Abstract: Nodes, widely exist in bifurcated channels, have essential impact on river bed evolution. We explored the impact of nodes on bifurcated channel evolution and provided guidance for river regulation by combining mathematical modelling and riverbed evolution analysis. Madang reach, which lies in the downstream of Yangtze River, is a typical slightly-bent and bifurcated channel. Many sandbars or shoals bifurcate this reach, such as Gupaizhou sandbar, Mianwaizhou shoal and Guazihaozhou sandbar. There are some nodes formed by mountains in Madang Reach, like Xiaogushan, Penglangji, Madangji, and Madangzui. A 2-D mathematical model of Madang reach was established and verified. From the perspective of water flow and riverbed evolution, the impact of sub-branches’ diversion ratio variation on their upstream and downstream channels, and the nodes’ influence on riverbed evolution were further analysed. Results reveal that by controlling the node of Xiaogushan-Penglangji, the incoming flow at the inlet of Madang reach is stable, and is slightly affected by its upstream variation. Due to the modification of Madangji-Madangzui node, when the diversion ratio of Mianwaizhou shoal varies from 23.3% to 58.1%, its impact on main flow and river bed erosion & deposition only covers a limited distance of 2-2.5km downstream of Madangji.

Key words: bifurcated channel, node, diversion ratio, Madang reach, downstream of Yangtze River