Lagrangian flow measurements and observations of the 2015 Chilean tsunami in Ventura, CA

Abstract

Tsunami‐induced coastal currents are spectacular examples of nonlinear and chaotic phenomena. Due to their long periods, tsunamis transport substantial energy into coastal waters, and as this energy interacts with the ubiquitous irregularity of bathymetry, shear and turbulent features appear. The oscillatory character of a tsunami wave train leads to flow reversals, which in principle can spawn persistent turbulent coherent structures (e.g., large vortices or “whirlpools”) that can dominate damage and transport potential. However, no quantitative measurements exist to provide physical insight into this kind of turbulent variability, and no motion recordings are available to help elucidate how these vortical structures evolve and terminate. We report our measurements of currents in Ventura Harbor, California, generated by the 2015 Chilean M8.3 earthquake. We measured surface velocities using GPS drifters and image sequences of surface tracers deployed at a channel bifurcation, as the event unfolded. From the maps of the flow field, we find that a tsunami with a near‐shore amplitude of 30 cm at 6 m depth produced unexpectedly large currents up to 1.5 m/s, which is a fourfold increase over what simple linear scaling would suggest. Coherent turbulent structures appear throughout the event, across a wide range of scales, often generating the greatest local currents.

Understanding the Extreme Tsunami Inundation in Onagawa Town by the 2011 Tohoku Earthquake, Its Effects in Urban Structures and Coastal Facilities

“…They started being analyzed, depending on availability since the 2004 Indian Ocean Tsunami [Synolakis and Kong, 2006;Fritz et al, 2006;Geist et al, 2006]. Previous studies have estimated the tsunami flow depth in several areas that were affected by the 2011 Tohoku Tsunami by interpreting recorded videos during the tsunami [Fritz et al, 2012;Hayashi and Koshimura, 2013;Foytong et al, 2013;Kalligeris et al, 2016].…”

Modelling scour and deposition in harbours due to complex tsunami‐induced currents

“…Accurate modelling of sediment transport is directly linked to the precise description of the flow field, and vice versa as explained in the Introduction. As tsunamis tend to induce complex hydrodynamics in the nearshore (Lynett et al ., ; Borrero et al ., ; Kalligeris et al ., ) and those are not well captured by typical shallow water models, the Boussinesq model is adopted as the hydrodynamic model component. Boussinesq equations are depth‐integrated, phase‐resolving equations (i.e.…”

“…(), and Kalligeris et al . (). Thus, coastal sediment modelling based on Boussinesq‐type equations has resulted in more detailed descriptions of flow structure, making these equations more suitable for sediment transport calculations than those of other methods (e.g.…”

“…The Boussinesq model is used to more precisely identify nearshore hydrodynamics by considering higher-order impacts to the flow field, which are increasingly important as waves approach the shoreline (Raubenheimer, 2002). Recent advances in the use of Boussinesq-type equations in tsunami modelling, with a focus on nearshore hydrodynamics, are shown in works by Grilli et al (2007), Fuhrman and Madsen (2009), Son et al (2011), Lynett et al (2012), Borrero et al (2015), and Kalligeris et al (2016). Thus, coastal sediment modelling based on Boussinesq-type equations has resulted in more detailed descriptions of flow structure, making these equations more suitable for sediment transport calculations than those of other methods (e.g.…”

Precise Prediction of Coastal and Overland Flow Dynamics: A Grand Challenge or a Fool’s Errand

“…Here, this de-coupling implies cases that examine turbulent eddies and wakes in shallow flow (e.g. Lloyd and Stansby, 1997a,b [18,19]; Park et al, 2014 [24]; Kalligeris et al, 2016 [13]); in such cases, the eddies are of course forced by the long waves, but once generated are no longer locked to the wave motion. The significance of eddies for hazard mitigation, including the types of impacts they have caused in recent events, is discussed in Lynett et al (2012) [21].…”