Flood Hazard Mapping Using HEC–RAS Model: A Case Study of Ganges- Padma River, Kushtia, Bangladesh

Abstract

Bangladesh is one of the heavily populated regions that experiences frequent flooding, which
results in significant loss of life and property damage. Floods have become a major natural hazard
for Bangladesh because it is the world's largest river delta and is bounded by three major rivers:
the Ganges, the Brahmaputra, and the Meghna. This study presents a typical 2D flood hazard
mapping for a specific area called Kushtia of the Ganges – Padma River using the HEC – RAS
model.
This study aims to determine the application of the HEC-RAS 2D model coupled with flood
frequency analysis using HEC-SSP to prepare a hazard map in the Kushtia region. In this study, a
model was developed using the available data for the 2010 year for Kushtia Station (SW90) using
the SRTM DEM model, and then it was calibrated using the water level data. A 55-year peak
discharge (Kushtia Station) with a multi- return period of 2, 5, 10, 20, 50, and 100 years was
estimated using four distribution analyses. The best-fit distribution shows Pearson III as rank 1
with a return period of 2, 5, 10, 20, 50, and 100 years, with 44225.8 m3/s, 57177.7 m3/s, 65466.1
m3/s, 73167.9 m3/s, 82862.8 m3/s, 89971.8 m3/s respectively, with a 95% confidence level. The
simulation shows stable flooding for 2, 5, 10, 20, and 50 years but instability for the 100-year
return period. Though the water level (WL) difference with the observed data at first was large,
slowly it shows fewer differences during the dangerous period of August to September. Overall,
the HEC-RAS 2D flood hazard model can estimate the level of flood depths with satisfying results,
is useful in providing information about the depth and characteristics of floods for different river
communities, and can mitigate the destruction caused by floods.