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Figure: Waves surging over the seawall on Malè Island, Maldives in May 2011. This minor wave overtopping event resulted in moderate surface flooding and localized road closures. 

 

A new tool to predict wave driven flooding on mid-ocean atoll islands

The motivation – The impetus for this study was to better understand the vulnerability of atoll islands and their communities to rising sea level. One of the most significant hazards for communities in atoll environments is coincident large waves and high tides, allowing run-up surges to wash over the shoreline and flood the island surface. Waves surging across island surfaces can have devastating impacts on island infrastructure, freshwater and food resources. The increase in sea level associated with global climate change will result in more frequent and destructive wave overtopping events that will likely be a determining factor in how long atoll islands remain habitable. The goal of this research was to combine the primary controls on wave overtopping on coral reef shorelines to develop a simple predictive model that can be used to forecast susceptibility of islands to wave driven flooding at present and future sea levels.  

The development – Dr. Paul Kench (Simon Fraser University) and his postdoctoral fellow Eddie Beetham (University of Auckland) analyzed a large suite of numerical modeling simulations of wave transformation across coral reef systems and their interactions with shorelines. The results of this analysis are critical for understanding how differences in 1) offshore wave height, 2) coral reef flat depth, 3) reef flat width and 4) island elevation collectively influence the occurrence and magnitude of wave overtopping. This dataset was synthesized into a simple predictive model that can be used to calculate sea level rise and/or offshore wave height thresholds associated with wave driven flooding. The model is applicable to reef fringed coasts globally.

Its significance – The ability to calculate threshold conditions for wave overtopping on reef coastlines based on easily surveyed environmental parameters is a significant advance in understanding atoll island vulnerability to future sea level rise. This will allow communities on fringing reef shorelines to forecast and prepare for the impacts of future sea level rise. The advances presented in this paper will allow identification of the most at-risk locations, which is important for implementing strategic risk reduction and hazard mitigation strategies.

Read the paper“Predicting wave overtopping thresholds on coral reef-island shorelines with future sea-level rise” by Beetham, E; Kench, PS. (2018). Nature Communications 9:3997 DOI: 10.1038/s41467-018-06550-1.

Website article compiled by Jacqueline Watson with Theresa Kitos