Worldwide Experience of Sediment Flushing Through Reservoirs
Authors: Muhammad Asif Chaudhry, Habib-Ur-Rehman
Number of views: 259
Globally there are about 25,500 storage reservoirs with total storage volume of about 6,464 Bcm. The maximum number of reservoirs are in North America, i.e. 7205 with the total storage volume of about 1,844 Bcm, whereas minimum number of reservoirs are in Central Asia, i.e. 44, with the total storage volume of about 148 Bcm. Over the globe, average annual reservoir storage loss due to sedimentation varies from 0.1-2.3%, however, average annual world storage loss is about 1.0%. In order to combat the storage loss, the techniques used globally are: watershed management, dredging of deposited sediments, sediment routing/sluicing, sediment bypassing, density current venting and sediment flushing through reservoir, separately and also in combination. Each approach has its own limitations, depending on the site conditions. Sediment flushing technique is used by two ways i.e. Drawdown flushing and Emptying and Flushing. In Emptying and Flushing, the reservoir is emptied before the flood season, resulting in the creation of river-like flow conditions in the reservoir. The flow velocities in the reservoir are increased to such an extent that deposited sediments are remobilized and transported through the low level outlets provided slightly above the original riverbed level with sufficient flow capacity. Flushing is not a new technique and has been experienced for the last 6 decades on several reservoirs of the world. The results of the study reveal that there are about 50 reservoirs which are flushed, out of which flushing data is available for about 22 reservoirs only. However 6 reservoirs have been found with successful application of flushing operation and all other are flushed with low flushing efficiency. Flushing has been successfully implemented at Baira-India, Gebidem-Switzerland, Gmund-Austria, Hengshan-China, Palagnedraswitzerland, Santo-Domingo-Venezuela Reservoirs, while the unsuccessfully flushed reservoirs are: Chinese reservoirs, Gaunting, Heisonglin, sanmenxia, Shuicaozi, Naodehai, Nanqin, Guernsey-USA, Ichari-India, ouchi-Kurgan and Zemo-Afchar of former USSR, sufid-Rud-Iran, Warsak-Pakistan, Jensanpei-Taiwan, Khashm El Gibra-Sudan, Mangahao-Newzealand, and Cachi of Costa Rica.