INNER-SHELF CIRCULATION AND THE MAINTENANCE OF A RIPPLEDSCOUR DEPRESSION: WRIGHTSVILLE BEACH, NC, USA

摘要

Geological studies offshore of Wrightsville Beach, North Carolina revealedrnsubtle large-scale depressions (wavelengths between 100-200 m and crest to troughrnheights of 1 m) that trend normal to the coast. Originally, it was suggested that thesernserve as conduits for sand exchange between the shoreface and inner shelf during stormassociatedrndownwelling. More recent work has suggested that processes associated withrnalongshore directed flows may also influence the maintenance of these features. Yet,rndetailed examination of the hydrodynamics at this setting has been lacking. In this study,rn45 days of near-bed current measurements were used to test the existing hypothesesrnregarding the role of along and cross-shore flows in driving sediment transport at thisrnsite. Sediment transport estimates were made using a wave-current interaction andrnsediment transport model. The wind climate was found to dominate the flow. Sixrndifferent periods with different wind and flow conditions were analyzed in terms ofrnsediment transport. During these events, bedload transport is directed to the south withrnan offshore component, and suspended sediments are directed mainly along the coast tornthe southwest. Current and sea-surface elevation observations during these sedimentrntransport events provide no evidence of storm induced set-up and associatedrndownwelling.