Study on Characteristics of Bed Evolution and Overbank Floods in Meandering Channel Under Different Water and Sediment Discharges

The dynamic characteristics of water and sediment in a meandering channel are more complex than that in a straight channel. The bed evolution and the characteristics of overbank floods in bend are affected by the changes of flood and sediment discharge. The laboratory experiment was carried out in a curved flume under several flow discharges and sediment supplies in this paper. The water surface elevation, bed topography, water level of bend and longitudinal velocities along the main channel and the floodplain were measured in detail, and the effects of flow discharges and sediment supplies on bed evolution and overbank floods in the meandering channel were discussed. The calculation results of Lan Yunchang formula, Zhang Hongwu formula and Mao Peiyu formula for the water surface superelevation of the curved channel were compared, Lanyunchang formula could better predict the water surface elevation of the curved reaches with stable bedform under different flow and sediment discharges. The sediment supply had little effect on bed evolution in bend with inbank flows, for that most of the sediment supply was deposited in the upstream straight reach or transported to the downstream reach and only a small amount of recharge sediment was deposited in the bend reach. More upstream sediment was transported to the curved reach and deposited by overbank flows. With the increase of sediment supply, the sediment deposition in the curved main channel increased, which however had little effect on the water level and flow velocity in bend. When the flood discharge increased, the water level in the bend and the flow velocity in the concave bank increased significantly. The results indicated that the flood discharge was the key factor affecting the water level in the bend and the flow velocity in floodplain, and the upstream sediment supply was the secondary influencing factor. The flow velocity in floodplain in the 30-60° of 90° bend reach was higher than that in the main channel and upstream reach. The maximum flow velocity in the floodplain occurred in section 50°, which could reach 1. 3 times of the upstream flow velocity. The above results are of great significance for flood control and disaster reduction of meandering rivers. © 2022 Editorial Department of Journal of Sichuan University. All rights reserved.