Controlling factors on sediment partitioning at deltaic bifurcations: a mixed Eulerian-Lagrangian modelling approach

Sediment partitioning at river bifurcations plays a crucial role in determining the morphological evolution of river deltas. However, we still lack a comprehensive understanding of the controlling factors that determine how sediments are partitioned at bifurcations, especially for suspended-load dominated systems such as river deltas. We employed dorado, a Lagrangian reduced-complexity particle tracking model, and a 2D shallow-water hydrodynamic model to investigate this gap. First, we routed sediment particles on calibrated hydrodynamic simulations performed for the Wax Lake Delta. The resulting asymmetries in the sediment partitioning at bifurcations showed good agreement with available field data on sediment concentration and observations of the spatial distribution of sand deposits in the different delta branches. To better interpret our results and extend them to similar deltaic contexts, we developed a simplified model of deltaic bifurcation and analyzed the possible controlling factors on sediment partitioning. We show how different planform controls influence sediment partitioning at the bifurcation node, including channel width, bifurcation angle, and bed elevation differences between the anabranches. Our analysis helps understand preferential pathways for sediment transport in river deltas, with noteworthy implications for delta management.