Turbulent Advances of Breaking Bores: Physical Modelling in a Large Facility

In an estuarine system, the flood tidal wave may become a tidal bore during the early flood tide in a narrow funnelled channel under large tidal ranges. Herein new experiments were conducted in a large flume to investigate breaking tidal bores and the bore roller propagation. The results demonstrated several key features of tidal bores propagating in rectangular channels. The propagation of the breaking bore roller was a highly turbulent process. The celerity of the roller toe fluctuated rapidly with both longitudinal and transverse distances. The instantaneous longitudinal free-surface profile of the roller showed significant temporal and spatial fluctuations. The free-surface fluctuations were maximum shortly after the toe passage. The unsteady velocity measurements indicated large and rapid fluctuations of all velocity components during the bore passage. The velocity fluctuations yielded very significant Reynolds stress amplitudes and fluctuations. Instantaneous stress magnitudes in excess of 90 Pa were observed in laboratory, having the potential to scour large non-cohesive materials.