Estimation of the Total Baseflow of the Kathmandu Valley Using Monthly Streamflow Measurements from a Sub-Sample of Headwater Catchments

The available freshwater resources of the Kathmandu Valley (Valley) are adversely deteriorating in terms of both quality and quantity owing to haphazard urbanization, increasing population, inadequate wastewater management, and lack of effective water resource planning. Consequently, in recent years, there is a growing imbalance between water supply and demand in the Valley. Baseflow plays a significant role in sustaining surface flow in streams and rivers, especially during low flows or drier months of the year. It is influenced by several factors including catchment area, precipitation, evapotranspiration, stream orientation, stream length, presence of shallow aquifer and recharge areas, and so on. The quantification of baseflow is crucial for assessing the impacts of land use, climate, and human influences on water quantity. Therefore, understanding the estimate of baseflow is paramount to water resources management. This study aimed to assess a method to evaluate the total baseflow of the Valley using monthly streamflow measurements from a sub-sample of headwater catchments. For this, the discharge data collected by Smartphones For Water Nepal (S4W-Nepal) from 2018 to 2020 using Sontek Flowtracker was used. The streamflow data were used to construct the hydrographs and determine their respective baseflow values. Then, Inverse Distance Weighting (IDW) interpolation technique in Quantum GIS (QGIS) was used to assess the base flow across the Valley, and ultimately, the base flow of each watershed was determined by summing the baseflow values of all pixels that belonged to a watershed. This study will therefore provide a likely estimate of the total baseflow contributions of Valley.