Research on bed-load transport formula in the Cheng-Han Reach of the middle Yangtze River

After the impoundment of Three Gorges Reservoir, the sediment transport in the reach from Chenglingji to Wuhan of the middle Yangtze River is dominated by the bed load which plays important roles in bed morphological changes, and correspondingly the suspended load discharge is reduced significantly. In this paper, the formula of calculating the bed load transport rate in the above-mentioned reach has been studied. Based on the measured data of Luoshan and Hankou hydrology station, an exponential relationship between sediment discharge of bedload and flow discharge was established, and the transport rates of bedload at these two hydrology stations were calculated by this new relationship day by day. The result shows that the transport rates of bedload at Luoshan and Hankou hydrology station are proportional to the flow discharge with the power of 0.912 78. The multi-annual mean sediment discharges of bedload are 137×10⁴ t and 152×10⁴ t, respectively, which is focused in flood season. Finally, the modified Engelund, Einstein and Yalin formula based on the new relationship according to the measured data were examined. It is shown that the accuracy of each formula has been obviously improved after modification. The modified Yalin formula has the best performances; and then the modified Engelund formula; while the predictions of the modified Einstein formula were not as good as the former two. It is concluded that the modified Yalin formula is the most suitable for calculating the transport rate of bedload of Chenglingji-Wuhan reach, and can be used for the fluvial process analysis and numerical simulation of this reach.