Abstract
Coral reefs are effective natural coastal flood barriers that protect adjacent communities. Coral degradation compromises the coastal protection value of reefs while also reducing their other ecosystem services, making them a target for restoration. Here we provide a physics-based evaluation of how coral restoration can reduce coastal flooding for various types of reefs. Wave-driven flooding reduction is greatest for broader, shallower restorations on the upper fore reef and between the middle of the reef flat and the shoreline than for deeper locations on the fore reef or at the reef crest. These results indicate that to increase the coastal hazard risk reduction potential of reef restoration, more physically robust species of coral need to be outplanted to shallower, more energetic locations than more fragile, faster-growing species primarily being grown in coral nurseries. The optimization and quantification of coral reef restoration efforts to reduce coastal flooding may open hazard risk reduction funding for conservation purposes.
Highlights
Coral reefs help sustain the economy of 500 million people in tropical coastal communities (Hoegh-Guldberg et al, 2019), and protect them from wave-driven flooding and coastal erosion (Elliff and Silva, 2017; Reguero et al, 2018), especially in the face of climate change (Storlazzi et al, 2018)
We demonstrate the positive impact of coral restorations on adjacent coastal flood reduction potential, showing a promising example of a nature-based solution for vulnerable coral reef-lined coasts
Model results indicate that the wave reflection and dissipation across coral restorations can decrease potential coastal flooding up to 30%, the exact reduction efficiency being highly dependent on (1) the reef profile shape, (2) the location of the restoration on the profile, (3) dimensions of the restoration, and (4) hydrodynamic forcing conditions
Summary
Coral reefs help sustain the economy of 500 million people in tropical coastal communities (Hoegh-Guldberg et al, 2019), and protect them from wave-driven flooding and coastal erosion (Elliff and Silva, 2017; Reguero et al, 2018), especially in the face of climate change (Storlazzi et al, 2018). We utilized a physics-based, hydrodynamic model to evaluate how the height, width, and relative location of a restoration on various reef morphologies found in nature influences the wave-driven runup reduction potential of the restoration to provide information on their hydrodynamic performance and to guide restoration design for coastal hazard risk reduction. Such information will significantly increase the efficiency of coral restoration efforts, assisting a range of stakeholders in their efforts on coral reef conservation and management, and coastal hazard risk reduction, and possibly open new financing options for reef restoration via pre-disaster hazard mitigation funds or post-disaster restoration funds
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