Simulation of flow at an ungauged river site based on HEC-HMS model for a mountainous river basin

Considering the severity of a catastrophic flood in the Teesta river in India earlier, it is indispensable to assess the runoff at the basin’s ungauged outlet, Mekhliganj. Almost every other year, the downstream of the river is in spate during the monsoon months. Among the three gauging stations in the basin, Teesta Bazaar, Domohani, and Mekhliganj, streamflow data is unavailable at the latter one. In this context, this study focuses on estimating the runoff of the Teesta river basin at its outlet, Mekhliganj, using Hydrologic Engineering Center-Hydrological Modeling System (HEC-HMS) software, verifying the output from the model through the measured streamflow data at the other two upstream gauging locations, Teesta Bazaar and Domohani. The runoff has been estimated for daily precipitation from May to October, applying Soil Conservation Service (SCS), curve number (CN), and SCS unit hydrograph method. Subsequently, the model has been calibrated for 2001 and 2006 to optimize both the Muskingum routing parameters. The model has been validated for some specific years like 2004, 2012, 2013, and 2016, which experienced extreme deluge. The results for both the upstream gauging stations bear a good correlation between the computed and observed data, evaluated through the statistical indicators such as percentage error in peak flow (PEPF), percentage error in volume (PEV), Nash-Sutcliffe (NSE), and R2, consequently justifying the simulated result at the outlet. This study is necessary for this vast watershed area with limited gauging stations and an ungauged outlet to understand the basin response and its derived consequence. © 2021, Saudi Society for Geosciences.