Evolution of mid-channel bars in a braided river and complex response to reservoir construction: an example from the middle Hanjiang River, China

Using the middle Hanjiang River as an example, this paper deals with the development of mid-channel bars in a braided river, as controlled by channel boundary conditions; runoff and sediment load, as well as reservoir construction. Relations have been established between indices describing the mid-channel bars and the controlling variables, such as the channel width, the percentage silt-clay content in the channel boundary and the energy expenditure of flowing water. Bank erosion provides space and material for mid-channel bar formation, so bank erosion rate can be closely related to mid-channel bar indices. The middle channel bars exhibit a complex evolutionary response to the reservoir-regulated hydrological regime in the middle Hanjiang River. A descriptive model showing the complex response has been established.