The combined effects of synoptic-scale and local-scale meteorological events on bed stress and sediment transport on the inner shelf of the Middle Atlantic Bight

Vertical profiles of near-bottom currents and suspended sediment concentrations were measured on the inner shelf at 20 m depth off the US Army Corps of Engineers Field Research Facility at Duck, NC, U.S.A. over the month of October 1994. The observations embraced an initial period of calm conditions and a prolonged and evolving high-energy event. The data were analyzed to examine the effects of both synoptic and local-scale meteorological events on bed stress and resulting suspended-sediment transport. Four storm phases were identified and related to distinct sets of bottom boundary layer responses: (I) during the initial calm period of low bottom stress, non-diffusive suspended-sediment transport was confined within the thin wave boundary layer; (II) during the onset of the storm, increasingly diffusive suspended-sediment transport and active bedform changes prevailed in association with rapidly increasing wave boundary layer thickness and bed stress; (III) at the peak of the storm, wave boundary layer thickness and bed stress reached their maxima and caused high suspended-sediment transport and sheetflow conditions; and (IV) during the swell-dominated post-storm stage, bedforms developed and suspended-sediment transport was confined within the thick wave boundary layer because of the small current shear. Synoptic-scale winds with local wind perturbation controlled the near-bottom flow during Phase II, whereas local winds dominated during Phase III. Wave-current interactions were most intense during Phase III and were responsible for the high bottom stress.