Domino Effect of River Training in Large Sand-Bed Braiding Rivers

Abstract

Large sand-bed braiding rivers such as the Brahmaputra River form an enormous challenge to understand and to control. For efficient and sustainable management of these rivers, it is vital that we can predict the effects of river training works on the channel pattern and dynamics. In this study we used a computer model to simulate the dynamics of bars, islands and channel branches in a large sand-bed braiding river. We applied river training works in it to evaluate the nearby effects and the far-away effects. The results showed that a single river training work like bank protection or a groin can significantly affect the locations of bars, islands and channel branches far downstream. The downstream propagation of the effect of a river training work is a domino effect by means of bifurcation instability and bar shape adjustment. It means that a training work can adjust navigation channels, bank erosion and flooding over many kilometres downstream of the training work. Thus, a training work in a large sandbed braiding river not only has local effects on the flow and river bed, but can also have major economic and social impacts. This is both a sign to be very careful with river training in these rivers, and a great opportunity to change a long river reach by a single, relatively cheap river training work.