Reconstruction of Flood Event Occurred in Teesta Basin, Sikkim State, Eastern Himalaya: Combining Hydrodynamical and Hydrological Modelling

On October 4, 2023, a catastrophic Glacial Lake Outburst Flood (GLOF) originated from South Lhonak Lake (SLL) during a period of heavy rainfall in the Teesta basin, Sikkim Himalaya, resulting in widespread devastation and significant loss of lives. Therefore, this study intended to conduct the reconstruction of this flood event through an integrative approach, combining rainfall-generated runoff simulation and GLOF modelling using the Hydrologic Engineering Center - Hydrologic Modeling System (HEC-HMS) and Hydrologic Engineering Center - River Analysis System (HEC-RAS), respectively. The peak discharge estimated at Singtam from the HEC-HMS simulation, reflecting solely the rainfall effect, was 2409 m
³
/s. In this contrast, the HEC-RAS modelling, which encompasses both rainfalls-induced runoff and GLOF from SLL, reveals a peak discharge of 6562.95 m
³
/s. The results were optimised and validated by the flood parameter information of some active gauge sites of Central Water Commission (CWC) falls on the flood path. In summary, such studies improve the understanding by estimating and analysing the quantitative parameters of these events that occur during intense precipitation and sudden breaches of glacial lakes, coincidingly, which often occur in high mountain regions.