Run-Up and Surf Beat

Abstract

Measurements of velocity and elevation in the inner surf zone usually show that a substantial fraction of the total variance is at surf beat periods, roughly 30–200 sec. (Inman, 1968; Suhayda, 1971, 1974; Goda, 1975; Huntley, 1976; Wright et al., 1979; Holman, 1981; Wright et al., 1982; and others). A typical current record from an inner surf zone sensor at Torrey Pines Beach, and a low passed version of the same record are shown in Figure 9-1. Although wind wave motions are usually the most obvious component of the unfiltered cross-shore velocity field (upper panel), surf beat motions are certainly significant (lower panel). Below, we first briefly review some theoretical ideas about the nature and origin of surf beat. Then experimental evidence supporting the various theories is discussed, placing special emphasis on the NSTS Torrey Pines results.