wave period is assumed in the calculations. Given a deepwater significant wave 

 height and wave period, this model then assumes a Rayleigh wave height distri- 

 bution. At points in shallower water depths, this distribution is modified. 

 At each calculation point closer to shore the waves that break are removed from 

 the distribution. Determining whether a particular wave height breaks depends 

 on water depth and other factors (Goda, 1975). The significant wave height at 

 shallow-water points is then calculated from the modified distributions prob- 

 ability density function. At points closer to shore there is no assumption of 

 a particular wave height distribution but rather the distribution is modified 

 according to processes included in the model. 



The SPM method makes a further simplification relative to the irregular wave 

 model. It assumes a sinusoidal wave of a single period and wave height. As an 

 initial input to this technique, when the deepwater spectrum is available, the 

 period is set equal to the period for the peak of the wave spectrum and the 

 wave height equal to the significant wave height. These are reasonable choices 

 only if the spectrum has only one narrow peak. 



III. APPROACH 



Seelig (1979) generated design curves for wave height prediction using the 

 computer program GODAS (Seelig, 1978). For this study a modified GODAS program, 

 which includes refraction, was used to predict the wave height at the FRF pier 

 wave gage locations. The field measurements were made with several Baylor staff 

 gages mounted on the pier and one waverider buoy located 2.8 kilometers offshore 

 in a water depth of approximately 16.8 meters. The significant wave height and 

 peak period from the waverider buoy data were used as the deepwater wave inputs 

 to this wave height prediction program. The water depths at the several Baylor 

 gages were taken from weekly leadline soundings made along the pier, which were 

 corrected for the tide. 



An offshore bar is often present at the FRF. For the Baylor gage locations 

 shoreward of the bar where the water depth was greater than at the bar crest, 

 the depth at the bar crest was used as the input to the program. Seelig (1979) 

 recommends this approach when using the technique where an offshore bar is 

 present. The final input is the wave direction, which was measured from radar 

 imagery taken either simultaneously with or within an hour of the gage measure- 

 ments . 



During the period September 1978 to March 1979, a total of 21 cases were 

 chosen for study. As required by the irregular wave technique, single wave 

 train situations were selected. The data set included a variety of wave periods 

 (4 to 13 seconds) and significant wave heights (0.9 to 2.7 meters). 



IV. COMPARISON OF PREDICTIONS WITH MEASUREMENTS 



Preliminary comparisons of the irregular wave model predictions with the 

 measured significant wave height showed that an analysis of the results should 

 be segmented into three types of wave conditions: swell waves (waves propaga- 

 ting into FRF area which were generated offshore and are no longer receiving 

 energy input from local wind) , sea waves (waves still being generated by local 

 wind), and deepwater significant wave height, H , greater than 1.8 meters. 

 Figure 1 shows examples of each condition. The September wave spectrum shows 

 a prominent swell wave train. The plot of wave height versus location for the 



