Numerical models Water flow modelling of a steep slope HillVi Weiler and McDonnell, 2004,

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HazRi – Natural Hazards & Risks Triggering of Rapid Mass Movements in Steep Terrain (TRAMM) Christophe Ancey, Environmental Hydraulics Lab, EPF Lausanne; Perry Bartelt, Avalanches, Debris and Rock Fall, Swiss Federal Research Institute WSL; Lyesse Laloui, Soil Mechanics Laboratory, EPF Lausanne; Dani Or, Laboratory of Soil and Environmental Physics, EPF Lausanne; Jürg Schweizer, Snow and Permafrost Research, Swiss Federal Research Institute WSL; Sarah Springman, Institute for Geotechnical Engineering, ETH Zürich; Manfred Stähli, Mountain Hydrology and Torrents, Swiss Federal Research Institute WSL, Laurent Tacher, Engineering and Environmental Geology Laboratory, EPF Lausanne Contact: Manfred Stähli, Swiss Federal Research Institute WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland, +41 44 739 24 72, manfred.staehli@wsl.ch www.cces.ethz.ch/projects/TRAMM • The project in short • This project aims at enhancing understanding of triggering and initiation mechanisms, including the transition from slow to fast mass movement processes, and flow characteristics of shallow landslides, debris flows and snow avalanches. A primary focus is on the roles of heterogeneity and criticality of hydro-mechanical hill-slope processes. Formulation of a framework that capitalizes on similarities between the different hydrologically-driven mass movements will be a key-outcome of that project. • Innovation • - Synergies within the field of hazardous rapid mass movements are exploited. • General theories and models of release and mass flow are further developed for landslides, debris flows and snow avalanches • Multi-purpose platform enhancing scientific collaboration among the disciplines involved and promoting practical and academic educational missions related to rapid mass-release hazards. sequence of research questions and tasks and their links to overall project goals of TRAMM • Field studies • Wiler (Lötschental, VS): landslide experiment • Comprehensive characterization and soil hydrological measurements in a steep hillslope prone to landslides. • Impact of vegetation (roots) on hillslope stability. • Accoustic sensors in the soil to indicate upcomng failure. • Artificial triggering of the slope by means of irrigation. • Tössegg (canton Zürich): landslide experiment • Three years in-situ data on soil moisture, soil suction and lateral runoff along the steep meadow hillslope. • Suction-controlled direct shear tests on saturated and unsaturated samples. • Combined 2-d hydrological and stability simulation with the models VADOSE/W and SLOPE/W (commercial software). • Sprinkling experiment to determine dominant flow paths. • Illgraben (canton Valais): debris flow study site • Long-term observatory of debris flows • Determination of the relative importance of in-channel and near-channel initiation mechanisms • Direct measurement of debris flow entrainment correlated with instrumentation such as shear forces and water content. • Vertical wall outfitted with force sensors and geophones measuring the vertical velocity profile and near-instantaneous lateral and shear forces of debris flows. • Vallé-de-la-Sionne (canton Valais): snow avalanche site • Study of the dynamic behaviour of dense-flow and powder-snow avalanches and of the impact forces along their path • Simultaneous velocity, pressure and flow height measurements in combination with photogrammetric and videogrammetric measurements. • Fiber optical creep sensors planned to identify the role of visco-elastic deformations near the transition to rapid motion. • Wannengrat (Davos): snow avalanche site • Characterization of the snow layering using high-resolution penetrometry. • The slope will be fully equipped by an array of acoustic sensors detecting the breaking of snow bonds. • Modelling of the snow avalanche release with a Self-organized criticality model. Numerical models Water flow modelling of a steep slope HillVi Weiler and McDonnell, 2004, Journal of Hydrology, 285: 3-18. Conceptualizing the water balance in a spatially explicit manner at the hillslope scale. Self-organized criticality Hergarten, S. 2002: Self-Organized Criticality in earth systems. Springer Verlag Berlin Heidelberg New York. Hill-slope represented using a two- dimensional hexagonal grid having a water- or snow dependent mass and soil and root dependent bonds. A failure of bonds redistributes the mass to the neighbouring cells. Deterministic hydro-mechanical modelling Modelling the flow of geophysical fluids 1) Extension of a Navier-Stokes solver based on finite-volume level-set techniques. 2) Flow-depth averaged models (finite-volume scheme) applied to irregular topographies. Modeling framework: RAMMS (www.wsl.ch/forschung/forschungsprojekte/rapid_mass_movements) based on second-order solutions of the shallow water equations and on GIS input/output features. To date, the RAMMS modules include a 2D flow avalanche-dynamics model with entrainment and a 2D 2-phase debris flow model with entrainment (in testing). Simulation of the lateral soil water flow during a rainstorm in October 2004 along the Tössegg-hillslope using HillVi.