新水沙条件与整治工程下和畅洲汊道演变分析

和畅洲汊道是长江下游典型的江心洲分汊型河道，也是长江下游历史上演变最剧烈的河段之一。三峡水库蓄水后河段来沙大幅减少，和畅洲汊道演变与航道条件随之改变，为了抑制左汊发展、改善右汊航道条件，水利、交通部门先后在左汊口门、上中段修建了三道水下潜坝。在大量实测资料的基础上，分析了新水沙条件和整治工程双重作用下和畅洲汊道及其上游六圩弯道河床演变特征。分析结果表明:2009年后六圩弯道河床持续下切，伴随着局部岸线崩退和心滩发育等不利变化；三道潜坝限流作用显著，2019年左汊实测分流比约为64%，较2002年最高76%时下降12%；右汊河床经历了缓慢淤积到由淤转冲再到普遍冲刷的阶段性变化，航道条件得到改善；但左汊潜坝下游河床产生明显的局部冲刷，且发生两次崩岸事件，应引起重视。

Riverbed evolution characteristics in the Hechangzhou braided reach under new flow-sediment conditions and waterway regulations

The Hechangzhou river reach is a typical braided reach and one of the most violently changed reaches in the lower reaches of the Yangtze River. After the impoundment of Three Gorges Dam, the sediment outflow decreased greatly, the new features of river bed evolution showed up and the navigation conditions changed accordingly in Hechangzhou braided reach. In order to restrain the scour development in the left branch and improve the navigation conditions in the right branch channel, three underwater submerged dams in the left branch were successively built. Based on a large amount of measured data, the evolution characteristics of Hechangzhou braided reach were analyzed. Results show that the riverbed in the Liuwei reach continued to cut down in 2009, accompanied by occurrences of bank line collapse and development of central bar. The control effect of three submerged dams is significant, and the measured diversion ratio of left branch in 2019 was about 64%, 12% lower than that of the highest 76% in 2002. The riverbed in the right branch changed from slow deposition to general scour, and the navigation conditions were improved. However, the left branch has experienced a significant scour in the local reach and two bank collapse events happened, which should be paid enough attention to.