The variation of wave heights due to wave breaking, which is an important process of wave transformation during the propagation from deepwaters to shorelines, is studied by theoretical calculations with a random wave breaking model, laboratory experiments with irregular waves, and analysis of field observation data. A method of estimating the wave height variation in the surf zone is presented.
　The estimation method is based on the theoretical model for the deformation of wave height distribution by depth-controlled wave breaking. The water depth is adjusted for wave setup due to radiation stress and water level fluctuation due to surf beats. The experiments and field data have confirmed the validity of the method. The variations of significant and highest wave heights from deepwaters to shorelines are presented in the forms of diagrams and empirical formulae with the parameters of equivalent deepwater wave steepness and sea bottom slope.
　The wave nonlinearity in shallow waters is also discussed.