Looks like things are better than we thought.
Reservoirs are sustainable only as long as they offer sufficient water storage space to achieve their design objectives. Life expectancy related to sedimentation is a measure of reservoir sustainability. We used data from the Army Corps of Engineers, U.S. Bureau of Reclamation, and U.S. Geological Survey (Reservoir Sedimentation Survey Information System II (RESIS II) to explore the sustainability of American reservoirs. Sustainability varied by region, with the longest life expectancies in New England and the Tennessee Valley and the shortest in the interior west. In the Missouri and Colorado River basins, sedimentation and rates of loss of reservoir storage capacity were highly variable in time and space. In the Missouri River basin, the larger reservoirs had the longest life expectancies, with some exceeding 1000 years, while smaller reservoirs in the basin had the shortest life expectancies. In the Colorado River basin at the site of Glen Canyon Da, sediment inflow varied with time, declining by half beginning in 1942 becuase of hydroclimate and upstream geomorphic changes. Because of these changes, the estimated life expectancy of Lake Powell increased from 300 to 700 years. Future surprise changes in sedimentation delivery and reservoir filling area are expected. Even though large western reservoirs were built within a limted period. their demise will not be synchronous becuase of varying sedimentation rates. Popular literature has incorrectlyemphasized the possibility of rapid, synchronous loss of reservoir storage capacity and underestimated the sustainability of water control infrastructure.
Click on the figure (Annul Reservoir Storage Loss) to enlarge it.
"Rivers are roads which move, and which carry us whither we desire to go." ~Blaise Pascal