Geomorphic risk and social vulnerability in deltas and their environs: the case of Bangladesh

Coastal deltas are amongst the most densely populated places on Earth. More than 500 million people live in and around deltas, equivalent to 7% of the human population on 1% of the global land area. Yet, over 70% of the world’s largest delta systems are under threat from rising sea levels, subsidence, natural hazards, and anthropogenic interferences.
Deltas are fundamentally geomorphic features, and their ultimate sustainability relies on their intrinsic geomorphic balance. However, assessments of deltaic risk rarely consider the dynamic interactions between geomorphic processes and societal actions. This omission, or significant simplification, has undermined disaster risk reduction measures in many globally important deltas. This thesis therefore argues that geomorphic processes, such as subsidence, channel siltation, and riverbank and coastal erosion, should be considered as hazards, embedded into the overarching disaster risk management framework for deltaic systems. Based on the premise that risk comprises hazards, exposure and vulnerability, this thesis (i) identifies the key geomorphic hazards occurring in deltaic environments, (ii) assesses the societal exposure to these hazards, and (iii) explores the vulnerability of highly exposed populations.
The identified risk components are explored using the case study of Bangladesh, home to the Ganges-Brahmaputra-Meghna (GBM) delta, the world’s most populous and largest delta system. The thesis sets out through a systematic review of existing literature, which demonstrates that geomorphic hazards, such as erosion due to shoreline change and channel migration, as well as sedimentation and subsidence can increase flood risk, impact biodiversity, contaminate soil and groundwater, and displace thousands of people within the GBM delta. Subsequently, using high-resolution geomorphic hazard modelling, population, and poverty data, the thesis finds that currently 22 million people in Bangladesh are living within geomorphically hazardous regions, a figure that has increased by 5 million in the last 20 years. Of this exposed population, 86% are living in poverty, suggesting that poorer populations are disproportionately exposed to geomorphic hazards across Bangladesh.
Finally, this thesis concentrates on some of the most poverty-stricken and exposed communities to riverine hazards in Bangladesh to explore their vulnerability by measuring their resilience – defined as their coping, adaptive and transformative capacities. Using community-based data, the thesis shows that community efforts are centred on enhancing coping capacities through improved immediate response and recovery strategies. However, given the inevitability of temporary or permanent relocation as a result of erosion, longer-term adaptive and transformative capacities of the most critically vulnerable communities need to be urgently strengthened.
Overall, this thesis presents the first attempt to link geomorphic processes with societal dynamics within a deltaic disaster risk management framework. It also presents a novel approach of integrating ‘top-down’ geomorphic hazard assessments with ‘bottom-up’ community-level resilience information, arriving at a more nuanced understanding and evidence-base of overall deltaic geomorphic risk. The results of this thesis demonstrate that geomorphic processes need to be embedded in policy and management decisions, as the growing pressures of climate change, anthropogenic interventions, and socio-economic development within river catchments are threatening the long-term geomorphic sustainability of the world’s deltas.

Keywords: resilience
geomorphology
flooding
Bangladesh
delta
Ganges-Brahmaputra-Meghna
Advisor: Hall, J
Borgomeo, E