Response of Channel Sediment Budget to Flow and Sediment Inputs:An Example of the Yichang-Wuhan Reach,Yangtze River

The sediment deposition amount of the Yichang-Wuhan reach in the middle Yangtze River has been determined using the concept of sediment budget at channel-reach scale, based on which the fill-scour process of the middle Yangtze River in the period from 1956-1998 in response to the variation in sediment load and flow inputs has been studied. The results show that the studied river reach has a function of "more input, more output", and on average, 11.85% of the net input sediment was deposited in the studied river reach. Since 1956, the output sediment load of the studied reach had increased with time to 1980, followed by a decline. The increase before 1980 can be related with the decrease in the sediment load diverted through the three distributaries from the Yangtze main stream to the Dongtinghu Lake which is equivalent to the increase in the net sediment input, and with the man-made bend neck-cutoff, which increased the sediment-carrying ability of the river and thereby the river could transport more sediment to the outlet of the studied river reach. The decrease in the sediment load output after 1980 was directly related to the decrease in sediment load at Yichang station. A regression equation with data covering annual sediment amount of deposition in the Yichang-Hankou river reach and annual suspended load at Yichang station has been established, by which the critical suspended sediment load at Yichang station of 3×108 t/a was determined, and at which the Yichang-Hankou river reach might be in a non-fill, non-scour state.