INTEGRATION OF REMOTE SENSING AND ELECTRICAL RESISTIVITY METHODS IN GROUNDWATER POTENTIAL MAPPING OF AKURE, SOUTHWESTERN NIGERIA

Abstract

Water is one of the most essential natural resources which support both human activities and economic development. It plays a vital role in the sustenance of human life and existence, as it is commonly said, “Water is life”. Therefore, the search for potable water provided by groundwater using the most appropriate methods has always been the subject matter. The study delineated groundwater potential zones in Akure using integrated methods of remote sensing and electrical resistivity. Landsat and Shuttle Radar Topographic Mission (SRTM) data were used to produce lineament, geomorphological, drainage, slope, geological and land use/cover maps. On the basis of relative contributions of each of these maps towards groundwater potential in the area, weights were assigned to each map and then reclassified. All the reclassified maps were georeferenced using the same control points and integrated in GIS environment using simple additive weighting method for which the groundwater model map was generated and the results categorized into four potential zones, namely: very good, good, moderate and fair potential zones. Zones of fair groundwater potential occupy most parts of the study area followed by moderate, then the good and finally the very good groundwater potential zones. This is expected for a basement terrain like the study area where lateral discontinuities in lithology is not uncommon. The generated groundwater model map was then validated by borehole and electrical resistivity data. It was observed that good yield boreholes correlated with good groundwater potential zones and fair yielding boreholes to fair groundwater zones. Also, hand-dug well data was used to construct water head map which showed that the groundwater potential system is at a fair balance due to approximately equal zones of discharge and recharge. Furthermore, electrical resistivity data indicated six lithologic layers which are the topsoil, weathered lateritic layer, sandy soil, highly weathered basement rock, fractured basement rock, and fresh basement rock. However, the sandy soil, highly-weathered and the fractured layers constituted the aquifers zones in the study area. Also, the overburden thickness showed that the depth to fresh overburden thickness showed that the depth to fresh basement within the area ranges from 0m at outcrop points, through 10m in areas of averagely-shallow depth of weathering, to 30m in deeply-weathered areas and to about 70m in highly fractured basement rocks as observed in the north-western part of the study area. Finally, since the overburden thickness map reflected close to real subsurface conditions, it was reclassified, weighted and overlaid together with the groundwater model map produced by remote sensing method and a groundwater potential map of the study area was produced. The verified groundwater potential map of the area also delineated three areas of groundwater potentials: fair, moderate, good and very good. Thus, this study has successfully provided an improved understanding of the hydrogeological system of the area and further given a baseline data for future groundwater development.