Water Quality the Melamchi Khol. Impacts of Diversion of Water to Kathmandu Valley, Nepal

Abstract

This is a part report on water quality of an extensive EIA report on Melamchi Diversion Scheme. The Melamchi Khola between the Intake site and Indrawati Nadi, and the tributaries Ribal, Gohare, Gyalthun and Shindhu Khola are the river stretches that will be largely affected by the diversion of water from the Melamchi Khola. The main changs of Melamchi Khola will be: Reduced water flow, increased temperature, and increased concentration of major ions. All river sections will have increased eutrophication and increased turbidity especially during the construction period. According to the different alternatives for minimum water releases of 0.15, 0.5, and 1.5 m³/sec, the temperature of Melamchi Khola might increase with 4 °C, 3 °C, or 2 °C respectively. At the minimum relase of 0.15 m³/sec the salt concentration may increase 30-35 % at a distance of 10 km downstream the Intake site, and the rate of flow will be reduced by 90-95% compared to the natural flow in the dry season (November-May). The rest flow of 0.5 m³/sec will increase the salt content by about 25 %, and reduce the water discharge by 80 % of dry season flow before diversion.