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
Infilt Rate = 1.0 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
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
Compost Amended Soil
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
Retain Trees and Vegetation
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
Green Roofs
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
Bioretention
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
Permeable Pavement
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
Dispersion
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
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
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
Infilt Rate = 1.0 in/hr
Bioretention Cell (6" ponding) Sized for Predeveloped Forest Std
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
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
Infilt Rate = 1.0 in/hr
Bioretention Cell (6" ponding) Sized for Predeveloped Forest Std
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
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
Infilt Rate = 1.0 in/hr
Bioretention Cell (6" ponding) Sized for Predeveloped Forest Std
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
Infilt Rate = 0.25 in/hr
Infilt Rate = 0.5 in/hr
Infilt Rate = 1.0 in/hr
Bioretention Cell (6" ponding) Sized for Predeveloped Forest Std
Slope (M)
BR Area = Imp. Area x [(M x Precip) + B]
Y-Intercept (B)
Sizing Factor
Sizing EquationsSizing Equations
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
10 inch 10 inch ponding ponding depthdepth
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]
Sizing EquationsSizing Equations
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 + + 0.02690.0269 0.00060.0006 + 0.0002 + 0.0002
10 inch 10 inch ponding ponding depthdepth
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
Sizing EquationsSizing Equations
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
10 inch 10 inch ponding ponding depthdepth
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
Sizing EquationsSizing Equations
PP Area (sf) = Impervious Area (sf) x [M x Mean Annual Precipitation (in) + B]
BMPBMPDesign Infilt. Design Infilt. Rate (in/hr) Rate (in/hr)
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)
Sizing EquationsSizing Equations
BMPBMPDesign Infilt. Design Infilt. Rate (in/hr) Rate (in/hr)
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
Flow Control CreditsFlow Control Credits
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%
Flow Control CreditsFlow Control Credits
Facility TypeFacility TypeDesign Design VariableVariable
Flow Control Credit Flow Control Credit (Forest Standard)(Forest Standard)
Retained TreesRetained Trees EvergreenEvergreen 20% canopy area (min 100 20% canopy area (min 100 sf/tree)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%
Impervious Area Mitigated = Canopy Area x 20%
Flow Control CreditsFlow Control Credits
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%
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