Cyclic bar behavior viewed by video imagery

Several multiple bar systems along the Dutch coast exhibit cyclic behavior. On a time scale of years the bar system moves in a net offshore direction, but at some distance offshore the outer bar decays while a new bar is generated near the shoreline. This study deals with the bar system near Noordwijk (The Netherlands) which completes one cycle in about 4 years. In this paper we present the preliminary results of an analysis of about 2 year of hourly sampled video time-exposures of the Noordwijk surf zone, focusing on the decay of the outer bar. It appeared that the decay of the outer bar as recorded by the annual surveys of the nearshore bathymetry (JARKUS data base) is the net result of a series of morphological changes. Unfortunately, the analysis could not yet be conclusive about the hydrodynamic conditions that forced the decay of the outer bar. Further, support was found for the hypothesis that the outer bar controls the long term net behavior of the inner bar. Finally, the large scale, three-dimensional structure observed in the long term development of the bar system emphasizes the need for large scale monitoring of bar systems to understand their long term behavior.