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Liddesignandanalysis Liddesignandanalysis Presentation Transcript

  • low impact development robb lukes low impact development center june 2008 analysis and design
  • objectives
    • design storm approaches
    • modeling options
    • design case studies
      • bmp components
      • cost analysis
    • construction and maintenance
  • Q T Developed Condition, Conventional CN (Higher Peak, More Volume, and Earlier Peak Time) Existing Condition Hydrograpgh Pre/ Post Development Losses
  • Q T Developed Condition, with Conventional CN and Controls Existing Additional Runoff Volume Developed Existing Peak Runoff Rate Detention Peak Shaving
  • Q T Developed Condition, with LID- CN no Controls. Existing Reduced Runoff Volume Developed- No Controls Reduced Q p Minimize Change in Curve Number
  • Q T Developed, LID- CN no controls same Tc as existing condition. Existing More Runoff Volume than the existing condition. Developed, no controls Reduced Q p Maintain Time of Concentration
  • Q T Provide Retention storage so that the runoff volume will be the same as Predevelopment Retention storage needed to reduce the CN to the existing condition = A 2 + A 3 A 3 A 2 A1 Reducing Volume
  • Q T Provide additional detention storage to reduce peak discharge to be equal to that of the existing condition. Existing Predevelopment Peak Discharge Detention Storage
  • Q T Comparison of Hydrographs A 2 A 3 LID Concepts Conventional Controls Existing Increased Volume w/ Conventional
  • design storm approaches single event vs. continuous simulation - peak flows / - volume / hydromodification flooding - water quality
  • hydrologic analysis
    • NRCS (SCS) methods
      • curve numbers (0-100)
      • storm type (I, IA, II, III)
      • time of concentration
    • computed process simulations
      • ex. Hydrologic Simulation Program – Fortran (HSPF)
  • Models
    • Adaptable Stormwater Models
    • EPA Stormwater Management Model (EPA SWMM)
    • Source Loading and Management Model (SLAMM)
    • Prince George’s County BMP Evaluation Module
    • Western Washington Hydrology Model (WWHM3) / Bay Area Hydrology Model (BAHM)
    • LID Sizing Tools
    • Contra Costa Integrated Management Practice Calculator
    • California Runoff Volume Calculator
    • National LID Manual Technique
  • EPA Stormwater Management Model (EPA SWMM) Developer US EPA; Oregon State U.; Camp, Dresser and McKee (CDM) Rainfall Modeled Single Event and Continuous Watershed Size Large to Small Watersheds Primary Use Flooding, Quantity, and Quality Land Use & Source Area User defined land uses and source areas Application to LID Can be adapted to simulate LID controls, models storage and infiltration processes
  • Source Loading and Management Model (SLAMM) Developer Dr. Robert Pitt, U of Alabama; John Voorhees Rainfall Continuous Watershed Size Large to Small Watersheds Land Uses Residential, Commercial, Industrial, Highway, Institutional, and other Urban Source Areas Roofs, Sidewalks, Parking, Landscaped, Streets, Driveways, Alleys, etc. Primary Use Runoff Quantity and Quality Application to LID Infiltration, Wet Ponds, Porous Pavement, Street Sweeping, Biofiltration, Vegetated Swales, Other Urban Control Device
  • Prince George’s County BMP Evaluation Model Developer Tetra Tech Inc.; Prince George’s County Rainfall Continuous Watershed Size Site Level to Small Watersheds Land Uses Low-Medium-High Density Residential, Commercial, Industrial, Forest, and Agriculture Source Areas Impervious or Pervious Primary Use Runoff Quantity and Quality Application to LID Retention and conveyance options can be adapted to simulate various LID practices
  • Western Washington Hydrology Model (WWHM3) / *Bay Area Hydrology Model (BAHM) *Model to be released in July 2007 Developer Washington State Dept. of Ecology; AQUA TERRA Consultants; and Clear Creek Solutions, Inc. Rainfall Continuous Watershed Size Large to Small sites in 19 Counties of Western Washington Primary Use Runoff Quantity (Evapotranspiration, Surface Flow, Interflow, Groundwater Flow) Application to LID Ponds, Infiltration Trenches/Basins, Wetlands, Sand Filter, Gravel Trench Beds, Vaults/Tanks, Swales, Green
  • Contra Costa Integrated Management Practice Sizing Calculator Developer Contra Costa Clean Water Program; Dan Cloak Environmental Consulting Rainfall 35 years of continuous Contra Costa rainfall used to sizing factors Watershed Size Small Sites in Contra Costa County Primary Use Simplified method for IMP sizing Application to LID Limited sizing options are available for permeable pavement, dry wells, infiltration trenches/basins, vegetated or grassy swales, bioretention, and in-ground planters
  • National LID Manual Technique Developer US EPA; Prince George’s County Rainfall Single Event Watershed Size Small Sites in Contra Costa County Primary Use Estimates a developed sites retention and detention storage requirements Application to LID Applies to any IMP with retention storage: bioretention, infiltration, porous pavement, swales, and planters
  • Case Studies used to Demonstrate Models
    • Suburban Commercial Site
      • Contra Costa IMP Sizing Calculator
      • SWMM
      • SLAMM
    • Metro West: Dense Urban Site
      • SWMM
      • SLAMM
    • Village at Watt’s Creek: Traditional Neighborhood Development
      • SLAMM
      • Prince George’s Nomograph
    • Oak Creek and Government Center
      • Prince George’s County BMP Evaluation Model
  • Typical Suburban Commercial Site
    • Existing: Wooded
    • Proposed: 4.0 Acre Commercial Site: 2.25 Acres of Impervious Cover, and 1.75 Acres of Landscaping
  • Suburban Commercial Site Demonstration Goals
    • This site represents a small office park, retail, or other commercial project common to green field and fringe development. Numerous LID options are available for this type of development, including: swales, bioretention, permeable pavements, cisterns, and flow through planters.
  • Suburban Commercial Site Modeling Objectives
    • Maintain Pre-Development Peak Flows
    • Reduce, Treat, and Retain Site Pollutants
    • Groundwater Recharge
    • Size Best Management Practices to Meet California Stormwater Requirements
  • Suburban Commercial Site Contra Costa IMP Sizing Calculator
    • To meet Contra Costa County technical requirements for flow and treatment the following IMP sizes were calculated:
      • Bioretention cell must be sized to 1832 sf w/ underdrain
      • 420 linear ft of vegetated swales to treat and retain permeable /impervious parking lot.
    • IMP design criteria are stated in Appendix C of the Contra Costa County Stormwater C.3 Guidebook
  • Suburban Commercial Site LID Options Selected Source Areas Best Management Practice Roof (20000 sf) Sidewalk (2700 sf) Bioretention Cell w/ Underdrain -Contra Costa Sizing Tool: 1800 sf -3 ft of media depth -0.5 ft of surface storage depth Parking Lot and Loading Area (70,000 sf) Permeable Pavement -15000 sf, located in outer parking spaces -2.5 ft of aggregate depth Grassed Swale -420 linear ft -4 ft bottom width Landscaping Maintain Native Soil Structure Avoid Compaction Deep Soil Aeration
  • Suburban Commercial Site Modeling Results Rainfall: 1997 Continuous Historical Rainfall for Los Angeles CA. SWMM SLAMM Evapotrans. (acre-ft) Infiltration (acre-ft) Runoff (acre-ft) Runoff (acre-ft) Pre-Developed 0.11 4.29 0.08 0.25 Post-Developed 0.37 1.57 3.01 1.77 Post-Developed w/ LID 0.31 3.65 0.62 0.44 Reduction in Runoff w/ LID --- --- 79% 75%
  • Typical Suburban Commercial Site
    • 4 Acre Site
    • C Soils
    • Predevelopment:
    • 4 Acres of Forest
    • Proposed: Commercial Office Park 2.20 Acres of Imp. Cover 1.25 Acres of Landscaping 0.55 Acres of Forest
  • Suburban Commercial Site Demonstration Goals
    • This site represents a small office park, retail, or other commercial project common to green field and fringe development. Numerous LID options are available for this type of development, including: swales, bioretention, permeable pavements, cisterns, and flow through planters.
  • Suburban Commercial Site Modeling Objectives
    • Maintain Pre-Development Peak Flows
    • Reduce, Treat, and Retain Site Pollutants
    • Groundwater Recharge
    • Size Best Management Practices to Meet Washington Department of Ecology Standards
  • Suburban Commercial Site LID Options Selected Source Areas Best Management Practice Roof (0.5 acres) Bioretention Cell w/ Underdrain -2.5 ft of media depth -0.5 ft of surface storage depth Parking Lot and Loading Area (1.6 ac) Permeable Pavement -1.5 ft of aggregate base/subbase Sidewalk (0.1 ac) Landscaping (1.25 ac) Native Landscaping - sidewalk drains to landscaped area - amend soils - avoid compaction - deep soil aeration
  • Suburban Commercial Site Rainfall Data
    • Site Location: Issaquah, WA
    • Rain Gage: SEATAC
    • Precip. Factor: 1.333
  • Suburban Commercial Site Pre-Developed Condition
    • Developed – No Mitigation
    Half Permeable Pavement Parking Lot Full Permeable Pavement Parking Lot Half Per. Pvt. Lot & Bioretention Cell for Roof Runoff Suburban Commercial Site Half Per. Pvt. Lot & Amended Landscaping Soil
  • Suburban Commercial Site Peak Flow Results 2 yr-24 hr (cfs) 10 yr-24 hr (cfs) 100 yr-24 hr (cfs) Pre-Developed – Forest Condition 0.17 0.33 0.55 Developed – No Mitigation 0.89 1.28 1.77 Half Permeable Parking Lot 0.57 0.87 1.28 Full Permeable Parking Lot 0.51 0.71 0.96 Half Permeable Parking Lot & Landscaping Amended Soils 0.41 0.58 0.81 Half Permeable Parking Lot & Bioretention Cell for Roof Runoff 0.38 0.46 0.55
  • Suburban Commercial Site Peak Runoff Results
  • Suburban Commercial Site Yearly Peak Runoff Results (1948-1998)
  • WWHM3: Water Balance Comparison
  • Suburban Commercial Site Modeling Results Rainfall Data Used: Los Angeles 1997 SWMM SLAMM Evapotrans. (acre-ft) Infiltration (acre-ft) Runoff (acre-ft) Runoff (acre-ft) Pre-Developed 0.11 4.29 0.08 0.25 Post-Developed 0.37 1.57 3.01 1.77 Post-Developed w/ Per. Parking Lot and Bio. Cell 0.31 3.65 0.62 0.44 Reduction in Runoff w/ LID --- --- 79% 75%
  • Metro West Medium to High Density Mixed Use Development
    • Existing: Low Density Residential
    • Proposed: 52 Acre Pedestrian and Transit Oriented Mixed-Use Community: Townhomes, Condominiums, Apartments, Retail, Offices, and Public Spaces
    • Proposed LID: Bioretention, Permeable Pavement, and Green Roofs
  • Metro West Demonstration Goals
    • A high density development like Metro West may reduce the overall footprint of development, but it is at an extremely high density that will result in high runoff volume and peak rates and concentrated pollutant loads. Modeling will show that strategically placed and integrated best management practices will reduce or eliminate the need for large stormwater infrastructure.
    Source: Pulte Homes Corporation, Inc.
  • Metro West Modeling Objectives
    • Maintain Annual Load (Volume, Pollutants)
    • Manage Peak Storm Events (2-, 10-, and 100- yr. 24-hour)
    • Infrastructure Requirements per design manual and physical limitations
    • BMP Sizing based on current regulations
  • Metro West SWMM Model Results Rainfall Data Used: 1992 Washington Dulles Intl. Rain Gage (total of 41.26”) Runoff (acre-ft) Pre-Developed 6.2 Existing 24.2 Post-Developed w/ SWM 76.4 Post-Developed w/ SWM & LID 58.5 Reduction in Runoff w/ LID 77%
  • Metro West SWMM Peak Discharge Results for a 2yr-24hr storm Condition Areas A & B (cfs) Area C (cfs) Area D (cfs) Without LID Inflow 100.5 74.4 48.8 Outflow 9.5 20.8 11.6 With LID Inflow 84.0 61.0 36.7 Outflow 8.5 16.8 6.6 % Reduction in Outflow w/ LID 11% 19% 43%
  • Metro West SWMM Peak Discharge Results for a 10yr-24hr storm Condition Areas A & B (cfs) Area C (cfs) Area D (cfs) Without LID Inflow 178.7 130.7 85.8 Outflow 60.9 69.7 24.1 With LID Inflow 147.6 112.4 62.7 Outflow 47.8 42.4 21.3 % Reduction in Outflow w/ LID 22% 39% 12%
  • Village at Watt’s Creek LID Options
    • Rain Barrels
    • Bioretention Cells
    • Permeable Driveways/Alleys
    • Street Planters
  • Village at Watt’s Creek SLAMM Analysis Scenario Catchbasin With Sumps Residential Downspout Disconnection Residential Bioretention Cells Residential Rain Barrels Permeable Pavement for Alleys and Driveways Street Bioretention Planters No BMPs  #1 – All BMPs       #2 – Bio. Cells    #3 – Rain Barrels    #4 – Permeable Pvt.    #5 – Street Planters   
  • Village at Watt’s Creek SLAMM Runoff Reduction
  •  
  • National LID Manual Techniques
    • Based on NRCS Methods
    • Uses peak storm event
    • Q/V relationships
    • Nomographs that reflect Graphical Peak Discharge Method
  •  
  •  
  • 8% BMP Determining LID BMP Size
  • Village at Watt’s Creek National Manual Method
    • Existing CN: 70
    • Proposed CN: 85
    • Required Retention Storage Volume =(0.98in)(1ft/12in)(55 ac.)
    • = 4.5 ac.-ft
    Maintaining Pre-development Runoff Volume
  • Village at Watt’s Creek National Manual Method
    • Existing CN: 70
    • Proposed CN: 85
    • Required Retention Storage Volume =(0.75in)(1ft/12in)(55 ac.)
    • = 3.4 ac.-ft
    Maintaining Pre-development Peak Runoff Rates
  • Initial BMP Input Values BMP-A Calculation BMP-B Calculation Evaluation Factor Calculation Routing Sequence Cost Calculation BMP Model Runner Initial Run Results: Evaluation Factor & Cost Values New changeable variable values BMP Optimizer Solution Changeable Variables (C810) (num, min, max, increment) Control Target (C830) Input File Loader Evaluation Factor & Cost Values feed new possible solution to runner based on previous simulation result ArcGIS Map Interface BMP Simulation/Optimization DLL Prince George’s County LID Model BMP Model Input File
  • PG BMP Evaluation Model HSPF LAND SIMULATION – Unit-Area Output by Landuse – Existing Flow & Pollutant Loads Simulated Flow/Water Quality Improvement Cost/Benefit Assessment of LID design BMP Module BMP DESIGN – Site Level Design – SITE-LEVEL LAND/BMP ROUTING Simulated Surface Runoff
  • HSPF Land Use Representation
  • BMP Physical Processes
    • Possible storage processes include :
      • Evapotranspiration
      • Infiltration
      • Orifice outflow
      • Weir-controlled overflow spillway
      • Underdrain outflow
      • Bottom slope influence
      • Bottom roughness influence
      • General loss or decay of pollutant
      • (Due to settling, plant-uptake, volatilization, etc)
      • Pollutant filtration through soil medium
      • (Represented with underdrain outflow)
    • Depending on the design and type of the BMP, any combination of processes may occur during simulation
  • BMP Class A: Storage/Detention Overflow Spillway Bottom Orifice Evapotranspiration Infiltration Outflow : Inflow : Modified Flow & Water Quality From Land Surface Storage Underdrain Outflow
  • BMP Class B: Open Channel Outflow : Inflow : From Land Surface Overflow at Max Design Depth Open Channel Flow Evapotranspiration Infiltration Underdrain Outflow Modified Flow & Water Quality Modified Flow & Water Quality
  • Holtan Infiltration Model veg. parameter void fraction soil porosity soil f c D u (A) background f c D s
  • Phosphorus Lead Calibrated BMPs!!!
  • General Water Quality First Order Decay Representation Mass 2 = Mass 1 x e – k t Pollutant Removal is a function of the detention time
  • Underdrain Water Quality Percent Removal Mass out = Mass in x (1 - PCTREM) Underdrain percent removal is a function of the soil media Mass in = Surface conc * underdrain flow
  •  
  • Pre-Development Developed, No BMPs Developed, LID
  •  
  • Government Center Plan
  • Assessment and Outreach
    • Community meetings
    • Knocking on doors
    • Multimedia outreach
    • Tie-ins to other events
      • Garden clubs
      • Churches
      • Cleanups
    • Neighborhood walkthroughs
    • Identification of hot spots
    • ArcPad mapping
  • Model Screenshot
  • Government Center Results
  •  
  • Future Directions
    • More GIS integration with modeling software
    • EPA SWMM
      • EPA Study on SWMM BMP Modeling Improvements
      • Interface w/ SLAMM
    • July 2007, Bay Area Hydrology Model becomes available to the public
  • Conclusions
    • Continuous hydrologic simulation needed to evaluate stormwater treatment effectiveness.
      • The majority of runoff and stormwater pollution come from storms of 0.5” or less.
    • No runoff model is perfect. Factors to consider when choosing a model:
        • Goals (flow, quantity, quality)
        • User’s Skill Level
        • Project Size and Complexity
        • LID Modeling Capability
        • Available Precipitation Data
        • Cost Optimization
    • New regional models and tools are linking LID integration with regulatory compliance in a simple and easy to use way.
    • Recognize model limitations in results analysis
  • Construction
  • Maintenance
  • Regulatory Implications
    • Continuous hydrologic simulation needed to evaluate stormwater treatment effectiveness.
      • The majority of runoff and stormwater pollution come from storms of 0.5” or less.
  • Q T 2 3 4 5 6 7 Hydrograph Summary 2 3 4 1 Existing Developed, conventional CN, no control. Developed, conventional CN and control. Developed, LID-CN, no control. Developed, LID-CN, same Tc. Developed, LID-CN, same Tc, same CN with retention. Same as , with additional detention to maintain Q. 6 5 6 7 Pre-development Peak Runoff Rate 1
  • “ Initial” Low-Impact Development Hydrologic Analysis and Design
    • Based on NRCS technology, can be applied nationally
    • Analysis components use same methods as NRCS
    • Designed to meet both storm water quality and quantity requirements
  • Metro West Medium to High Density Mixed Use Development
    • Existing: Low Density Residential
    • Proposed: 52 Acre Pedestrian and Transit Oriented Mixed-Use Community: Townhomes, Condominiums, Apartments, Retail, Offices, and Public Spaces
    • Proposed LID: Bioretention, Permeable Pavement, and Green Roofs
  • Metro West Demonstration Goals
    • A high density development like Metro West may reduce the overall footprint of development, but it is at an extremely high density that will result in high runoff volume and peak rates and concentrated pollutant loads. Modeling will show that strategically placed and integrated best management practices will reduce or eliminate the need for large stormwater infrastructure.
    Source: Pulte Homes Corporation, Inc.
  • Metro West Modeling Objectives
    • Maintain Annual Load (Volume, Pollutants)
    • Manage Peak Storm Events (2-, 10-, and 100- yr. 24-hour)
    • Infrastructure Requirements per design manual and physical limitations
    • BMP Sizing based on current regulations
  • Metro West: LID Options
    • 9 iterations were modeled in SWMM to find an optimal sizing option for Bioretention Area and Permeable Pavement.
    • Rainfall:
    • Continuous
    • 1997 LA
    Option Chosen for SLAMM Analysis Bioretention (as % of rooftop area) Bioretention Storage Depth (in) Permeable Pavement (as % of paved area) % Reduction in Runoff Volume 3 24 5 21 5 24 5 67 5 24 10 70 5 24 25 78 5 24 50 80 5 24 100 80 5 30 10 73 5 30 25 78 5 36 10 76
  • Metro West SWMM and SLAMM Model Results Rainfall: 1997 Continuous Historical Rainfall for Los Angeles CA. SWMM SLAMM Evapotrans. (acre-ft) Infiltration (acre-ft) Runoff (acre-ft) Runoff (acre-ft) Pre-Developed 1.45 56.59 0.30 0.16 Existing 2.61 33.84 21.87 14.31 Post-Developed 4.67 15.87 37.70 27.04 Post-Developed w/ LID 4.78 42.45 11.03 6.53 Reduction in Runoff w/ LID --- --- 78% 76%
  • Choosing SWMM or SLAMM
    • SWMM
      • Goals include: flow routing, peak flow, volume, and pollutant loads
      • Complex site, many source area land types
      • Inputs for BMP performance equations are available
    • SLAMM
      • Goals include: runoff volumes & pollutant loads
      • Site has typical landuses
      • Standard BMPs, including swales and street sweeping are used
  • Metro West SLAMM Pollutant Load Results Sediment (ton) Phosphorous (lbs) Zinc (lbs) Post-Developed 2.05 20.10 12.07 Post-Developed w/ LID 1.36 16.04 3.11 % Reduction w/ LID 34% 20% 74%
  • Village at Watt’s Creek Traditional Neighborhood Development (TND)
    • 55 acre site consiting of mixed-use buildings, townhomes, two-family, single family homes on small lots
    • Other features, alley loaded lots, common green space, narrow and pedestrian friendly streets
  • Village at Watt’s Creek Demonstration Goals
    • Traditional Neighborhood Developments are an increasingly popular alternative to conventional suburban development. TNDs in combination with LID can mitigate development impacts, protect water resources and provide livable communities.
    Source: DC Office of Planning, LID Center, and Washington Council of Governments
  • Village at Watt’s Creek LID Options
    • Rain Barrels
    • Bioretention Cells
    • Permeable Driveways/Alleys
    • Street Planters
  • Village at Watt’s Creek SLAMM Runoff Reduction
  • CA Spreadsheet Total Site Area (acres) 5.74 Proposed Impervious Area (acres) 2.13     Required Area for Non-Structural Treatment (acres) 2.02 Required Volume for Structural Treatment (acre-ft) 2.09     Credit Options   Tree Planting 0.30 Disconnect Rooftop Runoff 0.46 Disconnect Non-Rooftop runoff 0.06 Use of Grass Swales 0 Sheet flow to streamway or setback 0 Pervious pavers 0.60 Green Roof 0     Final Area (acres) 0.60 Final Volume (acre-ft) 0.62
  • Village at Watt’s Creek SLAMM Runoff Reduction
    • Fully implementing all BMPs will be most effective at reducing runoff and pollutants but also most expensive.
    • Review of flow patterns, BMP capacity, and BMP placement is time consuming but can narrow down the most cost effective combinations.
  • California Volume Runoff Calculator Developer California State Water Resources Control Board Rainfall Uses Annual Rainfall Volume and 24 hr – 85th Percentile Storm Event Watershed Size Small Sites Primary Use Uses NRCS Method to calculate area required for non-structural and the required volume for structural treatment Application to LID Options limited to disconnected impervious surfaces, tree planting, pervious pavers, green roofs, stream buffer