EM 1110-2-1100 (Part II)
31 July 2003
Figure II-4-5. NMLONG simulation of wave height transformation (Leadbetter Beach, Santa Barbara,
California, 3 Feb 1980 (Thornton and Guza 1986))
where Qb is the percentage of waves breaking, fm is the mean wave frequency, and the maximum wave height
is based on the Miche (1951) criterion
H max = 0.14 L tanh( kd )
(II-4-18)
where k is wave number. Battjes and Janssen base the percentage of waves breaking on a Rayleigh
distribution truncated at Hmax. Baldock et al. (1998) show improved results and reduced computational time
by basing Qb on the full Rayleigh distribution (Smith 2001). Goda (2002) documented that although the wave
height distribution in the midsurf zone is narrower than the Rayleigh distribution, in the outer surf zone and
near the shoreline the distribution is nearly Rayleigh. This method has been validated with laboratory and
field data (e.g., Battjes and Janssen 1978; Thornton and Guza 1983) and implemented in numerical models
(e.g., Booij 1999). Specification of the maximum wave height in terms of the Miche criterion (Equation II-4-
18) has the advantage of providing reasonable results for steepness-limited breaking (e.g., waves breaking
on a current) as well as depth-limited breaking (Smith et al. 1997).
II-4-10
Surf Zone Hydrodynamics
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