Temporal and Spatial Evolution of Potential Energy, Kinetic Energy, and Momentum Flux in Tsunami Waves during Breaking and Inundation

A plethora of studies in the last decade described tsunami hazards and studied their evolution from the source to the target coastline but mainly focused on coastal inundation and maximum run-up. Nonetheless, anecdotal reports from eyewitnesses, photographs, and videos suggest counterintuitive flow dynamics, for example, rapid initial acceleration when the wave first strikes the initial shoreline. Further, the details of the flow field at or within tens of meters of the shoreline are exquisitely important in determining damage to structures and evacuation times. Based on a set of three-dimensional Lagrangian numerical simulations, the authors used a model to simulate solitary waves and analyze the spatiotemporal distribution of the potential energy, kinetic energy, and momentum flux during the breaking process. The wavefront accelerates when in the proximity of the shoreline due to the change in slope of wave path; hence, it is the most dangerous part of the tsunami at any time regardless of the H/d(0) wave ratio. The authors inferred that the highest destructive capacity of flow occurs when momentum flux reaches its maximum, and this takes place in the initial shoreline environment. This maximum coincides with the local maxima of the potential and kinetic energy, making the shoreline prone to the most turbulent and dangerous flow, during the breaking and inundation processes. Therefore, momentum flux is a more important variable, over and above potential and kinetic energy, to be considered in tsunami-hazard and mitigation evaluations as well as in nearshore structure design. (C) 2017 American Society of Civil Engineers.