Irregular Wave Energy Equal to Monochromatic Wave Energy 



192. Test T08 was conducted with an irregular significant wave height of Hij^ equal to 1.4 times the 

 monochromatic wave height used in base case T03. This provided approximately the same spectral wave 

 energy to the profile as present in the regular wave case, and under the Rayleigh assumption for wave 

 height distribution, corresponded to Hrms of the irregular waves being equal to the monochromatic wave 

 height. The purpose of this test was to examine whether equivalent energy levels are necessary to obtain 

 similar profile development between model regular and irregular wave physical model tests. 



193. It was originally thought the target significant wave height of 1.4 times the monochromatic wave 

 height had not been achieved in the flume. This condition had not been previously calibrated, and analysis 

 of the nearshore wave gage array (see Table B8 in Appendix B) made it appear as if the measured 

 significant wave height was too low. To further clarify the situation, the wave machine was calibrated 

 during the September 1989 series to produce the correct wave condition, and test T12 was run to duplicate 

 test T08. Wave measurement analyses and profile response were nearly identical for both T08 and T12. 

 This confirmed that test T08 represented the desired 41-percent increase in significant wave height, but 

 that reflected waves acted in some manner to decrease the nearshore wave heights as when compared with 

 the nonreflective calibration condition. Even so, the important aspect to remember is that the total wave 

 energy in the flume had been increased by 41 percent. 



194. Results from T12 are not documented in this report because they were essentially the same as 

 test T08. Test T12, however, did provide another example of experimental repeatability, and the 

 comparison is included as Figure E18. 



195. Comparisons between the irregular wave test T08 and the base regular wave case T03 revealed a 

 substantially different profile response to the increased wave energy. Figure 27 compares irregular wave test 

 T08 (solid line) with regular wave test T03 (dashed line) at various profiling stops. Additional comparisons 

 are given in Figure E16 in Appendix E. 



196. The increase in wave energy resulted in greater erosion of the berm area and also resulted in 

 movement of the sediment farther offshore than in the regular wave case. The comparison after 1,650 waves 

 also reveals a significantly different profile in the region of wave breaking and seaward of breaking. Visual 

 comparison between the results shown on Figures 26 and 27 clearly indicates that better correspondence 

 between regular and irregular wave tests was achieved if the significant wave height was made equal to the 

 monochromatic wave height. The relative differences between the two irregular wave tests are illustrated 

 on Figure 28 where the more energetic case is shown by the dashed line. (Also see full comparisons in 

 Figure E17 in Appendix E.) 



78 



