dation was followed, and the gages were funded for an additional winter season, 

 through March 1995. 



Analysis Methods 



The CDIP nearshore wave gage data were processed to give two types of 

 output for each record: spectra and parameters. These outputs, which were 

 customized to meet needs of the Kahului Harbor study, are briefly described 

 here. NDBC buoy data were analyzed with standard NDBC procedures. 



SIO provided customized spectra and parameters covering the time period 

 Nov 93 - Sep 94. Subsequent wave climate studies indicated that this data set 

 gives a reasonable representation of the wind wave and swell climate. Wind 

 wave and swell data from the winter of 1994-5 are comparable to the winter of 

 1993-4. Fewer extreme infragravity (long) wave events occurred in the winter of 

 1994-5 than in the winter of 1993-4. There were eight events with significant 

 wave heights for long (infragravity) waves H^^IS cm in 1993-4 and only 

 three such events in 1994-5 (Merrifield and Okihiro 1996). Also there were no 

 reported operational problems in the harbor during the winter of 1994-5. 

 Because of these considerations, harbor data from Nov 93 - Sep 94 were 

 considered sufficiently representative of the full measurement period for 

 validation of the numerical model and for relating numerical model results to 

 operational concerns. 



Spectra 



Time series from the CDIP gages were subjected to SIO's standard spectral 

 analysis for long records. The 8,192-sec records gave a spectral resolution of 

 0.000122 Hz. Spectral output files were created with energy values for the first 

 286 spectral frequencies, or spectral lines (up to a frequency of 0.0349 Hz, 

 corresponding to a wave period of 28.6 sec), followed by energy values for 

 higher frequencies (shorter wave periods) grouped into bands of width 0.01 Hz. 

 A total of 32 frequency bands were included, with central frequencies ranging 

 from 0.04 Hz (25 sec) to 0.35 Hz (2.9 sec). Thus the analysis system produced a 

 high-resolution spectrum for infragravity waves and a conventional resolution 

 spectrum for wind waves and swell. The wind wave and swell spectrum is 

 estimated with an unusually high level of confidence (high number of degrees of 

 freedom) because of the exceptionally long records. 



Parameters 



Spectral results were also condensed into a small number of parameters for 

 output (Table 3). Significant wave height and peak spectral period for long 

 waves were computed from the infragravity portion of the spectrum using the 

 same procedures traditionally used for wind waves and swell (short waves). The 

 Back Basin gage, used for water depth measurement, had a higher quality 

 pressure transducer than the other gages, and was more stable over long time 

 periods. 



Chapter 2 Field Wave Measurements 



15 



