LABORATORY STUDY OF WAVE TRANSFORMATION ON BARRED BEACH PROFILES

Abstract

In previously reported laboratory experiments, the authors found that incident waves with the same characteristics in deep water break differently on barred and plane-sloping beaches. For example, waves of greater steepness that plunge on plane beaches tend to collapse on barred beaches, and plunge distance on barred profiles is about half that on a plane sloping beach for a given wave steepness. In the present study, wave height transformation, reflection, and runup of monochromatic and random waves are investigated for barred and plane beach profiles in a wave tank, with deep-water wave steepness varied from 0.0085 to 0.09. For monochromatic and random waves, wave-height to waterdepth ratios are higher for waves breaking on bars, whereas just seaward of breaking these ratios are lower than on a plane beach. For plane and barred beaches, the ratios unite in the inner surf zone, and the magnitude and shape of wave spectra are the same at fixed points outside and inside the surf zone, except just shoreward of the break point, where the spectrum on a barred profile has the same shape but contains less energy. Despite differences in breaker-related quantities on barred and plane beach profiles, runup, reflection, and wave height transformation in the surf zone on barred profiles are mainly controlled by the plane beach slope on which the bar or reef is located, with only minor influence by a bar, even for extremely-shaped obstacles such as reefs.