Application of a GIS-Based DRASTIC Model for Groundwater Vulnerability Assessment: A Case Study of Lai City, Tandjile East Department, Southern Chad

Groundwater resource protection is a worldwide issue because groundwater plays a crucial role in meeting water supply demands for both natural ecosystems and human activities. Effective groundwater management and protection therefore require appropriate approaches for assessing contamination risks and identifying areas that are particularly vulnerable to pollution. In this study, a GIS-based DRASTIC model was applied to assess groundwater vulnerability in Lai City, southern Chad. Seven hydrogeological parameters were considered, namely depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone, and hydraulic conductivity. A weighted overlay analysis based on the DRASTIC Index (DI) was subsequently used to generate the groundwater vulnerability map of the study area. The results show that the DRASTIC Index values range from 119 to 175, enabling the study area to be categorized into three groundwater vulnerability classes: low, moderate, and high. The high-vulnerability class covers approximately 35% of the study area, highlighting areas that require particular attention for groundwater protection and management. The average and low class of vulnerability covers portions of the study area 31% and 34%, respectively. The northern and south-western portion of the catchment, namely Lai, Gabri Mbassa, Sategui, and Django, possesses high groundwater vulnerability. GIS-based Drastic model validation is performed via water quality parameters such as Nitrate and Total Dissolved Solids, with the accuracy of 97% and 75% respectively. The resulting groundwater vulnerability map provides a valuable tool for groundwater protection and sustainable land-use planning in Lai City and its surrounding areas.