Horizon 1 1 10 C-ACTI : Communications avec actes dans un congrès international Géophysique des sols et des formations superficielles : abstracts et résumés étendus G0ophysique des Sols et des Formations Superficielles : Colloque GEOFCAN 133-138 multigr. GEOPHYSIQUE SONDAGE ELECTRIQUE ZONE COTIERE AQUIFERE EAU DOUCE EAU DE MER SENEGAL DAKAR REGION SAINT LOUIS REGION 1997 1997/09/11-12 Paris ORSTOM fdi:010011230 FRE https://www.documentation.ird.fr/hor/fdi:010011230 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_7/geofcan/010011230.pdf Horizon (IRD) Resistivity methods were used with a vertical electrical sounding network to investigate the relationship between freshwater and saltwater along the northern coastline of Senegal, from Dakar to Saint-Louis. The water-table aquifer lies in quaternary sands with very low piezometric heads, less than one meter near the coast. The depth of the saltwater interface, as revealed by the water resistivity using Archie's formula, is consistent with a gentle slope of the watertable towards the sea. Along the coast, different hydrogeologic conditions were found : in the northern section, the system is rather uniform, with a stable saltwater edge ; in the Cap Vert peninsula, saltwater intrusion has already begun due to pumping, and the aquifer is in a preacrious condition, the saltwater edge seems to be presently blocked by a rise of the argilaceous basement. The influence of groundwater abstraction and of evaporation in freshwater coastal lakes can clearly be seen on the electric and hydrogeologic measurements. (Résumé d'auteur) 066GPHGEN