| Popis: |
In May 1999 a field campaign has been carried out at Omaha beach, a macrotidal beach situated along the coastline of Normandy in North France. This beach is characterised as a typical ridge and runnel beach and four intertidal bars can be distinguished. During a period of two weeks extensive morphological and hydrodynamic data have been collected. Key objective during the field period was to understand the three-dimensional development of the ridges and runnels and to recognise the processes responsible for origin and mobility of the ridges. The paper presented here attempts to combine integrated sand transport rates, measured by fluorescent tracers injected at the seaward flanks of the two highest ridges, with the residual topographic evolution of the intertidal beach. Fair weather conditions prevailed and as a result a slight onshore migration of the ridges has been monitored (max. 12 m). The dispersion of the tracer clouds reveals a dominance of cross-shore over longshore transport. However, this can not be comfirmed by the hydrodynamic data measured seaward of the breaker line. It illustrates the limited influence shoaling wave processes have on sand transport at the injection points during conditions of onshore bar migration. A predominance of swash action is assumed to be the main acting cross-shore sediment transportation process. |
