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.
