2025 Volume 13 Issue 2 Article ID: 24-16102
This study reports the influence of road and embankment network on the flood hydrodynamics of river floodplains in the Haor basin, Bangladesh. The topological setting of this part of the country is unique, low-elevation floodplain (about 20,000 sq km) of a complex river system surrounded by the Meghalaya Mountain range from north and east. During the monsoon season, this floodplain stays inundated for 6-7 months and is exposed to flash floods almost every year during pre-monsoon and monsoon seasons. In the last decade, the intensity of flood level and duration has increased. Along with climate change, rapid urbanization, and land use change, the construction of high-elevation roads in the Haor floodplain is being criticized for degrading the flood situation. In this investigation, a hydrodynamic analysis has been conducted using a HEC-RAS 2D model for a selected river system of this region by reproducing the historical flood events. The model has been calibrated and validated for existing condition against the observed water level with NSE values of 0.974 and 0.943, respectively. A separate set of simulations has been conducted with natural topography, excluding the road and embankment network from model topology. Where the reduction in peak flood level is more than 25 cm for 38% and 42% area in the floodplain for the monsoon flood of 2021 and 2022 and about 30% for the 2022 pre-monsoon flood. However, after a week from the peak period, the difference in water level between existing and natural conditions increased, which indicates a shortening in the flood duration. It has been found that 34 km out of 58 km high elevation road of the model domain obstructs significant amount of floodplain flow, suggesting that more cross-drainage structures in those road alignment will improve the flood condition.
