RESERVOIR SEDIMENTATION .1. DELTA AND DENSITY-CURRENT DEPOSITS

In China, where rivers draining loess soils have some of the highest sediment concentrations in the world, reservoir sedimentation is a serious problem that has been the subject of intensive investigation since 1957. This paper describes patterns of sediment deposition and erosion drawing on field measurements in China at the Sanmenxia, Guanting, Shanyiujiang, and Liujiaxia reservoirs, as well as the Shanshenggong barrage and Xijin hydropower station. The longitudinal and lateral geometry of reservoir deltas is described. It is shown that a marked change in grain size can occur at the downstream limit of the delta, even when this limit is not apparent from geometry. Density current data for Guanting reservoir are presented. Problems caused by reservoir sedimentation in China are described, including aggredation in the backwater region causing increased flood levels, elevated ground-water levels, and navigation impairment; deposition from or into a tributary; entry of sediments into hydropower turbines; and loss of beneficial storage.