Introduction

Over the past 20 years numerous studies have been undertaken to investigate flood damage reduction in the Chehalis River basin. These projects include work for FEMA, Lewis County, the Lewis County PUD and the US Army Corps of Engineers. Much of this work has focused on the development of a hydraulic model of the Chehalis River for the mainstem between Doty and Grand Mound and application of that model to simulate the “100-year flood”. Work for Lewis County and the PUD included application of the model to evaluate the potential benefits or impacts of various proposed flood damage reduction projects including upstream storage. Work by the Corps included evaluation of levee projects primarily along the main stem river near Chehalis and Centralia. 
 
These hydraulic analyses have provided insight into many issues related to floodplain management. However, the analyses to date have only considered the reach of the Chehalis River upstream of Grand Mound. The Chehalis River Flood Authority desires to extend the hydrologic and hydraulic modeling downstream from Grand Mound to the mouth of the Chehalis River at Grays Harbor and to use the extended and improved model to evaluate the potential impact of upstream flood damage reduction projects on downstream flooding.

The primary objective of the Chehalis River Basin Flood Authority’s lower Chehalis Basin Hydraulic Model Development contract with Watershed Science & Engineering (WSE) is to develop a hydraulic model to address the ESHB 2020 requirement “to complete the hydraulic model for the Chehalis river to calculate flood levels, flood damages, and benefits of proposed flood mitigation projects for the lower portions of the river”. Other, secondary objectives may be identified over the course of the project and addressed to the extent possible considering funding and schedule constraints.

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Resources

Contracting Documents

 TitleOwnerCategoryLast Updated
Content Type Hydraulic Model Development Work Plan (10-19-2011) larry@watershedse.com 5/31/2012
Content Type RFQ Evaluation Questions (8/12/2011) scottb@sbgh-partners.com 5/31/2012
Content Type Tributaries Analysis Work Plan (1-17-2011) larry@watershedse.com 5/31/2012
Content Type Watershed Science & Engineering Contract (9-16-2011) larry@watershedse.com 5/31/2012
Content Type WSE - West Team Work Plan Framework (9/30/2011) larry@watershedse.com 5/31/2012
Content Type WSE Stakeholder Information Request (9-16-2011) larry@watershedse.com 5/31/2012
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