Currents, drag, and sediment transport induced by a tsunami

Journal of Geophysical Research C: Oceans
By: , and 



We report observations of water surface elevation, currents, and suspended sediment concentration (SSC) from a 10-m deep site on the inner shelf in northern Monterey Bay during the arrival of the 2010 Chile tsunami. Velocity profiles were measured from 3.5 m above the bed (mab) to the surface at 2 min intervals, and from 0.1 to 0.7 mab at 1 Hz. SSC was determined from the acoustic backscatter of the near-bed profiler. The initial tsunami waves were directed cross shore and had a period of approximately 16 min. Maximum wave height was 1.1 m, and maximum current speed was 0.36 m/s. During the strongest onrush, near-bed velocities were clearly influenced by friction and a logarithmic boundary layer developed, extending more than 0.3 mab. We estimated friction velocity and bed shear stress from the logarithmic profiles. The logarithmic structure indicates that the flow can be characterized as quasi-steady at these times. At other phases of the tsunami waves, the magnitude of the acceleration term was significant in the near-bed momentum equation, indicating unsteady flow. The maximum tsunami-induced bed shear stress (0.4 N/m2) exceeded the critical shear stress for the medium-grained sand on the seafloor. Cross-shore sediment flux was enhanced by the tsunami. Oscillations of water surface elevation and currents continued for several days. The oscillations were dominated by resonant frequencies, the most energetic of which was the fundamental longitudinal frequency of Monterey Bay. The maximum current speed (hourly-timescale) in 18 months of observations occurred four hours after the tsunami arrived.
Publication type Article
Publication Subtype Journal Article
Title Currents, drag, and sediment transport induced by a tsunami
Series title Journal of Geophysical Research C: Oceans
DOI 10.1029/2012JC007954
Volume 117
Issue C9
Year Published 2012
Language English
Publisher American Geophysical Union
Publisher location Washington, D.C.
Contributing office(s) Pacific Coastal and Marine Science Center
Description 15 p.; C09028
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Journal of Geophysical Research C: Oceans
Country United States
State California
Other Geospatial Monterey Bay
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