Sediment transport in a surface-advected estuarine plume

• The non-dimensional number Y is found representing the ability of the plume system to deliver sediments to the alongshore coastal current.
• A critical range of settling velocities exist above which no transport in the costal current is allowed.
• Low magnitude and long-lasting floods promote sediment sorting in the continental shelf.
• Intermediate flood magnitudes at the limit between subcritical and supercritical flow maximize the alongshore sediment transport.
• Intermediate discharge durations maximize the alongshore sediment transport.

The interplay between suspended-sediment transport and plume hydrodynamics in a surface-advected estuarine plume is studied using a three-dimensional numerical model. Our analysis focuses on the formation of a sediment-rich alongshore current and on the effect of sediments on the structure of the recirculating freshwater bulge. We introduce the ratio YY between the traveling time of sediment along the bulge edge and the settling timescale. When YY<1, suspended sediments enter the alongshore coastal current. When YY>1 the sediments are deposited within the bulge. We find that a critical range of settling velocities exist above which no transport in the costal current is allowed. Critical settling-velocity values increase with river discharge. Therefore, low magnitude and long-lasting floods promote sediment sorting in the continental shelf. We further find that, for a given flood duration, intermediate flood magnitudes at the limit between subcritical and supercritical flow maximize the alongshore sediment transport. Similarly, for a fixed input of water and sediments, intermediate discharge durations maximize alongshore sediment transport.