Development of hierarchical fuzzy model for groundwater vulnerability to pollution assessment
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ORIGINAL PAPER
Development of hierarchical fuzzy model for groundwater vulnerability to pollution assessment Jawed Iqbal & Gopal Pathak & A. K. Gorai
Received: 4 December 2013 / Accepted: 2 April 2014 # Saudi Society for Geosciences 2014
Abstract There is a need to develop new modelling techniques that assess groundwater vulnerability with less extensive data and which are robust when data are uncertain and incomplete. In this present study, a hierarchical fuzzy system (HFS) model was developed to systematically quantify uncertainties associated with hydro-geological conditions of the site in groundwater vulnerability assessment. The need for hierarchical fuzzy expert systems can occur frequently for higher number of input variables. The HFS model was designed for seven input variables viz. depth to water table (D), net recharge (R), aquifer media (A), soil media (S), topography (T), impact of vadose zone (I), and hydraulic conductivity (C). The model was validated by the observed nitrate concentrations in groundwater. The HFS model was applied to groundwater vulnerability assessment in Ranchi district, Jharkhand, India. Sensitivity analysis of model was also demonstrated and compared the results with that of the existing method (DRASTIC model). It was observed that HFS model are better sensitive to the input parameters in comparison to that of the DRASTIC model. The present study offers a unique tool to policy makers for decision makings in groundwater management. Keywords Groundwater vulnerability assessment . Hierarchical fuzzy model . Sensitivity analysis
Introduction There are many examples of waste disposal/dumping in the land surface without any treatment that pose significant threats J. Iqbal : G. Pathak : A. K. Gorai (*) Environmental Science & Engineering Group, Birla Institute of Technology, Mesra Ranchi 835215, Jharkhand, India e-mail: [email protected]
to groundwater, and hence, to human health. Groundwater vulnerability assessment is a critical procedure in the course of related decision-making regarding suitable disposal/ dumping of waste sites. It offers sound bases for assessing and ranking the severity of potential of site for groundwater contamination. However, the insight about risk is limited by the randomness inherent in nature and the lack of sufficient information related to the chances of risk occurrence and the potential consequences of such occurrence. As a result, risk or vulnerability assessment is inherently linked with uncertainty (Wagner et al. 1992; Carrington and Bolger 1998). The concept of aquifer vulnerability to external pollution was introduced in 1960s by Margat (1968), with several systems of aquifer vulnerability assessment developed in the following years (Aller et al. 1987; Vrba and Zaporozec 1994; Sinan and Razack 2009; Polemio et al. 2009; Foster 1987). Most of the studies revealed that the reason behind the different vulnerability is the different hydro-geological settings. Many approaches were developed to evaluate aquifer vulnerability. These include proces
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