Sediment budget monitoring of debris-flow and bedload transport in the Manival Torrent, SE France

J.I. Theule (1) , F. Liébault (1) , A. Loye (2) , D. Laigle (1) , M. Jaboyedoff (2)

1 UR ETGR (ETNA) - Erosion torrentielle neige et avalanches
2 UNIL - Université de Lausanne = University of Lausanne

Steep mountain catchments typically experience large sediment pulses from hillslopes which are stored in headwater channels and remobilized by debris-flows or bedload transport. Event-based sediment budget monitoring in the active Manival debris-flow torrent in the French Alps during a two-year period gave insights into the catchment-scale sediment routing during moderate rainfall intensities which occur several times each year. The monitoring was based on intensive topographic resurveys of low- and high-order channels using different techniques (cross-section surveys with total station and high-resolution channel surveys with terrestrial and airborne laser scanning). Data on sediment output volumes from the main channel were obtained by a sediment trap. Two debris-flows were observed, as well as several bedload transport flow events. Sediment budget analysis of the two debris-flows revealed that most of the debris-flow volumes were supplied by channel scouring (more than 92 %). Bedload transport during autumn contributed to the sediment recharge of high-order channels by the deposition of large gravel wedges. This process is recognized as being fundamental for debris-flow occurrence during the subsequent spring and summer. A time shift of scour-and-fill sequences was observed between low- and high-order channels, revealing the discontinuous sediment transfer in the catchment during common flow events. A conceptual model of sediment routing for different event magnitude is proposed.

Mots clés: CHARRIAGE TORRENTIEL; TRANSPORT; SEDIMENT; MANIVAL TORRENT

Domaines: Sciences de l'environnement

J.I. Theule, F. Liébault, A. Loye, D. Laigle, M. Jaboyedoff. Sediment budget monitoring of debris-flow and bedload transport in the Manival Torrent, SE France. Natural Hazards and Earth System Sciences, 2012, 12, p. 731 - p. 749. ⟨10.5194/nhess-12-731-2012⟩. ⟨hal-00737846⟩