Nearshore Boxcore Data

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The content for this web page was taken from the Dissertation of Rebecca Lenel Beavers in the Department of Geology of Duke University entitled “Storm Sedimentation on the Surf Zone and Inner Continental Shelf” available in PDF format at the bottom of this page

Investigators

Rebecca L. Beavers, Peter A. Howd, William A. Birkemeier

Background

Ever since geologists realized that migrating bedforms deposit layered sediments like those preserved in rocks, they have attempted to relate the evolution of seabed morphology to internal sedimentary structures and external flow conditions. Along most coastlines, flows near the seabed are greatest during storms.Storm winds generate surface gravity waves that shoal in shallow water depths and undergo a series of nonlinear interactions when they break in the surf zone Elgar et al., 1990). Within surf zones, the region of active breaking waves, forces that result from the dissipation of breaking waves dominate circulation (Wright et al., 1991). These forces can increase bottom friction and sediment transport (Thornton and Guza, 1983), alter seabed morphology (Hay and Wilson, 1994), and create storm deposits (Smith et al., 1995) where these transported sediments accumulate. Due to the difficulty of monitoring the evolution of the seabed during storms, laboratory flumes have been the only previous setting where it was feasible to continuously monitor bed configuration and sample shallow stratigraphy created during simulated high-energy events This study presents some of the first field results of nearshore cores collected where the seabed elevation and hydrodynamic forcing are continuously measured by instrumentation during storms. The data were collected offshore of the US Army Corps of Engineers Field Research Facility in Duck, NC from 1994-1997. Continuous measurements of seabed elevation changes were made at 3 locations in 5.5, 8, and 13 m water depth and encompass a wide range of hydrodynamic conditions. Previous deployments on the inner continental shelf and the surf zone only lasted up to a few months (Wright et al., 1994a).

References

Objectives

Nearshore storm sedimentation on the surf zone and inner continental shelf has previously been documented by beach profiles and cores, but these methods usually provide only pre- and post-storm measurements. By connecting these discrete measurements with continuous sonar altimetry, seabed elevation changes during storms were used to interpret the stratigraphic signature of modern nearshore storm deposits and assess the seabed elevation variability documented by fairweather profiles.

Boxcores

During 1994-1997, the bipod instrument locations served as the site of over 150 diver-collected boxcores which provide a 15 cm wide x 30 cm deep section of the near surface sediments. Cores were collected during the calm summer months to serve as a fair weather baseline for cores collected directly after northeaster storms and hurricanes. This sediment coring program tested the correlation between seabed elevation changes recorded by the altimeters and the thickness of depositional units observed in the cores and investigated the spatial variability of sediments and preserved sedimentary structures in the vicinity of the bipods.

Storm Sedimentation on the Surf Zone and Inner Continental Shelf

Complete Dissertation in PDF format (4.2 megs)
Table of Contents

Funding Source

Duke University Marine Laboratory, US Army Corps of Engineers, Office of Naval Research, Geological Society of America, American Association of Petroleum Geologists, and the American Academy of Underwater Sciences


FRF|Sediment Home|Boxcore Collection|Boxcore Processing|Boxcore Data Catalog|Geologic Setting|Waves and Mean Currents|Instrumentation|References

This web site was created by Doug Call (Contract Student, University of Virginia) on July 31, 2001.