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Wave attenuation over foreshores is typically most relevant during storm conditions that create a surge (wind-induced water level set-up) in combination with high tidal levels. For the MI-SAFE viewer, a water level that has a probability of occurrence of 10%, i.e. once in 10 years, is considered to be the most relevant: this represents a storm that is both frequent enough to be relevant to users’ needs for planning coastal protection (a 1/100 or 1/1000 year condition may seem too extreme) and severe enough to be a serious threat to coastal regions. The representative water levels or hydraulic boundary conditions are derived from a global D-Flow Flexible Mesh model (Muis et al., 2016, Figure 9) that includes tides, storms and hurricanes. The output of this model is mapped to Dynamic and Interactive Vulnerability Assessment (DIVA) segments, so local anomalies can occur for coasts with irregular shapes (bays, estuaries). More extreme or locally tailored conditions are included in the Expert mode of the MI-SAFE viewer, which can take into account hydraulic boundary conditions that are specified by users -e.g. in local coastal management guidelines- or derived from dedicated modelling or field observations at the relevant location.
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