Coupling Effects of Unsteady River Discharges and Wave Conditions on River Mouth Bar Morphodynamics

River mouth bar formation is a key process in fluvial-deltaic morphodynamics. Subject to both fluvial and marine forcing, river mouth bar evolution becomes very complex when the variability of river discharges and wave conditions are taken into consideration. To assess the coupling effects of unsteady river discharges and wave conditions on mouth bar formation, numerical experiments using Delft3D-SWAN were conducted in this study. An extensive set of combined high-and-low river flows coupled with varying wave climate and sediment grain size were assumed to mimic the natural variability. Numerical model results suggested the existence of three regimes for mouth bar formation, classified as stable mouth bar, ephemeral mouth bar and absence of mouth bar, which were dictated by the relative wave strength during both onset and reworking stages. The boundaries between different regimes were also delineated through the numerical results, which were shown to be dependent on the sediment grain size. Scaled-up effects of the mouth bar formation regimes on deltaic distributary networks were further discussed. The findings have important implications for deltas and estuaries management to prevent coastal erosion, under altered hydrograph and wave climate induced by climate change and human intervention.