WAVE GROUP MODULATIONS IN CROSS-SHORE BREAKING PATTERNS

T.C. Lippmann, R.A. Holman

Abstract


The principal aim of this work is to quantify the long period (group) time scales associated with incident wave breaking in the surf zone. A video based sampling technique is employed to distinguish those waves which are breaking from those which are not. The technique relies on the gray tone contrast between higher luminance of turbulent generated bubbles and foam associated with wave breaking, and the darker, unbroken surrounding water. Video image intensity time series, I(x,y,t), are sampled across the width of the surf zone at 10 m increments, from just outside the shore break to the far offshore region of the wave breaking. Outside the point of minimum depth (at the bar crest), the width of the surf zone fluctuates over several hundred meters. In this region, low frequency oscillations in /, phase coupled to the crest of breaking incident waves, are associated with wave groups. Crossshore phase relationships indicate a shoreward progressive group structure up to the crest of the bar. Landward of the bar crest in the trough, low frequencies in / are uncoupled from group modulations seaward of the bar. Video data also show that wave breaking does not cease immediately as waves propagate past the bar crest, but continues well into the deeper water of the trough.

Keywords


breaking pattern; breaking waves; wave group; group modulations; cross-shore breaking

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