Distributions of Wave Steepness and Surf Parameter

Abstract

Predictions of wave action on slopes, and various wave- and depth-induced processes in the surf zone rely on two principal parameters: Wave steepness and surf parameter. For irregular waves, the theoretical distributions of these parameters are not known. Some studies suggest that wave steepness is described well by the Weibull and lognormal probability distributions. These distributions and thus their predictive utility depend on two key statistics, namely the mean and root-mean-square values of wave steepness. This study develops approximate theoretical forms of these statistics for narrow-band long-crested waves. For waves with steepness less than a Miche-Stokes type upper limit, comparisons with measurements from two severe storms show that the theoretical forms so derived and the resulting lognormal law in particular describes empirical data well. These results then permit the distribution of surf parameter to be approximated in a lognormal form also. Consequently, the nature and implications of such an approximation, resulting statistics and their plausible applications to breaker heights and types on slopes are explored.