Etude experimentale de l'interaction eau-sediment en zone de SWASH par velocimetrie doppler ultrasonore (VDU)

Abstract

The work presented in this thesis is a contribution to the determination of the field of flow velocity in porous media (interstitial flow velocity) in permeable bed of sediments, measured in the swash zone.

This latter is regarded as a true border between the marine field and the continental field and moreover, the ultimate place of the transport of the sediments in the flow of water mass according to the two phases of the swash. However the physical processes associated to the sedimentary transport were not studied until now only starting from analysis of the field speed within a fluid vein, owing to the fact that the majority of the models were established for flows on an impermeable bottom for a velocity at the bottom of the bed being null. The measurements done by the technique of Ultrasonic Doppler Velocimetry allowed to analyze the field of interstitial velocity in the case of a permanent flow on a free surface for beds with different porosities. This same principle of measurement was applied for the study of the process of the swash to a beach in a flume channel. The results obtained highlight a distribution of an exponential form of the field speed inside the sediment, a discontinuity speed to the interface water- sediment between the speed of a free flow and that of an interstitial flow leading, thus, to a significant difference in velocity gradient to the interface of the phase of exchange of water of two flows.