HR: 17:00h
AN: H34C-05    [Abstracts]
TI: Nearshore Sediment Budget: Correlating Volume to Shoreline Change, Outer Banks, North Carolina
AU: * Miselis, J L
EM: jmiselis@vims.edu
AF: Virginia Institute of Marine Science, 1208 Greate Rd., Gloucester Point, VA 23062 United States
AU: McNinch, J E
EM: mcninch@vims.edu
AF: Virginia Institute of Marine Science, 1208 Greate Rd., Gloucester Point, VA 23062 United States
AB: Though the importance of understanding the exchange of sediment between the shoreline and the nearshore has long been recognized, data capable of addressing the three-dimensional character of the system are lacking. The response of traditional cross-shore profiles to forcing is not representative of the entire beach because of alongshore variability of the beach and nearshore sandbar. Measuring changes in shoreline position along the coast permits analysis of alongshore shoreline variability, but does not account for the actual volume of sediment lost from and restored to the beach. Temporally and spatially variable erosional hotspots identified by List and Farris (1999) along the Outer Banks, North Carolina further confound the study of coastal sediment exchange in the region of interest. A geophysical survey (from Duck to Oregon Inlet) was carried out in order to understand the role of geological characteristics in the transport of sediment between the shoreline and nearshore. Contrary to the assumptions of many shoreline and shoreface change models, the modern sand layer observed over the 40-km study area is not infinitely thick and is highly variable. Modern sediment thicknesses were calculated to a continuous seismic reflection surface that spanned the survey area, the average being 0.42m $\pm$ 0.19m. Higher standard deviations (variability) in sediment thickness seem to be loosely related to the presence of shore-oblique sandbars as described by McNinch (in press). Nearshore sediment volume was calculated and relationships to nearshore morphology were explored. Though shore-oblique bars may not represent a large percentage of the total sand regionally (7.9%), locally their influence is much greater. Of the three areas in which bars were identified, the volume of sediment contained within the bars represented 44% of the total volume in the largest bar field, and 14% and 11%, respectively, in more minor bar fields. Nearshore sediment volumes correlated well (correlation coefficient $\sim$0.60) with long-term shoreline change data (50 year data set, NC Division of Coastal Management) suggesting that long-term trends in shoreline change may be related to the total amount of available sediment in the nearshore. Correlation analyses with short-term shoreline change data will also be explored. These preliminary data suggest that volume calculations considering the total amount of nearshore sediment above a continuous, non-sandy seismic reflection surface may be useful in the prediction of long-term shoreline change trends. The utility of this approach in predicting changes over shorter temporal and spatial scales is the subject of current research.
DE: 4546 Nearshore processes
DE: 3020 Littoral processes
DE: 3022 Marine sediments--processes and transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting