A simple model for current velocity profiles in combined wave-current flows

Abstract

Current velocity profiles in combined wave-current flows are investigated on the basis of available laboratory and field data. From the laboratory measurements of Van Doorn's (1982) S10RAL, S20RAL, M10RAL and M20RAL, it is found that there exists a boundary interaction layer (which includes the wave boundary layer) where the current eddy viscosity ϵ c is dominated by the wave motion inside the boundary interaction layer and then by the current upwards. Based on this finding, a new and simple model is developed to predict current velocity profiles in the presence of waves. The input parameters used in the model are wave height H, wave period T, water depth h, bed roughness K s, and a reference current velocity u ̄ r . In comparison with the former models of Christoffersen and Jonsson (1985), Coffey and Nielsen (1986) and Sleath (1991), the present model provides a simple method to explicitly calculate the wave friction factor, current friction velocity and current velocities without laborious iterations involved. Another new aspect of the model is that calculation of current friction velocities and current velocity profiles is quite simple and can be carried out with a simple scientific calculator. Results from the model are sufficiently accurate for engineering purposes.