DISCUSSION

Figure 5. Relative Coastal Vulnerability for Cumberland Island National Seashore. Click on figure for larger image.

The data within the coastal vulnerability index (CVI) show variability at different spatial scales (Figure 5). However, the ranked values for the physical process variables vary less over the extent of the shoreline. The value of the relative sea-level rise variable is constant at low vulnerability for the entire study area. The significant wave height vulnerability is moderate to high. The tidal range is moderate vulnerability (2.0- 4.0 m) for all of Cumberland.

Figure 4. Historic shoreline positions. Click on figure for larger image.

The geologic variables show the most spatial variability and thus have the most influence on CVI variability (Figure 5). Geomorphology in the park includes high vulnerability barrier island shoreline with continuous dune ridges and very high vulnerability washover-dominated or low discontinuous dune areas. Vulnerability assessment based on historical shoreline change trends varies from very low to high (Figure 4 A -E). Regional coastal slope is in the high vulnerability range over the entire extent of Cumberland Island.

The area along central Cumberland Island that may be most vulnerable to future sea-level rise (high vulnerability) has some of the highest rates of shoreline change on Cumberland Island (Figure 4 C) and high wave heights. Although some of the dunes in this area are the highest on the island, they are also actively migrating inland over maritime forest (Figure 3 C).

The most influential variables in the CVI are geomorphology, historical shoreline change rates, and significant wave height; therefore they may be considered the dominant factors determining how Cumberland Island will evolve as sea level rises. Geomorphology and significant wave height vary only between high and very high and moderate and high vulnerability, respectively; whereas the shoreline change variable ranges from very low to high.

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