GROUNDWATER POTENTIAL EVALUATION IN A TYPICAL HARDROCK TERRAIN USING GRRAT INDEX MODEL

Geological and geophysical surveys had been carried out in parts of Alagbaka area, Akure, southwestern Nigeria, with the aim of evaluating the groundwater potential using the Geology of the study area, Aquifer Resistivity, Bedrock Relief, Aquifer type and Thickness (GRRAT) index model. Geological and hydro-geophysical data were used to generate five thematic maps for Geology, Aquifer Resistivity, Bedrock Relief, Aquifer type and Thickness (GRAT) of the aquifer units in the study area. GRRAT ratings were obtained based upon a calculationof weight and range of each of the parameters. They were used to develop the GRRAT indexmap ofthe study area. The GRRAT index modelmap generated for the study area showed that the very low, low, moderate and high groundwater potential zones cover about 15%, 450/0, 35% and 5% respectively of the investigated area. This study concludes that the GRRAT index model can greatly increase the success rate of drill borehole projects and can also be a useful tool in the decision making process for groundwater development in a typical hard rock terrain.