Mount St. Helens Project. Cowlitz River Levee Systems, 2009 Level of Flood Protection Update Summary
ARMY ENGINEER DISTRICT PORTLAND OR
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USACE periodically updates the Levels of Protection LOP for the Cowlitz River levees as part of ongoing activities of the Mount St. Helens project. The most recent comprehensive LOP update prior to 2009 was performed in 1997 for the Cowlitz River Flood Hazard Study. Since 1997, there have been several interim assessments of the levee system, however a complete study of the hydrology, hydraulics, and levee index points were not performed for these interim assessments. The current 2009 LOP assessment for the Cowlitz River levees incorporates a detailed review of each component of the 1997 Cowlitz River Flood Hazard Study. This update includes Revisions to the Fragility Curve for the levees Revisions to the Cowlitz River discharge-frequency curve Revisions to the stage-discharge relationships based on a comprehensive Cowlitz River survey, performed in August 2009 by David Evans and Associates, from the Toutle River confluence, approximately River Mile RM 20, to the Columbia River confluence RM 0 Revisions to hydraulic and hydrologic uncertainty.
- Hydrology, Limnology and Potamology
- Civil Engineering