Field investigation of flow and bed erosion/deposition at the confluence of the Yellow River and Fen River

Abstract

In order to study the characteristics of flow structure and bed erosion/deposition at the confluence of the Yellow River and the Fen River, the three-dimensional velocity components, water depth, water level, and suspended sediment particle sizes of the typical sections were measured in field to analyze the bed morphology, the flow field structure, suspended sediment distribution, and the variation of the bed erosion or deposition. The results showed that the pattern of the flow field at the confluence essentially conforms to the conceptual model, but represented a relatively complex structure, owing to the dual influence of the convergent flows and the tanglesome bed topography. The spatial distribution of suspended sediment was affected by the flow velocity and eddy turbulence. The particle size of suspended sediment was approximately normal distribution. The median particle size ranged from 17.19μm to 140μm. The suspended sediment at the confluence center was mainly composed of upstream transfer sediment and resuspended local sediment near the bed surface. The riverbed morphology was highly complex with frequent changes in erosion and deposition. And there was a strip-shaped sand ridges at the center of the channel and a long-narrow scouring belt near the tributary side. In addition, the bed configuration was similar in the dry and normal season. Due to the sediment deposition, the bed elevation was higher in dry season than that in normal season. During the flood season, the washed bed was stated in a dynamic flattening period, as well as the sand ridge disappeared and the scour belt became shallow.