ASSESSMENT OF GROUNDWATER POTENTIAL ZONES IN OKEERO LGA OF KWARA STATE NIGERIA USING GIS-BASED INTEGRATED APPROACH

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Department of Engineering

ABSTRACT
In this study, Remote Sensing (RS), Land-sat 8 digital data, and digital elevation models (DEMs) from the Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER), Food and Agricultural Organization (FAO) along with other stereotypical data such as geology and rainfall were digitized and analyzed to create various thematic maps (geology, land use/cover, soil, drainage density, rainfall and slope maps) required for groundwater modelling in the study area. These thematic maps were assigned well-chosen weights and different rankings to the individual categories within each thematic map using Saaty's Analytical Hierarchy Process (AHP). The groundwater potential zones were achieved by overlaying the thematic maps using the spatial analysis tool in Arc-GIS 10.4. The result gotten was verified with pumping test data and well water levels. The results reflected that the study area had three groundwater potential zones namely, „high?, „moderate? and „low?, covering 30.27% 62.35% and 7.38% of the study area respectively, the total area is 438km2 out of which 132.58km2 is high potential zone, 273.1km2 is moderate zone and 32.32km2 is low zone. In addition, this study established that Oke-ero LGA has 65.7 million cubic meters (MCM) groundwater potential annually. From the survey output the average daily water demand in Oke-Ero is 75l/c/d, the total water demands across the LGA based on 2016 population estimate is 2.11 MCM/year with anticipated increase of 4.34MCM/year by 2040 and expected water demand increase rate of 3.2% annually. The result of correlation between final groundwater potential map and sample data from borehole yields showed90% accuracy while that of well levels indicated 84% close agreement. The results of this study set out that the GIS technology is a mighty instrument for larger area to assess groundwater potential, whereon apt locations for groundwater withdrawals could be indicated with greater certainty. This can be used as standard procedure for future planning and management of this paramount resource to ensure sustainable groundwater use and forthcoming magnification of drinking water and irrigation amplification in the area. Further, it is observed that the immediate methodology can be used as a clue for further research.