126 Shallow Water Wave Transformation through External Factors 



individual observations deviate considerably from the theory, on the average 

 the theoretical relationship seems to apply for all but the steepest storm waves. 

 One may conclude that friction cannot play a decisive role in the trans - 



** 1-5 



0-005 0010 



0015 



Initial steepness, 



0030 0-035 0040 



0020 0-025 



Ho 

 Z-o 



Fig. 57. Theoretical and observed ratio breaker height to deep water wave height as func- 

 tion of initial steepness (Sverdrup and Munk). 



formation of waves travelling from deep into shallow water. Sverdrup and 

 Munk state that a careful analysis of all available data covering slopes of 

 beaches from 1/20 to 1/100 shows that the loss of energy due to friction does 

 not exceed 10% of the original wave energy and is even much smaller on 

 the average. 



It is confirmed by a large number of observations in the laboratory and 

 in the field that surf waves start breaking at a ratio of depth and wave height 

 of 1 28. However, there are three exceptions not covered by the theory: 



(1) Abrupt changes in the beach slope may lead the waves to break already 

 at considerable depths. 



(2) Very steep storm waves break in water deeper than the depth indicated. 



(3) Very flat waves break in water of smaller depth than indicated. 

 After eliminating all cases of abrupt changes in beach slope from 555 



individual observations in different localities, the average observed ratio of 

 depth over breaker height equals 1-27 as compared to the theoretical value 

 of 1 28. Individual observations lie roughly between 11 and 15, and this 

 deviation cannot be altogether ascribed to accidental circumstances one 

 differing strongly from the next. The deviations will also result from the fact 

 that the profiles of individual breakers differ: some are steeper, others less 

 steep than the solitary wave. But on the average the breakers seem to resemble 

 the profile given by the solitary wave theory and follow the theoretical rules. 



