WATER QUALITY INDEX AND HEAVY METAL DISTRIBUTION IN THE SEDIMENTS OF BAGMATI RIVER ALONG THE KATHMANDU VALLEY BASIN IN NEPAL

The Bagmati River along the Kathmandu Valley Basin (Nepal) was studied to assess the water quality and the heavy metal distribution in the river sediments. The Bagmati River is among the most important rivers in Nepal where water availability is the lowest of all surface water bodies within the Kathmandu Valley and its surroundings. It flows through the center of the capital city Kathmandu, which is home to about 1.7 million people, and is a major source of water supply to its inhabitants. Water and sediment samples were analyzed from 10 sampling stations along the river. Average Water Quality Index (WQI) at each site was calculated using National Sanitation Foundation’s suggested nine water quality parameters, such as Dissolved Oxygen (DO), Fecal Coliform, Temperature, pH, Biochemical Oxygen Demand (BOD), Turbidity, Total Dissolved Solids (TDS), Nitrate, and Phosphate. The results showed extremely deteriorated water quality condition in the Bagmati River. Only 17% of the water samples represented good to excellent WQI category, with all of them from just two sites outside the vicinity of the urbanized area. 77% of the samples showed bad WQI, with remaining 6% as medium level WQI. High number of E. coli (well over 100,000 per 100ml) and very low DO (most of them below 5 mg/l) in the river along the urbanized section showed influence of direct sewerage disposal. Effect of agricultural activities in the river in terms of chemical pollution seems minimal as the nitrate and phosphate in water and total phosphorus in sediment samples were within the acceptable limits. Distribution of heavy metals is now being studied. The metals that are going to be analyzed are As, Mg, Pb, Cu, Fe, Ni, Cr, Cd, Mn, Zn, Co, and Al. Bagmati River inside the Kathmandu Valley has been heavily polluted in recent decades due to incessant population pressure and unsystematic waste disposal into the river. Lack of wastewater treatment facilities and direct sewerage disposal into the river have been the major constraints in the management of Bagmati River. The direct impact of this degraded water quality condition has been on the aquatic animals and plants, and the impoverished people directly relying on the river for drinking, washing, and agricultural activities.