HR: 0800h
AN: OS21B-1209    [Abstracts]
TI: Evolution of Rip and Cusp Bathymetry
AU: * Orzech, M D
EM: orzech@nps.edu
AF: Naval Postgraduate School, Dept of Oceanography, Monterey, CA 93943
AU: Thornton, E B
EM: thornton@nps.edu
AF: Naval Postgraduate School, Dept of Oceanography, Monterey, CA 93943
AU: Stanton, T P
EM: stanton@nps.edu
AF: Naval Postgraduate School, Dept of Oceanography, Monterey, CA 93943
AU: MacMahan, J H
EM: jhmacmah@nps.edu
AF: Naval Postgraduate School, Dept of Oceanography, Monterey, CA 93943
AB: Four months of nearshore rip channel and beach cusp bathymetry are cross-correlated and their temporal evolution is compared with changes in magnitude of wave energy and directional spreading at the location of the 2001 RIPEX experiment in Sand City, California. Owing to headlands and refraction, the wave climate consistently exhibits shore-normal waves conducive to quasi-stable rip/cusp morphology, in which the cross-shore location of rip channels often appears to coincide with beach cusp embayments. Bathymetry is measured using kinematic GPS navigated on jetski and ATV. Video estimates of rip channel locations are obtained from alongshore pixel intensity maxima in image timexes, while shoreline location is estimated using a pixel luminance criterion similar to that described by Aarninkhof (2003). Directional wave spectra are obtained from an offshore ADCP located in 12m of water. Rip channel locations are found to be significantly correlated with the horizontal position of the 2m beach contour. The decorrelation time is greater than the four-month data set, indicating that the morphology was stable during this summer/fall period. The morphologic system migrated slowly south at less than 1m/day, based on the rate of change of the spatial lag of maximum correlation between the initial and subsequent rip current locations. Video estimates of rip channels match better with their corresponding GPS measurements than video shoreline estimates match with the GPS-measured 2m contour. These data support the hypothesis that cusp embayments are erosional features of rip currents. (Reference: Aarninkhof, S., Nearshore Bathymetry derived from Video Imagery. Delft University Thesis, 25 November 2003.)
DE: 4546 Nearshore processes
DE: 4552 Ocean optics
DE: 4558 Sediment transport
DE: 3020 Littoral processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting