An integrated GIS based fuzzy pattern recognition model to compute groundwater vulnerability index for decision making

This study highlights the computational technique of groundwater vulnerability index to identify the aquifer’s inherent capacity to become contaminated benefiting from fuzzy logic employing various hydrogeological parameters in the framework of Geographic Information Systems (GIS). This is usually carried out by using GIS based overlay index method. DRASTIC is one of the widely used popular overlay index method to compute groundwater vulnerability index over the large geographical areas involving a variety of hydrogeological settings. DRASTIC method uses linear model to calculate vulnerability index and factors that pertinent to the groundwater vulnerability should be divided into ranges to employ rating value to each range. This system is unable to demonstrate a continuous output of vulnerability index from the easiest to be polluted to the most difficult to be polluted that is fuzzy nature of the groundwater vulnerability to contamination. In this paper, integrated GIS based fuzzy pattern recognition model is developed to generate the continuous vulnerability function benefiting from the same input parameters of DRASTIC method. Moreover, vulnerability variation resulting from fuzzy and DRASTIC model with respect to any single input variable, making other parameters constant, is computed taking the characteristics of selected hydrogeological settings to compare the output of fuzzy model with DRASTIC index. The ability of GIS based fuzzy pattern recognition model to generate continuous output of vulnerability index may be considered as a pronounced advantage over DRASTIC method. Groundwater vulnerability map has been developed utilizing its output in shallow groundwater aquifer of Kathmandu, Nepal as a case study. Finally, output of vulnerability models are tested by nitrate data which were measured from ninety sources from shallow groundwater systems of study area. In large geographical areas with limited data, the groundwater vulnerability maps provide important preliminary information to decision makers for many aspects of the regional and local groundwater resources management and protection.