Evaluation of index-overlay methods for groundwater vulnerability and risk assessment in Kathmandu Valley, Nepal

Sangam Shrestha; Ranjana Kafle; Vishnu Prasad Pandey

doi:10.1016/j.scitotenv.2016.09.141

Evaluation of index-overlay methods for groundwater vulnerability and risk assessment in Kathmandu Valley, Nepal

Sci Total Environ. 2017 Jan 1:575:779-790. doi: 10.1016/j.scitotenv.2016.09.141. Epub 2016 Sep 30.

Authors

Sangam Shrestha¹, Ranjana Kafle², Vishnu Prasad Pandey³

Affiliations

¹ Water Engineering and Management, Asian Institute of Technology, P. O. Box 4, Klong Luang, Pathumthani 12120, Thailand. Electronic address: sangam@ait.asia.
² Water Engineering and Management, Asian Institute of Technology, P. O. Box 4, Klong Luang, Pathumthani 12120, Thailand.
³ Water Engineering and Management, Asian Institute of Technology, P. O. Box 4, Klong Luang, Pathumthani 12120, Thailand; Center of Research for Environment Energy and Water (CREEW), 259 Chandramukhi Galli, Baluwatar, Kathmandu-4, Nepal.

PMID: 27693144
DOI: 10.1016/j.scitotenv.2016.09.141

Abstract

This study aimed at evaluating three index-overlay methods of vulnerability assessment (i.e., DRASTIC, GOD, and SI) for estimating risk to pollution of shallow groundwater aquifer in the Kathmandu Valley, Nepal. The Groundwater Risk Assessment Model (GRAM) model was used to compute the risk to groundwater pollution. Results showed that DRASTIC and SI methods are comparable for vulnerability assessment as both methods delineate around 80% of the groundwater basin area under high vulnerable zone. From the perspective of risk to pollution results, DRASTIC and GOD methods are comparable. Nevertheless, all the three methods estimate that at least 60% of the groundwater basin is under moderate risk to NO₃-N pollution, which goes up to 75% if DRASTIC or GOD-based vulnerabilities are considered as exposure pathways. Finally, based on strength and significance of correlation between the estimated risk and observed NO₃-N concentrations, it was found that SI method is a better-suited one to assess the vulnerability and risk to groundwater pollution in the study area. Findings from this study are useful to design strategies and actions aimed to prevent nitrate pollution in groundwater of Kathmandu Valley in Nepal.

Keywords: DRASTIC; GIS; GOD; Groundwater; Risk assessment; SI; Vulnerability assessment.