Study on the Stretching Mechanism of the lower Reach of the Distribution Estuary of Alluvial River after Lateral bypass flow-Taking Jingjiang Reach of the Yangtze River as an Example

Abstract

After diversion, alluvial rivers tend to widen in local areas downstream of diversion ports. The flow is dispersed and the main stream changes in a year are complex, which has a great impact on flood control, navigation and water intake. Taking the Jingjiang reach in the middle reaches of the Yangtze River as an example, according to its historical development, this paper describes the variation of the river regime in the downstream of the diversion ports. Based on the analysis of a large number of measured water and sediment data and the boundary conditions of Jingjiang reach, the characteristics of flow movement in the diversion port reach are studied by combining the solid model test. It is found that after river diversion, the distributary morphology of water flows along the river section changes, and the mainstream develops from concentration to dispersion, and the flow of river diversion will change with the variation of channel flow. Generally speaking, in dry season, because of the small diversion volume, the main stream downstream of the diversion port is far from the diversion port, while in flood season, the diversion volume increases, and the main stream affected by the suction of the diversion port is often close to the diversion port, which causes frequent changes of the main stream downstream of the diversion port in the year. In addition, when the mainstream develops from centralization to dispersion, the riverbank will be eroded by water flow, and the mechanical properties of the riverbank soil will change, and the riverbank gradually loses stability and subsequently collapses. The main reason for the widening in the lower reaches of the diversion estuary is a comprehensive effect due to the changes of the distributary morphology and the main stream position caused by the diversion and the geological conditions of the channel.