AQUIFER VULNERABILITY ASSESSMENT USING ANALYTIC HIERARCHY PROCESS AND GIS FOR UPPER PALAR WATERSHED

摘要

Ground Water is inherently susceptible to contamination from anthropogenic activities and remediation is very expensive and often impractical. Prevention of contamination is hence critical in effective ground water management. Aquifer vulnerability assessment aims at predicting areas, which are more likely than others to become contaminated as a result of activities at or near the land surface. Once identified, these areas could then be enforced with restricted land use or becomes focus of attention at preventing contamination of the underlying ground water resources. The upper palar watershed in Tamil Nadu, India is having conglomeration of tannery industries in Ambur and Vaniyambadi Towns. The effluent let out from these tannery industries leads to contamination of the Upper Palar Aquifer consisting primarily of Gneiss, Charnockite and Recent alluvium. In this paper, an attempt has been made to assess the Aquifer Vulnerability of Upper Palar Watershed using the DRASTIC Model. The DRASTIC Model uses the following seven thematic maps: Depth to Water, Recharge, Aquifer Media, Soil Media, Topography, Impact of Vadose Zone and Hydraulic Conductivity. The land use and soil map have been prepared using Geocoded IRS-1C Satellite Imagery. The topography layer is created using Survey of India 1:50,000 Scale Topographic Maps. The field data regarding water level in control wells is obtained from three user departments and have been converted to the same datum to compute the depth to water level. The Soil Map prepared by the Soil Survey and Land Use Organisation is used as the base map to prepare the Soil and Impact of Vadose Zone maps. The Hydraulic Conductivity values have been obtained from the field using pump test details and for certain areas where pump test details have not been available, representative values for the respective formation has been used. The Recharge layer is derived using the land use and soil map and these seven layers have been integrated using Arc View GIS Software. Analytic Hierarchy Process (AHP) has been used to arrive at the weights and ranks of the criteria and alternatives of the seven layers. A Visual Basic Software AHP has been written to compute the weights and ranks of the above thematic layers based on the relative weights input. The output from AHP generates a MS Access database for these thematic layers, which is then interfaced with Arc View using Avenue Codes. This paper aims at developing a user-friendly VB software interfaced with GIS for estimation of Weights and Ranks of the thematic layers for Aquifer Vulnerability Assessment and the results are presented.