Lagrangian Observations of Rip Currents
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 ($150), handheld, Differential Global Positioning Systems (DGPS) mounted on surf zone drifters. The inexpensive DGPS requires post-processing to achieve O(0.4m) position accuracy and O(0.01m/s) velocity accuracy. 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 surf-zone. 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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2007
- Accession Number
- ADA474395
Entities
People
- Jonathan D. Morrison
Organizations
- Naval Postgraduate School