All posts by Benjamin Rudaz

Field camp in Barcelonnette (French Alps)

Barcelonnette2014groupStudents from Geosciences (UNIL) and Geology (UNIL-UNIGE) master programs attended the Slope Instability Field Camp from June 1st to June 7th 2014.
On the menu, a close examination of the La Vallette landslide, a big slope instability in the heights of the Ubaye Valley, above the municipality of Barcelonnette, and a visit to the famous Riou Bourdoux, a torrent on which the torrential mitigation techniques were pioneered in the XIXth century.
Field mapping of cracks, bulges, water presence, as well as LiDAR acquisitions were carried out on the La Vallette site. The goal was to assess the general behaviour and volume of the moving mass, its geological and structural context, and to elaborate its hazard potential for the human settlements. Field data was combined with existing data (aerial photographs, existing DEMs, published litterature) and with numerical methods (Coltop 3D, SLBL, GIS tools) each evening.

A big thank you to our hosts at the Séolane center for the wonderful stay and to our guides on the field, Georges Guiter (ONF-RTM) and Alexandre Mathieu (Univ. Strasbourg).

Erosion monitoring – Project Roubinette is operational

The Institute of Earth Sciences is monitoring erosion dynamics in a study site in Draix (SE France), in cooperation with several other research groups, as part of Benjamin Rudaz’ PhD project, and in continuation of previous studies (A. Loye, P. Béchet, J. Duc).

This region is characterized by black marls outcrops, wheathered and eroded by the alpine mediterranean climate, resulting in a pluricentimetric annual erosion rate, which can be quantified and observed through high-resolution LiDAR-acquired DTMs. LiDAR campaigns began in 2007 for the Roubine catchment (~1400 m2), and thanks to a research grant from the Herbette Foundation, it will continue and develop on the Roubinette, a first-order gully of 140 m2 situated right by the Roubine.

The goals of this new research is to increase the precision when comparing LiDAR scans, by removing the vegetation, scanning from a higher position and combining LiDAR and photogrammetric methods.

Higher scanning position has been achieved with a 4 meters steel-beam tower, on top of which sits the LiDAR pad. This allows the scanner to view nearly 100% of the incised terrain. Also perched on the tower are 2 Harbotronics time-lapse packages, taking high-quality digital photograph every hour during the day. Their separation, as with human eyes, will allow 3D reconstruction of the terrain, on an hourly basis. This will complement LiDAR scans, which can be only done every few months. Finally, the setup is accompanied by a meteorological station, soil humidity sensors, and a concrete sediment catch which captures the outgoing water and sediments.

The installation was finalized during a field trip in march 2014, and is thus now fully operational. Stay tuned for future exciting results!


Pièce jointeRoubinette tower from catchment summit

Lauren Gavillet: Dynamique d’érosion et étude de stabilité d’un petit bassin versant alpin: le cas du Courset (VD, Switzerland)

Lauren Gavillet
Supervisor: Prof. Michel Jayboyedoff
Internal Experts: MSc. Pierrick Nicolet, MSc. Benjamin Rudaz
External Expert: Marcel Burri

The landslide triggered on August 26, 2005 by a heavy rain event, in the watershed of the Courset is the origin of this master thesis. To determine if this event was exceptional or if we can expect an intensification of erosion processes, the activity of the watershed is analyzed through its dynamic erosion and through analysis of the stability of slopes.

To collect interesting and useful informations on the watershed, a history of developments and events that have affected the watershed of the Courset is established. Geotechnical analyzes are performed to characterize the soils of the watershed. These results are then used to model the stability of slopes. Rainfalls in the region are also analyzed to be used in this modeling.

After a description of the watershed dynamics, longitudinal profiles and their knickpoints are identified in order to locate areas of the profiles that will be affected by erosion. The erosion potential of the entire watershed is also estimated. Past erosion is studied in light of the observed current activity.

A synthesis of the controversial quaternary filling hypothesis of the Lavey-Le Châtel glacial trough is established, and a new reconstitution is proposed.

Fête de la Science 2012 – Digne-les-bains

The “Fête de la Science” is a science popularization event, organized yearly by the french Ministry of High Education and Research, resulting in many “scientific villages” popping up in city squares. A team of CRET researchers was present in Digne-les-Bains, in south-eastern France, 13-14th of October 2012.

The link between CRET and this region comes from research conducted in Draix (15 km from Digne-les-Bains) on black marls erosion monitoring using LiDAR scanning. This project is one of many active in a “GIS” (Groupement d’Intérêt Scientifique), with 15 research groups implicated (mostly from France) around the study of erosion through many fields, from hydrology to pedology and biology.

The team presented the LiDAR instruments used in thoses studies, as well as a landslide simulation sandbox. Over 200 people came over the two days to ask questions, or to tell a story of their own regarding natural hazards or erosion in the region.