Assesement of Surface Water Availability of Kathmandu Valley Using SWAT Model

Abstract

The study used the Soil and Water Assessment Tool (SWAT) model to analyse the surface water availability in the Kathmandu Valley. The model was calibrated and validated at Khokana station of basin area 592 km² for the period from 2000 to 2015. To test the model’s performance for smaller subbasins, it was validated at Sundarijal station of basin area 16 km². The daily runoff simulation statistics indicated that the model’s performance was satisfactory and the model effectively captured the runoff trend for the entire basin and subbasin catchment areas. This study demonstrates that the model can be adopted for assessing stream flow within the basin by selecting appropriate parameter values. The calibrated and validated model was subsequently applied to determine the surface water availability in surrounding mountainous, forested regions less affected by urbanisation, by setting up the model at 66 watersheds. The results indicate that the upper reaches of the Bagmati River basin and its tributary, the Nakkhu River, possess substantial surface water resources that can be utilised to alleviate water stress in the valley.