Rip-current Persistent-foam Streaks Outside of the Surf Zone

Monday, 15 December 2014
Charlotte Benbow1, James H MacMahan1, Ad Reniers2, Ronald Brouwer3, Patrick Rynne4 and Matthieu A. de Schipper5, (1)Naval Postgraduate School, Monterey, CA, United States, (2)Delft University of Technology, Hydrolic Engineering, Delft, Netherlands, (3)Delft University of Technology, Delft, 5612, Netherlands, (4)University of Miami, Miami, FL, United States, (5)Delft University of Technology, Delft, Netherlands
Rip currents induce episodic pulses that transport surface material from the surf zone into the inner shelf. During certain energetic storm events for the rip-channeled system at Sand City, Monterey Bay, persistent-foam surface streaks are observed outside of the surf zone that outline the exiting rip current pulses. The persistent foam develops in the surf zone from mucus that is shed from diatoms in the breaking waves. The persistent foam streaks outside of the surf zone are surface convergences of the rip current front, and represent Lagrangian Coherent Structures. Aerial images are collected during these energetic events to explore the cross-shore mixing patterns. The images are geo-rectified and digitally enhanced for evaluating the surface streaks. The temporal and spatial evolution of the rip-current foam streaks is evaluated for their patterns, velocity, and offshore extent.