Optical Measurements of Tsunami Inundation and Debris Movement in a Large-Scale Wave Basin

Abstract

This paper presents optical measurements of debris movement and tsunami inundation over an unobstructed beach in a laboratory wave basin. The debris consisted of rectangular boxes and was placed unconstrained on a flat section raised above the basin floor with no still water on the raised section. Debris movement was measured using two overhead video cameras and a novel object-tracking algorithm. Two standard optical techniques, wave edge detection and particle image velocimetry, were used to compare optical and in situ measurements of fluid velocity. The debris motion (position, velocity) in the onshore direction was found to be repeatable, but the offshore motion varied between trials because of the irregular nature of the flow field during the return. For debris in free translation, as the number of debris specimens increased, the peak average velocity decreased and the onset of the peak was delayed in the onshore direction. In the offshore direction, the velocity was lower by a factor 4–6 and was independent of the quantity of debris. The decrease in the peak onshore velocity with increasing amount of debris was observed for debris that undergoes an initial rotation. The peak onshore velocity was nearly independent of whether the initial motion was purely translational or a combination of rotation and translation.