PHYSICAL PROCESS VARIABLES
The relative sea-level change variable is derived from the increase or decrease in annual mean water elevation over time as measured at tide gauge stations along the coast. The rate of sea-level rise in the Battery in NY is 2.77 +/- 0.05 mm/yr and 2.58 +/- 0.19 mm/yr in Montauk, NY, based on 144 and 53 years of data, respectively (Zervas, 2001). This variable inherently includes both eustatic sea-level rise as well as regional sea-level rise due to isostatic and tectonic adjustments of the land surface. Relative sea-level change data are a historical record, and thus only portray the recent sea-level trend (<150 years). Relative sea-level rise for Fire Island falls within moderate vulnerability.
Mean significant wave height is used here as a proxy for wave energy which drives the coastal sediment budget. Wave energy is directly related to the square of wave height:
E = 1/8 ρgH2
where E is energy density, H is wave height, ρ is water density and
g is acceleration due to gravity. Thus, the ability to mobilize and transport coastal sediments is a function of wave height squared. In this report, we use hindcast nearshore mean significant wave height data for the period 1976-95 obtained from the U.S. Army Corps of Engineers Wave Information Study (WIS) (see references in Hubertz and others, 1996). The model wave heights were compared to historical measured wave height data obtained from the NOAA National Data Buoy Center to ensure that model values were representative of the study area. For Fire Island, mean significant wave heights are between 1.3 and 1.4 m, which represents very high vulnerability.
Tidal range is linked to both permanent and episodic inundation hazards. Tide range data were obtained from NOAA/NOS for three ocean tide stations along the Atlantic Coast of Long Island; the values were contoured along the park shoreline and mapped to the 1-minute grid cells. All of Fire Island has a microtidal tide range (< 1 m) suggesting very high vulnerability.
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