Regular waves 



203. Examination of cross -shore transport rate distributions inferred 

 from successive profile change (Part V) shows that development of a bar or a 

 berm profile is closely related to the direction of net transport as offshore 

 or onshore, respectively. Thus, a criterion for predicting bar or berm 

 development can also be applied to predict the principal direction of net 

 cross -shore transport. Typically, if a bar forms, the main direction of 

 transport is offshore even if the bar receives a net contribution from the 

 shoreward transport of material originating from areas seaward of the bar (in 

 the situation of a relatively mild wave climate). A criterion which refers to 

 onshore/offshore transport will, in most cases, predict offshore-directed sand 

 movement if a bar is present and onshore -directed movement if a berm is 

 present. However, profiles between bar and berm type may have complex 

 transport distributions where a clear trend for onshore or offshore transport 

 is not apparent. This more complex transport pattern and resultant profile 

 change are left for future study and not pursued further here. 



204. From his laboratory experiments performed at small scale. Waters 

 (1939) (summarized in Johnson 1949) found that deepwater wave steepnesses 

 Hq/Lq greater than 0.025 produced a bar profile, whereas values less than 

 0.025 produced a berm profile. (Waters (1939) used the terminology 

 storm/ordinary profile.) This convenient rule of thumb is still commonly 

 applied to the field situation, but it is known to be incorrect for waves of 

 prototype scale, as first pointed out by Saville (1957). Rector (1954) 

 recognized the occurrence of a transition zone between bar and berm profiles 

 defined by wave steepness values in the range of 0.016-0.025 (for small 

 laboratory waves). Rector (1954) also developed an empirical equation for 

 predicting cross -shore transport direction based on wave steepness and the 

 ratio of median grain size to deepwater wavelength D/L^ . 



205. Kemp (1961) defined a "phase difference" parameter in terms of the 

 uprush time (time for the wave to travel from the break point to the limit of 

 uprush) and the wave period. The transition from a berm to a bar profile was 

 considered to occur if the uprush time equalled the wave period. (Kemp (1961) 

 used the terminology bar/step profile.) 



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