Surf Beat Generation by a Time-Varying Breakpoint

Abstract

Surf beat generally refers to low frequency long wave motions inside and outside the surf zone. However, although Tucker (1950) showed that surf beat could be correlated with the incoming incident short wave height, considerable uncertainty still remains about surf beat generation mechanisms and a number of possibilities have been suggested. These include edge waves, bound long wave release and reflection (Longuet-Higgins and Stewart, 1962) and direct generation by a time-varying breakpoint (Symonds et al., 1982; Schaffer, 1993). This paper considers this issue and presents new experimental results using bichromatic wave groups which show good agreement with the time-varying breakpoint model of Symonds et al. (1982). A numerical solution for the combined motion of the outgoing surf beat wave and the incident bound long wave also provides a good description of the long wave structure seaward of the breakpoint.