Experimental study of development and erosion of gravel mid-channel bar

Mid-channel bars occur in anabranching rivers. Fluvial processes of a mid-channel bar following variation of flow and sediment transportation are studied experimentally, which influences the equilibrium of flow and sediment transport in anabranching channel. The processes of development and erosion of a mid-channel bar were observed and measured under different flow discharges, sediment feeding rates, and with different grain sizes. A simplified model of bar head growth is established to analyze the rate of bar development. Results show that gravel deposition occurred along bar head from the branching point, and the left and right channels became sediment transport channels. There was little sediment deposition at the bar tail. In high flow discharge and low or no incoming sediment load experiments the bar head was firstly scoured and thence, extending scour occurred along the bar body. The sediment removed from the bar head was transported to downstream along the left and right channels, not deposited on the bar tail. Bar head deposition is a dominant process for gravel mid-channel bar growth. The growth rate is a function of sediment load, grain size, bed slope and branching angle.