SURF ZONE RESONANCE AND COUPLED MORPHOLOGY

John Chappell, Lynn Donelson Wright

Abstract


The edge wave hypothesis for periodic inshore morphology and circulation is tested for five beaches and is supported by resulting wave-current spectral and cross-spectral data. Beach types range from a reflective, narrow surf zone, case through various dissipative medium to high energy beaches including some with inshore bar-trough morphology and one broad surf zone troughless one. In all cases beachface reflectivity is moderately high (E < 2.5) and inshore resonance occurs, indicated by strong spectral peaks at lower than incident frequency with wave-current co-peaks being 90°out of phase. Several different edgewave frequency and mode combinations are indicated. The reflective beach shows an n = o subharmonic edgewave (i.e. at half incident wave frequency) which Guza and Davis (1974) predict as the most likely case, viz. the (o,o) triad. The troughless dissipative case shows a (1,0) edgewave triad; the same occurs in some bar-trough dissipative cases but in other cases is supplanted by the (o,o) sub-harmonic wave and/or by a lower subharmonic wave at h, incident frequency. The likelihood of a given edge .waveset appears to be regulated by surf friction, and a change of edge wave set appears likely to explain observed changes of inshore circulation.

Keywords


surf zone; resonance; morphology

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