8. Relative Risk Factors

The previous section discussed how the original 22 data variables within this data base were obtained and entered into the GIS. These data were directly digitized from maps or copied from computer tapes and imported into the ARC/INFO GIS, where the information was analyzed and the data values were incorporated into the 0.25° grid cells and 1:2,000,000 digitized line segments. The entry of these data into common formats (i.e., 0.25° grid cells and 1:2,000,000 digitized line segments) has made it possible to relate and manipulate the data to identify relationships among the different variables.

A vulnerable coastline is characterized by low coastal relief, subsidence, extensive shore line retreat, and high wave/tide energies (Gornitz et al. 1991). To simplify the manipulation process, seven of the original data variables were classified into seven new "risk" variables. Each risk variable ranges in value from 1 to 5 and indicates the cell's relative risk to erosion or inundation. The risk assignments for mean elevation, mean shoreline displacement, local subsidence trend, mean tidal range, and maximum significant wave height (i.e., the numeric data variables) are given in Table 3. The risk assignments for geology and geomorphology (i.e., the nominal data) are given in Tables 4 and 5, respectively. These risk assignments are discussed in greater detail in Gornitz et al. (1991), Gornitz and White (1991) and Gornitz et al. (1994) -reprinted in Appendix D.