Swash on a Natural Beach

Abstract

A field measurement was conducted in order to clarify the swash motion on a natural beach. It is found on this particular beach, which had a rather steep foreshore slope, that cross spectra calculated between the surface elevations, onshore velocities and the swash agree very well with those given by linear long two-dimensional standing wave theory in the lower frequency region than a certain value. This finding together with the observed f~ (f; frequency) high frequency saturation in swash spectra encourages a partial reflection model to describe the fluid motion in the inner surf zone, including the swash. The model developed shows a good agreement with the observed results, in which being employed an analogy to regular waves for the criticality of wave reflection. This model makes it possible to predict the swash spectrum for a given incident wave spectra and a given beach profile, as far as wave breaking takes place on a foreshore slope.

The development and calibration of an alongshore shingle transport formula

“…The results of a number of studies of the swash and uprush of waves breaking on beaches have been collacted to provide a basis for estimating H R . Savage [17] includes results for the runup height for gravel beaches but only for monochromatic waves, Mase [10], Mizuguchi [12] and Sawaragi and Iwata [18] include some measurements of spectra. The depth h b is estimated from the ratio H b jh b {= y), where H b is the wave height at break point.…”

Intertidal beach profile estimation from reflected wave measurements

“…(1) where α is the surf zone slope, and H and L the offshore wave height and wavelength respectively, assuming monochromatic waves and a planar slope. Numerous field observations show that this predictor does not work well for irregular waves and complex bathymetry such as two-slope beaches (Mizuguchi, 1984;Elgar et al, 1994;Miles & Russell, 2004). Studies such as Sutherland and O'Donoghue (1998) successfully link wave reflection to the ratio between inclined wall length and shallow water wavelength for the case of an impermeable sloping seawall.…”