233 / 2024-02-28 13:58:41

Research on the recent evolutionary rules and mechanisms of the Sima Bend in the Yangzhong River Section of the Lower Changjiang River

River channel evolution,modelling study,Mechanism,Sima bend,Yangzhong section of the Changjiang River

The curved channel is a widely existing river type in the middle and lower reaches of the Changjiang River. Due to the lateral water flow top flushing effect, the curved top of the curved channel has always been a key focus of bank collapse and river management. With the use of the Three Gorges Dam and its upstream cascade reservoirs, the middle and lower reaches of the Changjiang River are facing long-term and long-distance erosion and incision under the influence of "clear water discharge", exacerbating the occurrence of bank collapse in curved river channels. This article selects the Sima Bend in the Yangzhong section of the Lower Changjiang River as the research object. This bend has always been one of the famous dangerous sections in the Lower Changjiang River with the most severe bends and bank collapses. The adjustment of the river regime is complex and the difficulty of governance is high. Analysis of River Evolution shows that after the Three Gorges impoundment and operation, the amount of sediment from the upstream has decreased significantly, and the average sediment discharge in 2003-2022 was only 129 million tons. Under the extremely low sediment supply, the Lower Changjiang River continued to experience large floods in 2016, 2017, and 2020, and the flood bed building effect aggravated the erosion and incision of the Sima Bend. In 2011-2021, the general scouring depth reached 10~15m, and the bend top developed downstream, directly threatening the safe operation of the bank protection works and the harbor structures that have been implemented. This study also conducted numerical simulations and local physical model experiments. The results showed that under flood conditions, the main stream of the river was very close to the bank. The top scouring point was located in the left bank wharf area of the left branch of Luocheng Island, and there was a significant bend circulation in the vertical direction. This characteristic of the water flow results is the hydrodynamic reason for the continuous erosion of the nearshore riverbed in the area. The above study has been applied in the design scheme of the corresponding harbor front erosion protection project at the Sima Bend. The implementation of the project will significantly reduce the intensity of riverbed erosion, ensure flood control and engineering safety.