Fluid flow and sediment entrainment in the Garonne River bore and tidal bore collision

Abstract

Abstract:A detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred. The measured bore, within the Arcins Channel of the Garonne River (France), was undular in nature and was followed by well-defined secondary wave motion. Due to the local river geometry a collision between the Arcins channel tidal bore and the bore which formed within the main Garonne River channel was observed about 800 m upstream of the sampling site. This bore collision generated a transient standing wave with a black water mixing zone. Following this collision the bore from the main Garonne River channel propagated 'backward' to the downstream end of the Arcins channel. Velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level. The instantaneous velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore. Large Reynolds shear stresses were observed during and after the tidal bore passage, including during the 'backward' bore propagation. Large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion, consistent with the murky appearance of the flood tide waters.

Effect of recurrent sediment resuspension-deposition events on bioavailability of polycyclic aromatic hydrocarbons in aquatic environments

“…Then the cylinder was covered with a lid and kept under a static condition for 7 days. During sediment suspension, the perforated grids were oscillated with vertical amplitude of 3.2 cm (between 5.0 and 8.2 cm above from the sediment surface), and they were driven by the speed motor with 150 rpm, corresponding to 6.4 N/m 2 , which was in the range of erosion shear stress (0.2-75 N/m 2 ) found in natural rivers (Babaeyan-Koopaei et al, 2002;Keevil et al, 2015;Kimiaghalam et al, 2015;Krishnappan and Marsalek, 2002;Reungoat et al, 2014). Furthermore, the experimental parameters including water depth and the sediment thickness used in this study are similar to other simulation experiments Schneider et al, 2007).…”

Turbulence and turbulent flux events in tidal bores: case study of the undular tidal bore of the Garonne River

“…Field measurements were performed in the tidal bore of the Garonne River (France), at a site previously used by CHANSON et al (2011), REUNGOAT et al (2014) and KEEVIL et al (2015). The study CHANSON et al (2011) was primarily a proof of concept, while ADV operational issue was experienced and only part of entire data sets was useable.…”

Consideration of the Mechanisms for Tidal Bore Formation in an Idealized Planform Geometry

“…Tidal bores play a significant role on the ecology, morphodynamics, and sedimentary structures of an estuary (Chen et al, ; Donnelly & Chanson, ; Fan et al, , ; Fielding & Joeckel, ; Greb & Archer, ; Martinius & Gowland, ; Reungoat et al, ; Tessier et al, ), as well as on the social activities that take place in this environment. Turbulent mixing and dispersion are enhanced at the passage of a tidal bore (Koch & Chanson, ; Pan & Huang, ; Reungoat et al, ; Simpson et al, ; Tu & Fan, ), and significant bed erosion and sediment resuspension take place (Keevil & Reungoat, ; Khezri & Chanson, ; Wang & Pan, ); the bed material is then aerated being suspended and advected upstream with the bore and redeposited on the tide's retreat (Chanson et al, ; Furgerot et al, ; Lubin et al, ; Reungoat et al, ). This process has a positive and significant influence on the breeding of many small, estuarine invertebrates such as shrimps, mollusks, and worms, which in turn feed several species of fish and provide important feeding grounds for wading birds and estuarine wildlife (e.g., Chanson, ).…”