HR: 0800h
AN: OS21B-1234    [Abstracts]
TI: Tidal and Residual Currents Over Asymmetric Sandbanks
AU: * Sanay, R
EM: rsanay@geol.sc.edu
AF: Marine Science Program, Department of Geological Sciencies, University of South Carolina, 701 Sumter ST. EWS 617, Columbia, SC 29208 United States
AU: Voulgaris, G
EM: gvoulgaris@geol.sc.edu
AF: Marine Science Program, Department of Geological Sciencies, University of South Carolina, 701 Sumter ST. EWS 617, Columbia, SC 29208 United States
AU: Trowbridge, J H
EM: jtrowbridge@whoi.edu
AF: Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Warner, J C
EM: jcwarner@usgs.gov
AF: U.S. Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543 United States
AB: A 3-dimensional non-linear numerical model (ROMS) is used to study the tidal and subtidal flow over asymmetric (in cross-section) sandbanks with spatially varying bottom roughness similar to the sand ridges found presently in the southern North Sea. Such bottom roughness variations are mainly due to bedforms observed on the slopes of the banks. In order to isolate the bottom roughness effects, a series of numerical cases with different cross-bank profile and different orientation of the sandbank respect to the principal direction of the tidal current where carried out. The baseline case is an asymmetric bank with constant bottom roughness and nearly aligned with the incoming tidal forcing. In the baseline case, the incoming tidal forcing (linear semi-diurnal tide (M2)) is slightly modified over the flats but rectified over the banks, as expected from the nonlinear interaction with depth variations. As a result, M2 tidal ellipses incline toward the banks. Relative strong fourth (M4) and sixth-diurnal (M6) currents are generated over the banks. In general, M4 tidal ellipses show similar orientation as the semi-diurnal component, while the M6 tidal ellipses tilt in opposite direction than M2. In all the experiments residual flow show clockwise circulation around the banks, as expected from the torque from the Coriolis acceleration and bottom friction due to the presence of bottom depth gradients. The transverse (across-bank) balance is highly modified by changing the bank orientation and the bottom roughness. The numerical results are found to be in agreement with experimental data field from the Broken Bank at the North Sea.
DE: 4255 Numerical modeling
DE: 4512 Currents
DE: 4546 Nearshore processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting