standard deviation of 0.25. As shown in Figure 51, the distribution of the 

 breaker indices was somewhat positively skewed, and values ranged from 0.58 to 

 1.79. The steep slope that developed on the seaward side of the growing bar 

 caused the breaker index to increase with time, allowing the wave to break in 

 more shallow water. 



390. To evaluate this effect, results were compared with small-scale 

 laboratory data tabulated by Smith and Kraus (1988) for experiments made with 

 fixed plane bottom slopes typically more gentle than the seaward bar faces in 

 the CRIEPI cases . Figure 52 shows the distribution of the breaker index for 

 the small-scale experiment data, in analogy with Figure 51. Because of the 

 more gentle slopes, the average breaker index for the small-scale data was 

 only 0.82 (135 values), with a standard deviation of 0.18. If the beach slope 

 grows steep seaward of the break point, the breaker index should accordingly 

 be increased to account for the bottom slope effect on wave breaking. 



391. Correlation analysis showed that the breaker index depended mainly 

 on the slope before breaking and the deepwater wave steepness (see Galvin 

 1969, Weggel 1972, Singamsetti and Wind 1980, Sunamura 1981b). The slope was 

 evaluated as an average over that part of the beach profile seaward of the 

 break point where waves showed a marked increase in height due to shoaling 

 (typically in the range of 10-20 m) . The breaker index increased with an 

 increase in bottom slope and decreased with an increase in wave steepness. 



For profiles exhibiting bar development during a run, the average seaward 

 slope in general showed an increase with time (Part IV), causing an increase 

 in breaker index. Regression analysis between the aforementioned variables 

 explained 55 percent of the variation and indicated that the beach slope and 

 deepwater wave steepness could be combined to form the surf similarity 

 parameter tanfi/iti^/L^y^ (Battjes 1975) without loss of predictability. The 

 regression equation obtained is 



Hb 



= 1.14 



hv. 



tan/3 



(24) 



iHo/Lo 

 where tan/3 is the local beach slope seaward of the breakpoint. 



159 



