cartome.org

19 June 2001

Source: http://postoffice.nrlssc.navy.mil/abstract%2037.htm

WAVENUMBER-FREQUENCY STRUCTURE
OF INFRAGRAVITY SWASH MOTIONS

K. T. Holland
Naval Research Laboratory
Stennis Space Center, MS 39529-5004
R. A. Holman
Oregon State University
Corvallis, OR

Abstract

Alongshore separated time series of natural swash motions on a barred beach were obtained over a range of environmental conditions using a video technique. Wavenumber-frequency spectra of these data were computed to partition infragravity band energy levels associated with various wave types. For the frequencies 0.025 < f < 0.05Hz, 45% � 13% (one standard deviation) of the shoreline variance was associated with high mode (n > 2) edge waves and/or leaky waves, while approximately half of that amount was associated with low mode edge waves. Although gravity wave motions were also observed in a lower frequency band (0.001 < f < 0.025 Hz), a substantial portion of the variance (21 � 10%, with a maximum of 38%) was identified as a nondispersive wave form with wavenumbers well outside of the wavenumber-frequency bounds for gravity waves. This nongravity swash variance showed no significant dependence on mean alongshore current strength or mean alongshore current shear as measured in the surf zone. In addition, the celerities of these nondispersive waves measured in the swash zone were found to differ in magnitude, and in one instance sign, from celerities measured further offshore, implying a decorrelation of trough and shoreline fluid motions.

Sponsored by the Office of Naval Research and the US Geological Survey.

Published in the Journal of Geophysical Research, Volume 104, June 15, 1999.
Naval Research Laboratory Contribution Number NRL/JA/7442 98-0001.
Journal Article