Boulder Transportation on the Flat Bed by Dam Break

Abstract

Large coral boulders are usually deposited in coastal regions due to high-energy inundation events, such as tsunamis or storms. The study on physical mechanisms is an important issue in hydrodynamics and sedimentology. In this study, the dam break induced the transportation, and the initial movements of a boulder are simulated on a flatbed in a laboratory experiment using a microelectromechanical system (MEMS) and image analysis. The scaled-down modeled boulder made the three-dimensional reconstruction rebuild the shape and surface texture of a realistic boulder. The MEMS integrated with the modeled boulder autonomously measures the signals and numerically calculates corresponding postures and transportation in three submerged conditions of the modeled boulder in the hydrodynamic experiment. Experimental results show that the boulder transportation process is a typical two-dimensional general planar motion, which includes sliding along the transported direction and swaying around the [Formula: see text]-axis. Rolling and saltation are not dominant modes in the experiment. The results show that a complete transportation includes a variable speed movement in the initial motion, acceleration–deceleration to the uniform motion, and boulder stopping in the destination. The transported velocities of the modeled boulder are smaller than wave celerities. The maximum/minimum velocities and displacements occur in the partially and fully submerged conditions, respectively. The adjustment of the boulder’s posture is completed in the initial motion, and then the boulder almost keeps the same posture to move forward to the end. Moreover, the boulder is not driven when the nondimensional water depth is close to the critical condition.