Contribution of Landsat imagery to map vulnerable areas to seawater intrusion along the Mt.-Cameroon coastal area using lineaments pattern

Large overpopulated coastal areas are, nowadays, affected by seawater intrusion, and the contamination of the groundwater is a real threat. This paper aims to identify the zones along which seawater spreads in the Mt. Cameroon coastal region of Cameroon, and to map the most vulnerable areas to this threat. The results are based on the location of the contaminated boreholes, statistical analysis of automatic and manual lineaments, topographic and slope maps. The elaborated thematic maps allow identification of the fractured zones along which seawater can spread and the areas where the impact of this phenomenon could be more severe. The presence of a large number of contaminated coastal boreholes suggests that elevation (<100 masl), slope (<3 degrees) and fractures are the factors promoting the seawater intrusion along the narrow and flat coastal strip of study areas. The network of closely spaced and intersecting fractures along the gentle slope (<8 degrees) of the Mt. Cameroon, favour the boreholes contamination up to 4 km from the shoreline. Between the Mt. Cameroon and Limbe-Mabeta Massif, a wide NE-SW-oriented system of long and intersecting fractures, promote the inland seawater intrusion up to 10 km inland. The closely spaced and intersecting fractures along which seawater can easily spread has been reconstructed based on orientation, density and length of manual lineaments and the lineaments intersection map. Landsat 7 ETM + image is the one which provides the most reliable vulnerable zone with respect to lineament pattern in this region than both Landsat 8 OLI and Sentinel 1-A images.