Experimental Investigations on Hydrodynamic Characteristics of Tsunami-Like Hydraulic Bores Impacting a Square Structure

Abstract

Laboratory experiments investigated the effects of bed slope, initial impoundment depth, and still water level on the hydrodynamic characteristics of tsunami-like hydraulic bores generated by a rapid-release swing gate. Different reservoir impoundment levels and still water depths downstream of the gate were selected to generate both subcritical and supercritical bores. The bores propagated over an initial fixed bed section followed by a sand bed test section that was either horizontal or inclined with a 5% upslope. A square rigid structure was placed in the middle of the sand bed test section. Time histories of specific discharge and momentum flux were calculated from measured bore velocity and depth. The bore velocities increased with impoundment depth, and supercritical bores had greater velocity than subcritical bores. Regardless of flow regime, absolute bore heights reached their maximum value of approximately 45% of the impoundment depth at the beginning of the erodible sand section. For comparable supercritical bores, propagation over the inverse slope instead of a horizontal bed increased the wave height by approximately 40% and its peak velocity by 25%.