Abstract
In order to reduce the level of risk associated with borehole drilling, it is important to have detailed knowledge about the aquifer distribution. In a view to generating groundwater potential model of Lokoja and its environs, the detailed subsurface characterization was carried out using a GIS-based multi-criteria decision analysis approach. One hundred and twenty-four vertical electrical sounding (VES) data points were covered within the study area using the Schlumberger array of electrical resistivity surveys. Hydrogeological investigation of one hundred and twenty-four existing boreholes within the vicinity of the sounded VES points was carried out by measuring in situ parameters of each borehole such as borehole depth, elevation, static water level and borehole yield. A Multi-Criteria Decision Analysis-Analytical Hierarchy Process (MCDA)-AHP-based was carried out by estimating the probabilistic ratings for the classes of parameters used for modeling groundwater potential. Four groundwater potential influencing factors, namely coefficient of anisotropy, transverse resistance, aquifer resistivity and aquifer thickness, were classified and rated. The output of the multi-criteria decision analysis was processed in the GIS environment to produce a groundwater potential index map. The obtained model was validated by comparing it with in situ borehole yield data to determine the accuracy of the proposed model. The groundwater potential map generated classified the study area into low, medium and high yield zones. Areas with medium potential zones dominate the largest part of the with 66% area coverage, and the dominance of these zones was visible in the northern and western part of the study area. Areas with high groundwater potential exist toward the southern and eastern sections of the study area. This area was observed to be underlined with sandstone, siltstone and migmatite. The validation exercise carried out on the proposed model reveals a 70% prediction accuracy.
Highlights
The need for successful groundwater exploration planning and management for local and regional groundwater productivity mapping in the field of groundwater hydrology cannot be underestimated The importance of groundwater as a supply for a country’s socioeconomic growth is enormous, as it remains the most solved water sources in many areas due to underdevelopment of surface water
The longitudinal resistivity was interpreted to be the aquifer resistivity for areas underlined by basement rocks, while transverse resistivity was interpreted as aquifer resistivity for sedimentary terrain
These values were used as the aquifer resistivity in the study area since it is characterized by both longitudinal and transverse flow as described by Reiter (1981)
Summary
The need for successful groundwater exploration planning and management for local and regional groundwater productivity mapping in the field of groundwater hydrology cannot be underestimated The importance of groundwater as a supply for a country’s socioeconomic growth is enormous, as it remains the most solved water sources in many areas due to underdevelopment of surface water. Recent population growth has imposed significant stress on the existing. Groundwater occurrence in any rock presupposes the satisfaction of two factors: adequate porosity and permeability. Sedimentary rocks exhibit these properties due to their mode of occurrence and emplacement. Sedimentary deposits maintain primary porosity that determines their storage and permeability to a great extent (Ashraf et al 2018) which tends to make them exhibit good aquifer potential as compared to basement complex aquifers. Basement complex rocks are considered poor aquifers due to their
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