Primary controls of channel response in an alluvial river system are the flow duration curve, downstream base level, and grain size-specific sediment supply (

Spatial and temporal patterns in three-dimensional flow structure have been linked to channel processes and morphology in many environments, including river meander bends, confluences-diffluences, and bedrock canyons. However, there is not yet an understanding of how channelized and gradually distributed lateral outflows that are often prevalent in river deltas influence three-dimensional flow structure and sediment transport mechanisms. This study presents an analysis of 3D flow structure data collected from Wax Lake Delta, a naturally developing river-dominated delta in the northern Gulf of Mexico. Three hydrographic surveys were conducted using a boat-mounted acoustic Doppler current profiler (ADCP) at two sites: a channelized outflow zone and a distributary channel experiencing distributed lateral outflow. The flow structure was analyzed to identify secondary circulation cells induced by lateral outflow, which may influence the sediment transport to the islands. Spatial patterns in flow structure were also compared to previous numerical modeling and experimental studies on open channel diversions and compound channels. A conceptual model is developed linking the formation of secondary circulation cells and suspended sediment transport from the distributary channels to interdistributary islands in a delta. The results suggest that a transition from advective to turbulent diffusion transport mechanism may occur depending upon a threshold outflow momentum flux ratio which lies in between 0.211 km-1 and 0.375 km-1. This study provides the first detailed quantification of flow structure in an actively prograding river delta and offers important implications for coastal restoration by linking coastal sediment transport mechanism to patterns in flow structure.

Effect of lateral outflow on three-dimensional flow structure in a river delta, EarthArxiv.

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