长江宜昌-武汉河段泥沙年冲淤量对水沙变化的响应

运用泥沙收支平衡(Sedimentbudget)的概念确定长江中游宜昌-武汉河段的泥沙冲淤量,并运用数理统计方法,研究了泥沙冲淤过程对水沙变化的响应。研究表明,所研究河段的输沙具有“多来多排”的特性,在平均的意义上,年输入沙量为年输出沙量的1.1345倍,由此求得总净来沙中有11.85%淤积在河道中。河段出口输出沙量随时间而增大,大致在1980年达到峰值,然后再减小。1980年以前河段出口输出沙量的增大,与3口分沙减少(等价于河段净来沙增多)和下荆江人工裁弯(使河道输沙能力增大,因而可以将更多的泥沙输送到河段出口以下)有关,1980年以后的减少,则与宜昌站来沙量的显著减少有关。建立了1980～1997年间宜昌—汉口#河段年冲淤量与宜昌站年来沙量之间的回归方程,通过该方程估算出使宜昌汉口河段不淤的宜昌站临界来沙量为3亿t/a。为了定量评价宜昌站的来水量和来-沙量以及3口分水比和分沙比、宜昌站洪峰流量的变化对于河段冲淤量的相对贡献,我们以1980～1997年和1955～1997年两个时间系列的数据分别建立了多元回归方程。1980～1997年间的方程表明,宜昌站的来水量和来沙量以及3口分水比和分沙比、宜昌站洪峰流量的变化对宜昌—汉口河段年冲淤量的贡献率分别为6.23%、31.56%、25.77%、32.71%和3.73%。

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.