STORMWATER 101 May 2012

Transcription

1 STORMWATER 101 May 2012

2 Overview History Context and Basics Maps Systems Regulations Floodplains Impervious Surfaces Management Techniques Storm Sewer Design Footing Drain Disconnection Program (FDD) MS4 Stormwater Permit Stormwater Utility Science

3 History

4 4 Allen Creek with men on bridge, 1902

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7 Context and Basics Maps Systems Regulations Floodplains Impervious Surfaces

8 Huron River Watershed Context and Basics

9 Context and Basics

10 Context and Basics

11 Context and Basics

12 Stormwater vs. Wastewater Combined vs. Separated Systems City has a separated system Stormwater goes ultimately to Huron River None receives advanced treatment Sanitary goes directly to WWTP Footing Drain Flow (FDD Program) Context and Basics

13 History of Stormwater Regulations Pre-1970: No Federal regulation 1970: Clean Water Act Point source control Control runoff from large developments during large storm events 1979: City Stormwater Ordinance Control the 1% annual chance event Applies to Site Planned Development Context and Basics

14 History of Storm Water Regulation cont. 1990s: Clean Water Act reauthorization Changed focus to quantity and quality Municipal Stormwater Permits 1998: City Stormwater Ordinance Quality control added Current: Low Impact Development (LID) Control stormwater at source instead of at a system level Context and Basics

15 Overlapping Regulatory Jurisdictions Federal Clean Water Act Federal Emergency Management Agency (FEMA) State Mandates Total Maximum Daily Load (Phosphorous, E. coli, Total Suspended Solids, etc.) Regulations Lakes, Streams, Wetlands and Floodplains Michigan Building Code County (Washtenaw Co. Water Resources Commissioner) Context and Basics

16 Basics of City Stormwater Ordinance Chapter 63 Stormwater Management and Soil Erosion and Sedimentation Control Part of SESC Ordinance Adopts Rules of the Washtenaw County Water Resources Commissioner Applies to Site Planned Projects entire site - retrofit Applies to Single-Family Residential only additional impervious Establishes maintenance responsibility for the property owner Context and Basics

17 Basics of City Stormwater Ordinance Chapter 63 Stormwater Management and Soil Erosion and Sedimentation Control 5,000 to 10,000 sf of impervious surfaces First Flush 10,000 to 15,000 sf of impervious surfaces First Flush Bankfull Greater than 15,000 sf of impervious surfaces First Flush Bankfull 1% annual chance event Site Planned Projects Context and Basics

18 Regulated Storm Events First Flush = Runoff from the first ½ inch of rain 85% of all rain events 90% of pollutant load Bankfull 50% annual chance ~ 2.4 in 24 Hr. Fills a natural channel to the top of the bank. Controls the shape and form of natural channels 1% annual chance = 100-year storm ~ 4.36 in 24 Hr. Same event used by FEMA on flood maps Context and Basics

19 Floodplain Terminology Floodway Flood Fringe Mapped Floodplain = 1% annual chance Doesn t mean once every hundred years Context and Basics

20 Floodplains are here to stay Naturally occurring Whether they are mapped by FEMA or not. Can t manage 100% of stormwater 100% of the time Overland flow will occur There will always be a bigger storm Cost Feasibility Context and Basics

21 Floodplains don t go away Creeks have Floodplains Pipes still have Floodplains Context and Basics

22 What is a Floodplain? The Base Flood Elevation (BFE) increases as the watershed is developed Context and Basics

23 Impervious Issues What Is Impervious? im per vi ous/: adjective: Not allowing something to pass through; not penetrable. Why does it matter? If it doesn t soak in - it runs into the stormwater system, collecting pollutants as it flows Context and Basics

24 Impervious Issues Most of the impervious area associated with the City of Ann Arbor public streets is DIRECTLY CONNECTED. This is a direct conduit of flow and pollutants to the stormwater network. Context and Basics

25 Stormwater Runoff affected by: Impervious area Land cover Soil type Soil saturation and slope Size of storm (intensity and duration) Variability/uniqueness/distribution of storm event across the City Growing season (leaf-out conditions) Context and Basics

26 Stream degradation begins at when only 8% of the watershed is impervious. Context and Basics

27 Management Techniques Storm Sewer Design Footing Drain Disconnect Program MS4 Permit Stormwater Utility Science Data and Trends

28 Stormwater Management Systems Storm drains not designed to pass all storms 1980 s to current: pipes constructed to pass the 10% annual chance storm (prior was 20% annual chance storm) 1998 Study - $41,000,000 to get Allen Creek to current standards still could not carry all storm events 2012 $:61,000,000 Surcharge into street & low-lying areas will occur Effect on downstream communities Feasibility Management Techniques

29 Storm Sewer Design and Background City s storm sewer is designed to pass a standard storm. Current City Standard (10%/12-hour storm event) Representing standard engineering practice Older parts of the systems had variable designs, passing smaller storms City s storm sewer inlets have a physical limitation. ~2cfs per inlet Assuming the inlet is not obstructed by debris The streets & low-lying areas store excess rainwater Representing standard engineering practice Management Techniques

30 Where Does the Rain Go? Surface Runoff into storm drains and streams 70% 30% Storm Drain 23% Stream base flows, grass & trees Soaks Into Soil 7% I/I Footing Drains 5% 2% Other Sources 5% wastewater 95% stormwater Sanitary Sewer Based on data from the City of Ann Arbor systems Management Techniques

31 FDD Need to remove the rainwater flows from the sanitary sewer system. Disconnecting the footing drains from the house sanitary lead Installing a sump pump to move water from the footing drains into the storm water system. Management Techniques

32 MS4 Permit Program Code of Federal Regulations Stormwater Regs Requires municipalities to address the quality of stormwater runoff going into lakes, rivers and streams through various mechanisms 6 Minimum Measures : Public Education Public Involvement/Participation Illicit Discharge Elimination Plan (IDEP) Post-Construction SW Control Construction SW Runoff Control Pollution Prevention/Good Housekeeping for Municipal Operations Management Techniques

33 Current Status Implementing the City s Stormwater Management Program (SWaMP) What and How Enforceable Document Working with a Statewide collaboration team to move towards the next permit in 2013 from the EPA Draft Permit expected in June Member of a team of ~30 professionals representing MS4s from across the State of Michigan Management Techniques

34 What is a Stormwater Utility? A dedicated funding source to support an administrative organization that plans, designs, constructs and maintains a stormwater management system, sediment and flood control programs and projects, and provides stormwater education. Management Techniques

35 Stormwater Utility Formed in early 1980 s; updated 2007 Rates based on Impervious Area Cannot be used for first-time service (i.e., SAD) Revenue can only be used for capital, O&M, permit requirements Regulatory Proportionate to cost of service Property owners able to limit use of service Management Techniques

36 Rates Proposed 2012 (3.2% inc.) Single-Family and Two-Family Residential Measured impervious area Representative Quarterly charge Impervious Area Less than or equal to 2, acres $13.68 square feet Greater than 2,187 square 0.07 acres $23.94 feet to less than or equal to 4,175 square feet Greater than 4,175 square 0.12 acres $41.04 feet to less than or equal to 7,110 square feet Greater than 7,110 square feet 0.21 acres $71.82 Management Techniques

37 Ann Arbor Stormwater Utility Revenue 2007 = $4,041, = $4,777, = $5,190, = $5,298, = $5,396, Management Techniques

38 Management Techniques

39 Management Techniques

40 Key Points Flooding is a natural occurrence Flooding will occur whether there is built infrastructure or not Solutions are limited by societal tolerance (financial and physical intrusiveness) There always is a bigger rain event

41 Questions and Discussion

42 Stormwater Projects Water Quantity Water Quality Planning and Asset Management Education

43 Green Infrastructure Projects Mary Beth Doyle Park Wetland Preserve Pioneer HS Underground Detention West Park Stormwater Management Bens Street - Water Quality Unit and 100-year Detention Liberty Road Reconstruction - Detention and Water Quality Units Stadium Boulevard Reconstruction (multiple Phases) - Water Quality Units and Oversized Pipes Easy Street - Partial Permeable Pavers and several Rain Gardens Sylvan Avenue Porous pavement Willard Street Porous pavement Rain Gardens in City Parks Vets, Huron Hills GC, Gallup, Belize, etc. Packard Road - Swirl concentrators; oversized pipe Municipal Center - Zero Discharge Stormwater GIS and SWMM Model Numerous Creek Bank Stabilization (Malletts, Millers, Traver) Stormwater Education