Cross-Shore Variation of Wave Reflection from Beaches

The cross-shore variation of the local reflection coefficient R is examined under the assumptions of normally incident wind waves on beaches with alongshore uniform bathymetry. The existing three-gauge method is modified to estimate R for the sloping bottom. A new method is developed to estimate the incident and reflected root-mean-square (RMS) wave heights from the measured RMS wave height and wave setup. These methods are used to analyze six runs from the large-scale SUPERTANK data set. The estimated values of R are affected little by the formation of a bar and increase shoreward with the increased percentage of breaking waves. One set of the DELILAH field data on a barred beach is also analyzed using collocated pressure and velocity measurements. This data set confirms the negligible effect of the bar on the variation of R over the bar in the absence of wave-breaking on the bar crest. These crude estimates of R suggest that the reflected wind waves may not be negligibly small in comparison to the incident wind waves, especially inside the surf zone.