to 7 m. Although waves with periods as long as 25 sec have been recorded at
Grays Harbor, they are associated with wave heights of only 2 m. This inter-
relationship between Hs and Tp is central to the design of a submerged structure
such as the Grays Harbor spur because the potential for damage to the structure
has been observed to be strongly influenced by wave period (e.g., Ahrens 1987,
1989).
Figure A4.
25-year durations (hr) of Hs and Tp. based on measurements from
Grays Harbor CDIP buoy 3601
Spectral shape
The surface elevation spectra for nine of the 10 largest significant wave
heights measured at the Grays Harbor buoy are plotted in Figure A5. Modified
JONSWAP spectra (Goda 1987) were fitted using the measured Hm0, Tp and γ =
1.5 and 3.3. Unfortunately, the spectral data excludes the storm with the largest
wave height on record (Hs=9.74 m, Tp= 15.4 sec, 3 March 1999) because no
spectral data are available for this event. The spectral shapes in Figure A5 are
similar and suggest that the modified JONSWAP spectrum provides a reasonable
approximation to spectral shape for extreme waves approaching the project site.
A value of 3.3 was used for γ to generate irregular wave series for the flume tests
at CHC as it appeared to give a qualitative best fit to the average spectrum.
A5
Appendix A
Stability Analysis of a Submerged Spur, North Jetty, Grays Harbor, WA
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