Wave-Climate Asymmetry Influence on Delta Evolution and River Dynamics

On wave-influenced river deltas, wave-driven sediment redistribution affects river progradation, and therefore avulsions, while avulsions change where sediment is delivered to the coastline, affecting coastline shape. Coastline shape, in turn, affects sediment redistribution rates and patterns. Here we use a numerical model to investigate how the asymmetry of wave climates affects delta avulsion behaviors, which are coupled with delta shape evolution. Increasing wave-climate asymmetry tends to reduce (increase) the curvature of updrift (downdrift) delta flanks, by increasing (decreasing) local shoreline diffusivity. In our model experiments, reduced shoreline curvature restricts the possible updrift post-avulsion river mouth locations, while increased curvature expands the possible downdrift locations, favoring downdrift avulsions. However, under some wave climates, local diffusivity on the downdrift flank can become negative, leading to convexity and shoreline accretion, inhibiting downdrift avulsions. Increasing wave heights and decreasing superelevation threshold for avulsions both tend to reduce delta morphologic asymmetry, and therefore avulsion tendency.

Automated summary

The asymmetry of wave climates affects delta avulsion behaviors and shape evolution. Increasing wave-climate asymmetry reduces the curvature of updrift delta flanks and increases the possibility of downdrift locations. However, under certain conditions, wave climates may inhibit downdrift avulsions.