Mixing parameterization: Impacts on rip currents and wave set-up

Type Article
Date 2014-07
Language English
Author(s) Bennis Anne-Claire1, 2, 3, Dumas Franck2, Ardhuin FabriceORCID4, Blanke Bruno3
Affiliation(s) 1 : CNRS UCBN UR, UMR 6143, M2C, F-14000 Caen, France.
2 : IFREMER, DYNECO PHYSED, F-29280 Plouzane, France.
3 : CNRS Ifremer IRD UBO, UMR 6523, LPO, F-29200 Brest, France.
4 : IFREMER, LOS, F-29280 Plouzane, France.
Source Ocean Engineering (0029-8018) (Pergamon-elsevier Science Ltd), 2014-07 , Vol. 84 , P. 213-227
DOI 10.1016/j.oceaneng.2014.04.021
WOS© Times Cited 12
Keyword(s) Bottom friction, Vertical mixing, Wave set-up, Nearshore processes
Abstract Wave set-up is often underestimated by the models (e.g. Raubenheimer et al., 2001). Our paper discusses how the wave set-up may be changed by the inclusion of turbulent mixing in the bottom shear stress. The parameterization developed in Mellor (2002) for phase-averaged oscillatory boundary layer is used for this purpose. Two studies are carried out. The dependence of the parameterization on the vertical discretization and on the magnitude of the near-bottom wave orbital velocity is investigated. The function that distributes the turbulent terms over the vertical is modified, giving a good agreement with the average of the phase-resolved velocities, but an overestimation of the turbulent phase-resolved velocities. Applying that parameterization to simulate laboratory conditions in the presence of rip currents gives accurate magnitudes of the rip velocity, particularly in a fully coupled wave–current configuration, with an RMS error of about 4%. Compared to a model using the more standard Soulsby (1995) parameterization, the wave set-up is increased by about 12% when using the alternative parameterization. Thus the bottom shear stress is sensitive to the mixing parameterization with a possible effect of turbulence on the wave set-up. Further measurement and parameterization efforts are necessary for practical applications.
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