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Simultaneous Measurement of Horizontal and Vertical Velocities and Forces Beneath a Tidal Bore

Author(s): Muhammad Zain Bin Riaz; Shu-Qing Yang; Muttucumaru Sivakumar

Linked Author(s): Shuqing Yang

Keywords: Tidal bore; Incipient motion; Horizontal force; Vertical force; Physical modelling

Abstract: The development of a bore is a sudden change in water surface elevation represents the leading edge of the tidal wave propagating upstream. The impact of different types of forces under bores on sediment transport is not clear, hence specially designed experiments were conducted to clarify the mechanism of sediment initiation, although some physical experiments were performed during last two decades. In this study, a laser Doppler anemometer (LDA), a highly sensitive force sensor and ultrasonic displacement meters accompanied by video recordings were used to investigate simultaneously the incipient motion of sediment under tidal bores. No sediment motion was observed during the initial steady flow, but a transient sediment sheet flow motion was observed advected upstream during the breaking bore. The initiation of sediment motion was closely related to the passage of the breaking roller. According to the experimental results, upward vertical force due to swelling in free water surface before the roller toe was the main force in destabilizing the particles. Later, a large upstream longitudinal force was found to be the dom inant cause promoting upstream particle motion during the breaking roller passage.


Year: 2020

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