Velocity measurements made at two elevations off a rough sea floor in 18.3 m of water depth in the Strait of Juan de Fuca suggest the presence of a wave boundary layer. The wave velocities measured at 0.69 m off bottom are, overall, larger in magnitude and also shifted in time relative to the velocities measured at 1.85 m. These data were fitted to a two-parameter damped oscillator velocity model which was then used to obtain results on boundary layer thickness, bottom shear, and friction coefficient. The calculated boundary layer quantities are consisent with those from laboratory data and correspond to rougher flow conditions than those that have been observed in the laboratory. The damped oscillator model implies semiempirical relationships between the boundary layer quantities and the free stream velocity and period through an apparent bottom roughness parameter.