Runoff prediction of Surma basin by curve number (CN) method using ARC-GIS and HEC-RAS

Abstract

Bangladesh being a low-lying country is affected by floods easily that turns the Sylhet city more vulnerable to floods due to improper management of stormwater and failure in estimating runoff volume of Surma River. For this, CN value of the city area, the direct runoff of the area and the peak discharge value for different return periods were calculated. Meanwhile, geometric data and peak discharge were imported into HEC-RAS software to obtain flood depth and flood extend. Finally, an HEC-GeoRAS simulation resulted in a floodplain map. The inundation area found from the floodplain map covers 6.34% of the total study area for 2 years return period. To continue, 6.37%, 6.42%, 6.55%, 6.70% and 6.88% for 5 years, 10 years, 25 years, 50 years and 100 years return period respectively. These maps and relevant discharge data may help to understand the local flood risks and take up cost-effective measures.