crest duration, T , is the time difference between an adjacent zero up-cross 

 and a zero down-cross; zero indicates the MWL of the record. The significant 

 wave height, Hg, for irregular waves was computed by multiplying the root- 

 mean-square (rms) water surface displacement by four. All the analysis was 

 based on the assumption that there was no wave reflection in any of the 

 channels where data were collected. 



For irregular wave conditions the elevations of the wave crests were 

 ranked from the highest to the lowest and the probability of exceedance, p, 

 for various levels of probability were calculated. For example, rig qi indi- 

 cates a crest height with a probability of being exceeded by 1 percent of the 

 crest heights, i.e., p = 0.01. Since the larger waves were of the most 

 interest the following probability levels for crest heights were calculated: 

 p = 0.005, 0.01, 0.02, 0.05, 0.10, 0.135, 0.15. Dimensionless wave crest 

 height probability levels, (nc)p/Hs, for wave gages 1 and 4 of the test setup 

 shown in Fi gure 3 are tabulated in Appendix B. The mean dimensionless crest 

 duration, (T^/T)p, was also determined for the highest 5, 10, 15, 20, 25, 33, 

 and 100 percent or the wave crests for gages 1 and 4 and is tabulated in 

 Appendix C. 



2. Other Laboratory Tests Used . 



Weggel (1976b) conducted tests using nonsinusoidal blade motion to generate 

 cnoidal waves. These waves have Ursell numbers between 27 and 184 and are 

 relatively free of secondary waves. The cnoidal wave conditions are given in 

 Appendix E. 



Singamsetti and Wind (1980) studied the breaking of monochromatic waves 

 on a number of smooth laboratory slopes. The relative crest ele vation s at 

 breaking H^/Hb and the relative crest durations at breaking, iT^/l)-^ are 

 tabulated in Appendix A, where n^ is the height of the crest above I-IWL at 

 breaking, H^^ is the wave height at breaking, and T is the period of a 

 monochromatic wave. 



3. Prototype Data Used . 



Prototype wave data collected at FRF, Duck, North Carolina, are used in 

 this study, particularly the data measured during a major storm in October 1980 

 in which a large variety of wave steepnesses were observed. The gages were 

 Waverider buoys located 0.5, 3, 6, and 12 kilometers from shore in an area 

 where the bottom contours were generally straight and parallel. The dominant 

 wave direction was approximately along the line of the instruments. The data 

 were analyzed in the same manner as that previously described for the labora- 

 tory data. 



IV. TEST RESULTS AND PREDICTION TECHNIQUES FOR MONOCHROMATIC WAVES 



Monochromatic laboratory wave test results are compared with Dean's stream- 

 function wave theory (1974) and the resulting prediction techniques are 

 discussed. 



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