Simplified Sizing Tool for LID Practices in western Washington Alice Lancaster, PE Herrera Environmental Consultants

Simplified Sizing Tool Simplified Sizing Tool for LID Practices in for LID Practices in western Washingtonwestern WashingtonAlice Lancaster, PEAlice Lancaster, PEHerrera Environmental Herrera Environmental ConsultantsConsultants

Presentation OverviewPresentation Overview

WA NPDES permitWA NPDES permit Simplified tool: allows sizing of pre-Simplified tool: allows sizing of pre-

designed LID BMPs without designed LID BMPs without continuous modelingcontinuous modeling

Kitsap CountyKitsap County Western WA Western WA

lowlandslowlands

y = 0.420x

y = 0.293x

y = 0.210x

0

1,000

2,000

3,000

4,000

5,000

0 2,000 4,000 6,000 8,000 10,000

Contributing Impervious Area (sf)

Bio

rete

nti

on

Bo

tto

m A

rea

(s

f)

Infilt Rate = 0.25 inhr

Infilt Rate = 0.50 in/hr


Bioretention Cell (6" ponding) Sized for Predeveloped Forest Std

NPDES Permit NPDES Permit RequirementsRequirements Oregon Hydromodification ProvisionsOregon Hydromodification Provisions

– Assessment of hydromod impactsAssessment of hydromod impacts– Development strategiesDevelopment strategies

National ShiftNational Shift– LID, infiltrationLID, infiltration– MEP ->numerical stdsMEP ->numerical stds– Focus on flow durationFocus on flow duration

Western WashingtonWestern Washington– LID to maximum extent feasibleLID to maximum extent feasible– Numerical Std: Match pre-developed flow durationsNumerical Std: Match pre-developed flow durations– Continuous hydrologic modelingContinuous hydrologic modeling

Minimize impervious surfaces

Minimize disturbance to soils & vegetation

BMPs that reduce runoff using infiltration, evapotranspiration, or stormwater reuse

Examples….

Mimic predeveloped hydrologic function

BMPs to Reduce BMPs to Reduce HydromodHydromod




Examples….



Compost Amended Soil




Examples….



Retain Trees and Vegetation




Examples….



Green Roofs




Examples….



Bioretention




Examples….



Permeable Pavement




Examples….



Dispersion




Examples….



Rain Water Harvesting

Hydrologic ModelingHydrologic Modeling

Use of mathematical equations to estimate runoff as a result of:

Source: http://www.und.nodak.edu/

weather patterns, land use and topography.

Single-Event MethodsSingle-Event Methods

Single storm event (typically 24-hours) Simulate corresponding runoff (peak flow) Ex. SCS, SBUH, StormShed, xp-SWMM, HEC-

HMS

Ru

no

ff (

cfs)

Rain

fall (inch

es)

Rainfall (in)

Unmit. Runoff (cfs)

Mit. Runoff (cfs)

Time (hrs)

Continuous ModelsContinuous Models

Long-term rainfall and evaporation Simulate long-term runoff Flow durations -> period of time channels

experience elevated flows

Time (hrs)

Ru

no

ff (

cfs)

Rain

fall (inch

es)

Rainfall (in)

Unmit. Runoff (cfs)

Mit. Runoff (cfs)

Ex. HSPF, WWHM, MGS Flood

Challenges for RegionChallenges for Region

New BMPsNew BMPs New Modeling New Modeling

RequirementsRequirements New Standards -> New Standards ->

BMP size vary BMP size vary widely across the widely across the regionregion– Rainfall patternsRainfall patterns– Precipitation depthPrecipitation depth– Soil characteristicsSoil characteristics– Predeveloped Predeveloped

vegetation covervegetation cover

26 inches

68 inches

Objectives of ProjectObjectives of Project

Size BMPs without extensive Size BMPs without extensive calculations or continuous calculations or continuous modeling modeling

Streamline agency reviewStreamline agency review(“rule of thumb” sizing (“rule of thumb” sizing equations)equations)

Reduce barriers to LID Reduce barriers to LID implementationimplementation

Project SiteProject Site

Kitsap CountyKitsap County Interest in Interest in

integrating LIDintegrating LID Support plan Support plan

reviewersreviewers Allow design Allow design

without engineerwithout engineer Coming Soon to all Coming Soon to all western WA western WA lowlandslowlands

““Pre-Designed” BMPs: Pre-Designed” BMPs: prescribed prescribed depths, slopes, porosities, etc.depths, slopes, porosities, etc.

Sizing Equations: Sizing Equations: BMPs by contributing BMPs by contributing impervious area, infiltration rate & precipimpervious area, infiltration rate & precip

Flow Credits: Flow Credits: impervious surface impervious surface reduction creditsreduction credits

CalculatorCalculator

Sizing Tool SummarySizing Tool Summary

Sizing EquationsSizing Equations

Seattle Public Utilities

Infiltration BMPsInfiltration BMPs Function of Function of

contributing area, contributing area, infiltration rate & precip.infiltration rate & precip.

Bioretention CellBioretention Cell Permeable Permeable

Pavement Pavement FacilityFacility

Infiltration Infiltration TrenchTrench

Gravelless Gravelless ChamberChamber

Sizing Equations Sizing Equations “Pre-Designed” BMPs“Pre-Designed” BMPs

Bioretention CellBioretention Cell Permeable Permeable

Pavement Pavement FacilityFacility

Infiltration Infiltration TrenchTrench

Gravelless Gravelless ChamberChamber

Sizing Equations Sizing Equations Design ConfigurationsDesign Configurations

–No underdrainNo underdrain–Ponding: 2 to 10”Ponding: 2 to 10”–Side slopes 3H:1VSide slopes 3H:1V–12” bioretention 12” bioretention soil (18” for soil (18” for treatment) treatment) per Seattle specsper Seattle specs

Sized BMPs for range site conditionsSized BMPs for range site conditions– Western Washington Hydrology Model Western Washington Hydrology Model – Precipitation: 32, 36, 44, 52 in/yrPrecipitation: 32, 36, 44, 52 in/yr– Contributing Imp Area: 2,000 – 10,000 Contributing Imp Area: 2,000 – 10,000

sfsf– Design Infilt. Rates: 0.13 - 2.0 in/hrDesign Infilt. Rates: 0.13 - 2.0 in/hr

Developed RelationshipDeveloped Relationship– Contributing Imp Area and BMP AreaContributing Imp Area and BMP Area– Linear, typical Linear, typical RR22 at least 0.99 at least 0.99

Sizing Equations Sizing Equations Developed Using Continuous Developed Using Continuous ModelingModeling

y = 0.420x

y = 0.293x

y = 0.210x

0

1,000

2,000

3,000

4,000

5,000

0 2,000 4,000 6,000 8,000 10,000


Bio

rete

nti

on

Bo

tto

m A

rea

(s

f)





Sizing Relationships Sizing Relationships for Sites with 52” Annual Rainfallfor Sites with 52” Annual Rainfall

y = 0.420x

y = 0.293x

y = 0.210x

0

1,000

2,000

3,000

4,000

5,000

0 2,000 4,000 6,000 8,000 10,000


Bio

rete

nti

on

Bo

tto

m A

rea

(s

f)





Sizing Factors Sizing Factors for Sites with 52” Annual Rainfallfor Sites with 52” Annual Rainfall

BR Area = 0.21 x Imp. Area

y = 0.420x

y = 0.293x

y = 0.210x

0

1,000

2,000

3,000

4,000

5,000

0 2,000 4,000 6,000 8,000 10,000


Bio

rete

nti

on

Bo

tto

m A

rea

(s

f)





Sizing FactorsSizing Factorsfor Sites with 52” Annual Rainfallfor Sites with 52” Annual Rainfall

Sizing Factors

BR Area = SF x Imp. Area

42%

29.3%

21%

Sizing EquationsSizing Equationsfor Anywhere in Kitsap Countyfor Anywhere in Kitsap County

Sizing Factors

Bioret Area = SF x Imp. Area

y = 0.0092x - 0.0573

y = 0.0051x + 0.0317

y = 0.0034x + 0.0309

0%

10%

20%

30%

40%

50%

60%

25 30 35 40 45 50 55 60 65 70

Mean Annual Precipitation (inches)

Siz

ing

Fa

cto

r





Slope (M)

BR Area = Imp. Area x [(M x Precip) + B]

Y-Intercept (B)

Sizing Factor


BMPBMPDesign Infilt. Design Infilt. Rate (in/hr) Rate (in/hr)

Forest StandardForest Standard Treatment Treatment StandardStandard

MM BB MM BB

Bioretention CellBioretention Cell

6 inch 6 inch ponding ponding depthdepth

0.250.25 0.00920.0092 - 0.0573- 0.0573 0.00180.0018 - 0.0046- 0.0046

0.50.5 0.00510.0051 + 0.0317+ 0.0317 0.00120.0012 - 0.001- 0.001

1.01.0 0.00340.0034 + 0.0309+ 0.0309 0.00080.0008 - 0.00005- 0.00005

2.02.0 0.00260.0026 + 0.0269+ 0.0269 0.00060.0006 + 0.0002 + 0.0002


0.250.25 0.00670.0067 - 0.0381- 0.0381 0.00140.0014 - 0.0057- 0.0057

0.50.5 0.00400.0040 + 0.0067+ 0.0067 0.00090.0009 - 0.0026- 0.0026

1.01.0 0.00240.0024 + 0.0283+ 0.0283 0.00060.0006 - 0.0015- 0.0015

2.02.0 0.00180.0018 + 0.0301 + 0.0301 0.00050.0005 - 0.0008 - 0.0008 BR Bottom Area (sf) = Impervious Area (sf) x [M x Mean Annual Precipitation (in) + B]




MM BB MM BB



0.250.25 0.00920.0092 - 0.0573- 0.0573 0.00180.0018 - 0.0046- 0.0046

0.50.5 0.00510.0051 + 0.0317+ 0.0317 0.00120.0012 - 0.001- 0.001

1.01.0 0.00340.0034 + 0.0309+ 0.0309 0.00080.0008 - 0.00005- 0.00005

2.02.0 0.00260.0026 + + 0.02690.0269 0.00060.0006 + 0.0002 + 0.0002


0.250.25 0.00670.0067 - 0.0381- 0.0381 0.00140.0014 - 0.0057- 0.0057

0.50.5 0.00400.0040 + 0.0067+ 0.0067 0.00090.0009 - 0.0026- 0.0026

1.01.0 0.00240.0024 + 0.0283+ 0.0283 0.00060.0006 - 0.0015- 0.0015

2.02.0 0.00180.0018 + 0.0301 + 0.0301 0.00050.0005 - 0.0008 - 0.0008 Site Precip. = 49 Site Precip. = 49 inches/yrinches/yrBR Bottom Area (sf) = Impervious Area (sf) x [0.0026 x 49 + 0.0269] = Imp. Area (sf) x 0.1543




MM BB MM BB



0.250.25 0.00920.0092 - 0.0573- 0.0573 0.00180.0018 - 0.0046- 0.0046

0.50.5 0.00510.0051 + 0.0317+ 0.0317 0.00120.0012 - 0.001- 0.001

1.01.0 0.00340.0034 + 0.0309+ 0.0309 0.00080.0008 - 0.00005- 0.00005

2.02.0 0.00260.0026 + 0.0269+ 0.0269 0.00060.0006 + + 0.0002 0.0002


0.250.25 0.00670.0067 - 0.0381- 0.0381 0.00140.0014 - 0.0057- 0.0057

0.50.5 0.00400.0040 + 0.0067+ 0.0067 0.00090.0009 - 0.0026- 0.0026

1.01.0 0.00240.0024 + 0.0283+ 0.0283 0.00060.0006 - 0.0015- 0.0015

2.02.0 0.00180.0018 + 0.0301 + 0.0301 0.00050.0005 - 0.0008 - 0.0008 Site Precip. = 49 Site Precip. = 49 inches/yrinches/yrBR Bottom Area (sf) = Impervious Area (sf) x [0.0006 x 49 + 0.0002] = Imp. Area (sf) x 0.0296


PP Area (sf) = Impervious Area (sf) x [M x Mean Annual Precipitation (in) + B]


Forest StandardForest Standard

MM BB

Permeable Pavement SurfacePermeable Pavement Surface

depth depth calculatedcalculated

0.13 – 0.2490.13 – 0.249 0.0050.005 00

≥ ≥ 0.250.25 0.010.01 00

Permeable Pavement FacilityPermeable Pavement Facility

6 inch 6 inch

ponding ponding depthdepth

0.250.25 0.11000.1100 - 1.0536- 1.0536

0.50.5 0.01870.0187 + 0.4945+ 0.4945

1.01.0 0.00480.0048 + 0.3531+ 0.3531

PP Aggregate Depth (in) = M x Mean Annual Precipitation (in)



Forest StandardForest Standard

MM BB

Infiltration TrenchInfiltration Trench

18 inch 18 inch

depthdepth

0.130.13 0.02440.0244 -0.4918-0.4918

0.250.25 0.00970.0097 -0.1171-0.1171

0.50.5 0.00510.0051 -0.0445-0.0445

2.02.0 0.001300.00130 +0.0101+0.0101

Gravelless ChamberGravelless Chamber

Void space of Void space of 2.6 cf/ft2.6 cf/ft

0.130.13 0.00570.0057 -0.0695-0.0695

0.250.25 0.00380.0038 -0.0412-0.0412

0.50.5 0.00210.0021 -0.0104-0.0104

2.02.0 0.000720.00072 -0.00303-0.00303Length (ft) = Impervious Area (sf) x [M x Mean Annual Precipitation (in) + B]

Flow Control CreditsFlow Control Credits

Seattle Public Utilities

Impervious Impervious surface reduction surface reduction creditcredit

Degree standard Degree standard achievedachieved

Retained TreesRetained Trees Newly Planted Newly Planted

TreesTrees Green RoofGreen Roof DispersionDispersion Permeable Permeable

Pavement SurfacePavement Surface

Flow Control CreditsFlow Control Credits“Pre-Designed” BMPs “Pre-Designed” BMPs

Retained TreesRetained Trees Newly Planted Newly Planted

TreesTrees Green RoofGreen Roof DispersionDispersion Permeable Permeable

Pavement SurfacePavement Surface

Flow Control CreditsFlow Control CreditsDesign Configurations Design Configurations

– Evergreen and Evergreen and deciduous treesdeciduous trees

– Minimum 6” DBHMinimum 6” DBHLiterature review of infiltration, Literature review of infiltration,

evapotranspiration, evapotranspiration, interceptioninterception


Facility TypeFacility TypeDesign Design VariableVariable

Flow Control Credit Flow Control Credit (Forest Standard)(Forest Standard)

Retained TreesRetained Trees EvergreenEvergreen 20% canopy area (min 100 sf/tree)20% canopy area (min 100 sf/tree)

DeciduousDeciduous 10% canopy area (min 80 sf/tree)10% canopy area (min 80 sf/tree)

New TreesNew Trees EvergreenEvergreen 50 sf / tree50 sf / tree

DeciduousDeciduous 20 sf / tree20 sf / tree

Green RoofGreen Roof 4 inch depth4 inch depth 42%42%

8 inch depth8 inch depth 46%46%

DispersionDispersion NANA 77%77%

Permeable Permeable Pavement SurfacePavement Surface (3” subbase)(3” subbase)

Slope Slope ≤≤ 2% 2% 100%100%

Slope 2% - 5%Slope 2% - 5% 41%41%




Retained TreesRetained Trees EvergreenEvergreen 20% canopy area (min 100 20% canopy area (min 100 sf/tree)sf/tree)








Slope Slope ≤≤ 2% 2% 100%100%

Slope 2% - 5%Slope 2% - 5% 41%41%

Impervious Area Mitigated = Canopy Area x 20%




Retained TreesRetained Trees EvergreenEvergreen 20% canopy area (min 100 sf/tree)20% canopy area (min 100 sf/tree)








Slope Slope ≤≤ 2% 2% 100%100%

Slope 2% - 5%Slope 2% - 5% 41%41%

Impervious Area Mitigated = Green Roof Area x 42%Downstream BMP Sized for Green Roof Area x 58%

BMP Sizing CalculatorBMP Sizing Calculator

Guides designer through selecting Guides designer through selecting and sizing BMPsand sizing BMPs

DocumentatiDocumentation for project on for project submittalsubmittal

ConclusionsConclusions

Relatively easy method for designers to Relatively easy method for designers to select and size BMPsselect and size BMPs

Streamline agency reviewStreamline agency review– Rule of thumb sizing Rule of thumb sizing – Standard submittal worksheetStandard submittal worksheet

Reduces barriers to LID implementationReduces barriers to LID implementation Through Ecology grant will expand tool Through Ecology grant will expand tool

to western Washington lowlands in to western Washington lowlands in 2010-20112010-2011

Questions?Questions?

Alice Lancaster, PEAlice Lancaster, PEHerrera Environmental ConsultantsHerrera Environmental Consultantswww.herrerainc.comwww.herrerainc.comalancaster@herrerainc.com

206-441-9080206-441-9080

Documents

Simplified Sizing Tool for LID Practices in western Washington Alice Lancaster, PE Herrera Environmental Consultants