OPTICAL KINEMATICS OF WAVE-SWEPT SURGE CHANNEL RIP CURRENTS
Authors
Patria, Nicholas S.
Subjects
wave-swept surge channel
rip currents
unmanned aerial vehicle
rocky shoreline
foam
aerial imagery
rip currents
unmanned aerial vehicle
rocky shoreline
foam
aerial imagery
Advisors
MacMahan, James H.
Date of Issue
2018-12
Date
Publisher
Monterey, CA; Naval Postgraduate School
Language
Abstract
Aerial imagery of the rocky shoreline (RS) at Hopkins Marine Station in Pacific Grove, CA, was captured with an unmanned aerial vehicle. Imagery was georectified and post-processed to observe the surface flow of 2 persistent, stationary rip currents (rips) on the RS. Waves propagating toward the shoreline break as they interact with the irregular bathymetry. The collision of reflected waves in combination with a network of small feeder channels converge into a larger surge channel, directing a jet of water offshore. Breaking waves also create bubbles that inundate the shoreline with a dense bubble zone. Farther-extending bubbles within the rips were used to determine the cross-shore (CS) extent. Rip extents in channels 1 and 2 ranged between 14.3–49.2m and 8.8–33.1m. The respective mean extents were 33.1m and 18.1m. A dependence on wave height and tidal elevation is observed; as wave heights increase, the extent of the rips increases and, inversely, as tidal elevations decrease, extents increase. Slopes of ejected foam trajectories were measured for CS velocity. Calculated slopes show a velocity decay as the flow moves farther offshore. RS rips exhibit a direct offshore transport circulation. Drifters released from the shoreline immediately exited the surf zone and traveled along foam streaks, indicative of Lagrangian coherent structures. Maximum foam extents were observed at 154m, indicating surface material moving substantially offshore relative to the small surf zone.
Type
Thesis
Description
Series/Report No
Department
Oceanography
Organization
Identifiers
NPS Report Number
Sponsors
Funder
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Citation
Distribution Statement
Approved for public release; distribution is unlimited.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.