regular wave height used to develop the empirical basis of the numerical model. 



182. Larson and Kraus (1989) also developed a predictor for delineating erosive and accretive 

 conditions by assembling both prototype-scale and small-scale regular-wave laboratory data. In application 

 of the criterion to a collection of field observations, they found that the mean wave height of the field data 

 provided best correspondence to the regular-wave laboratory results. This further supports the conclusions 

 of Mimura, Otsuka, and Watanabe (1986). 



183. Uliczka and Dette (1987) compared profiles from regular and irregular wave tests in the 

 prototype-scale GWK wave tank. Each test began with a plane beach installed on a 1:4 slope with median 

 grain size of 0.33 mm. Regular wave heights of 1.5 m at periods of 6 sec were run intermittently in bursts 

 of up to 80 waves until an equilibrium was established. The irregular waves were generated with significant 

 height (i/1/3) equal to 1.5 m and peak spectral period of 6 sec; these conditions were run for intervals 

 totaling nearly 12 min until little change occurred between subsequent profiles. 



184. Uliczka and Dette (1987) reported the regular wave case reached an equilibrium state much faster 

 than the irregular wave case (4,000 waves as opposed to about 7,000 waves), and the total eroded volume 

 of sediment was approximately 20 percent greater for the regular wave case. They also observed that 

 sediment was not transported as far offshore in the irregular wave case, and the profile was smoother and 

 did not produce a breakpoint bar under irregular wave action. The lack of a bar feature was attributed to 

 the range of depths over which the irregular waves were breaking. Although the irregular wave condition 

 eroded approximately 20-percent less sediment, note that the irregular waves contained approximately 

 30-percent less total energy than did the regular wave case. 



185. The remainder of this section discusses the results obtained from tests conducted as part of the 

 present study. 



Irregular iJi/3 Equal to Monochromatic Wave Height 



186. Prior to placing the sand in the 6- ft wave tank, the wave machine was calibrated to produce an 

 irregular significant wave height at the nearshore gage location equal to the regular wave height of the base 

 case T03. Test T09 was conducted using this calibrated condition. The water depth at the nearshore gage 

 was suflSciently deep so that the measured statistical significant wave height was approximately equal to 

 the energy-based parameter Hmo- 



187. Subsequent analysis of water surface elevation data collected at the nearshore wave gages showed 

 values of the irregular wave statistic, //1/3, slightly higher than the target height of 0.66 ft (see Table B9 in 

 Appendix B). The increase over the nearshore gage values measured during low-reflection calibration tests 

 is attributed to wave reflection that increased the nonlinear aspects of the wave forms. 



75 



