Reclassification and weighting of the thematic layers was done using the Reclassify Tool in ArcMap, vector data was converted to raster format using the vector to raster tool.
All factors impacting groundwater recharge were each classified into 4 classes, 1 being the least suitable and 4 the most suitable. The reclassified layers were then weighted using the method similar as for Musa et al., 2000. The most influential factor given high weight while the least influential factor with the least weight on a scale of 0 to 100%. 0% meaning little or no influence while 100% having high influence. The sum of weights should always be equal to 100%. The reclassified layers were thereafter used as inputs in the weighted overlay tool in ArcMap 10.5 to generate a groundwater potential map.
Each thematic layer consisted of a grid cell. The grid cell in each of the thematic layer was categorized depending on its influence to groundwater potential. Finally, all thematic layers were combined using the groundwater potential model to produce final derived layers. An evaluation table was finally produced basing on the weights of influential factors for recharge with outputs reclassified into four groups; high, moderate, low and very low groundwater potential. The formula of Groundwater potential model was helpful when combining the layers in the overlay tool (Sener et al., 2005):
GP = Lt + Lu + S + Dd
Where:
Lt – Soil type
Lu – Land use
S – Slope
Dd– drainage density