Triangulation Approach for Mapping Groundwater Suitability Zones in Coastal Areas Around Lagos, Nigeria. Using Multi-Criteria Decision-Making Technique

ABSTRACT Water quality in Lagos's coastal area is prone to constant seawater intrusion due to its proximity to the Atlantic Ocean. Seawater intrusion in the coastal aquifer is a major challenge to human survival and therefore needs urgent attention due to deficiency in groundwater quality. This study applies integrated techniques to map groundwater suitability zone (GSZ) around the Lagos coastal area for sustainable development. The objectives were achieved by preparing eight different thematic layers that influence groundwater suitability viz; drainage density, geology, geomorphology, lineament density, rainfall, longitudinal conductance, slope, and transverse resistance. Weighting assignment, normalization and, pair-wise comparison of the thematic maps were done using Saaty’s Analytical Hierarchical Process (AHP) model before being integrated through the geographical information system (GIS) spatial analyst model with weight overlay to generate the overall groundwater suitability map. The integrated result reveals that 7% of the research location has very low suitability, 32.2% low, 47.8% moderate, and 13% high groundwater suitability. Thus, the groundwater suitability zone (GSZ) was validated via Electrical conductivity (EC) and total dissolved solids (TDS) and the result reveals a good correlation. The research has proven the efficacy of integrating different surface and subsurface data for effectively mapping the groundwater suitability zone (GSZ).