Lagrangian observations of rip currents
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Authors
Morrison, Jonathan David.
Subjects
Advisors
MacMahan, Jamie H.
Date of Issue
2007-09
Date
Publisher
Monterey, California. Naval Postgraduate School
Language
Abstract
A comprehensive field rip-current experiment (RCEX) was conducted from 14 April to 18 May 2007 in Sand City, California, on Monterey Bay. Lagrangian observations were made with inexpensive ( 1 50), handheld, Differential Global Positioning Systems (DGPS) mounted on surf zone drifters. The inexpensive DGPS requires post-processing to achieve accuracy O(0.4m) and O(0.01m/s). Thirty drifters were constructed and deployed in well-developed, rip-currents to map the circulation patterns for the first time in the field at a high spatial resolution. Drifter observations obtained during three-hour periods on seven different days under varying wave and tidal conditions describe eddies with a rotational period of 4.7min, confined to the surf-zone and coupled to the rip morphology. On average, three drifters per hour exited the surfzone. Dependent upon wave conditions, one or two eddies existed between 90m-spaced rip-channels, creating a seaward flow in the channels and shoreward flow over the shoals. Cross-shore volumetric flow rates for an alongshore transect through the eddy centers balance to a difference of less than 10% of the gross flow discharge. Velocity measurements obtained from drifter data are evaluated with velocities obtained from stationary, in-situ instruments.
Type
Thesis
Description
Series/Report No
Department
Organization
Naval Postgraduate School (U.S.)
Identifiers
NPS Report Number
Sponsors
Funder
Format
xiv, 43 p. : ill. (some col.) ;
Citation
Distribution Statement
Approved for public release; distribution is unlimited.