Longshore current profiles and lateral mixing across the surf zone of a barred nearshore

Abstract

Longshore currents were measured during a storm in a barred surf zone in the Great Lakes. Mean beach slope was 0.015, with three bars ranging up to 0.5 m in height. Comparisons with theoretical predictions revealed the effects of the bars on the horizontal structure of these currents and the degree of lateral mixing: (1) perturbations in currents are localized spatially but increase with bar relief; (2) currents are lower and higher respectively in the outer and inner surf zone than expected for a plane beach. The predictions of Longuet-Higgins (1972) provide a reasonable approximation where relief is low; (3) in the inner surf zone a plane beach solution suggests bars increase lateral mixing ( P ⋍ 1.0 ) by increasing the velocity gradients; (4) the barred slope model of Ebersole and Dalrymple (1981) most closely resembles the prototype; (5) use of planar beach equivalents for P or N in models for barred beaches, results in under-prediction of the appropriate eddy viscosity.