HR: 0830h
AN: NG31A-0607    [PDF]
TI: Nonlinear dynamics of alongshore shoreline position change: observations and modeling
AU: * Tebbens, S F
EM: tebbens@marine.usf.edu
AF: University of South Florida, College of Marine Science, 140 Seventh Ave., South, St. Petersburg, FL 33701 United States
AU: Murray, A B
EM: abmurray@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Box 90230, Durham, NC 27708 United States
AU: Burroughs, S M
EM: sburroughs@ut.edu
AF: Department of Chemistry and Physics, University of Tampa, Tampa, FL 33606 United States
AU: Ashton, A
EM: andrew.ashton@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Box 90230, Durham, NC 27708 United States
AB: The horizontal, shore-perpendicular change in shoreline position along the Outer Banks of North Carolina is a self-affine signal. We measure shoreline change by determining the horizontal change in position of the 0.8m contour at 20m intervals along the coast. The profiles are obtained from two LIDAR surveys performed in September 1997 and September 1998 as part of a collaborative USGS, NOAA, NASA project. For six selected sections of coast, wavelet analysis of the shoreline change signal indicates that the signal is self-affine with a scaling exponent that varies from 1.2 to 2.1. This self-affine behavior indicates that the shoreline change signal is non-stationary with long-range persistence. The scaling exponent is found to vary depending on the orientation of the shoreline, suggesting that these changes are driven chiefly by subtle gradients on alongshore transport associated with subtle deviations from a smooth shoreline. Recent modeling work has shown that when waves approach shore from deep water at relative angles greater than approximately $45\deg$, shoreline perturbations grow, causing alongshore-heterogeneous shoreline changes on any scale at which perturbations exist. Waves approaching from deep-water angles closer to shore-normal tend to smooth out the shoreline. The patterns of change over some extended time period will result at least partly from the interactions between the roughening and smoothing influences, which will depend on the regional wave climate, including the relative proportions of high and low wave-approach angles. The observed trend in scaling exponents found for the Outer Banks, with scaling exponent varying as a function of shoreline orientation, is predicted by the alongshore transport model.
DE: 3200 MATHEMATICAL GEOPHYSICS (New field)
DE: 3220 Nonlinear dynamics
DE: 4546 Nearshore processes
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting