correspondence is seen for 370, 750, and 1,450 waves (irregular waves) than is seen when the two conditions 

 were compared after equal numbers of waves (see Figure 26 and other comparisons in Appendix E). 

 However, the improved correspondence obtained by time-shifting the profiles is evident only after the first 

 300 waves. Prior to that point, profile comparisons are better when the morphological time scales were 

 equal. 



202. The observed trend for irregular-wave-induced profile evolution to take longer than corresponding 

 profile development in the regular wave tests is the same as observed by Mimura, Otsuka, and Watanabe 

 (1986) and Uliczka and Dette (1987). Qualitatively, the morphological time scale factor between irregular 

 and regular wave profile response was about 2; i.e., profile development took twice as long under irregular 

 waves. This rate is somewhat faster than indicated by the data published by Uliczka and Dette (1987). 



203. The tests described by Uliczka and Dette (1987) did not expose the 1:4 sloping concrete 

 revetment because the sand berm was sufficiently wide so as to preclude that possibility. During the tests 

 in the 6-ft tank, equilibrium was reached rapidly in both the regular and irregular wave cases after the 

 revetment weis exposed. This rapid move toward equilibrium may have been caused by sediment no longer 

 being available for offshore transport. This may partially explain the differences in profile evolution times 

 noted between the present tests and those of Uliczka and Dette. 



Conclusions Regarding Irregular Waves 



204. Movable-bed physical model tests conducted using irregular waves successfully reproduced profile 

 development observed using regular waves. Best results were obtained when the significant wave height of 

 the irregular waves Wcis chosen as the equivalent parameter to the regular wave height. This equivalence 

 was in a water depth sufficiently deep so that the Rayleigh distribution assumption was still valid, and 

 measured Hijz was approximately the same as measured Hmo- 



205. Profile evolution under irregular waves was slower by approximately a factor of two, although 

 there are no strong physical arguments to justify this factor other than observation. The slowing of erosion 

 may be caused by some waves in the irregular wave train moving sediment onshore. Qualitatively, this 

 follows the same trend observed by other investigators. 



206. Exposure of the revetment and subsequent depletion of the available sediment for transport on 

 the upper profile lead to rapid formation of the equilibrium profile in the irregular wave tests. This resulted 

 in the irregular wave case reaching equilibrium after nearly the same elapsed time as the regular wave case. 

 Absence of the revetment very likely would result in more lengthy profile development times for the 

 irregular wave case, as noted in the- experiments of Uliczka and Dette (1987), and this was demonstrated 

 during the irregular wave verification tests when the revetment was not exposed (see Part IV of this report). 



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