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

Abstract

Abstract. 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.

Methods for detecting channel bed surface changes in a mountain torrent – experiences from the Dorfbach torrent

“…CS are suitable for selective point-based and rough channelwide analysis. Several types of instruments are applied to determine the cross sectional geometry, including tape measures, levelling boards and levels (Stock and Dietrich, 2006), slope profilers (Santi et al, 2008), theodolites and total stations (Theule et al, 2012) or terrestrial laser scanners (TLS) (Wasklewicz and Hattanji, 2009). In areas with deep water, echo sounding combined with a geo-referencing system are suitable.…”

“…Breien et al (2008) based their cross section calculations on photogrammetric and light detection and ranging (LiDAR) data. In various studies, selective cross-sectional measurements are interpolated to estimate the debris yield of a channel section or to calculate erosion volumes (Theule et al, 2012) and lag rates .…”

“…Moreover, in the last few years, an amplification of debrisflow activity in the Alps is increasingly related to climate change or to general environmental changes (Harris et al, 2009;Keiler et al, 2010;Sattler et al, 2011). Consequently, improving the physical-based understanding of debris-flow processes is needed to integrate these insights into modelling approaches and comprehensive risk management (Jakob and Hungr, 2005;van Westen et al, 2006;Deubelbeiss and Graf, 2013). Erosion and deposition of channel bed material by debris flows are important aspects of the process dynamic (Iverson, 2004).…”

Comparative analysis of the differences between using LiDAR and contour-based DEMs for hydrological modeling of runoff generating debris flows in the Dolomites

“…These local, intense, convective rainfalls (Underwood et al, submitted) produce abundant runoffs at the feet of rocky headwater walls that are able to entrain large quantities of sediments and debris flows. Runoffgenerated debris flows, initially observed in laboratory facilities (Gregoretti, 2000a,b;Tognacca et al, 2000), are common both in the Alpine region (Berti and Simoni, 2005;Gregoretti and Dalla Fontana, 2008;Theule et al, 2012;Tiranti and Deangeli, 2015) and in other mountainous regions such as the Pyrenees (Hurlimann et al, 2014), Japan Alps (Imaizumi et al, 2006;Okano et al, 2012), Colorado and California (Cannon et al, 2008;Coe et al, 2008;Kean et al, 2012). The routing of debris flow in settled areas can cause damage and casualties.…”

Perceived risks of mountain landslides in Italy: stated choices for subjective risk reductions

“…Italy (Gregoretti and Dalla Fontana, 2008), as well as in the French Alps (Theule et al 2012) These problems are common in parts of Italy, the country providing the data and focus for this paper. 53…”