Modeling of Groundwater Yield Using GIS and Electrical Resistivity Method in a Basement Complex Terrain, Southwestern Nigeria

In this research, groundwater yield of Ibodi and its environs have been investigated using hydrogeologic data and vertical electrical sounding. The study was carried out with a view to providing information on the geoelectric characteristic of the subsurface sequence, bedrock topography, subsurface structural features and their hydrogeologic significance, in order to determine possible areas for groundwater yield zones. The study involved the use of Schlumberger vertical electrical sounding data at sixty-eight (68) stations. The results from depth sounding data interpretation revealed four subsurface geoelectric layers namely; the topsoil, weathered layer, fractured basement and the fresh basement The weathered layer and fractured basement constitutes the aquifer units with varying thickness. The second order parameters were determined from the interpretation of vertical electrical sounding results and used to determine the groundwater yield index value (G.W.Y.I) by multiplying the coefficient of anisotropy (λ) and total transverse resistance (T) i.e. (λ*T). The groundwater yield index value was used to model the groundwater yield map The groundwater yield of the entire study area was classified into very high, high yield, moderate yield, low yield and Very low yield. The boreholes data and static water level across the entire study area were used to validate the accuracy of the groundwater yield map and hence of the proposed methodology. The locations and names descriptions of these boreholes and static water level were displayed on the groundwater yield map. The validation was carried out by superimposing the boreholes and static water level data on the groundwater yield map.