Isotopic and hydrogeological studies in the southwest of the Dominican Republic

The southwest region is the poorest in the Dominican Republic because of its harsh environment. Two karstified limestone mountain ranges, which are folded and faulted, run across the area. Between the two ranges lies a lake, the Lago Enriquillo, whose surface is below sea level. Potential evapotranspiration exceeds precipitation in the lowlands and vice versa in the mountains. The rate of groundwater recharge measured for the Lago Enriquillo basin is from 98 to 120 mm/a. The mean altitude of recharge calculated using the stable isotopes was between 1000 and 2000 m a.s.l. The high orographic altitudes contribute more to recharging the Lago Enriquillo than to recharging the coastal areas of the Sierra de Bahoruco and the southern part of the Sierra itself. Mean residence time was determined from the variations in stable isotope concentrations, natural radioactive isotopes and low-water discharge rates, and it was deduced that flow rates are higher in the longitudinal zones of the Sierras than in transverse areas. The reason behind these phenomena has to do with zones of tectonic compression and dilatation. The karstified aquifer appears to be split into three levels, with storage capacity increasing with depth. Each level appears to be homogeneous from the point of view of the large scale field of flow. Possibilities for groundwater development seem most promising in the deep levels which surface at the feet of the Sierras, and more promising in the Lago Enriquillo basin than in others. The isotopic and hydrogeological studies have revealed five areas in the Lago Enriquillo basin where groundwater could be exploited in future. Such exploitation would be difficult in the other basins. (author). 4 refs, 14 figs