Interannual nearshore bar behaviour: An inter-site comparison

At Duck (N.C.) and four Dutch sites, subtidal nearshore sandbars have a multi-annual lifetime during which they are generated near the shoreline, move offshore through the surfzone, and decay offshore. We use complex empirical orthogonal function analysis to quantify bar length and bar amplitude across the surf zone, and to compute the average time interval (or, 'cycle period') at which bars are formed near the shore or decay offshore. Viewed as a function of mean depth, the bar length curves are statistically identical for all sites and the shapes of the bar amplitude curves are remarkably self-similar. Cycle periods range from ≈ 3.2 years at Duck to 16 years at one of the Dutch sites. The inter-site differences regarding bar amplitudes curves and cycle period could not be linked to differences in simple bulk statistics of the nearshore wave and waterlevel climate, or to differences in the nearshore bed slope.