Study on the effect and influencing factors of sand discharge of Xiluodu Reservoir in the Lower Jinsha River

The Lower Jinsha River is an important sediment-producing and sediment-transporting area in the Yangtze River basin. Since 2013, the third level Xiluodu Reservoir (XLDR) has directly intercepted the sediment of the Jinsha River, and its sediment discharge effect will affect its operation and the inflow of sediment into the Xiangjiaba Reservoir (XJBR) and the Three Gorges Reservoir (TGR). Based on the observation data of hydrologic sediment and river section, the sediment discharge effect of XLDR and its influencing factors were studied in this paper. The results showed that: ① From 2014 to 2019, the total sediment discharge of XLDR in was 14.9 million tons, and the sediment discharge ratio was only 3.1%, which was obviously smaller than the design value and the downstream XJBR and TGR. The sediment discharge of XLDR was mainly concentrated in the main flood season from July to September, accounting for about 71% of the total.② There were three main reasons for the small sand discharge ratio of XLDR. The first reason is the poor coordination between flood peak and sediment peak. The sediment peak often enters the reservoir area before the flood peak, which leads to greater probability of sediment deposition in the reservoir area. Secondly, the operation mode of XLDR determines that the reservoir area is in the state of large water depth and small velocity almost throughout the year, especially the long flood detention period, which weakens the dynamic condition of sediment transport. Third, in the initial state of the impoundment of XLDR, there are two natural hidden ridges in the reservoir area, which have obvious blocking effect on the sediment transport at the bottom of the reservoir area, and so that the density current sediment transport unable to reach the front of the dam.