HR: 09:25h
AN: OS31A-04    [Abstracts]
TI: Development of Sorted Bedforms in the Nearshore: Geology or Hydrodynamics?
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: Recent investigations of sorted bedforms and ripple scour depressions have focused largely on measuring or modeling hydrodynamic mechanisms that may explain the development of these features. In contrast, this study questions the role geology may play in the development of sorted bedforms in the nearshore, and specifically tests if certain pre-existing characteristics of the underlying, framework geology may be more conducive for their formation. Results from bathymetric and sub-bottom surveys from the nearshore of the North Carolina Outer Banks document: 1) clusters of shore-oblique bars with adjacent gravel-filled troughs that span the nearshore (2-12 m depths), 2) persistent or recurring bar and trough morphology through storms and fair weather, and 3) the gravel exposed in the shore-oblique troughs are surface outcrops of a much larger, underlying stratum. A total of five large clusters of shore-oblique bars and troughs were identified in the 56-km long field site. In every case, evidence of a buried paleo-fluvial channel was found underneath the groups of shore-oblique bars and troughs. The morphology and surface sediment distribution of much of the nearshore (approximately 85% of the field site), nevertheless, did not show any evidence of sorted bedforms. This site-specific occurrence differs from the inner shelf surveys conducted by the US Geological Survey, which reveal a nearly ubiquitous presence of sorted bedforms covering very large regions of the US East Coast. The similar morphology of sorted bedforms found on both the inner shelf and nearshore suggest the same physical processes may be responsible for shaping and maintaining them but it remains unclear what parameters- geology, hydrodynamics, or a combination thereof - dictate the location and initial development of these features in the nearshore. The US Army Research Office (Grant &35;DAAD19-02-1-0307) and the US Geological Survey North Carolina Cooperative (&35;02ERAG0034) supported this work.
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