Articles | Volume 4, issue 1
Research article
18 Jan 2016
Research article |  | 18 Jan 2016

Network response to disturbances in large sand-bed braided rivers

F. Schuurman, M. G. Kleinhans, and H. Middelkoop

Abstract. The reach-scale effects of human-induced disturbances on the channel network in large braided rivers are a challenge to understand and to predict. In this study, we simulated different types of disturbances in a large braided river to get insight into the propagation of disturbances through a braided channel network. The results showed that the disturbances initiate an instability that propagates in the downstream direction by means of alteration of water and sediment division at bifurcations. These adjustments of the bifurcations change the migration and shape of bars, with a feedback to the upstream bifurcation and alteration of the approaching flow to the downstream bifurcation. This way, the morphological effect of a disturbance amplifies in the downstream direction. Thus, the interplay of bifurcation instability and asymmetrical reshaping of bars was found to be essential for propagation of the effects of a disturbance. The study also demonstrated that the large-scale bar statistics are hardly affected.

Short summary
We studied the propagation of natural and human-induced perturbations in large braided sand-bed rivers using a physics-based 3-D model. The results show that the perturbations not only affect the local morphology but their effects amplify while propagating through the braided network. This occurs by destabilization of bifurcations in combination with reshaping of bars and branches. These results could have a major impact on the assessment of engineering measures in large braided sand-bed rivers.