WWHM 3 LID Stormwater Modeling Snohomish County August

WWHM 3 LID Stormwater Modeling Snohomish County August 2006 Doug Beyerlein, P. E. Clear Creek Solutions, Inc.

WWHM 3 LID Stormwater Modeling Presented at the August 2006 Snohomish County LID Workshop Everett, WA © 2006 Clear Creek Solutions, Inc. All rights reserved.

Clear Creek Solutions’ Stormwater 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 (WWHM 3) for Washington State Department of Ecology. • We teach WWHM and HSPF workshops.

Presentation Introduction What is LID stormwater modeling? How does LID stormwater modeling work? LID stormwater modeling results Questions & Answers

What is LID stormwater modeling? LID stormwater modeling is hydrologic and hydraulic computer modeling of low impact development practices to reduce stormwater runoff. Examples: 1. Dispersion of runoff on pervious surfaces 2. Green/vegetated/eco-roof 3. Rain garden/bioretention/landscape swale

Examples of stormwater LIDs Dispersion of impervious roof runoff on adjacent pervious lawn allowing some water to infiltrate before becoming stormwater runoff.

Examples of stormwater LIDs Green/vegetated/eco-roof Water is stored in the soil prior to runoff.

Examples of stormwater LIDs Rain garden/bioretention/landscape swale Water infiltrates into the soil before runoff.

Western Washington Hydrology Model version 3 (WWHM 3) Available free from the Washington State Department of Ecology web site: http: //www. ecy. wa. gov/programs/wq/stormwater/wwhm_ training/wwhm_v 3/index. html

How does WWHM 3 LID stormwater modeling work? WWHM 3 LID stormwater modeling works by: Explicitly modeling the changes in hydrology due to the LID.

How does WWHM 3 LID stormwater modeling work? WWHM 3 explicitly represents LIDs through S lateral flow basin elements S green/vegetated/eco-roof element S bioretention/rain garden/landscape swale element

How does WWHM 3 LID stormwater modeling work? Explicit representation: Dispersion is represented by an impervious lateral basin element connected to a pervious lateral basin element.

WWHM 3 dispersion by lateral flow Step 1: Lateral impervious basin

WWHM 3 dispersion by lateral flow Step 2: Lateral pervious basin

WWHM 3 dispersion by lateral flow Step 3: Connect impervious basin to pervious.

WWHM 3 dispersion by lateral flow Step 4: Connect impervious surface runoff to pervious.

WWHM 3 dispersion by lateral flow Step 5: Dispersion.

WWHM 3 dispersion by lateral flow Step 6: Add detention pond.

WWHM 3 dispersion by lateral flow Step 7: Size detention pond.

WWHM 3 green/eco-roof modeling Eco-roof modeled: Portland Hamilton Building Data provided by Portland BES

WWHM 3 green/eco-roof Step 1: Green roof element

WWHM 3 green/eco-roof Step 2: Connect to a vault

WWHM 3 green/eco-roof Step 3: Size vault

WWHM 3 bioretention/rain garden modeling Bioretention swales modeled: Seattle 110 th Street Data provided by Seattle Public Utilities

WWHM 3 bioretention/rain garden modeling Weir and vertical orifice outlet Native Soil Amended Soil (1 -3 layers) Underdrain (optional) Native Soil

WWHM 3 bioretention/rain garden Step 1: Basin and bioretention

WWHM 3 bioretention/rain garden Step 2: Add detention pond

WWHM 3 bioretention/rain garden Step 3: Size pond

WWHM 3 LIDs in series Green roof to lateral pervious basin to bioretention swale

WWHM 3 LID modeling results Green roof/eco-roof vs convention roof

WWHM 3 LID modeling results Seattle Roof Flood Frequency Comparison Return Period (years) Reduction 2 24% 5 20% 10 18% 25 16% 50 15% 100 15%

WWHM 3 LID modeling results Seattle Roof Flow Duration Comparison Conventional Runoff Eco-Roof Runoff

WWHM 3 LID modeling results Bioretention/rain garden modeling results:

WWHM 3 LID modeling results Seattle Bioretention Frequency Comparison Return Period (years) Reduction 2 66% 5 63% 10 64% 25 66% 50 67% 100 69%

Summary Stormwater LIDs reduce stormwater runoff and its associated problems. WWHM 3 is a powerful stormwater modeling tool to evaluate the benefits of using stormwater LIDs.

Summary Green/eco-roof and bioretention/rain garden elements are available in WWHM 3 PRO Basic. For more information go to: www. clearcreeksolutions. com

Questions? Contact Doug Beyerlein 425. 892. 6454 beyerlein@clearcreeksolutions. com Joe Brascher 360. 943. 0304 brascher@clearcreeksolutions. com