Direct measurements of the bottom friction factor beneath surface gravity waves

Abstract

This paper describes a detailed experimental study of the laminar and turbulent oscillatory boundary layer developed under the action of waves for the purpose of evaluation of bottom energy dissipation. The measurements were conducted on hydraulically smooth and immobile rough beds and under both monochromatic conditions and a spectrum of waves in a 50 m long wave flume. Bottom friction was measured in two different ways: (i) by a flush mounted shear plate, developed as part of the project and set at the bottom of the flume, (ii) by using the momentum integral equation and the measured velocity profile within the boundary layer. The velocity profile within the boundary layer was measured usi..