Stability of delta distributary networks and their bifurcations

Delta distributary networks are created by bifurcating channels that commonly split their discharges unequally. The origin and stability of these asymmetrical fine‐grained cohesive bifurcations are investigated here using Delft3D, a morphodynamic flow and sediment transport model. Results are compared to bifurcations on the Mossy delta, Saskatchewan, Canada, that have remained stable for decades. Over a range of channel aspect ratios, friction factors, and Shields numbers, we find three equilibrium functions relating the discharge ratio of the bifurcate arms at equilibrium to the Shields number. One function defines symmetrical configurations (equal partitioning of discharge), while the other two define asymmetrical configurations (unequal partitioning of discharge). Discharge asymmetries and morphologies of Mossy delta bifurcations are consistent with these predictions. Among the equilibrium bifurcations, only the asymmetrical type is stable to perturbations, such as a partial closing of one throat. This possibly explains why asymmetrical bifurcations are more common in nature.