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Rip currents are narrow jet-like currents, which flow seawards across the surf zone and extend several surf zone widths offshore. Typical speeds are about 1 m/s, but they have been reported as high as 2 m/s in mega-rips such as at Palm Beach, Australia [Short, 1985]. Rip currents are the most visible feature of near-shore circulation systems, often identified by sediments being carried offshore. Interest in studying rip currents is motivated by their strong offshore current, which is important to offshore sediment transport, shoreline evolution, dispersal of urban and farm run-off, pollutant transport, recruitment of biological species, and beach safety issues posing a hazard to swimmers.
RIPEX Objectives: A comprehensive one-month experiment is being conducted during April 2001 at Sand City to measure rip currents. The month of April was chosen for the experiment as the rip channels are well-developed and it is a transition month between winter and summer insuring a range of wave conditions. Owing to the near normal incident waves, the rip channels are relatively stable. This allows the placing of instrumentation in the rip channels with a high probability of success in measuring the rip currents (and recovering the instruments). The objectives are to measure the currents (surface, internal and vertical profiles) of the rip current system and its forcing (waves and wave breaking, pressure gradients due to wave set up/down, mass transport of the waves, and infragravity waves). A unique combination of in situ velocity and pressure sensors (Figure 2), remotely-sensed surface velocities and morphology, and bathymetry and vertical current profiles obtained from a moving platform to cover the range of the rip current spatial and temporal scales.
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