Sediment Transport Dynamics and Morphological Change in the Benin River Estuary

Estuarine sediment transport controls the morphological evolution of channel networks, tidal flats, and mangrove margins, with direct implications for navigation depth, habitat availability, and coastal flood risk. This study investigates the dominant sediment transport mechanisms and resultant morphological change in the Benin River Estuary, Delta State, South South Nigeria, over the period 2015 to 2024. The research employs a dual approach combining field measurement campaigns and process-based numerical modelling. Field campaigns involve acoustic Doppler current profiler transects at spring and neap tides to measure velocity and acoustic backscatter profiles as proxies for suspended sediment concentration, supported by calibration sediment samples filtered on Whatman GF/F membranes. Bedload transport is estimated using bedform tracking from repeated sub-bottom sonar surveys. A coupled Delft3D-FLOW-WAVE-MOR model is constructed using digitised bathymetric data and driven by tidal and wave boundary conditions derived from operational ocean model products. The model is validated against observed water levels and suspended sediment concentration profiles and used to simulate sediment transport fluxes and decadal morphological change under current conditions and under projected 15 percent reduction in freshwater discharge scenarios associated with upstream dam operation. Results are expected to reveal net seaward sediment export during flood season and landward transport during dry season, with the mangrove fringe acting as a seasonal sediment sink. Morphological modelling predicts accelerated channel shoaling under reduced discharge scenarios. Keywords: sediment transport, Benin River Estuary, morphodynamics, Delft3D, tidal estuary