Sediment supply dampens the erosive effects of sea-level rise on reef islands

Megan E Tuck,Paul S Kench,Gerd Masselink,Murray R Ford

doi:10.1038/s41598-021-85076-x

Megan E Tuck, Paul S Kench + Show 2 more

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https://doi.org/10.1038/s41598-021-85076-x

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Abstract

Large uncertainty surrounds the future physical stability of low-lying coral reef islands due to a limited understanding of the geomorphic response of islands to changing environmental conditions. Physical and numerical modelling efforts have improved understanding of the modes and styles of island change in response to increasing wave and water level conditions. However, the impact of sediment supply on island morphodynamics has not been addressed and remains poorly understood. Here we present evidence from the first physical modelling experiments to explore the effect of storm-derived sediment supply on the geomorphic response of islands to changes in sea level and energetic wave conditions. Results demonstrate that a sediment supply has a substantial influence on island adjustments in response to sea-level rise, promoting the increase of the elevation of the island while dampening island migration and subaerial volume reduction. The implications of sediment supply are significant as it improves the potential of islands to offset the impacts of future flood events, increasing the future physical persistence of reef islands. Results emphasize the urgent need to incorporate the physical response of islands to both physical and ecological processes in future flood risk models.

Highlights

Large uncertainty surrounds the future physical stability of low-lying coral reef islands due to a limited understanding of the geomorphic response of islands to changing environmental conditions
Added sediment dampened the erosive effects of rising water levels, the volume of the island above water level was still reduced by 39% and 23% when exposed to 1 m of sea-level rise (SLR) under 3 m and 4 m waves (Fig. 1H)
A robust understanding of coral reef island morphodynamics in response to shifts in sediment supply is critical for accurately predicting future island t rajectories[7]

Summary

Introduction

Large uncertainty surrounds the future physical stability of low-lying coral reef islands due to a limited understanding of the geomorphic response of islands to changing environmental conditions. The future physical stability of coral reef islands and the continued existence of atoll nations is widely considered at risk from the impacts of anthropogenic climate change, eustatic sea-level rise (SLR)[1,2]. Assertions of extreme and immediate island vulnerability to SLR are often founded on the results of flood risk assessments that simulate future sea levels on present-day island topography[2,13,14,16] These studies treat reef islands as geomorphologically inert structures, despite evidence that many islands have undergone significant changes in size, shape and position on the reef platform in response to changing sea level, wave conditions and sediment supply, over a range of spatio-temporal scales[8,17,18,19]

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