TABLE OF CONTENTS An estuary may become hypersaline if the salt flux F is not sufficient to evacuate the salt accumulation resulting from evaporation. The fresh water discharge of the Gambia is still too large for the estuary to become hypersaline, but the two estuaries bordering the Gambia to the North and to the South, the Saloum and the Casamance, are strongly hypersaline.
The Saloum has always been hypersaline. Measurements in the Saloum near a salt production farm go as far back as 1965 (Pag s and Citeau, 1990). The Casamance, however, although strongly influenced by evaporation, has only become hypersaline during the Sahelian drought, which started in the late 1970s. Around 1980, an ecological disaster took place in the Casamance. The fresh and brackish habitats turned hypersaline (up to 100 kg/m 3), blocking off migration routes for migrant species and stunting the growth of otherwise salt-tolerant vegetation (Savenije and Pag s, 1992).
Figure 5.11 shows model results of the Saloum against measurements at three locations along the estuary. It can be seen that pronounced hypersaline conditions have always existed due to the ephemeral character of the rivers entering the estuary. The fit of the model is not perfect. This is largely due to the lack of data on fresh water discharge into the estuary. A simple hydrological model had to be made on the basis of rainfall data to simulate inflow series. Moreover, hydrographical data on cross section and depth were scarce. Since the effect of evaporation on salt...
