水库群联合作用下长江中下游江湖关系响应机制

长江干支流水库群的总库容约占长江入海年均径流量的37.6%,水库群的联合作用改变了进入长江中下游江湖系统的水沙条件,引起江湖系统水沙输移、冲淤演变及江湖关系等发生新的变化,呈现新的特点。本文在综述近年来长江中下游江湖系统水沙输移与冲淤演变特性及江湖关系变化等研究成果的基础上,重点阐述水库群联合作用下长江中下游江湖关系响应机制,形成的主要认识有:水库群联合作用下中下游江湖系统的径流量及比例组成没有明显变化,但输沙量及比例组成发生显著变化,干流宜昌站变化最为明显;中下游河道由自然条件下的中沙河流变为少沙河流,江湖系统由自然条件下的累积性淤积转为持续冲刷,并在较长时期内进行重新塑造与调整;水库群的联合作用对江湖水沙交换与湖区冲淤产生影响,两湖枯水期有所提前,湖区泥沙沉积率显著下降,江湖关系总体趋于向好的方向调整。鉴于长江水沙条件变化的不确定性、人类活动影响的加剧与江湖系统演变的复杂性,今后仍须加强变化环境下中下游江湖系统响应机理研究。

Response mechanism of the river and lakes in the middle and lower reaches of the Yangtze River under the combined effect of reservoir groups

The total capacity of group reservoirs alongthe Yangtze River and its tributaries is about 37.6 % of the annual runoff of the Yangtze River. The combination of the group reservoirs has changed the water and sediment conditions of the rivers and lakes in the middle and lower reaches of the Yangtze River. This has in turn changed the water flow and sediment transport, erosion and deposition and the relationship be-tween rivers and lakes, which are the focus of this study. The results show that, under the combined ef-fect of group reservoirs, the runoff and the proportion of the middle and lower reaches of the rivers and lakes has no significant change, however, the sedimentation rate and proportion composition has significant-ly changed, particularly in Yichang station. The middle and lower reaches of the Yangtze River transfer from high sediment concentration under natural conditions to low sediment concentration, while the deposi-tion in rivers and lakes transfers from cumulative under the natural condition to continuous erosion and it will undergo adjustment in a longer period. The combined effect of the group reservoirs on water flow and sediment exchange, scouring and deposition in lakes causes the earlier arrival of the dry season in the Dongting Lake and Poyang Lake, great decrease of the sediment deposition rate in lakes and the overall re-lationship between the rivers and lakes tending towards to improvement. Due to the uncertainty of the chang-es of flow and sediment conditions in the Yangtze River, the human activities and the complexity of the evolution of the rivers and lakes system, it is necessary to further investigate the response mechanism of the middle and lower reaches of the rivers and lakes in the future.