Set-Up Driven Undertows on a Barred Beach

Philip D. Osborne, Brian Greenwood
1991 Coastal Engineering 1990   unpublished
Field measurements of cross-shore velocity and water surface elevation from a natural barred surf zone during two storm events confirm the presence of undertow. The undertow is characterized by: i) mean cross-shore velocities reaching 0.20 m s" 1 and directed offshore; ii) mean cross-shore velocity decreasing towards the surface with occasional reversals in the mean flow to a landward direction in the upper water column; iii) a strongly oscillatory velocity field with speeds increasing towards
more » ... he surface and a distinct landward skewness superimposed. The undertow is strongly correlated with set-up of the mean water surface. The set-up is characterized by: i) increasing values shoreward with perturbations closely following topography indicative of a primary forcing by waves; ii) maxima (0.35 m in the inner system) occurring over the bar troughs in association with decreasing wave height over the preceding bar crest as predicted by theory and laboratory experiments.
doi:10.1061/9780872627765.019 fatcat:vfnxt5fw4jhgxavxqbubgshi5y