Effects of Tide and Wave Directionality on Localized Tsunami-Induced Currents in Port and Harbors

Abstract

Here, we present the results of a numerical modeling study to investigate how the maxima of the tsunami-induced currents vary due to dynamic effects of tides and wave directivity. A sensitivity analyses was conducted in three harbors by coupling the tsunami with the tide signal at twelve different tide levels. We find that tsunami-tide interaction can change the maximum current speed experienced in a harbor by up to 25% for the events and harbors studied, and that this effect is highly site-specific. To evaluate the effect of wave directionality on maximum currents, three earthquakes with different magnitudes were devised along the Pacific, which were also tuned to create the same maximum near-harbor amplitude. Our analysis also shows that, for the harbor and sources examined, the effect of offshore directionality and tsunami frequency content has a very weak effect on the maximum currents experienced in the harbor. The much more important dependency on maximum currents is on the near-harbor amplitude of the wave, indicating that currents in a harbor from a tsunami generated by a large far-field earthquake may be reasonably well predicted with only information about the predicted local tsunami amplitude. This study was motivated by the hope of constructing a basis for understanding the dynamic effects of tides and wave directivity on current-based tsunami hazards in a coastal zone by the application of numerical simulation tools for hazard mapping purposes. The consideration of these aspects is crucial and yet challenging in the modeling of tsunami currents.

Probabilistic Tsunami Hazard Assessment in Meso and Macro Tidal Areas. Application to the Cádiz Bay, Spain

“…Several studies have been carried out to understand whether tide-tsunami interactions enhance/reduce tsunami elevation, flow speed, and arrival times. Based on observations and/or numerical experiments, various authors have found that tsunami inundation in rivers, inlets, harbors, and estuaries is strongly affected by tidal conditions (e.g., Kowalik et al, 2006;Kowalik and Proshutinsky, 2010;Zhang et al, 2011;Lee et al, 2015;Ayca and Lynett, 2016;Shelby et al, 2016;Tolkova, 2016;Ayca et al, 2017). Causes of tidetsunami interaction are attributed to tidally induced currents and changes in the depth altering the background conditions during the propagation of the tsunami from its source (Weisz and Winter, 2005), both effects are small in the open ocean but increase as the tsunami shoals, mainly in coastal and bathymetric particular configurations as energetic tidal channels communicating large bodies of water or coastal configuration that can induce resonance effects between large scale shallow shelfs, narrow channels, islands, etc.…”