GEOLOGIC VARIABLES

The geomorphology variable expresses the relative erodibility of different landform types (Table 1). These data were derived from 1994 1 meter resolution digital orthophotos (Table 2). In addition, field visits were made within the park to ground-truth the geomorphologic classification. The geomorphology of CACO varies from low vulnerability glacial cliffs to very high vulnerability barrier shoreline (Figures 3-8).


Shoreline erosion and accretion rates for CACO were calculated from existing shoreline data provided by USGS, Massachusetts Office of Coastal Zone Management, and Woods Hole Oceanographic Institution Seagrant (Thieler et al., 2001 and O’Connell et al., 2002). Shoreline rates of change were calculated at 20 m intervals (transects) along the coast using a linear regression technique to derive the rate of shoreline change over time (see Dolan,1985, for a general discussion of shoreline change calculation methods). The rates for each transect within a 1-minute grid cell were averaged to determine the shoreline change value used here. Shoreline change rates on CACO range from +2 m/yr (low vulnerability) to -2 m/yr (high vulnerability) (Figure 9 A-C).


The determination of regional coastal slope identifies the relative vulnerability of inundation and the potential rapidity of shoreline retreat because low-sloping coastal regions should retreat faster than steeper regions (Pilkey and Davis, 1987). The regional slope of the coastal zone was calculated from a grid of topographic and bathymetric elevations extending landward and seaward of the shoreline. Elevation data were obtained from the National Geophysical Data Center (NGDC) as gridded topographic and bathymetric elevations at 0.1 meter vertical resolution for 3 arc-second (~90 m) grid cells. These data were resampled to 1-minute resolution (Figure 2). Regional coastal slopes for CACO vary from very low vulnerability to very high vulnerability (Figure 10 A-D).

Back to Top