A Customized FuzzyAHP - GIS based DRASTIC-L model for intrinsic groundwater vulnerability assessment of urban and peri urban phreatic aquifer clusters

The groundwater vulnerability analysis addresses the degree of sensitivity of groundwater system towards changes in both intrinsic/inherent and extrinsic factors. With this aim, an integrated FAHP-GIS-based modified DRASTIC (DRASTIC-L) method was followed in order to address the response of various hydro-geological indicators towards attenuation of pollutant to sub-surface hydrological regime in two differently urbanized clusters of Kozhikode district in Kerala, Southern India. Rating for the DRASTIC-L factors was derived with the aid of Fuzzy based Analytical Hierarchical Process (FAHP). Spatial and non-spatial information was integrated into a GIS environment. The resultant spatial data thus generated depicted that about 71% of urban and 22% of peri-urban zones of the study area, which are characterised by porous and permeable vadose media with shallow groundwater table, have a high to very high vulnerability index value. Majority of highly vulnerable urban area extends 0-10 km from the coastal line and has a dense population. Of the total study area, 8% urban and 38.5% of peri-urban area with low index value indicated that the groundwater in the zone is protected from contaminant's leaching due to its inherent hydrogeology. Low porous vadose media and the presence of steep slope terrain favors this low vulnerability. Besides the remaining area shows moderate vulnerability to contamination. Single - parameter and map-removal sensitivity analyses highlighted that vadose zone characteristic has the highest influence on vulnerability assessment. The resultant vulnerability index values validated with composite groundwater quality index data depicted the significant correlation among them. Thus, the groundwater vulnerability index map is an efficient tool for water-sensitive urban development.