RIVER FLOW CONTROL ON INTERTIDAL MUDFLAT SEDIMENTATION IN THE MOUTH OF A MACROTIDAL ESTUARY

During this ten-year period, we observed a reduction of the surface of the mudflat (lower foreshore of the intertidal mudflat) by 32.3% (equivalent to 1.33 km²). The upper foreshore of the intertidal zone (salt marsh-mudflat boundary), however, is less affected by these hydrodynamic modifications. These modifications are connected to the multiannual variability of hydrological flow rates which control the positioning of the turbidity maximum, source of the sedimentary material deposited in this intertidal zone. During wet periods, sedimentation rates increase by + 17 cm.y^-1, while during the drier one (when the turbidity maximum is located upstream of the estuary) we observed an erosion rate of 7.6 cm.y^-1. Sedimentary deposition events in the mudflat resulting from spring tides are less frequent during dry periods, and they deposit a smaller quantity of sediment (-23% of total deposit mass per event). Due to lower flow rates coupled with the impacts of local development, flood currents have become dominant. It contributes to bring sandy or silty sediments on the mudflat of which the slope has increased 350% over 8 years, due to erosion.