Major ions and irrigation water quality assessment of the Nepalese Himalayan rivers

摘要

Water quality analysis of the Himalayan rivers for irrigation was carried out in 2013 that include the Dudh Koshi, Indrawati, Gandaki and Bagmati rivers from Nepal. Former three rivers originate at high altitudes and are glacier-fed rivers, whereas the Bagmati River originates at the high hill and flows through the capital city of Nepal. The river water samples were collected at 93 sites representing river from lowlands, mid-hills and high mountains of the Himalayas. Nine major ions -(Na+, -K+, -Mg2+, -Ca2+, -F-, -Cl-, SO2 4, HCO- 3 and NO- 3), pH, EC and TDS were analyzed so as to assess the water quality for irrigation. Irrigation water quality was assessed by calculating sodium adsorption ration (SAR), soluble sodium percentage (SSP or %Na) and water quality index (WQI). Although SAR indicated that all the water samples were having low values and could be suitable for the irrigation purpose, some sites from the Bagmati River were having high class of EC, rendering it not good for irrigation. Similar results were indicated by %Na as well as WQI results where low water qualities were observed from some highly contaminated sites in the city area. This clearly indicates the impacts of urbanization (anthropogenic) in river water quality for the irrigation in the Himalayan rivers of Nepal.