The erosion—deposition process and associated control mechanisms of the Nanliu River subaqueous delta, Southern China coast

Abstract

Understanding the erosion–deposition process of sediments and the associated controlling mechanisms in subaqueous deltas is important for coastal environment protection. In this study, field observations and numerical simulations were performed for the Nanliu River subaqueous delta in Guangxi Province (Southern China) to investigate the sediment dynamic processes at the bottom boundary layer. The results show that the sediment resuspension mainly occurs during periods of spring tides and is mainly controlled by the wave action. When the seabed is free from erosion, suspended sediment settling caused by lateral transport is an important source of maintaining near bed suspended sediment concentration. It was also found that increasing the shear parameter could facilitate the formation of flocs, after which the small flocs tend to merge to large flocs. Finally, by performing a consistency analysis between the seabed erosion and deposition processes obtained from numerical simulation, and the changes of seabed level recorded by the equipment during the field observation, we determined that the local erosion coefficient was 5 × 10-5 kg/m2•s. The one-dimensional simulation is also capable of revealing the general trend at the seabed where it is first subjected to erosion and then deposition, as indicated during the field measurements.