Sediment transport over an intertidal mudflat: field investigations and estimation of fluxes within the “Baie de Marenngres-Oleron” (France)

This contribution analyses the various hydrodynamic forcings responsible for sediment dynamics over the intertidal mudflat of Brouage (Baie de Marennes-Oléron). This mudflat is characterized by a gentle slope and an extensive ridge and runnel network. The sediment dynamics have been thoroughly investigated by continuous measurements of turbidity, waves and tidal currents, core measurements and bed level monitoring. Turbidity measurements highlight the importance of waves to the sediment resuspension over the mudflat. Conversely, higher turbidities during spring tides in the channel, further offshore, indicate the major contribution of the tide to sediment transport within the embayment. Overall, a large amount of mobile sediment is consistently present within the bay, either as suspensions during spring tides, or as fluid mud deposits in the runnels of the mudflat during neap tides. Residual sediment fluxes, computed from the measurements, proved to be onshore during spring tides, but offshore during periods of wave domination. Finally, a sediment dynamics overview for the area is proposed on the basis of the flux estimations.