Network response to internal and external perturbations in large sand-bed braided rivers

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.