Estimates of wave decay rates in the presence of turbulent currents

A full-depth numerical model solving the free surface flow induced by linea r water waves propagating with collinear vertically sheared turbulent curre nts is presented. The model is used to estimate the wave amplitude decay ra te in combined wave current flows. The decay rates are compared with data c ollected in wave flumes by Kemp and Simons [J Fluid Mech, 116 (1982) 227; 1 30 (1983) 73] and Mathisen and Madsen [J Geophys Res, 101 (C7) (1996) 16,53 3]. We confirm the main experimental finding of Kemp and Simons that waves propagating downstream are less damped, and waves propagating upstream sign ificantly more damped than waves on fluid at rest. A satisfactory quantitat ive agreement is found for the decay rates of waves propagating upstream, w hereas not more than a qualitative agreement has been observed for waves pr opagating downstream. Finally, some wave decay rates in the presence of fav ourable and adverse currents are provided in typical field conditions. (C) 2001 Elsevier Science Ltd. All rights reserved.