Urban Pollution of Bagmati River Corridor within the Densely Populated Kathmandu Valley in Nepal

Abstract

The Bagmati River within the Kathmandu Valley in Nepal was studied for its water quality and heavy metal distribution in the riverbed sediments. Water and sediment samples were collected from 10 sites for chemical analysis. The Water Quality Index (WQI) of the river was calculated using nine water quality parameters recommended by the National Sanitation Foundation (NSF): Dissolved Oxygen (DO), E. coli, temperature, pH, Biochemical Oxygen Demand (BOD), turbidity, Total Dissolved Solids (TDS), nitrate, and phosphate. Out of the 100 water samples, 77 were in the Bad category, six in the Medium category, and the remaining 17 were in the Good to Excellent categories. The two parameters that significantly impacted the WQI values were DO (range: 0.07 – 8.25 mg/L) and E. coli (range: 200 – 1.3 × 10⁷ number per 100 ml). The highly impacted zone has urban/industrial land use where the average TDS (592 mg/L) is 34% higher than that observed (442 mg/L) at the urban sites immediately upstream. Sediment samples were analyzed for heavy metals of major environmental concern: As, Co, Cr, Cu, Mn, Ni, Pb and Zn. The urban/industrial areas are highly vulnerable to future impairment, especially with their possible influx from the numerous industrial sources.