To restore the channels of the Columbia River for navigation and the Toutle and Cowlitz rivers for flood control, the U.S. Army Corps of Engineers dredged more than about 85 million m³ (110 million yd³) of sediment from the rivers within three years of the 1980 eruption of Mount St. Helens. In June 1980, Congress appropriated more than $200 million for this effort. Faced with the possibility of dredging for an unknown length of time to keep the channels clear, the Corps of Engineers chose instead to build a sediment-retention structure across the Toutle River beginning in 1987; the structure was completed in 1989.