Effects of Tides and Currents on Tsunami Propagation in Large Rivers: Columbia River, United States

Abstract

To better understand the effects of river flow and tidal stage on the propagation of realistic tsunami waves up large rivers, simulations of the Columbia River (United States) were carried out. The two-dimensional depth-averaged version of the advanced circulation model was used. The model was forced with open boundary tides, tidal potential, and river flow. Simulations without tsunami waves demonstrated excellent agreement with numerous tidal gauging stations in the domain. A Cascadia Subduction Zone earthquake and associated tsunami were then considered by prescribing a rapid temporal change in the bathymetric/topographic grid. The simulations were repeated over a wide range of river flow conditions and a wide range of tidal phases. In each simulation, the tsunami was characterized in terms of the variation of its amplitude with upriver distance, how much land was inundated, and its propagation speed up the estuary. Although river flow is a dominant mechanism in the Columbia River in terms of stratification and surface currents, it was found to have only a minor effect on the propagation and inundation of the tsunami. The effect of tidal phase was more pronounced and more complex.