PART IV: RESULTS 



120. Principal results of the study are presented in this chapter. 

 Breaker heights and depths, plunge and splash distances, and vortex areas were 

 determined from videotape. Measurements were made for 10 successive waves and 

 averaged for use in analysis. The video playback device was a Sony 5650 pro- 

 fessional editing machine, consisting of two playback machines and one 13— in. 

 and one 19— in. monitor. Playback speed could be varied down to freeze frame. 

 Wave height decay and wave reflection were obtained by analysis of resistance- 

 type wave gage records. The horizontal uprush of the wave was determined 

 visually and converted to a vertical distance above SWL to acquire wave runup. 

 Breaker type was also observed and recorded during testing. 



121. Totally, 120 tests were performed, including 96 base tests with 

 monochromatic waves, 11 variations of the base monochromatic wave tests, and 

 12 tests with irregular waves. The first monochromatic test modeled the wave 

 conditions over a solid model of the bar formed during a movable-bed test 

 conducted by Saville (1957) in a large wave tank. This pilot test was per- 

 formed to validate the bar depth criterion of Larson and Kraus (1989) to be 

 used to design the bars. 



122. Visual observations during the series of tests showed that the 

 return flow over the shoreward slope of the bars influenced the breaking wave 

 characteristics. A strong return flow was present if the cross-sectional area 

 of the surf zone was small, such as for tests with terraced bars. The return 

 flow also appeared to promote formation of a secondary wave in the trough of 

 the incident wave if / 8 1 was large compared with H /L . As water flowed 

 seaward over the bar, the water surface profile conformed to the shape of the 

 bar, much like critical water flow over a weir. For steeper bars, the water 

 surface profile over the bar was also steep, and the incident wave tended to 

 collapse or "trip" over the bar, rather than shoal and break by the depth- 

 limiting mechanism. The seaward bar angle necessary to cause wave tripping 

 decreased as H /L decreased; therefore, collapsing waves occurred for 

 gentler bar slopes with smaller wave steepnesses. Performance of tests over 

 the entire range of seaward bar angles with the smaller deepwater wave steep- 

 nesses was unnecessary because of the abnormal wave tripping effect. 



123. The influence of shoreward bar angle on wave breaking was not 

 found, which was attributable to the return flow. To quantify the effect of 



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