Turbulence and suspended sediment processes in the Garonne River tidal bore in November 2016

Abstract

A tidal bore is a water discontinuity at the leading edge of a flood tide wave in estuaries with a large tidal range and funneling topography. New measurements were done in the Garonne River tidal bore on 14-15 November 2016, at a site previously investigated between 2010 and 2015. The data focused on long, continuous, high-frequency records of instantaneous velocity and suspended sediment concentration (SSC) estimate for several hours during the late ebb, tidal bore passage and flood tide. The bore passage drastically modified the flow field, with very intense turbulent and sediment mixing. This was evidenced with large and rapid fluctuations of both velocity and Reynolds stress, as well as large SSCs during the flood tide. Granulometry data indicated larger grain sizes of suspended sediment in water samples compared to sediment bed material, with a broader distribution, shortly after the tidal bore. The tidal bore induced a sudden suspended sediment flux reversal and a large increase in suspended sediment flux magnitude. The time-variations of turbulent velocity and suspended sediment properties indicated large fluctuations throughout the entire data set. The ratio of integral time scales of SSC to velocity in the x-direction was on

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

“…The bore shape changes in response to changes in bathymetry in natural channels. This aspect is well documented in well-known systems (ROWBOTHAM 1983, CHANSON 2011a). This aspect is rarely observed in laboratory albeit a few exceptions (CHANSON 2011b, KIRI et al 2017.…”

“…(VERNES 1881). The bore propagation provokes intense sediment transport, linked to erosion, solid suspension and upwelling (GREB and ARCHER 2007, CHANSON et al 2011, KEEVIL et al 2015, FURGEROT et al 2016 as well as interactions with sediment bed forms (KEEVIL 2016, REUNGOAT et al 2017b. The flow field behind the tidal bore advects very high suspended sediment concentrations (SSCs), with observed concentrations in excess of 40 kg/m 3 (FAN et al 2014.…”

Hydrodynamics of tidal bores: turbulent propagation and sediment transport

“…The net sediment flux behind the tidal bore was 30 times larger than the ebb tide net flux and directed upstream. Following , similar results highlighting the massive upstream transportation of the suspended sediments due to tidal bores were recorded in Keevil et al (2015) and Reungoat et al (2014Reungoat et al ( , 2015Reungoat et al ( , 2017Reungoat et al ( , 2018Reungoat et al ( , 2019. Keevil et al (2015) presented a collision between the Arcins channel tidal bore and the bore which formed within the main Garonne River channel.…”

“…Most recent field works include the in-situ tidal bore observation on the Daly River in Australia (Wolanski et al, 2004), the Dee River in UK (Simpson et al, 2004), the Sélune River in France (Mouazé et al, 2010), the Seé River in France (Furgerot et al, 2013(Furgerot et al, , 2016, the Garonne River in France Keevil et al, 2015;Reungoat et al, 2014Reungoat et al, , 2015Reungoat et al, , 2017Reungoat et al, , 2018Reungoat et al, , 2019, the Qiantang River in China (Fan et al, 2014;Kawanisi et al, 2016;Tu & Fan, 2017), etc. In addition to the visual observation, flow velocity measurement was mainly conducted by deploying acoustic Doppler current profiler (ADCP) and ADV prior to tidal bore arrivals.…”

“…Overall, most previous field measurements highlighted the highly turbulent process of tidal bore propagations inducing rapid longitudinal velocity deceleration along with large fluctuations of freesurface elevations, unsteady flow velocities and Reynolds shear stresses. However, continuous insitu observation with monthly or annual time scales has not been realised due to the difficulty even in the most recent field deployments by Keevil et al (2015) and Reungoat et al (2014Reungoat et al ( , 2015Reungoat et al ( , 2017Reungoat et al ( , 2018Reungoat et al ( , 2019. On 18 September 2016, the Qiantang River Bore Observation Station (QBOS) was officially put into use by Zhejiang Qiantangjiang Administration Bureau (www.qgj.cn) in China.…”