A Study on Flood Inundation Mapping of Surma River Floodplain Under Extreme Flood Scenario

Abstract

Flood, a natural phenomenon that dominates the living conditions and the normal lives of millions of people worldwide, bringing in misery each year at fairly regular intervals. Bangladesh, a country lying at the confluence of the world's three largest and most important basins, namely the Ganges–Brahmaputra-Meghna (GBM) basin, is not only susceptible to flood due to its proximity to the basin but also due to the hydro-meteorological and topographical characteristics of the basins. The Surma, one of the major river systems in Bangladesh, comprises a small part of the greater Surma-Meghna system lying in the Sylhet basin. Originating in the hills of Shillong and Meghalaya in India, this river's main source is the Barak river, with a large and considerable catchment in the ridge and valley terrain of Naga-Manipur extending to 950 km in length, 340 km of which lies within Bangladesh. Flooding is a constant hazard in the region around the river system. To correctly and accurately assess the hazards caused by a flood, it is essential to develop data-driven models so that future variabilities can also be predicted. This study aims to develop a calibrated and validated HEC-RAS 1D/2D coupled model of the Surma river's flood plain to estimate the proper levee height to help effectively minimize inundated areas. The combined one and two-dimensional HEC-RAS model used for the study relies upon the proper execution of GIS and HEC-GeoRAS. Available hydrological data were used to calibrate and validate the model. The resultant levee height derived from these models’ use can help with the proper planning and management of the flood-ridden plain along the Surma river and ensure future disaster mitigation.