HYDROLOGIC AND HYDRAULIC MODELING OF THE DENSMORE DRAINAGE BASIN, SEATTLE, WA
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Client: Seattle Public Utilities, Seattle, WA

The City of Seattle contracted with Clear Creek Solutions to provide hydrologic and hydraulic modeling services to develop solutions to reduce flooding in the Densmore drainage system in the vicinity of 107th and Midvale caused by large events like the December 2007 flood.

The WWHM HSPF-SWMM model results were calibrated to the December 2007 flood to determine model accuracy. Once assured that the WWHM model of the Densmore basin was accurate, a stage frequency and stage duration analysis was performed on the node that represents the flooded area around 107th and Midvale. The model was then modified to include alternative analysis for possible solutions to the flooding issues around 107th and Midvale. This included culvert upsizing with potential downstream impacts modeled.

The Western Washington Hydrology Model (WWHM) was used to model the stormwater runoff from the 3,157-acre Densmore drainage basin. WWHM used HSPF to generate the stormwater runoff and SWMM to route the runoff through the City's conveyance system to Green Lake.

Flood frequency and other flow statistics were generated from the WWHM results. Capital improvements were included in the models to evaluate their performance prior to determining their recommended priority for implementation.