Numerical modeling of the performance of coral reef restoration projects to enhance wave energy dissipation and decrease coastal flooding

The geometric complexity of healthy coral reefs provides enhanced energy dissipation through additional drag and wave breaking when compared to other substrates such as sand or bare rock substrate. Recent studies have highlighted the role of coral reefs in coastal protection (Beck et al. 2017; Ferrario et al. 2014), while the recent destructive hurricanes affecting the Caribbean, especially Hurricanes Irma and María in 2017, have highlighted the vulnerability of reef-lined tropical coastlines to extreme events. In this study we use a one- and two-dimensional phase-resolving numerical wave model, SWASH (Simulating WAves till SHore), to analyze the benefits of coral reef restoration projects, specifically projects that do not include seabed modification (e.g. no submerged breakwaters) but that are focused on transplanting large numbers of coral reef colonies of Acropora palmata (elkhorn coral). After calibrating the model with field data, we examine the role of several parameters such as colony height and density, reef width, reef location from the shoreline, and sea state and offshore water levels. Results indicate that the effectiveness of coral reef restoration projects in enhancing wave dissipation and reducing coastal flooding are very sensitive to the cross-shore location of the centroid of the restored reef. These results are surprisingly consistent across a broad range of sea states, water levels and bathymetric configurations.