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 at Pensacola (2.14 +/- 0.15 mm/yr) was used for Santa Rosa and Perdido Key. The Dauphin Island station was used for the Mississippi islands, which recorded a sea-level rise rate of 2.93 +/- 0.59 mm/yr (Zervas, 2001). The sea-level rise variable inherently includes both eustatic sea-level rise as well as regional sea-level rise due to isostatic and tectonic adjustments. Relative sea-level change data are a historical record, and thus only portray the recent sea-level trend (50 - 150 years).

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 are representative of the study area. For GUIS mean significant wave heights range from 0.60 m (if Florida) to 0.70 m (in Mississippi). These wave heights are considered low vulnerability (Table 1).

Tide range is linked to both episodic and permanent inundation hazards. Tide range data were obtained from the National Ocean Service (NOS) for four ocean tide stations along the Gulf Islands National Seashore; the values were contoured along the park shoreline and mapped to the 1-minute grid. All of GUIS is microtidal, therefore classified as very high vulnerability.

Please note: To enable Netscape 6/7 to see the symbols on this page, you need to alter a configuration file in the Netscape program directory. Go to woodshole.er.usgs.gov/netscape.html