Abstract. Bangladesh, one of the most disaster-prone countries in the world, has a
dynamic delta with 123 polders protected by earthen dikes. Cyclone-induced
storm surges cause severe damage to these polders by overtopping and
breaching the dikes. A total of 19 major tropical storms have hit the coast in the last
50 years, and the storm frequency is likely to increase due to climate change.
The present paper presents an investigation of the inundation pattern in a
protected area behind dikes due to floods caused by storm surges and
identifies possible critical locations of dike breaches. Polder 48 in the
coastal region, also known as Kuakata, was selected as the study area. A
HEC-RAS 1-D–2-D hydrodynamic model was developed to simulate inundation of the polder under different scenarios. Scenarios were developed by considering
tidal variations, the angle of the cyclone at landfall, possible dike breach
locations and sea level rise due to climate change according to the Fifth
Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC).
A storm surge for a cyclone event with a 1-in-25-year return period was considered
for all the scenarios. The primary objective of this research was to present
a methodology for identifying the critical location of dike breaching,
generating a flood risk map (FRM) and a probabilistic flood map (PFM) for the
breaching of dikes during a cyclone. The critical location of the dike breach
among the chosen possible locations was identified by comparing the
inundation extent and damage due to flooding corresponding to the developed
scenarios. A FRM corresponding to the breaching in the
critical location was developed, which indicated that settlements adjacent to
the canals in the polders were exposed to higher risk. A PFM was developed using the simulation results corresponding to the
developed scenarios, which was used to recommend the need of appropriate land
use zoning to minimize the vulnerability to flooding. The developed
hydrodynamic model can be used to forecast inundation, to identify critical
locations of the dike requiring maintenance and to study the effect of
climate change on flood inundation in the study area. The frequency and intensity of the cyclones around the world are likely to
increase due to climate change, which will require resource-intensive
improvement of existing or new protection structures for the deltas. The identification and prioritization of the maintenance of critical locations of dike
breaching can potentially prevent a disaster. The use of non-structural tools such as
land use zoning with the help of flood risk maps and probabilistic flood
maps has the potential to reduce risk and damage. The method presented in
this research can potentially be utilized for deltas around the world to
reduce vulnerability and flood risk due to dike breaching caused by cyclone-induced storm surge.