Assessment of the Vulnerability of the Shallow Aquifer of the City of Sarh in Chad, using the Drastic Approach

The demography (3.4%) and the development of anthropic activities in the city of Sarh, constitute a risk of groundwater pollution. That is why a vulnerability map is determined to contribute to the protection of groundwater resources against possible pollution for future decision and allocation of land and activities. The present study interested the city of Sarh and had the objective to elaborate a vulnerability map to pollution by applying the DRASTIC method. The data required for this study are summarized in seven critical factors specific to the model applied (depth of the water table, net recharge, aquifer lithology, soil type, topography (slope), unsaturated zone lithology and hydraulic conductivity). They were acquired from several sources and converted by the GIS into thematic maps. For each critical parameter, a coefficient and a weight were assigned according to its importance in the DRASTIC model. The resulting map shows three classes of vulnerability; 36% of the Sarh region has very low vulnerability, 35% has low vulnerability and 29% has medium vulnerability.