WWHM3 LID Stormwater Modeling Snohomish County August 2006 Doug Beyerlein, P.E. Clear Creek Solutions, Inc. WWHM3 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 (WWHM3) 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 (WWHM3) Available free from the Washington State Department of Ecology web site:training/wwhm/wwhm_v3/index.html How does WWHM3 LID stormwater modeling work? WWHM3 LID stormwater modeling works by: Explicitly modeling the changes in hydrology due to the LID. How does WWHM3 LID stormwater modeling work? WWHM3 explicitly represents LIDs through lateral flow basin elements green/vegetated/eco-roof element bioretention/rain garden/landscape swale element How does WWHM3 LID stormwater modeling work? Explicit representation: Dispersion Dispersion is represented by an impervious lateral basin element connected to a pervious lateral basin element. WWHM3 dispersion by lateral flow Step 1: Lateral impervious basin WWHM3 dispersion by lateral flow Step 2: Lateral pervious basin WWHM3 dispersion by lateral flow Step 3: Connect impervious basin to pervious. WWHM3 dispersion by lateral flow Step 4: Connect impervious surface runoff to pervious. WWHM3 dispersion by lateral flow Step 5: Dispersion. WWHM3 dispersion by lateral flow Step 6: Add detention pond. WWHM3 dispersion by lateral flow Step 7: Size detention pond. WWHM3 green/eco-roof modeling Eco-roof modeled: Portland Hamilton Building Data provided by Portland BES WWHM3 green/eco-roof Step 1: Green roof element WWHM3 green/eco-roof Step 2: Connect to a vault WWHM3 green/eco-roof Step 3: Size vault WWHM3 bioretention/rain garden modeling Bioretention swales modeled: Seattle 110 th Street Data provided by Seattle Public Utilities WWHM3 bioretention/rain garden modeling Native Soil Amended Soil (1-3 layers) Weir and vertical orifice outlet Underdrain (optional) WWHM3 bioretention/rain garden Step 1: Basin and bioretention WWHM3 bioretention/rain garden Step 2: Add detention pond WWHM3 bioretention/rain garden Step 3: Size pond WWHM3 LIDs in series Green roof to lateral pervious basin to bioretention swale to bioretention swale WWHM3 LID modeling results Green roof/eco-roof vs convention roof WWHM3 LID modeling results Seattle Roof Flood Frequency Comparison Return Period (years)Reduction 224% 520% 1018% 2516% 5015% 10015% WWHM3 LID modeling results Seattle Roof Flow Duration Comparison Conventional Runoff Eco-Roof Runoff WWHM3 LID modeling results Bioretention/rain garden modeling results: WWHM3 LID modeling results Seattle Bioretention Frequency Comparison Return Period (years)Reduction 266% 563% 1064% 2566% 5067% 10069% Summary Stormwater LIDs reduce stormwater runoff and its associated problems. WWHM3 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 WWHM3 PRO Basic. For more information go to: Doug Beyerlein Joe Brascher Questions? Contact Doug Beyerlein Joe Brascher