Integration of Geophysical and Remotely Sensed Data in Regional Groundwater Evaluation in the Basement Complex of Ondo State, Southwestern Nigeria F.O. Akinluyi 1, M.O. Olorunfemi 2 and A.A. Omitogun 3 1 Department of Physics Adeyemi College of Education, Ondo, Nigeria 2 Department of Geology 3 Regional Centre for Training in Aerospace Surveys Obafemi Awolowo University, Ile-Ife, Nigeria

Outline Introduction Study Area Datasets Objectives Methodology (Lineament) Preliminary Results Further Study

Introduction Access to potable water in Ondo State, Nigeria, is inadequate due to shortfall in the public water supply. This has led people to resort to rain water harvesting, digging of shallow hand-dug wells and surface water sources such as streams or rivers. These water sources are highly susceptible to contamination because they are surface to near-surface. This necessitated the search for groundwater as an alternative source.

The Study Area It lies between latitudes and N and longitudes and E. Ondo State is underlain by both the Precambrian Basement rocks and sedimentary formations (Figure 1). The Basement Complex underlies the northern part (60%) of the state which constitutes the study area.

The Study Area Contd. Figure 1: Map of Ondo State Showing the Generalized Geology

Datasets

Datasets Contd. 3-D of the Study area

Objectives The objectives are to: (i) identify and extract geologically induced lineaments and other discontinuities from remote sensing data; (ii) carryout statistical analysis of the lineaments; (iii) evaluate hydrogeological characteristics by correlating and synthesizing VES data, borehole information, extracted lineaments, GRACE data and geology; (iv) carryout geoelectric survey based on (iii) in order to delineate the groundwater aquifer(s) and determine the layer resistivities and lateral extent; and (v) Classify the study area into different groundwater potential zones.

Methodology (Lineament) (i) Ondo State boundary in shapefile was used to subset Landsat ETM+ and ASTER GDEM. (ii) The following processing techniques were applied to the imageries: radiometric enhancement, Linear stretching, spatial enhancement, edge enhancement e.g. Sobel filter, spectral enhancement i.e. principal component analysis (PCA), Band ratioing and colour compsite. (iii) Combination of all images in (ii) in conjuction with DEM were used to digitize and generate lineament map. Rose diagram was generated from the lineaments.

Preliminary Results Figure 2 shows the spatial distribution of lineaments excluding exposed rock outcrops. The Rose diagram showed three (3) main lineament trends –: N-S, NE-SW, E-W.

Preliminary Results Contd. Figure 2: Lineament Map and Lineament Rose diagram of the Basement Complex Terrain

Further Study Lineament density map will be generated from Figure 2 as index of groundwater potentials. I will source for Vertical Electrical Sounding (VES) and Borehole (BH) data. I will acquire primary data i.e. VES and BH where there are data gaps. The above results will be integrated with GRACE data in order to classify the study area into high, moderate, low and very low groundwater potential zones.

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