation at this station totals 39.39 inches and is well distributed throughout the year. Maximum precipitation occurs during the month of September (3.89 inches) while the minimum month in terms of precipitation is February (2.12 inches). The annual snowfall in the winter months exceeds 54 inches, with heavy snow sometimes experienced in late April. Snow is produced as polar air masses travel south over unfrozen lake waters. The air masses absorb considerable amounts of moisture in these lower levels as they move over the Great Lakes. As the warm, moistened lower air parcels reach land and rise through the cold air above, heavy snow squalls are produced that are capable of depositing 12 to 24 inches of snow on the leeward side of the lake. Lake Erie is subject to this "lake effect" snowfall during November and December. As the lake surface freezes over, snowfalls of this type become less frequent. HYDROLOGY The portion of the watershed covered by this plan consists of approximately -- square miles of Erie County that drains to Lake Erie, excluding the Conneaut Creek watershed that empties into Lake Erie at Conneaut, Ohio. The designated Lake Erie Area watershed is actually a number of individual watersheds that drain into Lake Erie. The watershed also includes areas which drain directly into the lake without well defined stream channels. The major named streams and tributaries included in the Lake Erie Area watershed are listed in Table EII-2. U. S. Geological Survey Stream Gauging Stations The United States Geological Survey (U.S.G.S.) publication Water Resources Data for Pennsylvania indicates that two long term, currently operating stream gauging stations are located in the Lake Erie Area watershed. The first station is located on Raccoon Creek near West Springfield on the upstream side of a highway bridge on Sanford Road. The second gauge is on Brandy Run near Girard, 100 feet upstream from a highway bridge on Tannery Road. The Raccoon Creek station has been in Lake Erie SWMP 111-6 4026-02 operation since October 1968 while the period of record for the Brandy Creek gauge I dates back to May 1986. The U.S.G.S. also operates a crest gauge partial record station on Mill Creek at the 38th Street Bridge. Table 111-2 Named Streams Cascade Creek Mill Creek Crooked Creek Raccoon Creek Eightmile Creek Sevenmile Creek Scott Run Elliots Run Elk Creek Sixmile Creek Brandy Run Sixteenmile Creek Falk Run . Baker Creek Goodman Run Trout Run Halls Run Turkey Creek Lamson Run Twelvemile Creek Little Elk Creek Twentymile Creek Porter Run Walnut Creek Fourmile Creek Bear Run Garrison Run Beaver Run Marshall Run Wilkins Run McDannel Run . ............ .... .. . .. ........ ... ..... OEM Delineated Flood Prone Areas Stream reaches which are identified as prone to flooding under 100 year flood conditions in Flood Insurance Studies published by the U.S. Department of Housing and Urban Development are illustrated on Plate 111-3 (located in the map pocket appended to this report). Reported St6rmwater Problem Areas The delineated flood prone areas established by flood insurance studies relate primarily to stream flooding during major storm events. As such they do not provide information concerning more minor flooding problems or stormwater problems separate from stream flooding such as street flooding, soil erosion or stormwater pollution instances. Lake Erie SWMP 111-7 4026-02 Each of the municipalities in the watershed was contacted to solicit information relative to stormwater conditions which are perceived locally to be problems. In many cases, these problems may be somewhat localized, and related to local drainage limitations apart from stream flooding and may occur at a high frequency. Also, information relative to stormwater problems in addition to flooding (i.e., accelerated erosion, sedimentation and water pollution) was requested. Data obtained through these efforts were supplemented by a review of Flood Insurance Studies conducted in the watershed to produce the listing of identified stormwater problem areas that is presented in Table 111-3 and illustrated on Plate 111-3 (located in the map pocket appended to this report). A total of 109 specific problem areas were reported in 15 of the municipalities in the watershed. The predominant type of stormwater related problem reported by the municipalities is flooding. Over 70% of the individual problems were reported as flooding problems and additional approximately 20% of the problems were described as a combination of flooding accompanied by stream bank erosion and sedimentation. The remaining approximately 10% of the reported problems were attributed specifically to soil erosion and sedimentation. Suggested solutions were offered for 70 of the reported problem areas. The suggested solutions include structural approaches such as constructing new or increasing the capacity of existing storm sewers, increasing the capacity of culverts, and constructing stormwater detention facilities. Also included are such remedial actions as stream dredging for the removal of accumulated silt, the clearing of debris from trash racks, culvert and bridge openings and the removal of obstructions from the stream bed. Improvements to the existing storm sewer systems are the predominant types of solutions identified (51% of the cases). Efforts to clea@ the stream channel are offered as a solution to existing problems is roughly 29% of the cases. Providing erosion protection, increasing stream channel capacity, and employing runoff detention basins are identified as potential solutions to a much lesser extent. All of the suggested solutions offered restore or increase hydraulic capacities. It is important to note that the ultimate success of any of these efforts will require that the incremental increases in hydraulic capacity not be offset by future increases in stormwater runoff. The nature of the problems c urrently encountered in the watershed and the types of solutions increase the importance of effective stormwater management in the watershed. Lake Erie SWMP 111-8 4026-02 Table 111-3 Summary of Reported Stormwater Problems Number of Types of Map Properties Properties Code Municipality Description Stream/Location Reported Causes Frequency Affected Affected Pioposed Solutions PA Conneaut Township No response PH-1 Elk Creek Township Hooding Little Elk Creek Sedimentation n/a n/a A, R Stream dredging PC- I Eric City Flooding Mill Creek Volume > I per year 2- 10 R, C -.n/a PC-2 Erie City Flooding Cascade Creek Volume, illegal sanitary connections < I per year > 10 R Remove illegal connections sanitary sewers PC-3 Eric City Flooding Cascade Creek Volume, illegal sanitary connections < I per year 2- 10 R Remove illegal connections, sanitary sewers --clean-sewer-_ PCA Erie City Flooding Cascade Creek Volume < I per year 2- 10 R Charge grade, increase pipe size, remove illegal connections PC_5 Eric City Flooding Mill Creek Volume > I per year I C Separate sewers combined sewers PC-6 Erie City Flooding Unnamed Volume, velocity < I per year n/a n/a PC-7 Eric City Flooding McDanncl Run Volume < I per year 2-10 .-----R Clean Mouth, upsize pipe PD- I Fairview Borough Flooding, sedimentation Trout Ran Volume, obstmetion > I per year -2-10 A, I _n/a PD-2 Fairview Borough Erosion Trout Run n1a n/a >-10- R, C PD-3 Fairview Borough Flooding, erosion, _ Trout Run Volume, velocity > I per year 2- 10 _U, R _n/a PDA Fairview Borough flooding, erosion, Trout Run Volume, velocity, obstruction, > I per year 2-10 U, C n/a sedimentation, landslide direction PD-5 Fairview Borough Flooding Trout Run Volume > I per year > 10 R, C n/. PD-6 Fairview Borough Erosion, landslide Trout Run Volume, velocity > I per year _U n/a PE- I Fairview Township Flooding Bear Run Obstruction > I per year 2- 10 U. A. R Remove debris and beaver dams and.realign channel- PE-2 Fairview Township Flooding Unnamed Volume, direction > I per year 2- 10 R, I Increase storm sewer sizes, use .vate lake as retention brasin Fairview Township Erosion Trout Run Volume, veloci 2-10 U, R Install Velocity dissipators PE-3 Trout Run Volume, directi < I per year 2-10 < I per year PEA Fairview Township Flooding, erosion on U, R Install storm sewer--- Table 111-3 Summary of Reported Stormwater Problems Number of Types of' Map Properties Properties Code Municipality Description SLreani/Location Re tied Causes Frequency Affected Affected Proposed Solutions PE-5 Fairview Township Erosion Unnamed Velocity, direction > I per year 2- 10 R Install storm sewer PE-6 Fairview Township Flooding Unnamed Obstruction > I per year 2- 10 R Increase storm sewer sizc--- PE-7 Fairview Township Flooding Unnamed Volume > I per year 2-10 _R__ In-stall storm sewers & catch basins_ PE-8 Fairview Township Flooding, erosion Walnut Creek Volume, obstruction > I per year > 10 R Increase storm Sewer SiLC & install catch basins PE-9- Fairview Township Flooding, erosion Walnut Creek Volume, velocity > I Per Year > 10 R Install stinin sewers & catch basins PE-10 FairvicwTownship Flooding Walnut Creek Volume, direction, obstruction > I per year 2-10 U, R Remove debris and realign channel PE-11 Fairview Township Erosion Porter Run Volume, direction > I per year 2-10 U Install velocity dissipalor. lengthen culvert, realign channel PE-12 Fairview Township Erosion Elk Creek Volume, direction > I per year 2-10 U, A Install velocity dissipator PE- 13 Fairview Township Erosion Brandy Run Volume, velocity, direction > I per year R/U R Install velocity dissipator, lengthen culvert PE-14 - Fairview Township Flooding Trout Run Obstruction > I per year I- -Road flooding Remove debris, install debrisgratc PE-15 Fairview Township _floodir% erosion Unnamed Direction > I per year 2-10 R Install culvert PF- I Franklin Township Flooding Little Elk Creek Volume, obstructions < I per year n/a n/a- n/a PG-.I---- Gi.rard Borough No response PH- I Girard Township Flooding Unnamed Volume, velocity > I per year I R Storm sewer construction (completed) PI Greene Township None reported Pi- Greenfield Township No response PK- I tlarborcreck Township Flooding Fourritile Creek Lack of maintenance of drainage way > I per year 2-10 U, R Improved maintenance PK-2 Harborcreck Township Flooding Unnamed Volume > I per year > 10 R n/a PK-3 Harborcreek Township Flooding, erosion Unnamed Volume, obstruction < I per year > 10 R Improved maintenance PK_4 Harborcreck Township Flooding sixmile Creek Obstruction < I per year 2-10 R Improved maintenance PK-5 Harborcreck Township - Hooding Unnamed Volume, ohs - cdon > I per year > 10 R n/a PK-6 Hai Flooding Sixmile Creek Obstruction < I per year 2-10 _R n/a M M410 M M M= M M Table 111-3 Summary of Reported Stormwater Problems Number of Types of Map Properties Properties -Code- Muni'll'ality Description Stream/Location Reported Causes Frequency Affected Affected Proposed Solutions PK-7 - _11arborcreek Township Flooding Sixmile/Sevennaile Volume > I Per year > 10 R_ Impioved maintenance PK-8 Harborcreek Township Flooding Unnamed Lack of maintenance of drainage way > I per year > 10 U. R Improved maintenance PK-9 Harborcreck Township Flooding Sevenmile Creek Volume > I per year > 10 U, R Improved maintenance PLA Lake City Borough Erosion Unnamed Direction n/a I n/a -,n/a- PL-2 Lake City Borough Erosion, landslide Elk Creek Volume, direction n/a I n/a n1a _PL-3 -Lake City Borough Hooding Elk Creek Volume n/a >10 n/a n/a PL-4 Lake City Borough n1a unnamed n/a n/a n/a n/a n/a PL-5 Lake City Borough n/a Unnamed n/a n/a n/a n/a __n/a PL-6 LAke City Borough Wa Unnamd. tu'a. n1a. Pja ul'a Pja PL-7 Lake City Borough n/a Unnamed n/a n/a n/a n/a _n/a PL-8 Lake City Borough Flooding Unnamed Volume n/a 2-10 n/a n/a PL-9__ -U, kc City-Bo-rough n/a Unnamed n1a n/a > 10- n/a PIAO Lake City Borough n/a Elk Creek volume n/a I D/a n/a PI.- I I Lake City Borough Flooding Elk Creek Volume n/a > 10 PL-12 Lake City Borough Flooding. pollution Elk Creek Volume n/a > 10 n/a _n/a Pm4 Lawrence Pui k Township Flootling Four Mile Creek Obstruction < I per year > 10 R, C Keep sucains clear oftleluis, eliminate multiple bridge piers PM-2 Lawrence Park Township Flooding Four Mile Creek Obstruction < I per year I C Keep streams clear of debris, eliminate multiple bridge piers PN McKean Borough None reported PO_ I McKean Township Flooding Elk Creek Volume, obstruction. < I per year 2- 10 U, R. C. I n/a .PO-2 McKean Township Flooding, erosion Elk Creek Volume, velocity < I per year 2-10 R, C, I n/a PO-3 -McKean Township Flooding ElkCreek Volume < I per year 2-10 U, A. R, C. I _A/a POA McKean Township Flooding Elk Creek Volume < I per year 2-10 A. R n/a PP_ I Millcreck Township Flooding Mill Creek Volume, velocity < I per year I _R,C n1a PP-2 Millcreck Township Flooding Mill Creek I Volume -1-2-10 1 Roadway Enlargeculvert Table 111-3 Summary of Reported Stormwater Problems Numberof Types of Map Properties Properties Code Municipality Description Stream/Location Reported Causes Frequency Affected Affected Proposed Solutions PP-3 Millcreck Township Flooding Mill Creek Volume < I per year 2- 10 R,C Revamp @totin sewer syst -tit PP-4 Millcreck Township Flooding Mill Creek Volume < I per year 2- 10 R Install levees PP-5 Millcreck Township Flooding Mill Creek Volume < I per year 2- 10 R Enlarge Storm Sewers PP-6 Millcreek Township Flooding Mill Creek Volume, obstruction < I per year I R Clear channel PP-7 Millcreck Township Flooding Walnut Creek Volume < I per year 2- 10 R Revamp storm sewersystem PP-8 Millcreek Township- Flooding Walnut Creek Volume, obstruction > I per year > 10 It Install detention facility PP-9 Millcreck Township Flooding Walnut Creek Volume. obstruction < I per year 2-10 R Revamp storm sewer system PP-10- -Millcreck Township Flooding Walnut Creek Volume < I per year I C Reroute stor.m sewer PP- I I Millcreek Township Flooding Walnut Creek Volume < I per year 2-10 R_,.C -Dredge Beaver Run PP- 12 Millcrcek Township Flooding Walnut Creek Volume < I per year 2- 10 R, P Stormwater detention, revamp storm sewers PP- 13 Millereek Township Flooding, erosion, Scott Run Volume, velocity, driection, < I per year 2- 10 U. C Improve stream channel or install storm Landslide obstruction sewers- PP-. 14 Millcreck Township Flooding Cascade Creek Volume, obstruction < I per year > 10 R Revamp channel and son in sewer PP-15 Millcreek Township Flooding Cascade Creek Volume, obstruction < I per year 2- 10 C Enlarge box culvert PP- 16 Millcreck Township Flooding Cascade Creek Volume, obstruction < I per year 2- 10 C Enlarge storm sewer P P- 17 Millcreek Township Flooding Cascade Creek Volume, obstruction > I per year 2- 10 R, C Install storm sewer & add downstream capacity PP- 18 Millcreck Township Flooding, sedimentation Cascade Creek Volume, obstruction > I per year 2- 10 C Clear channel PP-19 -Millcreck Township Flooding Cascade Creek Volume. obstruction __?@ I per year 2- 10 C Clcarchannel- PP-20 __ Milicreek.Township--- Flooding Cascade Creek Volume < Iper year 2- 10 R Install storm sewer system PP-.21 -Millcreek Township Erosion, landslide Cascade Creek Volume, velocity > Iper year 2- 10 R.. P Siabilize slopes and channel PP-22 Millcreek Township Flooding Cascade Creek Volume, obstruction > I per year 2- 10 R Add detention capabilities and clear obstructions from culvert PP-23 -Millcrcek Township Flooding Marshall Run Volume, obstruction < I per year 2-10 R Provide detention & revamp storm sewer PP-24 Millereek Township Flooding, erosion, Unnamed Volume, velocity, obstruction > I per year 2- 10 R Clear basin and outlet sedimentation PP-25 Millcreek Township Flooding, sedimentation Marshall Run Volume, obstruction > I per year 2- 10 _R Revamp channel PP-26 Millcreek Township Flooding Marshall Run Volume, obstruction > I per y - 2- 10 R Install storm sewer system PP-27 Millcreek Township Flooding Marshall Run Volume, obstruction > I per year - 10 C Provide detention facilities PP-28 Millcreek Township Flooding Marshall Run Volume, obstruction > I per year I > 10 R, C Revamp storm sewer system or provide Table 111-3 Summary of Reported Stormwater Problems Number of Types of Map Properties Properties Code Municipality Description Stream/Location Reported Causes Frequency Affected Affected Proposed Solutions detention PP-29 Millcreek Township Flooding Marshall Run Volume, velocity > I per year 2- 10 C, I Revamp storm sewer system or provide detention PP-30 Millcreek Township Erosion, sedimentation Marshall Run Sedimentation > I per year I R_ Clear basin and outlet structure-- PP-31 Millcreck Township Flooding Marshall Run Volume, obstruction > I per year 2- 10 R Revamp storm sewers PP-32 Milicreek Township Flooding Marshall Run Volume, velocity, obstruction > I per year n/a Roadway Increase sic Win sewer capacity PP-33 -Millcreek Township Flooding Marshall Run Volume, obstruction > I per year 2- 10 R Divert stormwater, install storm sewer PP-34 Millcreek Township Flooding, erosion Marshall Run Volume, velocity, obstruction > I per year 2- 10 C Install debris deflector, extend storm sewer PP-35 Millcreck Township Erosion Unnamcd Velocity > I per year I R PP-36 Millcreck Township Flooding Wilkins Run Volume, obstruction > I per year- 2- 10 C Provide drainage PP-37- Millcreek Township Flooding, Wilkins Run Volume, obstruction < I per year 2- 10 C PP-38 Millcreck Township Erosion Unnamed Volume, velocity > I *pcr year 2- 10 R Install storm sewers, stabilize banks PP-39 Millcreck Township Flooding Unnamed Volume < I per year 2- 10 R. C Revamp storm sewers, install channel PP-40 Millcreek Township Flooding Unnamed Volume < I per year 2- 10 R. C Revamp storm sewers, install channel PP-4 I. Millcreck Township Flooding Unnamed Volume, obstruction < I per year 2- 10 Revamp storm sewers PQ North East Borough None reported PR- I N EastTownship Flooding Sixteen Mile Creek n/a ft/a n/a n/a n/a PR-2 North East Township Flo6ding Sixteen Mile Creek Volume n/a n/a n/a n/a PR-3 North East Township Flooding Sixteen Mile Creek Volume n/a n/a n/a n/a PR-4 North East Township Flooding, erosion Sixteen Mile Creek Volume, obstruction n/a n/a n/a _n/a PR-5 North East Township Flooding, erosion Sixteen Mile Creek Volume, obstruction n/a ft/a n/a Improve driveway sluice pipes .PR-6 North East Township Sedimentation Sixteen Mile Creek Volume, direction < I per year 2- 10 A,R,C -Divert flow------ PS Platea Borough None reported FT Springfield Township No response PU I SummitTownship Flooding Walnut Creek Volume > I per year 2- 10 R,C n/a Table 111-3 Summary of Reported Stormwater Problems Number of Types of Map Properties Properties Code Municipality Description Stream/Location Reported Causes Frequency Affected Affected Proposed Solutions Pv VenangoTownship None reported Pw Washington TownsNp None reported PX Waterford Township No response Py- I Wesleyville Borough Flooding Fourmile Creek Volume, velocity > I per year n/a -n/a ftha Westeyville Borough Flooding Fournaile Creek Volume, velocity > I per year n/a n/a nh PY-3 Wesleyville Borough Flooding Fourmile Cfeek Volume, velocity > I per year n/a n/a n/a Types of Properties Affected: A agricultural C commercial I = industrial R = residential U = undeveloped Development in Flood Hazard Areas Stream reaches identified as being prone to flooding under 100 year storm conditio ns in Flood Insurance Studies are identified previously in Plate 111-3. Development in the areas adjacent to these flood prone areas were characterized by analyzing the current land use within 100 feet of the identified flood prone stream reaches. This was accomplished by calculating the amounts land occupied by various land use classes that lie within the areas within 100 feet of each side of the identified stream reaches. This technique produced the approximate distribution of land use activities that lie in proximity to stream reaches identified as flood hazard areas in the Flood Insurance Studies. This information is summarized in Table 111-4. Information obtained from the watershed municipalities through the municipal questionnaire also provides an indication of the nature of development in areas affected by stormwater drainage problems. The municipalities were asked to indicate the types of properties affected by reported stormwater drainage problems and to estimated the approximate number of properties affected. Residential properties were identified as being affected by 76% of the problems for which the data was reported. Commercial properties were associated with 33% of the problems, agricultural or undeveloped in 20% of the cases, and industrial in 7% of the cases. Approximately 80% of the problems were reported to affect 10 or fewer properties and 20% were reported to affect more than 10 properties. Table 1111-4 Distribution of Land Use in Flood Prone Areas Percent of Total Area Land Use Classification Adjacent to Flood Prone Stream Reaches Residential Commercial / Industrial Mixed Residential Commercial Agriculture Forest Barren Lake Erie SWMP 1111-15 4026-02 . .. .. . ....... . ........ .... Stream obstructions are defined as structures or assembly of materials which may impede, retard or change flood flows. Typical obstructions include bridge crossings, culverts, piers, suspended pipelines, etc.. Information describing the dimensions, condition and flow capacity of approximately ????????? separate stream obstructions was assembled during the preparation of this plan. The approximate locations of these obstructions are illustrated in Plate 111-4 (located in the map pocket appended to this report). The prior 1981 Stormwater Management Plan served as the primary source of information describing the size and configuration of obstructions. This information was supplemented by field investigations and site visits to 77 obstruction locations. The capacities of the obstructions were estimated based upon field measurements and the application of procedures outlined in the U. S. Department of Transportation's publication Hydraulic Design of Highway Culverts. The estimated capacities represent submerged but not surcharged conditions with inlet control. Calculated obstruction capacities are presented in Table A-1, located in Appendix A. Capacities are presented in terms of adequacy as compared to estimated flood peaks at each location for various flood return frequencies. The flood peaks were estimated using the PSU IV Method for estimating flood peaks in ungauged Pennsylvania streams. ............... . . ................ .............. .......... ............... ... ................. .......... .......... ............. ... ........... Existing and Proposed Flood Protection Facilities The eleven existing and thirteen proposed existing flood protection facilities reported in the watershed are listed in Table 111-5. The approximate locations of these facilities are illustrated in Plate 111-5 (located in the map pocket accompanying this report). There are no regional flood control projects within the study area. The existing flood protection facilities are designed to provide localized flood protection and include stream channelization, stream bank protection, storm sewers and debris racks. The proposed facilities would also address localized flooding problems and include stream channel improvements, stream bank protection, and debris rack construction. Lake Erie SWMP 111-16 4026-02 Table M-5 Reported Flood Control Projects Map Year Code Tvpe of Flood Control Project Status Built Owner Reported Bv FC- I Millcreek Tube stream pipe Existing 1919 Erie City Erie City channel FC-2 Garrison Run Tube stream pipe -ffx@tsting - 1919 Erie City Eric City channel FC-3 Drift catcher (debris catch er) Before 1915 Erie City Erie Citv FC-4 Pipe (36") Existing 1991 Erie City Erie City FC-5 Storm sewer Existing 1991 Erie City Erie City FC-6 Storm sewer Existing 1991 Erie City Erie City FC-7 Storm sewer Proposed 1993 Erie City Erie City FC-8 Pipe channel Proposed n/a n/a Fairview Borough FC-9 Pipe channel Proposed 1994 Fairview Twp. Fairview Township FC-10 Pipe channel Proposed 1993 Fairview Twp. Fairview Township FC-1 I Channel realignment Proposed 1993 Private Fairview Township FC- 12 Channel realignment Proposed 1993 Private Fairview Township FC-13 Pipe channel Proposed 1994 Fairview Twp. Fairview Township FC-14 Pipe channel Proposed 1994 Fairview Twp. Fairview Township FC- 15 Gabions Proposed 1994 Private Fairview Township FC-16 Pipe channel Proposed 1995 Fairview Twp. Fairview Township FC-17 Pipe channeftation, riprap Existing 1992 Private Fairview Township FC-18 Channel excavation, riprap Existing 1992 Private Fairview Township FC-19 Creek stabilization Proposed n/a Lake City Borough Lake City Borough FC-20 Flood walls Existing 1940-1950 n/a Lawren cc Park Township FC-21 Debris rack Proposed n/a Lawrence Park Tw Lawrence Park Township FC-22 Channel excavation widening Proposed 1996 MiUcreek Township MWcreek Township FC-23 Retaining wall Existing 1956 Penn DOT _ Wesleyville, Borough FC-24 Bank Protection Existing 1959 Wesleyville Borough PA DER .. .... .. ...... . ............... .... . . ........ .. ........ @Sys Existing and Future Storm Sewer Systems The approximate locations of areas served by storm and combined sewer systems are illustrated on Plate 111-5. @ As one would expect, the areas served by piped stormwater collection systems largely correspond to the most densely developed areas of in the watershed. The construction of storm sewers has been identified in the municipal questionnaires as a suggested solution to stormwater drainage problems in Fairview Township, and Millcreek Township. While some storm sewer construction can be expected to occur in these and other currently developed areas in order to address localized stormwater drainage problems, most of the future storm sewer construction will occur as new areas of the watershed are developed. Therefore, future storm sewer system construction will occur as residential and commercial development progresses. The locations of such future storm sewer systems will correspond to the locations of future residential and commercial development. Financing Storm Sewer Construction Under current practice, storm sewer construction in currently developed areas is generally financed by the municipality in which the construction occurs. Usually, storm sewer construction in newly developing areas is financed privately by the land developer. Amendments to the Pennsylvania Infrastructure Investment Authority (PENNVEST) make -certain municipalities eligible to receive financial assistance from PENNVEST to construct stormwater management improvements. Eligible municipalities are those which are located within watersheds for which stormwater management plans have been approved by the Pennsylvania Department of Environmental Reso 'urces and which have enacted, or will enact, stormwater ordinances consistent with the approved plans. Examples of eligible stormwater projects include construction of detention / retention basins, upgrades of existing storm sewer systems and the installation of new storm sewer systems. Municipalities considering the construction of such facilities should investigate the potential for the receipt of funding assistance through the PENNVEST program. Lake Erie SWMP 111-18 4026-02 ................ .. . . .... .. . ... ... ....... ........ ......... ..................... ........... . ....... ..... .. Existing and Future Stormwater Control Facilities The survey of Lake Erie Area watershed municipalities conducted during the preparation of this plan requested information relative. to current and planned storinwater control facilities. Reported stormwater control facilities are listed in Table 111-6. The approximate locations of these facilities are illustrated on Plate 111-5. A total of 3@ and 21 proposed stormwater control facilities were reported. Nine municipalities reported either existing or proposed stormwater control facilities. Over 90 percent of the facilities reported control stormwater runoff by using detention / retention techniques. The majority of these facilities are stormwater basins or ponds. However, the use of parking lot ponding storage techniques was reported. Stormwater control through the use of facilities to induce ground water infiltration was reported in several instances. The relatively widespread use of stormwater control facilities is significant because it demonstrates that stormwater management requirements are being enforced in the watershed and indicates that the use stormwater control techniques is not foreign to developers in the area. ....... ... . . . .. . ............. . ............ ......... I I . ............. ..............I ............... ....... . ............ ............... Existing land use land cover patterns are displayed on Plate HI-6 and the distribution of land cover types in the Erie County portion of the watershed is summarized in Table HI-7. This information was determined based upon the analysis of satellite imagery obtained.in 1993. Table IH-7 Distribution of Existing Land Use in the Watershed Land Use Classification Percent of Watershed Area Residential Commercial / Industrial Mixed Residential Commercial Agriculture Forest Barren Lake Erie SWMP 111-19 4026-02 Table IH-6 Reported StorMW2ter Control Projects Map Type of Year Code Stormwater Control Project Status Built Comments Reported By SC-1 Retention basin -Ex-isting 1992 Existing storm system Erie City overloaded SC-2 Retention basin Existing 1987 Erie City SC-3 Dry well E ' ti 1993 Erie City 1987 New dev Erie City reduce flows to stream SC-4 Retention basin i= elopment to SC-5 Dry well Existing n/a Erie City SC-6 Dry well Existing n/a Parking lot drai age Erie City SC-7 Retention basin Proposed 1994 Erie City SC-8 Retention basin Existing 1992 Fairview Township SC-9 Infiltration device Proposed 1994 Perforated storm sewer Fairview Township SC-10 Detention/retention pond Existing 1987 Mobile home park Girard Township SC-1 I Detention basins Existing 1990-1992 Behrend College Harborcreek Township SC-12 Detention basin Existing 1992 Subdivision Harborcreek Township SC-13 Detention basin Existing 1987 Shopping plaza Harborcreek Township SC-14 Detention basin Existing 1993 Tire center Harborcreek Township SC-15 Infiltration basin Existing 1990 Garden center I-larborcreek Township SC-16 Detention basins Proposed 1997 Subdivision Harborcreek Township SC- 17 Detention basin Proposed 1994 Subdivision Harborcreek Township SC-18 Detention basin Proposed 1993 Commercial development Harborcreek Township SC-19 Detention basin Proposed n/a Subdivision Lake City Borough SC-20 Detention basin Proposed n1a Subdivision Lake City Borough SC-21 Detention basin Proposed n1a Subdivision Lake City Borough SC-22 n/a Proposed n/a Subdivision Lake City Borough SC-23 Detention basin Proposed n/a Subdivision Lake City Borough SC-24 Underground storage Existing 1989 Industrial Millcrrek Township SC-25 Detention basin (dry) Existing 1982 Subdivision Mfllcreck Township SC-26 Detention basin (dry) Existin 1993 Subdivision Millcreck Township SC-27 Detention basin (dry) Existing 1991 Sui;!-v-ision Millcreek Township SC-28 Detention basin (dry) Existing 1990 Subdivision Millcreek Township SC-29 Detention basin (dry) Existing 1992 Subdivision MfflcreckTownship SC-30 Detention basin (dry) Proposed 1995 Millcreek Township SC-31 Detention basin (dry) Proposed 1997 Millcreek Township SC-32 Detention basin (dry) Proposed 1997 Millcreek Township SC-33 Detention basin (dry) Proposed 1994 Millcreek Township SC-34 Detention basin (dry) Proposed 1995 Millcreek Township SC-35 Detention basin (dry) Proposed 1997 Millcreek Township SC-36 Detention basin Existing 1991 Subdivision North East Township SC-37 Detention basin Existing 1993. School North East Township SC-39 Detention basin Existing 1990 School North East Township SC-39 Detention basin Existing 1993 Subdivision North East Township SC-40 Detention basin Existing 1992 Commercial North East Township SC-41 Detention basin Pro osed 1994 Subdivision North East Township SC-42 Detention basin Pro sed 1994 Subdivision North East Township SC-43 Detention basin --- Proposed 1994 Subdivision North East Township SC-44 Detention basin Proposed 1994 Subdivision North East Township SC-45 Infiltration, Underground Tanks Existing 1992 Commercial Summit Township SC-46 Detention basin Existing 1990 Commercial Summit Township SC-47 Detention basin Existing 199 1 Commercial Sununu Township SC48 Underground tanks Existing 1992 Commercial SurnmitTownship SC-49 Parking lot ponding Existing 1993 Commercial Summit Township SC-50 Detention basin Existing 1990 Commercial Summit Township SC-51 Detention basin Existing 1990 Church - Summit Township SC-52 Detention basin Existing 1993 Commercial Summit Township SC-53 Detention basin Existing 1992 Subdivision Summit Township SC-54 Underground tanks 1993 Commercial Summit Township SC-55 Detention basin Existing 1992 Commercial SummitTownship SC-56 Detention, sedimentation ponds Existing 1972 Landffll SummitTownship SC-57 Detention basin P posed 1994 Commercial Summit Township SC-58 Farm pond Existing 1960 Venango Township SC-59 Pond Existing 1980 Venango Township SC-60 Pond 1986 Venango Township High density residential, commercial and industrial land use classes predominate in the northern areas of the watershed and in the areas immediately adjacent to the Lake Erie Area. The density of commercial and residential development generally decreases as one moves 0 southward and away from the banks of the Lake Erie Area. In the upper reaches of the south-most portions of the watershed, open space and agricultural land uses predominate. Table 111-8 contains 1990 U.S. Census population densities for each of the municipalities in the watershed. The data presented therein is indicative of the wide variation in development density in the watershed. Table 111-8 Municipality Population Densities Population Population Density Density Municipality (persons / sq. mi.) Municipality (persons / sq. mi.) Conneaut Township 44.7 McKean Borough 697.6 Elk Creek Township 50.2 McKean Township 123.0 Erie City 4,941.7 Millcreek Township 1,587.1 Fairview Borough 1,420.0 North East Borough 3,551.5 Fairview Township 282.0 North East Township 148.2 Franklin Township 49.6 Platea Borough 141.5 Girard Borough 1,199.6 Springfield Township 85.4 Girard Township 149.0 Summit Township 221.1 Greene Township 132.2 Venango Township 51.3 Greenfield Township 52.4 Washington Township 91.0 Harborcreek Township 441.8 Waterford Township 67.9 Lake City Borough 1,399.4 Wesleyville Borough 7,310.0 Lawrence Park Township 2,268.4 Potential future land development patterns in the Erie County portion of the watershed were o"btained from-the Erie County Department of Planning. Projected future land use / land cover patterns are indicated on Plate RI-7. Projected future land cover statistics are presented in Table IR-9. Lake Erie SWMP 111-21 4026-02 Table 111-9 Distribution of Future Land Use in the Watershed Land Use Classification Percent of Watershed Area Residential Commercial / Industrial Mixed Residential Commercial Agriculture Forest Barren Lake Erie SWMP 111-22 4026-02 LAKE ERIE AREA WATERSHED STORMWATER MANAGEMENT PLAN SECTION IV WATERSHED TECHNICAL ANALYSIS - MODELING ......... .... ........... ........... . . ....... ............ ...... ... . . ........ ...... The requirement for assessing the watershed wide impact of the implementation of stormwater runoff controls demands the use of computerized hydrologic modeling techniques to estimate stormwater runoff rates under various conditions. Digital computer modeling refers to the use of sets of mathematical expressions (algorithms) to reproduce key behavioral aspects of the natural system. This section contains a discussion of the modeling approached used in the preparation of the Lake Erie Area Watershed Stormwater Management Plan. .... . .......... ........... .. .............. ... ...... . . ............ .. :- .. .. ..... .... 11 ................. . .... ....... ... 11 . ....... ..... ......... . There are a number of hydrologic modeling. techniques available for estimating stormwater runoff based upon ground cover and precipitation conditions. The Penn State Runoff Model (PSRM) wa's selected for use in the Lake Erie Area Watershed. PSRM was selected for use in this watershed for a number of reasons, including: 1. PSRM offer *s the ability to analyze the timing of flow combinations originating from various locations throughout a watershed. This capability is particularly important in the evaluation of the effects of various stormwater control techniques throughout a watershed. 2. PSRM is suitable for use for both urban and rural watersheds. I PSRM offers flexible data input and output modes. IV- 1 Lake Erie SWMP 4026-02 4. PSRM is has generally been the model of choice for use throughout Pennsylvania for the preparation of watershed stormwater management plans under Act 167. 5. Continuing development of PSRM and training.in its use is supported by the I Pennsylvania Department of Environmental Resources and the Pennsylvania State University. M. Overview Input data requirements for PSRM include the following parameters: 1. Watershed Representation Data A. Tributary Area (Subbasin) Physical Features 1. Tributary land areas 2. Land slopes 3. Overland flow lengths B. Tributary Area (Subbasi n) Hydrologic Features 1. Composite runoff curve numbers 2. Percentage imperviousness 3. Initial abstraction estimates C. Drainage (Reach) System Features 1. Conv eyance system (streams- and conduits) capacities 2. Conveyance system travel times B. Rainfall Inputs 1. Rainfall volumes 2. Rainfall distribution Lake Erie SWMP IV-2 4026-02 Subbasin Physical Features PSRM develops runoff hydrographs for individual portions (subbasins) of a watershed which are then routed and combined in a manner corresponding to the' network of streams that link the subbasins. Consequently, the initial task in the development of the modeling data base was the delineation of subbasins within the watershed. The designated Lake Erie Area watershed actually consists of a number of small to moderately sized streams which drain to Lake Erie and areas along and near the shore of the lake which drain directly to the Lake Erie essentially through overland flow. Therefore the overall watershed was first divided into subwatersheds. These subwatersheds, in turn, were further divided into subbasins. Subwatersheds were delineated based upon topographic features so as to 1) define the major stream drainage basins; and 2) accurately represent the topology of the watersheds. Delineated subwatersheds and selected characteristics are listed in Table IV-1 and delineated in Plate IV-1. Plate IV-1 is Appended to the rear of this report. Table IV- I Delineated Subwatersheds Drainage Drainage Drainage Area Area Area Subwatershed (Acres) Subwatershed (Acres) Subwatershed (Acres) Cascade Creek 6,650 Sixmile Creek 12,220 10.0 Mile Run * 3,540 Crooked Creek 13,600 Sixte'enmile Creek 12,100 11.5 Mile Run * 1,270 Eightmile Creek 4,510 Trout Run 4,080 26.9 Mile Run * 880 Elk Creek 57,960 Turkey Creek 31440 29.0 Mile Run * 1,260 Fourmile Creek 7,280 Twelvemile Creek 9,310 39.9 Mile Run * 1,280 Garrison Run 1,360 Twentymile Creek 22,080 40.9 Mile Run * .1,340 McDaniel Run 2,000 Walnut Creek 24,430 41.5 Mile Run * 2,850 Mill Creek 8,750 3.2 Mile Run * 560 Direct Runoff 19,700 Raccoon Creek 5,000 3.9 Mile Run * 1,250 Sevenmile Creek 5,430 , 6.7 Mile kun * 1,600 Note: Unnamed tributaries that have been designated with the distance of their mouths from the western boundary of Erie County Subbasin boundaries comprising the modeled subwatersheds were defined so as to as closely as practical produce hydrologically homogeneous areas as well as to adequately model hydrologically significant features such as tributaries, major storm sewers, and significant obstructions. A total of 1,498 subbasins were delineated. Lake Eric SWMP IV-3 4026-02 Subbasin boundaries comprising the modeled subwatersheds were defined so as to as closely as practical produce hydrologically homogeneous areas as well as to adequately model hydrologically significant features such as tributaries, major storm sewers, and significant obstructions. A total of 1,498 subbasins were delineated. United States Geological Survey (U.S.G.S.) 7.5 minute quadrangle topographic mapping and local storm sewer facilities maps were used as the basis for defining subwatersheds and subbasins. The subbasin boundaries were delineated on the U.S.G.S. base and digitized to facilitate subsequent analysis. Once digitized, the subbasin areas were calculated. Subbasin areas average 133 acres in size. Stream locations were digitized and added to the data base. Representative overland flow widths for each subbasin were calculated based upon an analysis of the digitized stream locations and subbasin boundaries. Digital Elevation Model (DEM) data obtained from U.S.G..S. served as the source of digital terrain data used to produce slope summaries for each subbasin. DEM quadrangles were mosaicked to fully cover the watershed. Slope in percent and aspect in degrees were calculated from the raw elevation data and were used to determine representative ground slopes for each of the subbasins. Subbasin Hydrologic Characteristics The principal subbasin specific hydrologic characteristics of interest in this analysis are the composite Soil Conservation Service (S.C.S.) runoff curve number and percentage of impervious area for each subbasin. Percent of impervious area is defined as the percentage of the total subbasin area covered by surfaces which are essentially impermeable to 'water. The runoff curve number is a indication of the amount of surface runoff which may be expected to be produced as a result of a storm event. This runoff potential is influenced by land cover and soil conditions. The determination of impervious 'percentages and curve numbers required the classification of land cover and soil types. Lake Erie SWMP IV-4 4026-02 Land Cover/ Land Use Classification Landsat thematic mapper multispectral digital data was used to provide the necessary land use and land cover information. Impervious Area Statistics Impervious area statistics for each subbasin were estimated based upon the land cover and land use through the relationships of impervious area components of various land use / land cover classes developed and published by the U.S. Soil Conservation Service. Soils Group Classifications The spatial distribution of soils (aggregated by S.C.S. hydrologic soil groups) was defined through the use of S.C.S. soils maps and reports for Erie County and Chautauqua County in New York. The various soil types were scan digitized into the geographic information system database. The various soil types were aggregated the appropriate hydrologic soil groups based upon U.S. Soil Conservation Service (S.C.S.) procedures. This procedure produced the data set used to create the hydrologic soil group map presented previously in Section III, Calculation of Runoff Curve Numbers The factors that determine runoff curve numbers (CN) are the hydrologic soil group and land cover type and condition. The S.C.S. has developed and published tables which provide runoff curve numbers for each intersection of hydrologic soil group and land cover type. Geographic Information system (GIS) methods were used to digitally combine the land use / land cover and hydrologic soil group themes to yield a set of associations between surface type and soils units. These associations were referenced to the S.C.S. information to attach the appropriate runoff curve number. Further processing within the GIS determined composite runoff curve numbers for each of the subbasins in the watershed. Lake Erie SWMP IV-.5 4026-02 Modeling Subbasin Data File Production All of the subbasin information necessary for PSIZIM modeling was represented in the GIS system as digitized themes. Once these data were resident in the GIS, the necessary analyses were performed to develop the required PSRM input data set. This data set is common to all subwatersheds and subbasins in the watershed and is keyed to assigned subbasin identification numbers. The version of PSIUM used in this modeling effort has the capability of reading the appropriate individual subbasin characteristics data directly from the common subbasin data file. Stream Reach Hydraulic Characteristics Important input data requirements of the PSRM are estimates of the times of travel in each of the modeled stream reaches and the bankfull capacity of each reach. Travel Time Estimates Travel time is calculated as the length of the reach divided by the average velocity. Stream reaches were defined in conjunction with the delineation of watershed subbasins as described previously. The length of each reach was determined by direct measurement from the U.S.G.S. maps. Stream reach velocity estimates were based upon cross section information available from Flood Insurance Studies (FIS) completed within the watershed. This data was used in conjunction with empirical relationships between stream cross section measurements, discharge and mean velocity to produce velocity estimates for stream reaches for which no FIS information is available. Velocities for channelized stream segments, major storm sewers, and long culverts were calculated based upon reported and/or field'measured dimensional information. Estimated velocities were divided by measured lengths to produce estimates of times of travel for each stream reach for input into PSRM. IV-6 Lake Erie SWMP 4026-02 Bankfull Capacity Estimates The estimation of bankfull capacities in the natural stream reaches in the Lake Erie Area watershed was performed based upon information reported in the literature which essentially states that bankfull capacities in natural streams approximate the 2-year return -frequency flood discharge rate (Leopold, 1953; Brush, 196 1; Harvey, 1969; and Brown, 1979). The estimates of the 2-year flood for each stream reach were using. Procedure PSU-IVfor Estimating Design Flood Peaks on Ungauged Pennsylvania Watersheds. Discharges calculated using this procedure were used as initial bankfull capacity estimates for natural stream reaches. Full flow capacities for improved stream reaches and major storm sewer pipes or culverts were calculated based upon slope and dimensional information. -Modeling Stream Reach Data File Production The stream reach data required for PSRM modeling of the watershed was compiled into a single reach data file. This input file contains stream time of travel and capacity data keyed to each of the identified reaches modeled during this planning effort. Rainfall Characteristics Rainfall Intensity-Duration-Frequency Rainfall depth-duration-frequency (DDF) values for the Lake Erie Area watershed are summarized in Table IV-2. These data were calculated using the charts describing rainfall intensity-duration- frequency JDF) data presented in the Pennsylvania Department of Transportation IDF Field Manual. This document divides the state of Pennsylvania into five regions of relatively uniform rainfall patterns. Intensity-duration-frequency and depth-duration-frequency (DDF) relationships for each of the five regions ar .e presented in the form of design charts. The Lake Erie watershed lies in Region 3. Lake Erie SWMP IV-7' 4026-02 Table IV-2 Rainfall Depth - Duration - Frequency Data Return Period Rainfall Rainfall Rainfall Rainfall (Years) (3-hour) (6-hour) 0 2-hour) (24-hour) 2 - year 1.54 inches 1.84 inches 2.20 inches 2.62 inches 5 - year 1.84 inches 2.21 inches 2.65 inches 3.15 inches 10 - year 2.22 inches 2.70 inches 3.23 inches 3.75 inches 25 - year 2.54 inches 3.13 inches 3.84 inches 4.61 inches 50 - year 2.99 inches 3.68 inches 4.48 inches 5.34 inches -100 - year 3.37 inches 4.18 inches 5.14 inches 6.19 inches Rainfall Distribution The distribution of rainfall within the overall storm event is relevant to the modeling effort. The U.S. Soil* Conservation Service (SCS) has developed synthetic rainfall distribution patterns which include maximum rainfall intensities for the selected design frequency arranged in a sequence that is critical for producing peak runoff. SCS has developed four synthetic distributions from available National Weather Service data that are applicable in various areas of the United States. The SCS Type 11 distribution represents design storm conditions appropriate for the region in which the Lake Erie Area Watershed is located. Since the SCS Type II storm distribution is supported by significant research activity, is widely used in stormwater runoff calculations throughout the area and its use is incorporated directly in the frequently employed SCS stormwater runoff computational procedures it was selected for use in the Lake Erie Area Watershed model. @.C4LL6M:jq"/;VERLF'ICA .. ...... ............ As was discussed in Section III, there are three gauging stations that are operated by the U.S.G.S. located in the Lake Erie Area Watershed. The gauges are located on Raccoon Creek, Brandy Run (a tributary of Elk Creek), and Mill Creek. The. Mill Creek and Brandy Run gauges provide peak discharge estimates for.strearn flows suitable for use in calibrating the model. Peak discharge data were obtained for the Brandy Run gauge for a storm that occurred on, August 28, 1990 and for the Mill Creek gauge for a storm that IV-8 Lake Erie SWMP 4026-02 occurred on October 18, 1988. Hourly rainfall records for these dates as reported at the Erie Airport were also obtained. The Penn State Runoff Model was loaded with the observed hourly rainfall records and the model peak strearnflow estimates were compared to the observed results. Initial estimates for the Manning's "n" values for pervious and impervious surfaces were adjusted until optimal calibration was obtained. The model calibrated to values of 0.22 for the Manning's "n" value for pervious surfaces and 0.08 for the Manning's "n" value for impervious surfaces. The literature reports that values for Manning's "n" range from 0.03 to 0.45 for pervious surfaces ranges and from 0.01 to 0.013 for impervious surfaces. The calibrated model estimates a peak discharge of 930 cubic feet per second (cfs) for the August 28, 1990 storm at the Brandy Run gauge. The reported gauged peak discharge for this storm is 836 cfs. The model, therefore, predicts the storm peak flow to within I I percent of the reported value for this actual event. The model estimates a peak discharge of 2,317 cfs for the October 18, 1988 storm at the Mill Creek gauge. The reported gauged peak discharge for this storm is 2,550 cfs. The model, therefore, predicts the stonn peak flow to within 9% of the reported value for this actual event. The August 28, 1990 storm produced 3.29 inches of rain over an eleven hour period. This approximates an I I year return frequency event. The October 18, 1988 storm produced 2.89 inches of rain over a six hour period. This approximates a 16 year return frequency event. The ability of the model to predict actual observed peak discharges to within approximately 10 percent for these relatively rare events indicates acceptable model caliabration. N Existing Conditions Runoff and streamflow rates- were estimated under current conditions using the PSRM for each of the subwatersheds selected for detailed modeling. The model was run for the mean annual, 5, 10, 25, 50 and 100 return frequency volumes associated with 3, 6, 12 and 24 hour duration storm events. In all, model output was developed for 24 storm conditions for each of the 24 subwatersheds included in the modeling program. The results of this modeling effort are summarized in Appendix B. Lake Erie SWMP IV-9 4026-02 In reviewing the model results, it is important to recognize that the strearnflow estimates developed as part of this plan have been developed by modeling the runoff produced by rainfall volumes with a range of return frequencies distributed according to the SCS Type II Distribution. Since this distribution is designed to maximize runoff from any given rainfall volume, this procedure produces conservatively high runoff rate estimates suitable for the design of local controls. As a result, the strearnflow estimates contained in Appendix B are likely to be higher that estimates produced using other methods that employ statistical analyses of reported flood frequencies. Future Conditions The PSRM wa s used to estimate runoff and strearnflow rates under projected future development conditions. This was accomplished by revisin g the S.C.S. runoff curve number and percent impervious estimates in the model subbasin database to reflect the projected future land use / land cover characteristics as presented in Section III. The model was then run under these conditions to produce estimates of future runoff and strearriflow rates for the 24 hour, 50 year return frequency storm. Model output for each of the modeled subbasins is provided in Appendix B and summarized at the mouth of each subwatershed in Table IV-3. TABLE IV-3 COMPARISON OF EXISTING AND FUTURE PEAK DISCHARGES (24 HOUR, 50 YEAR FREQUENCY EVENT) IV-10 Lake Erie SWMP 4026-02 "W LAKE ERIE AREA WATERSHED STORMWATER MANAGEMENT PLAN AU SECTION V DEVELOPMENT OF WATERSHED TECHNICAL STANDARDS AND CRITERIA EUROD.UCHON. As was discussed previously in Section 1, the basic standard for stormwater management as established by Act 167 is that those involved in activities which can generate additional stormwater runoff, increase its velocity, or change the direction of its flow must be responsible for controlling and managing the runoff so that these changes will not cause harm to other persons or property throughout the watershed. This mandate requires comprehensive storinwater planning at a watershed level and the development of standards and criteria for managing stormwater to prevent adverse impacts, both at a particular site and anywhere downstream where the potential for harm can be reasonably be identified. Specifically, the primary prerequisite for effective stormwater management in the watershed is the development of standards which specify allowable stormwater discharges from land development activities. Standards must also be developed which address issues associated with the control of velocity, direction and quality, if appropriate. The standards must be accompanied by associated criteria which for the basis for the design and assessment of activities instituted to comply with those standards. :.CVN2W Ev..@-Y ClUTER-M. .......... A key element in the development of this stormwater management study is the definition of the characteristics of the rainfall events against which the developed control standards must be Applied. Specifically, the rainfall events which the stormwater control measures must adequately handle need to be defined. The objective of the analyses discussed in the following paragraphs was to describe characteristics of storm events which will serve as the basis for the evaluation and design of effective control measures in the Lake Erie Area Watershed. V - 1 Lake Erie SWMP 4026-02 The critical rainfall event characteristics are as follows: 1. An identified duration or length of the particular rainfall event. 2. An identified rainfall intensity or distribution or pattern of precipitation falling over the duration of the event. 3. An identified frequency of occurrence or the expected time interval between occurrences of the given precipitation event. 4. An identified volume or total amount of rainfall that can be expected for the particular event. Storm Distribution The selection of the appropriate distribution of rainfall within the overall storm event was discussed in Section IV. For the reasons specified therein, the Soil Conservation Service (SCS) Type II rainfall distribution was selected for application to the development of control standards and the design of actions to be taken to satisfy those standards. Storm Duration Storm duration refers to the length of time over which the specified amount of precipitation falls. This factor is of concern because rainfall duration has a direct effect upon the resulting runoff volume and peak rate of discharge. The length of the rainfall period contributing to the peak runoff rate is related to the time for runoff to travel from the hydraulically most distant point of the watershed to a point of interest (time of concentration). In general, largest peak discharges result when the storm duration roughly equals the time of concentration in the watershed. In small watersheds the critical storm duration may be measured in minutes, while in large watersheds or basins the time of concentration may be measured in days. In the Lake Erie watershed, the appropriate storm duration for use in the development and application of control standards was selected using the hydrologic model. The PSRM was used to estimated peak discharge rates throughout the watershed for the mean annual, 5, 10 25, 50 and 100 year return frequency storms of the following candidate durations: 3 hour, 6 hour, 12 hour and 24 hours. The model runs produced estimates of the peak discharges at 1438 points throughout the watershed for each of the four candidate Lake Erie SWMP V-2 4026-02 durations. For 86% of the 1438 subbasins modeled in the watershed, the 24 hour durati on storm produced the largest peak rate of discharge. The 6 hour and 3 hour storms produced the largest peak rate of discharge for 13% and 1% of the subbasins, respectively. Moveover, the 24 hour duration storm is the critical event for 22 out of the 27 modeled subwatersheds which drain approximately 95% of the study area. A supporting consideration in the selection of the storm duration for use in the Lake Erie Area Watershed is the fact that the popular Soil Conservation Service Technical Release 55 Urban Hydrology for Small Watersheds procedure for estimating runoff and peak discharges is based upon a 24-hour storm, duration. This procedure is extensively used within the region and nationally in the production of stormwater control plans for proposed land development. Adoption of a storm duration criteria other than 24 hours would effectively preclude the use of this most popular computational procedure. For the reasons discussed above, 24 hours has been selected as the appropriate storm duration criteria for application throughout the watershed. It is recognized that the use of shorter durations will be appropriate and permissible in the design of stormwater collection facilities. However, the selection and application of controls to the discharge of runoff from developing sites will be based upon the 24-hour storm duration criteria. Storm Return Frequencies and Precipitation Volumes General Storm return frequency refers to the average interval in years over which a storm event of a given precipitation volume can be expected to recur. For example, reference to a "10-year" storm with an associated 3.75 inch 24 hour duration storm volume indicates that a storm producing 3.75 inches of rainfall over a 24 hour period on-the average can be expected to occur approximately every ten years. Another way to consider this storm is that, on the average, a storm producing 3.75 inches of rainfall over a 24 hour period has approximately a ten (10) percent chance of occurring in any given year. Storm duration and volumes for return frequencies ranging from 2-years to 100-years were presented previously in Section IV of this report (Table IV-2). This data is presented graphicall y below in Figure V- 1. V-3 Lake Erie SWMP 4026-02 Figure V-1: Precipitation Volumes 8.0 CIO ..............*............ 6.0 ........ ..............0..... ................ . ........... .......................... ct .1-4 4.0 CIA 2.0 storm Duration 3-Hour 6-Hour 12-Hour 24-hour 0.0 0 20 40 60 80 100 120 Retum Period (Years) As is indicated in Figure V-1, precipitation amounts increase with increasing return periods reflecting the obvious fact that the larger the rainfall event the more infrequent the occurrence. As one would expect, larger rainfall amounts produce larger stream discharges. This is illustrated in Figure V-2 for various streams in the watershed. The estimates of stream discharges reflected in Figure V-2 were produced using the Penn State Runoff Model developed for the Lake Erie Area Watershed. The Pennsylvania Department of Environmental Resources "Storm Water Management Guidelines" describe design frequencies as the peak rates of discharge for which the components of drainage systems are designed. Reoccurrence intervals used for design typically range from 2 to 100 years. Individual drainage system components are generally assigned design storm frequencies based upon an evaluation of such factors as the size of the area drained and the potential for damage produced as a result of inadequate drainage as characterized by the size of the affected area, the nature and characteristics of land use in the affected area (i.e., residential, commercial, industrial uses). Components of the initial drainage system such as storm sewers and inlet Lake Erie SWMP V-4 4026-02 structures generally a designed for relatively high frequency events ranging upwards to the 10-year storms. Major drainage system components are generally designed for less frequent, larger storms such as the 25-year and 50-year events. Flood protection projects typically are designed to accommodate conditions produced by the I 00-year storm events. Design frequency criteria for the construction of conveyance facilities such as storm sewers, pipes, culverts, bridge openings and spillways are contained in a number regulations and design manuals, including: regulations produced relative to the Pennsylvania Dam Safety and Encroachments Act, and the Pennsylvania Flood Plain Management Act; Pennsylvania Department of Transportation design criteria; Pennsylvania Soil and Erosion Control Manual; and the Water Pollution .Control Federation Manual of Practice No. 9: Design and Construction of Sanitary and Storm Sewers. These references provide ample guidance under the law and standard engm*eenng practice to permit local municipalities to establish local requirements for traditional stormwater facilities design commensurate with local conditions. There are, however, no state level criteria for stormwater discharges as they relate to total discharge volumes and rates from new land development. Moreover, unlike the generally site specific conduit construction criteria, site runoff criteria must be established based upon watershed wide considerations. Consequently, this watershed plan presents specific criteria relative to storm frequencies to be used in controlling total stormwater discharge volumes and rates from new site development. Upper and L*ower Storm Frequency Criteria Limits For this study the design storm frequency criteria were selected to respond to watershed conditions and to meet the objective of Act 167 to minimize stormwater damage now and in the future. The following example serves to illustrate the design storm frequency criteria selection rationale. The following table contains pre-development and post-development peak rates of discharge for a hypothetical development. V-5 Lake Eric SWMP 4026-02 Table V- I Hypothetical Storm Discharge Rates Under Various Return Frequency Conditions Design Storm Condition 2 - Year 10 -Year 100 - Year Pre-development 50 cfs 75 cfs 100 cfs Post-development 100 cfs 150 cfs 200 cfs Two conclusions may be drawn for the data presented in this table: 1. If the design storm frequency criteria require that only the 100-year event be used as a point of control, the post-development discharge for the 2- and 10-year storms will be greater that the pre-development rate and- runoff from the development may cause downstream harm at the more frequent storm events. 2. If the criteria require that only the 2-year event be applied, damage ma y result from increased runoff during the less frequent storm conditions. If the stormwater conveyance system from this hypothetical development site to the river were capable of accommodating flows generated under 100-year return frequency storm conditions controlling discharges under simply a I 00-year storm freque *ncy criteria would be acceptable. However, information obtained from local municipal questionnaires and data produced through an analysis of existing obstruction capacities identified a number of locations where flooding occurs as frequently as-once per year. The municipal questionnaires identified 5.0 locations within the watershed at which flooding occurs on average at least once per year (Table 111-5). In addition, it.is generally accepted that the, bankfull capacity of natural stream channels approximates the mean annual flood. As a result, flows in excess of the mean annual flood frequently produce localized flooding. Consequently, the mean annual (2-year) event has been selected as the lower limit design storm frequency criteria. V-6 Lake Erie SWMP 4026-02 The I 00-year frequency storm was selected for use in the watershed for the following reasons. 1. The survey of obstructions identified 52 obstructions with capacities less than the 100-year flood (Table A-1). A failure to control runoff under storms of these frequenci 'es would exacerbate flooding conditions at these sites as well as those sites with even smaller capacities. 2. Control of the 100-year frequency runoff would serve to preserve the 100- year flood plain and floodway boundaries as defined in the flood insurance studies completed in the watershed. These boundaries provide the basis for on-going flood plain management in the area. Permitting increased runoff at the 100-year return frequency conditions would result in an expansion of the flood zones and substantially increase the potential for damage. 3. The use of a 100-year frequency for the upper limit of the criteria would afford a high degree of protection commensurate with the highly developed urbanized areas existing at the base of most of the watersheds. Intermediate Frequency Criteria In setting the upper and lower limit for return frequency storms to be controlled, it is assumed that runoff produced from discharges occurring events occurring at all intermediate frequencies will also be controlled. In other words, the stormwater control facilities would regulate discharges such that the post-development discharges would match the pre-development discharges at the 3-year, 4-year, 5- year frequency storms and so on through the 100-year frequency event. Since it would clearly be impractical to design for such a multitude of conditions and cumbersome to review managen ent plans produced on such a basis. Intermediate return frequency events were selected as reasonable points at which to verify that the runoff control system performance will generally parallel pre- development conditions between the 2- and 100-year limits. The selected check V-7 Lake Eric SWMP 4026-02 points and the manner in which they approximate modeled actual runoff rates at various return frequencies are illustrated in Figure V-3. Figurie V-3 Design Storm Control Points 16,000 14,000 C4 .......... .. 12,000 ........... a) - 10,000 8,000 Actual Discharges 6,000 Control Point Approximations 4,000 2,0001 0 20 40 60 80 100 120 Storm Return Frequency (Years) The following storm frequency check points have been selected for inclusion in the stormwater management criteria: 1. 2-year frequency storm; 2. 1 0-year frequency storm; 3. 25-year frequency storm; and 4. 1 00-year frequency storm. The rationale for the selection of the upper and lower check points was described previously. The reasons for selecting the 10-year and 25-year frequency storm intermediate check points are as follows: 1. The use of these two intermediate points are effective in producing a curve of runoff rate verses storm return frequency which reasonably closely Lake Erie SWMP 4026-02 approximates the observed modeled relationship between the two variables (as illustrated in Figure V-4). 2. The 10-year and 25-year events are the most frequently referenced recommended design storm for a wide range of stormwater drainage facilities. Precipitation Volumes Precipitation volumes to be used in the design and evaluation of stormwater control measures in the Lake Erie Area Watershed are presented in Table V-2. Table V-2 Design Rainfall Volumes (24 - Hour Storm Durations) Volume Mum Period (Inches) 2 - year 2.62 10 - year 3.75 1 25 - year 4.61 10 - Ye 6.19 Ms ..T @-D.' :.S ............. ............... ... ...... .. .... .. . ....... ............. General Approach The basis for the establislunent of runoff control standards is contained in the Storm Water Management Act. The statement of legislative findings contained in the Act (Section 2 of the Act) presents the following findings: "(1) Inadequate management of accelerated runoff of storm water resulting from development throughout a watershed increases flood flows and velocities, contributes to erosion and sedimentation, overtaxes the carrying capacity of streams and storm sewers, greatly increases the cost of public facilities to carry and control storm water, undermines flood plain management and flood control Lake Eric SWMP V-9 4026-02 efforts in downstream communities, reduces ground water recharge, and threatens public health and safety. (2) A comprehensive program of storm water management, including reasonable regulation of development and activities causing accelerated runoff, is fundamental to the public health, safety and welfare and the protection of the people of the Commonwealth, their resources and the environment." Section 3 of the Act defines the duty of persons engaged in the development of land as foll ows: "Any landowner and any person engaged in the. alteration or development of land. which may affect storm water runoff characteristics shall implement such measures consistent with the provisions of the applicable storm water plan as are reasonably necessary to prevent injury to health, safety or other property. Such measures shall include such actions as are required: (1) to assure tlaat the maximum rate of storm water runoff is no greater after development than prior to development acfivities; or (2) to manage the quantity, velocity and direction of resulting storm water runoff in a manner which otherwise adequately protects health and property from possible injury.11 The most effective method means of safisfying the Act based upon the statements of legislative findings and definition of duty would be to control land development activities such that both the total volume and rate of runoff from new development are identical to that which occurred before development i.e., post-development runoff volume and rates identical to pre-development conditions. If this could be accomplished, stormwater runoff from the new development would not produce any effect on downstream flows, eliminating any concern relative to the creation of downstream damage potentials. Lake Erie SWMP V - 10 4026-02 Unfortunately, however, most land development activities involve the conversion of land use from a type which exhibits a relatively low runoff potential to a higher runoff potential type. This factor produces a typical effect upon runoff as illustrated in Figure V-4. As is indicated in Figure V-4, land development typically produces increases in both total runoff volumes and peak rates of discharge. As is indicated in Figure V-5, measures can be taken to manage stormwater runoff by reducing the increase in total runoff volume and/or control peak rates of discharge. Techniques which may be used to minimize the increase in total runoff volume are described in Section VI of this report. These techniques generally consist of measures which minimize the extent of land cover changes from pervious to -impervious areas and/or artificially induce infiltration to ground water. While these measures can be effective in reducing increases in runoff volumes, it is usually impractical to entirely avoid runoff volume increases attendant with most land development activities. Consequently, as indicated in Figure V-5, post-development hydrographs produced through the implementation of runoff volume reduction measures typically produce hydrographs with peak rates of discharge and total volumes falling between pre- development and uncontrolled post-development conditions. Because it is impractical to entirely avoid increases in total runoff volume, the inevitability of some degree of runoff volume increases must be accepted and the primary emphasis of the stormwater control criteria must be placed upon the control of peak discharge rates. In order to minimize the potential for damage, the basic, minimum stormwater runoff control criteria to be applied in the watershed is that post-development peak discharges rates must not exceed pre- development peak discharge rates. Methods of controlling peak discharge rates from new development are presented in Section VI of this report. In general, they consist of measures which essentially retain and delay the controlled release of runoff so as not to exceed pre-development rates. The typical results of the application of peak discharge control measures in addition to feasible runoff volume reduction provisions are illustrated in Figure V-5. As is indicated in Figure V-5, although the post-development total runoff volumes fall between pre- development and uncontrolled post-development volumes, the peak rate of discharge approximates the pre-development peak rate. This is accomplished by extending the time duration of time the peakrate of discharge occurs. Instead of an instantaneous peak as occurs in the pre-development condition, the peak discharge occurs over an extended period of time. This characteristic attenuation of peak discharge rates necessitates the development of additional standards designed to avoid the development of associated downstream problems. The derivation of these sup plemental standards is discussed below. V - I I Lake Erie SWMP 4026-02 Figure V-4 Figure V-5 Uncontrolled Runoff Controlled Runoff Runoff Hydrographs Runoff Hydrographs Post-Development Post-Development (uncontrolled) (uncontrolled) Post-Development (volume reduction) Pre-development Pre-development Post-Develoy-ment (volume re uction and peak discharge control) % % Elapsed Time Elapsed Time Total Runoff Volumes Total Runoff Volumes Pre-development ----------- Post-Development ----------- (uncontrolled) Pre-development Post-Development -------------- (volume reduction) Post-Development Post-Development (uncontrolled) (volume & peak Total Volume controlled) Total Volume oil. Release Rate Percentage Concept General Concept It is through the development and application of release rate percentage based, peak discharge standards that the stormwater management plan truly assumes a watershed wide status. The investigations which serve as the basis for the establishment of release rate percentage represent the principal means through which the watershed wide implications of control strategies are evaluated, considered and incorporated into specific control standards. T he general concepts behind the development and application of release rate percentage based stormwater management criteria are discussed below through the use of the hypothetical watershed illustrated in Figure V-6. Figure V-7 contains the total hydrograph for flows at the point of interest as well as the hydrographs for flows generated in each of the five (5) subbasins as they reach the point of interest. As is illustrated in Figure V-7 and summarized in Table V-3, the peak discharge at the point of interest is sum of the discharges originating from each of the upstream subbasins as they coincidentally reach the point of interest. Table V-3 Example Hydrograph Combination Pre-Development Conditions Peak Discharge at Discharge at Point of Interest Subbasin Mouth During Wa rshed Peak Subbasin Time Discharge Time Discharge Number (Minutes) fs) (Minutes) (cfs) 1 20 200 70 0 2 50 650 70 650 3 40 500 70 400 4 50 500 70 300 5 30 300 70 150 Total 1,500 Lake Erie SWMP V - 13 4026-02 HYPOTHETICAL WATERSHED I %2 3 % 4 Point of Interest 5 FIGURE V-6 SUBBASIN HYDROGRAPH 1,600 - 1,500 cfs Watershed Peak Rate of Runoff 1,400- -Total Flow Hydrograph -731,200- con W lb 0 1,000 - 02 800- 650 cfs '50 0 cfs 600- cy ,-500 cfs 0 400 cfs ;-T 400- 3 00 cf s 00 cfs 1200 cf@-,--. 200 5 4 3 2- cfs--/. I., ........ 0 0 10 20 30 40 50 60 70 80 90 100 110 120 @0 50 cf 2/1 Time in Minutes FIGURE V-7 The potential effects of land development occurring in Subbasin 3 upon the runoff hydrographs for Subbasin 3 and the e.,-,tire hypothetical watershed are illustrated in figure V-8 and are tabulated in Table V-4. Figure V-9 illustrates the effects of the institution of stormwater controls which serve to limit post-development peak discharge rates to the pre-development discharge rate through flow detention. As is indicated by the hydrographs presented in Figure V-8, limiting the peak discharge in this manner would serve to extend the period over which the pre- development discharge occurs. The result of this flow attenuation is described by the data presented in Table V-4. Following development and the institution of the specified controls, Subbasin 3 would contribute 500 cfs to the watershed peak at the point of interest rather than the 400 cfs contributed in the pre-development state. This would produce a 100 cfs increase in the watershed peak despite the control of Subbasin 3 peak discharges to pre-development levels. Table V-4 Example Watershed Impacts of Flow Attenuation (Subbasin 3) Peak Contribution to Watershed Runoff Watershed Peak Peak Condition (Cfs) (cfs) (cfs) Pre-development 500 400 1,500 Post-development (uncontrolled) 1 10 490 1,590 Post-development (100% Release Rate) 500 500 Post-development (Reduced Release Rate) 400 400 1,500 This situation can be avoided if the post-development runoff rate is controlled so that the peak rate of runoff does not exceed the rate of flow contributed to the watershed peak. The effects of controlling peak rates of runoff in the example situation are presented graphically in Figure V-9 and in tabular form in Table V-4. As is indicated, selection of the proper allowable post-development peak discharge rate in consideration. of contribution to downstream flows can avoid unintentional increases in peak stream discharges as a consequence of efforts to limit runoff from the new development(s). The methodology used to determine the allowable peak rate of post-development discharge in the previous example can be generalized as follows: @1.500 Lake Erie SWMP V - . 15 4026-02 SUBBASIN HYDROGRAPH (100% RELEASE RATE) 1,800 - NOTE: Only Subbasin No. 3 is shown. Watershed Peak Rate of Runoff 1,600- Watershed Peak Post-development - Rate of Runoff (100% release rate) Pre-development Q=1,600 cfs 1,400- Q=1,500 cfs C4 '05 1,200- 1b 1,000- Uncontrolled 7 10 cfs - Post-Development 800- Runoff Post Development with U lb discharge from 600 - Detention Basin 500 cfs C, 400- 200- .500 cfs: Pre-development 3 Runoff 0 1 1 . I I . 0 10 20 30 40' 50 60 - 70 80 90 100 110 ' 120 Time in Minutes FIGURE V-81 1,600 SUBBASIN HYDROGRAPH (REDUCED RELEASE RATE) - NOTE: Only Subbasin No. 3 is shown. Watershed Peak Rate of Runoff 1,400- Post-development (reduced release - Watershed Peak 0 Runoff U Rate of rate) 1,200 % Pre-development =1,500 cfs % Q=1,500 cfs % 0-1,000- % Uncontrolled 710 cfs: .2 800 Post-Development Release Rate from U Runoff Detention 400 cfs 600 - lb Post-Development 400- 200- ':: @Pr ed"e'v`el'o`p` m* e n t 3 0 r Po .%%% ' I st-dev 0 e 'o me r nt @4*@,OOL7 re ease ate, Q 1600 cfs 7 10 cfs 0 10 20 30 40 50 60 70 80 100 110 120 Time in Minutes FIGURE V-9 EQUATION 1 Pre-development Subbasin Peak Discharge Contribution to Watershed Peak Pre-development Subbasin Peak Discharge r 7-Assigned Release Rate Percentage EQUATION 2 Pre-development Subbasin Peak Discharge X Assigned Release Rate Percentage Allowable Post-development Peak Discharge The application of these two equations to the determination of appropriate post- development peak discharge rates defines the release rate percentage concept of stormwater management. This concept was developed to be fully responsive to the intent and requirements of Pennsylvania Act 167. The release rate percentage concept provides performance standards for storm drainage control in a watershed. The significance of this approach lies in the fact that the concept provides an effective tool for comprehensive watershed stormwater management. Determination ofRelease Rate Percentages The previous paragraphs introduced the release rate percentage concept using a simplified example, The following discussion presents the general strategy that was used to apply this concept in the Lake Erie Area watershed. The intent of the release rate percentage concept is to identify the general characteristics of subbasin interactions and combinations and defin e their relative impacts on total stream flows. This information is used to calculate the assigned release rate percentages as described previously. For areas modeled, the general approach employed in the Lake Erie watershed was to establish release rate percentages for each subbasin by determining the peak rate of runoff from the subbasin and its contribution to peak discharges in downstream reaches. This was accomplished using the Penn State Runoff Model described in Section IV of this report. The specific steps in the approach are as follows: Lake Erie SWMP V - 17 4026-02 1. Perform overall watershed modeling u sing the Penn State Runoff Model. 2. Identify the modeled flow contribution that a particular subbasin contributes to each of the modeled downstream reaches. 3. Calculate the release rate percentage for each subbasin at each downstream reach. 4. Assign a single release rate percentage for each subbasin which will I adequately protect all downstream reaches. Areas not included in the modeling effort were assigned a release rate percentage of 100%. In these areas, which were previously identified in Chapter IV, runoff drains essentially directly to Lake Erie. Due to these circumstances, the stormwater management goals can be achieved through the application of a uniform standard requiring that post-development peaks shall not exceed the pre- development peak discharge rates (i.e., a release rate percentage of 100%). Assigned Release Rate Percentages Assigned releas e rate percentages for the Lake Erie Area watershed are tabulated in Table V-5 and illustrated in Plate V-1. Please note that in both Table V-5 and Plate V-1, the subbasins have been aggregated into "Release Rate Percentage Areas". Application of the Assigned Release Rate Percentages As indicated previously, the release rate percentage concept is a tool for watershed level stormwater management, developed to ensure that the application of runoff control plans for individual sites consider downstream stormwater runoff implications. As such, the release rate percentage fanctions as a performance standard; that is, it defines an end result which is to be attained. Under this approach, an individual developer can select and design those drainage control measures that are mostappropriate to the site as long as the applicable release rate percentage for the subbasin.is met. It is important to note that the assigned release rate percentages must be applied only to actions which control peak runoff through detention, retention or other methods which attenuate runoff discharges. Applicable stormwater control techniques are discussed in. Section VI of this report. V_ 18 Lake Erie SWMP 4026-02 Table V-5 Assigned Release Rate Precentages V- 19 Lake Erie SWMP 4026-02 In order to use the release rate for a particular site in one of the delineated release rate percentage areas, the developer should follow the following general sequence of actions. 1. Compute the pre-development and post-development runoff for the specific site using an approved method for the 2, 10, 25 and 100 year storms, using no stormwater management techniques. If the post-development peak rate is less than or equal to the pre-development rate, the requirements of Act 167 and this plan have been met. If the post-development runoff rate exceeds the pre-development rate, proceed to Step 2. 2. Apply on-site stormwater management techniques to increase infiltration and reduce impervious surfaces. Recompute the post-development runoff rate for the 2, 10, 25 .and 100 year storms; and if the resulting post-development rate is less than or equal to the pre-development rate, the requirements of this plan have been met. Otherwise, stormwater detention or retention will be required and the developer should proceed to Step 3. 3. Multiply the assigned release rate percentage for the area times the pre-development peak runoff rate to determine the allowable total peak runoff rate from the development. Design the necessary detention/retention facilities to meet the allowable peak runoff rate standard. It should be noted that stormwater storage can be provided on or off site. The possibility for regional or off-site facilities is an option which can be considered as a means to more efficiently provide the needed facilities, in terms of both cost and land requirement considerations. In many areas, the best solution may.be for several development sites to share ajoint facility. Municipalities may also benefit from this approach. They may maximize development in prime development areas by providing regional or distributed storage through the use of natural or artificial takes, floodplains and steep sloped valleys which are unsuitable for development. However, where off site storage is to be used, the developer must ensure that no flooding or harm will be caused by runoff between the new development and the off site storage area. This may require the protection of the stream channel or the construction of a storm sewer to convey runoff to the storage site. Lake Erie SWMP V-20 4026-02 PERMISSIBLE RUNOFF COMPUTATIONTECIEVIQUES GENERAL A number of techniques and methods have been developed and are used to estimate rates and volumes of runoff from land. Runoff computation techniques permissible for use in developing runoff control plans pursuant to the requirements of this Plan have been identified. It is recommended that municipalities require land developers to limit the computation techniques employed to one or more of those listed. The list of permissible techniques includes a cross section of the most commonly used computation methods entailing a range of approaches, levels of effort and required access to computer, facilities. The list affords developers the opportunity to select from a suite of techniques. At the same time, the number of techniques which the local reviewing engineer must be familiar with is kept to a manageable number. In addition, the use of inapplicable, unproven or inaccurate techniques is prohibited. PERMISSIBLE RUNOFF COMPUTATION TECHNIQUES The recommended permissible runoff computation techniques are as follows. Soil Conservation Service Urban Hydrology Method (TR-55) 2. Soil Conservation Service Model (TR-20) 3. U. S. Army Corps of Engineers Flood Hydrograph Package (HEC-1) 4. Penn State Runoff Model Engineers involved in the preparation of stormwater control plans and reviewers of such plans should review the pertinent information relative to the use and applicability of each of these methods. It is important that the assumptions implicit and explicit in each of the techniques be understood and that the techniques are properly applied. Lake Erie SWMP V - 21 4026-02 LAKE ERIE AREA WATERSHED STORMWATER MANAGEMENT PLAN 4:U SECTION VI STORMWATER MANAGEMENT TECHNIQUES JrNTRODUCTION One of the key features of the Stormwater Management Act 167 is its mandate to implement comprehensive stormwater runoff control practices. The Act requires stormwater planning at the watershed level in such a manner that adverse impacts of storm runoff are prevented, both at a particular site and at every potential flood prone location downstream from the watershed. Therefore, any stormwater management technique must consider runoff impacts on the watershed. St udies in recent years have identified a number of methods of reducing the impact of development on storm peaks. Many management practices indicate the ingenuity of the planning, engineering and regulatory agencies. In particular, the publications of Soil Conservation Service (SCS) of Department of Agriculture (USDA), U.S. Environmental Protection Agency (EPA) and American Public Works Association (APWA) are quite comprehensive and aid in expanding some of the management practices reported in this section. The present-day emphasis. on detention or reduction of urban runoff within the contributing source area represents a remarkable shift in runoff control strategy that h as occurred only just recently [Kibler and Aron, 1980]. This trend toward on-site runoff abatement includes control measures that either reduce the runoff directly at the source or delay the arrival of runoff contributions at some critical points downstream. Attesting to the strength of this trend is the large 'and growing number of publications describing various on-site control measures. Notable contributions in thi s regard include those by Poertner [1974, 78] on stormwater detention practices; Becker et al. [1973] on rooftop storage; Aron et al. [1976] on general runoff abatement measures including infiltration trench design; Montgomery County Soil Conservation District on storage detention ponds; ASCE, The Urban Land Institute, and the National Association of Homebuilders vi-I Lake Erie SWMP 4026-02 [1976] on residential runoff abatement measures; and Field [1978] and Field and Lager [1975] for comprehensive reviews of structural and nonstructural measures. Methods applicable to almost all watersheds are based on the principles of velocity reduction, -infiltration enhancement, detention and retention storage, etc. However, site- specific conditions in a given watershed may lead to the development of innovative control measures. All the methods are designed to control sediment, pollution and stormwater within the watershed. Although the design of stormwater control facilities is usually completed by engineers and landscape architects, key policy questions should first be answered by local officials. Preferences of. local residents concerning level of protection, aesthetics, m aintenance . responsibilities, and cost allocation should be assessed by local officials, not professionals. After community stormwater management policies have been established, detailed design or design review of particular controls and measures can be carried out [Clinton River Watershed Council, 1984]. Where practical, control measures should be designed to exploit the beneficial uses of the stormwater such as recreational and aesthetic benefits and recharge of underground aquifers. In many cases this can be the decisive factor in approval of a new land development. The intent of this chapter is to review the existing storm water management techniques and make recommendations on their applicability, from many different perspectives such as suitability for the study watershed, cost, effectiveness, advantages, disadvantages and maintenance.etc. ............... . .............................. ............. .... . ..... ....... .. . .... -1 ...I. ..... . .........-... _ _ ............ ......... .......... . EVNCEff Of 7V"W4 ....... TER@ .. ....... I..... ---- ............. ........... ............. I------ ..................... ........ ..... .. ....................... ... ....... ....... ... ........... ...... -1 ............. .... ...... ...................... I------ ...... ......_...... ........ .... Early stormwater management efforts concentrated on transporting the runoff as quickly as possible from a storm location, by routing it through storm sever systems. As the urban development increased in the watershed, such a flood control effort resulted in the worst flooding conditions downstream, due to increased total flow, peak flow rate, stream velocity and flow depth. Land development causes an increase in the rate of runoff from the site, resulting in an increased peak flow rate. Changing a natural channel to a concrete-lined ditch or a storm sewer system increases the velocity and reduces the travel time to downstream locations. A reduction in the travel time may make the peak flow rate from one watershed, to contribute or in the worst case to coincide with the peak flow rate of some other watershed(s). This again results in an increased peak flow rate. Detaining the storm water and releasing the maximum rate over a longer period of time may also induce the same adverse effect. VI-2 Lake Erie SWMP 4026-02 It ishow recognized due to above mentioned problems that, the most logical and effective approach to control the storm runoff is to maintain the natural runoff flow characteristics. This can be accomplished in general by maximizing natural infiltration processes, reducing impervious surfaces, preserving floodplains, and controlling storm runoff in the watershed. There are numerous, technically acceptable techniques which have varying degrees of applicability in the . study area, depending on the site and watershed characteristics. Some of the most widely used ones will be described here, along with a brief discussion of their key- features, advantages and disadvantages, and typical costs. It will be up to each individual developer to select the techniques that are most appropriate to the project and site. It is most likely that in most situations, a combination of on-site controls will be the most appropriate and least costly stormwater management system. Nevertheless, some alternatives must be carefully analyzed. For example, when several detention basins are used, their interaction must be considered, since a combination of the timing of their releases could aggravate downstream flooding father than alleviating it. Also, the efficiency and costs of many of management alternatives vary from one location to another. Many of the alternatives, such as on site storage basins, erosion control, and flow reduction alternatives, may be feasible only for areas of new development [Kibler, 1982]. To determine the most appropriate set of techniques for a particular site, several factors should be evaluated- 1. Soil characteristics (i.e. soil permeability, erodibility) 2. Topography 3. Subsurface conditions 4. Drainage patterns (i.e. proximity to stream flooding problems) 5. Proposed land uses 6. Costs 7. General advantages and disadvantages of each technique. VI-3 Lake Erie SWMP 4026-02 STORMWATER RUNOFF PROBLEMS, FLOODING During high intensity, or long duration storms the existing infiltration capacity of soils mav be exceeded and surface storage filled to capacity. Once this happens, runoff occurs in 'the form of overland and channel flow. During some high runoff and relatively infrequent storm events, if the existing watercourses have insufficient capacity to convey surface flows, they get flooded. Natural floodplains provide some benefits by serving as reservoirs, natural recharge basins, collectors of pollutants, wildlife habitats etc. As floodplain or upstream areas are developed, this natural beneficial phencimenon, becomes a disaster due to its increased frequency and magnitude. Thus, new developments increase the flood problems and damage downstream as compared to predevelopment. There are many ways to reduce the impact of new development on flooding. Some general concepts to consider in determining which solutions are applicable to a study area are listed below: 1. Limit development of floodplains and prohibit development in floodways 2. Increase infiltration 3. Reduce runoff rates 4. Store precipitation and runoff where it falls and release it slowly 5. Keep water confined in adequate pipes or channels 6. Protect areas subject to flood damages 7. Build flood control measures 8 Limit erosion and sediment transport EROSION AND SEDIMENTA TION When raindrops hit bare soil, the cumulative effect is the splashing of the hundreds of tons of soil into the air. , Some particles are washed into streams or downstream areas VI-4 Lake Erie SWMP 4026-02 unless the velocity is very low or the soil is protected by some means. This phenomenon is called erosion. The runoff from new land developments can result in erosion both on- site and off-site. Once soil erosion begins, the soil particles transported by runoff and water currents begin to settle down in downstream drainage ways, which is called sedimentation. Sedimentation may result in blockages of natural watercourses, plugging of culverts and storm sewers, smothering of vegetation, filling of reservoirs, etc. The sedimentation occurs at increased rates during and following land development because graded areas are left in an unprotecte*d state. Data collected by Brandt [1972] shows that erosion rates on land undergoing development can be 2,000 times the erosion rate of forested lands. Erosion problems in the Lake Erie Area Watershed are particularly significant in the vicinity of the bluffs along the Lake Erie beach. Unless properly collected and transported, runoff in the vicinity of the bluffs can collect on the surface of the bluffs, near the crest. As the collected water percolates into the ground, it moves out through the bluff face. This excess water adds extra weight and stress to the bluff, causing erosion and extreme slumping. This ultimately can lead to loss of property and threats of damage to residential, commercial, and industrial properties. General concepts to be followed for minimizing erosion and sedimentation include the following: 1. Protect the soil surface to withstand effects of rainfall and runoff 2. Limit soil erosion through site management practices 3. Store rainfall and runoff where it originates and release it slowly 4. Catch sediment before it enters natural drainage ch annels Activities specifically appropriate to drainage in the vicinity of the shore line bluff areas include.- VI-5 Lake Erie SWMP 4026-02 1. Collection of surface runoff in properly designed stormwater collection and conveyance systems. 2. Conveyance of surface water runoff to the base of the bluffs thorough outfalls equipped with energy dissipation devices. POLLUTANT TRANSPORT Runoff from developed areas contains more pollutants than from natural watersheds. These pollutants include heavy metals, BOD, and high concentration of suspended solids. Heavy metals and BOD generally increase as the area is developed and reach a plateau when the development has stabilized. Suspended solids increase during first two years following the disturbance of land for development. The impacts of these pollutants depend on the existing quality and use of the receiving waters. If the newly developed area drains into a supply reservoir, an increase in the amount of pollutants could be very significant. In other cases, the impacts may be difficult to determine and are often long- term, subtle, and persuasive rather than immediate. ... ... ..... EL IWM ....... OMMM swww4m. @ @.. I I OT . ......... . ............. .... .. Many methods are available to alleviate the impact of urbanization on the quantities and rates of stormwater runoff. Maryland Interim Watershed Management Policy [APWA, 198 1 ] states, "When engineering a site for stormwater management, two overall concepts must be considered: 1) the perviousness of the system should be maintained or enhanced, and 2) the rate of runoff should be slowed. Land development methods which tend to reduce the volume of runoff are preferred over methods which tend to increase the volume of runoff." Many of the steps taken to reduce flooding also have significant effects in reducing erosion, sedimentation and stream pollution and may reduce the need for capital-intensive storin sewer systems. All things considered, the most advantageous means o f* controlling stormwater runoff from new developments is by minimizing the amount -of increased runoff volumes produced. If it were possible to complete the new development in a manner such that there would be no change in either the volume or peak rate of discharge after develo pment there would be essentially no stormwater related impacts. While it is VI-6 Lake Erie SWMP 4026-02 recognized that, in most cases, it may not be possible to accomplish the goal of making both post-development runoff volumes and peak rates of runoff match pre-development conditions, reasonable efforts should be made to minimize increases in total runoff volumes prior to the design of supplemental controls designed to control peak discharge rates. It is recommended that land developers be encouraged to take reasonable and applicable steps to incorporate features into their developments which will serve to minimize increases in stormwater runoff volumes. R UNOFF VOL UME RED UCTION MEASURES Following are brief descriptions of measures which may be taken to limit increases in total runoff volumes resulting from new developments. The applicability of these measures is highly site specific and dependent upon the nature of the development. However, it is recognized that the potential application of these techniques be seriously considered early in the design of land development activities. Limit the Amount ofLand Disturbed The added volume of runoff produced' as a result of the development of "virgin" land is directly related to the amount of land cover changed from its natural state to a more impervious condition (usually paved). Consequently, increases in runoff volumes can be minimized to the extent that land cover disturbances can be minimized. Individuals involved in land development activities, should, therefore, be encouraged to optimize their development activities from the standpoint of accomplishing the basic objectives of the development while minimizing the amount of paved areas used and natural areas disturbed. VI-7 Lake Erie SWMP 4026-02 Utilize Terraces, Contoured Landscapes, Runoff Spreaders, Diversions and Grassed or Rock-Lined Waterways These measures increase the time of concentration by increasing length of overland flow, and thus lowering the flood peak. They will provide the additional benefit of reducing total runoff by infiltration if the site has well-drained soils. Runoff spreaders spread runoff or direct it into a system of terraces. Terraces are more suitable for reducing erosion from agricultural and non-urban areas and conserving soil moisture. They reduce effective slope length and runoff concentration. About 90% of the soil that is moved is deposited in the terrace channels. In contouring, crop rows follow field contours to prevent erosion and runoff. It can reduce average soil loss by 50% on moderate slopes and less on steep slopes. It must be supported by terraces on long slopes. There are no soil or climatic limitations on practicing contouring, but it is not feasible on very irregular topography. Grassed waterways or swales stabilize vegetation on drainage channels. For"velocities of up to 8 ft/sec runoff is reduced by grass channels, if correctly graded and stabilized. Detailed design information for this category of alternatives can be obtained from the Soil Conservation Service's Engineering Field Manual for Conservation Practices. Use of Infiltration Devices Infiltration devices are used to reduce flood peaks by releasing all or part of the stored runoff into the ground water. The infiltrated water may appear a short distance downstream as surface water at a later time. However, the runoff hydrograph at the outlet point should be much lower and.drawn out in time than that from runoff delay techniques [Aron, 1975J. An example application of infiltration storage techniques is provided in Figure VI-I. VI-8 Lake Erie IWMP 4026-02 Figure VI-1 Example Application of Roof and Parking Lot Infiltration Facility Irv Von Drain Pipes 0 Storinwater Roof Infiltration Facility Overflow to 0 Detention Downspouts Facility Soils comprised of sands and/or silty sands have high infiltration capacities, and therefore are well suited for infiltration storage. Soils comprised of fine silts and clays have low infiltration capacities and therefore, are not suitable for constructing infiltration devices over them. Deep soil sampling should be performed to assess the feasibility 'of water loading the various geological strata for purposes of stormwater disposal. Percolation tests, pumping tests, and soil sampling should provide useful data about the depth, size, and location where subsurface storage Js practical. In the Lake Erie Area Watershed, a number of the soils have properties which can limit the applicability of infiltration storage. Therefore, this alternative should be used with caution. If this method is proposed as the primary means to reduce runoff, for large development sites or for sites located in landslide-prone soil locations, a soil engineer's report should be obtained. Moreover, infiltration systems should not be used where there is a < VI-9 Lake Erie SWMP 4026-02 reasonable probability the runoff may be contaminated (e.g. industrial sites, commercial parking lots, etc.). The following techniques for stormwater control are based on the principle of encouraging infiltration to ground water. Seepage or Recharg, e Basins Figure VI-2 shows a typical design of a seepage or recharge basin. In this method, runoff is collected in various storm drainage systems and then passed into large excavations called seepage or recharge basins designed to allow a large percentage of annual rainfall to recharge an underlying aquifer. In addition to reducing runoff volumes, this method offers to put the stormwater to beneficial use by allowing a large percentage of runoff to recharge an aquifer. Figure VI-2 Seepage or Recharge Basin Surface Runoff via Graised Swile Bypass tbr Excess Runoff E.mergency Stormwater Overflow Drainage system WW Sediment Trap Splash Pad 2" Coarse Sand Generally, the infiltration basins must be located in aquifer recharge areas, but they may be used whenever the water table is more than 48", below the ground surface. If they are used as the only means of stormwater control, their size must be sufficient to store the area's maximum design rainfall VI-10 Lake Erie SWMP 4026-02 from all paved 'areas. However, seepage or recharge basins are economically more feasible if designed to recharge a limited amount of the runoff that is produced by rainfall events and to overflow relatively early during intense rainfall events. Control of this overflow may require the use of additional stormwater management facilities. As indicted above, when seepage basins are used there is a need to consider the impacts of the type and quality of runoff being infiltrated; e.g., water quality impacts on ground water, and possibility of the pit being sealed by the salts in the water. Seepage basins should not be used where there is a significant potential for pollution of the ground water. In order. to maintain good infiltration rates, the bottom of the basin should be kept silt free by using a. sediment trap. In addition, an emergency overflow structure is 6Figure 0M-3 required to bypass excess Seepage Pits runoff. Seepage Pits or Dry Wells Seepage pits are small excavations designed to overflow during intense storms, but reduce flood peaks by encouraging infiltration to ground water. They can be effectively used at the sites where soil permeability is over 0. 15 ft/day and water table is more than 48" below the bottom of the pit. There are two important design considerations associated with seepage pits: (1). RA" Sofid Lim the minimum size depends, on porosity of the soil How Map Lake Erie SWMP VI-II 4026-02 porosity of the soil and design storm) should be sufficient to maintain predevelopment infiltration rate; (2) side area should be at least two times larger than the bottom area. Figure VI-3 shows three seepage pit designs each with an alternative overflow mechanism. Seepage Beds or Ditches Seepage beds dispose of runoff by infiltration it into the soil through a system of perforated pipes laid in ditches. The runoff should be allowed to pass through a sediment trap as shown in Figure 1, with a bypass structure to drain runoff from extreme rainfall events. They are not suitable for sites with water tables less than 48" deep and extremely low permeability. A typical design of a seepage bed is shown in Figure VI-4. Figure Vi-4 Seepage Bed I Alit, r @dh 2" Straw 12" Topsoil or Paper 10A. 12" Gravel (0 1. 18" Gravel 10 Foot Minimum Separation Dutch Drains Dutch drains are employed in residential developments. They are simply ditches either filled entirely with gravel or covered with top -soil and seeded. Very wide drains are usually covered with brick lattice or porous block as shown in Figure VI-5. The drains may either be located directly VI-12 Lake Erie SWMP 40 26-02 under the roof eaves along the length of a building, or runoff can be routed from downspouts to the dutch drain. Table VI-5 Dutch Drains Brick Lattice Porous Block Grass If dutch drains are the only means of stormwater disposal in a development, they should be able to drain area's design rainfall alone, and therefore their siz e will be quite large. More often two to four feet drains are combined with other control alternatives for partial stormwater management using dutch drains. Porous Pavement Porous pavement is a special asphalt mixture designed to pass water at a high rate to a specially prepared subbase. The special subbase is thicker than a normal gravel subbase and is composed ZARIN of coarse graded stone supplying SIB large void spaces to store VI-13 Lake Erie SWMP 4026-02 runoff. Figure VI-6 shows a typical porous pavement cross-section. The base aggregate is designed to have about 40% voids ratio. Regardless of design traffic number (DTN), a minimum surface thickness of 4" should be provided. Also, the combined surface and base thickness should not be less than anticipated frost penetration. Porous pavements have shown very positive results in regard to permeabilities, wear resistance and freezing - thawing effects. However, the main problem with porous pavements is that of pore clogging by muddy tires. PEAK DISCHAR GE CONTROL DEVICES Peak discharge control devices are those which control peak discharges rates by either lengthening the runoff path of the storm water or storing it and releasing it at a controlled rate. The runoff delay may vary between 15 to 30 minutes for very small areas to several hours for drainage basins of larger extent. A common goal of delay devices is, however, the disposal of all stored water before a second storm might hit. The stored water must be allowed to release at a flow rate that is designed not to cause harm. Delay of runoff is accomplished by two basic principles of detention and retention. Detention is defined as detaining a large portion of the runoff from a storm, for a time period approximately equal to the natural runoff duration. Retention, on the other hand, is defined as holding of runoff for some time period longer than the natural runoff period. There are following alternatives available based on the principle of runoff delay. There are a number of on-site locations for temporary storage of precipitation and runoff are generally considered: 1. Storage in ponds and lakes 2. Rooftop storage 3. Underground storage VI-14 Lake Erie SWMP 4026-02 4. Parking lot storage 5. Blue-green storage 6. Multiple use storage areas In. planning on-site storage methods, one should consider existing physical, social and economic limitations of the area. What may be a good solution at one site, may be inappropriate at another. Detention and Retention Basins Detention and retention basins take a variety of forms. Some are wet (filled with water all of the time) and some are dry (filled with water only during storms). Some are designed as a continuation of a stream or river (on-strearn basins) while others are separate from the river (off-site basins). Off-strearn basmis are usually connected to the water course by pipes or swales. Dry Ponds As the name implies, dry ponds are designed to be normally dfy with the ability store a portion of the stormwaterduring a storm event and then release the stored volume slowly and safely. Typically they are used in areas where runoff volume has been increased and it is desirable to reduce the runoff rate. Retention basins are used when extreme limits on downstream flow rate or velocity are required. The outflow rate'will be relatively low and extended over a longer period of time as compared to the outflow period of detention basin. This requires large amounts of storage for detaining stormwater for periods greater than 24 hours. Figure VI-7 shows a typical detention basin design. One detention basin can be designed to control the stormwater from 2, 10, 25 and 100-year VI-15 Lake Erie SWMP 4026-02 design storm events, by constructing multi-stage outlet structures. The outlet flow discharge rate from the basin will depend on the return period of the design storm. Table V1-7 1@pical Detention Basin Design Upper Outlet Top of Dam Water Surface During Design Storm Spillway Elevation ChanneIInlet"__--'--------._ _.@ A, Lower Outlet Q+:11*.ng Basin Extra Excavation for Wet Basin I Elevadon Pipe Inlet Rip Rap opo Dam Extent of Inundation During Design Storm Upper Outlet Channel Inlet .---Low Flow Channel Lower Outlet Trash Rack Stilling Basin Emergency spillway Plan RooftopRetention Rooftop retention utilizes the built-in structural capabilities of rooftops to store a certain amount of rainfall that falls on them. In many cases, existing roof structures require little modification to function as retention structures. On fla t rooftops, drains must be designed with proper outlet capacities to control release VI-16 Lake Erie SWMP 4026-02 rates to the design level. Overflow Figure VI-8 mechanisms should be provided to Examples of Rooftop Detention preclude danger from overloading. Devices Special considerations of roof 4qU Roof Drain water tightness may be necessary Typical Roof Systern with Controlled when water is to be detained for Release Drain and Overflow Scupper longer time periods or where Drain Hole frequent freezing and thawing are Strainer prevalent. Figure VI-8 illustrates several types of roofto'p retention devices. On sloping roofs, the Pipe retention can be achieved by Showing Inlet Hole providing findams. Findams are actually about 4" high gravel Table V1-9 ridges at 15 to 30 ft spacing as Roof Ponding With Gravel Dikes shown in Figure VI-9. Individual wedge-shaped ponds would build Coarse Gravel Blanket Ponded Stornswater UP behind. these "minidikes". Fine Gravel Dike Through laboratory studies it was found that a series of five dikes of Sloping Roof 1/4 inch gravel placed on roofs of Downspout Draining onto BUILD]NG 1% slope will cut the peak runoff runoff rate by 50% and extend the runoff time by about 30 minutes [Aron, 1975]. Finer gravel would naturally delay the runoff further. The effectiveness of the rooftop storage is a fimction of the actual area affected by such storage. It is most effective when used as an integral part of a larger stormwater runoff control plan. Detailed structural analyses of the structure should be completed to assure that the added roof load represented by stored water can be safely supported. Moreover, additional maintenance -should be anticipated on roofs subject to leaf accumulation. VI-17 Lake Erie SWMP 4026-02 Wet Ponds Permanent or wet ponds are detention/retention structures filled with water all the time with adequate detention capacity to store the design floods above normal ponds level. Overflow spillways must be provided to bypass or discharge flows into floodways on the peripheries of the ponds so that safe water-storage elevations are not exceeded nor banks breached. For extremely large ponds, adequate design precautions should be taken to minimize possible shoreline erosion due to ice, wind and wave action. Sediment accumulation and water pollution due to roadside accumulations of salts, copper, and asbestos from brake linings, grease, oil, and heavy metals, are the disadvantages associated with wet ponds. Such deleterious material should be screened out from the drainage system by interception and. disposition before it reaches stormWater storage ponds. In some locations municipal, state or federal safety standards regarding the depth and volume of water will have to be met. These ponds are unquestionably more aesthetically appealing than a typical dry detention basin. In addition, they can be designed to provide some recreational benefits. North Park Lake is an example of a permanent pool. Figure 10 shows some suitable locations in a site plan for a residential development [Becker et al., 1973]. The main difficulty with wet ponds lies in the frequent unavailability of land. Dry ponds can be made rather inconspicuous as an integral part of the landscaping or as lawn areas for office buildings. For example, depressed front lawn areas can be designed to detain runoff from intense storms and to serve as building's green space in dry season. The outlet pipes allow the ponds to drain in 12 to 24 hours, and a certain amount of water undoubtedly filters into the ground [Aron, 1975] - thus drying the areas and returning them to a suitable condition for dry weather uses. VI-18 Lake Erie SWMP 4026-02 Underground DetentionlRetention Tanks This alternative involves the construction of underground holding tanks or large sized pipes as a means of providing controlled runoff from the site. In areas where land is expensive or surface topography is not suitable, these tanks can serve the same function as basins, while conserving land area. Outflow control devices may consist of small gravity pipes, or weirs. In some applications pumping may be required to discharge the stored runoff. This method can be quite expensive because of high material construction costs and possible pumping requirements; however, they may be appropriate in situations where land area is at a premium. An example general design of an underground stormwater detention facility is illustrated in Figure VI- 10. Figure VI-10 Underground Detention Facility Parking Lot Parking Lot Surface Surface Inlet Grates Ac ess Pit Inlet Grates F 7, . . .......... . .... . . . ..... Outlet Pipe Slop%.. Access Pit Oriface Slope Oversized Pipe Plate Oversized --144 @hce C6 Pipe 0 Plate Outlet Pipe Proffie View Plan View VI-19 Lake Erie SWMP 4026-02 Parking Lot Detention Parking lots cover a major portion of commercial developments and are, therefore, large contributors of stormwater runoff. Stormwater runoff can be detained on parking lot sites by shallow basins or swales. If properly designed, this measure can be quite effective. Initial construction costs implementing these measures are only a small percentage above the construction cost of conventional parking lots. Arrangements of areas in a parking lot to accept ponding should be planned so that pedestrians are inconvenienced as little as possible. A 7" design depth is not unreasonable for parking locations in the remote areas of lots [APWA, 198 11. The facility should be designed to drain completely and avoid formation of ice. Design considerations should recognize the possible use of porous asphalt, provided the subgrade has an adequate infiltration capability. Expansive and/or collapsing type soils may preclude this solution. An alternative to impervious paving of parking areas is the substitution of grassy strips. The ground surface of the planting strip is depressed and driving lanes are graded to direct the storm runoff into the depressions. The strips. should be filled with pervious soil to allow a maximum of infiltration, and planted with a Fescue-type grass which is both resistant to occasional swamping and dry soil conditions. The strips should be oriented perpendicular to the parking lot slope and surrounded by broken curbs to protect them from being overrun by cars. Blue-Green Storage Incorporation of stormwater storage in urban drainage ways traversing roadways is a version of detention ponding that has been identified as the blue green concept. Topographical characteristics of many land areas adjacent to roadway embankments make them very much adaptable for use as detention facilities. This can be achieved by designing the culverts to pond where appropriate, as shown in Figure VI- 11. Many drainage structures can be designed to operate in this fashion. Roadway embankments at control points should be stabilized and protected to minimize erosion effects of retained water. VI-20 Lake Erie SWMP 4026-02 Figure VI-11 Road Embankment Stormwater Detention Stormwater Impoundment Stream-@ A Q'S ...... . . . . . . A A PL4N Roadway Stormwater Culvert Impoundment Embanlanent WrA Secdon A-A J Detention within Pedestrian Plazas and Malls On-site detention in heavily congested areas can be incorporated effectively in the design of pedestrian plazas, malls, and other similar type developments. The ponding requirement can be accomplished at selected locations with very shallow depths (I to 3 in) to avoid public inconvenience. Frequent maintenance and suitable discharge control devices designed to satisfy the architectural objectives of the land development are necessary in developments of this type. VI-21 Lake Erie SWMP 4026-02 Multiple Use Impoundment Areas These areas utilize sites having primary functions other than runoff control. In new developments, such multiple use should be incorporated into the primary design. For example, open space and grassed areas provided in the land development to enhance the aesthetic appeal can also be used as storinwater detention facilities. This can be accomplished by providing stormwater release controls such as weirs, orifices, small diameter pipes and gates etc. A hard-surface basketball or tennis court can be designed to drain adjacent grassed or paved areas. The stormwater would collect in grass swales around the edge of the court, seep through a gravel drain to retain the sediment load, and discharge onto a porous asphalt surface. Some type of emergency drain should be provided. Positive drainage toward the control devices is essential to avoid the swampy conditions, weed growth and increased maintenance costs. For optimum operation of control structures, it is also essential to screen out the floating debris from the inlet stormwater. RELA TIVE AD VANTA GES AAD DISAD VANTA GES Table VI- I gives a brief summary of principal urban runoff abatement practices and their associated relative advantages and disadvantages. As was expressed previously, the runoff volume reduction measures which simultaneously reduce runoff peaks offer significant advantages from the perspective of both local and watershed wide effects. However, since there are limitations inherent in the volume reduction techniques, it is likely that an overall storrawater control plan will include a combination of applicable volume reduction features and peak discharge control features (i.e. detention and/or retention facilities). Selection of the best combination of techniques to be used in a particular instance should be made by the developer in consultation, or at least with the concurrence, of the municipal reviewer. VI-22 Lake Erie SWMP 4026-02 TABLE VI_ I ADVANTAGES AND DISADVANTAGES OF ON-SITE CONTROL METHODS METHOD T ADVANTAGES DISADVANTAGES REDUCTION OF RUNOFF / INFILTRATION STORAGE Dutch Drains - Reduces the total volume - Looses efficiency if of runoff. intensive storms follow in - Reduces the peak runoff rapid succession. discharge rate. - Subject to clogging by - Enhances the groundwater sediment. supply. - Limited to application - Provides additional water for small sources of run- for vegetation in the off only, i.e., roof area. drains, small parking - Reduces the size of down- lots, tennis courts. slope stormwater control - Maintenance is difficult facilities. when the facility becomes clogged. - Limited application in poor infiltration soils. Porous Pavement - Reduces the total volume - More prone to water of runoff. stripping than conven- - Reduces the peak runoff tional mixtures. discharge rates. - Subject to clogging by - Enhances the groundwater sediment. supply. - Water freezing within the - Provides additional water pores takes longer to thaw for vegetation in the and hirnits infiltration. area. - Motor oil drippings and* - Reduces the size of down- gasoline spillage may slope stormwater control pollute groundwater. facilities. - Limited application in - Less costly than conven- poor infiltration soils. tional pavements for most - recent studies suggest applications. that porous pavement's - Safety features - superior advantage will reduce skid resistance and visi- withtime. bility of pavement markings. - Provides pavement drainage without contouring. TABLE Vl- I ADVANTAGES AND DISADVANTAGES OF ON-SITE CONTROL METHODS METHOD ADVANTAGES T_ DISADVANTAGES Prevents puddling on the surface. Seepage/Recharge - Reduces the total volume i Must be fenced and Basins of runoff. I ugularly maintained. - Reduces the peak runoff If porosity is greatly discharge rates. reduced, it maybe - Enhances the groundwater necessary to bore seepage supply. holes or pits in the base. - Construction borrow pits No filtering supplied by often can be converted to the topsoil. a large seepage basin to - Usefulness limited in poor serve multiple areas. infiltrations soils. Seepage Pits - Reduces the total volume - Looses efficiency if of runoff. intensive storms follow in - Reduces the peak runoff rapid succession. discharge rates. - Subject to clogging by - Enhances the groundwater sediment. supply. - Maintenance is difficult - Provides additional water when the facility becomes for vegetation in the clogged. area. - Limited utility in poor - Reduces the size of down- soils. slope stormwater control facilities. Seepage Beds/Ditches - Reduces the total volume - More expensive than other of runoff. infiltration techniques. - Reduces the peak nmoff - Replacement of entire discharge rates. system if clogging by - Enhances groundwater sediment should occur. supply. Maintenance of sediment - Reduces the size of down- traps must be frequent and slope stormwater control consequently more facilities. expensive. - Distributes stormwater over a larger area than other infiltration TABLE VI-I ADVANTAGES AND DISADVANTAGES OF ON-SITE CONTROL METHODS METHOD ADVANTAGES DISADVANTAGES techniques. May be placed under paved areas if the bearing capacity of the paved area is not affected. Safer than seepage or recharge basins. Terraces, Diversions, Increases the overland On poorly drained soils, Runoff Spreaders, flow time, increasing the these techniques may leave Grassed Waterways, time of concentration and ground waterlogged for and Contoured Land- allowing for increased extended periods after scapes infiltration. storms. - Vegetative swales are vegetative channels may less expensive than curb require more maintenance and gutter systems. than curb and gutter systems. Roadside swales become less feasible as the nuniber of driveway entrances requiring culverts increase. DELAY OF RUNOFF Rooftop Retention - No additional land - Leaks may cause damage to requirements. buildings and contents. - Not unsightly or a safety - Stored runoff will greatly hazard. increase the load imposed - May be adapted to existing on structural support. structures. This increased construc- tion expense may be greater than the savings resulting from reducing the size of downslope stormwater management i facilities. TABLE VI_ I ADVANTAGES AND DISADVANTAGES OF ON-SITE CONTROL METHODS METHOD T ADVANTAGES -7 DISADVANTAGES Parking Lot Detention - Adaptable to both - May cause an inconven- existing and proposed ience to people. parking facilities. - Ponding areas are prone - Parking lot storage is to icing, requiring more usually easy to incorpo- frequent maintenance. rate into parking lot design and construction. Multiple Use Serves more than one Difficult to maintain the purpose. Employing areas of porosity of multi-use areas. grass, a certain amount of stormwater will infiltrate and improve the quantity of water recharged by natural filtering processes. If porous pavement is used on basketball or tennis courts, additional infil- tration will be provided. De.tention/Retention - Offers design flexibility for Facilities that empty out Basins adapting to a variety of uses. completely can have an - Construction of ponds is unsightly nature and be a relatively simple. detriment to the developments. - May allow significant Difficulty in establishing a reduction in the size of regular maintenance program. downslope stormwater In a residential development, management facilities. it may be difficult to - May have some recreational determine whose responsi- and aesthetic benefits if bility it is to pay for the runoff is not carrying maintenance program. heavy sediment loads. Consumes land area which could be used for other purposes. TABLE VI- I ADVANTAGES AND DISADVANTAGES OF ON-SITE CONTROL METHODS METHOD ADVANTAGES T_ DISADVANTAGES Permanent Ponds Will provide both a Stormwater runoff having a reduction in peak runoff high sediment or pollutant rates and a source of load should not be controlled recreation in any residential in existing ponds because of area. its adverse impact on the - Only minor modifications may be natural conditions. required to adapt an existing pond for use as a permanent stormwater management facility. - Wildlife habitat and wetlands may be preserved Underground - Minimal interference with Subsurface excavation Retention/ traffic or people. could be extremely expen- Detention Tanks - Can be used in existing as sive depending upon the well as newly developed type and amount of rock areas. encountered. - Potential for using storm- Access for maintenance water for nonpotable uses. may be difficult if proper design features are not provided. STPRMWA TER QUALITYBESTMANAGEIVENT PRAC77CES The volumes and rates of stormwater runoff from land developments are a major concern in stormwater management. However, they are not the only consideration. The impacts of stormwater runoff upon water quality are becoming of increasing concern. The predominant categories of pollutants that have been identified in stormwater runoff from developed areas are listed below. sediments 9 organic enrichment nutrients 9 toxic pollutants pathogens 0 salts There are a number of methods through which the negative effects of stormwater runoff pollution can be minimized. These. methods are generally referred to as best management practices for stormwater quality control (BMPs). These best management practices are generally low cost, relatively low technology methods of reducing the pollutant contenf of stormwater runoff. The following sections describe the most commonly employed stormwater quality BMPs. As is indicated by the following information, most of the stormwatcr quality BMPs also are effective in controlling the volumes and rates of stormwater runoff produced by new land developments and were presented previously in the context of stormwater flow control. It is fortunate that the most effective stormwater management controls have the dual benefits of reducing stormwater quantities and improving runoff quality. Vegetative Best Management Pracdces All of the following practices rely on various forms'of vegetation to enhance the pollutant removal, habitat value, or appearance of a development site. Although in practice each technique, by itself, is usually not capable of entirely controlling increased runoff and pollutant export for A development site, they can improve the performance and amenity value of other BMPs. These practices, therefore, should be considered as an integral part of every development site plan. VI-28 Lake Erie SWMP 4026-02 Limiting the Amount of Land Disturbed (Urban Forestry) Limiting the amount of land disturbed and/or replanting vegetation following completion of construction can reduce pollutants in stormwater runoff in several ways: 1) through plant uptake and storage, 2) by reducing the volume of stormwater runoff and the associated pollutants, 3) through filtering, and 4) by preventing soil erosion. With careful landscape design, as much as 50% of a residential lot can be converted into an attractive natural setting of trees, shrubs, and ground covers. The extent to which pervious, vegetated areas can be preserved and/or created will have a direct effect upon the volume of stormwater runoff and the quantities of associated pollutants that will be produced. Moreover, the cost of maintaining the vegetated areas is relatively low and the aesthetic value to the overall development can be quite high. Grassed Swales Figure VI-12 Grassed swales are typically applied in Illustration of Grassed Lined Swale residential developments and highway medians as an alternative to curb and gutter drainage systems. Figure VI-12 presents an example of a grassed swale. Grassed swales remove pollutants throu gh the filtering action of the grass, deposition in low velocity areas, and by infiltration into the subsoil. These mechanisms are most effective in removing particulate effective in removing particulate pollutants Figure VI-13 and have a negligible effect on soluble Illustration of Rock Lined Channel pollutants. Swales are generally less expensive to construction than curb and gutter. systems and maintenance is relatively low cost, generally consisting of normal lawn maintenance activities such -as mowing and watering as needed. VI-29 Lake Erie SWMP 4026-02 A variation to grassed swales is a rock lined waterway (Figure VI-13). A rock lined waterway consists of a channel lined with rock. These channels are generally less effective that grassed swales in the removal of pollutants due to a reduced filtering through the grass. However, some suspended pollutants are removed through deposition in low velocity areas. Filter Strips Filter strips are similar to grassed swales in many respects. However, they differ in that they are designed to only accept overland sheet flow and are not intended to serve a dual purpose as a conveyance facility. In practice, runoff from an adjacent impervious area is evenly distributed across the filter strips. To perform properly, a filter strip must be: 1) equipped with some sort of level spreading device; 2) densely vegetated with a mix of erosion resistant plant species that effectively bind the soil; 3) graded to a uniform, even, and relatively low slope, and 4) be at least as long as the contributing runoff area. Filter strips are especially effective when constructed as a buffer between the development activities and adjacent streams, curbs, and swales. They can also be used to protect surface infiltration trenches from clogging by sediment. An example of an application of filter strips is presented in Figure VI-14. Figure VI-14 Example Application of Vegetated Filter Strips Top elevationof strips Berms placed perpendicular oi s6r6e conto6i, 'and to top of strip to prevent directly abuts trench concenWated flows WMded Off sui rauss er s Stone trench acts as 5% strip slope or less levelspreader VI-30 Lake Erie SWMP 4026-02 The pollutant removal mechanisms in filter strips are similar to those presented previously for grassed swales. As is the case with grassed swales, filter strips are particularly effective in removing particulate pollutants such as sediment, organic material, and many trace metals. Filter strips are relatively inexpensive to establish and cost almost nothing if preserved during site development. A creatively landscaped filter strip can become a valuable community amenity, providing wildlife habitat, screening, and stream protection. The open space created by the filter strips can also be applied toward meeting established development density limitations that may be contained in local ordinances. Constructed Wetlands There are two prevalent types of constructed wetlands in use: 1) shallow constructed wetlands (Figure VI- 15) and 2) wet detention systems (Figure V1- 16). Constructed wetland systems perform a series of pollutant mechanisms, including sedimentation, filtration, adsorption, microbial decomposition, and - vegetative uptake to remove sediment, nutrients, oil and grease, bacteria, and metals. While constructed wetlands can be very effective in the removal of the broad range of pollutants encountered in stormwater runoff, it is important that they be properly designed, sited, and maintained. The critical design consideration is the Figure VI-15 Schematic of a ShaHow Constructed Wetland VL 6 inches deep Inflow 6 inches r less or less Levelspreader Forebay 2-31% mechanism (3 ft deep) 0 - 12 inches deep Outflow fit. Gradual slope VI-31 Lake Erie SWMP 4026-02 maximization of the detention time in the wetland through proper sizing and configuration to prevent short circuiting. Figwe VI-16 Example Wet Detention Wetland S-Ystem Baffle or Skimmer Outflow 0 ---------- - ----------- r --- 2R Inflow --------- Treatnientvolunie..,_ 0 Ar-OR / grease littoral, skimmer zone (3.5ft) Slope (10:1 desirable; Sediment sump 4:1 minimum) Deeper area Siting of wetlands can be difficult due to the importance of soil properties (chiefly permeability) to performance, size requirements, and concerns relative to potential nuisance insect breeding. In addition, created wetlands become a resource area that will subsequently be protected by federal and state laws. InfilOation Facilities Infiltration facilities permanently capture runoff so that it soaks to the ground water. As was presented previously, to the extent of their capacity to handle the volumes of stormwater runoff produced, they are very effective in controlling stormwater runoff flows. They also can be very effective in removing pollutants. Pollutant removal in these BMPs occurs primarily through infiltration, which eliminates the runoff volume or lowers it by the capacity of the facility. Currently, the three types of facilities commonly employed to remove pollutants from stormwater runoff through infiltration are: 1) infiltration'basins; 2) infiltration trenches / dry wells; and 3) porous pavements (grassed swales, which also promote infiltration were discussed previously under vegetative practices). e or r fl ........ 77 n ow -tto = @(35ft) @@@op VI-32 Lake Erie SWMP 4026-02 Infiltration Basins Infiltration basins are similar to dry ponds, except that infiltration basins have only an emergency spillway and no standard outlet structure (see Figure VI-17). All flow entering an infiltration basin (up to the capacity of the basin) is retained and allowed to infiltrate into the soil. Infiltration basins provide pollutant removal through volume. reduction, filtration, and settling. They are particularly effective in removing bacteria, suspended solids, insoluble nutrients, oil and grease, and floating wastes. They are less effective in removing dissolved nutrients, some toxic pollutants, and chlorides. Therefore, infiltration basins should not be used in cases where the runoff can be suspected to contain significant amounts of those pollut-rtnts. Figure VI-17 Example Infiltration Basin Layout Flat basin floor with M'. dense grass turf Inlet Rip-rap settling basin and Riprap level spreader outfall protection Back-up underdrain Emergency spillway VI-33 Lake Erie SWMP 4026-02 Infiltration basins often have relatively large land requirements and require a suitable soil to be effective. Accumulating runoff must be able to infiltrate the soil in the bottom of the basin. Typically sand and loam, with infiltration rates greater that or equal to 0.27 inches per hour are the preferred soils. Soils with percolation rates meeting this criteria exist throughout the watershed. However, high or seasonally high water tables predominate throughout most of the watershed. For infiltration to occur, ground water levels should be located at least 2 to 4 feet below the bottom of the basin. Consequently, the use of infiltration basins will not be practical throughout most of the Lake Erie Area Watershed. In filtration Trenches IDry Wells Subsurface infiltration practices, such as infiltration trenches or dry wells force rtmoff into the soil to recharge ground water'and remove pollutants. Filtration is the primary pollutant removal mechanism active in these facilities. They effectively remove suspended sediments, floating materials, and bacteria.. They are less effective at removing dissolved materials. The soil infiltration rate and structure size are the most important considerations in the design of infiltration structures. The soils underlying the structures must be tested to determine their infiltration capacity and the ground water level. The soil must neither be too impermeable to runoff nor to rapidly permeable. Moreover, a distance of at least 2 feet should be maintained between the bottom of the infiltration structure and the mean high ground water elevation. Due to the nature of prevailing conditions in the area, siting of infiltration facilities must be made carefully throughout the Lake Erie Area Watershed. Porous Pavement By allowing. stormwater to infiltrate into the soil, porous pavements can reduce runoff volume and pollutant discharge. Porous pavements can remove significant amounts of both soluble and particulate pollutants. Porous pavement is primarily designed to remove pollutants deposited from the atmosphere, as coarse solids can VI-34 Lake Erie SWMP 4026-02 clog the pavement pores. As a result, porous pavements are generally designed into parking areas that receive light traffic. As is the case with all of the infiltration systems, the effectiveness of porous pavements for pollutant removal is highly dependent upon soil characteristics and ground water levels. The soils under the pavement system must produce adequate infiltration and ground water levels should be 2 to 4 feet below the bottom of the paving and subbase system. Proper maintenance of porous pavements is important and can be extensive. The pavement must be kept free of coarse particles that can clog the pavement and prevent runoff from infiltrating. The pavement must, therefore, be regularly inspected and cleaned with a vacuum sweeper and high pressure jet. Detention Facilities One of the most common structural methods of controlling runoff is through the construction of ponds to collect runoff, detain it, and release it to receiving waters at a controlled rate. Pollution reduction during the temporary period of runoff storage results primarily from the settling of solids. Detention facilities, therefore, are most effective at reducing the concentrations of solids and the pollutants that adhere to solids, and less effective at removing dissolved pollutants. The three types of detention facilities commonly used to remove pollutants from stormwater runoff are extended detention dry ponds, wet ponds, and constructed wetlands. The first two types of facilities are discussed below. Constructed wetlands were introduced previously under the topic of vegetative methods. Extended Detention Dry Ponds As was discussed previously in regard to flow control devices, dry ponds are frequently used to control peak discharges by temporarily detaining runoff. They are designed to completely drain at the conclusion each rainstorm event. When designed to achieve pollutant load reductions, the design of the ponds are VI-35 Lake Erie SWMP 4026-02 modified to achieve longer detention times than are necessary solely to adequately control peak discharges. Generally, the ponds are designed to retain a specified runoff.volume for a period of time sufficient to achieve the desired pollutant removal. This requires sufficient storage volume and an outlet flow control devices to accomplish the desired flow detention. Dry ponds should also include a low flow channel designed to reduce erosion; vegetation on the bottom of the pond to promote filtering, sedimentation, and uptake of pollutants. In addition, dry pond designs frequently include upstream structures to remove coarse sediments and reduce sedimentation and clogging of the outlet. An example of a layout of an extended detention pond is illustrate in Figure VI- 18. Figure VI-18 Schematic of a Dry Extended Detention Pond Lower Stage Embanlanent Top Stage @Wer Extended Detention ZV Control Device Emergency ew . . . . . . . Spillway 10 Year Water Surface Elevation 2Year- Riprap Apron Gravel ei Plan View Maintenance of water quality dry ponds is important. Regular mowing, inspection, erosion control, and debris and litter removal are necessary to prevent excessive sediment buildup and vegetative overgrowth. Also, periodic nuisance VI-36 Lake Erie SWMP 4026-02 and pest control could be required. The primary constraints to siting dry ponds are land requirements, topography, and depth to bedrock. Wet Ponds The design of wet ponds is similar to that of dry ponds. In wet ponds, however, stormwater runoff is directed into a co nstructed pond or enhanced natural pond, in which a permanent pool of water is maintained. Once the capacity of a wet pond is exceeded, collected runoff is discharged through an outlet structure or emergency spillway. An example of a wet pond sys tem is presented in Figure 0VI- 19. Pond VI-37 Lake Erie SWMP 4026-02 The primary pollutant removal mechanism in wet ponds is settling. The ponds are designed to collect stormwater runoff during rainfall and detain it until additional stormwater enters the pond and displaces it. While the runoff is detained, settling of particulates and associated pollutants takes place in the pond. Wet ponds can also remove pollutants from runoff through vegetative uptake. Wet ponds should be vegetated with native emergent aquatic plant species, which can remove dissolved pollutants such as nutrients from the runoff before it is discharged to the receiving water. Wet ponds are typically designed with a number of different water levels. One level has a permanent poll of water. The next level periodically is inundated with water during storm. This level should be vegetated and relatively flat to promote settling and filtering of sediments and vegetative uptake of nutrients. The highest level will be inundated only during extremely heavy rainfall. This level should also be vegetated. Sizing of wet ponds is determined by requirements for storage volumes and desired detention times. Maintenance requirement for wet ponds include periodic sediment removal (approximately once every 10 to 20 years), mowing, and litter removal. Factors affecting siting include land requirements, soil conditions (soils should not be excessively porous and ground water tables should be relatively high), and topography. Summary of Water Quality Best Management Practices As was indicated in the preceding discussion, there are a number of techniques that represent best management practices for reducing pollution associated with stormwater runoff. These techniques all also have application in efforts to control runoff volumes and peak rates of dicharge. Consequently, appropriately designed stormwater management facilities can improve runoff water quality while achieving the required control of stormwater discharge flows. Table IV-2 contains a comparison of the pollutant removal effectives for the range of BMPs discussed under various design approaches. As is indicated in Table VI-2, the effectiveness of the BMPs varies. It is important, however, to recognize the water quality benefits that are offered and to consider these benefits in the overall selection and design of stormwater management controls. VI-38 Lake Erie SWMP 4026-02 Table V1-2 Comparative Pollutant Removal of Stormwater BMP Designs Best Management V Z6 Overall Practice / Design Effectiveness Key Grassed Swale Design 1 00000 e Low 0 0 to 20% Removal Filter Strip Design 2 (@ (@ (@ 0 Low (@ 20-to 40% Removal Design 3 0 0 0 Low C) 40 to 60% Removal Design 4 Moderate 60 to 80% Removal Porous Pavement a Design 5 Moderate 80 to 100% Removal D .esign 6 High Insufficient Knowledge Design 7 High Infiltration Basin Design 5 Moderate Design 6 0 3 (3 (A 0 (a High Source: DER Special Protection Waters Implementation Design 7 High Handbook Infiltration Trench Design 5 Moderate Design 6 Q1 (3 3 Q1 0 Q1 High Design 7 High Wet Pond Design 8 Moderate Design 9 0 0 C@ Q0 (D Moderate Design 10 0 QO (3 3 (a (9 High Extended Detention Pond Design I I (D Moderate Design 12 Moderate Design 13 High Design 1: High dope swales with no check dams Design 8: Permanent pool equal to 0.5 inch storage par a .ropervious acre Design 2:. Low gradient swales with check don Dmiga9: permanent pool equal to 2.5 (Vr); -bote, Vr equals the mean storm nmoff Design 3: 20 foot wide turfstrip Design 10: permanent pool equal to 4.0 (Vr); where, Vr equals the mews stom nmoff Design 4: 100 foot wide forested strip with lavel spreader Design 11: First - flush runoffvolume detamed 6-12 hours Desiga5: facility emiltrates first -flush: 0.5 inch mnoff/ imperviotni sere, Design 12: Runeff volume produced by 1.0 inch dawned for 24 hours Design 6: Facility exfilaztes we inch rveall'volume per impervious acre Design 13: As in design 12, but with sh"ou, marsh, in bottom stage Design 7: Facility exfiltrates all rueoff up to 2 year design storm VI-39 Lake Erie SWMP 4026-02 EROSIONAND SEDIMENTA77ON CONTROL MEASURES The ability of storm water runoff to transport material is a function of flow velocity and the erosion resistance of the material. As stormwater runoff flow rates increase, the flow velocity increases and more eroded.material is transported. As the water travels down the watershed, channel gradients reduce flow velocity and sediment begins to be deposited in streams and storm sewers. This process, known as sedimentation, continues as the flow rate and flow velocity reduces. New developments further increase the sedimentation problem by removing natural vegetation and making the bare ground susceptible to erosion. The following principles should be practiced for urban soil erosion and sedimentation control. I .Keep disturbed areas small: Areas vulnerable to erosion should be disturbed the minimum amount possible. As much natural cover as possible should be retained and protected. The construction plan should be phased whenever possible in small units and in sequence such that only the area being developed is exposed. All other areas should have a good cover of vegetation or mulch. 2. Stabilize and Protect Disturbed Areas: Mechanical and/or structural methods and vegetative methods are available for stabilizing disturbed areas. These methods include seeding, mulching, sodding, retaining walls, terracing, use of chemical stabilizers, and others. 3. Keep Runoff Velocities Low: Removal of existing vegetative cover and the resulting increase in impermeable surface during development increase both the volume and velocity of runoff. Short slopes, low gradients and the preservation of natural vegetation cover help to keep stormwater velocities low and thus limit soil erosion. VI-40 Lake Erie SWMP 4026-02 4. Protect Disturbed Areas from Runoff. Protective measures that can be utilized to prevent water from entering and running over disturbed areas are diversions, waterways, structures etc. 5. Retain Sediment within the Site Area: Sediment can be retained by two methods: filtering runoff as it flows, and detaining sediment laden runoff for a period of time large enough to allow the soil particle settle. Sediment basins, vegetative filter strips, terraces and sediment barriers may be used to retain sediment. However one should not rely solely upon vegetation filter strips, since sediment may rapidly render such areas useless by killing the vegetation. 6. In-stream Control: After precipitation and runoff has concentrated, an outlet channel is needed for safe release of the water off the site. This outlet channel needs to be protected from erosion. A wide, shallow grassed water way can be a very good method. Channels with steeper gradients need structural protection along with, or instead of vegetative measures. Typical structural measures include: earth dams with a full flow pipe through the fill, weirs, flood gates, and check dams. In designing such facilities, it is important to consider the effects of the dam or embankment on upstream properties. The design must include safety features in the form of spillways and bypasses to prevent overtopping which can cause embankment failure. The details on the design and implementation of practices described above and many others can be obtained from the Soil Conservation Service and the County Conservation District. @[email protected]@@@VE.RS.US.STO TEA. .. ..... .. .. ..... . . ........ :TIVES AGEMENT "A .... .. .... . . . .. ... ........... .... ... . .. It was mentioned earlier that the soil characteristics at the development site, such as soil permeability, water capacity, frost penetration etc. play ail 'important role in the selection of gtormwater management alternatives. This section gives specific soil information for the Lake Erie Area Watershed and discusses the soil characteristics and their impact on alternative storinwater management techniques. VI-41 Lake Eric SWMP 4026-02 Soil information for Erie County can be obtained from the publications, "Soil Survey of Erie County, Pennsylvania". These publications are prepared by Soil Conservation Service of U.S. Department of Agriculture. The survey has a general soil map showing in color, the soil associations in the county. A soil association is a landscape that has a distinct pattern of soils in defined proportions. The soil association map should not be used to determine the soil type, for selecting stormwater water management alternatives. The reason is that, a general soil map is intended to be a general guide in evaluating large areas such as a watershed, or in county-wide planning for community development. It is not a suitable map for selecting a site for locating a stormwater detention or retention facility. For example, this map can be used to establish a generalized idea, that Ellery and Alden Silt Loam s 'oils. constitute a major soil type in the Lake Erie Area Watershed. Also, the survey tells that these soils have seasonal high water tables ranging from 0 to 10 inches below the surface, thus having severely limited application for infiltration storage. Thus, a general rule can be established that infiltration storage alternative should not be approved in the Ellery and Alden Silt Loam soils unless the occurrence of the ground water table at shallow depths has been ruled out by on-site engineering tests. Table VI-3 presents some relevant properties of the Lake Erie Area Watershed soils significant to the use of various stormwater management techniques. Table VI-4 indicates the suitability of the soils for some generalize construction activiities associated with stormwater management alternatives. General conclusions that can be drawn from the information contained in Tables VI-3 and VI-4 include the following. 1. Activities designed to minimize the creation of impervious surfaces will be appropriate throughout the watershed. 2. The construction and operation of dry and wet ponds will generally be feasible throughout the watershed, although consideration must be given to site specific soil conditions. .3. The use of large scale induced infiltration systems will generally be limited by soil and ground water conditions that frequently are not suitable for those techniques. VI-42 Lake Erie SWMP 40 26-02 Table VI-3 Lake Erie Area Watershed Relevant Soil Properties Depth to Seasonal Depth To High Ground Water Bedrock Percolation Rate Soil Name (Inches) (Inches) (Inches/Hour) Allis Silt Loam 0-12 18 0.2-2.0 Beach and Riverwash 0 >48 > 8.3 Beach Sand (stabilized) 0-24 >120 > 6.3 Berrien Fine Sandy Loam 9-28 > 120 0.2-2.0 Birdsall Silt Loam 0-18 >120 0.2-0.63 Candice Silt Loam 0-18 > 120 0.2-0.63 Caneadea Silt Loam 12-30 >72 0.2-2.0 Chagrin Silt Loam 0-30 >72 0.63-6.3 Chagrin Very Gravelly Loam 12-36 >72 2.0-20.0 Conotton Coarse Sandy Loam 18-72 >120 0.2-6.3 Dune Sand >24 >72 >20.0 Dalton Silt Loam 18-72 >120 0.2-20.0 Ellery and Alden Silt Loam 0-10 >72 0.2-2.0 Erie Silt Loam 6-18 >96 0.2-2.0 Fredon Loam -0-18 >72 0.2-6.3 Halsey Loam 0-12 >120 0.2-6.3 Howard Gravelly Silt Loam >24 > 120 0.63-6.3 Langford Silt Loam 18-30 >120 0.63-2.0 Lobdell Silt Loam 0-18 >48 0.2-6.3 Mahoning Silt Loam 18-30 >120 0.2-0.63 Manlius and Lordstown >24 >30 0.2-2.0 Mardin Gravelly Silt Loam 18-30 >120 0.2-2.0 Miner Silt Loam 0-6 >72 0.2-0.63 Muck and Peat >24 >48 <0.2 Ottawa Fine Sandy Loam >24 >120 <0.2 - 2.0 Ottawa Loamy Fine Sand >24 >120 0.2-6.3 Phelps Gravelly Silt Loam 18-30 >120 0.2-0.63 Platea. Silt Loam 6-18 >120 0.2-2.0 Rimer Fine Sandy Loam 0-30 >120 0.2-0.63 Scio Silt Loam 18-30 @-72 0.2-2.0 Sloan Silt Loam 0-10 >72 0.2-0.63 Sloan Silty Clay Loam 0 >72 0.2-0.63 Trumbell Silt Loam 0-18 >120 0.2-0.63 Unadilla Fine Sandy Loam >24 >72 0.63-2.0 Volusia, Gravelly Silt Loam 0-18 >96 0.2-2.0 Volusia Silt Loam 0-18 >96 0.2-2.0 Wallingion Fine Sandy Loam 0-18 >120 0.2-0.63 Wallinkton Silt Loam 0-18 >120 0.2-0.63 Wauseon FIne Sandy Loam 0-18 >72 0.2-2.0 Wayland Silt Loam 0-18 >72 0.2-2.0 Williamson and Collamer 18-30 >120 0.2-2.0 Wooster Gravelly Silt Loam >24 T-->i2o 2.0-6.3 Table VI-4 Lake Erie Area Watershed Limitations to Suitability of Soils for Stormwater Management Alternatives Soil Name Ponds Building Sites Diversion Terraces Allis Silt Loam Shallowness High water table; shallow Shallow to bedrock to bedrock Beach and Riverwash Rapid permeability Flooding None Beach Sand - Stabilized Rapid permeability Flooding None Berrien Fine Sandy Rapid permeability Seasonally high water table; None Loam Unstable substratum Birdsall Silt Loam None High water table None Canadice Silt Loam None High water table; unstable None Chagrin Fine Sandy None Unstable None Conotton Coarse Sandy Rapid permeability Flooding None Dalton Silt Loam None Seasonally high water table; None unstable substratum Dune Sand - Rapid permeability Unstable Rapid permeability Ellery and Alden Silt None High water table None Erie Silt Loam None Seasonally high water table None Fredon Loam - Quicksand High water table Quicksand Fresh Water Marsh Flooding FGding Flooding Halsey Loam Ouicksand High water table None Howard Gravelly Silt Rapid permeability None None Langford Silt Loam None High water table None Lobdell Silt Loam None High water table None Mahoning Silt Loam None Seasonally high water table None Manlius and Lordstown Shallowness Shallow to bedrock Shallow to bedrock Mardin Gravelly Silt None None None Loam Mardin and Volusia None Seasonally high water table None Gravelly Silt Loams Miner Silt Loam None High water table None Muck and Peat Unstable Unstable Unstable Ottawa Fine Sandy Loam Rapid permeability None None Ottawa Loamy Fine Rapid permeability Unstable None Sand Phelps Gravelly Silt None None None Loam Platea Silt Loam None Seasonally high water table None Rimer Fine Sandy Loam Quicksand Seasonally high water table None Scio Silt Loam None Seasonally high water table None Sloan Silty Clay Loam None Flooding None Trumbull Silt Loam None Seasonally high water table None Unadilla Fine Sandy None None None Loam Volusia Gravelly Silt None Seasonally high water table None Loam Wallington Fine Sandy Quicksand Seasonally high water table None Loam Wallington Silt Loam None Seasonally high water table None Wauseon Flne Sandy Quicksand Seasonally high water table None Loam Wayland Silt Loam None Flooding None Williamson and Collamer Quicksand Seasonally high water table None Fine Sandy Loarns I Williamson and Collamer None Seasonally high water table None Silt Loams Wooster Gravelly Silt Rapid permeability None None Loam OPERATION AND MAINTENANCE CONSIDERATIONS Most stormwater control facilities or systems must be monitored and maintained regularly following construction to assure effective operation, long life and compatibility with the local setting. Table VI-5 contains a summary of key operation and maintenance considerations for the storrawater management alternatives discussed previously. As is indicated in Table VI-5, there is range of operation / maintenance items which must be performed depending upon the type of stormwater management techniques employed. It is recommended that individual municipal stormwater management ordinance require that the enumeration of specific recommended operation and maintenance activities be be outlined by the design engineer at the time applications for permit approval are made. The designer of the facilities should be in the best position to define the maintenance requirements associated with the facilities being proposed. However, operation and maintenance plan should be reviewed in consideration of the general requirements presented in Table VI-5. The approved set of operation and maintenance activities should then be used as the basis of an on-going operation and maintenance plan. Also, provisions should be made in the appropriate ordinances or regulations to provide for effective mechanisms through which the completion of critical maintenance can be assured. 11BLIC VCEPTAN-.CE:@. TEN TION: .......... ... ...... ...... ......... On-site detention, also has the disadvantage of not having wide spread public acceptance. This is mostly because the individuals have to spend extra dollars to satisfy the runoff control regulations. Also, they are concerned about the safety of their children also, which are usually attracted toward the ponds. Therefore, it is highly recommended to. employ multi-purpose use of detention facilities. In the minds of a community, the multi-purpose use of such a detention facility greatly improves the perception that such a facility is a justifiable expense by the public or by the private developer [APWA, 198 1 Detention ponds are excellent examples of multi-purpose adaptability. When conceived and designed artistically, they can support different kind of activities throughout the year, such as, water sports and fishing. During winter months, shallow detention ponds with a permanent pool of water provide opportunities for ice skating in some parts of the country. VI-45 Lake Erie SWMP 4026-02 6 0 Pu 0 PO 0-0 110 u 0 @u 0 a o- 0 0 CO CD a CD 0 0 0 CL 0 (M 0 0 0 0 W t-4 Cr Q. En CD CD rA tv u CD CD CD a rA CD CD CD CD CD Ch ca. 0 rA UQ r- Gn CD CD 0 w 0 0 CD CD I=. CD rA 0 CD 0 CD UQ a CL Dredging @-4 0 CD a-, a Debris / Sedimentation Removal CD 10 Weed Control CD .A Insect Control Mechanical Maintenance Mowing Cleaning Repair Inspection A detention basin that. is dry between runoff events can be used for field sports such as football, soccer, baseball, and various passive recreational pursuits such as badminton, model airplane operation, shuffleboard, croquet, and picnicking. Some detention basins may double as tennis or baseball courts. It might be difficult to convince some developers that the benefits derived from recreation outweighs the cost of the land plus construction costs. However, should the recreation area be redesigned as a multi-purpose recreational/detention basin, the cost would look insignificant compared to the cost of upgrading a storm drainage system or the amount of potential flood damages. Detention facilities may also contribute to the protection and preservation of wildlife habitats and other natural resources. , One example is a 602 ha (244 ac) tract in Chester County, Pennsylvania, where 315 homes were to be constructed. Approximately 84 ha (34 ac) of open space were provided containing two detention ponds designed to store runoff from the 100-year rainstorm. One year following the completion of the detention ponds, wildlife was observed returning to its former habitat. Geese have nested and fish have returned to the streams and newly constructed channels. The dual purpose utilization of stormwater detention facilities as wetlands represents a potential useful means of coping with the increasingly stringent wetland protection requirements and associated wetland replacement activities. Although multiple uses are a better alternative for securing the community acceptance, maintenance costs for such facilities may be higher. Therefore, when considering multiple uses, it is important to look at all the associated costs and intangible benefits, to determine if it is practical to proceed with the multiple use concept. -:XX . ......................- A survey conducted by APWA in 1980, based on 325 respondents, revealed that there have been two -drownings reported at the detention facilities. It is therefore, very essential to take precautions in design and selection of storm water management alternatives, to minimize hazards. Embankment slopes, railings, fencing and other features are obvious considerations. The importance of designing and constructing outflow structures and dams with safety considerations in mind should never be ignored. In general, the approa&es that can be used to promote safety are [APWA, 198 1 VI-47 Lake Erie SWMP 4026-02 1. Keep people off the detention facility site 2. Provide escape aids 3. Make the onset of the hazards gradual 4. Eliminate the hazards The designers and reviewers of stormwater control facilities, particularly those using detention / retention facilities should pay particular attention to incorporating appropriate safety features in the design of the facilities. Special attention must be given to the design of outflow structures to satisfy the safety considerations. Water currents constitute a distinct hazard to persons who enter a detention pond or basin during periods when stormwater is being discharged. The force of the currents may push a person into an outflow structure or may hold a victim under the water where a bottom discharge is used. Several features designed to either eliminate or reduce such hazards are illustrated in Figures VI-20 and VI-21. Figure VI-20 illustrates two versions of desi gns for non-submerged outlets: 1) curvilinear trash/safety racks for standard flared end sections and 2) narrow flume outlets. Both of these designs represent methods which tend to reduce the potential for persons to be drawn into or trapped against the outlet devices. Figure VI-21 presents suggested safety features for submerged outlets: 1) outflow velocities and hence the associated hazards can be reduced through the use of a porous dam type of outlet facility; and 2) the illustrated safety rack for submerged outlets reduces the entrapment potential and provides a means of egress from the basin. As is also illustrated in Figure VI-2 1, drowning hazards can also be reduced by using a floating inlet for a ba'sin outlet structure. The floating inlet -reduces the drowning hazard by eliminating the water force which could trap a person at the outflow structure. VI-48 Lake Erie SWMP 4026-02 Table VI-20 Suggested Safety Features for Non-Submerged Outlets fill 111111 10 Plan View Plan View Elevation A A- Elevation Isometric Detail of Louver Section A - A Section A - A Curvilinear Trash/Safety Rack Narrow Flume Outlet For for Standard Flared End Sections Detention Ponds VI-49 Lake Eric SWMP 4026-02 Figure VI-21 Suggested Safety Features for Submerged Outlets Ladder Rungs -low, Flow Control Safety Rack for Submerged Outlets Holes to fill Receptacle Runott and Initiate Floating A,ttinuated Detention Runoff Filter Fabric Rock 4W Infiltration Porous Dam for Detention Ponds With Low Velocity Discharge Floating Inlet With Recessed Receiving Receptacle . .. ...... .... ...... ..... . ......... . DISM LAE A T6 GENERU The stormwater management techniques discussed thus far. have been geared primarily to on-site control methods. It is likely that on-site controls will be the predominant form of stormwater management in the Lake Erie watershed. Off-site, distributed storage is, VI-50 Lake Erie SWMP 4026-02 however, an alternative or adjunct to on-site control techniques which should be recognized and considered for use where appropriate. Simply defined, distributed storage is the process of utilizing the most suitable site or sites for regional detention facilities. The combination of on-site detention and distributed storage approaches may significantly improve the capability of land developers and communities to control stormwater on a watershed basis. Distributed storage may also offer a means of accommodating development in a manner which minimizes total costs and optimizes land utilization through the sharing of a single, strategically located detention or retention facility. Finally, the use of distributed storage may increase the feasibility of dual or multi-purpose facilities. For example, certain recreation areas might easily be used to provide temporary stormwater storage; natural or artificial ponds and lakes can serve both recreation and stormwater management objectives; and stormwater management facilities may be constructed as replacement wetlands. .... ... ... The institution of stormwater management regulations throughout the watershed will require that land developers include provisions in their land development plans to limit increases in the volume of runoff and to control peak rates of stormwater discharges to levels specified in the local ordinances. These standards will be presented as performance standards. That is, the standards will set limits on the peak rate of discharge permitted from the development site without specifying the exact methods to be used in order to meet the standards. The owner of the development will be affor*ded a high degree of flexibility in the selection and design of the specific measures to be incorporated into the design of the development. This will permit the developer to select and arrange the various available control techniques in a manner that is most efficient for the particular information and that best accommodates the intended use of the development. Nevertheless, the various stormwater control techniques offer differing degrees of benefit. For example, measures such as the preservation of pervious areas, the use of filter strips and buffers, and the use of vegetated swales offer the following significant advantages: 1. Minimization of total runoff volumes VI-51 Lake Erie SWMP 4026-02 2. Promotion of aquifer recharge 3. Stormwater pollution reduction 4. Ease of construction and maintenance 5. Low construction and maintenance costs 6. Preservation of open space The opportunity for realizing these benefits is lost if no effort is made to utilize these techniques and the stormwater performance standards are satisfied solely through the construction of detention facilities. It is important, therefore, that the land developers be encouraged to make use of the fall range of available control techniques in an integrated approach that maximizes the attributes of each. To that end, the municipal stormwater ordinances should encourage the land developers to select the general types of stormwater controls used in his/her stormwater management plan in the general order of preference: 1 . Maximization of infiltration on-site by minimizing land disturbance, maximizing the amount of pervious surfaces incorporated in the development, and creating vegetated strips and buffer areas. 2. Flow attenuation through the use of operi'vegetated swales, rock lined channels, and natural depressions 3. Stormwater detention / retention structures (dry, wet, multi-purpose) An example of a land development that employs the broad range of applicable. control techniques is present in Figure VI-22. Tlie concept illustrated in Figure VI-24 is an approach to providing stormwater management techniques in a manner that incorporates them into the overall design of the development while using the flow and pollution control capabilities of each technique in an integrated stormwater management and overall land development plan. VI-52 Lake Erie SWMP 40 26-02 Figure VI-22 Example of Development Integrating Variety of Stormwater Control Techniques r e Ir A 4A Techniques Employed A: Wet detention pond F: Multi-use dry detention area B: Grassed swale G: Dutch drains under roof eves C: Oringinal growth woodlands preserved H: Pervious surface walkways D: Rock-lined channel 1: Parking lot detention storage E: Grassed strips J: Grassed strips in parking area . @ NOAA COASIAL SERVICES CTR LIBRARY I ! 3 6668 14111483 7 1 1 1 1 1 1 1. I I I I I I I I I I I I