Morphodynamics of river-influenced back-barrier tidal basins: The role of landscape and hydrodynamic settings

We investigate the morphodynamics of river-influenced barrier basins numerically, with a particular emphasis on the effects of landscape and hydrodynamic settings. The simulated morphologies are qualitatively comparable to natural systems (e.g., tidal inlets along the East Coast of the USA). Model results suggest that the basin morphology is governed by the relative importance of tidal and fluvial forcing which is reflected, to the first-order approximation, in the ratio (r(Q)) between the mean tidal and river discharge. In agreement with empirical knowledge, the model indicates that riverine influence can be neglected when r(Q) is larger than 20. On the other hand, the river may dominate when r(Q) is smaller than 5. Pronounced differences in morphodynamic evolution are observed for different landscape settings (i.e., initial basin bathymetries and river inflow locations), indicating their fundamental importance in governing the evolution of barrier basins. Model results also show that the addition of a river tends to compensate the flood dominance in the tidal basin. Overall, the river flow has limited influence on the volumetric change of tidal flats, while it plays a more important role in determining the depth of the tidal channels and the size of the ebb delta. The riverine sediment source appears to be more important in shaping the basin morphology when the fluvial forcing is stronger. Finally, we show that the presence of a large river in a tidal inlet system influences the performance of the widely adopted relation between tidal prism and inlet cross-sectional area.