Groundwater Recharge Zone Mapping Using GIS-based Analytical Hierarchy Process and Multi-Criteria Evaluation: Case Study of Greater Banjul Area

Abstract

Remote sensing (RS) and Geographic Information System (GIS) play a crucial role in understanding groundwater potential recharge in semi-arid areas. In this present study, groundwater recharge zone map is delineated for the shallow aquifer in the Greater Banjul Area (GBA) using GIS, RS and Multi-Criteria Evaluation (MCE) technique utilizing seven criteria (geology, land-use/cover, slope, drainage density, soil texture, groundwater fluctuation and aquifer transmissivity). Analytical Hierarchical Process (AHP) is used as MCE technique to normalize the weights of the various criterion. Each class of the different themes was assigned suitable score and normalized using a Fuzzy membership algorithm. Thematic layers were integrated using Weighted Linear Combination (WLC) in a GIS platform to generate groundwater recharge zone maps. The recharge map thus obtained was divided into four classes (poor, moderate, good, and very good) based on their influence to groundwater recharge. Results indicates that about 10.5 % of the total study area falls under ‘poor’ and ‘moderate’ zone and cover the estuarian portion of GBA, 40% of the total area falls under ‘very good’ zone which is a good indication for future artificial recharge planning and potential drilling of boreholes.