Technical Guidance Manual for Puget Sound December 2012 THIS PAGE INTENTIONALLY LEFT BLANK Low Impact Development Technical Guidance Manual for Puget Sound December 2012 WSU Puyallup Research 326 East D Street & Extension Center Tacoma, WA 98421 2606 West Pioneer 360.464.1232 Puyallup, WA 98371 [email protected] www.pierce.wsu.edu Author and project co-lead: Curtis Hinman, Washington State University Extension Faculty Project co-lead: Bruce Wulkan, Puget Sound Partnership Design and layout: AHBL Illustrations: AHBL (except where noted) Research, facilitation and external review: VEDA Consulting Publication No. PSP 2012-3 THIS PAGE INTENTIONALLY LEFT BLANK Acknowledgements Technical Advisory Committee Bruce Barker MGS Catherine Benotto Webber Thompson Mark Buehrer 2020 Engineers Art Castle Building Industry Association of WA Rich Geiger Mason Conservation District Kathy Gwilym SvR Design Kas Kinkead Cascade Design Collaborative Tim Kurtz City of Portland Alice Lancaster Herrera Chris May Kitsap County David McDonald City of Seattle Matt Miller Associated Earth Sciences Ed O’Brien Department of Ecology Tracy Tackett City of Seattle Bruce Wulkan Puget Sound Partnership Craig Young Snohomish County Contributors Michael Bledsoe Pervious Concrete Inc. Patrick Carey Hadj Designs Jeff Cox Triad Associates Drena Donofrio Seattle Public Utilities Rick Gagliano PIN Foundations Erica Guttman Washington State University Extension Robin Kirschbaum HDR Andy Marks Puget Sound Concrete Specification Council David McDonald Seattle Public Utilities Ed O’Brien Department of Ecology Robert Pine Pine and Swallow Environmental David Smith Interlocking Concrete Pavement Institute Paul Thompson Urban Forestry Services, Inc. Brian Taylor AMEC Funding Portions of this project were produced with support from the Puget Sound Partnership. Washington State University Extension contributed in-kind support for this project. THIS PAGE INTENTIONALLY LEFT BLANK Table of Contents Glossary........................................................................................................................................................................................................................................i 1. Introduction..............................................................................................................................................................................................................................1 1.1 Puget Sound Hydrology..................................................................................................................................................................................2 1.2 Impacts of Urbanization.................................................................................................................................................................................2 1.3 Current Stormwater Management.........................................................................................................................................................9 1.4 Low Impact Development..........................................................................................................................................................................10 2. Site Assessment.....................................................................................................................................................................................................................17 2.1 Stormwater Site Plans..................................................................................................................................................................................18 2.2 Soil and Subsurface Hydrology Characterization.....................................................................................................................22 2.3 Hydrologic Patterns and Features.........................................................................................................................................................27 2.4 Native Forest and Soil Protection Areas.......................................................................................................................................27 2.5 Wetlands.................................................................................................................................................................................28 2.6 Riparian Management Areas (RMA)...................................................................................................................................................29 2.7 Streams.....................................................................................................................................................................................30 2.8 Floodplains....................................................................................................................................................................................30 2.9 Sub-basin Delineation....................................................................................................................................................................................31 2.10 Site Mapping Process.............................................................................................................................................................................32 3. Site Planning & Layout.................................................................................................................................................................................................35 3.1 Urban Redevelopment and Infill..............................................................................................................................................................37 3.2 New Suburban Development...................................................................................................................................................................47 3.3 Commercial Development...........................................................................................................................................................................69 3.4 Road Crossings....................................................................................................................................................................................................72 4. Vegetation & Soil Protection & Reforestation.......................................................................................................................73 4.1 Native Vegetation and Soil Protection................................................................................................................................................75 4.2 Re-establishing Native Vegetation.......................................................................................................................................................80 4.3 Maintenance of Protected Areas.............................................................................................................................................................82 5. Precision Site Preparation, Construction & Inspection of LID Facilities......................................83 5.1 Precision Site Preparation...........................................................................................................................................................................84 5.2 Techniques to Minimize Site Disturbance..............................................................................................................................86 5.3 Inspection of LID Facilities...........................................................................................................................................................................86 5.4 Construction Sequencing of LID Facilities.........................................................................................................................................90 Table of Contents, cont. 6. Integrated Management Practices......................................................................................................................................................97 6.1 Bioretention...........................................................................................................................................................................98 6.2 Amending Construction Site Soils....................................................................................................................................................149 6.3 Permeable Pavement..................................................................................................................................................................................161 6.4 Urban and Suburban Trees....................................................................................................................................................................203 6.5 Vegetated Roofs..............................................................................................................................................................................................217 6.6 Minimal Excavation Foundation Systems......................................................................................................................................227 6.7 Roof Rainwater Collection Systems...................................................................................................................................................233