Scour Mechanics of a Tsunami-Like Bore around a Square Structure

Abstract

This study presents a detailed analysis of the mechanics of scour around a square structure due to an inland-propagating tsunami-like bore using physical modeling. A series of hydraulic bores was simulated using the dam-break method in a flume at the University of Ottawa Hydraulics Laboratory. The dam-break bore was generated by releasing water from an impoundment through a rapidly opening swing gate. A novel video-recording system was used to record the evolution of the scour and vortex structure around the structure; image processing allowed tracking of the time and spatial evolution of the scour around the structure. In addition, different characteristics of a generated bore, final scour topography, and the relationship between scour depth and bore characteristics are assessed. The test program was designed such that propagation over the dry bed, typical of the first tsunami-induced inundation, was investigated. It was found that the high velocity and relatively short duration of a tsunami-like bore can induce rapid scour around the structure. The deeper bore depth over dry bed conditions resulted in faster rates of infiltration and scour. Furthermore, it was found that the longer duration of a turbulent bore induced more scour depth compared to that produced by a height-equivalent solitary or long wave.