长江和畅洲左汊潜坝工程对汊道演变的影响

长江镇扬河段和畅洲左汊潜坝工程是首次在长江主汊中采用全断面潜坝形式实施的汊道控制工程,工程建成后使和畅洲左汊分流比上升的势头得到有效遏制,基本实现了工程预期目标。为研究潜坝工程对和畅洲汊道近期演变的影响,比较了潜坝工程建成前后汊道平面、断面、分流比、槽蓄量等要素的变化;分析了来水来沙条件、上游河势变化、河床边界条件等因素对汊道的影响;从两汊道阻力变化对比、相对引水深变化及上游流速分布的改变等方面,初步探讨了潜坝工程对汊道的影响机理。结果表明,潜坝工程建成后和畅洲汊道发生了有利变化,而潜坝工程是和畅洲汊道近期演变朝着有利方向变化的主要因素。

Effect of Submerged Dike in the Left Branch at Hechang Sandbar on the Evolution of River Branches

The submerged dike in the left branch of Zhenjiang-Yangzhong(Zhen-Yang) river reach at Hechang sandbar,which was constructed across the whole section,was the first branch control project in the main branch of Yangtze River.To investigate the effect of submerged dike on the branch evolution at Hechang sandbar,we compared the branch plane,section,split ratio,and channel storage capacity before and after the submerged dike construction,and analyzed the impact of incoming flow and sediment,upstream river regime variation,as well as riverbed boundary conditions on the branch.Last but not the least,we discussed the mechanism of submerged dike influencing on the branch in terms of river resistance variation,relative depth of water diversion,and variation of flow velocity distribution on the upper reaches of the two branches.Results indicate that the submerged dike has restrained the rise of water-diversion ratio in the left branch.Deposition is found to be dominant in the left branch,while giving its way to erosion in the right branch.The anticipated result of the project is materialized in general.The submerged dike is the principal factor leading to a beneficial evolution of the river branch at Hechang sandbar.