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Coastal Vulnerability Assessment of Point Reyes National Seashore (PORE) To Sea-Level Rise
U.S. Geological Survey Open-File Report 2005-1059

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 Point Reyes Link to Methology Page Link to Geologic Variables Page Link 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

Figure 8. Rate of relative sea-level rise for Point Reyes National Seashore.
Figure 8. Rate of relative sea-level rise for Point Reyes National Seashore.Click on figure for larger image.

The relative sea-level change variable is derived from the change in annual mean water elevation over time as measured at tide gauge stations along the coast. The rate of sea-level rise for Point Reyes, CA is 2.51 +/- 1.27 mm/yr based on 25 years of data (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 portray only the recent sea-level trend (< 150 years). Relative sea-level rise for Point Reyes is moderate vulnerability based on water elevation data at Point Reyes, CA (Figure 8).

Figure 9. Mean Significant Wave Height for Point Reyes National Seashore.
Figure 9. Mean Significant Wave Height for Point Reyes National Seashore. Click on figure for larger image.

Mean significant wave height is used here as a proxy for wave energy which drives coastal sediment transport. 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 1956-75 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 Point Reyes, mean significant wave heights are between 0.2 and 2.6 m, which represents very low to very high vulnerability (Figure 9).

Figure 10. Mean Tidal Range for Point Reyes National Seashore.
Figure 10. Mean Tidal Range for Point Reyes National Seashore. Click on figure for larger image.

Tidal range is linked to both permanent and episodic inundation hazards. Tide range data were obtained from NOAA/NOS published benchmarks from Drakes Bay. Mean tidal range is 1.19 m; therefore Point Reyes was classified as high vulnerability (1.0-2.0 m) with respect to tidal range (Figure 10).

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