The input data are the wave period, the mean beach slope, and the width of the plotting window. The beach slope is the a in the water depth relationship for a planar beach: h = a x , where x is the offshore distance.

The applet here shows the cross-shore variation of the edge wave motion with time; in the alongshore direction (y), the waves vary with cos(lambda y), where the longshore wave number lambda is given in the applet window.

Using shallow water theory, the water surface displacements of the first three edge wave modes are shown, along with their wave numbers (color-coded and in units of 1/m). The mode numbers correspond to the number of zero (mean water level) crossing by the wave form. To determine the wave length of the edge waves, divide the wavenumber from the display window into 2 Pi.

Ref: Eckart, C., "Surface Waves in Water of Variable Depth," Scripps Institution of Oceanography, Wave Rept. 100, S.I.O. Ref. 51-12, 99 pp, 1951.