How did water quality vary along India's Rispana River?

Details

To evaluate seasonal changes in water quality and quantity in the Rispana River, a Ganges tributary in the Dehradun region of India, researchers calculated a water quality index (WQI) at four major locations using the weighted arithmetic method. They collected 16 samples across the pre-monsoon (April 2022), monsoon (July 2022), post-monsoon (November 2022), and winter (January 2023) seasons. The WQI calculation considered temperature, dissolved oxygen (DO), pH, electrical conductivity (EC), total dissolved solids (TDS), E-coliform, sulphate, total alkalinity (TA), total hardness (TH), and biochemical oxygen demand (BOD).

WQI ranged from 44.53, rated good, at site 1, Kairwaan Gaon, during the monsoon to 302.69, rated unfit for drinking, at site 4, Mothrowala, before the monsoon. Water was unfit for domestic purposes in 75% of samples; the abstract identifies DO, BOD, and coliform as contributing factors exceeding permissible limits in all samples. The researchers attributed the decline in water quality mainly to sewage discharge, effluent from commercial sites, and urban runoff.

Average total coliform levels were 1849.6 MPN before the monsoon, 2419.6 MPN during the monsoon, 2419.6 MPN after the monsoon, and 1546.25 MPN in winter. Seasonal average E. coli values ranged from 1306.8 to 1888.1 MPN. The pollution load, including physicochemical and bacteriological factors, increased as the river flowed downstream through urban locations.

Streamflow was observed to be very low except during the monsoon, when it was about 1500 cfs; the researchers attributed this to greater freshwater extraction upstream and unplanned changes in the catchment basin, with an extensive decline in freshwater availability for domestic use downstream in Dehradun city. During the monsoon, greater streamflow from rainwater influx maintained the WQI in the good-to-moderate category. Land use/land cover (LULC) analysis of the Rispana basin showed a reported 71% increase in urbanization, from 24.16% to 41.55%, over the 15-year span of 2003–2017.

The study identifies potential natural and human-caused contributors to the river's deterioration and provides a water-quality-index baseline for aquatic and ecological rejuvenation of the watershed through proper management with public participation. It offers insights for water-resource management toward smart-city objectives and Sustainable Development Goal 6, and calls on urban and municipal authorities to help revive this domestic water resource.