WAVE TRANSFORMATION ON A ROCKY SHORELINE

Abstract

Two month-long experiments were performed to evaluate wave transformation across a rough rocky reef at Hopkins Marine Station, Monterey Bay, California. Outside of wave breaking, approximately 30% of the measured wave energy flux by sea and swell waves was dissipated over 140m. The bottom roughness of the rocky reef is defined by the standard deviation of bottom vertical variability (σb) and is 0.9 m. The energy dissipation, 〈εf〉, is related to bottom friction resulting in energy friction factor (fe) found to range between 0.03 and 43.8. An empirical power-law relationship was developed for fe as a function of wave orbital excursion (Ab) and σb. Inside of wave breaking at the shallow-water stations (h<2 m), wave heights, Hrms, collapsed to a non-linear relationship as a function of h that was lower than the estimated wave breaking parameter for this site, γ=0.29. An analytical model for shallow-water wave transformation on a plane sloping bottom with bottom friction only was derived matching the observed results. In deeper stations (h>2m), wave transformation is due to a combination of friction and wave breaking. Field-estimated fe ranged 3.8–8.2. These parameters were applied within the Thornton and Guza wave transformation model from 1983, and tested across the measurement array resulting in skill ≥ 0.9. The wave response to being frictionally dominant has important implications in describing biological communities within a rocky environment.