Tidal bore hydrodynamics and sediment processes: 2010–2016 field observations in France

Abstract

ABSTRACT A tidal bore is a compressive wave, advancing upstream in an estuary when the flood tidal flow starts. It is observed when a macro-tidal flood flow enters the funnel shaped river mouth with shallow waters. Its upriver propagation impacts the natural system, with sediment scouring and suspension. The tidal bores of the Garonne and Sélune Rivers in France were extensively investigated between 2010 and 2016. Instantaneous velocity measurements were conducted continuously at high-frequency (50 to 200 Hz) during each bore event. In the Garonne River, instantaneous sediment concentration data were obtained and the sediment properties were systematically tested. The nature of the observations was comprehensive, regrouping hydrodynamics and turbulence, sedimentology and suspended sediment transport. The key outcomes show that the tidal bore occurrence has a marked effect on the velocity field and suspended sediment processes, including a sudden flow deceleration and flow reversal during the bore passage. The turbulent Reynolds stresses present large instantaneous amplitudes, with rapid fluctuations, during the tidal bore. The sediment flux data imply considerable mass transport rates during the first hour of flood tide. This unique review of field data further shows a number of common features, as well as the uniqueness of each individual event.