Assessment of Bagmati river pollution in Kathmandu Valley: Scenario-based modeling and analysis for sustainable urban development

Water pollution remains a challenging issue for the sustainable development of Kathmandu Valley despite several infrastructural, awareness-raising and policy measures. The paper assesses the sustainability of the surface water resources of Kathmandu valley by analyzing the water quality parameters such as Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD). The case study of Bagmati River pollution is analyzed for current and future wastewater production and treatment scenario based on the two important indicators of aquatic health. The DO and BOD were simulated to assess river pollution along a 25 km stretch between Sundarijal and Chovar. Water Evaluation And Planning (WEAP) model was used to simulate the current (year 2014) and future (year 2020 and 2030) river water quality conditions. The results showed that the water quality of the Bagmati River is relatively better during monsoon season due to higher river flow in comparison to the dry season. A comparison of simulated DO and BOD values for 2020 and 2030 with 2014 values indicated that the water quality of the Bagmati River within Kathmandu Valley will not significantly improve as a result of the planned wastewater treatment plants requiring additional countermeasures. The study pointed out the inefficiencies of the current practice of discharging untreated sewage into the surface water and causing largely in the river water and unsuitability of river water of water from the Gaurighat to the Chovar area. It is recommended to integrate river water pollution management and maintain ecologically to achieve the healthy urban development.