Runup characteristics of a tsunami-like wave on a slope beach

Abstract

Solitary waves (SWs) are often applied to the investigation of the hydraulic characteristics of tsunamis. However, SWs not only have a considerably narrower distribution than an actual tsunami but also have a smaller volume. By examining the 2011 Tohoku tsunami, we found that the volume ratio (V/V0) of the tsunami observed from the GPS buoy to the SW ranged from 2.54 to 14.76. This study proposes a tsunami-like wave (TLW) generation method which improves the shortcomings of existing SWs and has characteristic similar to an actual tsunami to better represent such wide-waveform tsunamis. Numerical analysis was performed by considering the TLW with various waveforms. In SWs, the maximum runup on the slope and the beginning of the rundown at the shoreline occur almost simultaneously. In a TLW, in contrast, rundown starts first under the influence of gravity before reaching the maximum runup height on the slope. As the waveform distribution becomes wider, the time difference between the beginning of the rundown and the maximum runup increases. The runup height increases as V/V0 increases within a certain range, but the rise slows beyond this range. Correlation of newly proposed friction parameters with the TLW breaking conditions, breaking wave types, and non-dimensional runup was also analyzed.