Redefinition of Shore-Breaker Classification as a Numerical Continuum and a Design Shore-Breaker

Abstract

Based on an initial appraisal of data, new considerations are used on which to base a least equivocal numerical definition of shore-breaking waves. Redefinition is based on the amount of the wave crest. H”_b, measured from the wave crest top down, involved in shore-breaking, and is given by: H”_b/ H_b = tanh 0.4 ξ_b where H_b is the shore-breaking wave height, and ξ_b is a slightly modified version of the surf similarity parameter. The above equation also appears to represent the position at which the maximum impact pressure in a shore-breaking wave occurs. Relating equations are: z_max/Hb = 2.12 - tanh 0.4 ξ_b or z_{max SWL}/ H_b = 0.84 – tanh 0.4ξ_b in which z_max and z_{max SWL} the vertical distance above the bed and still water level (SWL) at shore-breaking respectively, where the maximum horizontal impact pressure occurs. Available impact pressure data indicates that the shore-breaker with the most destructive potential has a value of ξ_b = 1.0. This results in a design shore-breaking wave which imparts the greatest horizontal impact at a distance of O.62 H_b above the wave trough or 0.46 H_b above the SWL. Recalibration of the numerical results suggests the following modification in the existing descriptive shore-breaker type scale: ξ_b < 0.64, spilling shore-breakers; ≅ 0.64 to5.0, plunging shore-breakers; > 5.0, surging shore-breakers.