Toutle River Sediment Retention StructureEdit profile
Coordinates: 46°21′42″N 122°33′06″W / 46.36153°N 122.551728°W / 46.36153; -122.551728
The Sediment Retention Structure is a 1,800-foot-long (550 m), 184-foot-high (56 m) earthen dam on the North Fork of the Toutle River in Washington. Its construction was completed by the US Army Corps of Engineers in 1989. Its purpose is to retain sediment created since the 1980 eruption of Mount St. Helens, to prevent the sediment from becoming a hazard to navigation on the Toutle, Cowlitz and Columbia Rivers.
The Corps of Engineers expects the lake behind the dam to be completely filled with sediment by 2035 with 258 million cubic yards (197 million m3) of sand, gravel and sediment. However, the basin is already filled as of 2011.