Study on the Impact of Sandbar Evolution on Flood Control in the Jingjiang Reach of the Middle Yangtze River under New Water and Sediment conditions

Abstract

After the impoundment and operation of the Three Gorges Project, the water and sediment conditions in the middle and lower reaches of the Yangtze River have changed significantly, and the impact of sandbar evolution on flood control safety has become increasingly prominent. Taking the Jingjiang reach in the middle Yangtze River as the study area, this research investigates the evolution of sandbars and its impact on flood control under the new water and sediment conditions. The results show that, following the impoundment of the Three Gorges Reservoir, the evolution of sandbars exhibits several notable features: marked differentiation in erosion patterns at different elevations; erosion processes concentrated in the flood season; the growth and decline of sandbars strongly influenced by the release of clear water; and predominantly erosional trends on point bars. The impacts on flood control are manifested as follows: in meandering reaches, point bars on convex banks are dissected by momentum exchange between the main channel and the bar and by secondary reciprocating flow (e.g., at Tiaoguan), while point bars on concave banks are scoured by centrifugal forces (e.g., at Qigongling). In braided reaches, the stability of bar bodies decreases and mid-channel bars shrink (e.g., at Taipingkou). In straight transitional reaches, oblique inflow scours the toes of sandbars (e.g., at Wuguizhou). The evolution of sandbars triggers shifting of the main flow, weakens the river-regime control function, and leads to changes in flow impingement and near-bank scouring, thereby endangering levee stability and threatening regional flood control safety. In response, countermeasures are proposed, including strengthening the monitoring and early warning of sandbar evolution, accelerating the systematic treatment of riverbank collapse, improving the emergency protection system, establishing a long-term mechanism for emergency protection, and deepening research on sandbar evolution. The findings can provide scientific support for flood control, disaster reduction, and river management.