STUDY ON SEDIMENT PROBLEM IN CHONGQING PRIMARY CITY ZONE IN FLUCTUATING BACKWATER REACH OF THREE GORGES RESERVOIR

摘要

After the commission of the Three Gorges Reservoir, the primary city zone of Chongqing Reach will be in the middle and upper reaches of the fluctuating backwater region of the Three Gorges Reservoir. Comparing with natural situations, the law of sediment scour and deposition will be changed to some extent. The law of scour and deposition shows that sediment deposition often dominates in flood periods. Sediment transportation reduces greatly after the flood season and ceases due to reservoir impoundment The transporting sediment period delays until the next drawdown period. Accumulated deposits occur on the river bed. The deposits of suspended sediment load dominate in the reach. After the operation of the Three Gorges Reservoir, the flow condition of Chongqing harbor and the navigation channel is obviously improved. However, with the increasing sediment deposit, under the unfavorable combination of water and sediment conditions, the navigable channel during the drawdown period will be affected in the wide reaches and the concave bank regions; the shoals will be influenced greatly by the confluence and the main stream swinging greatly reaches. In order to reduce sediment deposits and improve the harbor and navigable channel conditions, three approaches are put forward, such as building reservoirs to trap sediment in the upper reach of main and branch rivers, optimizing reservoir regulation schemes to benefit sediment transportation and taking regulation works. The research results of the physical and mathematical models of Yangtze River Scientific Research Institute and the observation data analysis indicate that the three methods are effective.