Author(s): A. Vali Khojeini
Keywords: Reservoir sedimentation; Flushing operation; Sefid-Rud reservoir; Downstream impacts
Abstract: The Sefid-Rud Dam is situated in northern Iran, at Manjl. Sedimentation was a serious problem and caused storage loss at the rate 37 Mm 3 ·yr -1. Because of rapid storage loss, since 1980 the flushing operation has practiced for remove of deposited sediments from the reservoir. Hydraulic flushing involved reservoir drawdown by opening a low-level outlet to temporaily establish streamline flow along the impounded reach, eroding a channel through the deposits and flushing the eroded sediment through the outlet. Annual reduction of storage before flushing was 2.5% and became 1.8% after flushing operation. Average concentration during the flushing periods was 40 g·l -1. Sediment released by flushing was redeposited somewhere downstream: in the stream channel, downstream reservoir, water intakes and delivery systems, the sea, etc. The reclaimed volume of the reservoir during flushing was considerable, but the discharge with high concentration has caused cavitations on radial gates. The discharged silts have caused heavy losses to irrigation network and river delta. It has affected the quality of water, wild life and thus, the ecosystem of the region. The outgoing sediment load by flushing operations results in retrogression set by the impoundment in the downstream parts. The recorded observation and the results obtained are in this paper.