Coastal erosion risk assessment in the dynamic estuary: The Meghna estuary case of Bangladesh coast

Erosion is one of the predominant hazards in coastal Bangladesh. For implementing effective adaptation and mitigation strategies, assessment of risk to coastal erosion is crucial. This study aimed to assess the levels of risk to coastal erosion in the Meghna estuary, a major erosion-prone area in the coastal region of the country impacted by abrupt changes in hydrological and geomorphological conditions. Using physical, environmental, and socio-economic geospatial data, this is the first attempt in assessing erosion risk and characterizing three main risk components: hazard, vulnerability, and exposure at a regional extent in the estuary. A total of 19 indicators were considered, and statistical methods assisted with the Analytic Hierarchy Process (AHP) were used for the construction of hazard, vulnerability, and exposure indices, which were then integrated to calculate erosion risk comprehensively at the lowermost administrative unit (union) level throughout the study area. The results of hazard and vulnerability analyses depicted 35.72% and 46.69% areas as highly hazard-prone and highly vulnerable to erosion, respectively. Assessment of the exposure index exhibited 42.25% area as highly exposed to coastal erosion in the estuary. Finally, the results quantified different levels of risk as very high (14.91%), high (19.36%), moderate (23.40%), low (23.91%), and very low (18.41%). Among 161 coastal unions, 45 unions were identified as high to very high erosion risk-prone areas, located in the coasts of Bhola, Noakhali, and Barishal districts including their major islands. The validation result confirmed a reasonable level of acceptance of the calculated risk map, despite several data limitations. The geospatial distribution of different risk categories presented in this paper can assist relevant authorities with reliable spatial information in formulating improved erosion risk mitigation policies in the most dynamic estuary of the country.