Vertical profiles of longshore currents
Soares Costa Ventura, Carlos Manuel da.
Thornton, Edward B.
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The vertical structure of the mean longshore current is examined on three strong current days during the DUCK94 experiment and it is found well described by a logarithmic profile (mean correlation coefficient for all 22 profiles, 0.98). This hypothesis works better in the trough where turbulent bottom boundary layer processes are predominant than over the bar, where breaking wave induced turbulence generated at the surface modifies the profile. A relationship between near bottom vertical velocity profiles and bottom roughness was found. The bed shear stress coefficient varied by an order of magnitude across the surf zone (0.001-0.05). For the three days considered, it is concluded that the bed shear stress coefficient increased with increasing bottom roughness, and therefore is an important parameter to characterize the bottom boundary layer. The influence of the wind is parameterized by an exponential approximation that works well in 50% of the analyzed profiles. This parameterization assumes that the residual Data Normal distribution of data is only due to the wind and does not consider the alongshore component of mass transport velocity, which is assumed small. These results should be treated carefully since there were obtained for only three days over a barred beach with strong longshore currents and cannot be generalized without further studies.
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