DANE COUNTY EROSION CONTROL AND STORMWATER MANAGEMENT MANUAL. To be used in conjunction with Chapters 11 & 14 of the Dane County Code of Ordinances

Transcription

1 DANE COUNTY EROSION CONTROL AND STORMWATER MANAGEMENT MANUAL To be used in conjunction with Chapters 11 & 14 of the Dane County Code of Ordinances 2 nd Edition January 2007

2 DANE COUNTY EROSION CONTROL AND STORMWATER MANAGEMENT MANUAL ACKNOWLEDGEMENTS The 2 nd Edition of Dane County s Erosion Control and Stormwater Management Manual was prepared by the following Dane County Land and Water Resources Department Staff: Jeremy Balousek, Kevin Connors, Deb Flanders, Josh Harder, Michele Hartmann, Angela Hull, Sue Jones, Pete Jopke, Michelle Richardson, Ryan Shore, Jess Starks and Pat Sutter. Preparation of the 1 st Edition of this manual was funded in part by a Wisconsin Department of Natural Resources Urban Nonpoint and Stormwater Planning Grant. Thanks to all who contributed to the 1 st Edition: Dane County Staff: Jeremy Balousek, Kevin Connors, Jon Frie, Marcia Hartwig, Sue Jones, Pete Jopke, Mike Kakuska, Kamran Mesbah, Michelle Richardson, Aicardo Roa, Ryan Shore, Brian Standing, Amy Wagner, Michelle Woldt Dane County Erosion Control and Stormwater Management Manual Advisory Group: Rod Zubella, Vierbicher Associates Mike Rupiper, City of Fitchburg Warren Myers, Town & Country Engineering, Inc. Greg Held, Held & Associates Inc. Steven I. Apfelbaum, Applied Ecological Services Mary Anne Lowndes, Wisconsin Department of Natural Resources Kevin Kirsch, Wisconsin Department of Natural Resources Jim Bertolacini, Wisconsin Department of Natural Resources Bill Suick, D Ononfrio Kottke, for the Madison Area Builders Association Jerry Gray, Village of Cross Plains Others: Ann Dansart (formerly Dane County Lakes and Watersheds, now MSA Professional Services) Kathleen Arrington (UW-Madison Department of Soil Science) Professor John Norman (UW-Madison Department of Soil Science) Timothy Wilson (UW-Madison Department of Soil Science) Dave Roberts (USDA Natural Resources Conservation Service) Yamilette Suarez (USDA Natural Resources Conservation Service) Don Hammes (Yahara Fishing Club, Madison Fishing Expo, Dane County Conservation League) Shary Bisgard (Dane County Lakes and Watershed Commission) Bill Sands (formerly Dane County Land Conservation Division) Ken Johnson (Wisconsin Department of Natural Resources) ACKNOWLEDGEMENTS 01/02/07

3 DANE COUNTY EROSION CONTROL AND STORMWATER MANAGEMENT MANUAL TABLE OF CONTENTS HOW TO USE THIS MANUAL... iii CHAPTER 1 THE ORDINANCE Ordinance Background Ordinance Applicability and Administration... 2 Preliminary Review Letter... 5 Administration... 5 Models Accepted... 5 Fees... 5 Enforcement State Nonpoint Program Redesign Implications for Dane County Site and Regional Planning... 6 Site Planning Techniques to Minimize Stormwater Runoff... 6 Identify and Avoid Sensitive Areas... 7 Minimize Impervious Surfaces... 7 Case Example: St. Francis Addition to the Village of Cross Plains... 9 How to Credit Conservation and Low-Impact Design Regional Stormwater Treatment Watershed-wide Planning for Stormwater Management CHAPTER 2 EROSION CONTROL Erosion and Erosion Control...15 Understanding Erosion Erosion Control Dane County Erosion Control Standards and Requirements The 7.5 Tons/Acre/Year Standard Calculating Soil Loss from Construction Sites...21 Universal Soil Loss Equation for Construction Sites USLE Spreadsheet Description of Spreadsheet Columns...22 Variable Descriptions...22 Button Controls...25 Example Soil Loss Calculation Gully and Streambank Erosion...28 CHAPTER 3 STORMWATER Stormwater and the Hydrologic Cycle...29 The Hydrologic Cycle Stormwater and the Hydrologic Cycle Hydrographs Stormwater Management Standards and Requirements Sediment Control Requirements...41 TABLE OF CONTENTS 01/02/07 i

4 DANE COUNTY EROSION CONTROL AND STORMWATER MANAGEMENT MANUAL 3.4 Policy for Oil and Grease Control Runoff Rate Determining Runoff Rate Using TR Stable Outlets Channel Lining Infiltration Thermal Control Thermal Standards...43 Locator...45 Thermal Considerations...46 Thermal Model Description Maintenance Requirements APPENDIX I MANAGEMENT PRACTICES... I.A-1 APPENDIX II INFILTRATION MODELING... II-1 APPENDIX III HYDROLOGY... III-1 APPENDIX IV BASIN EFFICIENCY... IV-1 ii TABLE OF CONTENTS 01/02/07

5 DANE COUNTY EROSION CONTROL AND STORMWATER MANAGEMENT MANUAL HOW TO USE THIS MANUAL This manual is designed to help landowners, developers and consultants meet the requirements of Dane County s Erosion Control and Stormwater Management Ordinance and aid in the erosion control and stormwater management permit process. Chapters 1 through 3 include information on why erosion control and stormwater management is needed, the standards that must be met, who needs a permit, and the steps to obtain an approved plan and permit. The Appendix includes a list of approved management practices that will assist landowners and builders in selecting a combination of practices to meet the performance standards set by the ordinance. This is not an all-inclusive manual. Users will still need to refer to technical guidance manuals. Other practices not included in the manual may be used as long as they meet performance standards. This manual is available on the web at Additional printed copies are available for $20 + $5 for shipping. Please help Dane County improve this manual by providing suggestions for future editions. Submit proposed changes and additions by mail or . To be notified by when manual updates are available from the web, please request that your name be added to the registry. Dane County Land and Water Resources Department 1 Fen Oak Court, Room 208 Madison, WI lwrd@co.dane.wi.us HOW TO USE THIS MANUAL 01/02/07 iii

6 DANE COUNTY EROSION CONTROL AND STORMWATER MANAGEMENT MANUAL iv TABLE OF CONTENTS 01/02/07

7 CHAPTER 1 THE ORDINANCE 1.1 ORDINANCE BACKGROUND The Erosion Control and Stormwater Management Ordinance was designed to help protect Dane County s lakes, streams, wetlands and quality of life by reducing the negative impacts of sediment, rainfall, melting snow and other water runoff. The ordinance establishes countywide standards for the quantity and quality of water that runs off land under construction in urban and rural areas, including farms. It also provides flexibility in meeting those standards, recognizing the unique characteristics of each project and site. The Erosion Control and Stormwater Management Ordinance builds on the construction site erosion control requirements that have been in effect since The Dane County Board of Supervisors adopted the Erosion Control and Stormwater Management Ordinance effective August 22, 2002, acting on the recommendation of the Dane County Lakes and Watershed Commission after 11 public hearings and hundreds of hours of meetings with citizens, technical experts, developers, builders, local municipalities, and other stakeholders. The Board found that construction site erosion and uncontrolled stormwater runoff from land disturbing and land development activities have significant adverse effects upon regional water resources including the health, safety, property and general welfare of the community, diminishing the public enjoyment and use of natural resources. The Board also found that effective erosion control, sediment and stormwater management depends on proper planning, design, timely installation and continued maintenance of erosion control and stormwater management practices. Specifically, they found that soil erosion and stormwater runoff can: carry sediment, nutrients, pathogens, organic matter, heavy metals, toxins and other pollutants to regional lakes, streams and wetlands; diminish the capacity of water resources to support recreational and water supply uses and a natural diversity of plant and animal life; clog existing drainage systems, increasing maintenance problems and costs; cause bank and channel erosion; increase downstream flooding; reduce groundwater recharge, which may diminish stream base flows and lower water levels in regional lakes, ponds and wetlands; contaminate drinking water supplies; C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7 1

8 increase risk of property damage and personal injury, and; cause damage to agricultural fields and crops. Effective January of 2006, revisions to the erosion control and stormwater management ordinance were made to meet state standards for infiltration and to make shoreland erosion control requirements of Chapter 11 consistent with Chapter 14. Dane County chose to adopt the state s infiltration standards, with few modifications. One significant change was a sunset date for the caps that limited that amount of area required to be dedicated to infiltration (State rules require only one percent of a residential site and two percent of a nonresidential site to be dedicated to infiltration). The other significant change was the elimination of the design storm approach (utilizing TR-55) to meet the infiltration requirements. The Dane County Lakes and Watershed Commission also assembled an infiltration taskforce to explore regulatory alternatives to caps and evaluate stormwater infiltration in Dane County. The taskforce included members from the academic, development, municipal, regulatory communities, and watershed groups. After nearly a year of work, the taskforce returned to the Dane County Lakes and Watershed Commission with a full report including a unanimous recommendation to remove the caps and include an alternative recharge performance standard. The revised infiltration requirements were adopted in August of 2006, and are now effective. 1.2 ORDINANCE APPLICABILITY AND ADMINISTRATION Construction site erosion control plans and permits are required for any of the following: Land disturbance more than 4000 square feet. Land disturbance on a slope more than 12%. Land disturbance involving excavation and/or filling more than 400 cubic yards of material. Land disturbance of more than 100 lineal feet of road ditch, grass waterway, or other area where surface drainage flows in defined, open channels. New public or private roads or access drives longer than 125 feet. Development that requires a subdivision plat. Land disturbance less than 4000 square feet that has a high risk of soil erosion or water pollution, as determined by local ordinance administration. Land disturbance of any size in the shoreland zone, which includes any of the following areas: o Within 300 feet of the ordinary high-water mark of any navigable water or 1000 feet of a lake or pond. o Within the 100 year floodplain. o Within 75 feet of the shoreland or inland wetland district. Stormwater management plans and permits are required for any of the following: Development that results in the cumulative addition of 20,000 square feet of impervious surface to the site (since August, 2001). Construction of agricultural buildings where the new total impervious surface area exceeds 20,000 square feet. Development requiring a subdivision plat. 2 C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7

9 Commercial or industrial development that requires a certified survey map. Redevelopment exceeding 4000 square feet of land disturbance where the site is predominantly developed to commercial, industrial, institutional or multifamily residential uses. Other development or redevelopment that may have significant downstream impacts as determined by the local approval authority (In unincorporated areas, this is the Dane County Land and Water Resources Department (LWRD) Director). If the site requires erosion control and stormwater management plans and permits, one combined plan and permit is issued. Site is defined in the ordinance as any bounded area described in the erosion control plan or stormwater management plan. Some land disturbing activities may be exempt from county and state erosion control requirements. Certain state building projects and highway projects are subject to Wisconsin Administration Code Chapter Trans 401. Refer to Dane County Chapters 11.05(2) and for a complete exemption list. Figure assists in determining which types of permits would be required for projects being considered. C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7 3

10 START HERE *Refer to Dane County Ordinances Will the land-disturbing activity occur within 300 feet of the ordinary high water mark (OHWM) of a navigable water, in the 100 year flood plain, or within 75 feet of the shoreland or inland wetland district, or within 1000 feet of a lake or pond? NO YES SHORELAND EROSION CONTROL PERMIT REQUIRED (See section 2.2) Will the land disturbing activity: (1) Disturb an area in excess of 4000 square feet? (2) Occur on a slope of greater than 12%? (3) Involve the excavation or filling, or a combination of excavation and filling, in excess of 400 cubic yards of material? (4) Disturb more than 100 lineal feet of road ditch, grass waterway or other land area where surface drainage flows in a defined open channel? (5) Create a new public or private road longer than 125 feet? (6) Require a subdivision plat? (7) Have a high risk of eroding soil or polluting water or significantly impacting a sensitive area? NO TO ALL AT LEAST ONE YES Is the land-disturbing activity: (1) Directly related to the planting, growing and harvesting of agricultural crops? (2) Limited to the construction of agricultural buildings that create a new total impervious surface area (including gravel) of less than 20,000 square feet? EROSION CONTROL PERMIT NOT REQUIRED EROSION CONTROL PERMIT REQUIRED (See section 2.2) NO TO ALL EXEMPT FROM ORDINANCE Is the proposed development: (1) a one- or two-family dwelling unit regulated by Wisconsin s Uniform Dwelling Code with an existing driveway and on slopes <12% and limited to less than 4000 sq. ft. of land disturbing activity outside the footprint of the house? (2) a state building project subject to s (13) Wis. Stats. or state highway project subject to Trans 401? AT LEAST ONE YES NO TO ALL AT LEAST ONE YES Does the land development or development activity: (1) Result in the cumulative addition of 20,000 square feet of new impervious surface area? (2) Involve redevelopment and/or an alteration of existing development greater than 4,000 square feet on sites where uses are predominantly commercial, industrial or multifamily? (3) Require a subdivision plat? (4) Require a certified survey map (for property intended for commercial or industrial use)? (5) Significantly increase downstream runoff volumes, flooding, soil erosion, water pollution or property damage, or significantly impact a sensitive area? NO TO ALL STORMWATER PERMIT NOT REQUIRED AT LEAST ONE YES STORMWATER PERMIT REQUIRED (See Section 3.2) Figure Permit Selection Chart 4 C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7

11 Preliminary Review Letter A preliminary review letter provides a potential permit applicant with an initial evaluation of whether erosion and stormwater control standards can be met for a proposed site, lot layout, or construction design. A preliminary review is required to qualify for certain shoreland erosion control plan requirement exceptions. This general review is intended to assist applicants in preparing general site plans and other submittals necessary to obtain an erosion control and/or stormwater permit. A preliminary review letter does not guarantee that an erosion or stormwater control plan will be approved or that a permit will be issued. Although cities and villages are not required to include a preliminary review process in their ordinances, Dane County strongly encourages use of this practice. The early consultation before lot line, road and infrastructure decisions have been made is especially helpful for first-time or one-time developers. Administration The ordinance sets countywide standards and gives the necessary flexibility to local governments and developers so they can administer and meet those standards effectively and efficiently. The ordinance is administered by the Dane County Land and Water Resources Department, Land Conservation Division, in unincorporated areas (towns). Cities and villages (incorporated areas) administer the ordinance if they have adopted stormwater and erosion control standards at least as restrictive as the county ordinance. Models Accepted The various models currently accepted for use in calculating hydrology, infiltration, soil erosion rates, water quality impacts and temperature impacts include P8, RECARGA, TR-55, SLAMM, USLE (RUSLE2, when available), TURM, and Stokes Law. Land Conservation Division staff review new analytical tools for use with the Erosion Control and Stormwater Management Ordinance. The user community is encouraged to submit models for consideration. The LWRD Director, per Section 14.53(3) of Dane County Code of Ordinances, may approve new models. Description of the model, relevant mathematical analysis, relevant supporting documentation, simplicity of model, consistency of parameter estimates and sensitivity of results to changes in parameter values will all be considered when evaluating new models. Fees The ordinance allows local authorities to establish their own fee schedules for erosion control and stormwater management permits within incorporated areas. In unincorporated areas, fees are set by Dane County. Enforcement Dane County will work with municipalities for consistent enforcement of the county minimum standards. C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7 5

12 The ordinance requires builders, developers and other site planners to submit erosion control and stormwater management plans. If a site is not in compliance with its plan as determined by inspection, a stop-work order may be issued and the administrator may levy fines. If a city or village does not adopt standards at least as restrictive as the county ordinance or has adopted county standards but the Lakes and Watershed Commission finds that they are not effectively administering and enforcing them, the Dane County Land and Water Resources Department will administer the provisions of the ordinance in that municipality. 1.3 STATE NONPOINT PROGRAM REDESIGN IMPLICATIONS FOR DANE COUNTY In response to two state legislative acts, the state of Wisconsin has been working for the past several years to redesign its nonpoint source programs. The redesign resulted in eight administrative rules, one of which is NR 151, Runoff Management. NR 151 includes construction site and postconstruction runoff pollution performance standards. The complete text of the rule can be found on the Department of Natural Resources web site, at: Dane County staff worked closely with DNR staff throughout development of the Dane County Erosion Control and Stormwater Management Ordinance and its amendments. Compliance with Dane County s Erosion Control and Stormwater Management standards have been deemed more restrictive or equivalent to the standards contained in NR SITE AND REGIONAL PLANNING Site Planning Techniques to Minimize Stormwater Runoff Good stormwater management does not begin with site disturbance and construction. Decisions about lot layout, building density, location of public rights-of-way, protection of sensitive areas, and preservation of open space all have an impact on the quality and quantity of stormwater runoff. To encourage early consideration of these issues, the Dane County Erosion Control and Stormwater Management Ordinance includes a voluntary Preliminary Review consultation that takes place before land is platted and the final design is set (refer to page 5, the Preliminary Review Letter section of manual). When using site-planning techniques to control stormwater, designers should keep local zoning, land division and building codes in mind. Many communities have adopted site design or land division criteria to serve a variety of land use goals that may or may not directly relate to stormwater runoff. Examples include: preserving neighborhood or rural character protecting specific natural or scenic resources promoting smooth traffic flow allowing for future land division ensuring adequate pedestrian, bicycle or emergency vehicle access Usually, such goals complement or reinforce good design for stormwater control. However, in some cases, such as choosing between grid-pattern or cul-de-sac street layouts, the designer may need to strike a balance between competing land use goals. For example, in a community seeking to promote 6 C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7

13 traditional neighborhood design, engineered stormwater basins may be preferable to a curvilinear street layout. Many techniques can be employed during the site planning and design stage of development to reduce the volume of runoff, thus reducing the need for structural practices to store and treat stormwater. Design and location of stable outlets for site runoff is also important to consider at this time, to avoid causing problems for downstream neighbors. Consider implementing the following techniques to minimize the volume of stormwater runoff. Identify and Avoid Sensitive Areas Local variations in topography, soil types, vegetation and hydrology can have a significant influence on the nature and amount of stormwater runoff. The first step in site planning for stormwater management should be identification and mapping of areas that: contain features that could be adversely impacted by stormwater runoff (such as wetlands, floodplains, lakes, streams, and shallow fractured bedrock); in their natural state, contribute to infiltration, soil and water retention, groundwater recharge or temperature control (such as highly pervious soils, native grasslands, woodlands or hydric soils); provide natural drainage ways for surface water runoff (such as intermittent or perennial streams, natural or artificial drainage ways); or could be a source of sedimentation, channelized flow or erosion if disturbed (such as steep slopes or easily eroded soils). Development should be designed and construction operations planned to avoid disturbing these areas wherever possible. Federal, state or local regulations protect some natural features, such as wetlands or navigable waterways. Changes in volume and direction of stormwater flow resulting from development or other stormwater practices should be carefully designed and controlled to avoid secondary impacts to natural areas. For example, increased runoff volume can erode streambeds and banks or damage natural wetlands without careful consideration early in the planning process. Working around sensitive areas should be incorporated as part of the preliminary design, which not only avoids these areas but also highlights them as natural amenities that add value to the development. These sensitive areas complement the functions and values provided by the countywide network of open space corridors. Minimize Impervious Surfaces Imperviousness is the primary source of runoff. Hence, the single most effective means of reducing runoff volume is by minimizing the site s impervious surface area. Streets and Roads Road length. Minimize subdivision roadway length by using a roadway layout with the least pavement length suitable for the site s topography and other planning goals. Road width. Work within local zoning requirements and planned unit development provisions to minimize road width by narrowing road sections and/or reducing on-street parking. On-street parking may be restricted to one side of the street or eliminated altogether. Pavement and right- C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7 7

14 of-way width must still meet minimum standards described in local land division and zoning ordinances, and should allow for safe vehicular travel and emergency vehicle access. Design road patterns to match landforms. In rolling terrain, for example, local streets should branch from collector streets and end in short loops or cul-de-sacs, where consistent with other local ordinances and land use goals. Some local ordinances and plans seek to create traditional grid patterns or limit the use of cul-de-sacs to address traffic, neighborhood character or other design objectives. Lot Layout Rooftops. Reduce the impervious rooftop area by minimizing the building footprint of houses or utilizing green roof technology. Use vertical space rather than horizontal house layouts. Driveways. Where permitted under local driveway, zoning or land division ordinances, reduce impervious driveway area by using shared driveways, limiting driveway width, using pervious pavement, and using reduced building setbacks. Parking lots. For commercial sites, reduce overall impervious area by providing compact car spaces, eliminating excessive or unnecessary spaces, utilizing shared parking, minimizing stall dimensions, incorporating efficient parking lands, and using pervious materials in spillover parking areas. Site and Lot Vegetation Predevelopment vegetation. Maintain as much predevelopment vegetation as possible. Vegetation prevents erosion and absorbs water and, therefore, reduces runoff volume. Swales. Use shallow grassed roadside swales, boulevards and sunken parking lot islands with check dams instead of curb and gutter storm drain systems to handle runoff, wherever possible. Natural buffers and drainage ways. Maintain natural buffers between development sites and water bodies. Buffers slow runoff, remove sediment and enhance infiltration. Natural depressions and channels should be maintained to slow, store, and infiltrate water. Preserve and Reproduce Pre-Development Hydrologic Conditions Utilize natural drainage flow paths. Dane County strongly recommends the use of grass waterways, vegetated drainage channels and/or water quality swales along street right-of-ways or back lots to channel runoff without abrupt changes in the direction of flow. Restore soil permeability. Use practices such as deep tilling, chisel plowing and incorporating organic matter into the upper soil layer to restore soil infiltration capacity on heavily disturbed sites. When soil is compacted its capacity to infiltrate water is greatly diminished. On heavily disturbed sites where practices are used to restore soil permeability, the county may waive the requirement to lower the soil permeability class rating in hydrologic calculations. Compaction mitigation is required when disturbed green space is included in recharge calculations (refer to Chapter 3). Minimize directly connected impervious area. Downspouts and driveways should be directed to pervious areas, where feasible. This reduces the directly connected impervious area, promotes infiltration and reduces the velocity of runoff water. Other strategies for minimizing connected impervious area include directing sheet flow through vegetated areas and locating impervious areas so they drain to vegetated buffers or other pervious areas. Use bioretention and other practices to increase infiltration. Bioretention basins are engineered practices that use natural processes, including microbial soil processes, infiltration, and evapotranspiration 8 C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7

15 to improve stormwater quality. Rain gardens, often very attractive, are one type of practice commonly designed for residential lots to soak up rainwater from roofs, driveways, and lawns. A detailed design manual addressing sizing, costs, species, etc. is available from the Wisconsin Department of Natural Resources and UW Extension Rock trenches or rock beds can also be used as a conduit to more permeable layers with higher percolation rates. The Appendices list design and maintenance recommendations for these and other practices. Case Example: St. Francis Addition to the Village of Cross Plains The St. Francis Addition is a 72-acre, 80-lot subdivision in the Village of Cross Plains that demonstrates good site planning. Brewery Creek, a cold-water community and a tributary to the cold-water community of Black Earth Creek, runs through the site. During the site planning process, hydric soils to be avoided were mapped, as well as permeable soils where infiltration practices could be located. Figure shows the soil permeability analysis prepared for the preliminary plat, identifying the ideal locations for infiltration practices. A comprehensive study was designed to evaluate both the physical and biological in-stream response resulting from this development. The results of this study concluded that the erosion control and stormwater management plans that were designed and implemented by the developer of the subdivision were effective in mitigating the harmful effects of runoff to Brewery Creek. The complete USGS publication can be viewed in PDF at C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7 9

16 Figure St. Francis Addition Permeability Analysis Following the site analysis, a site plan was prepared which incorporated the following practices: naturally vegetated buffer to Brewery Creek protected existing wooded areas deep tilling to increase infiltration and reduce other effects of soil compaction stormwater storage and infiltration swales behind all house sites stormwater storage and infiltration swales within cul-de-sacs and boulevards narrower street widths (16 boulevard lanes; 28 street widths wherever possible) Figure is a detail from the site plan, indicating infiltration and other practices. 10 C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7

17 Stormwater storage infiltration swale Swale Buffer strip Hydric soils Figure Detail from St. Francis Addition Plan How to Credit Conservation and Low-Impact Design Many of the practices and techniques discussed above are commonly referred to as conservation design or low-impact design. Figure compares a conventional subdivision layout with a subdivision incorporating conservation design practices. During plan review, conservation design and other practices will be evaluated to ensure that the plan meets or exceeds ordinance requirements. Less imperviousness results in less runoff to treat or store, resulting in smaller structural practices needed to comply with requirements, resulting in lower development costs (related to structure size). Reducing peak rate and runoff volume also means less land will need to be set aside for peak rate and volume control which may result in less engineering design, and may contribute to lower development costs. Common open space Conventional Subdivision Conservation Subdivision Figure Comparing conventional and conservation subdivisions. Source: Ordinance for a Conservation Subdivision, UWEX, Brian Ohm. Dane County encourages conservation design by providing incentives in the ordinance for features commonly associated with conservation or low impact practices. When developers incorporate such practices, they reduce the runoff that needs to be treated by other engineered C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 /

18 practices. Limiting the disturbed area may reduce construction costs and minimize the need for erosion control practices. Dane County s ordinance fee structure also provides an incentive for reducing imperviousness and minimizing land disturbance. Permit fees are calculated based on amount of disturbed area and amount of impervious area. Regional Stormwater Treatment Dane County s Erosion Control and Stormwater Management Ordinance does not prohibit regional treatment for stormwater management. A regional stormwater treatment facility can increase efficiency of treatment and ease maintenance. These facilities improve sediment trapping with a larger pool of water in the detention pond, and avoid problems that can arise from many smaller onsite treatment facilities all releasing water at the same time. Regional facilities, however, are not adequate for meeting the soil loss standard during land disturbance and may not be the best strategy for stormwater infiltration. Cities and villages in Dane County that have adopted regional stormwater plans may want to establish a fee-in-lieu program and identify its requirements in their ordinances. Fee-in-lieu programs allow developers to pay a fee rather than install on-site control measures where these may not be desirable. The fee is put into a dedicated fund to recoup the costs for construction, operation, and maintenance of regional or multipurpose detention facilities. Fee-in-lieu may not be used as an alternative to meeting the county s minimum standards. Dane County s ordinance allows municipalities that establish a fee-in-lieu program to allow owners of sites served by an off-site stormwater management facility to pay a fee-in-lieu of on-site control. However, the ordinance requires that these municipalities only allow this if the regional facility is in place at the time of land disturbance, is designed and adequately sized to provide a level of stormwater control capable of meeting county standards, and has a legally-obligated entity responsible for its long-term operation and maintenance. Regional facilities must be in place at the time of land disturbance to prevent situations where a landowner pays a fee-in-lieu of on-site control, yet the regional facility is never built, or built after a delay of years, resulting in uncontrolled and untreated stormwater runoff. Watershed-Wide Planning for Stormwater Management The Dane County ordinance, while focusing on plans and practices to meet the erosion control and stormwater needs of particular sites, complements watershed-wide planning. Ideally, stormwater management should be conducted as part of a watershed plan. In watershed-wide planning, communities can work together across municipal boundaries to identify potential locations for regional stormwater treatment facilities, and coordinate on-site basins and outlets to reduce the effect of combined peak discharges after storm events. They can also collectively identify areas where stormwater detention facilities should not be located, e.g. in hydric or alluvial soils, and target areas where they are preferred, e.g. deep sandy soil. Such a collaborative approach may result in significant cost savings from economies of scale and shared responsibility. 12 C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 / 0 7

19 Sources An Introduction to Better Site Design in The Practice of Watershed Protection. Edited by Thomas R. Schueler and Heather K. Holland. The Center for Watershed Protection, Ellicott City, MD pp Bioretention as a Stormwater Treatment Practice in The Practice of Watershed Protection. Edited by Thomas R. Schueler and Heather K. Holland. The Center for Watershed Protection, Ellicott City, MD pp A Model Ordinance for a Traditional Neighborhood Development by Brian W. Ohm, James A LaGro Jr., and Chuck Strawser, 2001, University of Wisconsin-Extension (available at: e.pdf). Rain Gardens: A household way to improve water quality in your community brochure published by the Wisconsin Department of Natural Resources and University of Wisconsin-Extension in February, ( - rain) UW-Extension Publication GWQ 034. Low-Impact Development: An Integrated Design Approach, June 1999, Prince George's County, Maryland, Department of Environmental Resources. Dane County Land Use and Transportation Plan. June Dane County Regional Planning Commission. How to Build A Rain Garden. brochure published by Dane County Lakes and Watershed Commission, 2006 (available at: C H A P T E R 1 T H E O R D I N A N C E 0 1 / 0 2 /

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21 CHAPTER 2 EROSION CONTROL 2.1 EROSION AND EROSION CONTROL Understanding Erosion Erosion occurs when soil particles are detached from the land surface and carried downslope by moving water. Figure illustrates how this process commonly occurs. First, a raindrop s velocity increases as it approaches the soil surface. This velocity, plus the drop s weight, provides sufficient energy at impact to detach soil particles. Once detached, upslope soil particles are carried by runoff until the flow spreads out, the gradient decreases and energy dissipates. As the flow loses the energy needed to suspend particles, it deposits the particles as sediment. Figure Conceptual Model of Erosion Dane County construction sites are highly susceptible to erosion for several reasons. First, soil is easily detached from the land surface because vegetation and the surface layer of organic soil are stripped. Second, heavy machinery compacts the soil causing it to lose infiltration capacity, which increases the volume of water that becomes runoff and the potential to wash soil downhill. Third, since there is no vegetation to spread runoff into sheet flow, it is more likely to concentrate and cause gully erosion. Fourth, Dane County soils are comprised of large amounts of silt, which is easily detached from the other soil particles. Erosion Control There are a variety of strategies for minimizing soil loss from construction sites. These include preventing soil detachment, diverting runoff around disturbed areas, and trapping sediment carried C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 /

22 by runoff before it leaves the site. The most important strategy for controlling construction site erosion is preventing soil particle detachment through soil stabilization. Vegetation should be reestablished as soon as possible after land is disturbed. In the meantime, other erosion control practices, such as polymer application, erosion matting, and mulching, must be in place. A second line of defense is to prevent runoff from contacting detached soil particles by diverting runoff around disturbed areas. Diversions minimize the opportunity for runoff to entrain detached soil particles and carry them offsite. Finally, when soil particles are detached and carried by runoff, practices that slow and/or trap sediment must be installed to prevent suspended sediment from leaving the site and entering water bodies. Figure is an illustration of how erosion prevention, diversion, and inlet protection can be integrated to minimize erosion. Hydroseeding Erosion matting Diversion Diversion Mulching Sediment trap Outlet protection Figure Construction Site Erosion Control, Adapted from Association of Bay Area Governments, 2006, DANE COUNTY EROSION CONTROL STANDARDS AND REQUIREMENTS To minimize erosion from construction sites and protect the county s lakes and streams from sediment pollution, the Erosion Control and Stormwater Management Ordinance requires that plans for all construction sites include practices that meet the standards in Table Sheet and Rill Erosion Gully and Streambank Erosion Table Standard Purpose Applicability Maximum allowable cumulative soil loss is 7.5 tons/acre/year Prevent gully and streambank erosion Minimize soil loss and prevent water quality and aquatic habitat degradation Minimize soil loss and prevent water quality and aquatic habitat degradation All sites requiring an erosion control plan All sites requiring an erosion control plan 16 C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 / 0 7

23 In addition, submitted erosion control plans must address the following 19 required elements. 1. Detailed, written description of how the site will be developed to ensure appropriate practices are being proposed and can implemented with the proposed construction schedule. 2. Plan drawing of site to show the location of property lines, lot dimensions, limits of disturbed area, limits of impervious area, land cover type, natural and artificial water features, 100-yr flood plain boundaries, wetland boundaries, and locations of proposed erosion controls. 3. Direction of runoff flow to determine effects of stormwater quantity and quality. 4. Watershed size for each drainage area to determine how much of the area to be developed is affected by other drainage flowing through the construction site; to design culvert sizes and drainage channels; to determine the sediment produced by the site under construction. 5. Provisions to prevent mud tracking off site including the tracking pad design (length, depth, etc.). 6. Provisions to prevent the delivery of sediment to stormwater conveyance systems to ensure capacity is not compromised and sediment is not transported off-site to receiving waters. 7. Universal Soil Loss Equation worksheet(s) to show the 7.5 ton/acre/year soil loss standard is being met. 8. Provision for sequential steps mitigating erosive effect of land disturbing activities including a series and schedule of practice installation to mitigate the increase in runoff and the pollutants it carries. 9. Time schedules for completion and installation of all elements of the erosion control plan to calculate the amount of sediment that will leave the site and to select the site practice(s). 10. Fertilizer and seeding rates and recommendations to illustrate how the disturbed areas will be returned to stable conditions. 11. Itemized estimated cost (including labor) of erosion control practices to determine the applicability of a financial security document. 12. Design discharge for ditches and structural measures to accommodate a 10-year, 24-hour storm and safely pass the 100-year, 24-hour storm event. 13. Cross sections of, as well as profiles within, road ditches to ensure non-erosive velocities. 14. Culvert sizes to maintain water quantity control to pre-development conditions and ensure that the time of concentration of runoff does not affect existing structures. 15. Runoff velocities to illustrate that they are not erosive and to ensure all slopes are stable. 16. Proof of a stable outlet to ensure that stormwater is being discharged from the site at a nonerosive velocity. 17. Copy of preliminary review letter, permits, or approvals by other agencies to ensure applicable permits have been applied for. 18. Any other information necessary to reasonably determine the location, nature and condition of any physical or environmental features of the site. 19. Acknowledgment that any proposed changes to the erosion control plan will be submitted for approval prior to implementation to ensure the plan and site stay in compliance. In order to assist in meeting the standards and requirement set forth by the ordinance, Tables and list practices that could be used to achieve the performance standards. The table briefly describes where practices should be used along with maintenance requirements, environmental concerns and any special considerations for the practices. A more descriptive explanation of each practice is provided in the Appendices. C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 /

24 18 C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 / 0 7 Non- Structural Practices Construction Scheduling Deep Tilling Mulching Polymer Application Seeding, Permanent Seeding, Temporary Sod Surface Roughening Applicable Standard 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year Applicability to Sites Widely applicable Widely applicable on sites where heavy grading has occurred Widely applicable Applicable on sites that are not actively being graded Widely applicable Widely applicable Widely applicable Widely applicable Maintenance Requirement Low Very Low Moderate Moderate Moderate; Low once established Moderate; Low once established Low after establishment Moderate Environmental Concerns None None Limited effectiveness on steep slopes depending on the type of mulch Risk of adverse impacts if over applied Possible erosion during establishment; fertilizer runoff Possible erosion during establishment; fertilizer runoff Fertilizer runoff; Overwatering Erosion may increase if not done on the contour of the slope Special Considerations Can greatly reduce erosion from a site Should be timed after grading has occurred; Buried Utilities Must be reapplied/replaced frequently and crimped Must be re-applied if site is disturbed after initial application Must match seed mix with the time of year and site conditions; Requires > 3" of topsoil Effective for a maximum of 1 year; Requires > 3" of topsoil May need to be staked on steep slopes & channels; Proper selection of species; Requires > 3" of prepared topsoil Need a specially selected tracked or wheeled vehicle Appendix Page # Table Non-Structural Erosion Control Practices, Adapted from Massachusetts Stormwater Technical Handbook (1997) I.C-2 I.D-1 I.M-2 I.P-3 I.S-3 I.S-4 I.S-7 I.S-15 D A N E C O U N T Y E R O S I O N C O N T R O L A N D S T O R M W A T E R M A N A G E M E N T M A N U A L

25 C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 / Structural Practices Vegetated Buffer Strip Diversion, Permanent Diversion, Temporary Erosion Matting Gabion Sediment Basin Sediment Trap Silt Fence Slope Drain, Temporary Stone Check Dam Stone Tracking Pad Stone Weeper Stormwater Inlet Protection Applicable Standard 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year, Prevents Gully Erosion 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year; Prevents gully erosion 7.5 Tons/Acre/Year; Prevents gully erosion 7.5 Tons/Acre/Year 7.5 Tons/Acre/Year; Prevents gully erosion 7.5 Tons/Acre/Year Applicability to Sites Applicable when already installed Widely applicable Widely applicable Widely applicable on low to moderate slopes Applicable to vegetated ditches and swales Applicable to sites with a drainage area of <25 acres Applicable to sites with a drainage area of <25 acres Widely applicable Applicable on sites that are vulnerable to convey runoff downslope Applicable to vegetated ditches and swales, Drainage areas <2 acres Widely applicable Applicable to vegetated ditches and swales, Drainage areas <2 acres Widely applicable Maintenance Requirement Low Moderate Moderate Low Low Low Low High Moderate Low to Moderate Low to High Low to Moderate Moderate to High Environmental Concerns None Possible erosion of diversion structure if diverted runoff carries a large sediment load Possible erosion of diversion structure if diverted runoff carries a large sediment load Limited effectiveness on steep slopes Does not remove smaller suspended solids Maximum sediment removal capacity of 60-80%; Does not remove fine silts and clays Maximum sediment removal capacity of 60-80%; Does not remove fine silts and clays Sediment transport; High rates of failure if not properly installed and maintained; Disposal Possible erosion around inlet & outlet Does not remove smaller suspended solids None Does not remove smaller suspended solids Ineffective for large storm events; Limited effectiveness with large sediment loads Table Structural Practices, Adapted from Massachusetts Stormwater Technical Handbook (1997) Special Considerations Sufficient/suitable land area; Must be used in conjunction with other practices Must be carefully designed to prevent property damage May need frequent repair/replacement; Channel must be stabilized on slopes with a grade of >2% Proper installation Usually used in conjunction with other practices May need frequent repair/replacement; Sufficient/ suitable land area; Proper design and construction May need frequent repair/replacement; Sufficient/ suitable land area; Proper design and construction Longevity, proper installation Pipe Size Cost-effective; Must use >3" clear stone May need frequent cleaned/replacement; used in conjunction with other practices Appendix Page # I.V-1 I.D-3 I.D-4 I.E-1 I.G-1 I.S-1 I.S-2 I.S-5 I.S-6 I.S-8 I.S-11 I.S-12 I.S-13 D A N E C O U N T Y E R O S I O N C O N T R O L A N D S T O R M W A T E R M A N A G E M E N T M A N U A L

26 2.3 THE 7.5 TONS/ACRE/YEAR STANDARD Research has shown the average soil loss on uncontrolled construction sites is approximately 30 tons/acre/year. By limiting soil loss from construction sites to 7.5 tons/acre/year, an average reduction of at least 75% from uncontrolled conditions will be achieved. By analyzing the USDA Natural Resources Conservation Service s definition of particle size distribution for Plano Silt loam (Figure 2.3-1), a soil that is similar to the majority of Dane County s soils, it is shown that in order to achieve a trapping efficiency of 75% during construction, the 5 micron (µm) particle will need to be trapped. EXPECTED TRAP EFFICIENCY (%) µm particle trapped, achieving a 75% reduction PARTICLE SIZE TRAPPED (microns) Figure Particle Size Distribution for Plano Silt Loam, Source: National Soil Survey Characterization Database In Dane County, it is not feasible to trap particles smaller than 5 µm from a cost/benefit and engineering standpoint. In a pond that is two feet deep, trapping the 5 µm particle requires a settling time of 6 hours, which is feasible for pond design. However, the particle settling time increases exponentially with decreasing particle size (Figure 2.3-2). For example, trapping the 3 µm instead of the 5 µm particle increases the required settling time from 6 to 24 hours, but only increases the expected trapping efficiency by 5%. Designing a pond with a settling time of 24 hours would be much more costly and require a larger land area. Thus, a soil loss standard lower than 7.5 tons/acre/year would provide small additional benefit at a very high cost. Dane County s approach is equivalent to the intent of the performance standards for construction sites in the Department of Natural Resources Chapter NR 151, Wis. Adm. Code (refer to Chapter 1, section 1.3). 20 C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 / 0 7

27 Hours Particle Settling Time (2 foot depth) Particle Size (microns) Figure Particle Settling Time 2.4 CALCULATING SOIL LOSS FROM CONSTRUCTION SITES The Dane County Land and Water Resources Department has developed an Excel worksheet that calculates soil loss from construction sites. This spreadsheet uses the Universal Soil Loss Equation (USLE) to determine whether the combination of proposed erosion control practices will limit soil loss from sheet and rill erosion to 7.5 tons/acre/year or less. The USLE, its variables, and an example calculation are provided below. Note that the USLE estimates soil loss from sheet and rill erosion only. It does not predict soil loss resulting from high channel velocities, gully erosion or streambank erosion. Universal Soil Loss Equation for Construction Sites A = (R) x (% R) x (K) x (LS) x (C) x (P) A: Computed Soil Loss Rate (ton/acre) R: Annual Rainfall Factor (150 for Dane County) % R: The percentage of the annual R factor that has passed to date K: Soil Erodibility Factor (based on soil type) LS: Slope Length/Steepness Factor (based on slope length and percent slope) C: Land Cover Factor (based on condition of soil cover) P: Not used for construction site calculations. The P factor accounts for the effect of support practices such as contouring, strip cropping, or installing terraces in an agricultural setting. This factor does not apply to construction sites. USLE Spreadsheet An Excel spreadsheet for use in calculating soil loss is available online at Figure shows what the user sees online. This spreadsheet calculates soil loss from inputs entered by the user. Note that the user only needs to enter the following information: type of land disturbing activity in column 1, begin date in column 2, soil map unit in column 6, slope in column 7, and slope length in column 8. The remainder of the USLE variables are automatically determined or calculated by the spreadsheet, based on the input data. C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 /

28 Figure USLE Spreadsheet Description of Spreadsheet Columns Column # Variable Type 1 Land Disturbing Activity pull-down menu 2 Begin Date entered by user 3 End Date automatically calculated 4 Period % R automatically calculated 5 Annual R Factor automatically calculated 6 Soil Map Unit entered by user, or use button 7 Soil Erodibility K Factor automatically calculated 8 Slope entered by user 9 Slope Length entered by user 10 LS Factor automatically calculated 11 Land Cover C Factor automatically calculated 12 Soil Loss automatically calculated 13 Percent Reduction to Meet Ordinance automatically calculated Variable Descriptions Land Disturbing Activity (pull-down menu) The land disturbing activity relates to the type of disturbance that is occurring on the ground. The land disturbing activity inputs must be selected from the pull-down menu. 22 C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 / 0 7

29 Activity Inputs: bare ground mulch with seed seeding sod end Usually the initial disturbance occurs when the ground is left bare due to stripping vegetation, grading, or other actions that leave the soil devoid of cover. The application of a minimum of 1.5 tons/acre straw or other comparable mulch. Enter this if the seeding and mulching are done at the same time. It is not necessary to also enter seeding if this input is used. Requires 60 days of cover establishment during the growing season. Mulching is recommended on all disturbed areas that are to be seeded to control erosion and establish cover. The application of permanent or temporary seeding without the use of mulch. Not to be used with mulch with seed. Requires 60 days of cover establishment during the growing season. The installation of sod for cover establishment. This entry is made at the end of cover establishment. It is recommended that a 60 day cover establishment period be used. Refer to notes listed under Date. (Required Input) Begin Date (entered by user) The date the planned land disturbing activity begins, e.g. 5/15/07. The activity is assumed to continue until the next activity is entered. A 60-day cover establishment period, during the growing season, is recommended for the establishment of seeding. Notes: 1. Permanent seeding should be completed by September Temporary seeding should be completed by October 15. Temporary seeding of oats or sudan grass are normally sown between May 15 and July 15, and rye grass or winter wheat are normally sown between July 15 and September 15. To minimize competition, it is recommended that the temporary seeding be incorporated into the soil prior to application of permanent seeding. 3. When the seeding dates are later than the date guidelines, the end of the cover establishment period should be extended to May 15 of the following spring to allow for growth. End Date (automatically calculated) The date when the land disturbing activity ends. This cell is automatically calculated when the next Begin Date is entered. Period % R (automatically calculated) The percentage of the annual R factor calculated for the period from one land disturbing activity to the next. The % R is the percentage of the annual R factor that has passed to date. In the Midwest over half of the rainfall energy occurs during July, August, and September. Final raindrop energy is the primary cause for soil detachment. For these reasons, the R factor needs to be adapted to the construction schedule of the project. Annual R factor (automatically calculated) The rainfall factor, R, is the number of erosion index units in a normal year s rain. The erosion index is a measure of the erosive force of a specific rainfall. The rainfall, or R factor represents the total C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 /

30 amount of rainfall energy that occurs during an average year. The R factor was developed by using the average 30-minute storm intensity and raindrop energy. In Dane County the rainfall factor is 150. R = (EI30)/100 = (energy of rainstorm x max. 30 minute intensity)/100 Soil Map Unit (entered by user) The soil-mapping unit symbol for the predominant soil type in the area of the land disturbing activity, e.g. PnB. This information is available in the published soil survey of Dane County at the Land and Water Resources Department office or may be accessed by clicking the Soil Types button. Soil Erodibility K Factor (automatically calculated) The erosiveness of a specific layer and type of soil. The spreadsheet uses the highest K factor published for the soil type, typically a subsoil layer. The USLE s soil erodibility, or K factor represents a soil s ability to resist breakdown and erosion. The factor is determined by documenting erosion of a soil in a bare condition on a unit test plot. The higher the erosion rates, the higher the K factor will be. On construction sites, the subsoil K factor is used because topsoil is usually stripped. The K factor can be found in soil characterization tables. The soil properties that affect erodibility are: 1) soil structure, 2) soil particle size distribution, 3) permeability, 4) organic matter content, and 5) iron content-aluminum oxides (e.g. whether the subsoil has a high clay content). These are listed for Dane County soil series in appendix A of this manual. Slope (entered by user) The percent slope for the representative portion of the disturbed area, regarding overland flow and not channel flow, e.g.,.05 or 5 (depending on version of Excel). Slope Length (entered by user) Slope length (in feet) is measured along the overland flow path from the top to the bottom of the slope of the representative disturbed area. Channel lengths are not included in the slope length. LS Factor (automatically calculated) The program calculates this ratio based on the relationship between the percent slope and the length of slope of the representative disturbed area. The slope length/steepness or LS factor in the USLE equation relates the length and steepness of the slope. The rate of erosion increases exponentially as the length of the slope becomes longer. Erosion rates rise even more drastically as the steepness of the slope increases. The function used to calculate LS is: LS=(L/76.6) M (65.41Sin 2 θ+4.56sinθ+0.065) Where: L= slope length in feet θ= angle of slope (in degrees) M= 0.2 for slopes <1% M= 0.3 for slopes 1.0 to 3.0% M= 0.4 for slopes 3.0 to 4.5% M= 0.5 for slopes >4.5% 24 C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 / 0 7

31 Land Cover C Factor (automatically calculated) The cover and management factor is the ratio of soil loss from an area with a specified cover and management practice to that from a unit plot of bare land. The input from the Land Disturbing Activity corresponds to the C factor value. The C, or land cover factor, is the ratio of soil loss from an area with specified cover and management to the corresponding loss from a clean-tilled, continuously fallow condition. It is based on the type and condition of the cover on the soil surface. In construction site erosion control, the cover is extremely important. The vegetative cover provides the needed protection from rainfall impact and runoff water. If the condition of the cover is poor, the C factor will be higher. Conversely, when the vegetation is well established, the erosion and C factor will be reduced. C factors for construction sites can be found from tables in Predicting Rainfall Erosion Losses, published by the USDA. Commonly used C factors are: Bare Ground 1.00 Seeding 0.40 Seeding and Mulching 0.12 Sod 0.01 Soil Loss (automatically calculated) The predicted value of soil loss (tons per acre) that corresponds to the time period of each land disturbing activity. This value is calculated using the equation: A=(% R) x (R) x (K) x (LS) x (C). Percent Reduction Required to Meet Ordinance (automatically calculated) The percentage value in the TOTALS row corresponds to the reduction in soil loss necessary to comply with Dane County s Erosion Control and Stormwater Management Ordinance. It is required that the cumulative soil loss rate not exceed 7.5 tons per acre for all sites. Compliance with the ordinance standards can be achieved by: 1. Adjusting the management of the disturbed area, i.e., tightening schedule or installing erosion control measures. 2. Installing a sediment basin or other sediment control measures below the disturbed area. 3. Obtaining cooperative efforts of adjoining landowners. Button Controls: Detention Requirements Clicking on the Detention Requirements button will cause a pop-up box to appear that returns the size of the soil particle that would need to be trapped to obtain compliance with the Dane County Erosion Control and Stormwater Management Ordinance soil loss standard (7.5 tons/acre/year). The soil particle size distribution used for the calculation is a Plano silt loam, a typical and common distribution for Dane County. If the percent reduction is greater than what can theoretically be trapped by a single sediment control structure, a message stating Trap efficiencies greater than 80% are not possible with detention alone. is returned. If there is no reduction necessary to comply with the ordinance, clicking the Detention Requirements button will return: Detention is not necessary. The soil loss rate is below standards. C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 /

32 Soil Types Clicking on the Soil Types button will activate a combo box listing the soil mapping units and soil descriptions for Dane County soil types. Once highlighted and OK is clicked, another pop-up box will appear asking if the user wants the soil mapping unit to be automatically entered into the spreadsheet. Print Sheet Once the spreadsheet is completed, clicking the Print Sheet button will print a copy using the proper layout and print range. Help Page Clicking the Help Page button will activate a help page. Use one of the Back to USLE buttons on the help page to return to the spreadsheet. Example of Soil Loss Calculation Assumptions Need to calculate the soil loss from construction of a 25,000 sq. ft. mini-warehouse Plan to break ground on April 1, 2007 Site stabilization is planned to be completed by seed and mulch by August 12, 2007 The soil type was found in the Dane County Soil Survey to be Kidder Loam, 2 to 6% slopes (soil map unit = KdB) The representative slope on the site is 4.5% and has a length of 50 feet 1. Select the initial land-disturbing activity. When breaking ground on a construction site the landdisturbing activity will be bare ground, which can be selected from the pull-down menu. This represents the fact that soil will be exposed from this date on. 2. Enter the date that you expect to break ground, 04/01/07, in the next column. 3. In the Soil Mapping Unit column enter KdB. 4. Under the column titled Slope (%), enter the representative slope percentage, Enter the slope length in feet, 50, in the next column. 6. Go back to the Land Disturbing Activity column and just below the bare ground row select mulch with seed from the pull-down menu. 7. In the next column enter the date that you expect to seed and mulch the site, 08/12/07. The rest of the columns in this row will fill in automatically. 8. In the next row in the Land Disturbing Activity select end from the pull-down menu. 9. Under the date column enter a date, at least sixty-days after the site is expected to be seeded and mulched (10/12/07) during the growing season. This represents the time necessary to establish vegetative cover. If the seed and mulch date had been after September 15, the end date would have been extended to May 15 of the following year to allow for 60 days of establishment during the growing season. 26 C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 / 0 7

33 Below is an example of how the spreadsheet should look. 04/01/ /12/ /12/ /12/ /12/2007 Figure Spreadsheet from Example USLE Calculation As can be seen from the calculation, a reduction of 42% is still necessary to comply with the ordinance. This can be accomplished in a number of ways including reducing the time that the ground is left exposed, changing the time of year that construction takes place and/or designing erosion control practices to reduce the amount of soil that leaves the site. Other USLE Spreadsheet Notes: If the slope or schedule that is required for the calculation is not representative of the whole site, more than one calculation may be submitted. The area with the higher expected soil loss would then need to receive different erosion control treatment than the other areas on the site. When a slope is dramatically changed by grading during the bare ground period and it is desired to take credit for this change, select another bare ground row under Land Disturbing Activity and enter its corresponding date. Then enter a new slope and/or slope length in the appropriate columns. If the site is to be graded, but the entire site is to be stabilized by methods other than vegetation establishment (i.e., by paving or gravelling), skip the seed and mulch or sod activities and select end. C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 /

34 When sites are to be temporarily seeded and mulched, enter land disturbing activities of bare ground, seed and mulch, and end. The date for end will be when grading is expected to resume. Under these rows select bare ground, seed and mulch, and end for the second phase of grading. 2.5 GULLY AND STREAMBANK EROSION Gully erosion is caused by concentrated overland flow of surface water in depressions and drainage ways. The surface water s erosive force removes topsoil while increasing energy as it moves downslope. Once an unprotected gully begins to form, lateral erosion takes place, widening the gully and undercutting the sides where additional soil is removed. Preventive practices and proper management of gullies are required on construction sites. Streambank erosion removes soil along the banks and bed of a channel. The erosion is the result of high flow within the stream channel after rain events. The erosive force of the flow causes undercutting of the banks, which deposits large amounts of sediment directly into the stream channel. The sediment is then carried and deposited downstream. Practices and management techniques to prevent gully and streambank erosion can be found in Table with additional description, design and maintenance recommendations found in the Appendices. 28 C H A P T E R 2 E R O S I O N C O N T R O L 0 1 / 0 2 / 0 7

35 CHAPTER 3 STORMWATER 3.1 STORMWATER AND THE HYDROLOGIC CYCLE The Hydrologic Cycle The hydrologic cycle, illustrated in Figure 3.1-1, is the movement of water from the atmosphere to the earth s surface. Water moves through one or more components of the cycle including evaporation, transpiration, runoff, precipitation, infiltration, percolation and its eventual return to the atmosphere. In an undeveloped area, with natural ground cover such as forest or meadow, a significant portion of precipitation infiltrates into the soil. This water is filtered and cooled as it travels underground. Some infiltrated water is subsequently discharged into rivers and streams as baseflow. Baseflow provides a steady contribution of high quality water to lakes, streams and rivers. Other infiltrated water descends deeper underground to the water table and recharges aquifers. Groundwater recharge replenishes the supply of underground water that can be extracted for domestic use and irrigation. Another portion of precipitation is returned to the atmosphere through a combination of evaporation and plant transpiration called evapotranspiration. Where there is natural ground cover, all of these processes together serve to minimize the percentage of precipitation that becomes runoff, the water that flows over that land surface into streams and other surface water bodies. Condensation Moist Air Condensation Evaporation from rivers, soils, lakes Transpiration Precipitation Precipitation Evapor from ation Lake Evaporation Runoff Interception Soil Moisture Infiltration Seepage Groundwater Throughflow Figure The Hydrologic Cycle, Adapted from: The Physical Environment: An Introduction to Physical Geography, C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 /

36 Stormwater and the Hydrologic Cycle Urbanization dramatically affects the hydrologic cycle by altering the relative percentage of precipitation that contributes to groundwater, evapotranspiration, and runoff relative to the natural ground cover. Specifically, urbanization increases runoff by decreasing the amount of water that infiltrates into the ground and is taken up and transpired by plants. This is because water cannot infiltrate into, and plants cannot grow on, impervious surfaces such as pavement and rooftops. Figure illustrates how watershed imperviousness affects the magnitude of each of the hydrologic cycle components. Increased stormwater runoff not only decreases baseflow and groundwater recharge, but also increases the amount of water that runs off the surface, picking up and carrying pollutants to lakes, streams, rivers and wetlands. The increased surface runoff increases flooding frequency and severity while the increased input of pollutants degrades water quality and aquatic habitat. 40% Evapotranspiration 38% Evapotranspiration 10% Runoff 20% Runoff 25% Shallow Infiltration 25% Deep Infiltration 21% Shallow Infiltration 21% Deep Infiltration NATURAL GROUND COVER 10-20% IMPERVIOUS SURFACE 35% Evapotranspiration 30% Evapotranspiration 30% Runoff 55% Runoff 20% Shallow Infiltration 15% Deep Infiltration 35-50% IMPERVIOUS SURFACE 10% Shallow Infiltration 5% Deep Infiltration % IMPERVIOUS SURFACE Figure Impact of Impervious Area on the Hydrologic Cycle Fluxes, Adapted from: Prince Georges County Department of Environmental Resources Programs and Planning Division Low-Impact Development Design Strategies: An Integrated Design Approach. Department of Environmental Resources, Prince Georges County, Maryland. 30 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7

37 Baseflow Water table River Water table Baseflow Figure Baseflow Baseflow is the groundwater that constantly supplies rivers and streams with high quality water. When imperviousness decreases infiltration to groundwater, baseflow decreases. Adapted from: Water Resources Management Practicum, 2000, Dam Repair or Removal: A Decision-making Guide. Hydrographs Stormwater hydrographs are plots of runoff discharge versus time. They illustrate a site s response to a storm event. The highest point on a hydrograph represents the peak flow rate following a storm, and the area under the graph represents the total volume of runoff generated by the storm. Figure shows the significant difference between a pre- and post- development hydrograph. Specifically, Figure shows that development increases the volume, peak flow rate and duration of stormwater runoff following a storm event. Q (Discharge) Postdevelopment, without BMPs Predevelopment T (time) Figure Pre- and post- development storm hydrograph The increase in impervious surfaces increases the volume of runoff produced because it reduces infiltration, thus reducing baseflow. The impacts of these changes (Table 3.1-1) include increased flooding, erosion, channel widening, habitat loss, and streambed erosion. C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 /

38 Flooding Erosion Channel Widening Streambed Alteration Water Quality Degradation Habitat Loss Increased Volume Increased Peak Flow Increased Peak Flow Duration Decreased Base Flow Changes in Sediment Loading Increased Pollutant Loading Table Effects of Imperviousness Adapted from: Urbanization of Streams: Studies of Hydrologic Impacts, EPA 841-R , 1997 The Dane County Erosion Control and Stormwater Management Ordinance sets management standards to attenuate the adverse impacts of stormwater. Specifically, stormwater management practices must be designed and installed at new developments to meet ordinance requirements. Management practices must be designed to maintain predevelopment peak flow for the 2- and 10- year, 24-hour storm events, so that the post-development hydrograph is similar to Figure In order to attenuate the adverse impacts of sediment loading, the ordinance also requires that the stormwater management practices be designed to trap the 5 µm particle for the 1-year, 24-hour storm event. Q (Peak discharge) Predevelopment Shaded area represents additional runoff created by development (with out infiltration practices) Postdevelopment, with detention T (time) Figure Hydrograph with stormwater detention practices installed Note from Figure that conventional, stormwater detention practices can affect the timing and magnitude of the peak flow rate, but do not equate the volume of pre- and post- development runoff. This is because these management practices retain water and release it at a peak rate equal to predevelopment conditions, but do not facilitate infiltration and evapotranspiration. In order to decrease runoff and partially mitigate the adverse impacts of increased imperviousness, the county 32 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7

39 ordinance requires that a percentage of the average annual predevelopment infiltration (stay-on) be infiltrated. Residential developments must achieve 90 percent of the average annual predevelopment infiltration (stay-on), while nonresidential development must achieve 60 percent. When more than 1 percent of a residential site, or more than 2 percent of a nonresidential site is needed to meet the stay-on performance standard, a performance standard aimed at meeting a recharge goal may be utilized. The recharge standard requires that a minimum of 7.6 inches of precipitation becomes recharge on an average annual basis. An in-depth explanation of the county infiltration standards and practice modeling is found in Appendix II. The county also strongly recommends infiltration practices be used to meet thermal impact standards, where appropriate, since they have the added benefit of decreasing runoff. Finally, site planners should use techniques that minimize imperviousness and reduce runoff (refer to Section 1.4). If all of these techniques are utilized, the volume of post-development runoff will approach the volume of predevelopment runoff, reducing the effects of development on lakes and streams. Dane County stormwater standards should be met through the most effective, economical, and practical combination of management practices. Selection must be site specific and depends on the site conditions (land use, topography, slope, water table elevation, and geology) and applicable standards (rate, volume, sediment, oil and grease and thermal control). There are three types of management practices that can be used to attenuate stormwater impacts. Dane County recommends utilization of these three methods in the order listed below: 1. Site planning to minimize the volume of runoff originating from the site. 2. Nonstructural techniques, including good housekeeping practices, to minimize the amount of pollutants that come into contact with runoff. 3. Construction and maintenance of structural management practices to capture and treat stormwater runoff. Incorporating these management techniques into the site planning process requires that project proponents identify the site s physical characteristics, use models and other analyses to determine if applicable standards are being met, and consider the cost and feasibility of maintaining the proposed management practices. Refer to Figure on the next page for the stormwater planning and permitting process. C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 /

40 Identify significant site characteristics. Stormwater Permit Required Depth to water table Drainage area Sensitive natural resources on or near the site Depth to bedrock, bedrock type Soil type (HSG, USDA textural class, hydric classification) Thermally sensitive water resources impacted by the site (DNR designated cold water communities ) Preliminary Review Letter Utilize Site Design techniques to minimize the adverse impacts of development and the need for structural management practices Minimize impervious area Preserve sensitive natural areas Maintain existing site hydrology including drainage divides Restore soil structure Submit Stormwater Plan Utilize non-structural techniques to minimize pollutant sources. Draft stormwater plan using approved management practices, according to specifications in the WI DNR Technical Standards, Wisconsin Field Office Technical Guide, this manual or other approved standards. Analyze pre- and post-development runoff and infiltration using TR-55 and RECARGA or other model approved by the Dane County LWRD Director. Sediment control for 1-year, 24-hour storm event Peak flow for 2- and 10-year, 24-hour storm event Structures safely pass 100-year, 24- hour storm event Infiltration for average annual rainfall Determine most appropriate structural management practices given site characteristics, cost of practice maintenance, and quantity and quality of controls required. Management Practice Assessment Use model results to assess the need for structural management practices to meet peak discharge, infiltration and sediment control requirements Use Thermal Urban Runoff Model to assess the need for structural management practices to meet thermal requirements (if needed) Determine if oil and grease control is required Evaluate stable outlet configurations Figure Dane County Stormwater Site Planning and Permitting Process 34 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7

41 3.2 STORMWATER MANAGEMENT STANDARDS AND REQUIREMENTS The Dane County Erosion Control and Stormwater Management Ordinance requires that all sites needing a stormwater plan and permit install practices that comply with the following standards. Runoff Rate Stable Outlet Sediment Control: new construction Sediment Control: redevelopment Oil and Grease Control Thermal Control Infiltration Standard Purpose Applicability Practices must be designed to maintain pre-development peak runoff rates for the 2-year and 10-year, 24-hour storm event, and safely pass the 100-year storm event. For agricultural land, the maximum runoff curve number that can be used in hydrologic calculations for HSG A, B, C and D is 51, 68, 79 and 84, respectively. On sites that are heavily disturbed, the soil permeability class must be lowered by one. Discharges from new construction sites must have a stable outlet capable of carrying the designed flows at a non-erosive velocity. Practices must be designed to retain all soil particles greater than 5 microns, for the 1-year 24-hour storm event. Practices must be designed to retain all soil particles greater than 20 microns for the 1-year 24-hour storm event. Treat the first 0.5 inch of runoff using the best oil and grease removal technology available. Include provisions and practices to reduce runoff temperature. Practices must be designed to maintain 90 percent of the predevelopment infiltration (residential development) and 60 percent of the predevelopment infiltration (nonresidential). If more than 1 percent of a residential or 2 percent of a nonresidential site is needed to meet the stay-on goal, the practices must be designed to meet the 7.5 inch recharge goal (while dedicating a minimum of 1 percent of the site for residential and 2 percent for nonresidential). Submitted plans must also satisfy the following requirements: Prevent and/or minimize stream channel scouring, bank alteration and erosion, and downstream flooding. Prevent downstream property damage and erosion. Reduce total suspended solids in stormwater by 80%, with the expected result being a 50% reduction in phosphorus and heavy metals. Reduce total suspended solids in stormwater by 40%. Prevent oil and grease pollution in lakes and streams. Prevent damage to thermally sensitive aquatic habitat. Decrease runoff volume and promote infiltration and groundwater recharge. All new development requiring a stormwater plan. All sites requiring a stormwater plan. All sites requiring a stormwater plan. Redevelopment resulting in exposed surface parking lots and associated traffic areas. Commercial and industrial sites, and all other sites where the potential for pollution by oil or grease exists. Sites in thermally sensitive watersheds, (see map, p. 48) unless an approved thermal model indicates that postdevelopment site runoff temperature will not increase. All new development requiring a stormwater plan. C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 /

42 1. A narrative describing the proposed project, as it relates to the implementation of designed practices 2. Proposed schedule for completion and installation of all elements of the stormwater management plan 3. A map showing drainage area(s) for each watershed area showing assumed time of concentration flow path 4. A summary of runoff peak flow rate calculation, by watershed area, including: a. pre-existing peak flow rates b. post-construction peak flow rates with no detention c. post-construction peak flow rates with detention d. assumed runoff curve numbers (RCNs) e. time of concentration (T c ) used in calculations 5. A complete site plan and specifications, signed by the designer which includes: a. property lines and lot dimensions b. all buildings and outdoor uses, existing and proposed, including all dimensions and setbacks c. all public and private roads, interior roads, driveways and parking lots. Show traffic patterns and type of paving and surfacing material d. all natural and artificial water features, including, but not limited to lakes, ponds, streams (including intermittent streams), and ditches. Show ordinary high water marks of all navigable waters, 100-year flood elevations and delineated wetland boundaries, if any. If not available, appropriate flood zone determination or wetland delineation, or both, may be required at the applicant s expense e. depth to bedrock f. depth to seasonal high water table g. the extent and location of all soil types as described in the Dane County Soil Survey, slopes exceeding 12%, and areas of woodland or prairie h. existing and proposed elevations (referenced to the North American Vertical Datum of 1988, where available) and existing and proposed contours in the area requiring a shoreland erosion control permit i. elevations, cross sections, profiles, and details as needed to describe all natural and artificial features of the project j. soil erosion control and overland runoff control measures, including runoff calculations as appropriate k. detailed construction schedule l. copies of permits or permit applications required by any other governmental entities or agencies m. any other information necessary to reasonably determine the location, nature and condition of any physical or environmental features of the site n. location of all stormwater management practices o. all existing and proposed drainage features p. the location and area of all proposed impervious surfaces q. the limits and area of the disturbed area 6. Engineered designs for all structural management practices 36 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7

43 7. Proof of stable outlet capable of carrying the design flow at a non-erosive velocity 8. For new development, trap 5 micron soil particle (80% reduction in TSS) for the 1-year, 24- hour storm event 9. For redevelopment, trap 20 micron soil particle (40% reduction in TSS) for the 1-year, 24- hour storm event 10. Treat first half inch of runoff for control of oil and brease from commercial or industrial areas 11. For residential development infiltrate 90% of the predevelopment infiltration volume and for non-residential development infiltrate 60% of the predevelopment infiltration volume 12. If the site is located in the watershed of a DNR-designated coldwater community, provisions and practices to reduce the temperature of runoff for sites that drain to a coldwater resource as identified in the ordinance (refer to Thermal Locator, p. 45) 13. Identification of the entity responsible for long-term project maintenance 14. A maintenance plan and schedule for all permanent, privately owned stormwater management practices 15. Copy of recorded affidavit required by s.14.49(3)(d) for privately owned stormwater practices 16. Copy of Preliminary Review Letter (PRL), if applicable 17. Evidence of financial responsibility to complete work proposed in plan A letter of credit (LOC) is required if the estimated cost of implementing the proposed practices is greater than $ The local authority may establish off-site stormwater management and associated fees, provided that provisions are made to manage stormwater by an off-site facility, and provided that all of the following conditions for the off-site facility are met: a. the facility is in place b. the facility is designed and adequately sized to provide a level of stormwater control that meets or exceeds the ordinance standards c. the local approval authority is satisfied that the facility has a legally obligated entity responsible for its long-term operation and maintenance In order to assist in meeting the ordinance requirements, Tables and list practices that could be used to achieve the stormwater performance standards. The table briefly describes where management practices should be used along with maintenance requirements, environmental concerns and any special considerations for the practice. A more descriptive explanation of each practice is provided in Appendix I. Other practices may be used to meet erosion control or stormwater management standards if first approved by the Dane County LWRD Director. C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 /

44 38 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7 Non-Structural Practices Minimizing Impervious Areas Native Plants Parking Lot/Street Sweeping Surface Roughening Tree Planting Applicable Standard Thermal, Rate Control, Infiltration Infiltration, Rate Control 20% TSS Goal 7.5 Tons/Acre/year Thermal Applicability to Sites Limited application to retrofit sites Widely applicable Widely applicable Widely applicable Widely applicable (excluding berms and streambanks) Maintenance Requirement Low Low Moderate Low Low Environmental Concerns None None Sediment and debris collected may be contaminated with heavy metals Erosion may increase if not done on the contour of the slope Canopy may shade out ground level vegetation Special Considerations May reduce improvement costs Careful selection of native species; Requires a cover crop during establishment Hi-Vac trucks are more efficient Need a specially selected tracked or wheeled vehicle Careful selection of native species; Size; Proper spacing Table Non-Structural Stormwater Management Practices, Adapted from Massachusetts Stormwater Technical Handbook (1997) Appendix Page Number I.M-1 I.N-1 I.P-1 I.S-15 I.T-1 D A N E C O U N T Y E R O S I O N C O N T R O L A N D S T O R M W A T E R M A N A G E M E N T M A N U A L

45 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / Structural Practices Bioretention Basin, Dry Basin, Wet Vegetated Buffer Strip Constructed Wetland Diversion, Permanent Gabion Grassed Swale Infiltration Basin Infiltration Trench or Bed Applicable Standard 80% TSS; 40% TSS; Infiltration; Oil and Grease; Thermal; Rate Control 80% TSS; 40% TSS; Thermal; Rate Control 80% TSS; 40% TSS; Rate Control 80% TSS; Rate Reduction 80% TSS Stable Outlet 80% TSS; 40% TSS; Stable Outlet Stable Outlet Infiltration; Rate Control; Stable Outlet; Thermal Infiltration; Rate Control; Thermal Applicability to Sites Widely applicable Widely applicable, Larger drainage areas needed Widely applicable Widely applicable Applicable on sites with medium-fine textured soils; Requires a large drainage area Applicable to vegetated ditches and swales Widely applicable Widely applicable Moderately restricted to sites with suitable soils; Requires a substantial area to meet standards Highly restricted to sites with small drainage areas and proper soils; Depth to water table and bedrock; Slopes Maintenance Requirement Moderate Low to Moderate Low Low High Moderate Low to Moderate Low to Moderate Low to Moderate High Environmental Concerns Potential for groundwater contamination if not designed, sited, constructed and maintained properly Provides less water quality improvement than Wet Basins Possible thermal impacts; low bacteria removal; May attract undesirable wildlife None Possible downstream warming, releases nutrients in the fall Possible erosion of diversion structure if diverted runoff carries a large sediment load Does not remove smaller suspended solids Restricted use for areas with high pollution potential Potential for groundwater contamination; Restricted use for areas with high pollution potential Potential for groundwater contamination; Restricted use for areas with high pollution potential Table Structural Stormwater Practices, Adapted from Massachusetts Stormwater Technical Handbook (1997) Special Considerations Cost; Use native plus or root stock; contamination from salt; construction timing Sufficient/suitable land area; Design considerations; Sediment forebay Sufficient/suitable land area; Design considerations; Sediment forebay Sufficient/suitable land area; Careful selection of species; Must be used in conjunction with other BMPs Sufficient/suitable land area, Cost; Careful design; Biomass harvesting Must be carefully designed to prevent property damage Carefully size stone Pretreatment; Check dams; Careful design Sufficient/suitable land area; Proper construction; Compaction avoidance 80% TSS pretreatment Recommended with careful soils evaluation & 80% TSS pretreatment Appendix Page Number I.B-1 I.B-2 I.B-3 I.V-1 I.C-1 I.D-3 I.G-1 I.G-2 I.1-1 I.I-2 D A N E C O U N T Y E R O S I O N C O N T R O L A N D S T O R M W A T E R M A N A G E M E N T M A N U A L

46 40 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7 Structural Practices Lined Waterway or Outlet Oil & Grease Filter Oil & Grease Separator Pervious Pavement Rain Garden Stone Check Dam Stone Crib Stone Outlet Protection Stone Weeper Subsurface Drain Applicable Standard Stable Outlet Oil and Grease Removal, 1st 1/2 inch of runoff Oil and Grease Removal, 1st 1/2 inch of runoff Infiltration; Thermal; Rate Control 80% TSS; 40% TSS; Rate Control; Infiltration 80% TSS; 40% TSS; Rate Control; Stable Outlet Thermal Stable Outlet Widely applicable to outlets Thermal; Rate Control Applicability to Sites Widely applicable Applicable on small impervious areas (With less than 1 acre of drainage) Applicable on small impervious areas (With <1 acre of drainage) Applicable on areas with very low traffic volumes Applicable on sites with drainage areas less than 2 acres Applicable to vegetated ditches and swales Widely applicable, especially in urban areas Widely applicable Applicable to vegetated ditches and swales Widely applicable Maintenance Requirement Low to Moderate Moderate to High Moderate to High Moderate Low Low to Moderate Low to Moderate Low Low to Moderate Low Environmental Concerns Alters natural cover Limited pollutant removal Limited pollutant removal, does not remove soluble pollutants Potential for groundwater contamination Susceptible to clogging Does not remove smaller suspended solids Limited effectiveness with large storm events Limited effectiveness with large storm events Does not remove smaller suspended solids Provides limited sediment and pollutant removal Table Structural Stormwater Practices, Cont., Adapted from Massachusetts Stormwater Technical Handbook (1997) Special Considerations Sufficient/suitable land area; Runoff velocities Cost and Frequent Maintenance Proprietary device must be approved Limited use in cold climates, Durability, Potential to clog Sufficient/suitable land area, proper soils Use clear or washed stone Needs to be properly sited Sufficient/suitable land area; Carefully size stone Carefully sized stone Must have stable outlet Appendix Page Number I.L-1 I.O-1 I.O-2 I.P-2 I.R-1 I.S-8 I.S-9 I.S-10 I.S-12 I.S-14 D A N E C O U N T Y E R O S I O N C O N T R O L A N D S T O R M W A T E R M A N A G E M E N T M A N U A L

47 3.3 SEDIMENT CONTROL REQUIREMENTS For new development, the ordinance requires stormwater practices be designed to retain all soil particles greater than 5 microns for the 1-year, 24-hour storm event. For redevelopment resulting in exposed surface parking lots and associated traffic areas, the ordinance requires that stormwater practices be designed to retain soil particles greater than 20 microns for the 1-year, 24-hour storm event. Although not required by the ordinance, the following goals should be met whenever possible. The design, suggested location, and implementation of proposed practices should be included in the plans. For existing development, design practices to retain soil particles greater than 40 microns on the site, resulting from a 1-year, 24-hour storm event. For street reconstruction, design practices to retain soil practices greater than 20 microns on the site, resulting from a 1-year, 24-hour storm event. 3.4 POLICY FOR OIL AND GREASE CONTROL The ordinance requires that all stormwater plans for commercial and industrial developments and all other areas where the potential for oil or grease exists must include practices to treat oil and grease in the first 0.5 inches of runoff. The best available oil and grease removal technology must be used. Oil and grease removal practices are generally combined with other stormwater runoff management practices and are obtained through commercial sources. Information regarding choice, installation and maintenance of these management practices is best obtained from the manufacturer. Sites that must control the first half-inch of runoff for oil and grease include: vehicle fueling and service areas commercial buildings with drive-though areas parking lots with more than 40 stalls convenience stores other areas that are determined to have the potential for oil and grease pollution 3.5 RUNOFF RATE The ordinance requires that all stormwater facilities be designed, installed and maintained to effectively accomplish the following: Maintain predevelopment peak runoff rates for the 2-year, 24-hour storm event (2.9 inches over 24 hours) Maintain predevelopment peak runoff rates for the 10-year, 24-hour storm event (4.2 inches over 24 hours) Safely pass the 100-year, 24-hour storm event (6.0 inches over 24 hours) The ordinance requirements for water quantity apply to individual sites and not the entire watershed. It is more difficult to control the larger storms with the practices installed on an individual site. C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 /

48 Municipalities may consider large regional facilities, sited as part of municipal and regional stormwater planning, in order to manage stormwater from larger storms. Determining Runoff Rate Using TR-55 Technical Release 55 (TR-55), or Urban Hydrology for Small Watersheds (NRCS 1986), is a model that calculates storm runoff volume, peak rate of discharge, hydrographs (refer to Section 3.1), and storage volumes for stormwater facilities. This model was developed for small watersheds (10 square miles or less), especially urbanizing watersheds, in the United States. A revision was made in June of 1986 that incorporated results of subsequent research and other changes based on experience with the original edition. TR-55 begins with a rainfall amount distributed uniformly over a watershed over a specified time period. Mass rainfall is converted to mass runoff and runoff travel time routed through segments of a watershed is used to create a runoff hydrograph. The ordinance requires that TR-55 specified curve numbers for land uses must be used in hydrologic calculations, except for agricultural land subject to stormwater standards. For agricultural land, the maximum runoff curve number used in calculations shall be 51 for Hydrologic Soil Group (HSG) A, 68 for HSG B, 79 for HSG C, and 84 for HSG D. Calculation of post-development runoff must account for changes in permeability class due to the soil characteristics and site compaction. Areas with high equipment traffic shall be considered heavily disturbed. Areas with limited equipment traffic will be considered lightly disturbed. Developers are required to lower one permeability class for all hydrologic calculations, unless practices such as deep tilling, chisel plowing, and incorporating organic matter into the upper soil surface have successfully restored soil structure. The TR-55 Program with additional documentation and a presentation can be found on NRCS s web site at: STABLE OUTLETS The ordinance requires that discharges from new construction sites have a stable outlet capable of carrying designed flow at a non-erosive velocity. Outlet design must consider both flow capacity and duration. This requirement applies to both the site outlet and the ultimate outlet to stormwater conveyance or water body. Stable outlets are an integral part of well-designed erosion control and stormwater management practices. Stable outlets allow stormwater and erosion control structures to function properly and provide a way for runoff to be discharged without causing damage to downstream properties or water bodies. A stable outlet can be a grassed waterway, vegetated or paved area, grade stabilization structure, underground outlet, rock chute, rock lined channel or stable watercourse. Stable outlets must have the capacity to handle the designed outflow from the stormwater or erosion control structures they serve. If the outlet is to be vegetated, it should be constructed and established before installation of other stormwater or erosion control structures. Verify that the channel lining is adequate to carry the design to velocity and volume. 42 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7

49 Channel Lining To prevent channels from eroding, an analysis of the channel velocity must be performed to determine the required control practice(s). Where velocities are higher than 5 feet per second or where the channel must carry prolonged flow, the channel should be lined with riprap or other armoring material. Channel linings shall be designed based on the expected channel velocity from the 10-year, 24-hour storm event. 3.7 INFILTRATION Infiltration reduces runoff volumes and depends on rainfall intensity, slope of the infiltrating surface, the permeability of soils and subsoils, soil moisture, content, vegetation and temperature. During infiltration, water enters from surface storage into soils via the combined effects of gravity and capillary forces. The capillary forces are inversely proportional to the diameter of pores. As the process continues, the pore space becomes filled and the capillary tension decreases. Under saturated conditions, flow is mostly due to gravity. The ordinance requires that a percentage of the average annual rainfall be infiltrated unless the applicant can demonstrate that the practice is likely to result in groundwater contamination. Infiltration is all precipitation that does not leave the site as surface runoff, and is referred to as stayon. For residential developments, 90 percent of what infiltrated in the predevelopment condition (predevelopment infiltration) must be infiltrated. For nonresidential development, 60 percent of predevelopment infiltration must be infiltrated. If more than one percent of a residential development or two percent of a nonresidential development is needed to meet the infiltration standard, infiltration practices may be alternatively designed to meet an average annual recharge goal of 7.6 inches. If the ordinance requirement is met with the recharge methodology, a minimum of one percent or two percent of the site (for residential or nonresidential development respectively) must be dedicated to the infiltration practices. 3.8 THERMAL CONTROL Thermal Standards The ordinance requires that the increase in runoff temperature originating from sites in cold-water community watersheds must be reduced, unless results of a thermal impact model approved by the Dane County LWRD Director show that the temperature increase of post-development runoff from the site will be zero. Affected sites are those located within the watershed of a river or stream identified by the Wisconsin Department of Natural Resources as: A Cold Water Community as identified through NR (3)(a), NR 104, Wisconsin Administrative Code, and Class I, Class II, and Class III Trout Streams identified in Wisconsin Trout Streams, DNR publication PUB-FH or its successor Rivers or streams proposed by the Wisconsin Department of Natural Resources as Cold Water Communities and Class I, II, and III Trout Streams C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 /

50 Drainage divide Watershed Tributary streams Main river Figure Watersheds A watershed is the land area that drains to a common location (typically a water body and its tributaries). For this reason, watershed boundaries are also called drainage divides. Practices to reduce the temperature of runoff must be installed if a site is located anywhere within the watershed of a thermally sensitive water body. Figure shows these water bodies and the boundaries of their watersheds. 44 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7

51 Figure Stream Segments Requiring Thermal Control. The proposed and existing cold-water watersheds in Dane County, current as of July 9, 2002, are subject to change. The WDNR may change stream classifications as they are warranted. A current list and map of affected watersheds is available for reference at the Dane County Land Conservation Division or at: Locator To determine whether a parcel of land is located within the watershed of a cold-water stream, Dane County has developed a user-friendly locator available at: under data and technology (Arrington, Kathleen GIS Application to Thermal Impact in Urban Areas. MS Thesis, UW- Madison Soil Science Department) The locator performs a preliminary assessment to determine whether the property is located within a cold-water watershed using the unique parcel number of the property or other locating information. C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 /

52 (Parcel numbers are available from Access Dane at: As a result of this assessment, the web site will inform the user if thermal practices are required in the storm water management plan. Thermal Considerations The increase of impervious surfaces in urban areas is a major source of thermal pollution in cold climates and threatens the health of cold-water ecosystems (Galli, J Thermal Impacts Associated with Urbanization and Storm Water Best Management Practices. Maryland Department of Environment). Research shows that the average stream temperature increases directly with the percentage of impervious cover in the watershed. Impervious areas absorb energy from the sun, which causes them to become warmer. As water runs over these areas, it absorbs some of that heat energy and is warmed, causing thermal pollution in lakes, rivers, and streams. Impervious areas also compound the problem by reducing infiltration, which in turn increases the volume of runoff that is created, leading to higher permanent stream temperatures in the summer months. Stream water temperature is a major limiting factor for cold-water fisheries, as all biological activity is related to temperature. Temperature is a characteristic of water quality and is very important in chemical and biochemical processes, particularly those involving biochemical activity. Higher stream temperatures result in lower dissolved oxygen (DO) concentrations and may cause biological oxygen demand (BOD) to increase. Temperature increases in streams can also result in behavioral changes of fish and macro invertebrate communities (aquatic insects), as these species have specific water temperature preferences and tolerance limits. Over time, the cumulative impact of individual development sites will increase water temperature, permanently affecting habitat in the stream. By mitigating runoff and water temperature impacts, the stream community will benefit not only from maintained stream temperature, but also from a decline in the amount of sediment, nutrients, and pollution that reaches receiving waters. Thermal Model Description One model that can be used to estimate thermal impacts is the Thermal Urban Runoff Model (TURM) (Norman, J.M. and A. Roa Effects of the Natural Environment and Urban Runoff on Stream Temperatures). The University of Wisconsin and the Dane County Land Conservation Division developed the model to estimate runoff temperature from urban watersheds. The thermal impact from impervious areas was documented in a study at Token Creek subwatershed, where collected data was compared to the results calculated by TURM. This model accounts for the fact that storm water not only absorbs heat from impervious surfaces, but that it also cools these surfaces, reducing the ability of the impervious surfaces to heat runoff from additional rainfall. However, TURM does not account for the inherent variability of rainfall due to changes in intensity and the type of storm, as the model assumes that the rainfall is uniform over the entire duration of the event. Field data collected at Token Creek subwatershed indicates that storm water runoff from highly urbanized areas has the potential to increase the temperature of receiving waters by as much as 23 F (Roa, A., J.M. Norman, T.B. Wilson, and K. Johnson Thermal Impact Analysis of Token Creek Subwatershed and Validation of Temperature Urban Model (TURM)). Other model considerations include: (1) the amount and temperature of impervious area; 46 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7

53 (2) the ambient air temperature; (3) the gain or loss of heat through the passage of water through management practices; (4) the net change in heat due to tree canopy; (5) the heat loss through evaporation; (6) the time and duration of storm events, and; (7) the difference in the time of concentration of vegetated areas and impervious surfaces. Other thermal impact models may be used if they are approved by the Dane County LWRD Director. Figure Example Screen from TURM 3.9 MAINTENANCE REQUIREMENTS All stormwater management practices must include a maintenance plan, which describes the entity responsible for long-term upkeep of the practice and the type of maintenance required. The maintenance plan must be deed recorded prior to permit issuance. The plan should also include C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 /

54 accessibility to the site and the level of maintenance required. Long-term maintenance costs should be considered when selecting a practice. Some practices may be inexpensive to implement, but longterm maintenance activities of the practice may be costly. As part of an approved erosion control or stormwater permit, maintenance requirements are enforceable per Section 14.49(8) of the Dane County Erosion Control and Stormwater Management Ordinance. The county will maintain a database of permitted stormwater practices and will periodically perform inspections to assure the maintenance requirements set forth in the approved plan are being met. 48 C H A P T E R 3 S T O R M W A T E R M A N A G E M E N T 0 1 / 0 2 / 0 7

55 APPENDICES APPENDIX I MANAGEMENT PRACTICES Basin, Dry Basin, Wet Bioretention Basin Constructed Wetlands Construction Scheduling Deep Tilling Dewatering Diversion, Permanent Diversion, Temporary Erosion Matting Gabion Grassed Swales Infiltration Basin Infiltration Trench or Bed Lined Waterway or Outlet Minimizing Impervious Areas Mulching Native Plants Oil and Grease Filter Oil and Grease Separator Parking Lot/Street Sweeping Pervious Pavement Polymer Application Proprietary Stormwater Devices Rain Garden Sediment Basin Sediment Trap Seeding, Permanent Seeding, Temporary Silt Fence I.A-1 I.B-1 I.B-2 I.B-3 I.C-1 I.C-2 I.D-1 I.D-2 I.D-3 I.D-4 I.E-1 I.G-1 I.G-2 I.I-1 I.I-2 I.L-1 I.M-1 I.M-2 I.N-1 I.O-1 I.O-2 I.P-1 I.P-2 I.P-3 I.P-4 I.R-1 I.S-1 I.S-2 I.S-3 I.S-4 I.S-5 A P P E N D I C E S T A B L E O F C O N T E N T S 0 1 / 0 2 / 0 7

56 Slope Drain, Temporary Sod Stone Check Dam Stone Crib Stone Outlet Protection Stone Tracking Pad Stone Weeper Stormwater Inlet Protection Subsurface Drain Surface Roughening Tree Planting Vegetated Buffer Strips I.S-6 I.S-7 I.S-8 I.S-9 I.S-10 I.S-11 I.S-12 I.S-13 I.S-14 I.S-15 I.T-1 I.V-1 APPENDIX II INFILTRATION MODELING Infiltration Practice Design Regulatory Approach to Infiltration Target Stay-On Requirement Target Recharge Requirement RECARGA Frequently Asked Questions and Definitions II-1 II-1 II-2 II-3 II-4 II-5 APPENDIX III HYDROLOGY Design Storm for Dane County Permeability Class vs. Hydrologic Soil Group III-1 III-2 APPENDIX IV BASIN EFFICIENCY Basin Design Volume of Storage Required Approximate Detention Basin Routing for Type II Storms Calculating Trapping Efficiency Settling Velocities for Spherical Particles Stokes Law IV-1 IV-1 IV-2 IV-2 IV-4 A P P E N D I C E S T A B L E O F C O N T E N T S 0 1 / 0 2 / 0 7

57 APPENDIX I MANAGEMENT PRACTICES The following pages are comprised of practices that are designed to help meet the erosion control and stormwater management requirements as set forth by the county ordinance. This list is a representative sample of available practices. Alternative practices are encouraged and may be used as part of an erosion control or stormwater plan if they meet the requirements of the site and are approved by the LWRD Director. However, no single practice is capable of meeting all the needs of an individual site. As a result, practices should be used in series as part of a comprehensive management plan. The technology that drives erosion control and stormwater management is constantly evolving. As a result, practices may be added, revised, or deleted at the discretion of the Dane County Land Conservation Division. The following pages provide general design information and are broken down into the following sections: GENERAL... This section provides basic information about the practice, such as its purpose, how it works, and where it is applicable. ADVANTAGES... This section discusses the benefits of the practice, such as cost-effectiveness, versatility, maintenance requirements, etc. DISADVANTAGES.. This section discusses the negative aspects of the practice, such as cost, environmental effects, limits of the practice, etc. DESIGN... This section provides the design criteria for the various parts of the device, such as sizing requirements, capacity, shape, etc. CONSTRUCTION... This section provides information that may be needed during the installation and construction phase of the project, such as preparations, timing, special considerations, etc. MAINTENANCE... This section discusses the maintenance needs of the practice, an integral part of the success of any management practice. EFFICIENCY... This section discusses credit that will be given for each practice that is implemented. Efficiencies are determined in a variety of ways and are dependant upon the proper design, installation, and maintenance of the practice. Not all practices have efficiencies associated with them. A P P E N D I X I 0 1 / 0 2 / 0 7 I.A-1

58 I.A-2 A P P E N D I X I 0 1 / 0 2 / 0 7

59 BASIN, DRY GENERAL A dry basin temporarily retains stormwater and gradually releases it to a conveyance structure (refer to Grassed Swales, pg. I.G-2; Lined Waterway or Outlet, pg. I.L-1; or Subsurface Drain, pg. I.S-14). Its purpose is to reduce stormwater peak flow rates and trap sediment particles. By trapping sediment, associated pollutants are also removed. Dry basins are designed to drain completely within 48 hours of the storm event. Dry basins are often utilized in thermally sensitive watersheds, as they do not increase the temperature of the runoff. These structures also provide only limited pollutant removal and accumulated sediment is often resuspended by subsequent storm events. As a result, dry basins should be used in conjunction with other management practices. DESIGN FOREBAYS Forebays are small sediment traps required at all basin inlets. Forebays, which are separated from the rest of the basin by a berm, receive runoff and prevent concentrated flow from entering the basin, allowing sediment to settle out before reaching the main basin. They simplify maintenance by concentrating sediments and extending the holding capacity and life of the basin. VOLUME Each basin should be designed according to the individual characteristics of the site. The basins should be sized to achieve the sediment reduction goal and safely pass the 100-year storm event. Refer to the NRCS website ( for the most up-to-date NRCS standards. SHAPE AND SLOPE Dry basins should be designed with a length to width ratio of at least 3:1 in a shape that ADVANTAGES Reduces peak flows Able to be used in thermally sensitive areas DISADVANTAGES Requires a relatively large land area Generally not practical in areas where the drainage area is less than 10 acres Accumulated sediments may be resuspended if not removed between storm events Provides marginal removal of pollutants increases detention time, such as a long, narrow shape or a teardrop shape. If these shapes are not feasible, baffles should be installed to increase the flow path. The bottom of the basin should be sloped towards the outlet to ensure proper drainage and prevent standing water. Forebays should have an area equal to 10-25% of the basin s surface area, with a length to width ratio of at least 2:1 to provide proper flow. The side slopes of the basin should not exceed a 4:1 ratio and should not be less than 10:1. Slopes in this range prevent excessive erosion and makes maintenance tasks both easier and safer and provide adequate drainage. The banks of the basin should not exceed a height of 20 feet and should be overbuilt by at least 10 percent to allow for settling and subsidence (should be consistent with the NRCS standards). To prevent the erosion of the structure, the banks and the bottom of the basin should be seeded with vegetation that is tolerant of inundation or should be lined with stone (refer to Seeding, Temporary, pg. I.S-4; Native Plants, pg. I.N-1; or Lined Waterway or Outlet, pg. I.L-1). A P P E N D I X I B A S I N, D R Y 0 1 / 0 2 / 0 7 I.B-1.1

60 OUTLETS The basin outfall must be designed to handle the structure s peak flow rate and must discharge to a stable outlet (refer to Stone Outlet Protection, pg. I.S-9). Outlet structures may incorporate a perforated riser or gabion basket and should be resistant to clogging. They may incorporate trash racks, skimmers, or other devices. Outlets should be designed with stability in mind and should be able to endure frost heave and settling. Dry basins must also incorporate an emergency spillway into the design of the structure to safely pass flows that exceed the design capacity of the basin. Emergency spillways prevent large flows from overwhelming the capacity of the basin without causing damage to the outfall structure and should discharge to a stable outlet (refer to Stone Outlet Protection, pg. I.S-10; or Lined Waterway or Outlet, pg. I.L-1). CONSTRUCTION be restored to its original design volume and depth after construction is complete MAINTENANCE Trash and other debris should be removed regularly to prevent clogging Dry basins should be inspected at least twice a year to ensure they are operating properly and to check for any potential problems, such as: sediment accumulation, subsidence, erosion, damage to the emergency spillway, and woody vegetation Accumulated sediment should be removed from the basin as necessary METHOD TO DETERMINE PRACTICE EFFICIENCY Dry basins reduce peak flows and act as a sediment-trapping device. The method to determine the efficiency for this practice is located in Appendix IV on page IV-1. A dry basin may be used during construction to treat site runoff, but must I.B-1.2 A P P E N D I X I B A S I N, D R Y 0 1 / 0 2 / 0 7

61 SOURCES 1. Conservation Practice Standard: Water and Sediment Control Basin, Code 638. Natural Resource Conservation Service. South Dakota. March Georgia Stormwater Management Manual. Volume 2: Technical Handbook. Atlanta Regional Commission. Atlanta, Ga Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Stormwater Management. Volume Two: Stormwater Technical Handbook. Massachusetts Department of Environmental Protection. Boston. March A P P E N D I X I B A S I N, D R Y 0 1 / 0 2 / 0 7 I.B-1.3

62 I.B-1.4 A P P E N D I X I B A S I N, D R Y 0 1 / 0 2 / 0 7

63 BASIN, WET GENERAL A wet basin (or a wet pond) is a constructed stormwater basin that retains a permanent supply of water while also temporarily accumulating stormwater runoff. Its purpose is to reduce stormwater flow velocity and trap sediment and other associated pollutants. Stormwater enters the basin and is temporarily retained, allowing pollutants to settle out. Pollutants, such as metals, nutrients, sediment, and organic substances, are removed in wet detention basins by the settling of particulates, biological uptake, consumption, and decomposition. Wet basins can be used in residential, commercial, and industrial areas if the contributing watershed is large enough. Generally, the watershed should be at least 10 acres to ensure a constant supply of water to maintain water depth in the basin. Due to the permanent ponding of water, wet basins can remove large amounts of pollutants and are more effective in removing plant nutrients than most other management practices. The large volume of storage in the basin helps to reduce peak discharges from storm events, which, in turn, reduces downstream flooding while limiting streambank erosion. ADVANTAGES Capable of removing both solid and soluble pollutants One of the most effective and reliable devices for removing pollutants from stormwater Wildlife habitat is created when the ponds are properly designed and maintained Can be aesthetically pleasing if designed properly, which can increase adjacent property values Pond sediment does not have to be manually removed as often as other management practices DISADVANTAGES Pond requires a relatively large land area Generally not practical in areas where the drainage area is less than 10 acres Pond discharge usually consist of warm water, so their use may be limited in areas with temperature sensitive fisheries Improperly maintained ponds may result in nuisance odors, algae blooms, and rotting debris Provides a potential breeding ground for mosquitoes if not designed properly Safety An Example of a Wet Basin Source: Adapted from the United States Environmental Protection Agency A P P E N D I X I B A S I N, W E T 0 1 / 0 2 / 0 7 I.B-2.1

64 DESIGN FOREBAYS/INLETS Forebays, which are separated from the rest of the basin by a wall or berm, receive runoff and prevent concentrated flow from entering the basin, allowing sediment to settle out before it reaches the basin. They also simplify maintenance by concentrating sediments and extending the holding capacity and life of the basin. Forebays should have an area equal to 10-25% of the basin s surface area, with a length to width ratio of at least 2:1 to provide proper flow. Forebays should be located opposite of the basin s outlet to increase detention time. VOLUME AND SURFACE AREA Each basin should be modeled and built according to the individual characteristics of the watershed in which it is being placed, as each watershed will have a different hydrologic makeup. There is a direct correlation between the size of the basin and the pollution removal rate, the larger the basin, the greater the removal rate of sediment and pollutants from the runoff. Each basin must be designed to handle the runoff produced from the 2 and 10 year, 24- hour storm event for its watershed, and also be able to safely pass the 100-year storm event. The volume of the basin should also be sufficient to provide for the storage of accumulated sediment as well as the runoff from these storm events. The surface area of the basin will vary as well based on location; however, a minimum area of 0.25 acres is recommended to sustain the permanent ponding of water. SHAPE Wet basins should be designed so that the previously held stormwater is replaced by the newer stormwater, a process referred to as plug flow. Plug flow allows the water to remain in the basin long enough to facilitate the settling of sediment and the adsorption of pollutants and sediment. Failure of the basin to do so is called short-circuiting. To avoid short-circuiting, the basin should be designed with a length to width ratio of 3:1 in either a long, narrow shape or a teardrop shape. These shapes encourage proper mixing of the water column and increase the amount of time the stormwater remains in the basin. In addition, these shapes lessen the amount of sediment stirring caused by wind, allowing pollutants to remain settled in the sediment. If these shapes are not feasible, structures that lengthen the flow path, such as gabions and baffles, should be installed. BASIN SLOPES The side slopes of the basin should not exceed a 4:1 ratio and should not be less than 10:1. Slopes in this range prevent excessive erosion and makes maintenance tasks both easier and safer, while providing enough slope to provide adequate drainage. Submerged slopes should consist of two types: an aquatic bench and the pool slopes. Aquatic benches should extend at least ten feet from the water s edge and have a slope with a 10:1 ratio. This shallow area promotes the growth of aquatic vegetation and also increases the safety of the basin, allowing someone who has fallen in to quickly regain his or her footing. Pool slopes are located toward the center of the basin beyond the aquatic shelf. These slopes will depend on the soil stability of the site, but in general should not exceed a 2:1 ratio, as banks are likely to become unstable at higher ratios. DEPTH Basins should be constructed with an average depth of 3-6 feet, with depths varying throughout. Shallow basins tend to remove a greater percentage of solids than deep ones. Depths greater than 10 feet may encounter low oxygen levels and thermal stratification, and are generally not recommended unless measures are taken to ensure proper oxygen content. The aquatic shelf of the basin should include shallow areas with depths ranging from 6-18 inches to promote the growth of aquatic vegetation and to improve the safety of the basin. SEDIMENT CONTROL Wet basins should remove, at a minimum, 80% of the total suspended solids from the runoff generated from the site. To increase the effectiveness and the life of wet basins, sediment forebays or other pretreatment devices may be used and are recommended. Forebays and other pretreatment devices act to slow runoff before it enters the basin, allowing I.B-2.2 A P P E N D I X I B A S I N, W E T 0 1 / 0 2 / 0 7

65 pollutants and larger sediments to settle out before reaching the basin. In addition, the basin design should incorporate sediment accumulation over a period of at least 25 years to ensure the proper holding capacity over the life of the basin. OUTLETS Each basin should have 2 outlet structures, a principle outlet and a dewatering outlet. The principle outlet slowly releases the water to the receiving waters, while the dewatering outlet, which is used on a limited basis, allows the basin to be drained quickly for maintenance purposes. Both types of outlets should allow access to maintenance personnel while restricting access to the general public. Outlets should be designed with stability in mind and should be able to endure frost heave and settling. In addition, all outlets should be designed to resist obstruction, which may be accomplished in several ways, including the use of skimmers and trash racks. CONSTRUCTION Wet basins may be used during construction to treat site runoff Once construction is complete, the basin must be returned to its original design volume and depth MAINTENANCE Maintenance costs are estimated at 3-5% of construction cost per year Wet basin should be inspected at least twice a year to ensure they are operating properly and to check for any potential problems, such as: subsidence, erosion, tree growth on the embankment, sediment accumulation around the outlet, and damage to the emergency spillway Sediment should be removed from the basin as necessary, usually between every 5 and 25 years the frequency of this event depends on the design of the basin and forebay and the occurrence of any large loading events METHOD TO DETERMINE PRACTICE EFFICIENCY Wet basins reduce the flow velocity of runoff, allowing suspended particles to settle out. In addition, these devices remove nutrients, heavy metals, and other pollutants from stormwater by utilizing several biological processes. The efficiency for this practice is dependant upon the size of the basin, the size of the drainage area, and other site characteristics. As a result, the efficiency for this practice must be calculated using factors unique to each site. For more information, refer to Appendix IV, Basin Efficiency, on page IV.1. SOURCES 1. Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Stormwater Management. Massachusetts Dept. of Environmental Protection. Volume Two: Stormwater Technical Handbook. Boston. March Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April A P P E N D I X I B A S I N, W E T 0 1 / 0 2 / 0 7 I.B-2.3

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67 BIORETENTION BASIN GENERAL Bioretention basins are infiltration devices used for the treatment and infiltration of stormwater runoff. A bioretention basin is made up of several layers, which treat stormwater as it is filtered. These basins remove pollutants and reduce runoff volume and temperature. Bioretention basins can be used as a stand-alone method of stormwater treatment or in conjunction with other stormwater management practices. Bioretention basins are best suited to treating small drainage areas adjacent to runoff source areas, such as parking lots or streets. Appropriate placement of bioretention basins is important because of the need for proper maintenance. For example, basins located in open, visible areas are more likely to be properly maintained and, in turn, provide aesthetic value. Also, bioretention basins should not be used near foundations, basements, roads, or on sites with high water tables or steep slopes. Bioretention basins are susceptible to clogging with sediment and, therefore, should not be used for erosion control during construction. DESIGN For complete design of bioretention basins, please refer to DNR Standard Bioretention basins should be designed with careful consideration given to each of the following key components: drainage area and pretreatment, ponding zone, vegetation and mulch layer, engineered soil layer, storage layer, underdrain, and sand/native soil interface layer (refer to Figure 1). DRAINAGE AREA AND PRETREATMENT The maximum drainage area allowed for a bioretention basin is 2 acres and the drainage area should not contribute significant sources of sediment. To maintain flow towards the basin, slopes should not be less than 0.5% for paved areas and 1% for ADVANTAGES Promotes infiltration of stormwater Reduces pollutants in runoff Decreases peak flow rates and volumes of runoff Helps preserve base flow in streams Reduces temperature impacts of runoff DISADVANTAGES Not suitable for construction site erosion control Susceptible to clogging Damaged by runoff with large amounts of salt-based deicers Not suitable for drainage areas larger than 2 acres vegetated areas. In any case, the slopes toward the basin should not be greater than 20%. Although not required, pretreatment options should be explored. Pretreatment is intended to reduce the initial amount of pollutants in the runoff going to the basin. Several options for pretreatment are available, including settling basins, vegetated swales, and filter strips. Pretreatment should be chosen based upon site conditions and constraints. PONDING ZONE The ponding zone receives and holds runoff until it has an opportunity to infiltrate. The ponding depth may not exceed 12 inches and the drawdown time must be a maximum of 24 hours. The side slopes of the ponding area should not be steeper than a 2:1 horizontal to vertical ratio. VEGETATION AND MULCH LAYER The vegetation and mulch layer is the first layer to be infiltrated by the runoff. When establishing the vegetation layer, plants or plant plugs should be used rather than seed. When choosing what type of vegetation to use, native species that are able to handle the different environmental conditions of a basin should be selected. Turf grass or invasive plants shall not be used to vegetate the basin. A P P E N D I X I B I O R E T E N T I O N B A S I N 0 1 / 0 2 / 0 7 I.B-3.1

68 The mulch used shall be hardwood to prevent excessive floating and be free from any foreign material. The mulch should be spread in a uniform layer 2-3 inches thick. ENGINEERED SOIL LAYER The engineered soil layer is composed of sand, compost and topsoil. The compost must meet the Wisconsin Department of Natural Resources Specification S100 for compost. The sand must meet the specifications found in the DNR technical standard 1004 and the topsoil must be classified as a sandy loam, loamy sand or loam texture soil according to the USDA classification system. The engineered soil layer must have a minimum depth of 36 inches. If gravel is used for the storage layer, a layer of pea gravel with a 4-inch maximum depth may be used between the engineered soil layer and the gravel storage layer. The pea gravel layer can be considered part of the 36-inch soil layer and prevents the engineered soil from settling down into the storage layer. STORAGE LAYER The storage layer promotes infiltration. Since infiltration is the only way water is able to exit the storage layer, it is an important component of the bioretention facility. A storage layer is necessary when the native soil has an infiltration rate of less than 3.6 inches per hour. The maximum depth of the storage area is 48 inches. The storage layer may be composed of sand or clear washed stone of uniform size (i.e. 3 inch clear stone). UNDERDRAIN An underdrain pipe should be placed at the top of the storage layer as a stable outlet for runoff that cannot be infiltrated as quickly as needed. The pipe must be a minimum of 6 inches in diameter and made with materials that can withstand large loads. The perforations in the underdrain should allow the pipe to drain at full capacity, while maintaining the integrity of the pipe. In order to prevent clogging in the underdrain pipe, the pipe must be protected with either filter fabric or a filter sock. If the storage layer is sand, filter socks must be used. When a filter sock is used, the openings in the sock must be small enough to keep out sand particles, but must not restrict the flow through the perforated pipe. Another acceptable option of pipe protection is a layer of pea gravel. If pea gravel is used, it must be a layer 4 inches thick to be adequate. The pea gravel must be washed and large enough that it will not fall through the perforations in the pipe. The underdrain must have a clean-out port that can be accessed as needed for maintenance. The underdrain must discharge to a stable outlet, such as swales or storm sewers. If it is possible for backflow to occur, a check valve should be installed. SAND/NATIVE SOIL INTERFACE LAYER An interface layer is necessary when the infiltration rate of the native soil is less than 3.6 inches per hour. The interface layer shall be formed by a layer of sand three inches deep, which is vertically mixed with the native soil to a depth of 2 to 4 inches. OTHER CONSIDERATIONS To regulate the maximum ponding depth of the basin, overflow devices such as a weir or standpipe should be installed. The discharge from these overflow devices must be directed to a stable outlet. If the basin does not include an underdrain, observation wells must be installed to monitor the basin function. Observation wells must be positioned in the center of the area to be monitored. The maximum area served by one well is 1,000 square feet. CONSTRUCTION Runoff shall not be allowed in the basin until after the tributary area is stabilized Construction of the basin should only occur during suitable site conditions - if construction of the basin occurs during saturated soil conditions, the soil in the device could be unnecessarily compacted Compaction of the soils used for the bioretention device must be avoided - heavy equipment may not be used in the construction of the basin The engineered soil shall be premixed before placement and be dry enough to prevent clumping and compaction I.B-3.2 A P P E N D I X I B I O R E T E N T I O N B A S I N 0 1 / 0 2 / 0 7

69 The engineered soil should be placed in several 12-inch deep lifts The basin should be mulched before the planting of the vegetation in order to prevent compaction MAINTENANCE Accumulated sediment in pretreatment devices should be removed as needed Bioretention basins should be inspected semi-annually Additional mulch should be added at least once a year and as needed to maintain 2-3 inches of cover Bioretention basins should be inspected monthly for signs of erosion and sediment accumulation - all necessary repairs should be performed immediately METHOD TO DETERMINE PRACTICE EFFICIENCY A properly designed bioretention basin that has been sized to meet the applicable infiltration performance standard is assumed to have a sediment reduction efficiency of 80% and oil and grease removal that meets county treatment standards. In order to determine the infiltration performance of this practice SLAMM, RECARGA or other approved models may be used. Additional information regarding acceptable modeling of infiltration practices is found in Appendix II. 6 to12-inch Ponding Zone 2 to 3-Inches of Hardwood Mulch 36-Inches of Engineered Soil 8 to 12-Inches of Pea Gravel* Type B Geotextile * 6-Inch Perforated PVC Pipe* Sand/Native Soil Interface Layer* 12 to 48-Inches of Storage* (sand or washed stone) *Elements marked with an asterisk are required when the design infiltration rate of the soil is less than 3.6 inches per hour Figure 1. Bioretention Basin Layers SOURCES 1. United State Environmental Protection Agency. Stormwater Technology Fact Sheet: Bioretention. Publ. EPA-832-F Office of Water, Washington D.C., Wisconsin Department of Natural Resources. For Sizing Infiltration Basins and Bioretention Devices to meet State of Wisconsin Stormwater Infiltration Performance Standards. DNR Technical Notes. Last Update: July A P P E N D I X I B I O R E T E N T I O N B A S I N 0 1 / 0 2 / 0 7 I.B-3.3

70 I.B-3.4 A P P E N D I X I B I O R E T E N T I O N B A S I N 0 1 / 0 2 / 0 7

71 CONSTRUCTION SCHEDULING GENERAL Construction scheduling involves the coordination of three construction-planning activities: Site Phasing, Limiting Site Disturbance, and Construction Sequencing. Site phasing reduces erosion from a site by reducing the amount of soil exposed at any one time by staging construction activities. Limiting site disturbance preserves areas that are highly susceptible to erosion and maintains them as vegetated areas. Construction sequencing involves planning land disturbance activities to coincide with the installation of best management practices. These tools, when combined, reduce land disturbance, protect highly erodible areas, provide for timely installation of necessary erosion control practices, and promptly restore protective cover after disturbance. The result is that the disturbed soil is left exposed for a shorter period of time, significantly reducing soil loss. SITE PHASING Site phasing involves planning construction activities so that land disturbance is performed in stages. Rather than disturbing an entire site, only those areas under active construction are disturbed. Subsequent areas are then cleared as the construction process progresses, while previously disturbed areas are stabilized with surface protection techniques. The soil surface is left exposed and unprotected for shorter periods of time, resulting in a significant reduction in soil loss. Therefore, fewer erosion control practices are required, which may also reduce maintenance requirements and costs. LIMITING SITE DISTURBANCE Limiting site disturbance is a planning tool that can significantly reduce soil loss from a site. Early in the planning process, highly erodible ADVANTAGES Widely applicable and effective Cost-effective May preserve wildlife habitat and be aesthetically pleasing if properly implemented, which can increase property values DISADVANTAGES Requires good communication between contractor, developer, and designer to ensure that the schedule is realistic and properly implemented May require that certain activities be performed multiple times on different portions of the site areas, such as steep slopes and unstable soils, can be identified. Those areas can be designated as undisturbed and protected during construction to prevent soil loss. Undisturbed areas may also act as buffers, reducing runoff velocities and reducing soil loss when compared to disturbed conditions. CONSTRUCTION SEQUENCING Construction sequencing requires the developer or planner to consider all facets of site preparation and construction, including sensitive areas of the site, before any work is performed. A construction sequencing plan is created by compiling a list of the practices to be installed and a list of construction activities to be performed. The two lists are then combined to determine what activities must be in place before other activities begin. The result is that all erosion control practices are in place and online before any land disturbance activity begins, reducing erosion from the site. A P P E N D I X I C O N S T R U C T I O N S C H E D U L I N G 0 1 / 0 2 / 0 7 I.C-2.1

72 Considerations for Construction Sequencing Construction Activity* Schedule Consideration Construction access - Construction entrance, construction routes, equipment parking areas Sediment traps and barriers - Basins, traps, silt fences, and outlet protection Runoff control - Diversions, dikes, and outlet protection Runoff conveyance system - Stabilize stream banks, storm drains, channels, inlet and outlet protection, channels, and slope drains Land clearing and grading - Site preparation, cutting, filling and grading, sediment traps, barriers, drains, diversions, surface roughening Surface stabilization - Temporary and permanent seeding, native grasses, mulching, sodding, and riprap Building construction - Buildings, utilities, and paving Infiltration Practices - bioretention basins, infiltration basins, rain gardens, infiltration trenches/beds Landscaping and final stabilization - Topsoiling, trees and shrubs, permanent seeding, mulching, sodding, riprap First land disturbing activity - stabilize bare areas immediately with gravel and temporary vegetation as construction takes place. Install principal basins after construction site is accessed. Install additional practices as needed during grading. Install key practices after principal sediment traps and before land grading. Install additional practices during grading. Where necessary, stabilize stream banks as early as possible. Install principal runoff conveyance system with runoff control measures. Install remainder of system after grading. Begin major clearing and grading after principal erosion control practices have been installed. Clear and grade only as needed. Install additional measures as necessary. Mark trees and buffer areas for preservation. Apply temporary or permanent stabilization measures immediately on all disturbed areas where work is delayed or complete. Install necessary practices before work takes place. Must be installed during final stabilization or when runoff can be diverted and prevented from disturbing the site to avoid being filled with sediment during construction. Last construction phase - Stabilize all open areas, including borrow and spoil areas. Remove and stabilize all temporary practices. * Maintenance activities are required throughout the construction process. Inspections shall be performed at least weekly and after all storm events. All necessary repairs shall be made immediately. CONSTRUCTION AND MAINTENANCE Remove all temporary practices after the site has been permanently stabilized Amend the schedule as needed to account for delays encountered during construction METHOD TO DETERMINE PRACTICE EFFICIENCY The efficiency of this practice is derived from limiting the amount of time that areas of the site are left bare and exposed. To determine the efficiency of this practice, use the new, shortened exposure time and replace the pre-existing one in the USLE and recalculate. The difference between the two equations is the efficiency for the practice. However, efficiency is based upon densely established vegetation and, as a result, no credit is given until establishment has been achieved and maintained (refer to Seeding, Permanent, pg. I.S-3; Seeding, Temporary, pg. I.S-4; or Sod, pg. I.S-7). I.C-2.2 A P P E N D I X I C O N S T R U C T I O N S C H E D U L I N G 0 1 / 0 2 / 0 7

73 SOURCES 1. Chapter 3: Erosion and Sediment Control Laws. Natural Resource Conservation Laws. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Indiana Handbook for Erosion Control in Developing Areas. Indiana Department of Natural Resources, Division of Soil Conservation. Indianapolis Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April A P P E N D I X I C O N S T R U C T I O N S C H E D U L I N G 0 1 / 0 2 / 0 7 I.C-2.3

74 A P P E N D I X I C O N S T R U C T I O N S C H E D U L I N G 0 1 / 0 2 / 0 7 I.C-2.4

75 CONSTRUCTED WETLANDS GENERAL Constructed wetlands are artificial wetland systems that are designed to collect and temporarily store runoff. These devices reduce stormwater flow velocity and trap sediment and other associated pollutants. Stormwater enters the wetland and is temporarily retained, allowing pollutants to settle out. Pollutants, such as metals, nutrients, sediment, and organic substances, are removed by the settling of particulates, biological uptake, consumption, and decomposition. Constructed wetlands can be used in residential, commercial, and industrial areas if the contributing watershed is large enough to maintain water depth in the basin. Their implementation also depends on several site factors, including soil types, depth to bedrock, depth to groundwater, and available land area. Due to the permanent ponding of water, constructed wetlands can remove large amounts of pollutants and are more effective in removing nutrients than most other management practices. The large volume of storage helps to reduce peak discharges from storm events, which, in turn, reduces down-stream flooding and streambank erosion. However, constructed wetlands are designed primarily to treat stormwater and should not be considered restored or mitigated wetlands. Accumulated sediment can reduce the capacity, life span, and effectiveness of constructed wetland systems. As a result, they are best used in conjunction with other management practices. ADVANTAGES DESIGN Wildlife habitat is created when the ponds are properly designed and maintained, including habitat for mosquito predators Can be aesthetically pleasing if designed properly, which can increase adjacent property values Capable of removing both solid and soluble pollutants Reduces peak flows DISADVANTAGES Requires a large land area Generally requires a large contributing watershed Pond discharges usually consist of warm water, so their use may be limited in areas with temperature sensitive fisheries Improperly maintained wetlands may result in nuisance odors, algae blooms, and rotting debris Cost Constructed wetlands may be designed with irregular and curvilinear shorelines in a variety of configurations depending upon the individual needs of the site. Regardless of design, these devices should be capable of controlling the runoff from the 1-year, 24-hour storm event. FOREBAYS/INLETS Forebays, which are separated from the rest of the wetland by a gabion or berm, receive runoff and prevent concentrated flow from entering the device, allowing sediment to settle out before it reaches the wetland (refer to Gabion, pg. I.G-1.1). They also simplify maintenance by concentrating sediments and extending the holding capacity and life of the A P P E N D I X I C O N S T R U C T E D W E T L A N D S 0 1 / 0 2 / 0 7 I.C-1.1

76 structure. Forebays should have an area equal to 10-25% of the wetland s surface area, with a length to width ratio of at least 2:1 to provide proper flow and a depth of 2-4 feet. Forebays should be located opposite of the outlet structure to increase detention time and should provide access for the removal of accumulated sediment. SHAPE Constructed wetlands should be designed so that the previously held stormwater is replaced by the newer stormwater, a process referred to as plug flow. Plug flow allows the water to remain in the wetland long enough to facilitate the settling of sediment and the adsorption of pollutants and sediment. To encourage plug flow, the wetland should be designed with a length to width ratio of at least 3:1. These shapes encourage proper mixing of the water column and increase retention time. In addition, these shapes lessen the amount of sediment stirring caused by wind, allowing pollutants to remain settled in the sediment. If these shapes are not feasible, structures that lengthen the flow path, such as gabions and baffles, should be installed. SOILS Soils should have infiltration rates low enough so that base flow or stormwater runoff can maintain a permanent pool of water in the wetland. Sites with highly permeable soils or those that are close to the water table should incorporate an impermeable liner into the design to facilitate ponding and to prevent stored water from mixing with groundwater. After the basin has been excavated and graded, at least 4 inches of soil should be placed in the basin. This layer, which should also be applied on top of any liner, provides a substrate necessary for plant growth. DEPTH The depth requirements for each constructed wetland are dependant upon the individual characteristics of each site. However, they should be constructed with varying depths to encourage biological diversity and to improve pollutant removal. Shallow depths encourage vegetative growth and are more effective for pollutant removal than deeper areas and should have a surface area that it equal to or larger than deeper areas. Deeper areas provide storage capacity and facilitate sedimentation while providing habitat for submerged and floating species of vegetation. Aquatic benches should be incorporated into the design of deep pools. These benches improve the diversity of the pool and the safety of the practice and should be 3-10 feet wide with 10:1 slopes. VEGETATION Vegetation may be planted from seed or by applying a layer of wetland soil to the depression. When seeding is necessary, plant selection will depend upon individual site characteristics of the site. However, care should be taken to avoid the use of invasive and exotic species. Selected species should be capable of thriving in hydric conditions. In many applications, vegetation can be established by applying a layer of wetland soils to the basin. Wetland soils generally contain a large number of seeds that will propagate under proper hydrologic conditions. OUTLETS Constructed wetlands should have an outlet structure that is designed to handle the peak flow of the structure and should discharge to a stable outlet (refer to Stone Outlet Protection, pg. I.S-10). Outlet structures should incorporate a multi-stage riser and should be resistant to clogging and may incorporate trash racks, skimmers, or other devices. Outlets should be designed with stability in mind and should be able to endure frost heave and settling. Constructed wetlands should also incorporate an emergency spillway and a de-watering outlet into the design of the structure. Emergency spillways are designed to safely pass flows that exceed the design capacity of the basin. These structures prevent large flows from overwhelming the capacity of the structure without causing damage to the basin or downstream structures and should discharge to a stable outlet. A de-watering outlet is a gate controlled drain that is capable of draining the wetland within 24 hours. They are used on a limited basis for maintenance purposes. I.C-1.2 A P P E N D I X I C O N S T R U C T E D W E T L A N D S 0 1 / 0 2 / 0 7

77 CONSTRUCTION Constructed wetlands should be kept flooded after excavation and final grading until vegetation is planted Outlets should allow access to maintenance personnel while restricting access to the general public MAINTENANCE Accumulated sediment should be removed from forebays as needed Inspect the outlet and emergency spillway after all large storm events for erosion and displacement- all repairs should be made immediately Trash and other debris should be removed as necessary Gabions, berms, and other hydraulic control structures should be inspected after large storm events for damage- all repairs should be made immediately Constructed wetlands should be inspected during and after ice break-up for damage and blockage Plants should be cut and removed in the fall to prevent the release of stored nutrients and other pollutants METHOD USED TO DETERMINE PRACTICE EFFICIENCY Constructed wetlands reduce the flow velocity of runoff, allowing suspended particles to settle out. In addition, these devices remove nutrients, heavy metals, and other pollutants from stormwater by utilizing several biological processes. The efficiency for this practice is dependant upon the size of the wetland, the size of the drainage area, and other site characteristics and the proper design, installation, and maintenance of the constructed wetland. As a result, the efficiency for this practice must be calculated using factors unique to each site. For more information, refer to Appendix IV, Basin Efficiency, on page IV.1. Embankment 100 year level Normal pool elevation 25-year level Trash rack or skimmer Multi-stage riser Emergency spillway Reverse slope pipe De-watering outlet Typical Outlet Structure Source: Georgia Stormwater Management Manual A P P E N D I X I C O N S T R U C T E D W E T L A N D S 0 1 / 0 2 / 0 7 I.C-1.3

78 SOURCES 1. Georgia Stormwater Management Manual. Volume 2: Technical Handbook. Atlanta Regional Commission. Atlanta, Ga Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Pennsylvania Handbook of Best Management Practices for Developing Areas. Pennsylvania Association of Conservation Districts. Harrisburg Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul I.C-1.4 A P P E N D I X I C O N S T R U C T E D W E T L A N D S 0 1 / 0 2 / 0 7

79 DEEP TILLING GENERAL Deep tilling (or subsoiling) is a practice that rips the soil perpendicular to the direction of flow. This creates a cut in the soil that results in a series of horizontal ridges and depressions, which slows runoff and encourages infiltration and deposition, decreasing soil loss from a site. In addition, deep tilling relieves soil compaction and increases pore space, fostering plant growth by increasing nutrient availability and water retention. Deep tilling may be performed on a wide variety of sites to mitigate erosion. However, safety may become an issue on steeper slopes, as ordinary construction equipment may be prone to rollover. In these instances, alternative practices, such as diversions, slope drains, or construction sequencing may be necessary (refer to Diversion, Temporary, pg. I.D-4; Slope Drain, pg. I.S-6; or Construction Scheduling, pg. I.C-2). Because deep tilling does not protect the soil from raindrop impact, it is best used in conjunction with other management practices, such as mulch, erosion matting, and seeding (refer to Mulching, pg. I.M-2; Erosion Matting, pg. I.E-1; or Seeding, Temporary, pg. I.S-4). 4-5 feet ADVANTAGES EQUIPMENT Cost-effective Prevents sheet and rill erosion Fosters vegetative growth Effective way to mitigate soil compaction Low maintenance DISADVANTAGES May be difficult on sites with slopes steeper than 3:1 Low practice efficiency The effectiveness of deep tilling depends on the type of equipment used. Heavy, tracked machinery is used to pull heavy steel shanks through the soil, perpendicular to the slope. Tracked machinery is used because it provides the stability, horsepower, and weight required to achieve a depth of 2-3 feet. Other types of equipment, such as large tractors or other large wheeled vehicles may experience difficulties when attempting to till to these depths. Generally, the vehicle will pull 2 shanks, which are usually parabolic in shape, positioned behind the tracks of the vehicle, and should be spaced 4-5 feet apart. Parabolic shanks, in addition to creating larger ridges than straight shanks, generally require less power to pull and are better suited for this purpose. 2-3 feet V-Shaped Wedge Deep Tilling Compacted Zone Source: Colorado State University Extension 2-6 inch ridge height SOILS The length and size of the shank used will also depend upon the type of soil and the depth of compaction, as soils should be ripped at least 1 to 2 inches below the hardpan layer or compacted zone. Soils should be tested with a soil probe or soil penetrometer to determine the extent of compaction and the required depth. Deep tilling should be practiced in dry soils, as it more effectively breaks up the soil and leaves larger ridges on the surface. Deep tilling in wet soils, A P P E N D I X I D E E P T I L L I N G 0 1 / 0 2 / 0 7 I.D-1.1

80 although it generally is easier and requires less power, often results in minimal soil fracturization between the shanks. CONSTRUCTION AND MAINTENANCE Shanks should be spaced 4-5 feet apart Must be performed on the contour Areas that have been deep tilled should be inspected after each storm event for signs of erosion, with necessary repairs made immediately METHOD TO DETERMINE PRACTICE EFFICIENCY Deep tilling prevents soil loss by reducing the flow velocity of runoff. The efficiency of this practice is dependant upon the depth of tillage and the height of the ridge that is produced by the shank. Efficiency is also dependant upon site disturbance. Any disturbance that may cause compaction, such as vehicular traffic, greatly reduces the efficiency and requires that the practice be repeated. However, when properly performed, deep tilling yields an efficiency of up to 20%, which may be taken for the time period between the completion of the practice and the application of seed. Shank Deep Tilling with 2 Shanks (Top View) SOURCES 1. Jones, Alice J., Bashford, Leonard L., and Grisso, Robert D. Subsoiling in Nebraska. Publication No. NF University of Nebraska Cooperative Extension. 3. Peterson, M., and Ayers, P. Managing Soil Compaction. Publication No Colorado State University Cooperative Extension Roa-Espinosa, A. An Introduction to Soil Compaction and the Subsoiling Practice Schueler, Thomas R., and Holland, Heather K. Eds. Can Urban Soil Compaction be Reversed? The Practice of Watershed Protection. Center for Watershed Protection. Technical Note 108 Pages Ellicott City, Maryland, Schueler, Thomas R., and Holland, Heather K. Eds. The Compaction of Urban Soils. The Practice of Watershed Protection. Center for Watershed Protection. Technical Note 107. Pages Ellicott City, Maryland, I.D-1.2 A P P E N D I X I D E E P T I L L I N G 0 1 / 0 2 / 0 7

81 DEWATERING GENERAL Dewatering is a practice where sedimentladen water is pumped into a compartmented container, settling basin, filter, or other appropriate best management practice to trap and retain sediment. This practice detains sediment generated during the removal of water from a site prior to discharging it off-site and/or to waters of the state. Dewatering applies where sediment-laden water must be removed for construction. The selection of a dewatering practice is dependent upon the predominant soil texture encountered at the dewatering site with consideration given to pumping rates, volumes and device effectiveness. Users of the practice of dewatering should be conscious of applicable federal state, and local laws, rules, regulations, or permit requirements governing the use and placement of dewatering. SITE ASSESSMENT The proposed site must be assessed and documented to determine the site characteristics that will affect the placement, design, construction and maintenance of dewatering activities. Characteristics such as ground slopes, drainage patterns, runoff constituents, soil types, soil conditions, sinkholes, bedrock, proximity to regulated structures, natural resources, and specific land uses must be included in the site assessment. The documented site assessment should include the following: Soil textural class for dewatering areas with investigation extending below grading and trenching depths Storm sewer and sanitary locations Potential contaminates already in the soil, such as odor or discoloration other than sediment, or an oily sheen on the surface of the sediment-laden water notify DNR Spills Reporting if present Seasonally highest water table depth Transport method and distance to receiving waters Discharge outfall locations The Wisconsin Department of Natural Resources (WDNR) must be contacted when dewatering discharge will enter a WDNR listed Exceptional Resource Water, Outstanding Resource Water, or a wetland in an area of special natural interest. Additionally, if the discharge of the dewatering activity were to directly or indirectly enter a stream, the discharge flow rate must not exceed 50 percent of the peak flow rate of the 2-year, 24-hour storm event. General criteria applicable to dewatering activities are outlined in WDNR Conservation Practice Standard, Code No SOILS ADVANTAGES Reduces the amount of sediment leaving the site Allows for a more in-depth site assessment additional necessary erosion control measures may be identified DISADVANTAGES Must abide by multiple government laws and standards and obtain appropriate permits Requires frequent maintenance May be costly The selection of the dewatering practice depends upon the predominant soil texture encountered at the dewatering site. Refer to Figure 1, the USDA Soil textural triangle, to assist with classifying the soil of the site. Figure 2, Dewatering Practice Selection Matrix, illustrates acceptable dewatering options and their effective ranges. Pumping rates, volumes, and device effectiveness must also be considered when selecting a practice. A P P E N D I X I D E W A T E R I N G 0 1 / 0 2 / 0 7 I.D-2.1

82 Figure 1: USDA Soil Textural Triangle Source: WDNR PRACTICES Dewatering can be preformed in a variety of ways and should be selected based upon the individual site characteristics. The accepted dewatering practices are geotextile bags, gravity based settling systems, passive filtration systems, and pressurized filtration systems. GEOTEXTILE BAGS Geotextile bags are gravity-based filter bags not contained within any vessel or enclosure. Geotextile bags are widely used on sites where there is no available space for a sediment basin. The footprint of the bag, however, should be no smaller than 100 square feet. They lie on the ground and are designed to collect silt and sediment from pumped water. Sediment-laden water is pumped from the site and discharged into the bag that is securely attached to the discharge pipe. The almost sediment-free water discharges through the walls of the bag, while the sediment is retained inside the bag. Disturbing the bag may break up the cake of collected sediment and reduce its efficiency. Geotextile bags should be sized according to the particle size being trapped, expected flow or pumping rate per square foot of fabric and a 50% clogging factor. Geotextile bags should meet the criteria listed in Table 1. Polymers may be used to enhance the efficiency of the geotextile bags, but must meet the performance requirements of WDNR (refer to Polymer Application, pg. I.P-3). Property Test Method Type I Value Type II Value Maximum Apparent Opening Sizes Grab Tensile Strength ASTM D mm mm ASTM D lbs. 300 lbs. Mullen Burst ASTM D psi 580 psi Permeability ASTM D cm/sec 0.2 cm/sec Fabric Nominal Representative Weight 8 oz 12 oz Table 1: Properties for Geotextile Bags Source: Adapted from WDNR GRAVITY BASED SETTLING SYSTEMS The settling of particles is the primary means of treatment for gravity based settling systems. Therefore, sufficient detention time is required when using this practice. Practices include portable sediment tanks, sediment traps, sediment basins and wet detention basins. WDNR approved polymers can also be used to enhance the settling (refer to Polymer Application, pg. I.P-3). Portable sediment tanks are intended to settle only sands, loamy sands, and sandy loams. If polymer is added, these tanks will additionally be I.D-2.2 A P P E N D I X I D E W A T E R I N G 0 1 / 0 2 / 0 7

83 appropriate for settling loams, silt loams and silts. Portable sediment tanks should be at least three feet deep and have a minimum of two baffled compartments. The inlet and outlet pipe should be a minimum diameter of three inches. To account for the settling of suspended sediments, one must determine the appropriate size of a tank. Multiply the pumping rate (gallon per minute) by 1.83 (a factor that includes the conversion from gpm to cfs and the particle settling velocity for Soil Class 1) to calculate the surface area of a tank in square feet. Sediment traps and basins are temporary sediment control devices, while wet detention basins are generally permanent structures designed to address post-construction pollutant reduction requirements. The design, installation, and operation of sediment traps and basins should meet WDNR requirements (refer to Sediment Basin, pg. I.S-1 and Sediment Trap, pg. I.S-2, Basin, Wet, pg. I.B-2). PASSIVE FILTRATION SYSTEMS Passive filtration systems also rely on filtration as the main means of removing sediment. The distribution of particle size in the stormwater influences sediment removal efficiency. Manufactured filters should be sequenced from the largest to the smallest pore opening. Available are sand media filters with automatic backwashing features that can filter to 50 µm particle size, screen or bag filters that can filter down to 5 µm, and fiber wound filters that can remove particles down 0.5 µm. Other practices include filter tanks, filter basins, vegetative filters, grassed swales, and filtration fabric and should be installed, operated, and maintained according to manufacturer recommendations and WDNR (refer to Vegetated Buffer Strips, pg. I.V-1). PRESSURIZED FILTRATION SYSTEMS Designed to handle higher flow rates, pressurized filtration systems have the water flowing through the media pressurized, rather than depending solely on filtration. Pressurized filters are composed of individual filters that are most effective when larger particles have been removed by prior treatment with a weir tank, sand filter, etc. Practices include portable sand filters, wound cartridge units, membranes and micro-filtration units. Pressurized filters have automatic backwash systems that are activated by a fixed pressure drop across the filter. Returning backwash water to the tank may be necessary if the volume of the backwash water is minor or substantially more turbid than the stormwater stored in the tank. Further means of treatment, such as land application, and disposal may be necessary to complete treatment. Wound cartridge units are used when secondary filtration of sediments is necessary to remove fine particles such as clays. It is capable of removing sediment larger than mm, but is most effective when used after larger particles have been removed by other treatment methods. Other practices include portable sand filters, membranes, micro-filtration, and polymers and should be installed and maintained according to manufacturer recommendations and WDNR (refer to Polymer Application, pg. I.P-3). MAINTENANCE Sediment must be frequently removed from devices and properly disposed of to maintain effectiveness Dewatering must be monitored and recorded on a daily log Install, operate, and maintain pressurized filtration systems by following manufacturer recommendations METHOD TO DETERMINE PRACTICE EFFICIENCY Dewatering practices reduce the amount of suspended sediment in water that must be removed from a site through filtering methods. The efficiencies for these practices vary by the type of device used and soil texture, pumping rates, volumes and device effectiveness. Devices that are constructed on site will have an efficiency that is determined by calculating the settling efficiency for the device. I.D-2.3 A P P E N D I X I D E W A T E R I N G 0 1 / 0 2 / 0 7

84 Type of Dewatering Practice Geotextile Bags Type I Type II Gravity Based Settling Sediment Tank Coarse Texture Medium Texture Fine to Very Fine Texture Sandy, Loamy Sands, and Sandy Loams Loams, Silt Loams, and Silts Clay Loams, Silty Clays and Clay Sediment Trap (Temporary) Use Standards 1063 or 1064 Sediment Basin (Temporary) Use Standard 1064 Wet Detention Basin (Permanent) Use Standard 1001 Passive Filtration Filter Tank Filter Basin Soil and Texture Classification Notes Vegetative Filter Pressurized Filtration Portable Sand Filter Wound Cartridge Units Membranes & Micro-filtration Other Practices Sanitary Sewer Discharge Pump Truck Alternative Method Effectiveness depends upon the width of the filter and the runoff rate of flow. See Standard 1054 for design guidelines. The contractor shall provide a certification sheet from the manufacturer specifying performance of the device based on the soil type and pumping rate. Very effective but high maintenance requirements Transported to treatment facility Discuss alternate options with regulatory authority Key: Effective range of device: Device applicable but may not be cost effective: Effective range with addition of polymer: Notes: (1) The effectiveness of many practices can be enhanced through the use of polymer mixture (2) Soils classification shall be done in accordance to an accepted method (i.e. USDA, AASHTO) (3) Standard 1063 Sediment Trap (4) Standard 1064 Sediment Basin (5) Standard 1054 Vegetated Buffer for Construction Sites (6) Standard 1001 Wet Detention Basin (7) Discuss alternate options with the regulatory authority Figure 2: Dewatering Practice Selection Matrix Source: Adapted from WDNR SOURCES 1. Construction Site Erosion Control and Stormwater Management Procedures for Department Actions. Wisconsin Administrative Code, Department of Transportation. November Dewatering. Conservation Practice Standard. Wisconsin Department of Natural Resources. November Dewatering, Construction Practices for Environmental Stewardship. AASHTO Center for Environmental Excellence. November Preliminary Data Summary of Urban Storm Water Best Management Practices. United States Environmental Protection Agency. Washington, D.C I.D-2.4 A P P E N D I X I D E W A T E R I N G 0 1 / 0 2 / 0 7

85 DIVERSION, PERMANENT GENERAL A permanent diversion is a vegetated channel that is designed to intercept and collect runoff, diverting it down slope to an area that is less susceptible to erosion. Diversions are constructed upslope of areas where erosion is likely to occur and, by reducing runoff velocities, allow sediments and soluble pollutants to settle out. Permanent diversions can be used in residential, commercial, and industrial areas and include: graded surfaces to redirect sheet flow, dikes, berms, and conveyance structures such as swales, channels, gutters, and drains. DESIGN CAPACITY Permanent diversions should be designed, at a minimum, to convey the runoff from a 10 year, 24-hour storm event with at least 0.3 foot of additional capacity (freeboard). However, it is recommended that diversions that protect roads and urban areas have a capacity sufficient to transport runoff from the 25 year, 24-hour storm event. In addition, the designed capacity must take into account any soil settling that may occur. While the amount of settling that occurs will depend upon the type of soils present on site, a minimum value of 10% should be used. ADVANTAGES Can significantly reduce erosion from a site Removes sediment and soluble pollutants Can be aesthetically pleasing if designed properly, which can increase adjacent property values DISADVANTAGES Requires a relatively large land area Are not recommended down slope of high-sediment producing areas Ineffective on sites with slopes greater than 15% SHAPE AND SLOPE Permanent diversions may be parabolic, trapezoidal, or V-shaped with a minimum ridge width of 4 feet. Side slopes should be flatter than 3:1, as steeper slopes may be unstable and make maintenance activities more difficult. Channel slopes will depend upon the topography of the site, but should be designed so that sheet flow is sustained and water velocities are maintained below 5.0 ft/s. Permanent Diversion Original Elevation d = Design Depth An Example of a Permanent Diversion Source: Adapted from United States Natural Resources Conservation Service A P P E N D I X I D I V E R S I O N, P E R M A N E N T 0 1 / 0 2 / 0 7 I.D-3.1

86 PERMISSIBLE VELOCITIES FOR DIVERSIONS (FT/S) CHANNEL VEGETATION SOIL TEXTURE BARE CHANNEL POOR FAIR GOOD Sand, silt, sandy loam, and silty loam Silty clay loam and sandy clay loam Clay Source: Adapted from Wisconsin Field Office Technical Guide OUTLETS The outlet selected for each diversion will vary upon the needs of each site. Outlets should be stable and non-erosive and may be vegetated, paved, rock-lined with geotextile fabric, or drain tiled. If a vegetated outlet is chosen, it must be constructed before the rest of the diversion to allow time for the vegetation to become established. Outlets may also incorporate riprap or gabions to further prevent erosion and reduce the velocity of outflows. VEGETATION Plant species selected for permanent diversions should meet the following criteria: Native species may be used with careful selection (refer to Native Plants, pg. I.N-1) Species should be tolerant to frequent inundation as well as extended dry periods Species should be resistant to matting Species should form a dense cover Avoid exotic, noxious, and invasive species CONSTRUCTION AND MAINTENANCE Vegetation should be established immediately after grading is complete to prevent erosion of the structure Until vegetation is established, diversions should be inspected after each rainfall for signs of erosion After establishment, permanent diversions should be inspected annually to ensure that they are operating properly and to check for any potential problems Mowing should be performed only during dry periods using light equipment to prevent soil compaction METHOD TO DETERMINE PRACTICE EFFICIENCY Diversions effectively reduce the slope length by diverting runoff away from slopes and other areas that are prone to erosion. The efficiency for this practice is thus derived from the reduction in slope length that it provides. To calculate the efficiency, simply use the new, reduced slope length in place of the pre-existing one in the USLE and recalculate. The difference is the efficiency for the practice. SOURCES 1. Construction Site Diversion. Conservation Practice Standard. Wisconsin Department of Natural Resources. November Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Wisconsin Field Office Technical Guide. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C I.D-3.2 A P P E N D I X I D I V E R S I O N, P E R M A N E N T 0 1 / 0 2 / 0 7

87 DIVERSION, TEMPORARY GENERAL A temporary diversion is a channel constructed across a slope that is designed to intercept and collect stormwater, diverting it down slope to an area that is less susceptible to erosion. Temporary diversions reduce runoff velocities, allowing sediment and soluble pollutants to settle out before leaving the site. Temporary diversions are primarily used for construction sites and include graded surfaces to redirect sheet flow, dikes, and berms. Diversions may be constructed upslope to protect exposed sites from upland runoff or down slope of sites to collect any sediment that occurs from erosion. DESIGN CAPACITY Temporary diversions should be designed, at a minimum, to convey the runoff from a 2 year, 24-hour storm event with at least 0.3 foot of additional capacity (freeboard). Temporary diversions may drain an area of no greater than 5 acres. SHAPE AND SLOPE Temporary diversions may be parabolic, trapezoidal, or V-shaped with a minimum ridge width of 2 feet. ADVANTAGES Can significantly reduce erosion from a site Removes sediment and soluble pollutants Low cost Existing fill may be used for construction DISADVANTAGES Requires a relatively large land area Ineffective on sites with slopes greater than 15% Has a maximum life span of 12 months Side slopes should be flatter than 3:1, as steeper slopes may be unstable and make maintenance and repair activities more frequent. Channel slopes depend upon the topography of the site, but should be designed so that sheet flow is sustained and water velocities are maintained below 5.0 ft/s. Channel slopes that exceed 2% require stabilization from vegetation or erosion matting. In addition, the slope behind the dike must be great enough to assure proper drainage, but must be flat enough so that erosion of the structure does not occur during high volume periods of runoff. Compacted Soil 2 Min. 18 Min. Flow 6 Typical A Typical Temporary Diversion Source: Natural Resources Conservation Service A P P E N D I X I D I V E R S I O N, T E M P O R A R Y 0 1 / 0 2 / 0 7 I.D-4.1

88 PERMISSIBLE VELOCITIES FOR DIVERSIONS (FT/S) CHANNEL VEGETATION SOIL TEXTURE BARE CHANNEL POOR FAIR GOOD Sand, silt, sandy loam, and silty loam Silty clay loam and sandy clay loam Clay Source: Adapted from Wisconsin Field Office Technical Guide OUTLETS The outlet selected for each diversion will vary upon the needs of each site. Outlets should be stable and non-erosive and may be vegetated, paved, rock-lined, or drain tiled. If a vegetated outlet is chosen, it must be constructed before the rest of the diversion to allow time for the vegetation to become established. Outlets may also incorporate riprap or gabions with geotextile fabric to prevent erosion to the structure and to dissipate the energy of outflows. VEGETATION If temporary diversions are used longer than 30 days, vegetation must be established (Diversions used less than 30 days must be mulched). Plant species selected should meet the following criteria: Native species may be used with careful selection (refer to Native Plants, pg. I.N-1) Species should be tolerant to frequent inundation as well as extended dry periods Species should be resistant to matting Species should form a dense cover Avoid exotic, noxious, and invasive species CONSTRUCTION AND MAINTENANCE Diversions should be mulched immediately after grading to prevent erosion of the structure Temporary diversions should be inspected for damage after each rainfall Routine inspections should be performed weekly - any damage should be repaired immediately METHOD TO DETERMINE PRACTICE EFFICIENCY Diversions effectively reduce the slope length by diverting runoff away from slopes and other areas that are prone to erosion. The efficiency for this practice is thus derived from the reduction in slope length that it provides. To calculate the efficiency, simply use the new, reduced slope length in place of the pre-existing one in the USLE and recalculate. The difference is the efficiency for the practice. SOURCES 1. Construction Site Diversion. Conservation Practice Standard. Wisconsin Department of Natural Resources. November United States Department of Agriculture. Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Wisconsin Field Office Technical Guide. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C I.D-4.2 A P P E N D I X I D I V E R S I O N, T E M P O R A R Y 0 1 / 0 2 / 0 7

89 EROSION MATTING GENERAL Erosion matting consists of a wide variety of organic or synthetic mats and blankets placed on the soil surface to reduce erosion from a site caused by concentrated runoff and raindrop impact. These devices are anchored to the exposed surface and help hold the soil in place by forcing runoff to pass through the matting, reducing its velocity and its ability to erode the exposed surface. This practice is often used on sites where the gradient of the slope is such that mulching, by itself, is ineffective. It is implemented on slopes and in conveyance channels after final grading to prevent erosion and promote the establishment of permanent vegetation. TYPES Erosion mats and blankets are available commercially in many varieties of materials and life spans and, depending upon the type selected, may be used above or below grade. Traditional mats and blankets are biodegradable and may be composed of straw, wood, coconut fiber, or a combination and are held in place with netting on one or both sides of the mat. Turf-reinforcement mats (TRMs) are permanent devices, constructed from various types of synthetic materials, which ADVANTAGES Effective practice for stabilizing soil Reduces flow velocity Encourages the establishment of vegetation and suppress weed growth May increase infiltration DISADVANTAGES Has a limited life span Reduced effectiveness with concentrated flows Not applicable on sites where the slope is steeper than 2:1 are buried below the surface to help stabilize the soil. The life span of these devices will vary depending upon the type of netting and material used. As a result, careful selection is crucial to the practice s effectiveness. A current listing of approved erosion mats is available from the Product Acceptability List Committee on the Wisconsin Department of Transportation s web site at: al.htm. APPLICATION AND INSTALLATION Erosion mats and blankets should be applied to the site beginning on the upslope edge, following all of Proper Installation of Erosion Matting in a Channel Source: Greenfix America A P P E N D I X I E R O S I O N M A T T I N G 0 1 / 0 2 / 0 7 I.E-1.1

90 the manufacturer s specifications. The blanket should then be unrolled down the slope in a loose, uniform manner, without stretching the material and avoiding any wrinkles that may appear. This maximizes the effectiveness of the practice by promoting contact between the ground surface and the blanket, thus avoiding the possibility of concentrated flows from developing beneath the surface of the blanket. Wherever possible, the material should be large enough so that one continuous sheet is applied over the entire channel or slope. Joints, where necessary, should be overlapped and stapled together. Vertical joints should be overlapped 2-4 inches and stapled at least once every 4 feet while horizontal, or end joints, should be overlapped 10 inches or more, with the upslope blanket overlaying the one down slope. Horizontal joints should be stapled together at least once every 12 inches to promote stability. In addition, mats and blankets must be anchored every 4 feet across the entire surface of the practice to ensure that they remain in place, however, they may not be used on sites with slopes steeper than 2:1. Erosion blankets should be anchored by either hardwood pegs or metal staples. The staples should be 11 gauge or higher and possess a 1-2 inch crown. Staple length, measured from top to bottom after bending, is dependant upon the soil conditions present on site. Staples and stakes must be at least 6-inches long for compacted soils, while loose, sandy soils require a length of 10 inches or more. CONSTRUCTION AND MAINTENANCE Erosion mats and blankets should be installed immediately after the site has been graded and seeded Installation should follow the manufacturer s instructions to ensure the effectiveness of the practice Erosion mats should be inspected after each rainfall event for damage (evidence of undercutting or rill and gully formation) with all necessary repairs made immediately All other maintenance activities should follow the manufacturer s specifications Proper Installation of Erosion Matting on Slopes Source: Greenfix America METHOD TO DETERMINE PRACTICE EFFICIENCY The efficiency of erosion matting is dependant upon many factors, including site characteristics and the type of material used. However, in general, when properly applied and maintained, erosion matting provides the same efficiency as mulch (up to 88%; as derived by using a USLE C factor of 0.12) but may be used in areas of concentrated flow and on steeper slopes. Proper Anchoring of Erosion Blankets Source: Greenfix America I.E-1.2 A P P E N D I X I E R O S I O N M A T T I N G 0 1 / 0 2 / 0 7

91 SOURCES 1. Channel Erosion Mat. Conservation Practice Standard. Wisconsin Department of Natural Resources. November Greenfix America. Product Brochure Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Natural Resources Conservation Service Natural Resources Conservation Service Planning and Design Manual. Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul A P P E N D I X I E R O S I O N M A T T I N G 0 1 / 0 2 / 0 7 I.E-1.3

92 I.E-1.4 A P P E N D I X I E R O S I O N M A T T I N G 0 1 / 0 2 / 0 7

93 GABION GENERAL Gabions are rock-filled, multi-celled, PVC coated wire baskets that are placed in ponds (as an outlet structure), swales, and vegetated channels to dissipate the water s energy. Gabions absorb a great deal of the water s energy by forcing water to pass through the voids in the structure, which reduces its velocity, promoting sedimentation and reducing channel erosion. Gabions may be used in swales and vegetated channels that outlet to sediment traps and basins. They are very versatile structures that may conform to a wide variety of situations and sites and may be constructed on site or purchased commercially. As a result, materials should be selected carefully to ensure proper function and stability. DESIGN The size of the structure will depend upon the site, but should have a height of at least 1 foot; have a minimum bottom width of 3 feet; and should extend across the entire conveyance structure with slopes no steeper than 2:1. In addition, gabions must be underlain with geotextile filter fabric to protect the structure from undercutting, which may cause the failure of the device. The stone selected for use in gabions will vary depending upon the individual needs of the site, but should be 1 to 8 inches in diameter and be clear of fines and other sediment. Gabions may be filled by mechanical methods, but it is generally recommended that they be filled by hand. Hand filling ensures that the entire volume of the gabion is occupied, increasing the strength and durability of the practice. Baskets are constructed of PVC coated wire mesh that is resistant to corrosion. After they have been filled, the gate should be closed tightly and securely wired shut. ADVANTAGES Additional structures, if necessary, may be used and should be securely wired to existing gabions. CONSTRUCTION Relatively inexpensive Requires little maintenance Easy to construct Can be aesthetically pleasing if designed properly, which may increase adjacent property values Supports plant life Excellent for retrofit applications DISADVANTAGES Adjoining materials may require additional stabilization to prevent erosion To maintain its shape, the basket shall be braced with wire supports in both directions Gabions are anchored into the walls of the channel laterally and to the ground vertically by weight - buried portions must be wrapped with 12 ounce, non-woven filter fabric To prevent the erosion of downstream materials, stone should be placed at the toe of the structure Gabions should be underlain by geotextile filter fabric To encourage passing of floatable debris and prevent clogging, stone should be placed in front of the gabion at a 3:1 slope An Example of a Gabion A P P E N D I X I G A B I O N 0 1 / 0 2 / 0 7 I.G-1.1

94 MAINTENANCE Gabions should be inspected periodically and after all storm events for evidence of undercutting and the erosion of adjacent materials Gabions may require additional stone to offset settlement and loss METHOD TO DETERMINE PRACTICE EFFICIENCY Gabions reduce the amount of suspended sediment in stormwater by reducing the flow velocity of water. The efficiency for this practice is determined by calculating the settling efficiency for the device from the equation below. CALCULATING FLOW THROUGH A GABION Q Cross-Section Profile Q 3 2 h W = 1/2 2 L L D Q = Total flow through dam (cfs) h = Ponding depth in basin (ft) W = Total length of dam(ft) L = Horizontal flow path length (ft) D = Average rock diameter (ft) I.G-1.2 A P P E N D I X I G A B I O N 0 1 / 0 2 / 0 7

95 A Typical Gabion Structure SOURCES 1. Georgia Stormwater Management Manual. Volume 2: Technical Handbook. Atlanta Regional Commission. Atlanta, Ga National Catalog of Erosion and Sediment Control and Stormwater Management. Guidelines for Community Assistance. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April A P P E N D I X I G A B I O N 0 1 / 0 2 / 0 7 I.G-1.3

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97 GRASSED SWALES GENERAL Grassed swales (or vegetated channels) are gently sloping, densely vegetated earthen channels that collect and transport stormwater and reduce the temperature of the water. These channels slow runoff and filter out suspended solids and pollutants while promoting infiltration, retaining runoff for a period of less than 24 hours. Stormwater enters the channel and is slowed by the dense vegetation that grows in the swale. As the runoff s velocity is lowered, sediments and pollutants are removed by the filtering action of vegetation. Grassed swales may be used in conjunction with or as an alternative to curb and gutter systems, and may be used as a pretreatment device. They can be used on sites up to 50 acres in size, with the number and length of the swale depending upon the topography of the site and the size of the contributing watershed. DESIGN SOILS Hydrologic soil groups A, B, and C are suitable with some restrictions, while coarse sands and gravel, by themselves, are generally not recommended because they provide little support for vegetation and have high infiltration rates, providing limited treatment ability. Soils with low permeability are also not recommended, as they do not allow the runoff to infiltrate during the short ponding period. 10 yr, 24-hour storm event ADVANTAGES Relatively low cost Easily to construct and maintain Can be aesthetically pleasing if designed properly Very effective in preventing erosion Capable of carrying large quantities of stormwater DISADVANTAGES DIMENSIONS AND SLOPES The length and width of swales will depend upon the individual characteristics of the site and must be capable of conveying the runoff from the 10 yr, 24- hour storm event and should also prevent erosion of the channel during this storm event. In general, however, swales should be between 2 and 8 feet wide. Widths greater than eight feet are not suggested, as channelized flow is likely to result. Maximum Ponding Depth Ineffective in flat areas and areas with very steep slopes Removes a small amount of pollutants Culverts reduce the effectiveness and feasibility of grassed swales Reduced effectiveness with large storm events Effective only as a pretreatment device on highly developed sites as it does not meet the 80% reduction in total suspended solids Example of a Grassed Swale Source: Modified from United States Natural Resources Conservation Service A P P E N D I X I G R A S S E D S W A L E S 0 1 / 0 2 / 0 7 I.G-2.1

98 Swales may provide a shallow ponding area for runoff, with a maximum depth of 18 inches. The side slopes of the swale should have a horizontal to vertical ratio no greater than 3:1, and generally a ratio of 4:1 or flatter is recommended. These slopes increase the surface area of the channel, make maintenance tasks easier, and improve the safety of the device. Longitudinal slopes are generally dependant upon the topography of the site, but they should prevent runoff velocities from exceeding 5.0 feet per second. In most cases, swales function best with a longitudinal slope of 1-3%. Slopes less than 1% may cause excessive ponding and sediment deposition, while slopes greater than 4% often result in high velocities. High velocities increase the potential for channel erosion, and may require that stone check dams or erosion matting is installed on such steep slopes (refer to Stone Check Dams, pg. I.S-8; and Erosion Matting, pg. I.E-1). Stone check dams are vertical drops of between 6 and 24 inches that help to reduce the slope of the channel and the velocity of the water. Their use is limited, however, as they often require additional energy dissipating structures and must be spaced at least feet apart to prevent erosion of the channel. SHAPE Swales should be designed with a trapezoidal shape. V-shaped swales are not recommended as they may erode during high flows. VEGETATION Plant selection will depend upon individual site characteristics such as the length of inundation in the swale and the amount of light available. Native species provide many benefits when compared to other species and are strongly encouraged. However, native species should be selected carefully (refer to Native Plants, pg. I.N-1). Care should also be taken to avoid the use of invasive and exotic species. Whatever the species that is selected, it should be tolerant to inundation, have the ability to form a dense sod, and resist matting. In roadside situations, vegetation should be tolerant of salt. In instances where time is not available for the proper establishment of seed, sodding or temporary seeding is generally preferred. Vegetation should be maintained between 3 to 8 inches in height, and should extend above the ponding depth at all times. Fertilizer and pesticide use, if necessary, should be applied sparingly and only during dry periods of the year to prevent further runoff pollution. MAINTENANCE Swales should be inspected periodically during the first year of use and after all major storm events in perpetuity for possible erosion to the channel Trash and other debris should be removed seasonally Stone check dams should be inspected for evidence of bypassing Channelization, barren areas, and low spots within the channel should be repaired and reseeded Accumulated biomass should be removed periodically METHOD TO DETERMINE PRACTICE EFFICIENCY Grassed swales are designed as stormwater conveyance channels and provide little treatment ability. As a result, no efficiency is given for this practice. SOURCES 1. Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis New York State Storm Water Design Manual. New York State Department of Environmental Conservation. New York Stormwater Management. Massachusetts Dept. of Environmental Protection. Volume Two: Stormwater technical Handbook. Boston. March I.G-2.2 A P P E N D I X I G R A S S E D S W A L E S 0 1 / 0 2 / 0 7

99 4. Water Related Best Management Practices in the Landscape. U.S. Department of Agriculture, Natural Resources Conservation Service and Center for Sustainable Design at Mississippi State University. Washington, D.C A P P E N D I X I G R A S S E D S W A L E S 0 1 / 0 2 / 0 7 I.G-2.3

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101 INFILTRATION BASIN GENERAL Infiltration basins are depressions that collect and store stormwater until it can infiltrate into the subsoil. Sediment settles out in the device, and nutrients, metals, and organic material are adsorbed by the soil as the water infiltrates. Infiltration basins may also be designed to reduce peak flows from a site if the storage capacity of the device is increased and a stable outlet structure is included in the design. Infiltration basins are appropriate on sites with highly permeable soils and drainage areas of less than 15 acres. Infiltration basins should not be used near foundations, basements, or roads or on sites with high water tables, steep slopes, or clay soils. In addition, these devices must not be used on sites with large concentrations of soluble pollutants, as groundwater contamination may result. While these structures effectively treat the runoff volume from small storms, larger storm events quickly overwhelm the capacity of the device and render it ineffective. Basins are also susceptible to clogging from sediments and, as a result, they must be used in conjunction with other management practices, such as pretreatment for sediment removal. DESIGN Infiltration basins are depressions that collect and temporarily store runoff and should be designed to drain within 48 hours. To prevent erosion of the basin and to increase the infiltration capacity of the practice, they should be lined with vegetation that is tolerant to frequent inundation (refer to Seeding, Permanent, pg. I.S-3.1; or Native Plants, pg. I.N-1.1). The effective infiltration area must receive runoff that has been pretreated. ADVANTAGES Increases discharge to the groundwater Preserves base flow in streams Removes sediment, nutrients, and organic material from stormwater May be designed to reduce peak flows Reduces thermal impacts of runoff DISADVANTAGES Limited functionality with frozen ground May cause ground water pollution if not sited properly Susceptible to clogging Requires frequent maintenance Not applicable on sites with high sediment loads or sites with large concentrations of hydrocarbons Stormwater must be delivered to the basin from pretreatment devices at non-erosive velocities to prevent erosion of the structure. The pretreatment device must provide TSS reduction of 80% for a 1- year, 24-hour storm event. Pretreatment for oil and grease separation may be necessary depending on tributary source areas. Basins receiving runoff from rooftops only do not require pretreatment. The depth of the basin is dependant upon the infiltration rate of the soil and the retention time of the structure, and should have a length to width ratio of 3:1. The bottom of the basin must be at least 3 feet above the seasonally high water table to prevent groundwater contamination. Side slopes must be 3:1 or flatter to promote uniform infiltration and safety while making maintenance tasks, such as mowing, easier. A drawdown device must be included to provide winter pass through, and allow for timely maintenance. In order to prevent channelized flow and extended localized ponding, large basins should be divided into multiple cells. Level spreaders that distribute the runoff over the effective infiltration area of each cell A P P E N D I X I I N F I L T R A T I O N B A S I N 0 1 / 0 2 / 0 7 I.I-1.1

102 should be utilized. A drawdown device must be included for each cell in the basin. An emergency spillway should be incorporated into the design of the structure to safely pass flows that exceed the design capacity of the basin. These structures prevent large flows from overwhelming the capacity of the structure without causing damage to the basin or downstream structures by discharging to stable outlets (refer to Stone Outlet Protection, pg. I.S- 10.1; or Lined Waterway or Outlet, pg. I.L- 1.1). CONSTRUCTION Construction of the basin should not commence until the entire site has been stabilized to prevent sediment clogging Care should be taken during all phases of construction to prevent the compaction of soils in and around the practice Stabilize infiltration basins immediately after construction is completed MAINTENANCE Accumulated sediment in pretreatment devices must be removed as needed Infiltration basins need to be inspected for signs of erosion and bare spots after all storm events until vegetation has become well established - all necessary repairs shall be performed immediately METHOD TO DETERMINE PRACTICE EFFICIENCY If the basin includes a forebay that is used for sedimentation, the sediment removal efficiency calculations in Appendix IV: Basin Efficiency may be used to calculate the level of pretreatment. In order to determine the infiltration performance of this practice SLAMM, RECARGA or other approved models may be used. Additional information regarding acceptable modeling of infiltration practices is found in Appendix II. SOURCES 1. Georgia Stormwater Management Manual. Volume 2: Technical Handbook. Atlanta Regional Commission. Atlanta, Ga Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul Wisconsin Department of Natural Resources. For Sizing Infiltration Basins and Bioretention Devices to meet State of Wisconsin Stormwater Infiltration Performance Standards. Last Update: July I.I-1.2 A P P E N D I X I I N F I L T R A T I O N B A S I N 0 1 / 0 2 / 0 7

103 INFILTRATION TRENCH/BED GENERAL Infiltration trenches and beds are rock filled depressions that collect and store stormwater until it can infiltrate into the subsoil. Sediment settles out in the device, and stone and subsoil adsorb nutrients, metals, and organic material as the water infiltrates. Infiltration trenches and beds may also be designed to reduce peak flows from a site if the storage capacity of the device is increased and an outlet structure is included in the design. These structures are applicable on sites with highly permeable soils and drainage areas of less than 15 acres. Infiltration trenches should not be used near foundations, basements, or roads or on sites with high water tables, steep slopes, or clay soils. In addition, these devices shall not be used on sites with large concentrations of soluble pollutants, as groundwater contamination may result. While these structures effectively treat the runoff volume from small storms, larger storm events quickly overwhelm the capacity of the device and render it ineffective. Trenches are also susceptible to clogging from large sediments and, as a result, they should be used in conjunction with other management practices. DESIGN Infiltration trenches and beds are shallow excavations that are filled with coarse stone and collect and temporarily store runoff. The distinction between trenches and beds is typically based upon geometry, with trenches having a greater depth than width and beds having a greater width than depth. They are appropriate on sites with relatively small drainage areas and are often used to treat the runoff from impervious surfaces. These structures are 3-10 feet deep and are filled with 3-4 inch diameter clear stone. ADVANTAGES Removes sediment, nutrients, and organic material from stormwater May be designed to reduce peak flows DISADVANTAGES Limited functionality with frozen ground May cause groundwater pollution if not sited properly Susceptible to clogging Requires frequent maintenance Not applicable on sites with high sediment loads or sites with large concentrations of hydrocarbons The trench width should be at least 4 feet wide, while the length will depend upon the individual site characteristics, but should be designed with a maximum retention time of 24 hours and must be large enough to safely handle the runoff from small storms. Infiltration trenches should be constructed in soils with a design infiltration rate of at least 0.13 inches per hour (see values listed in Appendix II). In addition, the bottom of the trench must be at least 3 feet above the seasonally high water table to prevent groundwater contamination and to prevent groundwater from flooding the trench and rendering it ineffective. Infiltration trenches are highly susceptible to clogging with sediment. As a result, geotextile filter fabric must be used to line the trench to prevent the surrounding soil from mixing with the stone. Runoff directed to a trench must be routed through a pretreatment device before entering the trench. Pretreatment of the runoff will help to prevent clogging of the trench from sediment as well as preventing groundwater contamination from pollutants contained in the runoff that is being infiltrated to the groundwater. Basins receiving runoff from rooftops only do not require pretreatment. A P P E N D I X I I N F I L T R A T I O N T R E N C H O R B E D 0 1 / 0 2 / 0 7 I.I-2.1

104 To divert large flows, a subsurface drain may be placed in the center of the trench, 2 feet from the surface, to prevent these flows from bypassing treatment (refer to Subsurface Drains, pg. S-14.1). CONSTRUCTION Do not construct until the entire site has been stabilized to prevent clogging Care must be taken during all phases of construction to prevent the compaction of soils in and around the practice MAINTENANCE Remove accumulated sediment in pretreatment devices at least twice a year To monitor drainage from infiltration trenches, an observation well may be installed and should be checked after all storm events to ensure that water is draining properly METHOD TO DETERMINE PRACTICE EFFICIENCY When properly designed and used in conjunction with proper pretreatment, stone trenches (not beds) meet the county standard for oil and grease removal. In order to determine the infiltration performance of this practice SLAMM, RECARGA or some other approved model may be used. Additional information regarding acceptable modeling of infiltration practices is found in Appendix II. SOURCES 1. Georgia Stormwater Management Manual. Volume 2: Technical Handbook. Atlanta Regional Commission. Atlanta, Ga Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul I.I-2.2 A P P E N D I X I I N F I L T R A T I O N T R E N C H O R B E D 0 1 / 0 2 / 0 7

105 LINED WATERWAY OR OUTLET GENERAL Lined waterways or outlets are channels lined with stone and provide for non-erosive conveyance of runoff or concentrated flow in areas where grassed waterways or unlined channels are inadequate or not permissible. These practices are applicable on sites where vegetation cannot be established due to shading; where a lining is required to control erosion; where high velocities, steep grades, seepage, prolonged base flow, or wetness would cause erosion; or where use by people or animals precludes the use of vegetated channels. Lined waterways or outlets are designed as conveyance channels and do not enhance water quality or reduce peak flows. As a result, they are best used in conjunction with other management practices. DESIGN Lined waterways or outlets should be designed to convey the maximum designed outflow from the structure or structures that it serves. The maximum flow velocities for stone linings are determined from the median diameter of the stone (D 50) placed in the channel. However, on slopes steeper than 10%, a slope adjustment factor must be used. The channel should be designed with cross sections that are triangular, parabolic, or trapezoidal. Side slopes should be 2:1 or flatter with a minimum freeboard of 0.25 feet above the designed flow depth. STONE Lined waterways or outlets should consist of clean, angular stone that is resistant to weathering. The stone should be sized by ADVANTAGES Cost-effective Relatively easy to construct Prevents erosion to receiving structures DISADVANTAGES Large storm events may displace rock Removal of accumulated sediments is difficult Not applicable on steep slopes using the median stone size (D 50). Once the D 50 has been selected, 50% of the stone, by weight, should be larger than the D 50. However, the diameter of the largest stone should not exceed 1.5 times the D 50 size. The remaining portion of the stone should be well graded with a sufficient amount of smaller stones to fill the voids between the larger stones. The depth of the stone should be equal to the maximum stone size plus the thickness of any bedding or filter material. However, under no circumstances should the stone placed in the channel reduce the designed cross section of the channel. Maximum Velocities for Various D 50 Sizes and Shapes Maximum Velocity (ft/sec) D 50 Cubical (inches) D 50 Spherical (inches) A P P E N D I X I L I N E D W A T E R W A Y O R O U T L E T 0 1 / 0 2 / 0 7 I.L-1.1

106 Slope Adjustment Factors for Allowable Velocity Manning s n Values for Various Rock Sizes Slope (horizontal to vertical) Slope ft/ft Adjustment factor Diameter (inches) n 3: : : : : : : CONSTRUCTION 10: : : Source: Natural Resources Conservation Service Construction should be completed before any water is allowed through the outlet In applications where damage is possible to the outlet structure, the stone should be hand placed MAINTENANCE Lined waterways and outlets should be inspected after all storm events for displaced stones all necessary repairs should be made immediately Accumulated sediments should be removed periodically METHOD TO DETERMINE PRACTICE EFFICIENCY Lined waterways and outlets are designed as stormwater conveyance channels and provide little treatment ability. As a result, no efficiency is given for this practice. SOURCE 1. Wisconsin Field Office Technical Guide. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C I.L-1.2 A P P E N D I X I L I N E D W A T E R W A Y O R O U T L E T 0 1 / 0 2 / 0 7

107 MINIMIZING IMPERVIOUS AREAS GENERAL Minimizing impervious areas provides more areas for stormwater to infiltrate, reducing the amount of stormwater that leaves a site. In addition, less impervious area reduces the urban heat island effect and reduces construction and maintenance costs. The amount of impervious area can be reduced in a variety of ways. Streets can be laid out differently and designed narrower, vegetation can be incorporated into street design, or driveways may be designed narrower, constructed with alternative materials, or shared with neighbors. However, all of these methods require that the developer, contractor, and the designer work together to plan and implement these practices. DESIGN STREET DESIGN One of the easiest ways to reduce the amount of impervious surface is to design and build narrower streets. Many communities require widths of 32 to 40 feet to provide 2 lanes of traffic and parking on both sides of the street. However, if parking ADVANTAGES Produces less runoff Cost-effective Narrower streets reduce speeds Improves aesthetics DISADVANTAGES Options may be limited by local ordinances Proper soils are required for infiltration practices is restricted to one side of the street, streets can be designed with widths as narrow as 22 feet without sacrificing emergency vehicle access or safe traffic flow. Streets may also be laid out differently. A typical grid system results in approximately 20,800 lineal feet of impervious surface, while alternative layouts that utilize cul-de-sacs, such as loops and lollipops, result in as little as 15,300 lineal feet of impervious surface when applied over the same area. Cul-de-sacs may be designed with the smallest practical radius, generally 40 feet, as this radius will accommodate most emergency vehicles. Cul-de-sacs may also incorporate a vegetated center that is designed to collect runoff from the surrounding pavement and Gridiron Fragmented Parallel Warped Parallel Loops and Lollipops Lollipops on a Stick 20,800 19,000 16,500 15,300 15,600 Approximate Lineal Feet of Pavement Source: Prince George s County, Maryland A P P E N D I X I M I N I M I Z I N G I M P E R V I O U S A R E A S 0 1 / 0 2 / 0 7 I.M-1.1

108 function as a rain garden, while grassed swales may be used in addition to, or as an alternative to traditional curb and gutter (refer to Rain Gardens, pg. I.R-1; or Grassed Swale, pg. I.G-2). However, streets should be designed according to the individual needs of the development. Population density should be taken into consideration when designing street width, as it affects both traffic volume and the number of parking spaces that are required. In addition, many communities have ordinances requiring minimum street widths or certain types of street layout that must be followed. As a result, planners should check all local zoning ordinances for such requirements before proceeding. DRIVEWAY DESIGN Rethinking driveway design is another way to minimize the amount of impervious area that is created by development. Driveways may be designed with shorter lengths, constructed with alternative materials, or shared with neighbors and should be designed to drain into the yard rather than into the street. However, in some instances, the setbacks required by local ordinances may require developers to obtain a variance before implementing these practices. Many driveways are built with additional parking capacity that largely goes unused, resulting in unnecessary impervious area. Driveways that meet the minimum setback requirements or those that are tapered to one lane as they meet the street are two options that are available. On street parking, if available, may be utilized to provide additional parking as needed. Driveways may also be constructed using alternative materials and methods. Vegetation may be incorporated into driveways, between the driving lanes, to allow runoff to infiltrate. In these types of driveways, grass is typically planted in strips no more than 3½ feet wide and is bordered by pavement, at least 1 foot wide, that is used for vehicle traffic. Pervious pavement systems (refer to Pervious Pavement, pg. I.P- 2) or pavement blocks may also be used. An example of Tapered Driveway Design Source: Adapted from Valley Branch Watershed District These methods allow water to infiltrate through them while providing the benefits of traditional pavement systems. They are generally recommended for overflow parking areas or in front of a third garage stall, however, as frequent use may require maintenance more often than other forms of pavement. Residents may also share driveways as a way to reduce imperviousness. This option is especially applicable for longer driveways, which may branch off into individual driveways. In addition to reducing the amount of runoff that leaves their property, residents will enjoy cost savings in maintenance and snow removal. CONSTRUCTION An example of a Shared Driveway Care should be taken to avoid unnecessary compaction of soils- deep till as necessary Vegetation should be selected carefully- for further information, refer to Native Plants, pg. I.N-1; Seeding, Permanent, pg. I.S-3; Seeding, Temporary, pg. I.S-4; and Tree Planting, pg. I.T-1 Pavement will settle after installation and care should be taken to ensure that it does not settle below the adjacent soil surface, as this may connect impervious areas. I.M-1.2 A P P E N D I X I M I N I M I Z I N G I M P E R V I O U S A R E A S 0 1 / 0 2 / 0 7

109 SOURCES 1. Alternative Stormwater Best Management Practices Guidebook. Valley Branch Watershed District Lake Elmo, MN. 2. Better Site Design Green Parking. Center for Watershed Protection Center for Watershed Protection, Inc., Ellicott City, MD. 3. Better Site Design Narrower Residential Streets. Center for Watershed Protection Center for Watershed Protection, Inc., Ellicott City, MD. 4. Low Impact Development Design Strategies. Prince George s County. Department of Environmental Resources, Programs and Planning Division Largo, MD. 5. Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Stormwater Management. Massachusetts Dept. of Environmental Protection. Volume Two: Stormwater Technical Handbook. Boston. March A P P E N D I X I M I N I M I Z I N G I M P E R V I O U S A R E A S 0 1 / 0 2 / 0 7 I.M-1.3

110 I.M-1.4 A P P E N D I X I M I N I M I Z I N G I M P E R V I O U S A R E A S 0 1 / 0 2 / 0 7

111 MULCHING GENERAL Mulching is the application of material to the soil surface to protect it from raindrop impact and overland flow. Mulch covers the soil and absorbs the erosive impact of rainfall and reduces the flow velocity of runoff, significantly reducing soil loss from a site. Mulch may be applied after the site has been rough graded to control erosion. It provides a temporary cover that reduces soil loss and allows vehicular and foot traffic over the area. Mulch also provides benefits to the site beyond erosion control. Mulch forms a blanket over the soil, and moderates its temperature, conserving moisture and providing an environment conducive to seed germination. Mulch should be applied within 48 hours of the completion of seeding, or in hydroseeding applications, simultaneously (refer to Seeding, Permanent, pg. I.S-3 and Seeding, Temporary, pg. I.S-4). Mulching is a versatile practice that is applicable on sites where sheet flow is maintained and slopes do not exceed 3:1. Mulch has a limited life span, which varies with the material used and site conditions. It may not be used in channels or other areas where concentrated flow may occur. In these situations, erosion blankets or mats, which are more effective and may have a longer life span, should be used (refer to Erosion Matting, pg. I.E-1). Mulching, while effective for smaller storm events, may not prevent erosion during larger storm events and is best used in conjunction with other management practices. TYPES Mulch is available in a variety of types and should be selected based upon the individual site characteristics, such as slope, soil type, size, and time of year the mulch is applied. Regardless of the material selected, it must ADVANTAGES be free of weed and grass seeds that may compete with the establishing seed. STRAW Cost-effective Easy to apply Protects the soil surface from raindrop impact, preventing erosion Reduces evaporation from the soil and moderates soil temperature Aids seed germination and establishment and hinders weed growth DISADVANTAGES Ineffective on slopes steeper than 3:1 Ineffective with large storm events May require frequent maintenance Straw is the most commonly used mulching material as it is cost effective and easy to apply. Straw from small grains, such as winter wheat, oats, and rye are generally used and can be spread by hand or with mulching equipment. Because straw is susceptible to the wind, it must be anchored to the soil by an approved method. WOOD CHIPS, BARK, AND WOOD FIBERS Wood chips are often used as landscape mulches and in specialized applications. They are generally more expensive, but do not require anchoring and may be obtained from a variety of sources. The wood used for mulch may be a hard or soft wood and shall be free of mold, sawdust, and other foreign materials, such as bonding agents and other chemicals. Like all other organic mulches, wood chips are biodegradable. However, as wood chips degrade, they typically absorb a significant portion of the available soil nitrogen, making it unavailable for the establishing seed. Thus, depending upon the nitrogen content of the soils present on site, nitrogen fertilizer may need to be applied along with wood products to encourage the establishment of seed. A P P E N D I X I M U L C H I N G 0 1 / 0 2 / 0 7 I.M-2.1

112 Tree bark, often obtained as a byproduct of the timber industry, is also used in landscape plantings and in areas that will not be closely mowed. Bark differs from wood chips in that it degrades faster and thus does not require added nitrogen. Wood fibers consist of hard or soft wood that has been shredded in a hammermill, tub grinder, or other mechanical means. While wood fiber may not be used as a mulching material by itself, it is often used in conjunction with straw mulch in hydroseeding applications on steeper slopes and in critical areas. APPLICATION RATE Mulch should be applied so that the soil surface is uniformly covered. This coverage rate corresponds with the application standards included in the following table. However, actual application rates may vary depending upon the individual site characteristics and the type of mulch used. The following table is intended for use as a planning tool only. Application Rates by Material Material Straw Wood Chips Wood Fiber Bark Rate Per Acre 1-2 tons 5-6 tons ton 35 cubic yards Source: Adapted from NRCS Planning and Design Manual Notes From small grains, should be tacked down or crimped Treat with 12 lbs. of Nitrogen per acre; not to be used for fine turf May be hydroseeded, not for use in hot weather Should be applied with a mulch blower or by hand. Not to be used with asphalt tackifiers. Mulch may be applied by hand or by mechanical methods. Mechanical methods are generally much faster and more costeffective, but may not distribute the mulch as evenly as hand application. For hand application, the area to be mulched should be divided into sections with an area of 1000 square feet. Each section should then be evenly covered with pounds of straw (roughly equivalent to 1½ - 2 bales). This method results in an application of 1½ to 2 tons per acre with a uniform thickness of 5-7 pieces. ANCHORING Certain types of mulches, such as straw and wood fibers, are easily displaced by the wind and water. To keep them in place and effective, mechanical or chemical anchoring methods are applied. Mechanical means of anchoring include crimping and the use of erosion netting. Crimping is accomplished by a tractor drawn implement, similar to a farm disc, which draws the mulch into the soil profile in one piece. Crimping shall be performed on the contour of the land to prevent the formation of rills or gullies that may result from other application methods. Erosion nets, which are constructed of various materials such as plastic, wire, jute, cotton, or paper, are anchored on top of the mulch to hold it in place. Erosion nets are available in many types with a wide range of life spans. As a result, careful selection and adherence to all manufacturers specifications are crucial to their success. Chemicals, called tackifiers, may also be used to hold mulch in place. Tackifiers hold the fibers together and reduce their susceptibility to wind and water erosion. Many types of tackifiers are available, including latex based products, asphalt emulsifiers, and natural products, such as guar gum. The type of product used will depend upon the characteristics of the site and the type of mulch used, however, regardless of the material selected, application should follow all of the manufacturers specifications. CONSTRUCTION All grading activities shall be completed and the area seeded before mulch is applied (except in hydroseeding applications) Tackifiers shall not be applied in windy conditions Mulch, when applied correctly, will have a uniform thickness of 5-7 pieces I.M-2.2 A P P E N D I X I M U L C H I N G 0 1 / 0 2 / 0 7

113 MAINTENANCE Mulch shall be inspected weekly and after each storm event (including windy days) for signs of displacement and rill erosion. Necessary repairs and/or replacement shall be performed immediately to preserve effectiveness. Inspections shall continue until vegetation has been permanently established. METHOD TO DETERMINE PRACTICE EFFICIENCY Mulching efficiency is dependant upon many factors, including site characteristics, type of mulch used, rate of application, and atmospheric conditions. However, in general, when properly applied, mulching provides an efficiency of up to 88% (derived by using a USLE C factor of 0.12). SOURCES 1. Illinois Urban Manual. A Technical Manual Designed for Urban Ecosystem Protection and Enhancement. United States Department of Agriculture, Natural Resources Conservation Service. Washington, D.C Indiana Handbook for Erosion Control in Developing Areas. Indiana Department of Natural Resources, Division of Soil Conservation. Indianapolis Mulching Fact Sheet. Center for Watershed Protection Center for Watershed Protection, Inc., Ellicott City, MD. 4. Mulching for Construction Sites. Conservation Practice Standard. Wisconsin Department of Natural Resources. November Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis National Catalog of Erosion and Sediment Control and Stormwater Management. Guidelines for Community Assistance. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Wisconsin Field Office Technical Guide. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C A P P E N D I X I M U L C H I N G 0 1 / 0 2 / 0 7 I.M-2.3

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115 NATIVE PLANTS GENERAL Native plants provide densely vegetated areas that collect and slow runoff, encourage infiltration, and filter out sediments and soluble pollutants. In addition, native plants are adaptable to most any area, add aesthetic beauty and provide habitat for wildlife. Native species are applicable on any area in which final grading has been performed. Native species require a longer period of time to become established, and are generally more costly and more difficult to establish than nonnative vegetation. However, due to their dense nature and deep root systems, they offer a much higher degree of infiltration and are an attractive alternative to other types of vegetation. DESIGN VEGETATION Native species have vast root systems that may extend more than 10 feet below the surface, allowing them to access hard to reach water and nutrients and grow successfully in poor soils and during dry periods. These extensive root systems also stabilize the soil and protect water quality because fertilizers and pesticides are often not required. Above ground, many species grow in dense clumps that reduce runoff velocities and increase infiltration. Additionally, native species absorb large quantities of water, greatly reducing the amount of runoff that leaves a site. Native species grow differently than non-native species, as they generally establish their root systems before fully developing above ground. Most native species grow only 2 to 3 inches during the first year while some will lie dormant for up to five years. As a result, the planted area may look less than desirable the first year, consisting more of weeds than native species. In subsequent years, however, the native plants will The species of native vegetation selected will vary greatly depending upon the characteristics ADVANTAGES of the site. Soil type, slope, site use, out-compete the weeds and will begin to flourish. maintenance, growth rate, bloom time, hydrology, sun/shade mix, and the time of year it is planted are all factors that must be weighed when selecting vegetation. For more information on species selection, please refer to the Acceptable Native Species for use in the Shoreland Zone in Dane County publication at: eptable_native_plants.pdf. Native species may be established from transplants or seed. Native transplants are available commercially and decrease the time required for establishment by 1 to 2 years, but greatly increase the cost of the practice. Seeding is economical but requires up to 3 years before the plants become established. However, regardless of the species or method selected, careful species selection is crucial. Care should be taken to ensure that the plant or seed is grown locally. Plants or seed of the same species may be obtained from other parts of the country, but may produce less than desirable results. Exotic or invasive species should be avoided. EROSION CONTROL Cost-effective Drought resistant Low maintenance Do not require application of fertilizers, pesticides, or regular irrigation Provide a diverse habitat for wildlife Prevent erosion once established DISADVANTAGES Take longer to establish Require periodic biomass removal (burning) To prevent erosion during the establishment period, additional management practices are A P P E N D I X I N A T I V E P L A N T S 0 1 / 0 2 / 0 7 I.N-1.1

116 often required. However, due to the slow germination process, the use of heavy erosion blankets and mats is not recommended as the seed may rot. Rather, clean straw mulch that is free of weeds and other seeds may be used. Mulching rates for use with native species differ than those used for non-native species and it is generally recommended that mulch should be applied at no more than 1 ton per acre (refer to Mulching, pg. I.M-2). The use of companion vegetation is also a viable method for controlling erosion during establishment. It provides cover and minimizes weed growth while stabilizing the soil and preventing soil loss. Relatively non-competitive, annual species of vegetation, such as those listed in Temporary Seeding (pg. I.S-4) may be used for this purpose, provided the seeding rate is cut in half. SEEDBED Native plants generally do not require extensive seedbed preparation, as a rough surface may actually stimulate certain species of seed. Rather, native species require only 3-4 inches of uncompacted topsoil to grow. If necessary, soils should be deep tilled to relieve compaction (refer to Deep Tilling, pg. I.D-1). A sod cutter should be used to remove existing vegetation from the site, as it minimizes the amount of soil that is disturbed during removal. Overturning the soil exposes weed seeds to sunlight and promotes their growth, which creates competition for native species. Fertilizers should not be used with native species. Not only do native plants not require such amendments, they actually may hinder their establishment by promoting weed growth. Pesticides and irrigation are also generally unnecessary, as native species are well adapted to local conditions. SEEDING Seed should be applied uniformly following the supplier s recommendations by broadcast seeding, hydroseeding, or drill seeding. Broadcast seeding involves scattering the seeds on the soil surface by hand or mechanical means and is best utilized on smaller areas and for patching applications. After application, the site should be raked and firmed with a roller or cultipacker. Seeded areas should then be mulched to provide protection for the seed and to reduce erosion before the vegetation becomes established (refer to Mulching, pg. I.M-2). Hydroseeding and drill seeding are more costly than broadcast seeding and are used on larger sites to maximize the application s cost effectiveness. Hydroseeding, a method that mixes the seed and water together into a slurry, is applied on areas that may be difficult to seed with alternative means. Other amendments, such as tackifiers, polymers, and/or fiber mulch are often added to the slurry, which is sprayed on, to protect the seed and to promote its growth. Drill seeding utilizes a drill or cultipacker seeder to inject the seeds beneath the soil surface. Seeding depth should not exceed 1/8 of an inch. Drilling, while more costly than broadcast or hydroseeding, is generally very effective when performed properly because the seed is protected from wind, water, and wildlife. MAINTENANCE Native species require little maintenance beyond occasional mowing or periodic prescribed burns. Due to the fact that irrigation and the use of fertilizers, pesticides, and other amendments are unnecessary with native species, long term maintenance costs are generally much less than those associated with non-native species. Prescribed burns are required every 2-3 years to promote a healthy, diverse landscape. These controlled burns should only be performed once the vegetation has become established, usually during the third or fourth year. Burning clears away old vegetation and non-native species, leaving a warm, clear area that stimulates new growth. In addition, fire provides nutrients for the growing plants from the ash it leaves behind. Because of the potential for injury and property damage associated with this practice, only trained, experienced professionals should perform prescribed burns. Mowing is required during the first 2 years and may be used as an alternative to burning. Planted areas should be mowed to a height of 6-12 inches 2-3 times during the first year and once during the second year to prevent weeds from developing seed. Native plants grow slowly at first, and mowing to these heights will cause only I.N-1.2 A P P E N D I X I N A T I V E P L A N T S 0 1 / 0 2 / 0 7

117 minor, if any, damage to these species and allows them access to sunlight. During subsequent years, mowing may be performed as an alternative to prescribed burning. Mowing mimics burning by clearing the surface and allowing the sun to warm the soil, without the potential concerns associated with burning. When mowing, clippings should be removed wherever possible. These activities may be performed at varying times of the year. Varying the time of year that it is performed will stimulate different species and promotes a healthy, diverse ecosystem. Other maintenance activities should be performed as necessary. If weeding by hand, weeds should be cut as close to the surface as possible to prevent damage to the root systems of native species that may be caused by pulling. Seeded areas should also be inspected after all storm events for evidence of erosion. All necessary repairs should be made immediately. CONSTRUCTION All grading and tracking shall be completed before seeding begins All management practices should be installed and online before seeding Maximum seed depth of one eighth of an inch To promote growth, seeding should not be performed during excessively wet conditions, as soils may become excessively compacted METHOD USED TO DETERMINE PRACTICE EFFICIENCY Native plants reduce erosion by providing cover and stabilizing the surface. However, due to the length of time required for establishment, no efficiency is given for this practice. SOURCES 1. Broughton, J. In Defense of the American Landscape. Landscape Architect and Specifer News. Volume 13, No. 11. November Broughton, J. Landscaping with Natives. The Landscape Contractor. Oct Flinchum, M. A Guide to Selecting Existing Vegetation for Low Energy. Circular 489. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. June Landscaping with Native Plants. United States Environmental Protection Agency. Washington, D.C Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis A P P E N D I X I N A T I V E P L A N T S 0 1 / 0 2 / 0 7 I.N-1.3

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119 NATIVE PLANTS GENERAL Native plants provide densely vegetated areas that collect and slow runoff, encourage infiltration, and filter out sediments and soluble pollutants. In addition, native plants are adaptable to most any area, add aesthetic beauty and provide habitat for wildlife. Native species are applicable on any area in which final grading has been performed. Native species require a longer period of time to become established, and are generally more costly and more difficult to establish than nonnative vegetation. However, due to their dense nature and deep root systems, they offer a much higher degree of infiltration and are an attractive alternative to other types of vegetation. DESIGN VEGETATION Native species have vast root systems that may extend more than 10 feet below the surface, allowing them to access hard to reach water and nutrients and grow successfully in poor soils and during dry periods. These extensive root systems also stabilize the soil and protect water quality because fertilizers and pesticides are often not required. Above ground, many species grow in dense clumps that reduce runoff velocities and increase infiltration. Additionally, native species absorb large quantities of water, greatly reducing the amount of runoff that leaves a site. Native species grow differently than non-native species, as they generally establish their root systems before fully developing above ground. Most native species grow only 2 to 3 inches during the first year while some will lie dormant for up to five years. As a result, the planted area may look less than desirable the first year, consisting more of weeds than native species. In subsequent years, however, the native plants will The species of native vegetation selected will vary greatly depending upon the characteristics ADVANTAGES of the site. Soil type, slope, site use, out-compete the weeds and will begin to flourish. maintenance, growth rate, bloom time, hydrology, sun/shade mix, and the time of year it is planted are all factors that must be weighed when selecting vegetation. For more information on species selection, please refer to the Acceptable Native Species for use in the Shoreland Zone in Dane County publication at: eptable_native_plants.pdf. Native species may be established from transplants or seed. Native transplants are available commercially and decrease the time required for establishment by 1 to 2 years, but greatly increase the cost of the practice. Seeding is economical but requires up to 3 years before the plants become established. However, regardless of the species or method selected, careful species selection is crucial. Care should be taken to ensure that the plant or seed is grown locally. Plants or seed of the same species may be obtained from other parts of the country, but may produce less than desirable results. Exotic or invasive species should be avoided. EROSION CONTROL Cost-effective Drought resistant Low maintenance Do not require application of fertilizers, pesticides, or regular irrigation Provide a diverse habitat for wildlife Prevent erosion once established DISADVANTAGES Take longer to establish Require periodic biomass removal (burning) To prevent erosion during the establishment period, additional management practices are A P P E N D I X I N A T I V E P L A N T S 0 1 / 0 2 / 0 7 I.N-1.1

120 often required. However, due to the slow germination process, the use of heavy erosion blankets and mats is not recommended as the seed may rot. Rather, clean straw mulch that is free of weeds and other seeds may be used. Mulching rates for use with native species differ than those used for non-native species and it is generally recommended that mulch should be applied at no more than 1 ton per acre (refer to Mulching, pg. I.M-2). The use of companion vegetation is also a viable method for controlling erosion during establishment. It provides cover and minimizes weed growth while stabilizing the soil and preventing soil loss. Relatively non-competitive, annual species of vegetation, such as those listed in Temporary Seeding (pg. I.S-4) may be used for this purpose, provided the seeding rate is cut in half. SEEDBED Native plants generally do not require extensive seedbed preparation, as a rough surface may actually stimulate certain species of seed. Rather, native species require only 3-4 inches of uncompacted topsoil to grow. If necessary, soils should be deep tilled to relieve compaction (refer to Deep Tilling, pg. I.D-1). A sod cutter should be used to remove existing vegetation from the site, as it minimizes the amount of soil that is disturbed during removal. Overturning the soil exposes weed seeds to sunlight and promotes their growth, which creates competition for native species. Fertilizers should not be used with native species. Not only do native plants not require such amendments, they actually may hinder their establishment by promoting weed growth. Pesticides and irrigation are also generally unnecessary, as native species are well adapted to local conditions. SEEDING Seed should be applied uniformly following the supplier s recommendations by broadcast seeding, hydroseeding, or drill seeding. Broadcast seeding involves scattering the seeds on the soil surface by hand or mechanical means and is best utilized on smaller areas and for patching applications. After application, the site should be raked and firmed with a roller or cultipacker. Seeded areas should then be mulched to provide protection for the seed and to reduce erosion before the vegetation becomes established (refer to Mulching, pg. I.M-2). Hydroseeding and drill seeding are more costly than broadcast seeding and are used on larger sites to maximize the application s cost effectiveness. Hydroseeding, a method that mixes the seed and water together into a slurry, is applied on areas that may be difficult to seed with alternative means. Other amendments, such as tackifiers, polymers, and/or fiber mulch are often added to the slurry, which is sprayed on, to protect the seed and to promote its growth. Drill seeding utilizes a drill or cultipacker seeder to inject the seeds beneath the soil surface. Seeding depth should not exceed 1/8 of an inch. Drilling, while more costly than broadcast or hydroseeding, is generally very effective when performed properly because the seed is protected from wind, water, and wildlife. MAINTENANCE Native species require little maintenance beyond occasional mowing or periodic prescribed burns. Due to the fact that irrigation and the use of fertilizers, pesticides, and other amendments are unnecessary with native species, long term maintenance costs are generally much less than those associated with non-native species. Prescribed burns are required every 2-3 years to promote a healthy, diverse landscape. These controlled burns should only be performed once the vegetation has become established, usually during the third or fourth year. Burning clears away old vegetation and non-native species, leaving a warm, clear area that stimulates new growth. In addition, fire provides nutrients for the growing plants from the ash it leaves behind. Because of the potential for injury and property damage associated with this practice, only trained, experienced professionals should perform prescribed burns. Mowing is required during the first 2 years and may be used as an alternative to burning. Planted areas should be mowed to a height of 6-12 inches 2-3 times during the first year and once during the second year to prevent weeds from developing seed. Native plants grow slowly at first, and mowing to these heights will cause only I.N-1.2 A P P E N D I X I N A T I V E P L A N T S 0 1 / 0 2 / 0 7

121 minor, if any, damage to these species and allows them access to sunlight. During subsequent years, mowing may be performed as an alternative to prescribed burning. Mowing mimics burning by clearing the surface and allowing the sun to warm the soil, without the potential concerns associated with burning. When mowing, clippings should be removed wherever possible. These activities may be performed at varying times of the year. Varying the time of year that it is performed will stimulate different species and promotes a healthy, diverse ecosystem. Other maintenance activities should be performed as necessary. If weeding by hand, weeds should be cut as close to the surface as possible to prevent damage to the root systems of native species that may be caused by pulling. Seeded areas should also be inspected after all storm events for evidence of erosion. All necessary repairs should be made immediately. CONSTRUCTION All grading and tracking shall be completed before seeding begins All management practices should be installed and online before seeding Maximum seed depth of one eighth of an inch To promote growth, seeding should not be performed during excessively wet conditions, as soils may become excessively compacted METHOD USED TO DETERMINE PRACTICE EFFICIENCY Native plants reduce erosion by providing cover and stabilizing the surface. However, due to the length of time required for establishment, no efficiency is given for this practice. SOURCES 1. Broughton, J. In Defense of the American Landscape. Landscape Architect and Specifer News. Volume 13, No. 11. November Broughton, J. Landscaping with Natives. The Landscape Contractor. Oct Flinchum, M. A Guide to Selecting Existing Vegetation for Low Energy. Circular 489. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. June Landscaping with Native Plants. United States Environmental Protection Agency. Washington, D.C Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis A P P E N D I X I N A T I V E P L A N T S 0 1 / 0 2 / 0 7 I.N-1.3

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123 OIL AND GREASE FILTER GENERAL Oil and grease filters are devices that are designed to remove oil, grease, sediments, trash, and other debris from stormwater by passing them through a filtering device. Oil and grease filters are most often used at gas stations, industrial sites, parking lots, loading areas, and anywhere hydrocarbons are likely to be present in large quantities. Because they generally operate underground, they are often used in retrofit applications where other management practices are not practical. In high flow situations, the volume of water may exceed the capacity of the filter chamber and stormwater may bypass the device without treatment. As a result, these practices are best used in conjunction with other management practices. DESIGN Oil and grease filters are proprietary devices that are available in a wide array of configurations from a variety of vendors and should be custom designed to meet the individual needs of the site. However, at a minimum, they shall be designed to treat the first ½ inch of runoff from the site and should provide sufficient volume as to ensure adequate detention time for the filtration of oil, grease, and sediment. CONSTRUCTION Installation should follow all manufacturers specifications Oil and grease filters must be water tight to prevent groundwater pollution Installation should provide access for maintenance activities. ADVANTAGES Filters may be installed off-line to prevent the capacity of the separator from being exceeded during large storm events MAINTENANCE Widely applicable Requires minimal land area Compatible with most storm drain systems Can be used in retrofit applications DISADVANTAGES Limited effectiveness with large storm events Provides little detention time Does not reduce peak flows Requires frequent maintenance All maintenance activities should follow the manufacturers recommendations and specifications. However, additional maintenance requirements may be required and are listed below. Oil and grease filters should be inspected regularly to ensure that the practice is functioning properly All accumulated oil, grease, sediment and other debris should be disposed of properly A P P E N D I X I O I L A N D G R E A S E F I L T E R 0 1 / 0 2 / 0 7 I.O-1.1

124 METHOD TO DETERMINE PRACTICE EFFICIENCY The manufacturer of the device determines the efficiency of this practice. It is dependant upon several factors, including the volume of water that enters the device and that proper maintenance activities are performed in a timely manner. Due to these factors and because oil and grease filters are rated based practices and are not designed to handle a specific storm event, efficiency is dependant upon external factors that are beyond the control of the designer. As a result, the efficiency for this practice is at the discretion of the LWRD Director. SOURCES 1. CEIT Virtual Trade Show: Stormwater. United States Environmental Protection Agency. New England Division Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis I.O-1.2 A P P E N D I X I O I L A N D G R E A S E F I L T E R 0 1 / 0 2 / 0 7

125 PARKING LOT / STREET SWEEPING GENERAL Parking lot and street sweeping prevents sediment, heavy metals, and other pollutants from reaching receiving waters by removing them from impervious areas before they reach storm drains. Impervious areas accumulate sediment, lawn and leaf trimmings, trash, and other debris, along with heavy metals and other pollutants. As stormwater flows over these surfaces, these substances are carried along with it, polluting waterways and increasing the sediment load of the water body. Parking lot and street sweeping is applicable on any impervious surface where a street sweeper may safely travel. Because removing smaller particles is often difficult, street sweeping should be used in conjunction with other practices (refer to Seeding, Permanent pg. I.S-3; Native Plants, pg. I.N-1; or Grassed Swales, pg. I.G-2) to minimize the amount of material that must be removed. METHODS Parking lot and street sweeping may be performed by one of two mechanized methods: broom sweeping or vacuum sweeping. Broom sweepers remove larger particles and are effective on wet surfaces. These sweepers are more economical than vacuum sweepers, but release dust into the air while in use. Vacuum sweepers are more effective at removing pollutant-laden fine particles, but are generally ineffective when used on wet surfaces. TIMING Parking lot and street sweeping should be performed as often as is practical and no less ADVANTAGES Reduces the amount of sediment, heavy metals and other pollutants that reach receiving waters Helps prevent storm sewers from clogging Improves aesthetics Especially effective when used in parking lots DISADVANTAGES Limited effectiveness on streets with parked cars Waste may contain heavy metals and other pollutants than twice a year. Increasing the frequency of the practice increases the amount of waste that is collected, and, as a result, increases the efficiency of the practice. Sweeping removes the materials that tend to accumulate in parking lots and on streets throughout the year, such as salt, sand, and other de-icing substances, along with trash and other debris. Leaves and grass clippings should also be collected to prevent them from entering and potentially clogging storm drains. The timing of these operations is important, as sweeping too late in the spring or too early in the fall will result in less than peak loads being collected, reducing the efficiency of the practice as well as increasing the pollution potential. Additional sweeping is recommended on surfaces with large traffic volumes, during and after construction activities, and after any other activity that causes sediment, pollutants, or other debris to accumulate on roadways and impervious areas. A P P E N D I X I P A R K I N G L O T / S T R E E T S W E E P I N G 0 1 / 0 2 / 0 7 I.P-1.1

126 DISPOSAL The waste that is collected by street sweepers may be separated by screening, which removes yard wastes, trash, and other debris. Leaves and grass clippings may be removed and sent to a composting facility, while trash and other debris may be recycled or sent to a landfill. Street sweepings may also be used as cover material for landfills or be landfilled themselves. However, sweepings often contain a wide variety of organic and inorganic pollutants and testing may be required to determine disposal options. As a result, street sweepings should be disposed with care. OPERATION AND MAINTENANCE Sweeping operations should prevent materials from being directed toward storm drain inlets Holding and disposal sites for collected materials should be located so that it is not washed back into storm drain inlets Sweeping should be performed prior to storm events to maximize the amount of waste collected Routine maintenance should be performed on street sweepers to keep them operating properly and effectively METHOD TO DETERMINE PRACTICE EFFICIENCY Parking lot/street sweeping may be used to help meet the 80% total suspended solids (TSS) reduction required by the ordinance. If a street sweeping program is implemented that includes regular sweeping that is performed properly and provides for proper disposal of accumulated materials, street sweeping, when used in conjunction with other management practices, provides a TSS reduction of up to 10%. SOURCES 1. Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Stormwater Management. 2. Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul Stormwater Management. Massachusetts Dept. of Environmental Protection. Volume Two: Stormwater Technical Handbook. Boston. March Urban Storm Water Best Practices Study. United States Environmental Protection Agency, Office of Water. Washington, D.C I.P-1.2 A P P E N D I X I P A R K I N G L O T / S T R E E T S W E E P I N G 0 1 / 0 2 / 0 7

127 PERVIOUS PAVEMENT GENERAL A pervious pavement system is a system that allows stormwater to percolate through small pores or gaps in the pavement. The purpose of these systems is to encourage infiltration by reducing the amount of runoff that is produced from a site. Runoff soaks through the voids in the pavement and into a basin that is filled with gravel, a layer of filter fabric, and a stone reservoir. These layers work together to both support the pavement above it and to speed percolation into the subsoil. There are several types of pervious pavement systems. They include: porous asphalt, porous concrete, modular perforated concrete block, and cobble pavers with porous joints. These systems can be used in any area with limited traffic flow, such as overflow parking lots and driveways. Heavy traffic causes the soil beneath the pavement to become compacted and obstructs the downward flow of the water, limiting the system s effectiveness. These systems should be used in conjunction with other ADVANTAGES Reduces the need for additional BMPs by reducing runoff Reduces temperature of runoff when compared to traditional pavement systems Can be aesthetically pleasing DISADVANTAGES Limits handicapped accessibility Ineffective in areas with high volumes of traffic May be damaged by snow removal activities Pores are easily clogged by sediment May increase the potential for groundwater contamination management practices to reduce the amount of sediment that reaches the pavement, as heavy loads of sediment can permanently clog the pores in the pavement, severely hindering the ability of the pavement to accept runoff. Berm Observation well Overflow Pervious pavement Gravel filter layer Stone reservoir Gravel filter layer Geotextile filter fabric An Example of Pervious Pavement Source: Adapted from the United States Environmental Protection Agency A P P E N D I X I P E R V I O U S P A V E M E N T 0 1 / 0 2 / 0 7 I.P-2.1

128 DESIGN SOILS Proper soils are necessary for pervious pavement systems to work correctly. The soil present on the site should have a permeability rate of at least 2 inches per hour and should be at least 4 feet thick to ensure that the pavement and the basin drain properly. STORAGE BASIN Pervious pavement is underlined by a storage basin that aids in the drainage of water from the pavement to the subsoil. The basin consists of a layer of woven geotextile filter, 2 layers of gravel, a stone reservoir, an overflow pipe, and an observation well. A geotextile filter with a high flow rate is placed on the bottom and along the sides of the basin. It is used because finer sediments, such as those contained in the subsoil, have a tendency to shift upward into the voids in the gravel and stone, reducing the infiltration capacity of the basin. The geotextile filter prevents this process from occurring, yet allows water to move freely through it. 2 layers of ½ inch gravel are placed in the basin: the first is located on top of the geotextile filter and the other directly beneath the pavement and above the stone reservoir. Both layers serve as a base for the layer above it; the top layer supports the pavement while the lower layer supports the reservoir above it and prevents settling under normal conditions. A layer of 1 ½ to 3-inch stone is located between the gravel layers. It acts as a reservoir for the runoff, cooling it as it slowly passes through the stone. A perforated overflow pipe is located at or near the top of the stone and helps prevent runoff from leaving the site during large storm events. When large amounts of runoff infiltrate the basin, the reservoir may not be large enough to handle all of the runoff produced. The overflow pipe, which has holes in the bottom of it, drains water from the top of the basin when the basin is filled, but allows water to percolate downward when it is not. To ensure the basin is working properly, an observation well is incorporated into the basin. Stretching the entire depth of the basin, it allows site owners to check the water levels in the basin and ensure that the runoff is infiltrating into the subsoil. As an added safeguard, the basin should be larger than the pervious pavement that is placed on top of it. If the voids in the pavement become clogged, the added surface area provides an overflow for any runoff that occurs. After paving, the remaining, exposed basin is covered with a decorative stone. PLACEMENT Pervious pavement systems should be placed in areas with limited traffic use and away from areas that see even occasional use by heavy machinery. Heavy machinery and large volumes of traffic cause the soil beneath the pavement to become compacted, causing the infiltration capacity of the soil to be reduced. CONSTRUCTION Pervious pavement failures occur most often during construction due to sedimentation that fills in the voids in the pavement. As a result, careful construction practices that significantly reduce the site s contact with sediment from construction vehicles and from around the site are essential to the success of these systems. Successful construction requires the use of stone tracking pads (refer to Stone Tracking Pads, pg. I.S-11) to reduce the sediment brought on site by vehicles and any practice that reduces the amount of sediment that runs off onto the site; such as buffers, filter strips, berms, or diversions. In addition, constant contact should be maintained between the contractor and the engineer to ensure that all aspects of the system are installed properly. The combination of these factors greatly increases the likelihood of a successful pervious pavement system. MAINTENANCE Proper maintenance of pervious pavement is crucial to its operation, but is similar to that required with traditional pavement. The main difference is that pervious pavement should be vacuumed by using a Hi-Vac truck or other device rather than swept. Sweeping may actually expedite sedimentation by brushing sediments into the pavements voids, blocking the percolation of runoff. Vacuuming removes sediment and debris without spreading it around and is more efficient at removing sediment than traditional street sweeping equipment. I.P-2.2 A P P E N D I X I P E R V I O U S P A V E M E N T 0 1 / 0 2 / 0 7

129 Vacuuming should be performed at least 2-3 times a year to ensure that water is infiltrating properly. In addition, signs should be placed at various locations throughout the site after construction is completed stating that pervious pavement is located on the site. The signs should warn heavy machinery and snow plow operators to avoid the area. METHOD TO DETERMINE PRACTICE EFFICIENCY Pervious pavement systems are designed as an infiltration practice and do not significantly reduce the amount of suspended sediment in stormwater runoff. As a result, no efficiency is given for this practice. SOURCES 1. Cahill, T. A Second Look at Porous Pavement/Underground Recharge. Center for Watershed Protection. Center for Watershed Protection, Inc., Ellicott City, MD Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Preliminary Data Summary of Urban Storm Water Best Management Practices (EPA-821-R ). U.S. Environmental Protection Agency. Washington, D.C. August A P P E N D I X I P E R V I O U S P A V E M E N T 0 1 / 0 2 / 0 7 I.P-2.3

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131 POLYMER APPLICATION GENERAL Polymers (PAM), or anionic polyacrylamides, are non-toxic, organic chemicals that can be applied to soil or water and will temporarily bond soil aggregates. The resulting soil surface is significantly more resistant to erosion than untreated soil. Water application of polymers promotes sediment flocculation and coagulation, thereby increasing settling velocity. PAM is applicable on a wide variety of sites, especially those with steep slopes where traditional practices, such as mulching, are rendered ineffective when used by themselves. PAM may also be used to improve the efficiency of devices that rely on settling of particles in water. This practice is usually used during and after site grading activities, prior to and during the establishment of seed, (refer to Seeding, Permanent, pg. I.S-3; and Seeding, Temporary, pg. I.S-4) or in situations where other practices are unavailable or ineffective due to weather conditions. The use of additional practices, such as mulching, (refer to Mulching, pg. I.M-2) may significantly increase the effectiveness of the practice. For water application, polymers may only be applied to runoff that has been captured in sediment control devices. Application of polymers in these devices helps sediment suspended in the water to settle out. Polymers may not be applied directly to any surface waters of the state, such as lakes or rivers. When used for water application, polymers should comply with Wisconsin Department of Natural Resource Technical Standard 1051, Interim Sediment Control Water Application of Polymers. SELECTION Polymers are available commercially in both granular and liquid forms in a wide variety of formulations. ADVANTAGES Effective in preventing erosion Cost effective May reduce turbidity Reduces erosion during winter months, when vegetation cannot be established Prevents crust formations DISADVANTAGES Must be reapplied whenever the soil is disturbed and after large storm events May increase the ph of runoff Limited life span Does not provide protection for seed in the summer months Over application may result in negative effects on plants and wildlife Must be approved by WDNR and WDOT before use Cannot be used within 30 feet of state water bodies However, both the Wisconsin Department of Natural Resources (WDNR) and the Wisconsin Department of Transportation (WDOT) must approve the polymer before it may be used. Polymers shall be utilized following all manufacturers instructions and specifications. A current listing of approved polymers is available from the Product Acceptability List Committee on the WDOT s web site at: al.htm APPLICATION As application rates will vary depending upon the product used, the time of year, and the individual site characteristics, PAM shall be applied following the WDNR and the manufacturer s specifications. Over application may result in reduced effectiveness and may have adverse effects on local plant and wildlife communities. As a result, land applied PAM may not be applied within 30 feet of any state water bodies. A P P E N D I X I P O L Y M E R A P P L I C A T I O N 0 1 / 0 2 / 0 7 I.P-3.1

132 Reapplication is required after any site disturbance and after large storm events. In addition, because PAM breaks down over time, reapplication, based on manufactures specifications, is required for the practice to remain effective. Additional practices, such as mulching, are strongly encouraged for use with polymers. The combination of these practices results in enhanced erosion protection, while increasing the success of germination by providing protection for seed. DOCUMENTATION Those utilizing PAM as an erosion control practice must maintain an inspection log that is readily attainable by Dane County Erosion Control Inspectors. Documentation requirements include: Date of application Rate of application Type of PAM applied (including manufacturer, product name and concentration) Specific area of the site that the practice has been applied Dates of inspection Date of construction activities on the application site Dates and amounts of rainfall on the site MAINTENANCE Applied areas shall be inspected weekly and after each rainfall event for evidence of rill and gully formation PAM shall be reapplied necessary per manufactures specifications PAM shall be reapplied after any site disturbance and after large rainfall events METHOD TO DETERMINE PRACTICE EFFICIENCY The efficiency of PAM is dependant upon the individual site characteristics, the type of polymer used, the rate of application, the time of year applied, and the use of additional practices. PAM efficiency is also dependant upon site disturbance. Any disturbance to the application area, such as vehicle traffic, grading, large storm events, etc., greatly reduces the efficiency of the practice and requires reapplication to prevent soil loss. However, when properly applied, PAM has the ability to reduce soil loss by 40%. SOURCES 1. Land Application of Anionic Polyacrylamide. Conservation Practice Standard. Wisconsin Department of Natural Resources. June Roa-Espinosa, A., Bubenzer, G.D. and Miyashita, E., Determination of PAM Use in Erosion Control on Construction Sites, 1 st Inter-Regional Conference on Environment-Water: Innovative Issues in Irrigation and Drainage, Lisbon, Portugal, September 1998 (Portuguese National Committee of ICID, 1998). 3. Roa, A. Screening of Polymers to Determine Their Potential Use on Construction Sites. Publication No , pp University of Idaho, Moscow, ID Roa-Espinosa, A., Bubenzer, G.D. and Miyashita, E. Sediment and Runoff Control on Construction Sites Using Four Application Methods of Polyacrylamide Mix. National Conference on Tools for Urban Water Resource Management and Protection, Chicago, February 7-10, 2000, pp. 278-(EPA, 2000). 5. Terrene Institute. Cheap, Efficient Erosion Control Really Works. Runoff Report. Volume 7, Number 3. May/June Tobiason, S, Jenkins, D, Molash, E, and Rush, S. (2001, January/February). Polymer Use and Testing for Erosion and Sediment Control on Construction Sites. Erosion Control Magazine. I.P-3.2 A P P E N D I X I P O L Y M E R A P P L I C A T I O N 0 1 / 0 2 / 0 7

133 PROPRIETARY STORMWATER DEVICES GENERAL Many companies offer devices or practices to treat stormwater runoff. These devices and practices use different mechanisms to remove pollutants from stormwater and therefore have differing levels of efficiency in meeting stormwater standards. Companies have the option to have their devices and practices reviewed to see if any stormwater requirements may be met by using their product. As of January 2, 2007 the following products (with accompanying design methodologies) have been reviewed and approved: ADVANTAGES Take up little space on site Usually out of sight May remove target contaminants for site Option for site retrofits and redevelopment DISADVANTAGES May not be cost effective Increased frequency of maintenance Reviewed Devices and Practices StormFilter Stormwater Management, Inc B NE Airport Way Portland, OR Design methodology reviewed and approved for meeting county stormwater standards for peak runoff rate, sediment control (new development and redevelopment), and oil and grease removal. A P P E N D I X I P R O P R I E T A R Y S T O R M W A T E R D E V I C E S 0 1 / 0 2 / 0 7 I.P-4.1

134 I.P-4.2 A P P E N D I X I P R O P R I E T A R Y S T O R M W A T E R D E V I C E S 0 1 / 0 2 / 0 7

135 RAIN GARDEN GENERAL Rain gardens are shallow depressions that are designed to collect stormwater and promote infiltration, minimizing the amount of runoff from a site. These infiltration areas are planted with native vegetation, which act as a natural sieve, absorbs excess nutrients, and filters out pollutants (refer to Native Plants, pg. I.N-1). Rain gardens should be located to intercept runoff along its natural path. When directing runoff naturally, grassed swales may be used as a conveyance structure (refer to Grassed Swale, pg. I.G-2). Rain gardens may be used on most any area of the site, excluding steep slopes, wetlands, floodplains, or in threatened or endangered species habitat. Rain gardens, while effective, generally are not designed for large storm events and, as a result, are best used in conjunction with other management practices. DESIGN BASIN Rain gardens should be designed to handle the 2-year, 24-hour storm and are most efficient with a storage volume that is equal to 10% of the impervious area of the site, with a maximum infiltration ponding depth of 12 inches. Side slopes of 6:1 or flatter are recommended to ensure the safety of the practice and to promote the establishment of vegetation. VEGETATION Rain gardens are planted or seeded with deeply rooted native vegetation systems because of their ability to absorb water, hardiness, natural beauty, and their ability to mitigate compaction. Plants must be selected to meet the needs of the site, wants of the individual users and, tolerate both wet and dry conditions. For all other selection criteria and specifics related to native species, please refer to the Native Plants section of this Appendix. To improve the year-round aesthetics of this practice, select species that bloom at various times throughout the spring and summer. SOILS ADVANTAGES Rain gardens are very versatile structures and can be constructed on most any type of soil. Clay soils will generally pond runoff water for at least 72 hours, while well drained or sandy soils will infiltrate water more quickly. Fine textured soils will require shallower ponding depths and increased area. CONSTRUCTION Reduces the amount of runoff from a site Improves aesthetics and provides habitat for mosquito predators and other wildlife Appropriate for either new or retrofit applications Low maintenance DISADVANTAGES Water quality impact from high traffic areas is unknown Longevity of the practice is dependant upon sediment accumulation and maintenance. Obtain all necessary permits and locate any underground utilities before construction begins Rain gardens should be located at least 10 feet from buildings To improve infiltration, compacted soils should be deep tilled to a depth of at least 12 inches (refer to Deep Tilling, pg. I.D-1) A P P E N D I X I R A I N G A R D E N 0 1 / 0 2 / 0 7 I.R-1.1

136 MAINTENANCE Rain gardens should be mulched until vegetation has become established, and once vegetation is established, it should be mulched as needed to help keep weeds down Plants should be watered at least weekly for the first 3 months, depending on the weather Vegetation should be weeded occasionally during the first year and at least twice a year (or as needed) after that All dead vegetation should be cut and removed once a year in the spring to allow for new vegetation growth METHOD TO DETERMINE PRACTICE EFFICIENCY Rain gardens are designed as an infiltration practice and do not significantly reduce the amount of suspended sediment in stormwater runoff. As a result, no efficiency is given for this practice. For purposes of Dane County Ordinances, rain gardens are not credited with sediment removal. An Example of a Rain Garden Source: Metropolitan Council. Adapted from Nassauer, et al., SOURCES 1. Applied Ecological Services. Confluence. Vol. 6, No. 1. Pg. 5. Spring Center for Watershed Protection. On-Lot Treatment Fact Sheet. Center for Watershed Protection, Inc., Ellicott City, MD How to Build A Rain Garden. brochure published by Dane County Lakes and Watershed Commission, 2006 (available at: 4. International Science News. Rain Gardens Help Replenish Dwindling Ground Water. April 25 th, Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Nassauer, J., B. Halverson, B., and Roos, S Bringing Garden Amenities Into Your Neighborhood: Infrastructure for Ecological Quality. Department of Landscape Architecture, University of Minnesota. Minneapolis. 7. Provisional Rain Garden Specification. City of Madison Engineering Division. December Taylor Creek Restoration Nurseries. Build Your Own Rain Garden. Perennial garden Design Sheet #1. 9. University of Wisconsin-Extension. Rain Gardens- A Household Way to Improve Water Quality in Your Community Virginia Department of Forestry. Rain Gardens. April 25 th, I.R-1.2 A P P E N D I X I R A I N G A R D E N 0 1 / 0 2 / 0 7

137 SEDIMENT BASIN GENERAL A sediment basin is a temporary ponding area, designed to catch and remove sediment from runoff while controlling the rate stormwater is released. Stormwater enters the basin and is impounded behind an embankment structure, temporarily ponding the water and allowing suspended sediments to settle out. As the water level in the basin rises and reaches its design depth, the water is drained by a riser, which releases only the relatively sediment free upper portion of the water column. As a result, the majority of the sediment is contained in the basin. Sediment basins, which consist of an embankment, a riser, and an outlet pipe, are generally temporary practices with a maximum life span of 18 months. If a permanent practice is desired, the sediment basin should be designed following the criteria set forth in the wet ponds section of this manual (refer to Wet Basin, pg. I.B-2). Sediment basins, which have a maximum efficiency of 70-80%, are applicable on sites with a maximum drainage area of 100 acres and are one of the most widely used practices for on-site erosion ADVANTAGES control. However, sediment basins should not be used on sites where the failure of the practice may endanger lives or property. DESIGN BASIN Cost-effective Capable of draining a large area (up to 100 acres) Maximum efficiency of 70-80% DISADVANTAGES Requires a large land area Ineffective with large storm events May require frequent maintenance Maximum lifespan of 18 months Ineffective for small sediment particles Sediment basins should be designed according to the individual site characteristics and must be capable of handling the runoff from the 10-year, 24-hour storm event. Basins, which may be designed with or without a permanent pool of water, are required to have a surface area at least 1.2 times the area needed Maximum design capacity 1-foot minimum freeboard Crest of emergency spillway Side slopes between 2:1 and 5:1 Sediment storage volume Riser crest (minimum 2 feet above sediment storage volume) Dewatering outlet Outlet An Example of a Sediment Basin Source: Adapted from Virginia Soil and Water Conservation Commission A P P E N D I X I S E D I M E N T B A S I N 0 1 / 0 2 / 0 7 I.S-1.1

138 to settle a mm particle. However, the surface area, as well as the rest of the features of the practice, should be designed with the individual site characteristics in mind. To increase trapping efficiency, the basin may be lengthened, thus increasing the volume and the detention time of the practice. However, trapping efficiency is a function of particle size rather than of basin size, and, as a result, larger basins may or may not increase efficiency. Basins should be teardrop shaped, with the inlet at the narrow end, and have a length to width ratio of at least 2:1 to ensure proper treatment of runoff. However, where site constraints prevent this design, baffles may be implemented to maximize the detention time and to prevent short-circuiting of the practice. The banks of the sediment basin shall be constructed of clean mineral soil, free of roots, debris, and oversized stones. They shall be constructed at least 10% higher than the design height to allow for any settlement that may occur. To encourage safety and stability, the banks shall have a maximum height of 15 feet. Those with heights between 10 and 15 feet must be at least 10 feet wide, while heights less than 10 feet require a minimum width of 8 feet. However, regardless of the height and width of the banks, slopes shall be designed with a horizontal to vertical ratio of 2:1 or flatter. SPILLWAYS AND OUTLETS Sediment basins shall be designed with a principal and an overflow spillway, whose size and capacity is dependent upon the drainage area served by the practice. At a minimum, however, principal spillways must be capable of handling the runoff from the 10-year, 24-hour storm event, while overflow spillways must be able to safely pass the 100- year, 24-hour storm event. Principal spillways, which provide the main outlet for the basin, consist of a riser and an outlet pipe. Risers control the volume of water present in the basin with a dewatering outlet, which can be designed in many ways to meet the needs of each site. The riser empties into the outlet pipe, which carries the water through the embankment structure to a stable outlet, where it is discharged. Risers and outlet pipes may be constructed from a variety of materials, such as PVC, corrugated metal, or concrete. Regardless of the material selected, all seams and joints should be sealed and watertight. Outlets must be held in place with a stable base, constructed of either steel or reinforced concrete. For sediment basins with risers less than 10 feet tall, the base must be at least twice as wide as the riser. Steel bases shall be at least ¼ inch thick and be overlain with at least 2 feet of compacted earth or stone. Concrete bases must be at least 18 inches thick and have the riser set in at least 9 inches. Sediment basins with risers that exceed heights of 10 feet require specific flotation calculations be performed using a safety factor of at least 1.2. Overflow spillways provide a safe outlet during very large storm events and prevent possible damage to the structure. They shall be designed trapezoidal in shape with a minimum bottom width of 8 feet. In addition, overflow spillways shall be at least 25 feet long and discharge at non-erosive velocities. Spillways must discharge to a stable outlet at nonerosive velocities. Outlets used for sediment basins shall follow the specifications discussed in the stone outlet protection portion of this manual (refer to Stone Outlet Protection, pg. I.S-10). CONSTRUCTION Sediment basins must be constructed and functional before any land upslope of the practice is disturbed Sediment basins should be constructed near the lowest point, near the edge of the site, to maximize the area served by the practice Sediment basins should be constructed with access for maintenance activities (such as clean out and disposal of accumulated sediment) The embankments must be constructed upon scarified ground (to a depth of 6 inches) and may not be built on frozen ground Sediment basins should be removed after the site has been stabilized and permanent BMPs have been established I.S-1.2 A P P E N D I X I S E D I M E N T B A S I N 0 1 / 0 2 / 0 7

139 MAINTENANCE The entire structure should be inspected weekly for damage and signs of erosion, with necessary repairs made immediately Accumulated sediment must be removed when it reaches ½ of the basin storage capacity METHOD TO DETERMINE PRACTICE EFFICIENCY Sediment basins reduce the flow velocity of runoff, allowing suspended particles to settle out. The efficiency for this practice is dependant upon the size of the basin, the size of the drainage area, and other site characteristics. As a result, the efficiency for this practice must be calculated using factors unique to each site. For more information, please refer to Appendix IV, Basin Efficiency, on page IV.1. SOURCES 1. Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis National Catalog of Erosion and Sediment Control and Storm Water Management. Guidelines for Community Assistance. United States Department of Agriculture, Natural Resources Conservation Service. Washington, D.C Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Sediment Basin. Conservation Practice Standard. Wisconsin Department of Natural Resources. November Schueler, T. R Improving the Sediment Trapping Efficiency of Sediment Basins. Center for Watershed Protection. Center for Watershed Protection, Inc., Ellicott City, MD. 6. Virginia Erosion and Sediment Control Handbook. Virginia Department of Conservation and Recreation. Division of Soil and Water Conservation. Richmond Wisconsin Field Office Technical Guide. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C A P P E N D I X I S E D I M E N T B A S I N 0 1 / 0 2 / 0 7 I.S-1.3

140 I.S-1.4 A P P E N D I X I S E D I M E N T B A S I N 0 1 / 0 2 / 0 7

141 SEDIMENT TRAP GENERAL A sediment trap is a small, temporary ponding area designed to catch and remove sediment from runoff. Runoff enters the trap and is impounded in a basin behind a stone weeper, reducing the velocity of the runoff and allowing suspended sediments to settle out. Sediment traps are applicable on sites with drainage areas of less than 5 acres and are typically placed in swales and other conveyance channels (refer to Grassed Swale, pg. I.G-2). To maximize the effectiveness of this practice, they should be located on the lowest point, near the edge of the site, to maximize the area served by the trap. Because sediment traps are, at best, percent efficient and are ineffective for smaller sized sediments, they are best used in conjunction with other BMPs. DESIGN Sediment traps must be designed for water quality control for storms up to the 1-year, 24- hour storm event. In addition, traps must also be capable of safely passing the 10-year, 24-hour storm event. Lengthening the basin, which increases the volume of the practice and detention time, may increase trapping efficiency. However, trapping efficiency is a function of particle size rather than of basin size, and, as a result, larger basins may or may not increase efficiency. BASIN The ponding area of a sediment trap shall have, at a minimum, a 2:1 length to width ratio. The banks of the basin shall be compacted during construction and must possess a maximum height of 5 feet, with a minimum top width of 4 feet and slopes 2:1 or flatter. The basin should be seeded, mulched, and lined with a geotextile filter fabric, whose opening size will vary depending upon the soil type that is present on site. ADVANTAGES OUTLETS Cost-effective Relatively easy to construct Low Maintenance DISADVANTAGES Low trapping efficiency for fine particles Ineffective with large storm events Maximum life span of 18 months Maximum drainage area of 5 acres The crest of the outlet must be 1 foot below the top of the embankment, with weir length and stone size dependant upon the area drained by the practice. All other outlet criteria for this practice should follow the design specifications discussed in the stone weeper section of this appendix (refer to Stone Weeper, pg. I.S-12). CONSTRUCTION Sediment traps should be operational before site grading begins Sediment traps should be removed after the site has been permanently stabilized MAINTENANCE Accumulated sediment shall be removed when it reaches ½ of the outlet Sediment traps shall be inspected for damage and repaired after each rainfall event If the sediment trap does not drain completely within 24 hours of a storm event, the geotextile and stone outlet should be cleaned A P P E N D I X I S E D I M E N T T R A P 0 1 / 0 2 / 0 7 I.S-2.1

142 METHOD TO DETERMINE PRACTICE EFFICIENCY Sediment traps reduce the flow velocity and allow sediment to settle out. The efficiency for this practice is dependent upon the proper design, installation, and maintenance of the structure. However, in general, sediment trap efficiency follows the ensuing graph. Approximate Trapping Efficiency Drainage area equals: Acres Acres Acres Acres Acre Particle Size (Microns) 2:1 maximum side slope 4 ft minimum 2:1 maximum side slope 1 clear stone- min. thickness of 1 ft 5 ft maximum Design settled top 21 minimum Cross Section 4 ft minimum Overfill 6 for settlement Geotextile filter fabric 5 ft maximum fill 2:1 maximum side slope Geotextile filter fabric 3 ft minimum Profile 1:1 maximum side slope Example of a Sediment Trap Source: Adapted from North Carolina Erosion and Sediment Control Planning and Design Manual A P P E N D I X I S E D I M E N T T R A P 0 1 / 0 2 / 0 7 I.S-2.2

143 SOURCES 1. Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis National Catalog of Erosion and Sediment Control and Storm Water Management. Guidelines for Community Assistance. United States Department of Agriculture, Natural Resources Conservation Service. Washington, D.C Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul Sediment Trap. Conservation Practice Standard. Wisconsin Department of Natural Resources. November A P P E N D I X I S E D I M E N T T R A P 0 1 / 0 2 / 0 7 I.S-2.3

144 A P P E N D I X I S E D I M E N T T R A P 0 1 / 0 2 / 0 7 I.S-2.4

145 SEEDING (PERMANENT) GENERAL Permanent seeding stabilizes disturbed areas with perennial vegetation. Dense, established vegetation protects the soil from raindrop impact, reduces flow velocities, increases infiltration and reduces soil loss from the site and is the most effective erosion control practice available. In addition, seeding is economical and adaptable to most any area, improving aesthetics and reducing dust and mud problems that are common on many construction sites. Permanent seeding is applicable on any area of the site on which final grading has been performed or on areas that will remain undisturbed for over 1 year. Permanent seeding can be performed until September 15 th, while dormant seeding should be completed after November 1 st. Seeding outside these dates greatly increases the failure rate of the practice and may require seeding to be repeated. To prevent erosion during the establishment period, additional management practices are often required (refer to Mulching, pg. I.M-2, Erosion Matting, pg. I.E-1, or Seeding, Temporary, pg. I.S-4). DESIGN VEGETATION Permanent vegetation provides effective erosion control only once densely established. Dense is defined as a stand of 6-8 inch vegetation that uniformly covers at least 70% of a representative 1 square meter plot. As a result, until vegetation is firmly established (generally 60 days after it has been planted) it cannot be relied upon to prevent soil loss from the site. ADVANTAGES Established vegetation can reduce erosion rates by up to 99% Cost-effective Easy to apply Requires little maintenance Increases infiltration and water retention Reduces dust DISADVANTAGES Use limited by the growing season Requires the addition of fertilizer on infertile soils greatly depending upon the characteristics of the site and the long-term maintenance requirements of the species. Soil type, ph, slope, site use, maintenance, growth rate, use of native or non-native species, and the time of year it is planted are all factors that must be weighed when selecting vegetation. Native species require a longer period of time to establish and are generally more costly and more difficult to establish than non-native vegetation. However, they offer many advantages over non-native vegetation. For further information on native species, please refer to the Native Vegetation section of this Appendix (pg. I.N-1). Careful species selection is crucial to avoid planting exotic or invasive species, as they may upset the local ecosystem s balance. In situations where establishment is more difficult, companion vegetation may be used in addition to or as an alternative to mulching. It provides cover and stabilizes the soil on steep slopes, during late planting schedules, and to give slower growing plants an opportunity to become established. Relatively noncompetitive, annual species of vegetation, such as those listed in the Temporary Seeding section of this appendix, may be used for this purpose, provided the seeding rate is cut in half. The species of vegetation selected will vary A P P E N D I X I S E E D I N G ( P E R M A N E N T ) 0 1 / 0 2 / 0 7 I.S-3.1

146 SEEDBED PREPARATION To be successful, permanent seeding requires a properly prepared seedbed. Areas that are limited by poorly drained soils, steep slopes, or that allow concentrated flow to develop should not be used for seedbeds unless amendments to correct the situation are made. Soils should be tested for nutrient content and ph to determine the amount, if any, of fertilizer or lime required. Over-application of these soil amendments is costly, ineffective, and may cause serious pollution problems. As a result, lime and slow releasing fertilizers should be applied only as needed and shall be incorporated into the soil to keep them on site and in the root zone. The organic content of the soil is also an important consideration when preparing the seedbed. Soils rich in organic matter possess high levels of nutrients and microorganisms, which improve the growth rate and require less fertilizer to be applied and increase the porosity of the soils. To improve the organic content of the soil, organic compost may be incorporated into the top ten inches of soil. A minimum of 3-4 inches of topsoil is required for permanent vegetation. It should be loose, uniform, and well pulverized to promote rapid growth. Compacted soils should be loosened to a depth of at least 6-8 inches by using a chisel plow or similar implement to ensure adequate pore space. APPLICATION Seed should be applied uniformly following the supplier s recommendations by broadcast seeding, hydroseeding, or drill seeding. Broadcast seeding involves scattering the seeds on the soil surface by hand or mechanical means and is best utilized on smaller areas and for patching applications. After application, the site should be raked and firmed with a roller or cultipacker. Seeded areas should then be mulched to provide protection for the seed and to reduce erosion before the vegetation becomes established (refer to Mulching, pg. I.M-2). Hydroseeding and drill seeding are more costly than broadcast seeding and are used on larger sites to maximize the application s cost effectiveness. Hydroseeding, a method that mixes the seed and water together into a slurry, is applied on areas that may be difficult to seed with alternative means. Other amendments, such as tackifiers, polymers, fertilizers, and/or fiber mulch are often added to the slurry, which is sprayed on, to protect the seed and to promote its growth. Drill seeding utilizes a drill or cultipacker seeder to inject the seeds beneath the soil surface. Seeding depth is set based upon the supplier s specifications, but generally is ¼ - ½ inch deep for grasses and legumes. Drilling, while more costly than broadcast or hydroseeding, is generally very effective when performed properly because the seed is protected from wind, water, and wildlife. CONSTRUCTION All grading and tracking shall be completed before permanent seeding begins All management practices should be installed and online before seeding Seedbed should be adequately prepared before seeding begins To promote growth, seeding should not be performed during excessively wet conditions, as soils may become excessively compacted MAINTENANCE Inspect seeded areas weekly after planting to ensure that vegetation is adequately established Seeded areas shall be inspected after each rainfall event to check for evidence of erosion and bare spots Reseed as necessary Add fertilizer as necessary at proper rates Mowing and spraying may be necessary to control weed growth Water seeded areas regularly until they become established I.S-3.2 A P P E N D I X I S E E D I N G ( P E R M A N E N T ) 0 1 / 0 2 / 0 7

147 METHOD TO DETERMINE PRACTICE EFFICIENCY The efficiency of this practice is derived from reducing the amount of time that the site is left bare and exposed. To determine the efficiency for this practice, use the new, shortened exposure time and replace the pre-existing one in the USLE and recalculate. The difference between the two equations is the efficiency for the practice. SOURCES 1. Indiana Department of Natural Resources. Indiana Handbook for Erosion Control in Developing Areas Division of Soil Conservation. 2. Metropolitan Council Minnesota Urban Small Sites BMP Manual. 3. Minnesota Pollution Control Agency Protecting Water Quality in Urban Areas, A Manual Natural Resources Conservation Service. Natural Resources Conservation Service Natural Resources Conservation Service Planning and Design Manual. 5. Natural Resources Conservation Service National Catalog of Erosion and Sediment Control and Storm Water Management. Guidelines for Community Assistance. United States Department of Agriculture. 6. Seeding For Construction Site Erosion Control. Conservation Practice Standard. Wisconsin Department of Natural Resources. November Stormwater Manager s Resource Center USDA. Wisconsin Field Office Technical Guide A P P E N D I X I S E E D I N G ( P E R M A N E N T ) 0 1 / 0 2 / 0 7 I.S-3.3

148 I.S-3.4 A P P E N D I X I S E E D I N G ( P E R M A N E N T ) 0 1 / 0 2 / 0 7

149 SEEDING (TEMPORARY) GENERAL Temporary seeding stabilizes disturbed areas with fast growing annual grasses, small grains, or legumes until permanent vegetation can be established. Dense, established vegetation protects the soil from raindrop impact, reduces flow velocities, increases infiltration, reduces soil loss from the site and is the most effective erosion control practice available. In addition, temporary seeding is economical and adds organic matter to the soil and reduces dust and mud problems that are common on many construction sites. Temporary seeding is applicable on any area of the site that will remain inactive for at least 21 days but less than 1 year. It is often used to prevent erosion between construction activities and during the winter months if established early enough. Due to its short-term nature, temporary seeding may be ineffective on its own and should be used in conjunction with other management practices. DESIGN VEGETATION Temporary vegetation provides effective erosion control only once densely established. Dense is defined as a stand of 6-8 inch vegetation that uniformly covers at least 70% of a representative 1 square meter plot. Until vegetation is permanently established on site (generally 60 days after it has been planted) it should not be relied upon to prevent soil loss. The species of vegetation selected will vary depending upon the soil type, slope, and the time of year it is applied. Common types of temporary vegetation include Wheat, Rye, Spring Oats, Annual Ryegrass and Sudangrass. These annual species establish themselves quickly under the proper growing conditions and require minimal maintenance. ADVANTAGES Cost-effective Easy to apply Requires little maintenance Increases infiltration and water retention Adds organic matter for permanent seeding Reduces dust DISADVANTAGES Use limited by the growing season Maximum life span of 1 year Requires the addition of fertilizer on infertile soils Care should be taken when selecting a species to avoid the use of exotic or invasive species, as they may upset the balance of the local ecosystem. Type of Cover Spring Oats Sudangrass Cereal Rye* Winter Wheat* Annual Ryegrass Minimum Seeding Rate 3 bushels per acre 35 lbs. per acre 2 bushels per acre 2 bushels per acre 25 lbs. per acre * Rye and winter wheat will be destroyed by seedbed preparation at the next permanent seeding period Source: Natural Resources Conservation Service The seeding rates, depths, and times of application supplied here are intended only as general guidelines. All manufacturers guidelines should be carefully followed to ensure the success of this practice. A P P E N D I X I S E E D I N G ( T E M P O R A R Y ) 0 1 / 0 2 / 0 7 I.S-4.1

150 SEEDBED PREPARATION To be successful, permanent seeding requires a properly prepared seedbed. Areas that are limited by poorly drained soils, steep slopes, or that allow concentrated flow to develop should not be used for seedbeds unless amendments are made. Soils should be tested for nutrient content and ph to determine the amount, if any, of fertilizer or lime required. Over-application of these soil amendments is costly, ineffective, and may cause serious pollution problems. As a result, lime and slow releasing fertilizers should be applied only as needed and should be incorporated into the soil to keep them on site and in the root zone. The organic content of the soil is also an important consideration when preparing the seedbed. Soils rich in organic matter possess high levels of nutrients and microorganisms, which improve the growth rate, require less fertilizer to be applied, and increase the porosity of the soil. To improve the organic content of the soil, organic compost may be incorporated into the top ten inches of soil. A minimum of 3-4 inches of topsoil is required for permanent vegetation. It should be loose, uniform, and well pulverized to promote rapid growth. Compacted soils should be loosened to a depth of at least 6-8 inches by using a chisel plow or similar implement to ensure adequate pore space. APPLICATION Seed should be applied uniformly following the supplier s recommendations by broadcast seeding, hydroseeding, or drill seeding. Broadcast seeding involves scattering the seeds on the soil surface by hand or mechanical means and is best utilized on smaller areas and for patching applications. After application, the site should be raked and firmed with a roller or cultipacker. Seeded areas should then be mulched to provide protection for the seed and to reduce erosion before the vegetation becomes established (refer to Mulching, pg. M-2.1). Hydroseeding and drill seeding are more costly than broadcast seeding and are used on larger sites to maximize the application s cost effectiveness. Hydroseeding, a method that mixes the seed and water together into a slurry, is applied on areas that may be difficult to seed with alternative means. Other amendments, such as tackifiers, polymers, fertilizers, and/or fiber mulch are often added to the slurry, which is sprayed on, to protect the seed and to promote its growth. Drill seeding utilizes a drill or cultipacker seeder to inject the seeds beneath the soil surface. Seed depth is set based upon the supplier s specifications, but generally is ¼ - ½ inch deep for grasses and legumes. Drilling, while more costly than broadcast or hydroseeding, is generally very effective when performed properly because the seed is protected from wind, water, and wildlife. CONSTRUCTION All tracking and grading should be completed before temporary seeding begins All management practices should be installed and online before seeding Seedbed should be adequately prepared before seeding begins To promote growth, seeding should not be performed during excessively wet conditions, as soils may become excessively compacted MAINTENANCE Inspect seeded areas weekly after planting to ensure that vegetation is adequately established, reseed as necessary Seeded areas should be inspected after each rainfall event to check for evidence of erosion and bare spots Add fertilizer as necessary at proper rates Water seeded areas regularly until they become established METHOD TO DETERMINE PRACTICE EFFICIENCY The efficiency of this practice is derived from reducing the amount of time that the site is left bare and exposed. To determine the efficiency for this practice, use the new, shortened exposure time and replace the pre-existing one in the USLE and recalculate. The difference between the two equations is the efficiency for the practice. I.S-4.2 A P P E N D I X I S E E D I N G ( T E M P O R A R Y ) 0 1 / 0 2 / 0 7

151 SOURCES 1. Indiana Handbook for Erosion Control in Developing Areas. Indiana Department of Natural Resources, Division of Soil Conservation. Indianapolis Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis National Catalog of Erosion and Sediment Control and Stormwater Management. Guidelines for Community Assistance. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul Seeding For Construction Site Erosion Control. Conservation Practice Standard. Wisconsin Department of Natural Resources. November Water Related Best Management Practices in the Landscape. U.S. Department of Agriculture, Natural Resources Conservation Service and Center for Sustainable Design at Mississippi State University. Washington, D.C Wisconsin Field Office Technical Guide. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C A P P E N D I X I S E E D I N G ( T E M P O R A R Y ) 0 1 / 0 2 / 0 7 I.S-4.3

152 I.S-4.4 A P P E N D I X I S E E D I N G ( T E M P O R A R Y ) 0 1 / 0 2 / 0 7

153 SILT FENCE GENERAL A silt fence is a temporary structure, constructed of woven geotextile fabric attached to posts, which minimizes the loss of sediment from a site and prevents sheet and rill erosion. These structures intercept runoff and force it to pass through the fabric, reducing its velocity and allowing suspended sediments to settle out upslope of the silt fence. Silt fences are typically used on construction sites to trap sediment on site and around soil piles and may not be used in channels, gullies, ditches, streams, or in any other area where concentrated flow may occur. These structures, which may be prefabricated or constructed on site, should be installed prior to site disturbance. Because silt fences have a high rate of failure without proper installation and maintenance, they are best used in conjunction with other BMPs. Silt fences must be removed and disposed of after the site has been stabilized and permanent BMPs have been established. DESIGN Silt fences must be designed to handle the runoff from the 10-year, 24-hour storm event, with a maximum drainage area of 0.25 acres per 100 feet of fence. ADVANTAGES Low cost Versatile DISADVANTAGES Ineffective for concentrated flows Requires frequent maintenance Maximum life span of 1 year Drainage area should not exceed 0.25 acres per 100 feet of fence length High rates of failure if not installed properly Ineffective on slopes greater than 50% Labor-intensive to install Silt fence height will vary upon the site and application of the practice, but must be between 14 and 28 inches, measured from the top of the fabric to the soil surface, and does not include any portion of the fence below ground. Silt fences should be installed in a crescent shape, parallel to the contour of the land, with the ends placed upslope of the center. This practice prevents water from escaping around the ends of the fence and forces it to pond behind it. Ponding depth must not exceed 2 feet, as greater depths greatly increase the likelihood of failure. Stabilized outlets should be placed at the ends of the fence to provide an overflow and protect the fence during larger storm events. Woven Geotextile Fabric 4 4 Hard Wood Stake Proper Entrenching of a Silt Fence Source: Wisconsin Department of Commerce A P P E N D I X I S I L T F E N C E 0 1 / 0 2 / 0 7 I.S-5.1

154 Silt fences are not recommended for use on slopes that exceed a 2:1 ratio. However, they may be used in series for flatter slopes if the spacing guidelines below are followed. Additional structures, however, do not increase the permissible slope length. MATERIALS FABRIC SILT FENCE SPACING GUIDELINES % SLOPE MAXIMUM SLOPE LENGTH DRAINING TO FENCE < 2% 100 feet 2 5% 75 feet 5 10% 50 feet 10 20% 25 feet > 20% 15 feet Source: Adapted from WDNR A woven geotextile fabric should be used and must meet the following criteria: Minimum grab strength of 100 pounds Pore size of between 50 and 140 microns Ultra-violet radiation stability of 90% (Using test method ASTM D-4355) The use of a top support device, such as a heavy-duty nylon cord or equivalent The fabric should be anchored by burying at least 8 inches in a 4x4-inch trench, with the bottom 4 inches of fabric extending upslope. Joints in the fabric should be minimized to prevent failure of the fence. Where joints are necessary, each end of the fabric should be securely fastened to a post. The posts should then be wrapped around each other to produce a stable, secure joint or may be overlapped to the next post. support. As a result, only the minimum dimensions are listed here. Steel posts must be at least 5 feet long with a strength of 1.33 lbs/ft. (2 kg/m) and have projections for the attachment of fasteners. Hardwood posts must be air or kiln dried and measure at least 1 1/8 inches square, with a minimum length of 3 feet for a 24-inch fence. All posts should be driven at least 20 inches below ground and should be spaced a maximum of 8 feet apart to provide proper support. The geotextile fabric should be attached in at least 3 places to the posts on the upslope side with either ½ inch staples, 50 lb. plastic zip fasteners, or wire fasteners. To prevent damage to the fabric from fasteners, the protruding ends should be pointed away from the fabric. For added strength and stability, silt fences may be reinforced with wire mesh. When used, the mesh should be installed behind (downslope) the geotextile fabric and in front (upslope) of the posts. The wire mesh should be attached to the fabric in at least 3 places, using wire fasteners spaced at a minimum distance of 2 feet. MAINTENANCE Silt fences should be inspected weekly and after each rainfall for damage all repairs should be made immediately Accumulated sediment should be removed once it reaches ½ the height of the fence to ensure that a proper storage volume is preserved behind the fence Silt fences should be replaced when worn out METHOD TO DETERMINE PRACTICE EFFICIENCY A silt fence prevents soil loss by reducing the flow velocity of runoff by forcing it through fabric. When properly installed and maintained, a silt fence with a 20-micron pore size yields an efficiency of 42%. SUPPORT Silt fences may be supported by either steel or hardwood posts. The strength, dimensions, and depth of the posts will vary upon the load that they are designed to I.S-5.2 A P P E N D I X I S I L T F E N C E 0 1 / 0 2 / 0 7

155 PROPER SILT FENCE INSTALLATION 1. Dig a 4 x4 trench 2. Stake fence on downslope side laying 8 of fabric in trench Flow 3. At joints, overlap for distance between 2 stakes Flow 4. Backfill and compact soil on the upslope side Flow Flow Source: North Carolina Erosion and Sediment Control Planning and Design Manual SOURCES 1. Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis North Carolina Erosion and Sediment Control Planning and Design Manual. North Carolina Sediment Control Commission, Department of Natural Resources and Community Development Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Silt Fence. Conservation Practice Standard. Wisconsin Department of Natural Resources. November A P P E N D I X I S I L T F E N C E 0 1 / 0 2 / 0 7 I.S-5.3

156 I.S-5.4 A P P E N D I X I S I L T F E N C E 0 1 / 0 2 / 0 7

157 SLOPE DRAIN (TEMPORARY) GENERAL A temporary slope drain is a flexible pipe that is designed to carry concentrated runoff from the top of a slope to the base of the slope without causing erosion. Runoff is intercepted upslope of a disturbed area and is routed to the slope drain, which carries the runoff to a stable outlet, where it is released at a non-erosive velocity into a sediment trap or basin. Temporary slope drains are applicable on sites with a maximum drainage area of 5 acres and on slopes 3 percent or steeper that have not yet been stabilized. This practice is used in conjunction with several other BMPs such as temporary diversions, stone outlet protection, and sediment traps and basins DESIGN PIPE SELECTION AND INSTALLATION The pipe should be constructed of a durable, ADVANTAGES Prevents gully erosion Relatively easy to install Inexpensive DISADVANTAGES Maximum life span of 2 years Maximum drainage area of 5 acres flexible, corrugated plastic with secure, watertight joints and a flared inlet portion. The size of the pipe will vary depending upon the drainage area of the site, but must not have a diameter that exceeds 30 inches. To prevent failure of the device during large storm events, the soil surrounding the pipe must be hand compacted, with the portion of the diversion or berm above the pipe at least twice the height of the pipe. In cases where the normal berm or 5 Berm height should equal twice the pipe diameter Geotextile filter fabric 3% Slope or greater Standard flared entrance section 4 Minimum length at less than 1% slope Proper Slope Drain Installation Source: Natural Resources Conservation Service National Catalog of Erosion and Sediment Control and Storm Water Management A P P E N D I X I S L O P E D R A I N, T E M P O R A R Y 0 1 / 0 2 / 0 7 I.S-6.1

158 Proper Sizing of Slope Drains Maximum Drainage Area (acres) Pipe Diameter (inches) Source: NRCS Planning and Design Manual diversion height is less than this, the portion above the pipe will be returned to the previous height by descending with a slope of 3:1 or flatter (refer to Temporary Diversion, pg. I.D-3). The pipe should be anchored to the slope according to the manufacturer s installation instructions. However, regardless of the model selected, it must be secured to the slope with grommets in at least 2 places spaced no more than 10 feet apart. At the base of the slope, a minimum of 4 feet of pipe should have slope of 1% or flatter before discharging in order to reduce the velocity of the runoff. INLETS To prevent erosion of the diversion structure, the inlet of the slope drain should be underlain with geotextile filter fabric. The type of filter fabric that is selected will vary upon the individual characteristics of the site, but must extend at least 5 feet from the inlet, with the edges keyed at least 6 inches into the ground. OUTLETS Proper Keying of Geotextile Filter Fabric Source: Greenfix America While all outlets must discharge runoff at nonerosive velocities, the outlet structure used will vary depending upon the amount of cover that is present on site. Unstabilized sites must be discharged into a sediment trap or basin, while stabilized sites may drain into a stone outlet (refer to Sediment Trap, pg. I.S-2; Sediment Basin, pg. I.S-1; or Stone Outlet Protection, pg. I.S-10). Geotextile Apron 5 Standard Flared Entrance Section 5 Compacted Earth Dike Stabilized Outlet Structure Anchors An Example of a Temporary Slope Drain Source: Natural Resources Conservation Service National Catalog of Erosion and Sediment Control and Storm Water Management I.S-6.2 A P P E N D I X I S L O P E D R A I N, T E M P O R A R Y 0 1 / 0 2 / 0 7

159 CONSTRUCTION & MAINTENANCE Construction of slope drains should be completed before any disturbance begins Slope drains should be inspected weekly and after each rainfall event and repairs made immediately METHOD TO DETERMINE PRACTICE EFFICIENCY The efficiency for this practice is derived from the reduction in slope length that it provides. To calculate the efficiency, simply use the new, reduced slope length in place of the pre-existing one in the USLE and recalculate. The difference between the two completed equations is the efficiency for the practice. SOURCES 1. Greenfix America. Product Brochure National Catalog of Erosion and Sediment Control and Storm Water Management. Guidelines for Community Assistance. United States Department of Agriculture, Natural Resources Conservation Service. Washington, D.C Natural Resources Conservation Service Planning and Design Manual. Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Protecting Water Quality in Urban Areas, A Manual. Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul A P P E N D I X I S L O P E D R A I N, T E M P O R A R Y 0 1 / 0 2 / 0 7 I.S-6.3

160 I.S-6.4 A P P E N D I X I S L O P E D R A I N, T E M P O R A R Y 0 1 / 0 2 / 0 7

161 SOD GENERAL Sod stabilizes disturbed areas with dense, permanent vegetative cover immediately after it is installed. Dense, established vegetation protects the soil from raindrop impact, reduces flow velocities, increases infiltration and reduces soil loss from the site and is the most effective immediate site stabilization practice available. Sod is applicable on any area of the site on which final grading has been performed. Most often, sod is applied to critical areas where immediate vegetation is required or on areas where seed establishment is difficult, such as in channels or on steeper slopes. It is also used as an alternative to seeding in residential and commercial applications and on golf courses and other areas where aesthetics are important. VEGETATION Sod, if properly maintained, provides dense vegetative cover throughout its life. However, if the sod is not properly cared for, the vegetation will die and the practice will be rendered ineffective. As a result, only densely established vegetation should be relied upon to provide erosion control. The species of vegetation selected will vary greatly depending upon the characteristics of the site and the long-term maintenance requirements of the species. Soil type, ph, slope, site use, maintenance, growth rate, and the time of year it is planted are all factors that must be weighed when selecting sod. In addition, sod that is to be applied in channels should be capable of withstanding the designed flow velocity for the channel. Only healthy, high quality sod that is free of exotic or invasive species, disease, and insect problems should be selected for use. Sod should be harvested uniformly under proper conditions. Cutting during extremely ADVANTAGES Established vegetation can reduce erosion rates by up to 99% Provides immediate erosion control Applicable on steep slopes, channels, and other areas where seed establishment may be difficult Good success rate if properly applied and maintained Reduces dust DISADVANTAGES Requires frequent irrigation until the sod becomes established More costly than other vegetative methods Requires careful handling Requires at least 30 days to become established wet or dry weather may result in the failure of the practice and require re-application. To promote the success and viability of the practice, sod should be harvested no more than 36 hours before it is installed on site. SURFACE PREPARATION To be successful, sod requires a properly prepared surface. Areas with poorly drained soils may require that amendments be made before sod is installed. Topsoil should be loose, uniform, well pulverized, and available in sufficient quantities to promote rapid growth. Compacted soils should be loosened to a depth of at least 6-8 inches by using a chisel plow or similar implement to ensure adequate pore space. If less than 3-4 inches of topsoil are present on site, additional soil may be required. Soils should be tested for nutrient content and ph to determine the amount, if any, of fertilizer or lime required. Over-application of these soil amendments is costly, ineffective, and may cause serious pollution problems. As a result, lime and slow releasing A P P E N D I X I S O D 0 1 / 0 2 / 0 7 I.S-7.1

162 fertilizers should be applied only as needed and should be incorporated into the soil to keep them on site and in the root zone. The organic content of the soil is also an important consideration when preparing the surface. Soils rich in organic matter possess high levels of nutrients and microorganisms, which improve the growth rate, require less fertilizer to be applied, and increase the porosity of the soils. To improve the organic content of the soil, organic compost may be incorporated into the top ten inches of soil. To ensure adequate contact between sod and the soil, irregularities in the soil should be removed prior to application by smoothing and firming the soil with lightweight equipment. INSTALLATION Sod should not be applied on compacted soils, frozen soils, or on areas that have been treated with pesticides. Sod should be installed from March 15 th to October 20 th. However, installation may take place outside of these dates as long as temperatures remain above freezing and at least 30 days are available for establishment. Sod should be applied in a brick-like pattern perpendicular to the direction of flow. Care should be taken to avoid stretching and overlapping the sod. Joints in the sod should be tightly butted together, with angled ends overlapping each other. The sod should be moist and, on hot days, stored in the shade prior to application. The soil should also be watered lightly before installation to cool the soil and ensure the health of the roots. On slopes, installation should begin on the downslope edge and proceed upslope. On slopes that are steeper than 3:1 or in areas of concentrated flow, sod should be anchored with pegs or netting. After application, the sod should be rolled and irrigated until the soil is damp 4 inches below the surface. Irrigation should continue until the sod has become firmly rooted. Rolling, performed with a lightweight implement, encourages contact between the roots and the soil surface, while irrigation provides a favorable medium for growth. Together, these practices should ensure the successful growth of the sod and the erosion control capabilities of the vegetation. CONSTRUCTION All tracking and grading should be completed before sod is installed Sod should be installed no more than seven days after final grading of the site All management practices should be installed and online before sod is applied Surface should be adequately prepared and cleared of all trash and debris before sod is installed To promote growth, sod should not be installed during excessively wet or dry conditions MAINTENANCE Inspect sodded areas after all storm events for damage and repair or replace as necessary Sod requires at least 1 inch of water per week to become properly established Add fertilizer as necessary at proper rates Mowing should not be attempted for at least 3 weeks after application and should not at any time remove more than 1/3 of the shoot (grass should be maintained with a height of 2-3 inches) METHOD TO DETERMINE PRACTICE EFFICIENCY The efficiency of this practice is derived from reducing the amount of time that the site is left bare and exposed. Soil loss effectively ends with sod installation, which shortens the exposure time by 60 days when compared to seed and mulch. To determine the efficiency for this practice, use the new, shortened exposure time and replace the preexisting one in the USLE and recalculate. The difference between the two equations is the efficiency for the practice. I.S-7.2 A P P E N D I X I S O D 0 1 / 0 2 / 0 7

163 Flow Correct installation of adjoining pieces Correct installation of sod (May require staking) Incorrect installation of adjoining pieces Rolling the sod to achieve firm contact with the soil Irrigate immediately after installation to a depth of 4 inches Do not mow until the sod has become established Proper Installation and Maintenance of Sod Source: Adapted from the Natural Resources Conservation Service A P P E N D I X I S O D 0 1 / 0 2 / 0 7 I.S-7.3

164 SOURCES 1. Indiana Handbook for Erosion Control in Developing Areas. Indiana Department of Natural Resources, Division of Soil Conservation. Indianapolis Minnesota Pollution Control Agency Protecting Water Quality in Urban Areas, A Manual. Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis National Catalog of Erosion and Sediment Control and Storm Water Management. Guidelines for Community Assistance. United States Department of Agriculture, Natural Resources Conservation Service. Washington, D.C Natural Resources Conservation Service. Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Natural Resources Conservation Service. Water Related Best Management Practices in the Landscape. U.S. Department of Agriculture, Natural Resources Conservation Service and Center for Sustainable Design at Mississippi State University. Washington, D.C I.S-7.4 A P P E N D I X I S O D 0 1 / 0 2 / 0 7

165 STONE CHECK DAM GENERAL A stone check dam is a barrier constructed of stone that reduces the flow velocity of runoff, while minimizing channel erosion and promoting sediment deposition. Stormwater enters a swale or vegetated ditch and, under normal circumstances, is ponded temporarily behind the check dam in the sediment control basin. Ponding allows sediment and other pollutants to settle out, while allowing some water to infiltrate and evaporate. The water that remains is slowly passed through the check dam continuing on towards the outfall. In high flow situations, runoff is conveyed over the top of the stone. Check dams are best used in conjunction with other BMPs such as erosion blankets or mats (refer to Erosion Matting, pg. I.E-1). Stone check dams may be permanent or temporary and can be used in swales or vegetated ditches with a maximum drainage area of 10 acres. Check dams are often used on sites with ADVANTAGES Low cost Relatively easy to construct Reduces erosion and promotes sediment deposition DISADVANTAGES Requires periodic sediment removal Temporary check dams may be difficult to remove Effective only in channels that drain 10 acres or less Ineffective with large storm events slopes that are steeper than desired. Depending upon the slope of the channel and the individual site, multiple check dams may be needed to control runoff velocity. 2:1 Max. Slope 2 Min. Width 2:1 Max. Slope Natural Ground Flow 3-6 inch Clear Stone 1 Min. 5 Max. Sediment Storage 1-Foot Thickness of #2 Clear Stone SECTION VIEW Geotextile Filter Fabric, Type R A B A Geotextile Filter Fabric, Type R FRONT VIEW Sediment Storage Typical Stone Check Dam A P P E N D I X I S T O N E C H E C K D A M 0 1 / 0 2 / 0 7 I.S-8.1

166 DESIGN Check dams should consist of, at a minimum, a 1-foot layer of 1-inch washed stone over a 1-foot layer of 3 to 6-inch clear stone, free of fines and sand, underlain with a geotextile fabric. The size of the structure will depend upon the site, but should be 1-5 feet in height; have a minimum width of 2 feet; and should extend across the entire conveyance structure. In addition, the slopes should have a maximum ratio of 2:1, as greater slopes may become unstable and require excessive maintenance. The center of the check dam should be, at a minimum, 6 inches lower than the edges to allow water to flow over the top of the structure. SEDIMENT STORAGE BASIN The sediment control basin, which allows sediment and other suspended particles to settle out before passing through the check dam, should be constructed at the upstream foot of the check dam and extend across the entire conveyance structure. Sediment control basins should be sized according to the individual site characteristics, but must be at least 2-feet deep and 6 feet long to provide adequate storage capacity, with slopes not exceeding a 2:1 ratio. SPACING To discourage concentrated flow, water velocity in the channel can be reduced by using multiple check dams. The distance between check dams will depend upon the slope of the conveyance structure, but should be spaced so that the base of the upstream check dam is even with the peak of the downstream structure. As the slope of the conveyance structure is increased, the number of check dams that will be needed to prevent concentrated flow in the channel increases as well. As a result, check dams used in conveyance structures with slopes greater than 6% may not be practical. Ditch Grade (%) CONSTRUCTION Source: Metropolitan Council Check dams should be underlain by a geotextile filter fabric Check dams should be constructed immediately after grading is completed on the conveyance structure Caution should be taken to ensure that objects down stream of the check dam are not damaged from dislodged stones MAINTENANCE Check dams should be inspected for damage after each storm event - all damage should be repaired immediately Sediment that accumulates behind the check dam should be removed as necessary Additional stone may need to be added to ensure that the check dam retains its design characteristics METHOD TO DETERMINE PRACTICE EFFICIENCY Spacing (feet) Grades above 6% are not recommended The efficiency for this practice is derived from the reduction in slope length that it provides. To calculate the efficiency, simply use the new, reduced slope length in place of the pre-existing one in the USLE and recalculate. The difference between the two completed equations is the efficiency for the practice. I.S-8.2 A P P E N D I X I S T O N E C H E C K D A M 0 1 / 0 2 / 0 7

167 Ditch grade = 2% Note: the elevation of the bottom of the upslope check dam is the same as the top of the downslope dam Length 100 An Example of Proper Placement of Check Dams Source: Adapted from Metropolitan Council SOURCES 1. Ditch Check. Conservation Practice Standard. Wisconsin Department of Natural Resources. November Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Storm Water Management for Industrial Activities: Developing Pollution Prevention Plans and Best Management Practices. United States Environmental Protection Agency. Office of Water Water Related Best Management Practices in the Landscape. U.S. Department of Agriculture, Natural Resources Conservation Service and Center for Sustainable Design at Mississippi State University. Washington, D.C A P P E N D I X I S T O N E C H E C K D A M 0 1 / 0 2 / 0 7 I.S-8.3

168 I.S-8.4 A P P E N D I X I S T O N E C H E C K D A M 0 1 / 0 2 / 0 7

169 STONE CRIB GENERAL A stone crib is a designed basin that collects the first ½ inch of stormwater from a site and reduces its velocity by passing it through the basin. This action promotes sedimentation and reduces the temperature of runoff by utilizing the heat exchange capacity of the stone. As stormwater enters the stone crib, it is passed through a layer of pervious pavement block and pea gravel, which filter out sediment and other particles. It then mixes with the stone and any stored water in the crib, exchanging heat with the cooler F water. Trash and other large debris are collected upstream of the device by a gabion (refer to Gabion, pg. I.G-1). The cooled water is released slowly to a stable outlet structure (refer to Stone Outlet Protection, pg. I.S-10). Stone cribs are widely applicable, particularly in temperature sensitive watersheds. As these devices are only designed to provide treatment for the first ½ inch of runoff, large storm events may overwhelm the capacity of ADVANTAGES the practice. As a result, they are best used in conjunction with other management practices. BASIN Reduces the temperature of stormwater Widely applicable, especially in temperature sensitive watersheds Requires minimal land area Relatively cost-effective Low maintenance DISADVANTAGES Limited effectiveness with large storm events The basin should have side slopes of 3:1 or flatter, which should be lined with a layer of non-woven, highly permeable geotextile filter fabric. The filter fabric prevents the soil from mixing with the stone and thus reducing the capacity of the basin. The bottom of the basin, however, should not be lined as it may reduce the infiltration ability of the practice. Berm Gabion Monitoring well (optional) Pervious pavement block Pea gravel Stone Geotextile filter fabric A Typical Stone Crib Source: Adapted from the United States Environmental Protection Agency A P P E N D I X I S T O N E C R I B 0 1 / 0 2 / 0 7 I.S-9.1

170 A 3-4 foot layer of stone fills the majority of the basin and is placed on top of the geotextile filter fabric. The stone should be sized based upon the individual hydrologic conditions of the site, but should be well graded, with ½ of the stone larger than the median stone size, and free of fines and sand. The stone is covered with a layer of pea gravel that is at least 1 foot thick. The pea gravel should be properly compacted to allow maintenance vehicles access to the stone crib without damaging the structure. To prevent the pea gravel from settling and filling the pore spaces in the stone, a layer of non-woven, highly permeable geotextile filter fabric should be placed between the stone and the pea gravel. Finally, a layer of pervious pavement blocks is set on top of the pea gravel. The pavement blocks should be at least 6 inches thick and at least 30% pervious to allow water to infiltrate the basin. VOLUME The stone crib should be sized depending upon the individual characteristics of the site, but should be large enough to handle the first ½ inch of runoff from the site. Generally, the basin will have an area of 2,000-4,000 square feet with a depth of 3-4 feet. INLETS AND OUTLETS Stormwater should be conveyed into the stone crib through a stone-lined channel and a gabion (refer to Lined Waterway or Outlet, pg. I.L-1, and Gabions, pg. I.G-1). These structures reduce the flow velocity of the water and trap sediment and other debris before they reach the stone crib. They increase the longevity of the practice, as larger particles quickly clog the pores of the structure and reduce the effectiveness of the practice. The gabion should be at least 3 feet square with at least 1 foot extending above the surface. All other design considerations for inlets should follow the criteria set forth in the Lined Waterway or Outlet and Gabion sections of this appendix. The stone crib should discharge at non-erosive velocities to a stable outlet (refer to Stone Outlet Protection, pg. I.S-10). CONSTRUCTION Slopes surrounding the practice should be 6:1 or flatter to allow access for maintenance vehicles Stormwater should be delivered to the stone crib at non-erosive velocities MAINTENANCE Stone cribs should be inspected after large storm events any necessary repairs should be made immediately Accumulated sediment, leaves, trash, and other debris should be removed as needed METHOD TO DETERMINE PRACTICE EFFICIENCY Stone cribs are designed to trap sediment and reduce the temperature of the first ½ inch of runoff from a site. The efficiency for this practice is determined by running the Temperature of Urban Runoff Model (TURM). SOURCES 1. Preliminary Data Summary of Urban Storm Water Best Management Practices (EPA-821-R ). U.S. Environmental Protection Agency. Washington, D.C. August Roa-Espinosa, A., Norman, J., Wilson, T., Johnson, K. Thermal Impact Analysis of Token Creek Subwatershed and Validation of the Temperature Urban Model (TURM). Dane County Land Conservation Department I.S-9.2 A P P E N D I X I S T O N E C R I B 0 1 / 0 2 / 0 7

171 STONE OUTLET PROTECTION GENERAL Stone outlet protection is designed to release water from management practices at nonerosive velocities. An apron of heavy stone is placed at the outlet to prevent erosion by dissipating the energy of water as it flows over the stone. DESIGN SIZE Stone outlet protection must be capable of handling the peak outflow of the structure. For outlets which discharge into channels, the riprap apron should extend across the channel bottom and up the sides. If the outlet discharges onto a flat area, the upstream portion of the apron should be at least three times as wide as the pipe diameter. To determine the necessary length and width of the stone outlet protection, the following equations should be used, respectively: Q L = 1.7 * + D W = 3 * D 3 8 D In these equations, L is the apron length, W is the apron width measured at the end wall, Q is the flow rate for a 10-year storm event, and D o is the pipe diameter. The minimum thickness of the riprap apron is determined by multiplying the D 50 by 2. STONE Stone outlet protection should consist of clean, angular stone that is resistant to ADVANTAGES Cost-effective Relatively easy to construct Prevents erosion to receiving structures DISADVANTAGES Large storm events may displace rock Removal of accumulated sediments is difficult Not applicable on steep slopes weathering. Recycled concrete may also be used provided it has a density of at least 150 pounds per square inch and is clear of any steel or reinforcing agents. The stone should be sized by using the median stone size (D 50). Once the D 50 has been selected, 50% of the stone, by weight, should be larger than the D 50. The diameter of the largest stone should not exceed 1.5 times the D 50 size. The remaining portion of the stone should be well graded with a sufficient amount of smaller stones to fill the voids between the larger stones. Maximum Velocities for Various D 50 Sizes and Shapes Maximum Velocity (ft/sec) D 50 Cubical (Inches) D 50 Spherical (Inches) A P P E N D I X I S T O N E O U T L E T P R O T E C T I O N 0 1 / 0 2 / 0 7 I.S-10.1

172 A geotextile fabric barrier should be installed underneath the stone to prevent the stone from settling and to prevent erosion of the outlet structure. Care should be taken during construction to ensure that the fabric is not torn, cut, or punctured. Any damage should be repaired before proceeding with construction. Recommended Stone Gradation Manning s n Values for Various Rock Sizes Diameter (Inches) n Percent Passing by Weight Diameter (inches) x D X D D X D X D 50 CONSTRUCTION Side slopes should be 2:1 or flatter Bottom grade should be equal to zero The apron should be straight, without any bends Construction should be completed before any water is allowed through the outlet In applications where damage is possible to the outlet structure, the stone should be hand placed The apron must be at least 1.5 feet below the invert elevation of the outlet structure An Outlet to a Flat Area MAINTENANCE Stone outlet protection should be inspected after all storm events for displaced stones all necessary repairs should be made immediately Accumulated sediments should be removed periodically METHOD TO DETERMINE EFFICIENCY Stone outlet protection prevents erosion of the receiving structure by dissipating the energy of water. This practice is required with many management practices and, as a result, no efficiency is given for this practice. An Outlet to a Well-Defined Channel Source: Adapted from the Georgia Stormwater Management Manual I.S-10.2 A P P E N D I X I S T O N E O U T L E T P R O T E C T I O N 0 1 / 0 2 / 0 7

173 SOURCES 1. Catalog of Stormwater Best Management Practices for Idaho Cities and Counties. Idaho Department of Environmental Quality. 2nd Ed Georgia Stormwater Management Manual. Volume 2: Technical Handbook. Atlanta Regional Commission. Atlanta, Ga Manual for Erosion and Sediment Control in Georgia. Georgia State Soil and Water Conservation Commission. Fifth Ed. Athens, Ga Minnesota Pollution Control Agency. Protecting Water Quality in Urban Areas, A Manual. Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis National Catalog of Erosion and Sediment Control and Stormwater Management. Guidelines for Community Assistance. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Rock Outlet Protection Fact Sheet. Natural Resource Conservation Service, Wyoming A P P E N D I X I S T O N E O U T L E T P R O T E C T I O N 0 1 / 0 2 / 0 7 I.S-10.3

174 I.S-10.4 A P P E N D I X I S T O N E O U T L E T P R O T E C T I O N 0 1 / 0 2 / 0 7

175 STONE TRACKING PAD GENERAL A stone tracking pad is designed to limit the amount of sediment that is transported from a site by vehicles. Stone tracking pads remove sediment from the tires of vehicles by allowing the tires to sink in to the stone base slightly. This action, combined with the rolling motion of the tires, acts to knock loose the majority of sediment from a vehicle s tires. Stone tracking pads are generally used on construction sites at any point of entry and exit and must be installed as soon as the drive area has been graded. DESIGN Stone tracking pads should be at least 24 feet wide and 50 feet long, and constructed of 3-6 inch washed stone with a depth of at least 12 inches. On sites with clay soils, stone tracking pads must be underlain with a geotextile liner to prevent the stone from sinking into the soil. Surface water must be prevented from passing through the tracking pad, as even low flows may dislodge sediment and carry it off site. Flows may be diverted away from tracking pads or conveyed under and around them by using a variety of practices, such as culverts, water bars, or other similar practices. WASH RACKS On sites with heavy traffic or in muddy conditions, a wash rack may be required. Wash racks, which consist of a heavy-duty grate and a water collection system, remove sediment buildup from tires with water and increase the efficiency and lifespan of stone tracking pads by preventing sediment buildup. The water used must be collected on site and diverted to a settling basin, where suspended soil particles can be deposited before the water is allowed to leave the site. ADVANTAGES CONSTRUCTION A stone tracking pad should be installed as soon as the drive area has been graded Stone tracking pad should be removed from the site after construction is complete and the site has been stabilized MAINTENANCE Additional stone is required if existing stone becomes buried or if sediment is not being removed effectively from tires Sediment that is tracked onto the roadway must be removed immediately Tracking pads may require periodic cleaning to maintain the effectiveness of the practice, which may include the removal and re-installation of the stone METHOD TO DETERMINE PRACTICE EFFICIENCY Cost-effective Effective for erosion and sediment control Prevents tracking of sediment onto public roads DISADVANTAGES May require extensive maintenance if used on muddy sites A stone tracking pad reduces the amount of sediment that is removed from the site by construction vehicles and is a required practice on every construction site. As a result, no efficiency is given for this practice. A P P E N D I X I S T O N E T R A C K I N G P A D 0 1 / 0 2 / 0 7 I.S-11.1

176 50 Minimum Length 3 Min. Existing Ground Geotextile Liner (If Necessary) PROFILE Minimum 12 Base- 3-6 Stone Pipe (If Necessary) Earth Fill Existing Pavement 50 Minimum Length 10 Min. 24 Minimum Width 10 Min. Existing Pavement PLAN VIEW 10 Min. Source: Adapted from National Catalog of Erosion and Sediment Control and Storm Water Management SOURCES 1. Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis National Catalog of Erosion and Sediment Control and Stormwater Management. Guidelines for Community Assistance. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Natural Resources Conservation Service Planning and Design Manual. Construction Entrance/Exit. Natural Resources Conservation Service. Water Related Best Management Practices in the Landscape. U.S. Department of Agriculture, Natural Resources Conservation Service and Center for Sustainable Design at Mississippi State University. Washington, D.C Stone Tracking Pad and Tire Washing. Conservation Practice Standard. Wisconsin Department of Natural Resources. November I.S-11.2 A P P E N D I X I S T O N E T R A C K I N G P A D 0 1 / 0 2 / 0 7

177 STONE WEEPER GENERAL Stone weepers are outflow devices constructed of stone that reduce the flow velocity of runoff while minimizing channel erosion and promoting sediment deposition. Stormwater enters a swale or vegetated channel and, under normal circumstances, is ponded temporarily behind the weeper. Ponding allows sediment and other pollutants to settle out, while allowing some water to infiltrate and evaporate. The water that remains is slowly passed through the voids in the structure, continuing on towards the outfall. In the event of large storm conditions, runoff is conveyed safely over the top of the structure. As a result, stone weepers are best used in conjunction with other erosion control practices. Stone weepers may be used as outlet structures in swales and vegetated channels. They are very versatile structures that conform to a wide variety of situations, making them one of the most widely used practices in Dane County. DESIGN The size of the structure will depend upon the site, but should be 1-5 feet in height; ADVANTAGES Cost-effective Versatile Relatively easy to construct Reduces erosion and promote sediment deposition DISADVANTAGES Requires periodic sediment removal Ineffective with large storm events have a minimum top width of 2 feet; and should extend across the entire conveyance structure. Slopes should have a maximum ratio of 2:1, as greater slopes may become unstable and require excessive maintenance. In addition, stone weepers must be underlain with geotextile fabric to protect the structure from undercutting, which may cause the device to fail and result in channel erosion. The size of stone selected for use in stone weepers will vary depending upon the individual needs of the site. However, they should consist of, at a minimum, a 1-foot layer of 1-inch washed stone over a 1-foot layer of clear stone, free of fines and sand, sized to meet the requirements of the design storm. The entire structure must be underlain with geotextile fabric to prevent the stone from settling. 1 washed stone 1 1 Slopes 2:1 or flatter Flow Clear stone size as designed Geotextile fabric beneath stone An Example of a Stone Weeper Source: Adapted from the Illinois Natural Resources Conservation Service A P P E N D I X I S T O N E W E E P E R 0 1 / 0 2 / 0 7 I.S-12.1

178 # # # # # # # # # D A N E C O U N T Y E R O S I O N C O N T R O L A N D S T O R M W A T E R M A N A G E M E N T M A N U A L CONSTRUCTION To prevent the erosion of adjacent materials, stone should be placed at the toe and on the sides of the structure Stone weepers must be underlain by geotextile fabric Stone weepers shall be constructed immediately after grading is completed on the conveyance structure and be functional before the site upslope of the practice is disturbed Additional stone may be required to offset settlement and lost stones METHOD TO DETERMINE PRACTICE EFFICIENCY Stone weepers promote sedimentation by reducing the flow velocity of runoff. The efficiency for this practice may be found by using the equation below. MAINTENANCE Stone weepers shall be inspected periodically and after all storm events for evidence of undercutting and erosion CALCULATING FLOW THROUGH A STONE WEEPER # L Q h D W Q 3 2 h W = 1/2 2 L L D Q = Total flow through dam (cfs) h = Ponding depth in basin (ft) W = Total length of dam(ft) L = Horizontal flow path length (ft) D = Average rock diameter (ft) Source of calculating method: NAHB/NRC Designated Housing Research Center at Penn State University I.S-12-2 A P P E N D I X I S T O N E W E E P E R 0 1 / 0 2 / 0 7

179 SOURCES 1. Illinois Urban Manual. A Technical Manual Designed for Urban Ecosystem Protection and Enhancement. United States Department of Agriculture, Natural Resources Conservation Service. Washington, D.C Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis NAHB/NRC Designated Housing Research Center at Penn State University Stormwater Management. Massachusetts Dept. of Environmental Protection. Volume Two: Stormwater Technical Handbook. Boston. March A P P E N D I X I S T O N E W E E P E R 0 1 / 0 2 / 0 7 I.S-12.3

180 I.S-12-4 A P P E N D I X I S T O N E W E E P E R 0 1 / 0 2 / 0 7

181 STORMWATER INLET PROTECTION GENERAL Stormwater inlet protection devices are temporary practices designed to prevent suspended sediment from entering drainage systems such as culverts, catch basins, and storm sewers. These devices reduce the velocity of runoff by forcing it through a filtering device, temporarily ponding the water and encouraging suspended particles to settle out. Inlet protection is critical because it is often the last treatment measure that the stormwater receives before it enters receiving waters. Stormwater inlet protection devices are commonly used on sites where storm water drainage systems are operational prior to the permanent stabilization of the site. These devices vary according to the individual needs and characteristics of the site, but generally include: block and gravel sediment filters, excavated drop inlet sediment traps, and manufactured inlet protection. Whichever type of protection is selected, it must be able to handle the runoff from the 10-year, 24-hour storm event and drain an area no larger than 1 acre. ADVANTAGES Reduce the amount of sediment leaving the site Inexpensive Easy to construct DISADVANTAGES Require frequent maintenance to prevent clogging Ineffective for small particles and during large storm events May cause flooding Ineffective for drainage areas larger than 1 acre Due to their temporary nature, stormwater inlet protection devices require frequent maintenance and are best used in conjunction with other management practices. Wire mesh & filter fabric Concrete block Washed stone An Example of Block and Gravel Inlet Protection Source: Virginia Department of Conservation and Recreation A P P E N D I X I S T O R M W A T E R I N L E T P R O T E C T I O N 0 1 / 0 2 / 0 7 I.S-13.1

182 DESIGN BLOCK AND GRAVEL SEDIMENT FILTER Block and gravel sediment filters are applicable on a wide variety of sites with drainage areas of 1 acre or less, particularly those on which heavy volumes of runoff are expected. They may also be used when an overflow capacity is necessary to prevent excessive ponding on the site. These structures are constructed with concrete blocks, laid lengthwise on their sides with a height of inches. The blocks should be wrapped with a wire mesh, overlain with non-woven, pervious geotextile filter fabric, to prevent stone from washing through the openings in the block, which should be supported by 2 x 4 inch wood studs placed through the outer holes in the block. Geotextile filter fabric should be placed around the perimeter of the structure, extending at least 12 inches from the block. 1-3 inch washed stone should be placed on top of the fabric and against the block. The stone should be no more than 2 inches from the top of the concrete block with a slope of 2:1 or flatter. should be designed 2:1 or flatter. The drainage openings in the inlet structure should be sized so that the basin will drain completely within 24 hours of the designed storm. These openings should be closed once construction is complete The basin should be lined with erosion matting (Please refer to Erosion Matting, pg. I.E-1) or vegetation tolerant of frequent inundation to prevent erosion of the basin. Native vegetation (Please refer to Native Plants, pg. I.N-1) is encouraged; however, species should be carefully selected to ensure that exotic and invasive species are not planted. MANUFACTURED DEVICES Several types of pre-manufactured stormwater inlet protection devices are available for purchase and Dane County does not endorse any particular product. The products that have been included do not constitute a complete list of the products that are available for this purpose; rather, they represent a sample of pre-manufactured alternatives that are available for use on a case-by-case basis. EXCAVATED DROP INLET SEDIMENT TRAP Excavated drop inlet sediment traps are applicable for sheet flow on sites with drainage areas no larger than 1 acre. These devices consist of a rectangular shaped basin that surrounds the inlet with additional drainage openings for dewatering. The inlet is encompassed by 12 inches of ¾ to 1-inch stone with a slope of 3:1 or flatter, supported with a wire mesh and underlain with geotextile filter fabric. Basin size and shape will depend upon individual site characteristics, but must be capable of handling the runoff from the 10-year, 24-hour storm event. The basin should have a depth of 1-2 feet (measured from the top of the drain structure) with a minimum storage capacity calculated at a rate of 67 cubic yards per acre. Side slopes FloGard Plus Catch Basin Filter Insert for Flat Grated Inlet Source: KriStar Enterprises, Inc. I.S-13.2 A P P E N D I X I S T O R M W A T E R I N L E T P R O T E C T I O N 0 1 / 0 2 / 0 7

183 CONSTRUCTION Stormwater inlet protection should be installed before the drain becomes operational or site disturbance occurs Stormwater inlet protection should be removed after the site has been permanently stabilized and permanent BMPs have been implemented MAINTENANCE The Street Bag Inlet Protection Device WI DOT Type D Source: Earth and Road Corp. Stormwater inlet protection devices must be inspected and repaired after each rainfall event Accumulated sediment must be removed when it reaches ½ the original design depth Sediment that is removed shall be placed in an area that is not susceptible to erosion To prevent clogging, filter media should be cleaned or replaced periodically WI DOT Type A Inlet Protection Device Source: WDNR Catch-All Inlet Protection Device Source: Marathon Materials, Inc. Excavated Area Excavated Depth 1-2 feet below the top of the inlet Drain openings for dewatering Side slopes 2:1 Accumulated sediment ¾ to 1-inch stone supported by wire mesh and underlain by geotextile filter fabric Cross-Section of Excavated Drop Inlet Protection Source: Adapted from Missouri Department of Natural Resources A P P E N D I X I S T O R M W A T E R I N L E T P R O T E C T I O N 0 1 / 0 2 / 0 7 I.S-13.3

184 # # # # # # # # # D A N E C O U N T Y E R O S I O N C O N T R O L A N D S T O R M W A T E R M A N A G E M E N T M A N U A L METHOD TO DETERMINE PRACTICE EFFICIENCY Stormwater inlet protection reduces the amount of suspended sediment in stormwater by reducing the flow velocity of water. The efficiencies for these practices vary by the type of device used and by manufacturer. Devices that are constructed on site will have an efficiency that is determined by calculating the settling efficiency for the device. CALCULATING FLOW THROUGH AN INLET PROTECTION DEVICE # L Q h D W Q 3 2 h W = 1/2 2 L L D Q = Total flow through dam (cfs) h = Ponding depth in basin (ft) W = Total length of dam(ft) L = Horizontal flow path length (ft) D = Average rock diameter (ft) Source of calculating method: NAHB/NRC Designated Housing Research Center at Penn State University I.S-13.4 A P P E N D I X I S T O R M W A T E R I N L E T P R O T E C T I O N 0 1 / 0 2 / 0 7

185 SOURCES 1. Georgia Stormwater Management Manual. Volume 2: Technical Handbook. Atlanta Regional Commission. Atlanta, Ga KriStar Enterprises, Incorporated. FloGard Plus Product Brochure Marathon Materials, Incorporated. Catch-All Product Brochure Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis National Catalog of Erosion and Sediment Control and Stormwater Management. Guidelines for Community Assistance. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Protecting Water Quality A Construction Site Water Quality Field Guide. Missouri Department of Natural Resources. Water Protection and Soil Conservation Division. Kansas City Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul Storm Drain Inlet Protection For Construction Sites. Wisconsin Department of Natural Resources Conservation Practice Standard. November Water Related Best Management Practices in the Landscape. U.S. Department of Agriculture, Natural Resources Conservation Service and Center for Sustainable Design at Mississippi State University. Washington, D.C Wisconsin Construction Site Best Management Practice Handbook. Wisconsin Department of Natural Resources. Madison Virginia Erosion and Sediment Control Handbook. Virginia Department of Conservation and Recreation. Division of Soil and Water Conservation. Richmond A P P E N D I X I S T O R M W A T E R I N L E T P R O T E C T I O N 0 1 / 0 2 / 0 7 I.S-13.5

186 I.S-13.6 A P P E N D I X I S T O R M W A T E R I N L E T P R O T E C T I O N 0 1 / 0 2 / 0 7

187 SUBSURFACE DRAIN GENERAL Subsurface drains are tiles, pipes, or tubes installed below ground that collect and transport stormwater to an outlet. They are constructed from a variety of materials, including plastic, clay, and concrete and may be perforated to allow infiltration into the surrounding soil. They are used in areas with high water tables, poorly drained soils, or on slopes to prevent saturation and to remove the possibility of subsidence. They may also be used in areas where vegetation is needed to provide ground cover or as an outlet for detention areas and other structures with small drainage areas. Subsurface drains should not be relied upon to provide stormwater control by themselves, however, as they are designed as conveyance structures only and do not enhance water quality. As a result, they should be used in conjunction with other management practices. DESIGN TYPES There are two types of subsurface drainage systems. Relief drains are used to lower the water table to allow the growth of vegetation or are used to remove surface water in the direction of the slope. Interceptor drains are used on slopes to prevent the soil from becoming saturated and to prevent slippage. They are placed across the slope and generally drain to the side of the slope. CAPACITY The capacity of subsurface drains will depend upon the individual characteristics of the site, but should be large enough to completely drain the basin it serves within 24 to 48 hours. To ensure proper drainage, the conduit should be at least 3 inches in diameter and provide a minimum flow velocity of 0.5 feet per second. However, in areas where sediment is present in the water column in large quantities, the flow velocity ADVANTAGES Reduces the thermal impact of stormwater Improves drainage DISADVANTAGES Limited effectiveness enhancing water quality Cost Has a tendency to plug should be at least of 1.4 feet per second to prevent sediment accumulation in the drain. Maximum flow velocities vary depending upon soil type and are listed below. However, these flow velocities may be exceeded if a continuous perforated pipe or tube, enclosed with a geotextile filter fabric, is used. Perforations should not exceed ½ inch in diameter, and slotted perforations should not be wider than 1/8 inch. The geotextile prevents the soil surrounding the drain from migrating into the conduit. The fabric selected will depend upon the size of the particles surrounding the conduit and should be durable enough to last the life of the practice. In applications where subsurface drains are used as outlets for detention areas, geotextile filter fabric is recommended for all discharge velocities due to the potential for high sediment loads. Maximum Flow Velocities Without Protection Soil Type Maximum Flow Velocity (feet per second) Sand, sandy loam 3.50 Silt, silt loam 5.00 Silty clay loam 6.00 Clay, clay loam 7.00 Source: Natural Resources Conservation Service A P P E N D I X I S U B S U R F A C E D R A I N 0 1 / 0 2 / 0 7 I.S-14.1

188 INSTALLATION Subsurface drains should be installed in a trench with a firm foundation to ensure proper alignment. The sections of the conduit should be supported on the sides with suitable bedding material, which should be properly placed and compacted. This prevents the conduit from collapsing during backfilling operations. All fittings and couplers should be compatible with the conduit material and should be installed following the manufacturer s specifications. The trench should be free of stone or other materials that are larger than 1.5 inches in diameter. In applications where this is not feasible, the trench should be overexcavated by at least 6 inches and refilled to grade with ¼ inch pea gravel or gravel screenings as bedding material. Envelopes are used around subsurface drains as bedding material or to improve the flow characteristics of groundwater. They are not required to meet the gradation requirements of the filter material, but should be large enough so that it does not accumulate in the drain. In installations where it is necessary to install the drain below the water table or on unstable soils, special equipment, procedures, and bedding material may be required to prevent soil movement into the conduit or from plugging the envelope material. OUTLETS Subsurface drains should discharge through a rigid, continuous, non-perforated pipe that is free of joints and curves to a stable outlet that is designed to handle the maximum flow of the drain. The outlet should have the same invert elevation as the drain and should follow the design criteria for stone outlet protection (refer to Stone Outlet Protection, pg. I.S-10.1). CONSTRUCTION Subsurface drains should be located at least 50 feet from trees to prevent damage to the structure by roots Installation should take place when the soil is as dry as possible to minimize alignment and other problems The ends of the drain should be covered with a trash rack and rodent protection to prevent clogging All materials should be thoroughly inspected for quality before they are installed Backfilling should be performed carefully to avoid displacement, deflection, or damage to the conduit MAINTENANCE Drains should be inspected periodically to ensure that they are draining properly - all repairs should be made immediately METHOD TO DETERMINE PRACTICE EFFICIENCY Subsurface drains are designed as a conveyance practice and do not significantly reduce the amount of suspended sediment in stormwater runoff. As a result, no efficiency is given for this practice. SOURCES 1. National Catalog of Erosion and Sediment Control and Stormwater Management. Guidelines for Community Assistance. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul I.S-14.2 A P P E N D I X I S U B S U R F A C E D R A I N 0 1 / 0 2 / 0 7

189 SURFACE ROUGHENING GENERAL Surface roughening is a practice that abrades the soil surface with horizontal ridges and depressions across the slope, decreasing erosion by reducing runoff velocities. In addition, this practice also increases infiltration and fosters the establishment of vegetation. Surface roughening may be performed by tracking, grooving, or stair-stepping and is applicable on a wide variety of sites. It is especially effective on slopes with grades steeper than 3:1. To mitigate raindrop impact, it is used in conjunction with other best management practices, such as mulching and seeding (refer to Mulching, pg. I.M-2, Seeding, Temporary, pg. I.S-4, or Seeding, Permanent, pg. I.S-3). METHODS TRACKING Tracking is a method that utilizes the depressions formed by the tracks from bulldozers and other construction vehicles. The vehicle is operated up ADVANTAGES Cost-effective Promotes the establishment of vegetation Widely applicable DISADVANTAGES May result in soil compaction May make maintenance activities (such as mowing) difficult and down the slope and leaves behind horizontal depressions in the soil. These depressions interrupt the runoff s flow, reducing its velocity and erosive capacity. Tracking is generally not as effective as other surface roughening methods. To improve efficiency, tracking should be performed on slopes with gradients that are 3:1 or flatter, as its use on steeper slopes may not prevent concentrated flow from developing. Soil compaction is also a concern due to the weight of the tracking equipment, and as a result, Slope Tracking Source: Virginia Department of Conservation and Recreation A P P E N D I X I S U R F A C E R O U G H E N I N G 0 1 / 0 2 / 0 7 I.S-15.1

190 tracking should only be performed on sites with sandy soils. GROOVING Grooving is a method of surface roughening that creates a series of ridges and depressions across the slope on the contour and is generally used on steeper slopes. Grooving rippers, disks, spring harrows, chisel plows, or any equipment capable of operating safely on the slope may be used. Grooves shall be no more than 15 inches apart and should not measure less than twice the thickness of the topsoil. STAIR-STEPPING Stair-stepping is a grading method that creates stair steps on slopes to reduce runoff velocity and increase sedimentation. It is used on steeper slopes with soil material that is composed of soft rock and some subsoil. The size of the step will vary depending upon the individual characteristics of the site; however, vertical cuts should not exceed 1 foot, as larger cuts may decrease the practice s stability. Horizontal cuts should be longer than vertical cuts and should be sloped inward, toward the vertical face, to promote sedimentation in. Grooving Drainage 6-8 in. Greater than Vertical Stair Stepping Source: Adapted from Virginia Department of Conservation and Recreation I.S-15.2 A P P E N D I X I S U R F A C E R O U G H E N I N G 0 1 / 0 2 / 0 7

191 CONSTRUCTION AND MAINTENANCE Perform surface roughening only after all cuts and fills have been graded to their final shape Inspect slopes weekly and after all storm events for rill and gully formation with all repairs made immediately METHOD TO DETERMINE PRACTICE EFFICIENCY Surface roughening prevents soil loss by reducing the flow velocity of runoff. The efficiency of this practice is dependant upon site disturbance. Any disturbance that may disrupt the practice, such as vehicular traffic, greatly reduces the efficiency and requires that the practice be repeated. When properly performed, surface roughening yields an efficiency of up to 18%, which may be taken for the time period between the completion of the practice and the application of seed. SOURCES 1. Indiana Handbook for Erosion Control in Developing Areas. Indiana Department of Natural Resources, Division of Soil Conservation. Indianapolis National Catalog of Erosion and Sediment Control and Stormwater Management. Guidelines for Community Assistance. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Natural Resources Conservation Service Natural Resources Conservation Service Planning and Design Manual. Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul Virginia Erosion and Sediment Control Handbook. Virginia Department of Conservation and Recreation. Division of Soil and Water Conservation. Richmond A P P E N D I X I S U R F A C E R O U G H E N I N G 0 1 / 0 2 / 0 7 I.S-15.3

192 I.S-15.4 A P P E N D I X I S U R F A C E R O U G H E N I N G 0 1 / 0 2 / 0 7

193 TREE PLANTING GENERAL Tree planting stabilizes disturbed areas with perennial vegetation. Trees provide vegetated areas that collect and slow runoff, filtering out sediments and insoluble pollutants and encourage infiltration. In addition, they act as windbreaks and are adaptable to most any area, adding aesthetic beauty and providing habitat for wildlife. Trees are applicable on any area where mowing and other maintenance activities are difficult, in areas where establishing grasses is challenging, or for use in landscaping applications. Because trees may take years to develop adequate forest cover, they should be used in conjunction with other management practices, such as permanent or temporary seeding or native plants to prevent soil loss and to encourage infiltration (refer to Seeding, Permanent, pg. I.S-3; Seeding, Temporary, pg. I.S-4; or Native Plants, pg. I.N-1). VEGETATION The species of vegetation selected will vary greatly depending upon the characteristics of the site and the long-term maintenance requirements of the species. Soil type, site drainage, ph, slope, site use, maintenance, growth rate, size, the use of native or nonnative species, and the time of year it is planted are all factors that must be weighed when selecting vegetation. Careful selection is required to ensure that invasive or exotic species are not used, as they may upset the ecosystem s delicate balance. Soils should be tested for nutrient content and ph before planting to determine the amount, if any, of fertilizer or lime required. Over-application of these soil amendments is costly, ineffective, and may cause serious pollution problems. As a result, soil amendments should be applied only as needed and shall be incorporated into the soil to keep them on site and in the root zone. ADVANTAGES TREE PLANTING Low maintenance Aesthetically pleasing Stabilizes the soil DISADVANTAGES More costly than grasses Difficult to establish from seed Requires years to become fully established Trees are difficult to establish from seed, and, therefore, seeding is generally not recommended. Transplanting expedites establishment and, with proper care, is much more reliable. Trees are available commercially in a variety of sizes and species. However, larger trees generally take longer to recover from transplanting and will require more care than smaller trees. Trees are available with bare roots, with soil wrapped in burlap, container-grown, or tree spaded. Each type has different planting requirements, so care should be taken to ensure the success of the practice. Bare rootstock is purchased with the roots in peat moss or in a moisture-proof container. The roots should be kept damp and cool at all times to ensure the health of the plant. They should be planted deeper than they were in the nursery and only while dormant, such as in late fall or early spring. Medium to large trees should be planted ½ inch deeper, small trees 1 inch deeper, and evergreen trees ¼ inch deeper. Planting is generally accomplished with a tree spade, which is an implement with a steel plate that makes a V-shaped wedge in the ground. When planting, the roots should be placed in the hole straight down without twists or tangles. If necessary, roots may be trimmed to allow for proper planting. After planting, the soil around the plant should be watered and packed firmly to remove any air pockets that may be present in the soil. Container grown or burlap wrapped trees are purchased with the roots surrounded by soil. The amount of soil surrounding A P P E N D I X I T R E E P L A N T I N G 0 1 / 0 2 / 0 7 I.T-1.1

194 Insert bar and push forward to upright position Remove bar and place seedling at the correct depth Re-insert bar next to planting hole and pull away from the seedling, firming soil at the bottom of the roots Push bar toward plant, firming the soil at top of roots Fill in hole by stamping with heel Firm soil around seedling with feet Test planting by pulling lightly on seedling Plant seedlings upright Right Wrong Make the hole deep enough to accommodate all roots without bending Right Wrong Always plant in soil- never plant in leaves or other debris Planting Bare Root Seedlings Source: Natural Resources Conservation Service Planning and Design Manual the roots will vary depending upon the size of the tree, but in general, it should have a diameter of 12 inches for each inch of tree diameter. These types of trees may be planted year-round; however, deciduous trees are most successful in early spring, before leaves begin to emerge, while evergreen trees are most successful in early fall. The soil around the roots should be kept cool and damp at all times until planting to promote the health of the species. The planting hole should have a diameter twice as large as the soil surrounding the roots of the tree and deep enough so that the tree may be planted to the same depth as it was in the container. Planting the tree too deep may result in an unhealthy tree and should be avoided. The tree should be removed from the container or burlap carefully to prevent damage to the roots before planting. When excavating, the subsoil should be separated from the topsoil and the subsoil replaced with additional topsoil or amended with peat moss, compost, or manure before backfilling the hole. After planting, the area immediately surrounding the tree should be sloped toward the tree, creating a depression to hold water. A 2-3 foot area around the tree should be mulched to prevent weeds and other vegetation from competing with the tree (refer to Mulching, pg. I.M-2). However, care should be taken to ensure that a small, mulch-free ring is left around the trunk of the tree, as mulch may cause wood rotting fungi to damage the tree. Transplanted trees may require support to hold the tree in place until its roots become established. Small trees should be supported with vertical stakes, while larger trees often require the support of guy wires. Wires should be attached directly above the first branch of the tree, with a rubber hose in between the wire and the tree. The hose prevents abrasions, cutting, and other damage that may result from the wire. Wires and stakes should allow the tree some freedom of movement, as it allows the tree to strengthen its trunk and root system. All support systems should be removed once the tree has firmly established its roots. Additional protection may be required to prevent damage to young trees from the sun or from animals. In such instances, the tree should be wrapped from the trunk to the first branch with a fabric tree wrap until it has become firmly established. I.T-1.2 A P P E N D I X I T R E E P L A N T I N G 0 1 / 0 2 / 0 7

195 Trees that are wrapped in burlap or purchased in buckets should be planted at the same depth as the were in the nursery Soil should backfilled with a depression around the trunk Garden hose and wire Stakes Young trees should be wrapped Stakes Trees under 6 feet tall Trees over 6 feet tall Planting Burlap-Wrapped or Containerized Trees Source: Natural Resources Conservation Service Planning and Design Manual CONSTRUCTION All grading and tracking should be completed before planting begins Species should be adapted to the soils and the climate of the area Trees should be planted as soon as alternative ground cover is in place or has become established MAINTENANCE Transplanted trees must be watered frequently Weeds around the base of the tree should be removed as necessary Fertilizer should be added as necessary at proper rates METHOD TO DETERMINE PRACTICE EFFICIENCY Trees reduce erosion by providing cover and stabilizing the surface. However, due to the length of time required for establishment, no efficiency is given for this practice. A P P E N D I X I T R E E P L A N T I N G 0 1 / 0 2 / 0 7 I.T-1.3

196 SOURCES 1. National Catalog of Erosion and Sediment Control and Stormwater Management. Guidelines for Community Assistance. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Natural Resources Conservation Service. Water Related Best Management Practices in the Landscape. U.S. Department of Agriculture, Natural Resources Conservation Service and Center for Sustainable Design at Mississippi State University. Washington, D.C Planning and Design Manual for the Control of Erosion, Sediment, and Stormwater. U.S. Department of Agriculture, Natural Resources Conservation Service and Mississippi Department of Environmental Quality. Washington, D.C. April Protecting Water Quality in Urban Areas, A Manual. Protecting Water Quality in Urban Areas, A Manual. Minnesota Pollution Control Agency. St. Paul Stormwater Management. Massachusetts Dept. of Environmental Protection. Volume Two: Stormwater Technical Handbook. Boston. March Wisconsin Field Office Technical Guide. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C I.T-1.4 A P P E N D I X I T R E E P L A N T I N G 0 1 / 0 2 / 0 7

197 VEGETATED BUFFER STRIPS GENERAL Buffer strips are densely vegetated areas that collect and slow runoff, filtering out sediments and insoluble pollutants and encourage infiltration. Stormwater flows into a buffer strip over a level spreader, a device that converts concentrated flow into sheet flow. As the runoff flows through the vegetation, its velocity is reduced, releasing its load of suspended solids and promoting infiltration. Buffer strips are uniformly graded and are located down slope from disturbed or impervious areas or adjacent to waterways. Buffer strips are best used in conjunction with other management practices, however, as they do not significantly reduce peak flows or the volume of runoff. DESIGN LEVEL SPREADERS AND BERMS Maintaining sheet flow is critical to the proper operation of buffer strips. To ensure that concentrated flow is eliminated before runoff enters the buffer strip, a level spreader may be constructed at the top of the buffer strip. These devices disperse flows over a wide area, dissipating the energy of the runoff and creating sheet flow. ADVANTAGES Relatively low cost Easy to construct and maintain Can be aesthetically pleasing if designed properly Remove sediment and insoluble pollutants Increase the infiltration of runoff Can provide habitat for wildlife Can help stabilize stream banks DISADVANTAGES Ineffective in areas with high velocity runoff Require a large amount of land area Ineffective for large drainage areas Reduced effectiveness with large storm events Best used in conjunction with other management practices Common types of level spreaders are curb cuts, concrete weirs, and stone weepers or trenches. LENGTH, WIDTH, AND SLOPE Each buffer strip should be sized according to the individual characteristics of the site, taking into account the size of the area to be drained and the slope of the land that they are located on. Road Body of Water Buffer Strip ft. length An Example of a Vegetated Buffer Strip, Source: Adapted from California Stormwater Quality Association A P P E N D I X I V E G E T A T E D B U F F E R S T R I P S 0 1 / 0 2 / 0 7 I.V-1.1

198 Buffer strips that border impervious surfaces should stretch the entire width of the surface and have a minimum flow length of at least 25 feet, with a 20-minute detention time. Increased lengths enhance the treatment ability of the practice by increasing detention time. However, lengths greater than 40 feet generally result in channelized flow and require additional flow dissipaters. Regardless of the length, each buffer strip should not drain an area larger than ½ acre. Sites that border bodies of water may have additional requirements beyond this ordinance. For length requirements on this type of site, please contact your local WDNR office. The length of buffer strips is dependent upon the slope of the site. Slopes of 1-2 percent are recommended and may not exceed 6%. Steeper slopes encourage concentrated flow and may lead to channelization, while slopes flatter than 1 percent may result in ponding. Runoff velocities are determined by the detention time. VEGETATION Buffer strips only provide effective erosion control once the vegetation is densely established. Dense is defined as a stand of 6-8 inch sod-forming vegetation that uniformly covers at least 90% of a representative 1 square yard plot. As a result, until vegetation is firmly established, it shall under no circumstances be relied upon to prevent soil loss from the site. Plant species selected for buffer strips should meet the following criteria: Native species may be used with careful selection (refer to the Native Grasses section of this Appendix) Species should be tolerant to frequent inundation as well as extended dry periods Species should be resistant to matting Species should form a dense cover Avoid exotic, noxious, and invasive species CONSTRUCTION Buffer strips must be established before construction activity begins In order to be effective, buffer strips must be densely established MAINTENANCE Grassed vegetation should be cut and removed at least once per year Mowing should only be performed during dry periods using lightweight equipment to prevent soil compaction and damage to vegetation Buffer strips should be inspected weekly and after all major storm events to ensure they are operating properly and to check for any potential problems, such as the formation of rills and gullies, bare spots, and sediment accumulation Buffer strips should be inspected for the accumulation of sediment after all major storm events METHOD TO DETERMINE PRACTICE EFFICIENCY Buffer strips filter out sediment and other particles by reducing the flow velocity of runoff. The trapping efficiency of this practice is dependant upon the particle size and the flow length of buffer strip. RUSLE2, when available, has the ability to calculate the approximate efficiency of vegetative buffer strips. Buffer strips help remove suspended sediment from runoff by reducing the flow velocity. As the runoff velocity decreases, the sediment settles out. Buffer strips also help with reducing the amount of pollutants in the runoff since many pollutants are associated with the sediment. Studies have shown a suspended solid removal rate ranging between 40%-90%, with the efficiency of the buffer strip being dependent upon the quantity of runoff, length and steepness of the slope, as well as the vegetation used in the strip and the ability of the soil to infiltrate. Due to the number of variables affecting the performance of buffer strips, it is difficult to determine the exact efficiency of sediment removal for this practice. I.V-1.2 A P P E N D I X I V E G E T A T E D B U F F E R S T R I P S 0 1 / 0 2 / 0 7

199 SOURCES 1. California Stormwater BMP Handbook: Vegetated Buffer Strip. California Stormwater Quality Association. January Massachusetts Low Impact Development Fact Sheet: Grassed Filter Strips. Boston Metropolitan Area Planning Council. August Leeds, R, Brown, L. C., Sulc, M. R., and VanLieshout, L. Vegetative Filter Strips: Application, Installation and Maintenance. (AEX ) Ohio State University Extension. Columbus. 3. Minnesota Urban Small Sites BMP Manual. Metropolitan Council. Minneapolis Schueler, T. R. The Architecture of Urban Stream Buffers. Watershed Protection Techniques. Center for Watershed Protection, Terrene Institute, Washington, D.C Urban Storm Water Best Practices Study. United States Environmental Protection Agency, Office of Water. Washington, D.C Vegetative Buffer. Conservation Practice Standard. Wisconsin Department of Natural Resources. November Water Related Best Management Practices in the Landscape. U.S. Department of Agriculture, Natural Resources Conservation Service and Center for Sustainable Design at Mississippi State University. Washington, D.C Wisconsin Field Office Technical Guide. U.S. Department of Agriculture, Natural Resources Conservation Service. Washington D.C Wong, S.L. and R.H. McCuen The Design of Vegetative Buffer Strips for Runoff and Sediment Control. Civ. Eng. Dep., Univ. of Maryland, College Park, MD. A P P E N D I X I V E G E T A T E D B U F F E R S T R I P S 0 1 / 0 2 / 0 7 I.V-1.3

200 I.V-1.4 A P P E N D I X I V E G E T A T E D B U F F E R S T R I P S 0 1 / 0 2 / 0 7

201 APPENDIX II INFILTRATION MODELING INFILTRATION PRACTICE DESIGN Infiltration practices must be designed to meet the average annual infiltration goals included in the Dane County Erosion Control and Stormwater Management Ordinance. Infiltration practice design takes into account the physical characteristics of the site such as: water table, soil types, limiting layers, and tributary land use. In addition, infiltration practices may serve a dual purpose by mitigating thermal impacts. Bioretention basins are often designed to achieve the county requirement for oil and grease treatment and sediment removal. REGULATORY APPROACH TO INFILTRATION The Dane County infiltration standard is modeled after the Wisconsin Department of Natural Resources (WI DNR) standard. The standard is based upon requiring a percentage of precipitation infiltrated in the predevelopment condition (also known as predevelopment infiltration) to be infiltrated in the post development condition. For residential developments, 90% of the predevelopment infiltration must be infiltrated. For nonresidential sites, 60% of the predevelopment infiltration must be infiltrated. The county utilizes the same stay-on approach the WI DNR uses for modeling. Stay-on is defined as all precipitation that does not runoff. Therefore, stay-on includes evaporation, plant transpiration, and recharge. While commonly referred to as an infiltration standard, it is technically a stay-on standard. The county s regulatory approach differs from the WI DNR approach in two main ways. First, no eventbased goals for infiltration are included in the county s standard. Dane County s standard is based solely on an average annual goal and requires the use of continuous flow modeling. Second, there are no limits or caps placed on the amount of site area that must be dedicated to infiltration practices to meet the County s standard. If more than 1% of a residential development or 2% of a non-residential development must be dedicated to meet the stay-on goal, the Dane County standard allows designers to alternatively achieve a target average annual recharge goal of 7.6 inches. The target stay-on and target recharge goals are discussed in the following sections. A P P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7 I I - 1

202 TARGET STAY-ON REQUIREMENT Before an infiltration practice can be designed and sized the target stay-on requirement must be determined. The target stay-on is dependent upon the predevelopment curve number (CN). Target stay-on for residential and non-residential developments, for a range of predevelopment CNs, can be determined using figure Stay-on (Annual Infiltration) Requirement (inches/yr) Pre-Development Curve Number NR 151 Residential Req. NR 151Non-residential Commercial Req. Req. 100% Predevelopment Note: 100% Predevelopment represents infiltration under predevelopment conditions Figure 1 Target Stay-on Requirement as published in the WI DNR Technical Note for Sizing Infiltration Basins and Bioretention Devices. The target stay-on requirement is given in depth (inches per year), but it may be advantageous to convert this depth to a volume (cubic feet per year). A conversion equation is given in Figure 2. T v T d = 12 ( A ) s T v = Target Stay-on Volume (ft 3 ) T d = Target Stay-on Depth (in) A s = Area of Site (ft 2 ) Figure 2 Target Stay-on conversion from depth to volume I I - 2 A P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7

203 TARGET RECHARGE REQUIREMENT If more that 1% of a residential development or 2% of a non-residential development must be dedicated to meet the stay-on requirement, the designer may instead chose to design infiltration practices to meet Dane County s recharge goal. The target recharge requirement for Dane county is 7.6 inches per year. At the time of publication, the only accepted model for determining the amount of recharge achieved by an infiltration practice is RECARGA. When designing practices to meet the recharge goal, at least 1% of a residential development or 2% of a non-residential development must be dedicated to infiltration practices. Calculating Recharge There is no limit or cap on the amount of site area that must be dedicated to infiltration practices to meet the County s standard. If more that 1% of a residential development or 2% of a non-residential development must be dedicated to meet the stay-on goal, designers may alternatively design practices to achieve a target average annual recharge goal of 7.6 inches. The recharge calculation is based upon the RECARGA model output, Recharge. An example recharge calculation is provided in Figure 3. R = R + R Post F T Where: R = Post development recharge depth Post R F = Calculated facility recharge depth (from RECARGA) R = Calculated tributary recharge depth (from equation) T R = P T R Dane Where: P = Percent Pervious (decimal format) p R = 7.6 in/yr (Design Recharge Rate for Dane County) Dane Note: Equations are valid when the entire site drains to the infiltration facility. The facility recharge would need to be prorated if a portion of the site does not drain to the infiltration facility (see Example 2). Figure 3 Calculation of recharge for post-development condition A P P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7 I I - 3

204 Example 1: One-acre residential development The development consists of several single-family residences. The post development condition will is 60% impervious, 40% impervious. The entire site drains to a bioretention device. RECARGA gives a recharge depth of 5.0 inches. Then: and, R F = 5.0 in P = 0.40 p R Post = 5.0 in + (0.40 x 7.6 in) = 8.0 in Example 2: Five-acre commercial development The development consists of several storage units. The post development condition is 4.25 acres of impervious (85%) and 0.75 acres pervious (15%) acres of impervious area drains to a bioretention device. RECARGA gives a facility recharge depth of 8.2 inches. Then: and, R F = 8.2 in * (3.40/4.25) = 6.6 in P = 0.15 p R Post = 6.6 in + (0.15 x 7.6 in) = 7.7 in Figure 4 Example recharge calculations RECARGA The RECARGA model was developed to provide a design tool for evaluating the performance of bioretention facilities, raingarden facilities, and infiltration basins. The model is made available through the Wisconsin Department of Natural Resources (WI DNR) website, and can be downloaded free of charge. As with the use of any modeling software, it is important to understand the underlying principals and assumptions used to generate the model s results. Designers utilizing RECARGA modeling software are expected to read and understand the user manual prior to submitting plans that include modeling results. The following information is provided to supplement, not replace the information contained in the RECARGA user s manual. The guidance that follows is intended for permit applicants and designers submitting stormwater management plans to Dane County for review and approval. I I - 4 A P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7

205 Modeling Assumptions Modeling the performance of stormwater infiltration practices require numerous assumptions be made about the contributing drainage area (tributary areas) and the characteristics of the infiltration practice and native soil conditions. In an effort to ensure proper use of modeling software and consistency in regulation, several modeling assumptions must be followed. Acceptable model input values are summarized in Table 1. Table 1 Acceptable RECARGA modeling inputs for plans submitted to Dane County LCD Model Input/Parameter Engineered soil hydraulic conductivity Acceptable Value 3.94 in/hr Pervious CN 68* Maximum Ponding Zone depth for bioretention basins Maximum Ponding Zone depth for infiltration basins Root Zone depth for infiltration basins Storage Zone depth for infiltration basins 12 in 24 in 1 in 0 in * unless justified by existing or proposed vegetation (i.e. 58 for prairie vegetation) Table 2 Acceptable RECARGA modeling output results for plans submitted to Dane County LCD Model Output/Parameter Maximum Hours Ponded Acceptable Value < 96 hrs In addition to following the acceptable modeling inputs and outputs, the following guidelines must be followed to accurately represent the site, infiltration practice, and native soil conditions: The WI DNR Technical Standard 1002 Site Evaluation for Stormwater Infiltration must be used for determining all design infiltration rates. All treatment areas must be removed from the tributary area for calculation purposes so they are not double counted as pervious surfaces. FREQUENTLY ASKED QUESTIONS AND DEFINITIONS Frequently Asked Questions In late 2005, Dane County and City of Madison Staff met with DNR staff to discuss interpretation of NR 151 infiltration standards and related technical standards. County and City staff presented several specific questions concerning interpretations of sections of ch. NR 151, Wis. Adm. Code. Following the meeting, a memorandum was released to formalize the interpretive matters discussed at the meeting. The following text is taken directly from the memorandum dated January 20, A P P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7 I I - 5

206 The Correct Approach toward Infiltration The intent of the infiltration standard in ch. NR 151, Wis. Adm. Code, is to encourage infiltration of runoff. This requirement is tempered by a series of exemptions and exclusions for the purpose of minimizing the risk of groundwater contamination and addressing the practicality of implementation. These exemptions and exclusions were never intended to be evasive tools for developers and designers to avoid infiltration altogether. Developers and designers need to seek practical and sometimes innovative methods to meet infiltration requirements. Where infiltration standards are unable to be fully realized, then developers and designers need to meet the standards to the Maximum Extent Practicable (MEP). MEP is a term that provides flexibility in meeting a standard (or requirement). However, there needs to be unique site-specific reasons why a project is unable to fully meet a standard. If full attainment of a standard is impractical due to unique site conditions, then the standard is to be achieved to the furthest degree practical. For example, If a portion of a site is not acceptable for infiltration due to poor soils or high groundwater, directing runoff via gravity flow to other areas of the site that are suitable needs to be considered. If a shallow layer of clay soil is underlain by sandy soils suitable for infiltration then excavation of the clay layer may be warranted. If the only area on a site suitable for an infiltration basin is located up-slope of proposed impervious areas and the impervious areas have no other reasonable location, the designers are not required to pump water to meet the infiltration requirements in NR 151. However, decentralizing infiltration practices and installing rain gardens or other smaller practices around the site must be considered as a viable alternative. Proper implementation of NR 151 will require that some land or parcels will be needed for storm water management. The economic considerations regarding the loss of developable land are not a reasonable justification to prevent full attainment of a standard. The developer and designer shall not skew data or sampling methods to realize a predetermined outcome or rely on the exemptions and exclusions identified in ch. NR 151 to avoid infiltration, but rather they shall seek ways to maximize infiltration to the MEP. DNR Caveat: Please note that many of these questions have come up while dealing with commercial sites that fall under the jurisdiction of the Department of Commerce or local ordinances. In these cases, DNR responses are based on DNR implementation of NR 151 and where other authorities are controlling, those authorities must be consulted. Site Evaluation If the area that a developer proposes for infiltration is not on the best infiltrating area of the site and the best area is where the building is planned, is he/she required to re-site the facility to meet MEP? Answer: The planning for infiltration, as indicated in the Site Evaluation for Stormwater Infiltration technical standard, must be done early in the site development process so that infiltration can be accommodated. If the submitted documentation suggests that the developer did not place the infiltration device(s) on the best infiltrating soils, for sites under DNR jurisdiction, DNR will not require that the site be redesigned. However, the developer or designer can not claim exemption from infiltration by placing impervious areas over all usable soils (soils not excluded from infiltration). If this occurs for sites under DNR jurisdiction, site redesign can be required. What are the infiltration requirements if the only area on the site that is not excluded is up-hill of the impervious areas or where the impervious areas are planned? Answer: Pumping will not be required. However, other alternatives must be considered to achieve the infiltration goal. There are often several different infiltration options, so it is unlikely that pumping up-hill is the only alternative. If it is determined that with some excavation, a suitable soil layer may be reached, what is required in NR 151? If infiltration is required, to what depth is the developer required to excavate? I I - 6 A P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7

207 Answer: Although not specified by code, DNR believes that requiring excavation to a reasonable depth is acceptable. DNR supports the right of local administering authorities to select a minimum depth that they consider reasonable. Dane County and the City of Madison have adopted two feet as a minimum to define a reasonable excavation depth. What if a site doesn t have enough separation, but could be filled to meet the requirements? What level of filling would be required? Answer: Just like excavation, if the intent is to encourage infiltration, asking the developer to bring in suitable fill material, when it is practical to do so, to meet the separation distance is a reasonable requirement. DNR supports the right of local administering authorities to select a minimum depth that they consider reasonable. Dane County and the City of Madison have adopted two feet of fill as reasonable, provided positive drainage can be maintained. Many sites are filled as part of construction. If the native soil was not exempt, but fill material was placed and compacted, is the area now exempt? This seems like it may be an easy way for developers to create an exempt site. In the same manner, commercial sites that had significant grading during the plat phase may have been compacted and may now infiltrate less than 0.6 inches/hour. Are these sites considered exempt just because they were graded? If so, wouldn t this be an incentive to compact the soil on a site before applying for a storm water permit? Answer: Filling and compaction activities performed after implementation of NR 151 (October 2004) will not justify an exemption from the infiltration requirements. The infiltration requirements will be based on the native soils. Accordingly, these sites may be required to remove fill or mitigate compaction to meet the infiltration requirement. Where fill placement and compaction occurred prior to implementation of NR 151, the infiltration requirements will be based on both fill and native soil conditions. However, every effort must still be made to use infiltration practices, such as rain gardens for roof runoff. Use of Infiltration Technical Standards With regards to the cap, are there any requirements or restrictions on how much of the site runoff is directed to a device or the placement of the device on the site to receive flows? Answer: If the infiltration goals have been met and the infiltration area is at or below the cap, then there are no restrictions on placement of the device or requirements for flow diversion. If the infiltration goals are not realized by sizing a device to the cap, then all impervious surfaces should be routed through the infiltration device to maximize infiltration. Is a developer meeting the exclusion criteria if he/she says that the basin will be five feet deep and thus will not have proper separation from groundwater, even though the basin could be constructed shallower and meet the separation criteria? Answer: The developer needs to have a good reason why the device has to be so deep. Even then, he/she can still be required to look at other infiltration options and practices. Not all the practices have the same design depth requirements. In regards to the separation distances, where are they measured from? Answer: The separation distances are measured from the bottom of the infiltration device to the top of the seasonal high water elevation. The definition of bottom varies by device: For infiltration basins, rain gardens, and swales the bottom of the infiltration device corresponds to the surface elevation of the device (invert of the depression storage). For bio-retention devices, the engineered soil can be credited toward the separation requirements, however the gravel storage layer (if present) can not. This means, to comply with the 3-feet separation distance, a bio-retention device with 3-feet of properly engineered soil meets the separation requirements. To meet the 5-feet separation requirement, a bio-retention device needs 3-feet of engineered soil and an additional 2-feet of suitable soil (below the gravel storage layer). If suitable soil is not present, the engineered soil depth can be increased to 5-feet. In all cases, the seasonal high groundwater elevation shall be below the bottom of the gravel storage layer to maintain proper functioning of the device. For rock filled trenches or subsurface infiltration devices, the bottom of the device corresponds to the top of the native soil layer. A P P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7 I I - 7

208 What is the time frame for additional infiltration standards for swales, pervious pavement, and infiltration trenches? From a regulatory perspective this is a bit of a problem, since swales in SLAMM get too much credit. Answer: Improvements in SLAMM and the proper application of the swale routine in SLAMM should have alleviated this concern. Additional standards will be made available as staff allocation allows. Porous pavement Is the current means of addressing porous pavement not to treat it as an infiltration device (because an infiltration device requires pretreatment of parking lot runoff) but rather to allow the applicant to reduce the CN in the post developed situation or to treat it as pervious or open space? However, questions come up then in SLAMM if you direct rooftops to it. Does it count as being directed to a pervious or impervious surface? If using SLAMM, how is this treated - as an infiltration bed or as a large landscaped area? If using TR-55 what is the correct CN to allow for porous pavement? Also, are these areas given credit toward the cap? Answer: Given the current level of understanding on how porous pavement functions, and its effectiveness, the DNR is not ready to address these questions. Additional information needs to be collected. However, we can at this time say that porous pavement should not be used as an infiltration device receiving runoff from sources other than what falls directly on it through precipitation. Areas dedicated to porous pavement cannot be counted toward the cap. For rain that falls directly onto porous pavement, there does not need to be pretreatment prior to letting it move through the porous pavement. Underground arch storage and infiltration devices - They look like a pipe cut in half with an open bottom and they are placed under the parking lot. Runoff is typically directed to them after being pretreated by another prefab device such as Stormceptor or Downstream Defender. Are these devices allowable? Do they need pretreatment? If so what amount and do you count these areas toward the cap? Answer: The requirements for prefab subsurface infiltration systems are similar to infiltration basins with both requiring pretreatment and the area counted toward the cap calculated in the same manner. These devices are typically constructed at commercial development sites. The level of pretreatment for subsurface devices is currently established by Commerce in its plumbing code (s. COMM ). Commerce must decide whether the pretreatment guideline in the infiltration basin technical standard can apply to subsurface infiltration. Previous discussion on this matter has indicated that the current SOC standard requirement of 2' or 24 hours draw down whichever is less is not needed, and that the 24 hour draw down would be the enforcement mechanism in more open soils. Is this still the case? Answer: The 2-foot of depth or 24-hour draw down still applies to the depressional water quality storage volume. If peak flow control is combined with the device, the entire device must be drained within 72 hours. Is it true that applicants have a choice of using the design infiltration rates based on soil class or using in-field tested rates modified by the safety factors in the Site Evaluation for Stormwater Infiltration technical standard? Answer: Yes. Models for Infiltration Who is responsible for maintaining and providing support for RECARGA? Answer: DNR currently does not have the ability to support individual models. DNR will attempt to contract with the UW or others through the use of grant money to make upgrades and provide support as needed. What is the design infiltration rate in RECARGA for engineered soils? Answer: The default value currently used by RECARGA is 3.94 in/hr. Research has shown that the design infiltration rate of the engineered soils is generally not a critical factor in the proper design of a bio-retention device. If the designer is proposing a soil mixture that deviates from the soil mixture provided in the standard, testing may be warranted to establish an appropriate design infiltration rate. I I - 8 A P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7

209 TSS and Oil and Grease Control From the table under Considerations in the bio-retention technical standard, the sediment removal efficiency of a properly designed bio-retention device is purported to be 90%. Can this reduction be assumed if the bio-retention facility follows the design requirements of the technical standard? What if it is undersized due to the cap? Answer: Whether the practice is fully sized or undersized to meet the cap, a model is needed to calculate the TSS removal efficiency of a bio-retention device. The bio-retention technical standard is for the construction of a device to meet the infiltration requirement. Even though filtration does occur, the Criteria in the standard were never intended to serve as a design tool for TSS reduction. The informational table in the technical standard represents monitored results for unique conditions and serves only as guidance. It was not intended for use as a filtration standard. We will consider removing the table in a future revision if it continues to be misinterpreted. The consultants need to run SLAMM to determine TSS removal efficiency. Alternatively, RECARGA can be utilized by calculating the water volume infiltrated and multiplying that by the average influent concentration of TSS for each unique source area (obtained from SLAMM). Both SLAMM and RECARGA credit TSS reduction through infiltration (basin stay-on) and not filtration. The DNR does not currently have a filtration technical standard and we are hesitant to predict treatment rates for flows passing through the engineered soils and out the under-drain without further research. How much oil and grease is being removed by a bio-retention facility? Answer: Current research provides some guidance and indicates that bio-retention devices are effective in oil and grease removal for the portion of the runoff that is treated in the device. However, actual numbers are based heavily on site conditions. For subsurface infiltration, the pretreatment concentration requirement for oil/grease is specified by Commerce in its plumbing code. Commerce or its agent will have authority over these installations including determination of whether a bio-retention practice provides effluent of adequate quality for subsurface infiltration. Sweeping - if sweeping is used in an area - what type of credit do you want to use? SLAMM does not model parking lot sweeping, however shouldn t some credit be given? Answer: Sweeping is not an allowed practice to meet TSS reduction requirements for sites requiring a Construction Site Permit. This applies to new development, in-fill areas, and redevelopment as defined in NR 151. Credit for street sweeping can only be claimed for existing urban areas under a Municipal Permit. SLAMM vs. Control of the 5 micron standard - I want to be certain that for TSS control these standards are interchangeable and that it is the applicant s choice on which method to use for satisfying both agencies. Answer: The DNR uses the NURP particle size distribution and not the particle distribution for a silt loam soil and looks at TSS control on an average annual basis and not a design storm approach. Based on the NURP distribution, 80% control corresponds to between a 2 and 3 micron particle. SLAMM, P-8, or designs adhering to the technical standard (1001) are the best ways to show that the requirements are being met. Evaluation by Dane County of their design method that relies on a design storm approach and 5-micron particle size suggests that ponds sized using this method match well with the sizes obtained from the standard (1001), while SLAMM designs tend to have smaller surface areas. For now, both Dane County and DNR methods are acceptable. Definitions Bioretention - Bioretention is an upland water quality and quantity best management practice that uses the chemical, biological and physical properties of plants and soils to remove pollutants from stormwater runoff. Continuous flow modeling - Modeling that accounts for continuous input of rainfall/runoff information and utilizes a water budget to track the common hydrologic parameters of a given system. Hydrologic parameters are estimated for an extended period of time, encompassing multiple rainfall events. Event-based modeling - Modeling that predicts hydrologic parameters based on a single rainfall/runoff event, typically dealing with a time scale measured in hours. A P P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7 I I - 9

210 SOURCES 1. Dane County Stormwater Infiltration Taskforce, Jim Lorman Chair. Report of the Dane County Stormwater Infiltration Taskforce. July Wisconsin Department of Natural Resources. For Sizing Infiltration Basins and Bioretention Devices to meet State of Wisconsin Stormwater Infiltration Performance Standards. DNR Technical Notes. Last Update: July Wisconsin Department of Natural Resources. Central Office Memorandum, NR 151 Questions and Answers. January 20, I I - 10 A P E N D I X I I I N F I L T R A T I O N M O D E L I N G 0 1 / 0 2 / 0 7

211 APPENDIX III HYDROLOGY DESIGN STORM EVENTS for DANE COUNTY FREQUENCY (year) DURATION (hour) RAINFALL (inches) A P P E N D I X I I I H Y D R O L O G Y 0 1 / 0 2 / 0 7 I I I - 1

212 I I I - 2 A P P E N D I X I I I H Y D R O L O G Y 0 1 / 0 2 / 0 7

213 APPENDIX IV BASIN EFFICIENCY BASIN DESIGN Basins should be designed according to the percentage reduction required to meet the Dane County Erosion Control and Stormwater Management Ordinance. Basin design takes into account the physical characteristics of the site such as: water table, permeable layers, proximity to cold water streams and wetlands. In addition, basins often serve a dual purpose of controlling peak flow rates leaving the site to pre-constructed conditions. If the basin is located in the watershed of a cold-water stream, the design must consider thermal impacts. Possible ways to prevent stream warming from the basin include eliminating permanent pool storage and providing extended draw down by use of tile drainage. Basins must have the volume of storage necessary to settle the particle size necessary to meet either the soil loss standard during the construction phase or the 80% reduction in TSS for post-development. VOLUME OF STORAGE REQUIRED 1. From TR-55 find the pre-construction and post construction peak flow for the 1-year, 24-hour storm event. 2. Calculate the ratio of peak inflow to peak outflow. The inflow rate will be the post construction condition and the outflow rate will be the pre-development conditions. outflow inflow Q = o Qi < With the peak ratio, use the chart on the next page to find the ratio of storage volume to runoff volume. 4. The volume of storage necessary can now be calculated by multiplying the ratio from the table by the post-development runoff. V V s ro Volume of post-construction runoff = required basin volume A P P E N D I X I V B A S I N E F F I C I E N C Y 0 1 / 0 2 / 0 7 I V - 1

214 APPROXIMATE DETENTION BASIN ROUTING FOR TYPE II STORMS Source: Technical Release 55. United States Department of Agriculture, Natural Resources Conservation Service. Washington, D.C CALCULATING TRAPPING EFFICIENCY The sediment reduction is selected from the particle size versus expected efficiency for a Plano silt loam during construction. The expected efficiency is given by the USLE in the column named Percent reduction required to meet Ordinance. With this expected efficiency, use the chart below to obtain the particle size required to be retained in the pond. The particle size has a settling velocity that may be calculated using Stokes Law (see Appendix III). I V - 2 A P P E N D I X I V B A S I N E F F I C I E N C Y 0 1 / 0 2 / 0 7