The influence of the development of dunes on the stability of bifurcations in sand‐bed rivers

Abstract

AbstractChannel bifurcations are common features observed in fluvial landforms from upstream gravel‐bed rivers to downstream deltas. Extensive research has been carried out to study the stability and equilibrium configurations of bifurcations in the last two decades. However, existing studies generally employed oversimplified flow resistance equations, and the influence of the development of bedforms on the stability of bifurcations is rarely explicitly considered. The morphological features of bedforms in sand‐bed rivers vary with flow conditions, which in turn affect flow resistance and sediment transport processes. Such a mutual feedback process is expected to exert a significant influence on the evolution of a bifurcation. A theoretical one‐dimensional (1D) model is built, based on the classical model proposed by Bolla Pittaluga et al. in 2003, to evaluate the influence of the development of dunes on the stability of bifurcations. Results show that the development of dunes enhances the stability of symmetric bifurcations for low Shields stress conditions, whereas it exhibits an opposite effect under the situation of high Shields stress. The response of flow resistance to the perturbations of the Shields stress dominates over the response to the perturbations of the flow depth. In addition, based on the two‐dimensional (2D) model proposed by Redolfi et al. in 2016, this study compared the results of the 1D and 2D models taking into account the development of dunes, and evident differences between the models present at small Shields stresses. Meanwhile, 2D models with or without considering the influence of dunes exhibit different results as well. The results of this study demonstrate that considering the development of dunes is of significance when analysing the stability of bifurcations in sand‐bed rivers.