AQUIFER VULNERABILITY ASSESSMENT USING GIS AND DRASTIC APPROACH: THE NILE VALLEY AQUIFER, ASSIUT GOVERNORATE, EGYPT

Groundwater is a major water resource in Assiut governorate. Vulnerability assessment to delineate areas that are more susceptible to contamination from anthropogenic sources has become an important element for sensible water resources management and land use planning. Potential contamination of groundwater at any specified location depends upon several physical and environmental factors, such as depth to groundwater, soil type, groundwater recharge and of course aquifer composition. Few attempts have been made to assess the potential of groundwater contamination at the Nile Aquifer at Assiut governorate, however, these attempts focused on local, or site by site basis. This contribution aims at estimating a regional groundwater vulnerability assessment for the Nile Valley aquifer in Assiut governorate by applying DRASTIC model along with GIS (ArcMap 10.x) as an effective method for groundwater pollution risk assessment. The GIS technique has provided efficient environment for analyses and high capabilities of handling large spatial data and overlaying several thematic map layers. DRASTIC is an acronym for seven variables that control the groundwater contamination potential (Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of the vadoze zone, and Conductivity of the aquifer) designed for characterizing the hydrogeological setting and evaluating aquifer vulnerability. This approach allowed investigating the potential of groundwater pollution on a regional scale of the study area. Using the variables given in the DRASTIC model, successive GIS-theme maps were developed describing the geometry of the area as well as the groundwater quality. These map layers were then combined in GIS to formulate the final groundwater pollution potential map. Some parts of the Nile Aquifer at Assiut governorate were dominated by “High” vulnerability classes, especially within the urban areas and settlements, while other parts were characterized by “Moderate” vulnerability classes. The elevated desert fringes of the study area obviously displayed “Low” aquifer vulnerability.