Tidal hydrodynamics control sediment dynamics and sandbank evolution in the Casamance estuarine navigation channel

This study analyses the hydro-morphodynamics of the Casamance Estuary, a tropical microtidal system where tidal forcing governs morphological evolution during the dry season. The methodology couples a digital elevation model of differences analysis based on bathymetric surveys (DoD, 2008--2023) with a process-based numerical model (Delft3D), calibrated in situ and validated using SWOT satellite data. The results highlight a hydrodynamic segmentation driven by the non-linear distortion of the tidal wave. A pivotal point, located around 16.65° W, divides the estuary into two cells: a downstream sediment import cell (flood-dominated) and an upstream export cell (ebb-dominated). This configuration generates a residual convergence zone that acts as a permanent sediment trap. Examination of the sediment dynamics and sandbank evolution reveals a pulsed mechanism. Vertical storage phases during neap tides alternate with intense horizontal migration during spring tides, where centroid displacements exceed 100 m per cycle. Whilst the mobilisation of massive volumes (10 6 m 3) maintains the mouth equilibrium, the lateral progradation of sandbanks in the middle sector directly threatens the navigation channel. This work provides an essential scientific basis to optimise the contribution of modelling to the management of dredging campaigns for the navigation channel between Dakar and Ziguinchor.