HR: 14:10h
AN: H33L-03 [Abstracts]
TI: Video and GPS measurements of morphology and swash flow in beach mega- cusps
AU: * Orzech, M
EM: orzech@nps.edu
AF: Naval Postgraduate School, Oceanography Department
833 Dyer Rd., Rm 327, Monterey, CA 93943, United States
AU: MacMahan, J
EM: jhmacmah@nps.edu
AF: Naval Postgraduate School, Oceanography Department
833 Dyer Rd., Rm 327, Monterey, CA 93943, United States
AU: Thornton, E
EM: thornton@nps.edu
AF: Naval Postgraduate School, Oceanography Department
833 Dyer Rd., Rm 327, Monterey, CA 93943, United States
AB:
The alongshore locations of beach mega-cusps appear to be directly associated with the alongshore positions of
surf zone rip channels (Thornton et al., Mar. Geol. 240, 2007). Previous lab and field measurements have
detected mean alongshore "counter-currents" that are shoreward of rip channel feeder currents but flow in the
opposite direction (Haas et al., JGR 108-C7, 2003; MacMahan et al., draft, 2007). These counter-currents may
contribute to the development and persistence of mega-cusps on a beach with rip channel bathymetry.
The present analysis uses both video and GPS methods to map the flow patterns and morphology in the region
shoreward of several large rip channels in southern Monterey Bay, California. High frequency rectified color
images and B/W video pixel time series of the swash and surf zone are analyzed with particle imaging velocimetry
(PIV) methods to indirectly measure swash flow in the cusps. The accuracy of the video-based estimates is
tested against in-situ GPS measurements. The PIV-predicted surface flow field is compared with velocity vectors
generated by concurrently deployed, GPS-equipped mini-drifters. Shoreline mapping techniques are applied to
time-averaged video images to estimate the corresponding intertidal morphology and compared with in-situ
measurements made using a GPS-equipped ATV and personal watercraft. Preliminary results indicate that
nearshore counter-currents are intermittently present shoreward of rip channels and suggest that they act
together with the alongshore current to influence the evolution and migration of mega-cusps.
DE: 1824 Geomorphology: general (1625)
DE: 4512 Currents
DE: 4546 Nearshore processes
SC: Hydrology [H]
MN: 2007 Fall Meeting