Hydrological modeling of the selected flash flood-prone rivers

The flash flood of Sylhet in North-Eastern Bangladesh is generally caused by heavy rainfall. The most devastating flash floods occurred in 1988, 2007, 2010, 2017, and 2022. This study comprises three hydrological models using HEC-HMS in this work for the catchments of the Sari-Gowain River, Surma–Meghna River, Piyan River, and Dhala River, with a combined drainage area of around 4405 km². For this study, the observed rainfall dataset was from the Bangladesh Meteorological Department (BMD), and discharge and water level data were collected from the Bangladesh Water Development Board (BWDB). To develop the HEC-HMS model, the SCS unit hydrograph, SCS Curve number, and the Muskingum method were used as the transform parameter, the loss technique, and the routing parameter. Event-based and continuous hydrologic simulations were tested in hydrological modeling. The hydrologic model was simulated for 2009–2022 and validated with the secondary observed dataset. The event-based validation has carried out Nash–Sutcliffe efficiency and R² for the Surma–Meghna (0.71 and 0.79), Dhala River (0.40 and 0.46), Piyan River (0.49 and 0.5), and Sari-Gowain River (0.62 and 0.66) respectively. A reasonable model performance was obtained for the Surma–Meghna and Sari-Gowain rivers. Due to the lack of a continuous dataset, continuous hydrologic simulation of this study was not recommended. An event-based model is expected to be helpful in the decision support system for future planning.