长江上游干支流近期水沙变化及其与水库修建的关系

Recent Variations in Water and Sediment in Relation with Reservoir Construction in the Upper Changjiang River Basin

基于水文站实测的长系列水沙资料,运用统计方法研究了长江上游干支流的近期水沙变化。屏山站年输沙量的变化自1999年以后开始减小,扭转了1980～1998年的增加趋势。高场站年输沙量由1990～2000年的减小趋势,变化为2000～2007年的增大趋势。北碚站的年输沙量呈进一步减少的趋势。武隆站年输沙量改变了1990～2000年的增加趋势,2000～2007年显著减小。宜昌站的年输沙量延续了从20世纪80年代中期以来的减少趋势,2002～2007年急剧减小。采用输沙量-径流量双累积曲线方法进行了分析,发现各站双累积曲线上最近一次转折点的出现,均与水库的修建有关。基于双累积曲线估算了近期各站的减沙量(或增沙量)。研究还发现,近期屏山、北碚、武隆、宜昌4站含沙量均呈现减小趋势,与水库的拦沙作用密切相关。但是,岷江近期水电梯级开发的大规模展开,巨量弃土、弃渣进入河道,导致了2002～2007年间含沙量的增大。建立了宜昌站年输沙量与长江上游流域内累计水库库容量及宜昌站年径流量之间的回归方程,估算出它们对于长江上游产沙量变化的贡献率分别为71.4%和28.6%。这表明,水库拦沙是导致长江上游产沙量减小的主要原因。

Based on hydrometric data and using statistical method, the recent variations in water and sediment in the upper Changjiang River basin have been dealt with. The results indicate that annual sediment load at Pingshan station decreased after 1999, which changed the increasing trend during the period 1980 - 1998. Annual sediment load at Gaochang station increased after 2002, which changed the decreasing trend during the period 1990 - 2000. Annual sediment load at Beibei station decreased, which continued the decreasing trend. Annual sediment load at Wulong station markedly decreased after 2000, which changed the increasing trend during the period 1990 - 2000. Annual sediment load at Yichang station decreased sharply, which continud the decreasing trend since the mid - 1990s. It has been found that the occurrence of the recent break on all the double-mass curves for the above five stations can well be related with reservoir construction. Based on the double-mass curves, the amount of sediment reduction （or increase） has been estimated for each river. In recent years, suspended sediment concentration at Pingshan, Beibei, Wulong and Yichang stations shows a dereasing trend, which was caused by reservoir construc- tion. However, the huge amount of rock and soil dumped to the river during the construction of a number of dams on the Minjiang River resulted in an increasing trend in suspended sediment concentration. A regression equation has been established between annual sediment load at Yichang station and the total capacity of reservoirs in the up- per Changjiang River basin and annual runoff at Yichang station, based no which that the contribution of these two influencing variables to the variation in annual sediment load at Yichang station were estimated as 60.8% and 39. 2%, respectively. Thus, the sediment trapping by reservoirs is the marjor cause for sediment reduction in the upper Changjiang River.