Estimation of sand suspension in a secondary channel of an alpine river.

Estimation de la suspension sableuse dans un chenal secondaire d'une rivière alpine

B. Camenen (1) , Guillaume Dramais (1) , A. Buffet (1) , Fabien Thollet (1) , C. Le Bescond (1) , M. Lagouy (1) , Céline Berni (1) , Jérôme Le Coz (1)

1 RiverLy - Fonctionnement des hydrosystèmes

In this paper, we present some first attempt to measure graded sus-pension of sands in an alpine river. It is a real challenge to measure graded-suspensions of sands in such dynamic rivers. Specific measurements of the graded suspension in the middle of a secondary channel were attempted using a sampler that allows simultaneous sampling at three different elevations (5 cm, 10 cm, and 20 cm) above the bed. Very large concentrations (up to C = 40 g/l) of fine sediments in suspension were measured during a dam reservoir flush-ing event. It included large amounts of sand (from 10 to 60% of the measured concentration). A substantial graded suspension of sand was measured even for relatively low velocities. Sand fluxes estimates for varying bed shear stresses during the event are discussed. In particular, based on the measured bed shear stress, a semi-empirical formula developed for sand suspension is applied to test its ability to predict sand flux in alpine rivers. The sensibility of such formula to the grain size is very high whereas large uncertainties exist in the measure-ment (d50 varies from 0.1 to 0.3 mm depending on the sample), which makes its application difficult at the moment.

Mots clés: sand; rivers; mountainous area; suspended matter

Mots clés: SABLE; COURS D'EAU; ZONE DE MONTAGNE; MATIERES EN SUSPENSION

Domaines: Sciences de l'environnement

B. Camenen, Guillaume Dramais, A. Buffet, Fabien Thollet, C. Le Bescond, et al.. Estimation of sand suspension in a secondary channel of an alpine river.. River Flow 2018: 9th International Conference on Fluvial Hydraulics, Sep 2018, Lyon, France. 8 p., ⟨10.1051/e3sconf/20184004014⟩. ⟨hal-01929318⟩