Water quality zoning of Vishwamitri River to access environmental flow requirements through aggregation of water quality index

Environmental flow requirements, to maintain the functioning of freshwater-dependent ecosystems and restore rivers in ecologically acceptable conditions, depend upon the present water quality status of the river. Various stretches of Vishwamitri River vary in quality and quantity. Water quality index is a tool to converse information regarding water quality of various stretches of river and can be used for zoning them based on their present water quality status. Through such zoning, based on water quality index values as an integral component, Environmental flow requirements can be explored for Vishwamitri. In this paper, ‘Weighted Arithmetic Index’ method is used to find water quality index for both Vishwamitri and its tributaries using observed values of general physico-chemical parameters. The indices have been computed for pre-monsoon, monsoon and post-monsoon seasons at sixteen sampling stations, i.e. S-1 to S-16 along the Vishwamitri and eight sampling stations on its various tributaries. Based on the analysis, Vishwamitri is zoned in two various zones. Sampling stations, S-1 to S-7 represent Zone 1 which contains WQI values from 50 to 75. Sampling stations S-8 to S-16 represent zone 2 which contain WQI values more than 75. Zone 1 is rich with DO whereas zone 2 contains high BOD and less DO. The WQI value of Surya River, a major tributary of Vishwamitri, indicates that river water is suitable for irrigation purpose. The WQI values of tributaries and drains, draining wastewater to stretch of Vishwamitri within Vadodara city, represents water quality as mostly unsuitable for drinking, irrigation or industrial purpose.