Assessment of coastal flood risks in Patuakhali district

Abstract

The coastal Patuakhali district is highly susceptible to catastrophic flooding due to its geophysical location and it is one of the most dangerous challenges for this nation to save the coastal settlements from these frequent and extreme flooding events. However, the risk posed by coastal flood occurrences can be reduced with the formation and effective implementation of a sustainable flood management strategy, which is only feasible if the flood risk is accurately assessed. Thus, there was an urgent need for a detailed flood vulnerability, risk, and capacity assessment study in this area. This study attempted to provide a comprehensive assessment and mapping of coastal flood risk identifying most flood-vulnerable areas in the coastal Patuakhali district towards achieving efficient flood mitigation strategies. For generating a comprehensive coastal flood risk scenario, this study simultaneously applied both the people’s perception-based risk assessment with the help of MCDA, AHP, GIS and Remote Sensing (RS) based advanced methodologies. Based on the combined assessments of both people's perceptions, experiences, GIS and RS-based mapping, this study predicted a high flood risk for the studied area. Firstly, from people’s perception and expert opinions-based approach, this study estimated a high flood risk (0.886) for the coastal Patuakhali district. Individual hazard scores of 0.765 and vulnerability scores of 0.644 obtained during this assessment weren't very high, but when combined, they produced a significant flood risk due to the lower community capacity (0.556) to withstand flood damage. Similarly, the flood risk map developed with the weighted overlay tool of ArcGIS classified the majority of Patuakhali district's central, north-central, southern, and south-eastern char and island area as being in a very high flood risk zone due to its high population density, development of in-built infrastructure, lower elevation, flat topography, and lack of vegetation cover. A total of 10 flood-causing factors were considered throughout the mapping process, and the study identified the low slope gradient and the area's closeness to a stream, river, and sea as the main causes of coastal flooding in this location. This study furthermore finds out a number of structural and non-structural coastal flood protection and flood risk mitigation solutions with the active involvement of community members for effective flood mitigation. For the greatest effect, this study also recommended combining the use of structural and non-structural flood mitigation strategies rather than using either one alone. Additionally, a sense of ownership about different flood protective structures should be created among the local community people through their pro-active engagement of them for the effective maintenance and sustainability of these structures. Finally, the results of this study will be highly helpful to the relevant authorities and decision-makers, assisting them in developing comprehensive flood risk management plans and long-term flood mitigation strategies for coastal Bangladesh.