Numerical simulation of morphological evolution in a gravel-bed meandering river during floods: a case study on the Sai-Jiang river

The water velocity undergoes a significant increase during the initial stage of floods. The present study focuses on investigating the scours and silting occurring in an S-shaped gravel-bed river. The primary objective is to analyze the impact of 10-year flood events on both the riverbed and bank stability. This river is located in the Sai-jiang River reach, Fujian Province, China. A numerical model of riverbed scours and silting is herein tested. The research results indicate that the morphological evolution of the whole river section is affected in the early stage of flood evolution; however, in the later stage, some key places such as the bridge and the river land are still greatly affected. The apex of the river bend is in close proximity to the downstream river island, resulting in scour at the head of the river island that deviates from conventional patterns of head scour and tail siting. Furthermore, the presence of artificial structures like bridges exacerbates the scour and silting processes in river beds during flood events. For this case, the riverbed adjacent to the Banzhong Bridge pier experienced a widening of approximately 50 m and downstream extension of around 300 m, with a maximum vertical scouring depth of 2.87 m.