Swiss Federal Institute for Forest, Snow and Landscape Research WSL

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Edition: Mon 20.4., 17:00
Avalanche Bulletin

Dangerous mud: debris flows

We research debris flows by observing the flow properties of naturally-occurring debris flows mainly at the Illgraben field site. Observations include flow depth, basal forces, and velocity. Special measurement campaigns focus on measuring additional flow properties and to test novel sensors.

A debris flow is more powerful than a flood with sediment and can cause a correspondingly high amount of damage. (Image: WSL)
A debris flow is more powerful than a flood with sediment and can cause a correspondingly high amount of damage. (Image: WSL)


Understanding processes through field observation

In 2013, the Bielzug near Herbriggen, Gde. St. Niklaus (VS) was very active. The simulations with RAMMS::DEBRISFLOW showed potential flow and break out paths for a larger volumne. (GIF: WSL)
In 2013, the Bielzug near Herbriggen, Gde. St. Niklaus (VS) was very active. The simulations with RAMMS::DEBRISFLOW showed potential flow and break out paths for a larger volumne. (GIF: WSL)

We have installed several debris flow stations in the Swiss Alps which provide us with unique data sets to enhance our understanding of triggering and flow processes. Additionally, they provide an opportunity to test numerical models of debris-flow behavior for use in practical applications and to provide a basis for developing and testing new debris-flow early-warning systems.

A debris-flow monitoring station is currently in operation at Illgraben. Other stations were operated previously at Dorfbach (Randa), Schipfenbach (Preonzo), and Riasc (Olivone).

Debris flows at Illgraben occur several times a year, making the site useful for research. WSL has installed instrumentation in the catchment and along the channel to allow measurement of flow depth, flow velocity, mass density. The data serve as a basis to better understand the debris flow process, with special measurement campaigns to measure e.g. channel-bed erosion, the flow speed on top and bottom surfaces of the flow, and the generation and speed of individual surges within debris-flow events.

Thanks to the geological structure of Illgraben, several of these events occur each year, which makes it an ideal place to study debris flows. (Photo: Christoph Graf, WSL)
Thanks to the unique geology of Illgraben, several debris flows occur every year, making is a suitable location to study debris flows. Photo: Christoph Graf/WSL
When it rains, the yellowish loose rock material mixes with water and becomes a slushy mass that slides into the valley as a debris flow. It also carries larger pieces of rock. (Photo: Christoph Graf, WSL)
Rapid erosion of sediment from highly-fractured bedrock on steep hillslopes results in several debris flows every year mainly following intense rainfall. Photo: Christoph Graf/WSL

Laboratory Experiments

At WSL’s laboratory we study aspects of debris-flow behavior or test the performance of sensors when we have a specific research question requiring laboratory precision, e.g. Rickenmann et al., 2019 https://www.dora.lib4ri.ch/wsl/islandora/object/wsl%3A21073

The debris flow laboratory at the WSL offers the possibility to investigate debris flows at a small scale. This allows scientists to study, for example, flow behavior for various natural materials, investigate debris flow impact, explore the erosion process, and test instruments before deployment in the field. The channel is also used to illustrate the debris flow process for visitors.

Runout Modelling

The group has also contributed to the development and testing of models used to poredict the runout and erosion resulting from debris flows, mainly using the RAMMS model. In 2024 RAMMS was transformed into a spinoff company, RAMMS AG, although RAMMS continues to be used by WSL staff for teaching, consulting, as well as research (e.g. Bolliger et al., 2024 https://www.dora.lib4ri.ch/wsl/item/wsl:36479.

Applications

The results from our research expand on the knowledge of the complex and still insufficiently known phenomena of debris flows. The combination of experience with field observation, numerical modelling, and laboratory experiments can also contribute to improve methods and procedures used to assess natural hazards and assess the performance of protective measures. 

Since 2000, the WSL has been observing naturally-occurring debris flows at the Illgraben, an exceptionally active catchment located near the village of Susten (Leuk), in Canton Valais. The observation station is equipped with both standard and unique instrumentation, intended to provide information to help improve our understanding of the debris-flow process. Collaborators from many universities both within Switzerland and abroad use data from the Illgraben along with new observations to gain a better understanding of debris flows and their formation. See https://www.wsl.ch/illgraben

Short video about WSL research in the Illgraben (Gottardo Pestalozzi, WSL)

Contact

Publications

Projects

WSL strategic initiative: Climate Change Impacts on Alpine Mass Movements (CCAMM) 

Past projects: