The Castle Rock levee system
To protect the town of Castle Rock from lahars and from flooding, the US Army Corps of Engineers reinforced the towns levee system in 2009. The project involved grouting sand layers beneath the levee to eliminate seepage pathways that could undermine the levee as happened at New Orleans in hurricane Katrina. The levee was also raised 3 or 4 feet to meet revised flood frequency calculations. The Corps estimated in 1997 that the 1% probability event (i.e. the 100-year flood) would have a discharge of 97 kcfs whereas their 2008 report estimates 113 kcfs. The corresponding river elevations are about 53 and 56 feet compared to the new levee elevation of 60.9 feet at the Castle Rock bridge.
Photo by James Maynard © 2011 - free use with attribution [full-size jpeg]
Some additional resources:
Other images from US Army Corps of Engineers
Flood frequency data for the Cowlitz at Castle Rock (xlsx)
Geotechnical data for the Castle Rock levee system
Grain-size analysis for Cowlitz River bottom sediment
Cover images for USACE reports - click for links |
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