GIS-BASED FREQUENCY RATIO MODEL FOR GROUNDWATER POTENTIAL ZONATION IN PART OF IGOBA COMMUNITY SOUTHWESTERN NIGERIA

Abstract

This study applied a geographic information system (GIS) based frequency ratio (FR) model for groundwater potential assessment in a crystalline basement complex terrain, southwestern, Nigeria. Four geo-electrically derived groundwater potential conditioning factors (GPCFs) were used, namely; Aquifer resistivity (AQR), Aquifer thickness (AQT), Coefficient of anisotropy (COA), and Bedrock relief (BED). To apply the FR model, the well location inventories were partitioned randomly into 70% (45) for model training and 30% (19 wells) for model testing. The frequency ratio model algorithm was used to synthesize the GPCFs to produce the groundwater potential index (GWPI). The estimated GWPI were processed in the GIS environment to produce groundwater potential zonation map which enabled demarcation of the study area into five potential zones. The produced FR based model map was validated through the application of area under curve (AUC) approach and spatial attribute comparative scheme (SACS). The performance of the frequency ratio model was compared with that of analytic hierarchy process (AHP) approach based multi-criteria decision analysis (MCDA) model via both qualitative and quantitative SACS. The AUC validation approach for the FR model result is 0.6447 or 64% success rate and 0.6137 or 61% for prediction rate. The quantitative SACS result, established 63% and 31% for the FR model and AHP-MCDA model respectively. Similarly, the result of the qualitative SACS established 71% and 50% respectively for these models. The AUC result implies average performance for the FR model. The SACS result shows that the FR based model performed better than the AHP model, hence, the FR model is a better alternative for prediction of groundwater potential zones even when applied to GWCFs that are geo-electrically derived.