Wave breaking, perhaps the most visible nearshore phenomena, has long been a subject of research. Peregrine [1983] and Battjes [1988] provide excellent reviews of work to date including discussion of the onset of breaking (breaking criteria), types of breaking waves, details of the plunge process and the consequences of natural wave fields having a random distribution of wave heights.
Several observations have motivated further research on the details of wave breaking. First, previously-accepted models for longshore current generation by the dissipation of oblique incident waves were found to be clearly deficient on beaches with sand bars (expanded in a later section). Second, successful models of undertow (offshore-directed mean currents beneath the wave crest) were found to depend critically on knowledge of the vertical structure of wave dissipation.
Traditionally, it was assumed that the process of wave breaking was accompanied by an instantaneous transfer of momentum from the coherent wave motion (parameterized by the wave radiation stress) to the water column, forcing mean flows and pressure gradients. However, it has recently been realized that the turbulent kinetic energy (TKE) produced by wave breaking continues to carry momentum and that it is only with TKE dissipation that mean flow forcing finally occurs. Svendsen [1984] originally proposed the concept of a wave roller, a region of intense turbulence that lies on and is advected with the steep face of the breaking wave. Advection of the turbulent roller can cause shoreward shifts in current forcing patterns that may be most apparent in barred beach profiles. Since TKE production is primarily within this upper region of the water column [ Svendsen, 1987], vertical shears in cross-shore flows (undertow) can occur. Roller modeling is an important aspect of active research, focusing on consequences to vertical and horizontal mean flow structures and to the injection of turbulence into the water column in a manner that may influence suspended load sediment transport.