Intérêt de la connaissance des processus sédimentaires actuels sur la facade atlantique du plateau continental francais pour le contrôle des rejets industriels

The conditions of sediments transfert from a river medium to a sea medium may be used as guide for forecasting the industrial effluents diffusion. The investigation on river suspensions carried down to the sea shows that clay is the essential component, the maximum size of suspensed particles transfered down stream being very close to 500 microns. Within an estuary, the carried down suspended particles undergo a temporary storage and a mineralogical selection ; a certain amount of the river sediments is finally drained towards the open sea, but it is not possible to erclude the ability of the smallest sediments from the continental table-land to supply the estuary sedimentation. According to the continental table-land morphology, the suspended particles are they or are they not allowed to reach rapidly the abyssal medium ? As fur as the transports in contact with the bottom are concerned, it seems that masses carried down by rivers are stopped within estuaries, which, on the other hand, can be supplied doun stream with sediments from coastal or marine origin. Transports in contact with the bottom on the continental table-land are essentially located at La Manche outlets, according to the tide streams acceleration. It seems that all this results in a general motion towards a slope breaking of the continental table-land. Turbidity streams due to sandy sediments entrapped in canyons heads are therefore possible within this zone, but such a form of masses transfert is particularly active and characteristic of the Spanish border of Golfe de Gascogne. Our study shows that important material transferts exist ; it is possible to make clear, in a certain measure, the way and the qualitative aspect, but data is insufficient assess the masses flows in question. [NOT CONTROLLED OCR]