UW LID Workshop Bioretention Flow Control Modeling May 2008
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UW LID Workshop UW LID Workshop Bioretention Flow Control Bioretention Flow Control Modeling Modeling May 2008 May 2008 Doug Beyerlein, P.E. Doug Beyerlein, P.E. Clear Creek Solutions, Inc. Clear Creek Solutions, Inc.
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UW LID Workshop Bioretention Flow Control Modeling May 2008. Doug Beyerlein, P.E. Clear Creek Solutions, Inc. Clear Creek Solutions’ Stormwater LID Expertise. Clear Creek Solutions, Inc., provides complete range of hydrologic and stormwater modeling services. - PowerPoint PPT Presentation
Transcript of UW LID Workshop Bioretention Flow Control Modeling May 2008
UW LID WorkshopUW LID Workshop
Bioretention Flow Control Bioretention Flow Control ModelingModeling
May 2008May 2008
Doug Beyerlein, P.E. Doug Beyerlein, P.E.
Clear Creek Solutions, Inc.Clear Creek Solutions, Inc.
Clear Creek Solutions’ Clear Creek Solutions’ Stormwater LID ExpertiseStormwater LID Expertise
Clear Creek Solutions, Inc., provides complete range of hydrologic and stormwater modeling services.
• Clear Creek specializes in continuous simulation hydrologic modeling.
• We have 30+ years of experience modeling complex hydrologic and stormwater problems.
• We created the Western Washington Hydrology Model Version 3 (WWHM3) for Washington State Department of Ecology.
• We teach WWHM and HSPF workshops.
PresentationPresentation
IntroductionIntroduction
WWHM: Western Washington Hydrology WWHM: Western Washington Hydrology ModelModel
Bioretention Implicit Modeling Bioretention Implicit Modeling
Bioretention Explicit Modeling Bioretention Explicit Modeling
Seattle Bioretention Swale ModelingSeattle Bioretention Swale Modeling
Modeling ResultsModeling Results
SummarySummary
Questions & AnswersQuestions & Answers
Bioretention/rain garden/landscape swale:
Bioretention: Planter Box
Bioretention Reduces Runoff Volume:
1. Infiltration to native soil.
2. Evaporation and transpiration.
Flow Control Modeling
Continuous simulation: WWHM (HSPF)
Continuous simulation hydrology models the entire hydrologic cycle for multiple years.
Western Washington Hydrology Model (WWHM)
Developed for the State of Washington Department of Ecology.
Project Manager: Dr. Foroozan LabibDepartment of EcologyPO Box 47600Olympia, WA 98504-7600(360) 407-6439email: [email protected]
Western Washington Hydrology Model (WWHM)
Developed for the 19 counties of western Washington.
Part of Ecology’sStormwater ManagementManual
WWHM3
Available free from the Washington State Department of Ecology web site:
http://www.ecy.wa.gov/programs/wq/stormwater/
WWHM3
WWHM helps the user design facilities to meet the Washington State Department of Ecology’s flow control standards.
WWHM3
Ecology’s flow duration standard: based on erosive flows.
Erosive flow range: ½ of the 2-year to the 50-year
Disclaimer:
Bioretention by itself will not meet Ecology’s flow control standards…
but bioretention will reduce the size of a flow control facility (stormwater pond, vault, etc.).
Bioretention Flow Paths
Infiltration to Native Soil
Weir Flow
Inflow to Bioretention
Facility
Infiltration to Amended Soil
Underdrain Flow
Vertical Orifice Flow
Bioretention Flow Paths
Weir Flow
Underdrain Flow
Vertical Orifice Flow
Weir, vertical orifice, and underdrain flow all are subject to Ecology’s flow control standard (1/2 of 2-yr to 50-yr).
Bioretention Flow Paths
Infiltration to Native Soil
Infiltration to native soil is dependent on native soil characteristics.
WWHM: Bioretention Modeling Options
Bioretention can be modeled implicitly or explicitly:
PSAT (Puget Sound Action Team) recommends how to implicitly represent bioretention in WWHM2
WWHM3 explicitly represents bioretention
WWHM: Bioretention Modeling Options
Implicit modeling:
Represent bioretention as a pond filled with dirt. Reduce pond volume to volume of available void space.
Disadvantage: Assumes pond fills from the bottom up to the surface.
WWHM: Bioretention Modeling Options
Explicit modeling (current):
Check infiltration rate into amended soil vs. soil moisture volume available (surface ponding). Invert the stage-volume relationship so that the soil column fills from the top down.
Disadvantage: Simplifies the movement of water through the soil column.
WWHM: Bioretention Modeling Options
Explicit modeling (future):
dynamic hydraulic conductivity based on soil saturation levels conductivity computed based on the Van Genuchten equations discharge from a given soil layer is then computed based on conductivity, stage, and surface area
WWHM Bioretention Modeling Options cont’d:
Explicit modeling (future):
Soil parameters based on Rosetta parameters (Table 1).
WWHM Rosetta parameters* (Table 1).
Soil NameSoil Name SrSr SsSs KsKs nnCourse sandCourse sand 0.0520.052 0.3950.395 3.1623.162 0.5010.501Fine sandFine sand 0.0520.052 0.3640.364 2.5522.552 0.4040.404Sandy loamSandy loam 0.0300.030 0.3800.380 1.4451.445 0.3170.317LoamLoam 0.0610.061 0.3990.399 1.4791.479 0.1970.197Silty clay loamSilty clay loam 0.0770.077 .0475.0475 1.5131.513 .0184.0184Clay loamClay loam 0.0870.087 0.4450.445 1.4121.412 0.1330.133Peat***Peat*** 0.0990.099 0.8630.863 3.0503.050 0.2290.229Gravel loamy Gravel loamy sandsand 0.10.1 0.450.45 3.53.5 9.379.37
Gravel**Gravel** 0.020.02 0.420.42 1010 18.418.4
*Values taken from Schaap and Leij (1998).
**Values based on Hazen and Naval Facilities Engineering Command (NAVFAC).
***Estimation of Unsaturated Hydraulic Conductivity of Peat Soils, Schwarzela, et al.
WWHM Bioretention Modeling Options cont’d:
Explicit modeling (future):
The level of saturation of that soil layer is proportionate to the fraction of soil volume within a given stage:
Se = Sr + [1- (H / Hm) *(Ss-Sr)]
Where:Se = SaturationSr = Residual SaturationH = Stage (within layer)Hm = Height of the layerSs = Max saturation
WWHM Bioretention Modeling Options cont’d:
Explicit modeling (future):
Hydraulic conductivity K as a function of the saturation level within the soil layer is determined by the Van Genuchten equation:
K = Ks *Se^(1/2) * [1-(1-Se^(1/M))^M]^2
Where:Ks = Saturated Hydraulic ConductivitySe = SaturationM = 1-(1/n)n = Van Genuchten fitting parameter
WWHM Bioretention Modeling Options cont’d:
Explicit modeling (future):
Flow through the porous layers is determined using Darcy’s equation:
Q = As * K * S
Where:Q = Flow (inches/hour)As = Surface AreaK = Hydraulic Conductivity S = Stage
WWHM Bioretention ModelingSeattle Bioretention Swales
WWHM3 Bioretention Modeling
Drainage areas A, B, and C to bioretention swales.
WWHM Bioretention ModelingSeattle Bioretention Swales
WWHM Bioretention ModelingDownstream control structure:
Water infiltrates into the soil before runoff.
WWHM Bioretention Modeling
Native Soil
Native Soil
Native Soil
Amended Soil (1-3 layers)
Weir and vertical orifice outlet
Underdrain (optional)
WWHM3 Bioretention Modeling
WWHM3 bioretention element stores and infiltrates runoff.
SPU Bioretention CalibrationModel results: Seattle Swale N-2 (2004)
Amended soil infiltration rate = 3.0 in/hrNative soil infiltration rate = 1.9 in/hr
SPU Bioretention CalibrationModel results: Seattle Swale N-2 (2004)
Amended soil infiltration rate = 3.0 in/hrNative soil infiltration rate = 1.9 in/hr
SPU Bioretention CalibrationModel results: Seattle Swale N-2 (2004)
29-30 January 2004 storm event
SPU Bioretention Modeling ResultsSeattle Bioretention Frequency Comparison
Return Period (years) Reduction
2 66%
5 63%
10 64%
25 66%
50 67%
100 69%
Bioretention Modeling ResultsStormwater volume reduction:
Stormwater Reduction (%) for Seattle Soils
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Ratio of Rain Garden Area to Impervious Area
Red
uct
ion
Till Outwash
SPU Bioretention Modeling Results
SPU Rain Garden Sizing Analysis y = 0.0513x + 2.1419
R2 = 1
0
100
200
300
400
500
600
0 2000 4000 6000 8000 10000
Impervious Area (square feet)
Ra
in G
ard
en
Are
a (
sq
ft)
Linear (I = 0.25 in/hr 5" pond)
Figure 3. Rain Garden with Live Storage Depth of 5 Inches
SPU Bioretention Modeling Results
Figure 4. Rain Garden with Live Storage Depth of 10 Inches
SPU Rain Garden Sizing Analysis y = 0.0389x + 0.3604
R2 = 0.9999
0
50
100
150
200
250
300
350
400
450
0 2000 4000 6000 8000 10000
Impervious Area (square feet)
Ra
in G
ard
en
Are
a (
sq
ft)
Linear (I = 0.25 in/hr 10" pond)
Bioretention Modeling Results
For example:
For an impervious area of 5000 sq ft a bioretention area of 195 sq ft with 10” of surface ponding is needed (assuming a native soil infiltration rate of 0.25 inches/hour).
Bioretention Modeling Results
Summary: Bioretention works best for flow control when there is sufficient native soil infiltration.
Underdrain flows must still be mitigated to flow control standards.
Bioretention can reduce stormwater runoff volume, but additional mitigation will still be required to meet Ecology’s flow control standards.
Acknowledgements
Seattle Public Utilities (Tracy Tackett) and Washington State University (Curtis Hinman) provided the funding for the WWHM3 bioretention modeling.
For more information on WWHM3
bioretention modelinggo to:
www.clearcreeksolutions.com
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