2014 Volume 70 Issue 1 Pages 1-14
We examine a wave-current interaction, in particular current effects on waves (CEW), in a nearshore current system developed on a single-barred, rip channel topography. An Eulerian phase-averaged shallow water equation with a vortex-force formalism tightly coupled with WKB refraction equations is exploited to conduct a comprehensive numerical experiment. If CEW is taken into consideration, wave ray bending occurs to induce the prominent reduction of offshore extent of rip currents with near-normal offshore wave incidence. At deeper incident angles, longshore currents dominate over rip currents, resulting in eddying flows associated with shear instability around the bar crest. A diagnostic momentum budget analysis indicates that in the rip-dominant cases CEW alters the momentum balance significantly through modulation of the wavenumber field, leading to the enhancement of the onshore breaker acceleration and the pressure gradient force both in the alongshore and cross-shore directions. For the unstable longshore currents, CEW acts to diminish turbulence kinetic energy in the offshore region around the bar. Since the cross-shore turbulent intensity is more attenuated than the alongshore component, offshore eruption of the surfzone eddies is reduced by CEW.