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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union

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Earth Surf. Dynam., 4, 489-513, 2016
http://www.earth-surf-dynam.net/4/489/2016/
doi:10.5194/esurf-4-489-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
28 Jun 2016
Headwater sediment dynamics in a debris flow catchment constrained by high-resolution topographic surveys
Alexandre Loye1, Michel Jaboyedoff1, Joshua Isaac Theule2, and Frédéric Liébault2 1Risk-group – ISTE – Institute of Earth Sciences, University of Lausanne, Lausanne, Switzerland
2Université Grenoble Alpes, Irstea, UR ETNA, Saint-Martin-d'Hères, France
Abstract. Debris flows have been recognized to be linked to the amounts of material temporarily stored in torrent channels. Hence, sediment supply and storage changes from low-order channels of the Manival catchment, a small tributary valley with an active torrent system located exclusively in sedimentary rocks of the Chartreuse Massif (French Alps), were surveyed periodically for 16 months using terrestrial laser scanning (TLS) to study the coupling between sediment dynamics and torrent responses in terms of debris flow events, which occurred twice during the monitoring period. Sediment transfer in the main torrent was monitored with cross-section surveys. Sediment budgets were generated seasonally using sequential TLS data differencing and morphological extrapolations. Debris production depends strongly on rockfall occurring during the winter–early spring season, following a power law distribution for volumes of rockfall events above 0.1 m3, while hillslope sediment reworking dominates debris recharge in spring and autumn, which shows effective hillslope–channel coupling. The occurrence of both debris flow events that occurred during the monitoring was linked to recharge from previous debris pulses coming from the hillside and from bedload transfer. Headwater debris sources display an ambiguous behaviour in sediment transfer: low geomorphic activity occurred in the production zone, despite rainstorms inducing debris flows in the torrent; still, a general reactivation of sediment transport in headwater channels was observed in autumn without new debris supply, suggesting that the stored debris was not exhausted. The seasonal cycle of sediment yield seems to depend not only on debris supply and runoff (flow capacity) but also on geomorphic conditions that destabilize remnant debris stocks. This study shows that monitoring the changes within a torrent's in-channel storage and its debris supply can improve knowledge on recharge thresholds leading to debris flow.

Citation: Loye, A., Jaboyedoff, M., Theule, J. I., and Liébault, F.: Headwater sediment dynamics in a debris flow catchment constrained by high-resolution topographic surveys, Earth Surf. Dynam., 4, 489-513, doi:10.5194/esurf-4-489-2016, 2016.
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Short summary
The sediment supply and storage changes from major channels of the Manival catchment (French Alps) were surveyed periodically for 16 months to study the coupling between sediment dynamics and torrent responses in terms of debris flow events. The spatial and seasonal variability of sediment delivery is displayed and analysed. This study shows that monitoring the changes within a torrent’s in-channel storage and its debris supply can improve knowledge on recharge thresholds leading to debris flow.
The sediment supply and storage changes from major channels of the Manival catchment (French...
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