Remote sensing of transient rip currents and surface waves in a laboratory wave basin

Christine Marie Baker, University of Washington, Civil and Environmental Engineering, Seattle, WA, United States, Melissa Moulton, Applied Physics Laboratory University of Washington, Seattle, WA, United States, Margaret L Palmsten, Naval Research Laboratory, Stennis Space Center, MS, United States, Katherine L Brodie, U.S. Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, Field Research Facility, Duck, NC, United States and Nirnimesh Kumar, University of Washington, Department of Civil & Environmental Engineering, Seattle, WA, United States
Rip currents dominate the exchange of contaminants, pollutants, and larvae between the surf zone and the inner shelf. Transient rip currents, hypothesized to be generated by surfzone eddy coalescence, are stochastic, and their locations are not known a priori. The formation and evolution of transient rip currents were investigated with laboratory experiments using remote sensing, including visible-band cameras and LiDARs, and an array of in situ sensors. The O.H. Hinsdale Wave Research Laboratory's Directional Wave Basin at Oregon State University allowed for known offshore wave conditions incident on an alongshore uniform barred bathymetry. The lab environment was modified to enhance remotely sensed signals with biodegradable surfactant, seeding of the surf zone with tracers, and controlled diffuse lighting. The velocity field was measured with in situ Acoustic Doppler Velocimeters and video-based estimates of surface-currents. The sea surface elevation was measured with in situ pressure gages, cross-shore and alongshore-scanning LiDARs, and the application of stereo processing methods to 8 Hz images from three cameras. Wave statistics computed from stereo reconstructions are compared with statistics computed from the LiDAR and in situ pressure sensor measurements. The effectiveness of remote sensing approaches to reconstruct the wave field evolution in the breaking region is assessed. Eddy generation and the subsequent formation of transient rip currents is quantified with the time varying sea-surface evolution and velocity field estimates. A variety of laboratory conditions are analyzed to investigate forcing mechanisms that drive the formation of transient rip currents. Funded by NSF and a NDSEG Fellowship.