Low impact development robb lukes low impact development center june 2008 analysis and design.

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- CNno Controls.

Existing

Reduced Runoff Volume

Developed- No Controls

Reduced Qp

Minimize Change in Curve Number

Q

T

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

Q

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

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

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 compactiondeep 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



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


•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



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


• R outing

C++ (BMPOpt.dll)

GIS (shape/dbf)

C++ (BMPOpt.dll)


•R outing


•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









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)


• R outing


• 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.

Low impact development robb lukes low impact development center june 2008 analysis and design.

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