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Coastal Vulnerability Assessment of Olympic National Park to Sea-Level Rise, USGS Open-File Report 2004-1021

Map of Coastal Vulnerability

Skip past contents informationTable of Contents link to Title Page Link to Abstract Page Link to Introduction Page Link to Data Ranking Page Link to Olympic National Park Page Link to Methology Page Link to Geologic Variables Page Lilnk to Physical Process Variables Page Link to Calculating the Vulnerability Index Page Link to Results Page Link to Discussion Page Link to Conclusions Page Link to References Page

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 Neah Bay and Astoria were used for Olympic National Park (Zervas, 2001). Water level records from Toke Point in Willapa Bay were not used because the record is less than 50 years and the sea-level rise signal is likely affected by events such as El Niño. The sea-level rise variable inherently includes both global 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 (<150 years). The rate of relative sea-level change within Olympic is very low (<1.8 mm/yr)

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 beach material 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) (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 Olympic National Park mean significant wave heights range from moderate (2.0 - 2.25 m) to high vulnerability (2.25 - 2.60 m).

Tidal range is linked to both permanent and episodic inundation hazards. Tide range data were obtained from the National Ocean Service (NOS) for two ocean tide stations near Olympic National Park; the values were contoured along the park shoreline and mapped to the 1-minute grid cells. All of Olympic has a tide range between 2 and 4 meters suggesting moderate vulnerability.


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