Comparison of wind and wave forcing of longshore currents

Abstract Wind and wave forcing of longshore currents for varying wind conditions and beach slopes are compared using a numerical model. Waves are assumed to be locally generated by the same winds and fully arisen. The finite-depth TMA wind-wave spectrum is used to describe the radiation stress spectrum. Total wind force acting across the surf zone is proportional to surf zone width and therefore inversely proportional to beach slope. Wind force is not important for steep beaches. Total wave force is dependent of wave energy flux and wave direction at breaking, which are functions of the wind speed and direction. Wind force becomes increasingly significant relative to wave force, as wind speed and incident wind direction approaches parallel to shore. For obliquely onshore winds and a gentle beach slope (tan β = 0.01), wind force can be significant, with wind to wave force ratios ranging from 10 to 100% for winds between 10 and 30 m s−1 and wind and wave directions from 10 to 80°. Thus, under certain wind and wave conditions, wind force can be a first order term in the alongshore momentum balance.

[1]  G. Geernaert,et al.  Bulk Parameterizations for the Wind Stress and Heat Fluxes , 1990 .

[2]  W. Pierson,et al.  A proposed spectral form for fully developed wind seas based on the similarity theory of S , 1964 .

[3]  R. Dalrymple,et al.  NEARSHORE WATER CIRCULATION INDUCED BY WIND AND WAVES. , 1975 .

[4]  C. Walters.  Drag coefficient and roughness length determinations on an Alaskan Arctic Coast during summer , 1975 .

[5]  W. Rosenthal,et al.  Similarity of the wind wave spectrum in finite depth water: 1. Spectral form , 1985 .

[6]  E. Thornton,et al.  Observations of Steady Longshore Currents in the Surf Zone , 1986 .

[7]  Klaus Hasselmann,et al.  A parametric wave prediction model , 1976 .

[8]  T. Barnett,et al.  Recent advances in the study of wind waves , 1975 .

[9]  J. M. Hubertz.  Observations of local wind effects on longshore currents , 1986 .

[10]  S. Hsu.  Wind Stress on a Coastal Water Surface , 1972 .

[11]  D. Nummedal,et al.  WIND-GENERATED LONGSHORE CURRENTS , 1978 .

[12]  M. Longuet-Higgins,et al.  Radiation stresses in water waves; a physical discussion, with applications , 1964 .

[13]  S. A. Kitaigordskii,et al.  On Phillips' Theory of Equilibrium Range in the Spectra of Wind-Generated Gravity Waves , 1975 .

[14]  G. Taylor.  Skin Friction of the Wind on the Earth's Surface , 1916 .

[15]  Robert A. Holman,et al.  Setup and swash on a natural beach , 1985 .

[16]  D.J.T. Carter,et al.  Prediction of wave height and period for a constant wind velocity using the JONSWAP results , 1982 .

[17]  S. Hsu.  THE SHEAR STEESS OF SEA BREEZE ON A SWASH ZONE , 1970 .

[18]  G. Geernaert,et al.  Variation of the drag coefficient and its dependence on sea state , 1986 .

[19]  H. Vugts,et al.  Measurements of Drag Coefficients and Roughness Length at a Sea-Beach Interface , 1981 .

[20]  Edward B. Thornton,et al.  Transformation of wave height distribution , 1983 .