Deposition at a New Dam Near Mount St. Helens

Korsness, Mark A.; ,

Deposition at a New Dam Near Mount St. Helens

by Mark A. Korsness, US Army Corps of Engineers, United States,

Document Type: Proceeding Paper

Part of: Hydraulic Engineering

Abstract:

A sediment retention structure (SRS) is being constructed on the North Fork Toutle River in the state of Washington to trap sediments eroding off the 1980 Mount St. Helens debris avalanche. This structure has trapped 5.7 million cubic yards of material in its first 7 months of operation. The U.S. Army Corps of Engineers, Portland District, began construction of the dam to reduce predicted long-term sediment deposition in rivers downstream, causing an increased flood risk. A delta of sand and gravel started forming in the pool behind the structure immediately after closure and has caused deposition 3 miles upstream on an average slope of 0.6 of the original slope. Ground surveys, aerial photography, extensive sediment sampling and field monitoring have been incorporated to monitor the performance of the SRS, which will be completed in the fall of 1989.

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