low impact development robb lukes low impact development center june 2008 analysis and design
Jan 14, 2016
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
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T
Developed Condition, with Conventional CN and Controls
Existing
Additional Runoff Volume
Developed
Existing Peak Runoff Rate
Detention Peak Shaving
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T
Developed Condition, with LID- CNno Controls.
Existing
Reduced Runoff Volume
Developed- No Controls
Reduced Qp
Minimize Change in Curve Number
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Developed, LID- CN no controlssame Tc as existing condition.
Existing
More Runoff Volumethan the existing condition.
Developed,no controls
Reduced Qp
Maintain Time of Concentration
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T
Provide Retentionstorage so that therunoff volume willbe the same as Predevelopment
Retention storage needed to reduce the CN to the existing condition = A2 + A3
A3
A2
A1
Reducing Volume
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T
Provide additional detention storage to reduce peak discharge to be equal to that of the existing condition.
Existing
Predevelopment Peak Discharge
Detention Storage
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T
Comparison of Hydrographs
A2
A3
LID Concepts
Conventional Controls
Existing
Increased Volumew/ 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)
ModelsAdaptable Stormwater Models
EPA Stormwater Management Model (EPA SWMM)Source Loading and Management Model (SLAMM)Prince George’s County BMP Evaluation ModuleWestern Washington Hydrology Model (WWHM3) / Bay Area Hydrology Model (BAHM)
LID Sizing ToolsContra Costa Integrated Management Practice CalculatorCalifornia Runoff Volume CalculatorNational 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
VoorheesRainfall Continuous
Watershed Size Large to Small WatershedsLand Uses Residential, Commercial, Industrial,
Highway, Institutional, and other UrbanSource 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 ModelDeveloper Tetra Tech Inc.; Prince George’s County
Rainfall ContinuousWatershed Size Site Level to Small WatershedsLand Uses Low-Medium-High Density Residential,
Commercial, Industrial, Forest, and Agriculture
Source Areas Impervious or Pervious
Primary Use Runoff Quantity and QualityApplication to LID Retention and conveyance options can be
adapted to simulate various LID practices
Western Washington Hydrology Model (WWHM3) / *Bay Area Hydrology Model (BAHM)
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
*Model to be released in July 2007
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 ModelsSuburban Commercial Site
Contra Costa IMP Sizing CalculatorSWMMSLAMM
Metro West: Dense Urban SiteSWMMSLAMM
Village at Watt’s Creek: Traditional Neighborhood Development
SLAMMPrince George’s Nomograph
Oak Creek and Government CenterPrince George’s County BMP Evaluation Model
Typical Suburban Commercial Site
Existing: WoodedProposed: 4.0 Acre Commercial Site: 2.25 Acres of Impervious Cover,
and 1.75 Acres of Landscaping
Suburban Commercial SiteDemonstration 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 SiteModeling Objectives
Maintain Pre-Development Peak FlowsReduce, Treat, and Retain Site PollutantsGroundwater RechargeSize Best Management Practices to Meet California Stormwater Requirements
Suburban Commercial SiteContra 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/ underdrain420 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 SiteLID Options Selected
Source Areas Best Management PracticeRoof (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 depthGrassed Swale-420 linear ft -4 ft bottom width
Landscaping Maintain Native Soil StructureAvoid CompactionDeep Soil Aeration
Suburban Commercial SiteModeling Results
Rainfall: 1997 Continuous Historical Rainfall for Los Angeles CA.
SWMM SLAMMEvapotrans. (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 Site4 Acre SiteC SoilsPredevelopment: 4 Acres of ForestProposed: Commercial Office Park 2.20 Acres of Imp. Cover 1.25 Acres of Landscaping 0.55 Acres of Forest
Suburban Commercial SiteDemonstration 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 SiteModeling Objectives
Maintain Pre-Development Peak FlowsReduce, Treat, and Retain Site PollutantsGroundwater RechargeSize Best Management Practices to Meet Washington Department of Ecology Standards
Suburban Commercial SiteLID Options Selected
Source Areas Best Management PracticeRoof (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 SiteRainfall Data
Site Location: Issaquah, WARain Gage: SEATACPrecip. Factor: 1.333
Suburban Commercial SitePre-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 SitePeak 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 SitePeak Runoff Results
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
Pre-Developed
Developed Half of ParkingLot is
Pervious
Full ParkingLot is
Pervious
PerviousParking Lot,
Amended Soil
PerviousParking, Soil
Amendments,Bio. Cell forRoof Runoff
Pe
ak
Flo
w (
cfs
)
2 yr-24 hr 10 yr-24 hr 100 yr-24 hr
Suburban Commercial SiteYearly Peak Runoff Results (1948-1998)
00.20.40.60.8
11.21.41.61.8
1948 1958 1968 1978 1988
Yea
rly
Pea
k F
low
(cf
s)
PreDevelopment
Developed
Pervious Parking, Amended Soil, Bioretention Cell
WWHM3: Water Balance Comparison
Suburban Commercial SiteModeling Results
SWMM SLAMMEvapotrans. (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%
Rainfall Data Used: Los Angeles 1997
Metro WestMedium 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 WestDemonstration 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 WestModeling Objectives
Maintain Annual Load (Volume, Pollutants)Manage Peak Storm Events (2-, 10-, and 100- yr. 24-hour)Infrastructure Requirements per design manual and physical limitationsBMP 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 48.8Outflow 9.5 20.8 11.6
With LID Inflow 84.0 61.0 36.7Outflow 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 85.8Outflow 60.9 69.7 24.1
With LID Inflow 147.6 112.4 62.7Outflow 47.8 42.4 21.3
% Reduction in Outflow w/ LID
22% 39% 12%
Village at Watt’s CreekLID Options
Rain BarrelsBioretention CellsPermeable Driveways/AlleysStreet Planters
Village at Watt’s Creek SLAMM Analysis
Scenario CatchbasinWith Sumps
ResidentialDownspoutDisconnection
Residential BioretentionCells
Residential Rain Barrels
Permeable Pavement
forAlleys andDriveways
Street BioretentionPlanters
No BMPs
#1 – All BMPs
#2 – Bio. Cells
#3 – Rain Barrels
#4 – Permeable Pvt.
#5 – Street Planters
Village at Watt’s CreekSLAMM Runoff Reduction
National LID Manual Techniques
Based on NRCS MethodsUses peak storm eventQ/V relationships Nomographs that reflect Graphical Peak Discharge Method
Village at Watt’s CreekNational Manual Method
Existing CN: 70Proposed 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 CreekNational Manual Method
Existing CN: 70Proposed CN: 85
Required Retention Storage Volume =(0.75in)(1ft/12in)(55 ac.) = 3.4 ac.-ft
Maintaining Pre-development Peak Runoff Rates
HSPF LAND SIMULATION
– Unit-Area Output by Landuse –
PG BMP Evaluation ModelExisting Flow & Pollutant Loads
Simulated Flow/Water Quality Improvement Cost/Benefit Assessment of LID design
0
50
100
150
200
250
2/20/99 6/20/99 10/20/99 2/20/00 6/20/00 10/20/00
Time
Flo
w (
cfs)
0
1
2
3
4
5
6
7
8
9
10
Tota
l Rai
nfal
l (in
)
Total Rainfall (in) Modeled Flow
BMP DESIGN– Site Level Design –
SITE-LEVEL LAND/BMP ROUTINGSimulatedSurface Runoff
HSPF Land Use Representation
BMP Physical ProcessesPossible storage processes include:
EvapotranspirationInfiltrationOrifice outflowWeir-controlled overflow spillwayUnderdrain outflowBottom slope influenceBottom roughness influenceGeneral 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
Overflow Spillway
Bottom Orifice
Evapotranspiration
Infiltration
Outflow:
Inflow:
Modified Flow &Water Quality
From Land Surface
Storage
BMP Class A: Storage/Detention
Underdrain Outflow
BMP Class B: Open Channel
Outflow:Inflow:
From Land Surface
Overflow atMax Design
Depth
Open Channel Flow
Evapotranspiration
InfiltrationUnderdrain Outflow
Modified Flow &Water Quality
Modified Flow &Water Quality
Holtan Infiltration Model
veg. parameter
void fraction
soil porosity
soil fc D u
(A)
background f c
D s
f G I A S fa c 1 4.
b. Lead
0
20
40
60
80
100
0 20 40 60 80 100 120 140
Bioretention Depth (cm)
% R
emov
al
Box S1 Box S2 Box L
Greenbelt Landover
Phosphorus
0
20
40
60
80
100
0 20 40 60 80 100 120 140
Bioretention Depth (cm)
% R
em
ov
al
Box S1 Box S2 Box L
Greenbelt Landover
Phosphorus
LeadCalibrated BMPs!!!
General Water QualityFirst Order Decay Representation
Mass2 = Mass1 x e – k t
Pollutant Removal is a function of the
detention time
Underdrain Water QualityPercent Removal
Massout = Massin x (1 - PCTREM)
Underdrain Underdrain percent removal is percent removal is a function of the a function of the soil mediasoil media
Massin = Surface conc * underdrain flow
Government Center Plan
Assessment and Outreach
Community meetingsKnocking on doorsMultimedia outreachTie-ins to other events
Garden clubsChurchesCleanups
Neighborhood walkthroughsIdentification of hot spotsArcPad mapping
Model Screenshot
Government Center Results
C++ (BMPOpt.dll)
GIS (shape/dbf)
C++ (BMPOpt.dll)
O ptim izer•C onfiguration
•R outing
O ptim izer•C onfiguration
•R outing
(text/dbf)GIS (Shape/Grid)ISM D SF A rcG IS Interface
• O pen A rcV iew (A rcM ap)• Load ISM D SF.dll
ISM D SF A rcG IS Interface• O pen A rcV iew (A rcM ap)
• Load ISM D SF.dll
D ata M anagem ent• D efine/A dd G IS Layers and Tables
• D efine M odel Input Param eters
D ata M anagem ent• D efine/A dd G IS Layers and Tables
• D efine M odel Input Param eters
B M Ps D rainage A rea • Select B M P Types
• Select B M P Locations• D rainage A rea C om putation
B M Ps D rainage A rea • Select B M P Types
• Select B M P Locations• D rainage A rea C om putation
Visual Basic with ArcObjects
VBA (Spreadsheet)
N etw orkN etw ork
B M PProcess
Sim ulation
B M PProcess
Sim ulation
Post-ProcessorPost-Processor
FORTRAN (SWMM.dll)
Land Sim ulation• H ydrograph• Pollutograph
• R outing
Land Sim ulation• H ydrograph• Pollutograph
• R outing
C++ (BMPOpt.dll)
GIS (shape/dbf)
C++ (BMPOpt.dll)
O ptim izer•C onfiguration
•R outing
O ptim izer•C onfiguration
•R outing
(text/dbf)GIS (Shape/Grid)GIS (Shape/Grid)ISM D SF A rcG IS Interface
• O pen A rcV iew (A rcM ap)• Load ISM D SF.dll
ISM D SF A rcG IS Interface• O pen A rcV iew (A rcM ap)
• Load ISM D SF.dll
D ata M anagem ent• D efine/A dd G IS Layers and Tables
• D efine M odel Input Param eters
D ata M anagem ent• D efine/A dd G IS Layers and Tables
• D efine M odel Input Param eters
B M Ps D rainage A rea • Select B M P Types
• Select B M P Locations• D rainage A rea C om putation
B M Ps D rainage A rea • Select B M P Types
• Select B M P Locations• D rainage A rea C om putation
Visual Basic with ArcObjects
VBA (Spreadsheet)
N etw orkN etw ork
B M PProcess
Sim ulation
B M PProcess
Sim ulation
Post-ProcessorPost-ProcessorPost-ProcessorPost-Processor
FORTRAN (SWMM.dll)
Land Sim ulation• H ydrograph• Pollutograph
• R outing
Land Sim ulation• H ydrograph• Pollutograph
• R outing
Future Directions
More GIS integration with modeling softwareEPA SWMM
EPA Study on SWMM BMP Modeling ImprovementsInterface w/ SLAMM
July 2007, Bay Area Hydrology Model becomes available to the public
ConclusionsContinuous 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
Village at Watt’s CreekSLAMM Runoff Reduction
Runoff Reduction
0%10%20%30%40%50%60%70%80%90%
100%
Rain Barrels Permeable D/W BioretentionCells
All Three LIDOptions
LID Options
% R
un
off
Red
uced
100% Implementation 66% Implementation 33% Implementation
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.