DISCUSSION

The data within the coastal vulnerability index (CVI) show variability at different spatial scales (Figure 15). However, the ranked values for the physical process variables are constant over the extent of the shoreline. The value of the relative sea-level rise variable is constant at moderate vulnerability for the entire study area. The significant wave height vulnerability is very high, and the tidal range is microtidal for all of Fire Island, making it very high vulnerability.

The geologic variables show the most variability and thus have the most influence on the CVI value (Figure 15). Geomorphology in the park includes high vulnerability stable barrier island shoreline with dune ridges in the west, and very high vulnerability washover-dominated barrier beaches to the east. Vulnerability assessment based on historical shoreline change trends varies from very low to very high (Figure 14 A -E). Regional coastal slope is in the high vulnerability range for the extent of Fire Island.

The most influential variables in the CVI are geomorphology and shoreline change; therefore they may be considered the dominant factors controlling how Fire Island will evolve as sea level rises. Geomorphology varies at a greater spatial scale (20 km) than shoreline change (> 2 km). This spatial variation is apparent in the CVI where geomorphology divides Fire Island into the slightly higher vulnerability east and the slightly lower vulnerability west; the shoreline change variable resolves vulnerability within the larger geomorphologic framework.

Because of the development and high economic value of property along the coast and mainland of Long Island and concern about erosion, storm surge breaching of the barriers, future sea level rise, and mainland flooding, planning is underway by Federal and State agencies to address these issues. Alternatives such as large-scale nourishment of the beach and dunes along Fire Island are being considered. Implementation of beach nourishment could alter the CVI results presented here.

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