Cose 1 



Cose 2 



Cose 3 



*:_, 0.8 









o.e 



• 







0.8 



• 





?£ 0.6 









0.6 



■ 







0.6 



- 





!t^O.A 





i 





0.4 









0.4 



• 





5- 0.2 



1° ° 





H, 



A 1 . 



0.2 



- 







0.2 







u 



A * » . 



) 



0.2 0.4 



0.6 °0 0,2 



0.4 







02 0.4 





Free 



uency (Hz) 



Frequency 



(Hz) 





Fre 



quencjr (Hz) 



T 



= 



6.0$ 



14.0 3 









14.0 s 



H 

 d 



= 



0.572 



0.076 









0.572 



</«T 



= 



O0I42 



0.0026 









0.0026 



d/L 



= 



0.129 



0.052 









0.046 



"l 



= 





















'2 



= 



t.O 



1.0 









1.0 



"3 



= 



0.84 



0.51 









2.02 



'4 



- 



2.23 



1.89 









5162 





3d 



= 



H.2 







132 









6.8 



Figure 2. Wave profiles and energy spectra for 

 several cnoidal wave cases (record 

 length: 512 seconds; spectral band- 

 width: 0.00977 hertz). 



Another very in^ortant phenomenon is wave breaking, which for mono- 

 chromatic waves occurs in deep water approximately when the wave steep- 

 ness exceeds 0.14 or in shallow water when the ratio of wave height to 

 water depth exceeds 0,78. The heights of individual nearshore waves are 

 actually quite variable but generally conform to a Rayleigh distribution 

 (Thompson, 1974; Goda 1974; U.S. Army, Corps of Engineers, Coastal Engi- 

 neering Research Center, 1977). Thus, 13.5 percent of the waves can be 

 expected to be higher than the significant height and break farther sea- 

 ward than a wave with the significant height „ Breaking of a few very 

 large waves does not visibly affect the significant height, but when the 

 depth-induced breaking starts to affect many large waves, the significant 

 height decreases. Quantitative predictions of the decrease in significant 

 height as waves begin to break nearshore are given by Seelig and Ahrens 

 (in preparation, 1980) for a variety of wave steepnesses and beach slopes. 

 Their design curves, based on theory developed by Goda (1975), indicate 

 that breaking can begin to affect significant height when the ratio of 

 significant height to water depth is greater than about 0.5. This gen- 

 eral observation is consistent with field wave gage data presented by 

 Irie (1975). For a typical water depth at the gage of 5 meters, break- 

 ing might be expected to have affected all significant heights greater 

 than about 2.5 meters. 



15 



