Field validation of a nearshore circulation model for alongshore-nonuniform flows

Abstract

We investigate, theoretically and experimentally, the problem of modeling depth-integrated (2DH) surf zone circulation on an alongshore-nonuniform natural beach, with waves approaching from an arbitrary angle. An approximate theoretical model is developed, which captures the important effect of advection in the alongshore dynamics, and shows that a nondimensional parameter Re[subscript]s = khv₀/c[subscript]fU , the shallow water Reynolds Number, governs the response to alongshore-nonuniform forcing. Advection, in this model, appears as a filter in the alongshore direction, accounting for shifting and attenuation of nonuniform flow patterns, as is commonly observed in the presence of a background current v₀. The model is tested against fully-nonlinear 2DH solutions on idealized and natural beaches. The theory is further applied in the context of a fully-nonlinear 2DH hindcast of 455 hours of experimental data, using standard numerical codes. The filter model is used to predict and explain modeled dynamics, and hindcast accuracy, compared to the result when assuming alongshore-uniformity (the 1DH model). A new parameter is developed which quantifies the validity of the 1DH approximation, in terms of its ability to predict alongshore current on possibly-nonuniform beaches.