Bottom Slope: 1/50 



Bottom Slope: 1/10 





Theory (Hp/ioo/Ho) | 



y \ Ho'/Lo= 





/ ^^--^02 





,;/• 004 ^"~~-^ 





,' ^-~~. • 



~" 



' / y'' ^TJ=LrTj»fc— 



— *-«ir-=:'j 



/ ^ -^"T 





/ ,/ ^' ,006 





/ / / 





/ ■ '' ^ 





X ' *' ^ 





>/ - ''• / 





/^ ''-/ / 





/ / 





/ / 





/ / 





.' / 





/ . . . . 





'^ Leoend 



(HoVL.) (HoVuI 



'Si(Q020) •D.(Q042) 



*W(a02l) •EHO.OA.J) 



' 0.(0.026) k0j(0,054I 



- K (0.041) os.(0.056) 



05 10 15 



20 25 30 

 h/Ho 



H 



Ho' 10 



8 

 06 

 04 

 2 

 



H '/L -0 02 Theory 



/' ^-^004 



/yy L 006 









Legend 

 (Ho'/Lo) 

 ^^GO. (0021) 







--GK (0037) 

 ' GSj (0043) 











0.5 1.0 



1.5 20 

 h/Ho' 



25 30 3.5 40 



Figure 75. Irregular wave height variation across the surf zone on plane 

 beaches: theory versus laboratory data (after Goda, 1975). 



energy conservation equation (44) but then relied on entirely different 



energy dissipation relations (than Battjes) as briefly described in Chapter 



3. Figure 76 shows four separate cases of theory versus experiment. Here, 



the wave amplitude to amplitude at breaking (a/a^) is plotted for (a) 



horizontal, (b) plan 1:10 slope, (c) and (d) stepped beach profiles. Also 



shown are wave setup results (n/d ) not of interest here. 



B 



The theory (solid line) underestimates the wave height decay in all 

 cases. Better results were obtained (dashline) by using E = l/6pga^ 

 for the wave energy per unit area rather than the correct value of 

 E = ijpga^. The factor 1/6 was found empirically to give the correct 

 wave setup for step-type profiles. The necessary empiricism with this 

 theory makes it less attractive than the model of Battjes and Jansen (1978) 

 modified by the smoother, breaking cutoff criteria devised by Goda (1975). 



197 



