SEDIMENTARY ENVIRONMENTS IN THE LOWER SEN EGAL RIVER AFTER THE SETTLEMENT OF DIAMA AND MANANTALI DAMS

During the last decades, in the estuarine part of the Senegal river, n oticeable hydrological changes occurred. Downstream, from Gandiol to t he mouth, these changes may be related to the inlet migration as well as pronounced marine invasions during the drought of 1972-1982 but mai nly to the recent coming into operation of Diama retention dam. Upstre am, from Diama to Saint-Louis, low salinity waters, due to floodgate o pening, seem to generate sedimentary disturbance and faunal scarcity. In the Diama reservoir, the disappearence of polyhaline species has no t been truly compensated by freshwater species settling owing to the r emanent salinity and the extreme instability of this environnement.