Field and monitoring data of debris-flow events in the Swiss Alps

Abstract

Debris flow is a common process in the Swiss Alps and in other mountainous parts of the world. The understanding of debris-flow behaviour is essential to assess the hazards they present. An important approach towards improving the knowledge of debris-flow processes is the gathering of real-time data by debris-flow observation stations. Observation stations were established in three Swiss debris flow prone watersheds and equipped with video cameras, ultrasonic devices, a radar device, geophones, and rain gauges. In 2000, four significant debris flows were observed. The data provided useful information on the mechanics of debris flows and on the efficiency of the measuring devices. The observed debris flows are characterized by volumes between 5 000 and 35 000 m3, front velocities ranging from 2 to 5 m/s, and peak discharges between 20 and 125 m3/s. The analysis of the monitoring data revealed that ultrasonic and radar devices are very helpful tools, whereas the quality of the geophone signal strongly depends on the substrate on which the instrument is installed (i.e., bedrock versus unconsolidated material). Video images are useful to verify the data obtained by the other devices. A dynamic analysis of one debris flow was carried out and the simulated results are in fair agreement with the observed data.Key words: debris flow, Swiss Alps, monitoring, dynamic analysis.

Tree-Ring Reconstruction of Debris-Flow Events Leading to Overbank Sedimentation on the Illgraben Cone (Valais Alps, Switzerland)

“…This is why the number of reconstructed events might appear quite small as compared to other torrents analyzed with tree-ring analyses in the Valais Alps [17][18][19][20][21][22]. Since the beginning of the systematic debris-flow observation in the Illgraben torrent in the year 2000 [32,33] It is also obvious from the reconstruction that debris-flow surges did not leave the canyon and affect trees located on the cone itself since the 1950s, when several debris flows left GD in trees located on its western part in 1951, 1953, 1955 and 1957. This is also the moment of last activity in the currently abandoned channel which is bifurcating from the present-day canyon at ~720 m a.s.l.…”

“…As a consequence, a ~50 m high retention dam has been built in the departure zone as well as 21 check dams constructed in the canyon on the cone between 1967 and 1969 so as to retain the rockslide deposits in the middle reaches of the torrent and to prevent the release of large debris flows [31]. By the early 1980s, however, the retention dam was completely filled and could no longer prevent the release of new debris flows in the Illgraben torrent [32].…”

The dam-break problem for Herschel–Bulkley viscoplastic fluids down steep flumes

“…For the body, the leading-order terms of the governing equations are obtained by removing the contributions that depend on ε in Eqs. (19) and (20). As readily seen in the momentum equations, the bulk of the flow is in a nearly steady regime, where gravity acceleration is counterbalanced by the cross-stream gradient of the shear stress.…”

“…While small-scale laboratory experiments clearly demonstrated the potential of viscoplastic models to describe the behavior of fine mud and clay dispersions (e.g., kaolin, bentonite) [3,[13][14][15][16], large-scale indoor and outdoor experiments carried out with poorly sorted materials have shown a more contrasted and complex behavior: the flow properties depend a great deal on the flow organization, i.e., the existence of lateral levees, a front rich in coarse materials, segregation, as well as entrainment/deposition processes [9,17,18]. Field data and comparison with historical events have not settled this controversial issue [19][20][21][22][23] since traces left by debris flows could be interpreted using viscoplastic theory, whereas other clues argue in favor of a Coulomb behavior. The same difficulties arise in the rheology of lava, with an additional degree of complexity induced by temperature and phase changes [6,[24][25][26][27].…”

Exploiting LSPIV to assess debris-flow velocities in the field

“…Typical monitoring stations consist of geophones, ultrasonic sensors (or radar), and video cameras which satisfy the basic measurements of velocity, height, discharge, and visual validation. Some catchments also present multiple stations distributed throughout the debris-flow channel and some located in headwater channels (Berti et al, 2000;Marchi et al, 2002;Hürlimann et al, 2003;McCoy et al, 2010;Arattano et al, 2012;Navratil et al, 2013;Comiti et al, 2014).…”