In other words, a value of 1 represents the lowest risk and 5 represents the highest risk. The database includes both quantitative and qualitative information. Thus, numerical variables are assigned a risk ranking based on data value ranges, whereas the non-numerical geomorphology variable is ranked according to the relative resistance of a given landform to erosion. Increasingly higher erosion or accretion rates are ranked as correspondingly higher or lower risk.
Tidal range is ranked such that microtidal coasts are high risk and macrotidal coasts are low risk.
This decision was based on the concept that a large tide range is associated with strong tidal currents that influence coastal behavior. We have chosen to invert this ranking such that a macrotidal coastline is classified as low risk. Our reasoning is based primarily on the potential influence of storms on coastal evolution, and their impact relative to the tidal range. For example, on a tidal coastline, there is only a 50 percent chance of a storm occurring at high tide. Thus, for a region with a 4 m tide range, a storm having a 3 m surge height is still up to 1 m below the elevation of high tide for half a tidal cycle.