A simple description of wave breaking in shallow water is incorporated
in the Boussinesq equations by using the concept of surface rollers.
The roller is considered as a volume of water being carried by the wav
e with the wave celerity. The effect vf the roller is included in the
vertical distribution of the horizontal velocity, which leads tn an ad
ditional convective momentum term. The breaking criterion is related t
o the local slope of water surface and the thickness of the roller is
determined from simple geometrical considerations. Although the model
is simple, it is capable of representing a variety of processes such a
s the initiation and cessation of wave breaking, the evolution of wave
profiles before,, during and after wave breaking, the initial convers
ion of potential energy into forward momentum flux, and the associated
horizontal shift between the break point and the point where the setu
p in mean water level is initiated. Results are presented for regular
and irregular wave trains and comparison with measurements shows good
agreement.