Assessment of Groundwater Suceptiability to Nitrate Contamination Using GIS-Based Modified DRASTIC Model in the Rib Watershed, upper Abay Basin, Ethiopia

Abstract Groundwater is one of the most important sources of freshwater, contributing significantly to domestic, drinking, and irrigation needs around the world. However, its quality is deteriorating over time due to overexploitation and anthropogenic activities. The Rib watershed, located in the Tana sub-basin (Ethiopia), is a heavily cultivated and urbanising area. Therefore, this study attempted to assess groundwater vulnerability to pollution using the GIS-based Modified DRASTIC Model. Hydrogeological parameters and anthropogenic factors (land use/land cover) were used for assessment. The necessary data were collected from the field, downloaded from websites, concerned organizations, and laboratory experiments. The results showed that more than 73.24% of the watershed is under medium to high vulnerability, and highly vulnerable areas (22.48%) were confined to the Southern parts of the watershed (under built-up and cultivated areas. The vulnerability of groundwater in the watershed is highly influenced by aquifer media (24.1%), net recharge (21.75%), land use/land cover (15.1%), and depth of groundwater table (13.6%). Based on the observed data of groundwater quality parameters (turbidity, pH, and nitrate), high-vulnerable areas were more contaminated than medium and low-vulnerable areas. Therefore, the result indicated that the area is vulnerable to contamination calling for appropriate groundwater management. Hence, this finding helps to plan and minimize future contamination of groundwater by considering its vulnerability before high-risk activities are allowed. The investigators recommended that the overall quality of groundwater be investigated and that appropriate groundwater management be designed to reduce groundwater contamination.