长江中游通江湖泊对干流顶托作用变化规律

Study on the change of backwater effect of the connected lakes in the middle reaches of the Yangtze River

长江中游通江湖泊(洞庭湖和鄱阳湖)对干流的顶托作用直接关系到区域防洪安全。通过构造支流顶托强度指标并结合Copula函数,分析三峡水库蓄水前后两湖出流对长江干流顶托强度的变化和异同,讨论干支流流量分布和地形变化对两湖顶托强度变化的贡献。研究结果表明:①三峡水库蓄水后,对干流顶托强度变化方面,汛期洞庭湖变化不大、鄱阳湖明显减弱;枯水期洞庭湖略有增强、鄱阳湖变化不大。②干支流流量分布导致的汇流比变化和江湖交汇区地形调整综合影响导致了两湖蓄水后顶托强度变化的差异;三峡水库蓄水后,干支流流量分布变化使洞庭湖、鄱阳湖对干流平均顶托强度分别减弱5.11%和13.45%;干流河床冲刷加剧导致的交汇区干支流河床高程差增大使洞庭湖、鄱阳湖对干流平均顶托强度分别增强6%和0.9%。

The backwater effect of the connected lakes(Dongting Lake and Poyang Lake)in the middle reaches of the Yangtze River on its main stream is directly related to regional flood control safety.By constructing a tributary backwater intensity index and combining Copula functions,the changes and differences in the backwater effect of the outflows of the two lakes on the Yangtze River before and after the impoundment of the Three Gorges Reservoir were assessed.The contributions of changes in the distribution of main and tributary stream discharges in wet and dry seasons and topographic adjustments in the confluence area to the changes in the backwater effect of the two lakes were also evaluated.The study produced some important results:①After the impoundment of the Three Gorges Reservoir,during the wet season,the backwater effect of Dongting Lake changed little,whereas the effect of Poyang Lake weakened significantly.During the dry season,the backwater effect of Dongting Lake strengthened slightly,while that of Poyang Lake remained relatively unchanged.②The variations in the backwater effect following the impoundment were attributable to the cumulative impacts of alterations in flood confluence ratio and modifications in the confluence area topography.Following the impoundment of the Three Gorges Reservoir,alterations in the distribution of main and tributary stream discharges led to reductions of 5.11%and 13.45%in the average backwater effect of Dongting Lake and Poyang Lake on the main stream,respectively.Simultaneously,the increase in the elevation difference between the main stream and tributary riverbeds attributable to riverbed erosion resulted in increases of 6%and 0.9%in the backwater effect of Dongting Lake and Poyang Lake on the main stream,respectively.