Flood risk assessment due to cyclone-induced dike breaching in coastal areas of Bangladesh

Abstract

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.

The effects of changing land use and flood hazard on poverty in coastal Bangladesh

“…< 2 m). However, when the depth increases, shrimp or fish may escape and cause financial losses (Islam et al, 2019).…”

“…It was estimated for three types of LULC (i.e. agriculture, aquaculture, and residential) using the following equation (Islam et al, 2019):…”

“…were used to estimate direct tangible flood damage to residential and agricultural LULC. The depth-damage curve for aquaculture lands was obtained from Islam et al (2019) (Figure 3).…”

Combining Structural and Non-Structural Measures for Optimal Management of Urban Surface Runoff Collection (Case Study: Ariafar Bridge in Mianroud Canal)

“…Due to the fact that non-structural solutions are more managerial, flood damage can be greatly reduced by just spending a little time identifying and administering them in the right conditions. Structural measures research includes the following: Construction of flood diversion channel to reduce the storage and peak flow [1,2], Reservoir and detention dam [3][4][5][6][7][8], Construction of levee and dike to prevent water overflow [9][10][11], Channel improvement [12,13] and Installation of feeding wells and artificial feeding [14,15]. On the other hand, there are non-structural flood control measures that constitute mostly software and management aspects.…”

Impact of climate change and management strategies on water and salt balance of the polders and islands in the Ganges delta

“…The Ganges delta includes a unique coastal zone of great significance for food security, biodiversity conservation, and fisheries production 4 , 5 . The coastal zone of the Ganges delta in Bangladesh includes 139 polders which are low-lying tracts of land surrounded by dikes constructed in the 1960s and 1970s to protect farming lands from saline water intrusion and tidal floods 6 . A less-well-developed polder system exists in the Sundarbans region of the West Bengal in India 7 .…”