NDBC buoy. The distribution ofH sU>ng at the array and 6 m at the buoy over the 

 two-winter analysis period is shown in Figures 23 and 24. 



In general, the correlations were weak. A correction for the reduction in wind 

 wave energy at the array based on the direction of the deepwater waves provided 

 some improvement, but predictions of infragravity energy levels based on 

 offshore wind wave height still vary by a factor of five or more (Figure 25). The 

 study concluded that detailed inspection of the deepwater spectra, perhaps in 

 combination with a refraction-diffraction transformation model, would be needed 

 to significantly improve the predictions. 



Special events, harbor closing 



The only reported operational problem during the period of harbor wave 

 measurement was a closing of the harbor on 14-15 Mar 94. Figures 26-28 

 summarize CDIP array and NDBC buoy wave and meteorological measurements 

 during the event. Figure 29 helps put the event in perspective relative to the full 

 winter of 1993-4. The steepness parameter in the figure is the ratio of (HJ buoy to 

 deepwater wavelength based on (T,) buor Although {H) anaf (H shng ) array , and"° y 

 ( H s)buoy are ah high during the closure, they are not sufficiently high to distin- 

 guish the event as more extreme than other recorded events. The exceptional 

 condition during closure appears to be a combination of high winds, high wave 

 steepness, and long duration. Thus the harbor was apparently closed by a haz- 

 ardous short wave condition (steep, energetic waves with likely wind-induced 

 breaking). 



Special events, tsunami 



While tsunamis were not considered in the design of this study, the continu- 

 ance of the gages beyond the first year resulted in a fortuitous measurement of 

 the Shikotan tsunami on 4 October 1994 (McGehee and McKinney 1996). The 

 measurement represents one of the few large (approximately 1-m wave height) 

 tsunami time series sampled continuously at high frequency (1 Hz). The tsunami 

 wave period was approximately 30-35 min, or about 0.0005 Hz. Aside from the 

 scientific value, this data set provided an opportunity to examine the response of 

 the harbor to one instance of large-amplitude infragravity energy. 



Special events, extreme event parameters 



A more detailed documentation of extreme events recorded by the CDIP 

 gages is given in Appendix C. Included are tabular summaries of parameters for 

 observations with ( , // J ) amjy >200 cm for short wave extremes and H sh „ s >20 cm at 

 the array or Pier 2 for long wave extremes. 



Chapter 2 Field Wave Measurements 25 



