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.

Barrier Island Reconfiguration Leads to Rapid Erosion and Relocation of a Rural Alaska Community

“…Simulations by Nienhuis and Lorenzo-Trueba (2019) estimated barrier islands can be drowned by relative sea-level rise (RSLR) as low as 3.5 mm/y, but rates of 4 to 8 mm/y or greater are more likely required. Natural gravel barriers with a high cross-sectional area, like those in Port Heiden, can withstand greater sea-level rise rates if sediment is not removed from the system (Pollard et al ., 2022). The two tidal datums computed for Port Heiden show mean sea-level rates were 0.00 ± 1.00 mm/y between 1957 and 2013 (Table 2; datum computational error of 0.0396 m from NOAA, 2003).…”

Climate change: Consequences for neglecting the early warnings a brief testimony

“…The hydrological changes are highlighted in Arctic rivers dominated by the increase in water flow at the beginning of the 21st century (Peterson et al, 2002). Climate change and accompanying sea-level rise have increased the risk in the future due to chronic and acute pressures within the communities and ecosystems (Hinkel et al, 2018;Pollard et al, 2022). Sea level rise rate, sediment starvation, and undulating seafloor topographies can cause barriers to the founder or drowning (Emery et al, 2019), and the shoreface translates to a new landward position in a process described as 'overstepping' (Pollard et al, 2022).…”

The morphodynamic response of a gravel barrier to unimodal and bimodal storm wave conditions

“…During storms, gravel barrier systems can undergo far-reaching morphodynamic changes ranging from erosion of the barrier foreshore to breaching, complete inundation and rollback, affecting the adjacent hinterland Sallenger, 2000). The combination of restricted sediment supply, increasing storm frequency, and climate change-induced sea level rise, means that gravel barriers are becoming increasingly threatened (Vitousek et al, 2017;Pollard et al, 2022). Therefore, insights into the morphodynamic responses of gravel barrier beaches to storms are vital for developing sustainable strategies for their maintenance.Gravel and sand beaches behave differently to each other, (Buscombe and Masselink, 2006).…”

“…Those studies have been limited to consideration of the hydrodynamics without further analysing the amount of sediment transport and also by the short duration of the simulations. Pollard et al (2022) recently studied several key morphological parameters and how they govern gravel barriers' response to storm surges and rising sea levels. However, this study did not extend to bimodal wave conditions, a common occurrence in many coastal sites around the UK and elsewhere (Thompson et al, 2018;Vettor and Soares, 2020).…”