Real-Time Fine-Scale Measurement of Water Quality Parameters Along the Bagmati River in the Kathmandu Valley

Abstract

Real-time fine-scale data was collected along the Bagmati River, in Kathmandu Valley, using mobile and fixed sensor system during the winter season. The water quality parameters; pH, conductivity, total dissolved salt (TDS), salinity, oxygen reduction potential (ORP), dissolved oxygen (DO), and turbidity were measured in the space domain using a fixed sensor and mobile sensor (small rafting boat loaded with sensor) systems. The water quality parameters from the fixed sensor system revealed that the Bagmati River was comparatively less polluted upstream from Gokarna to Tilganga sites and molecular oxygen present in the water was enough to decompose organic pollutants. However, the water quality downstream from Tinkune to Balkhu sites was degraded drastically making it unfit for living organisms. Temporal variation of water quality attributes that human activity significantly enhanced pollutants which severely degraded the water quality in the daytime. The fine-scale space domain heat map data of the mobile sensor system also suggested that the water quality continuously deteriorated from Shankhamul to Sundarighat sites. The ORP value was always negative and decreased with downflow and becomes -263 mV near the Sundarighat Bridge. The mixing of tributaries and increment of solid waste and untreated sewer along the river enhanced pollutants excessively and decreased oxygen level to zero. The results attributed that decomposition of the sewer by microorganism consumed almost all oxygen which produced volatile compounds and generated malodorous odor downstream of Bagmati River.