Isotopic and hydrogeological investigations in the southwest region of the Dominican Republic

The southwestern part of the Dominican Republic is quite poorly developed. Two mountain ranges, that are strongly folded and faulted cross this area with the Lago Enriquillo in between, whose water level is below sea level. In the low lands evapotranspiration exceeds precipitation and vice versa in the high lands rising up to 2367 m.a.s.l. Water balance shows groundwater recharge of 181 a 227 mm/a in the catchment area of the Lago Enriquillo. With the aid of stable isotopes the mean altitude of groundwater recharge was determined to be in the range of 1000 and 2000 m.a.s.l. High altitudes contribute more to the catchment area of the Lago Enriquillo than to the neighbouring areas like the coastal area of the Sierra de Bahoruco and its southern foreland. Considering the regional distribution of stable isotopes in groundwater and determining its mean residence time by means of stable isotopes variations, the content of radioactive environmental isotopes and an analysis of recession flow in dry times leads to the result that discharge is quicker in longitudinal than in transverse direction of the mountain ranges. This is due to tectonic dilatation and compression in the respective directions. The aquifer seems to be subdivided in three floors with an increase of storage capacity with depth. On a large scale each floor has a more or less homogeneous groundwater flow field. The development of artificial recharge is mainly bound to the lowest floor along the low lands of the mountain ranges. From isotope results and hydrogeologic investigations there are five areas in the catchment area of the Lago Enriquillo for future exploitation. In the catchment areas neighbouring the Lago Enriquillo this seems to be problematic. (author). 5 refs, 14 figs, 1 tab