Quick-Scan Runup Reduction through Coral Reef Restoration in the Seychelles

Being a small island nation, Seychelles is highly exposed to natural hazards, especially coastal erosion, coastal flooding, flash flooding, and rock fall. In an effort to improve this understanding and explore potential sites for nature-based solutions – in the form coral reef restoration in particular – to reduce coastal flood risk, the World Bank and the GFDRR have financed a quick-scan analysis for three islands of the Seychelles (Mahé, La Digue, and Praslin) to identify candidate sites which have a high potential for the reduction of wave runup through coral reef restoration. This report, performed by Deltares, uses remote sensing and existing datasets to estimate key site parameters such as reef width, depth, roughness, and beach slope. Hydrodynamic forcing is assessed using wave and water level conditions. The reef morphology and hydrodynamic forcing is then used in the BEWARE system to estimate runup under a range of different scenarios, including reef roughness as a proxy for coral health. The report presents spatial maps of relative and absolute runup change for the three islands for various water levels and wave conditions, together with the digital data of the computed runup values. Intermediate data on the reef input parameters (reef width, reef slope, beach slope, and reef roughness) are also included.