Field observations of surf beat: 1. Progressive edge waves

Authors:
  • DHD. A. Huntley
    D. A. Huntley
  • RGR. T. Guza
    R. T. Guza
  • ETE. B. Thornton
    E. B. Thornton
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Abstract
Nineteen biaxial electromagnetic current meters have been used to determine the longshore and on/offshore structure of currents at surf beat periods (1–4 min). The sensors formed two linear arrays, a long‐shore array within the surf zone and an on/offshore array stretching from the shoreline to well beyond the breaker line. Analysis of the longshore current components yields a clear picture of progressive low‐mode edge waves, with frequency‐wave number dispersion relations which are in remarkably good agreement with predictions. Some separation of edge wave modes is found, with mode zero energy dominating in the frequency band 0.006 and 0.011 Hz and mode one between 0.015 and 0.025 Hz. On/offshore currents present a rather different picture which, while not inconsistent with the longshore currents, suggests that other sources of energy are also important to the on/offshore currents. These include standing edge waves probably formed by reflections at nearby Scripps Canyon, and motions which are nonresonantly forced by incoming wave groups.

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