Assessment and evaluation of groundwater vulnerability index maps of Upper Palar River Basin, Tamilnadu, India

Abstract

The present study focuses on the assessment of groundwater vulnerability in the Upper Palar river basin, Tamil Nadu, India using the DRASTIC method, which consists of seven parameters obtained from various sources and created as map layers. To determine the groundwater vulnerable zones, the net recharge parameter considered in the DRASTIC model is estimated by four different methods, viz., SCS-CN, Piscopo, Chaturvedi, and groundwater fluctuation recharge methods and the results were compared. The vulnerability maps were generated by four recharge estimation methods, such as water table fluctuation method, Piscopo, SCS-CN and empirical formulae of Chaturvedi methods. This vulnerability class were validated with the observed groundwater quality (nitrate concentration) measured from 30 wells in the study area. The results were classified into four categories such as low, moderate, high, and very high. From the results obtained using DRASTIC with the Chaturvedi method, very high vulnerability is observed in the southern regions and low vulnerability in the north and southwest regions. Using the Piscopo method, the very high vulnerability is distributed along the lower half of the river and southeast side, and the low vulnerability covers the north part of the river basin. Similarly using the SCS-CN method, the very high vulnerability is seen along the river basin and low vulnerability along the central-north and south regions. Using the groundwater fluctuation method, very high vulnerability falls under the small part of the southeast side, but low vulnerability covers the south-west and east sides of the river basin. The different methods adopted to estimate the recharge rate in the study revealed the dependency level of the vulnerability on that parameter. Also, the study area characteristic is best observed by the results of these four methods. All the four methods gave very good results and better knowledge about each factor and a better understanding of the groundwater susceptible zones to pollution in the study area. Among the four methods, Piscopo and WTF methods were found to be best applicable for the selected study area.