Channel pattern change downstream from a reservoir: An example of wandering braided rivers

Reservoir-induced channel pattern change is an issue of significance both in theory and engineering practice. Based on data from three major wandering braided rivers in China, namely, the Yongdinghe, the Hanjiang and the Yellow Rivers, as well as a laboratory experimental study, this paper deals with channel pattern change downstream from reservoirs. Complex response in channel adjustment has been observed in the field, and as a result a three-stage descriptive model has been established to describe the course of channel pattern change. Also, the three stages have been simulated successfully by a laboratory physical model. Although the observed tendency of channel pattern change of the three rivers is quite different, which has been a matter of controversy for many years among Chinese researchers, it can be satisfactorily explained by the present complex response model. Because of different boundary conditions, the duration of the three stages for the three rivers is different, so the channel pattern change of the three rivers shows a different tendency at each specific stage. The present study suggests that Schummʹs qualitative model for river channel metamorphosis should be modified when used for predicting reservoir-induced channel pattern change on a wandering braided river. Because the model has not taken into consideration the changing erosional resistance of channel boundary material and therefore the resultant feedback effect, it cannot predict the whole course of channel pattern change over a long period.