Velocity Profiles Above and Within the Wave Bottom Boundary Layer Over a Sloping Bottom

Theoretical solutions for the wave bottom boundary layer (WBL) are obtained using a viscoelastic turbulent closure model including sloping bed effects. The overlying free stream velocity is given by nonlinear Stokes wave theory for a sloping bottom. The viscoelastic closure scheme extends conventional eddy viscosity models by incorporating the effects of eddy relaxation and diffusion on vertical momentum exchange in the WBL, and gives improved predictions of observed velocity profiles. Field measurements of nearbed velocity profiles are then compared with theoretical solutions for a 2° bed slope. Field measurements were obtained in the lower 50 cm of the water column in 3.7 m depth with a coherent Doppler profiler. Results are presented from a storm event for flat bed. Within the region 8 cm above the bed, the observed velocity profiles change rapidly in amplitude and phase relative to potential flow theory, indicating the presence of the wave boundary layer. Furthermore, the observed vertical velocity profile in this region deviates significantly from the WBL theory for a horizontal flat bottom, but compares well with the sloping bottom theory presented here.