三峡围堰蓄水和初期蓄水期(2003-2008)宜都低水分汊河段冲淤变化

Erosion and deposition in Yidu forked bend reach at low-water level during cofferdam and initial impoundment periods of Three Gorges Reservoir (2003 - 2008)

宜都河段是典型的低水弯曲分汊河段。三峡水库的围堰蓄水和初期蓄水改变了宜都河段的来水来沙条件。根据宜都河段建库后原型观测资料,对由此引起的河床冲淤分布、深泓变化、沙石泓变化和洲滩变化进行了分析,并对其演变趋势做了预测。结果表明,三峡蓄水后,河段整体河势变化不大,冲淤调整以冲刷为主且主要集中于枯水河槽;南阳碛冲刷缩小,沙泓上浅区以刷深为主,下浅区以冲滩为主;石泓深泓冲刷下降,沙石泓冲刷进程的差异主要受水流动力条件与局部河床组成的影响。预计河段仍将维持低水分汊的基本分流格局,在未来一段时间内,两汊枯水期主、支汊的地位将持续稳固。

The Yidu reach is a typical forked bend reach at low-water level.During the cofferdam and initial impoundment periods of the Three Gorges Reservoir the water flow and sediment conditions of Yidu reach were changed.Based on the observed data in Yidu reach after the impoundment of the Three Gorges Reservoir,the paper analyses the erosion and deposition of the river channel and changes of thalweg and point bars and predicts the evolvement trend of the changes.The results illustrates that the general river regime of the reach has not been changed much after the impoundment and erosion dominated and focused in the low water channel.The Nanyang shoal was eroded and shrank.The water flow eroded the bed deeper in the upper shallow zone and eroded the shoal in the lower shallow zone of left branch with bed material of sand;the right branch with bed material of pebble and gravel descended by erosion.It was mainly the flow dynamic conditions and the composition of bed materials that led to the difference between erosion and deposition processes of the two branches.It is predicted that the basic forked bend pattern of low-water channel will not be changed in the next period of time.The position of the main and the branch channel will be maintained in the dry seasons.