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.
A regional groundwater quality evaluation was conducted in the deep Maastrichtian aquifer of Senegal through multivariate statistical analysis and a GISbased water quality index using physicochemical data from 232 boreholes distributed over the whole country. The aim was to 1) identify the water types and likely factors influencing the hydrochemistry, and 2) determine the suitability of groundwater for drinking and irrigation. Results showed that sodium, chloride, and fluoride are highly correlated with electrical conductivity (EC) reflecting the significant contribution of these elements to groundwater mineralization. The principal component analysis evidenced: 1) salinization processes (loaded by Na + , K + , EC, Cl − , F − and 3 HCO − ) controlled by water/rock interaction, seawater intrusion and cation exchange reactions; 2) dolomite dissolution loaded by the couple Ca 2+ and Mg 2+ and 3) localized mixing with upper aquifers and gypsum dissolution respectively loaded by 3 NO − and 2 4 SO − .The hierarchical clustering analysis distinguished four clusters: 1) freshwater (EC = 594 µs/cm) with mixed-HCO 3 water type and ionic contents below WHO standard; 2) brackish (Na-mixed) water type with moderate mineralization content (1310 µs/cm), 3) brackish (Na-Cl) water type depicted by high EC values (3292 µs/cm) and ionic contents above WHO and 4) saline water with Na-Cl water type and very high mineralization contents (5953 µs/cm). The mapping of the groundwater quality index indicated suitable zones for drinking accounting for 54% of the entire area. The occurrence of a central brackish band and its vicinity, which were characterized by high mineralization, yielded unsuitable groundwater for drinking and agricultural uses.
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