The Effect of Tributaries on Water Quality Parameters of Bagmati River

Abstract

Unplanned urbanization of Kathmandu city is creating many environmental issues, where worsening of Bagmati river water is one of the serious problems. The water quality of Bagmati river was characterized by collecting the real-time fine-scale data along the Bagmati river in the Kathmandu valley, using multi parameter sensor in winter season. The different physiochemical parameters viz., temperature, pH, conductivity, ORP, DO, salinity, TDS, and turbidity were monitored at 14 different locations from Gokarna to Balkhu. The spatial variation of water quality parameters revealed that the Bagmati river was comparatively less polluted between Gokarna to Tilganga and molecular oxygen present in the water was enough to decompose the organic pollutant. However, the water quality at downstream from Tinkune to Balkhu was degraded drastically making unfit for living organism. Temporal variation of water quality attributed that human activity significantly enhanced pollutants which severely degraded the water quality in the day time. The comparative study of water quality of Bagmati river and its tributaries showed that the chemical composition of the rivers were different from each other. Most of the parameters of all river water exceeded the WHO limit, ORP was positive for Bagmati river water but that was negative for other tributaries, which attributed that the tributaries of Bagmati river was highly polluted. The physiochemical parameters measured at upstream, downstream and at tributaries before mixing into the Bagmati river showed that tributaries and local pollutants from the human activities excessively loaded contaminants into the Bagmati river. The Water Quality Index (WQI) was varied between 25 to 50 for Bagmati river and its tributaries, which suggested that water quality of all rivers in the Kathmandu was bad. Keywords: Dissolved oxygen, oxidation reduction potential, pH, spatial variation, water pollution.