Bed shear stress coefficient within the surf zone

Abstract

An analytical formulation of the bed shear stress coefficient inside the surf zone is derived using the concept of radiation stress. A truncated Rayleigh p.d.f. is used to describe the wave field inside the surf zone and provides the input to calculate the variation of wave energy and longshore current as a function of wave height, water depth and distance to shore. The wave set-up is approximated using a sinusoidal wave solution. Field measurements of longshore current and waves within the surf zone are used to calculate the bed shear stress coefficient. The data consist of 647 data points selected from LEO program and 62 data points from Ingle (1966) observations, all taken along the Southern California coast. Frequency distributions and statistics are calculated for the bed shear stress coefficient. A mean bed shear stress coefficient to two significant decimal places is found to be 0.01.