Abstract: 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.

Key words: Zhen-Yang river reach, Hechang sandbar, submerged dike, river branch evolution