The maximum wave height before breaking Hm is calculated according to the formulation of Battjes and Janssen (1978):
(5.35)
where k is the wave number, h is the local water depth, and g1 and g2 are wave breaking parameters. g1 controls the wave steepness, whereas g2 controls the height-to-depth ratio.
Waves higher than or equal to Hm are assumed to break and, conversely, waves with a height less than Hm are taken as non-breaking.
In shallow water, the breaking criterion simplifies to
(5.36) 
The values of g1 and g2 that you select should be identical to the values used to specify wave breaking in the wave simulation. If you cannot remember these values by heart, you may take a look at the specification file used to run the wave simulation.
The dissipation of energy due to wave breaking may be reduced by increasing either g1, g2 or both.
Default values of 1.0 and 0.8 are used in MIKE 21 ST, in agreement with the default values in the Spectral Wave module, MIKE 21 SW.
The specified values for the two parameters will be checked against those used when generating the sediment transport table(s) for the sake of consistency.
