三峡对长江中下游干流汛末水位影响——2006~2011年实例模拟

IMPACT OF THREE GORGES RESERVOIR ON WATER LEVELS IN THE MIDDLE-LOWER YANGTZE RIVER AFTER FLOOD SEASON:SIMULATION STUDY DURING 2006-2011

为了阐明三峡水库调节对长江中下游汛末水位的影响,基于2006~2011年三峡试验性蓄水实例,采用长江中游江湖耦合模型定量解析了近6年因三峡水量调节直接引起的长江中下游水位变化分量。结果表明,三峡使长江中下游汛末水位提前快速消落,枯水提前约半月余;螺山、汉口和大通三站汛末水位因三峡的水量调节而分别下降0.7,0.6和0.41m。水位频率分布有明显变化,汛末中高水位区间内频率有所下降,而低水位频率则升高。三峡工程建成运行后每年汛末将集中蓄水,长江中下游供水量减少必成为常态。汛末水位的这些趋势性变化可能会对水资源利用和湿地生态造成影响,值得关注。

In recent years,the hydrological droughts frequently happened in the middle-lower Yangtze River.The Three Gorges Reservoir with just finished the pilot of impoundment is thus involved in the debates of these drought events.The objective of this paper is to quantify the impact of water regulation of Three Gorges Reservoir(TGR) on water levels in the middle-lower Yangtze River after flood season and to elucidate the real effect of the TGR on the lowering of water levels during this period.To separate the contribution component of the TGR regulation to the water levels from various influencing factors,a coupled hydrodynamic analysis model for the middle-lower Yangtze River was developed and validated using the measurements of water levels and discharges from 2006to 2011in three controlling hydrological stations.We quantified the changes of water levels in the recent six years from 2006to 2011when the TGR carried out pilot impoundment,based on the simulation results from two scenarios with and without the TGR.Quantitative contributions purely induced by TGR regulation were quantified accordingly.The results showed that TGR regulations would have a significant effect on the water levels after flood season in the middle-lower Yangtze River.The TGR regulation can make the water levels quickly decrease after flood seasons.And the TGR regulation can double the drawdown speed of the lake.It made the low water level occurred early about half a month in the middle-lower Yangtze River in the recent six years.The lowering of water level induced by TGR regulation was 0.70mat Luoshan,0.60mat Hankou,and 0.41mat Datong averagely from September 10to October 31.Among these months,the most significant lowering of water levels was found in October and the decreases of water levels were all over 1meter at the three stations.Apart from the magnitude of water levels,obvious changes were also observed in the frequency distributions of water levels at that time at three stations.The high water levels decreased in probability,while the probability of low water levels rised.The TGR regulation must decline water supply for the middle-lower Yangtze River after flood season because of its normal operation.Thus,it is worth noting that the changing tendency of water levels might affect the use of water resources and wetland ecosystems significantly.Meanwhile,we should also note that the clear water release should possibly make a long-distance bed scouring in the main stream of the middle Yangtze River.It may induce a decrease of water levels further.