The application of electrical methods in exploration for ground water resources in the River Malacatoya sub-basin, Nicaragua

Abstract

Nicaragua is being substantially affected by climate change, whose impact is to be seen in marked seasonal variations of climatic and hydrometric parameters. Rainfall has declined sharply over the last decade within a strip of land that runs parallel to the Pacific Ocean and extends from the extreme northwest of Lake Nicaragua (also known as Cocibolca) to the Departments of Madriz and Nueva Segovia and beyond the border with Honduras. Droughts and water shortages have changed the way of life of local inhabitants along the strip, which includes the Malacatoya sub-basin. Shallow aquifers and surface water levels have been notably reduced. This has increased the need to seek new water sources in the sub-basin from a flow-systems viewpoint, applying hydro-geological, geophysical and hydro-geochemical techniques to create a conceptual model of how the systems operate. This article describes the application of 10 Continuous Vertical Electrical Soundings (CVES) and nine Vertical Electrical Soundings (VES), accompanied by a geological evaluation. Taken together, these techniques permit the identification and characterization - in terms of space and depth - of the aquifer formations present in three sub-areas of the sub-basin. Geophysical results indicate that the thickest aquifers were to be encountered in the Río Malacatoya and Las Banderas quaternary units (unconfined aquifers). In these units, the flow is through porous media. In Teustepe, in the Río Grande de Matagalpa, Cerro Oluma, La Libertad and Santa Lucía tertiary units, the flow is through fractured media (semi-confined aquifers).