An estimation of gravel mobility over an alpine river gravel bar (Arc en Maurienne, France) using PIT-tag tracers

B. Camenen (1) , J. Le Coz (1) , André Paquier (1) , M. Lagouy (1)

1 UR HHLY - Hydrologie-Hydraulique

Passive Integrated Transducers (PIT) tag method to trace gravel particle is increasingly used to estimate gravel movements in mountainous rivers. Reported recovery percentages after one flood are often over 80%, demonstrating the effectiveness of this technique for small mountainous rivers. We used this technique to get detailed spatial information on particle movements on a gravel bar in an alpine river (Arc en Maurienne, France). Six patches have been placed on the gravel bar (three on the bar head in August 2008 and three along the secondary channel in June 2009). During this period, the main events correspond to flushing events of the upstream dams and reservoirs by dam managers, as well as short high flow periods in May 2009 due to snow melt. Only these events have an impact on the gravel bar since it is dry for lower flows. First results with PIT-tag technique indicate a very strong erosion of the head of the bar, especially on the side of the main channel. Two sample plots have been totally eroded and marked particles have moved to the main channel after the first and the second flushing events, respectively. The secondary channel shows lower dynamics. Recovery percentages were approximately 80% after each event until marked gravels reached the main channel through the first connecting cross-channel. Travel distances were independent of the particle diameter (40 to 300mm). The downstream part of the secondary channel and the tail of the gravel bar were not affected by the last flushing event in June 2009. Most of the surface of the downstream part of the gravel bar was dry during this event as a consequence of the May 2008 flood that significantly eroded the main channel. As a first conclusion, the PIT-tag method yields interesting results for the gravel bar dynamics but the investigation domain is limited in space (and time) for our study case. Indeed, we were not able to recover PIT-tag in the main channel and downstream.

Mots clés: TRACEUR; GALET; TRANSPORT SOLIDE; SEDIMENT; ZONE DE MONTAGNE; COURS D'EAU; EROSION FLUVIALE; ARC COURS D'EAU; MAURIENNE

Domaines: Sciences de l'environnement

B. Camenen, J. Le Coz, André Paquier, M. Lagouy. An estimation of gravel mobility over an alpine river gravel bar (Arc en Maurienne, France) using PIT-tag tracers. 5th International Conference on Fluvial Hydraulics (River Flow 2010), Sep 2010, Braunschweig, Germany. 8 p. ⟨hal-00546908⟩