The EXTREMA project aims at studying natural processes which generate very strong matter fluxes and their impact on the pollutants redistribution into the different geosphere compartments. The present study focuses on the transition area between the river and the microtidal coast. Its goal is to determinate the consequences of extreme meteorological and climatic phenomena like floods and storms above the sedimentation processes on a prodeltaïc area, known as a main river inputs storage area. Two sediments sampling campaigns, achieved at the Grand Rhône River mouth in March and October 2008, enabled to sample sediment cores in the sedimentary interface of the prodeltaïc front with a lap-time of 6 months. This period was marked by three floods in April, May and September, with flow rates comprises between 3000 m3.s-1 and 4200 m3.s-1, for a mean annual river discharge of 1700 m3.s-1. These floods brough high solid discharges in the water column, until 1g.l-1, whereas the mean concentration is about 50 mg.l-1. Flood deposits are perfectly identified through the analysis of grain size spectra and 7Be concentration measured in cores sampled after the floods. The comparative study of the deposits between the two sampling periods shows that the floods led to the deposition of at least 34 to 43 cm of sediments around the 20 m and 30 m isobaths. It enables to provide a qualitative and quantitative sedimentary balance of the solid matters transfers during flood periods (bottom and suspended discharge). © 2010 Socié té Hydrotechnique de France.