Gravel barrier resilience to future sea level rise and storms

Abstract

Globally, communities, ecosystems, and assets situated within the coastal zone will likely experience increased risk in the future owing to chronic and acute pressures associated with climate change and accompanying sea level rise. Gravel barrier islands represent an intermediate pathway between seaward hazards and vulnerable landward receptors and possess inherent morpho-sedimentary characteristics which allow coastal risk reduction functions. If gravel barriers are to be usefully and reliably integrated into broader coastal risk management strategies, there is a need to understand the extent to which these landforms are likely to remain resilient under future environmental conditions. Using the Blakeney Point Barrier System, southern North Sea, this study investigates the resilience of gravel barrier landforms to storm surge conditions under future sea level rise scenarios. Resilience is assessed through reference to barrier resistance, susceptibility to state change, persistence, and continued functional performance. Numerical modelling reveals that variable pre-surge barrier morphologies result in a spectrum of episodic resilience trajectories along the barrier frontage. This study also considers the role of humans in altering landscape resilience, demonstrating that previously managed barrier sections (through reprofiling to steepen and heighten the barrier) are more vulnerable to severe morphological change, and associated landward overtopping volume, compared to unmanaged barrier sections. This said, under moderate to high sea level rise, even unmanaged barrier sections failed to demonstrate resilience to storm surge forcing. Such insights help temper our expectations regarding the coastal erosion and flood risk reduction functions of gravel barriers in the face of global environmental change.