4. Breaking Waves . 



Waves are classified as breaking or nonbreaking according to two 

 different definitions. The first definition is based on whether a wave 

 breaks at or seaward of a structure toe (region I, Fig. 11). The second 

 and more inclusive definition is based on whether a wave breaks at all, 

 either on or seaward of the structure (in either region I or II, Fig. 11) 

 A nonbreaking wave by the second definition is assumed for some purposes 

 to represent total reflection on smooth slopes, although there is cer- 

 tainly energy loss on a rubble slope even if waves are nonbreaking. 



REGION 



n 



Structure 



Figure 11. 



Regions of breaking waves for depth-related instabilities, 



Jackson (1968a), for example, reported tests on rubble structures 

 with various armor units where waves were not breaking seaward of the 

 structure toe. He referred to "nonbreaking" waves; however, conditions 

 were such that some waves would be expected to break on the structure 

 when past the structure toe (region II, Fig. 11). 



Palmer and Walker (1970), however, studied runup on a 1 on 1.5 

 rubble slope fronted by a 1 on 50 beach. Their objective was the 

 design of a structure subjected to breaking waves—waves breaking 

 either on the structure or seaward of the structure toe. Their study 

 fits the second definition of breaking waves; i.e., breaking in either 

 region I or region II in Figure 11. 



Saville (1956) gave results of extensive smooth-slope testing, and 

 included waves breaking in both regions I and II (Fig. 11), but specific 

 conditions for breaking were not given. However, by comparing theoreti- 

 cal breaking wave conditions with some experiments for which the break- 

 ing wave conditions were given (e.g., Palmer and Walker, 1970), the 

 following discussion is considered applicable. 



Figure 12(a) shows an example dg/gT 2 curve for a structure sited 

 on a sloping beach; Figure 12(b) is for a structure sited on a flat 

 beach. For a wide range of H^/gT 2 values, there is a maximum rela- 

 tive runup (R/H^) for each dg/gT 2 curve. This maximum value may be 

 on a rather sharp, peaked curve or on a broad, flat curve. The positive 



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