CHANNEL PATTERN CHANGE DOWNSTREAM FROM A RESERVOIR - AN EXAMPLE OF WANDERING BRAIDED RIVERS

Reservoir-induced channel pattern change is an issue of significance b oth in theory and engineering practice. Based on data from three major wandering braided rivers in China, namely, the Yongdinghe, the Hanjia ng and the Yellow Rivers, as well as a laboratory experimental study, this paper deals with channel pattern change downstream from reservoir s, Complex response in channel adjustment has been observed in the fie ld, and as a result a three-stage descriptive model has been establish ed to describe the course of channel pattern change. Also, the three s tages 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 explai ned by the present complex response model. Because of different bounda ry conditions, the duration of the three stages for the three rivers i s different, so the channel pattern change of the three rivers shows a different tendency at each specific stage. The present study suggests that Schumm's qualitative model for river channel metamorphosis shoul d be modified when used for predicting reservoir-induced channel patte rn change on a wandering braided river, Because the model has not take n into consideration the changing erosional resistance of channel boun dary material and therefore the resultant feedback effect, it cannot p redict the whole course of channel pattern change over a long period.