Study on Flood and Sediment Joint Operation of Dadu River Downstream Cascade Reservoirs

There is large amount of high hardness sand in the water flow in Dadu river. The problem of sediment deposition is very prominent in the two early reservoirs, Gongzui reservoir and Tongjiezi reservoir. In order to decrease sediment deposition effectively and extend the service life of them, the sediment characteristics of Dadu river cascade hydropower stations are analysed, as well as changes of sediment deposition in Gongzui reservoir and Tongjiezi reservoir after Pubugou reservoir puts into operation. Flood forecast and pre-discharge operation theory are studied for utilizing the discarding water to improve sediment-flushing effect, and flood and sediment joint dispatching schemes of cascade reservoirs are proposed. In order to evaluate effects of joint dispatching schemes, SBED extended one-dimensional flushing sediment mathematical model of deposited reservoir is built, and the mathematical model is used for simulative computation of coming 20-years sediment-flushing effect. After that, the effects of different schemes are analyzed comparatively. Three conclusions can be drawn from the studying. Firstly, the sediment in Gongzui reservoir and Tongjiezi reservoir is obviously reduced after Pubugou reservoir puts into operation. Secondly, flood forecast, pre-discharge operation theory and creating sand-flushing conditions can obviously improve sediment-flushing effects and avoid wasting power generation water when the water levels and outflows of Pubugou reservoir, Gongzui reservoir and Tongjiezi reservoir are rationally controlled. Finally, the larger the inflows and the lower the water level of Gongzui reservoir and Tongjiezi reservoir is, the more obvious the sediment-flushing effects are. According to situations of power plant at the time, such as rules of flood controlling and operation requirements of flood discharge facilities, it is recommended that the inflow of Gongzui reservoir is controlled at about 4500m3/s, and timely lower the water levels of Gongzui reservoir and Tongjiezi reservoir to their dead water levels, when carrying out joint dispatching schemes.