Flood Mapping for Dharla River in Bangladesh using HEC-RAS 1D/2D Coupled Model

The densely populated Bangladesh is located in the south Asian sub-continent and is prone to flooding as being situated on the deltaic floodplain of the GangesBrahmaputraMeghna (GBM) River basin. Bangladesh has experienced periodic floods of severe magnitudes in 1974, 1984, 1987, 1988, 1998, 2000, 2004, 2007 and 2010. Dharla River, among one of the 57 trans-boundary rivers originated in the Himalayas, along with Brahmaputra River has a great influence on the recurring floods and erosion in north-western Bangladesh. Almost every year, excessive flooding caused by Dharla render thousands of people homeless with massive loss of crops and poultries. In this study, to identify the low lying areas prone to inundation and to reduce the uncertainty in flood mitigation measures, HEC-RAS based 1D/2D Coupled hydrodynamic model has been carried out for Dharla River. Boundary conditions for upstream and downstream have been defined by discharge of Taluk-Simulbari station and water level of Kurigram station respectively. Flow has been simulated under unsteady conditions, calibrated for the year 2013 and validated for the year 2014. Flood Inundation maps have been generated in the RAS mapper for the years 2010, 2013 and 2014 from the month June to October for highest water levels of each month. The validation of the generated flood map of 2010 has been performed using the Moderate Resolution Imaging Spectroradiometer (MODIS) flood map of 2010. A comparative analysis has been carried out between the maps generated by using HEC-RAS 1D/2D coupled model and using HEC-RAS 1D model and Arc-GIS reported in our previous work. Also, a correlation has been developed from the comparison. Proper floodplain management and the use of science and knowledge can reduce flood damages in a country like Bangladesh and hence this study could be important for proper planning and management of flood hazards caused by Dharla River.