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Hydraulic and Hydrologic Analyses of the May Creek Channel Restoration Project

Report cover, Hydraulic and Hydrologic Analyses of the May Creek Channel Restoration ProjectThe Hydraulic and Hydrologic Analyses of the May Creek Channel Restoration Project is a study evaluating the channel capacity of May Creek and to optimize a project design with excavation and thinning of in-channel vegetation at choke points along the creek. Analyses include: assessment of channel capacity for existing and proposed designs, assessment of flood frequencies and durations, assessment of channel competency to mobilize fine sediments and improve lifespan of the project, and assessment of impacts to erosivity in the ravine downstream of 148th Ave SE.

Two types of models were used for these analyses, HSPF and HEC-RAS. HSPF is an U.S. EPA hydrologic watershed model used extensively in the Puget Sound region. The original model used was developed for the May Creek Current and Future Conditions report (King County 1995). This model was updated with more current meteorology and channel routing to improve understanding of stream responses with longer periods of precipitation record and more accurate hydraulics. The HEC-RAS model used was last modified by Otak in 2006. For this study, new land survey work was completed in 2010 to update channel geometry and enhance resolution specific to this project study area, supporting simulation of several proposed channel restoration activities to reduce frequency of flooding without significant downstream impacts.

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For questions about the Hydraulic and Hydrologic Analyses of the May Creek Channel Restoration Project, please contact Doug Chin, Project Manager, King County Water and Land Resources Division.