Comparison of Model and Observed Nearshore Circulation

Abstract

Results from a two-dimensional numerical model for nearshore circulation induced by waves and wind are compared with observations made during two storms at a beach on Lake Michigan. Model-input data include bathymetry, offshore wave characteristics, wind histories, and local water-level changes. The predicted locations of the breaker zone are in rough accord with those observed during the storms. Data for comparison with model results consist of wave and current observations across the surf zone, especially those acquired by using a towed, instrumented sled. The comparisons show that the model often predicts peak currents near the breaker zone quite well, but underestimates the decay of wave height and the strength of longshore currents across the surf zone. Wave breaking on the bar-trough beach structure prevalent in this study apparently is not well represented by the model. An improved breaking criterion, treatment of breaking waves as traveling bores, and inclusion of horizontal mixing of momentum might add to better simulation of surf-zone currents.

Longshore current on a barred beach: Field measurements and calculation

“…Examination of the extensive DELILAH data set indicates that the presence of a broad peak in the current on the barred profile at Duck is typical. Allender et al [1978] reported similar current patterns on the barred profile near Zion, Illinois, in Lake Michigan.…”

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

“…However, with irregular bathymetry, variations in dissipation rates occur as a response to changes in the topographic gradients. For example, increased breaking over the bar crests results in local increases in the momentum flux gradient and higher current speeds at these locations; such a pattern was also found during field experiments by both Allender et al (1979) and Symonds and Huntley (1980). Furthermore, the presence of deeper water immediately landward of bar crests rapidly reduces wave breaking and thus the stress gradient.…”

Shore-Parallel Flows in a Barred Nearshore

“…This limitation is extreme where topographic effects-nearshore bars-introduce a potentially important modifying effect on current generation. Sonu (1972) provided a qualitative description of a spatially variable nearshore current in the presence of a bar but only very recently have more quantitative studies been undertaken (Meadows, 1977(Meadows, , 1978Symonds and Huntley, 1980;Allender et al, 1979;Allender and Ditmars, 1981). This paper presents the results of a field experiment designed specifically to examine the horizontal and vertical structure of the shore-parallel flow field across a non-tidal, barred nearshore under a wide range of incident wave conditions and to provide a dataset suitable for determining parameters describing the nearshore mixing and bed friction.…”