23 Aug 2023
 | 23 Aug 2023
Status: this preprint is open for discussion.

Analysis of autogenic bifurcation processes resulting in river avulsion

Gabriele Barile, Marco Redolfi, and Marco Tubino

Abstract. River bifurcations are constituent components of multi-thread fluvial systems, playing a crucial role in their morphodynamic evolution and the partitioning of water and sediment. Although many studies have been directed at exploring bifurcation dynamics, the conditions under which avulsions occur, resulting in the complete abandonment of one branch, are still not well understood. To address this knowledge gap, we develop a novel 1D numerical model, based on existing nodal point relations for sediment partitioning, which allows for the simulation of the morphodynamic evolution of a free bifurcation. Model results show that when the discharge asymmetry is so high that the shoaling branch does not transport sediments (partial avulsion conditions) the dominant branch undergoes significant degradation, leading to a higher inlet step between the bifurcates and further amplifying the discharge asymmetry. The degree of asymmetry is found to increase with the length of the downstream channels, to the point that when they are sufficiently long, the shoaling branch is completely abandoned (full avulsion conditions). To complement our numerical findings, we also formulate a new analytical model that is able to reproduce the essential characteristics of the partial avulsion equilibrium, which enables us to identify the key parameters that control the transition between different configurations. In summary, this research sheds light on the fundamental processes that drive avulsion through the abandonment of river bifurcations. The insights gained from this study provide a foundation for further investigations and may offer valuable information for the design of sustainable river restoration projects.

Gabriele Barile et al.

Status: open (until 19 Oct 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1551', V. Voller, 29 Sep 2023 reply
  • RC2: 'Comment on egusphere-2023-1551', Lorenzo Durante, 01 Oct 2023 reply

Gabriele Barile et al.

Gabriele Barile et al.


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Short summary
River bifurcations often show the closure of one branch (avulsion), whose causes are still poorly understood. Our model shows that when one branch stops transporting sediments, the other considerably erodes and captures much more flow, resulting in a self-sustaining process. This phenomenon intensifies when increasing the length of the branches, eventually leading to branch closure. This work may help to understand when avulsions occur, and thus to design sustainable river restoration projects.