The effect of large grooves on the damping of water waves

Damping of water waves in a wave tank with a grooved base has been studied both theoretically and experimentally. It is shown that, for grooves of triangular or approximately sinusoidal cross-section, the damping is increased by an amount proportional to the total surface area of the grooved surface, and is independent of the direction of flow with respect to the grooves. The theoretical model applies when the groove spacing is small compared to the fluid depth and wavelength of the waves, but is large compared to the viscous boundary layer thickness. By carrying out observations in two surface modes, it is shown that the observed increased damping is caused by the grooved surface alone and cannot be attributed to spurious surfactant effects.