For an accurate delineation of groundwater potential zones, a GIS-based multi-criteria evaluation (MCE) technique involving GIS, an Analytical hierarchical process (AHP) by Saaty (1992) and basic descriptive statistical techniques (percentages and charts) was employed in this study. Land use, soil, slope, geologic formation, lineaments and drainage density, as well as borehole logs of the study area, was put into perspective for the analysis while weightages consistent with the percentage influence of each factor on groundwater availability were calculated based on Saaty (1992) AHP model. Weighted overlay was then used to delineate the groundwater potential zones.
Multi-Criteria Analysis (MCA) is a valuable tool that we can apply to many complex decisions. It is most applicable to solving problems that are characterized as a choice among alternatives. It has all the characteristics of a useful decision support tool: It helps us focus on what is important, is logical and consistent, and is easy to use. For this research, MCA would be used to analyze the level of influence of all variables as shown in the table below in order to accurately delineate groundwater potential zones.
Weighted index overlay analysis is a simple mathematical model for a combined analysis of multi-parameters because of its spatial dimensionality and ability to integrate varying complementary and often unorganized bits of spatial data.
Each thematic map was assigned a weight depending on its influence on the movement and storage of groundwater (Nag, (2005); Dinesh et al, (2007); Avtar et al, (2010); and Preeja (2011)). The relative ranking of each thematic unit in a theme was assigned as a knowledge-based hierarchy using the Spatial Analyst tool. All thematic maps were reclassified and assigned suitable weightage. The raster maps of these parameters were assigned respective theme weight and their class weights. The individual theme weight was then multiplied by its respective class weight and then all the raster thematic layers were aggregated in a linear combination equation in a GIS Raster Calculator module.
