HR: 14:45h
AN: OS33A-06    [Abstracts]
TI: Morphologic Response and Sediment Redistribution of the Beach and Nearshore Sand Bars due to Extratropical and Tropical Storm Forcing: a Spatial and Temporal Analysis
AU: * Miselis, J L
EM: jmiselis@vims.edu
AF: VIMS, College of William and Mary, 1208 Greate Road, Gloucester Point, VA 23062 United States
AU: McNinch, J E
EM: mcninch@vims.edu
AF: VIMS, College of William and Mary, 1208 Greate Road, Gloucester Point, VA 23062 United States
AB: Shore-oblique bars and associated exposures of an underlying geologic stratum in the nearshore have been documented along the US East Coast and have been linked to shoreline erosional hotspots. While earlier studies acknowledged that the bedforms responded to extratropical and tropical storms, neither quantified the extent of sediment redistribution after the events. An approach that encompasses actual volume measurements across the nearshore-beach down to a non-sandy stratum and quantifies the response of the beach and the nearshore to the same hydrodynamic forcing will enable a better understanding of the exchange of sediment between the two regions. Total nearshore sediment volume has been shown to be a first-order contributor to the behavior of the shoreline. This volumetric approach is employed in the analysis of morphological changes and the redistribution of sediment in the nearshore and beach following storms. A regional survey from 2002 provides the initial, fair-weather morphologic state of the nearshore (1.5-15m water depth) spanning 40 km of the North Carolina Outer Banks. Four small-scale surveys were conducted in subsequent years, focusing on four 1-km² regions within the initial 2002 survey area. The smaller regions were selected on the basis of the morphological state observed during the 2002 survey and historical shoreline behavior. Data were collected in March 2003 following a Northeaster; in May 2003 following an extended period of fair weather conditions; in November 2003 following Hurricane Isabel; and finally, in June 2004 after another period of fair weather. A swath bathymetry system was used to collect bathymetry and side scan sonar (acoustic backscatter) and a high-resolution chirp sub-bottom profiler imaged the shallow sub-surface geology of the nearshore. In addition, RTK-GPS was used to map the sub-aerial beach at each 1-km² site from the toe of the dune to the water line for the May 2003, November 2003, and June 2004 sampling periods. This sampling regime and data set offers a unique opportunity 1) to compare the simultaneous response of the beach and the nearshore to storms and 2) to investigate how the response of the beach and the nearshore varies depending on sandbar morphology and differences in the geologic framework. Three-dimensional maps of the beach and nearshore, from the toe of the dune to the 15m isobath, are used to demonstrate changes in total shoreface volume after storms and during recovery. Understanding the redistribution of sediment in the context of volumetric change enables the quantification of the exchange of sediment between the beach and the nearshore during large-scale forcing events.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
DE: 4546 Nearshore processes
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly