Emptying Hengshan Reservoir to Flush the Sediment Out

Hengshan Reservoir is located in Shanxi Province in Northern China. It has multiple functions in water supply and flood control etc. It also has the first experimental double-curvature arch dam in China. This is a small reservoir on a steep stream. In the first eight years of operation, 24% of the reservoir capacity was occupied by sediment deposits. Flushing, which was undertaken with reservoir emptying in 1974, 1979, 1982 and 1986, was effective in restoring the lost storage capacity and indicated that flushing in every few years will be sufficient to maintain the long term reservoir use. 

In the 250 meters range in front of the dam, the sediment concentration of the flow was measured to be 1,200 kg/m3 and the total flushing time lasted 30 hours. The side slope developed by emptying the reservoir was 0.055. In the middle reach of the reservoir, the mud has very low water content, and it collapsed like Ichthyosis, even there are big chunk of mud floating on the water. In the upstream of the reservoir, the water content was even lower, the sediment deposition looked like crackings of a turtle. With the depth of the main channel being flushed to be higher, more and more mud from the side slope collapsed into the reservoir.