Morphodynamic Feedbacks on Deltaic Coasts: Lessons from the Wave-Dominated Danube Delta

In natural conditions, the dynamics of the Danube delta coast has been largely determined by the interaction between fluvial deposition and a strong southward wave-induced longshore transport near the mouths of the river. River-mouth morphodynamics is highly nonlinear, involving multiple feedbacks on the longshore sediment transport. These include a groin effect of the river plume and subaqueous delta, a shoaling effect of the downdrift offset subaqueous delta, and a barrier steering effect of the downdrift barrier islands or spits. As a result, a net sequestration of sediments occurs near the river mouth that aids and speeds up delta lobe development. Downdrift of the mouth, barriers may form after extreme river floods, but also due to increased shoreline instability under high angle waves. Although river mouth processes are complex, the resulting morphology of wave-dominated delta lobes exhibits a tendency to self-organize.