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Marquardt S.,ETH Zurich | Marquardt S.,Swiss Federal Institute for Snow and Avalanche Research SLF | Alzerreca H.,Higher University of San Andres | Hillmann E.,ETH Zurich | And 3 more authors.
Cuban Journal of Agricultural Science | Year: 2010

In the present study, habitat use and activity pattern of cattle grazing unattended and unrestricted in subtropical mountain forests were assessed. The study was conducted at study sites (Meringal: M and Rio Tarija: RT) during the dry season and the following prehumid season in southern Bolivia. Adult Criollo cows (n=15) with or without calves were observed from May to July (period P1, n=19 days) and August to November (period P2, n=17 days) in 6-minute interval samplings between 8 am and 4 pm. for their activity (grazing/browsing, resting, walking and other activities) in two different habitats (forest vs. riverside). The time spent grazing in the forests declined from Pl to P2 (M: 54% to 18%, P〈0.01; RT: 31% to 25%, not significant), while resting at theriverbanks increased (M: 3% to 74%, P<0.001; RT: 43% to 65%, not significant; in P1 and P2, respectively). As major driving forces for these changes in activity pattern and habitat use in the two seasons, climatic factors and protection against flying insects are discussed. The results illustrate the ability of Criollo cattle in adapting to a demanding environment and changing conditions, and show the importance of river- and lakesides in such unattended transhumance systems. Source


Hussin H.Y.,CNR Institute of Neuroscience | Quan Luna B.,Norwegian Geotechnical Institute | Van Westen C.J.,University of Twente | Christen M.,Swiss Federal Institute for Snow and Avalanche Research SLF | And 2 more authors.
Natural Hazards and Earth System Science | Year: 2012

The occurrence of debris flows has been recorded for more than a century in the European Alps, accounting for the risk to settlements and other human infrastructure that have led to death, building damage and traffic disruptions. One of the difficulties in the quantitative hazard assessment of debris flows is estimating the run-out behavior, which includes the run-out distance and the related hazard intensities like the height and velocity of a debris flow. In addition, as observed in the French Alps, the process of entrainment of material during the run-out can be 10-50 times in volume with respect to the initially mobilized mass triggered at the source area. The entrainment process is evidently an important factor that can further determine the magnitude and intensity of debris flows. Research on numerical modeling of debris flow entrainment is still ongoing and involves some difficulties. This is partly due to our lack of knowledge of the actual process of the uptake and incorporation of material and due the effect of entrainment on the final behavior of a debris flow. Therefore, it is important to model the effects of this key erosional process on the formation of run-outs and related intensities. In this study we analyzed a debris flow with high entrainment rates that occurred in 2003 at the Faucon catchment in the Barcelonnette Basin (Southern French Alps). The historic event was back-analyzed using the Voellmy rheology and an entrainment model imbedded in the RAMMS 2-D numerical modeling software. A sensitivity analysis of the rheological and entrainment parameters was carried out and the effects of modeling with entrainment on the debris flow run-out, height and velocity were assessed. © Author(s) 2012. Source


Kogelnig A.,University of Natural Resources and Life Sciences, Vienna | Surinach E.,University of Barcelona | Vilajosana I.,Worldsensing | Hubl J.,University of Natural Resources and Life Sciences, Vienna | And 3 more authors.
Natural Hazards and Earth System Science | Year: 2011

The paper analyses and compares infrasonic and seismic data from snow avalanches monitored at the Vallée de la Sionne test site in Switzerland from 2009 to 2010. Using a combination of seismic and infrasound sensors, it is possible not only to detect a snow avalanche but also to distinguish between the different flow regimes and to analyse duration, average speed (for sections of the avalanche path) and avalanche size. Different sensitiveness of the seismic and infrasound sensors to the avalanche regimes is shown. Furthermore, the high amplitudes observed in the infrasound signal for one avalanche were modelled assuming that the suspension layer of the avalanche acts as a moving turbulent sound source. Our results show reproducibility for similar avalanches on the same avalanche path. © 2011 Author(s). Source


Fischer K.,Matrisk GmbH | Schubert M.,Matrisk GmbH | Schaer M.,Swiss Federal Institute for Snow and Avalanche Research SLF | Margreth S.,Swiss Federal Institute for Snow and Avalanche Research SLF | Schellenberg K.,Tiefbauamt Graubunden
IABSE Conference, Geneva 2015: Structural Engineering: Providing Solutions to Global Challenges - Report | Year: 2015

When planning maintenance and repair actions, the owners of existing structures are often faced with the problem that the structure cannot be verified any more with the current design codes. The expected costs of retrofitting can be significant, which raises the question whether investments are proportionate or whether a lower reliability level can be accepted for a particular structure. The present paper shows how target reliabilities can be defined based on risk and efficiency considerations and how design values for loads and/or resistances can be derived from this design target. The focus is on avalanche loads on protection galleries, for which no standard probabilistic models exist. The derivation of probabilistic load distributions from scenarios and return periods estimated by experts is discussed. The methods are applied to a real structure in the Swiss Alps, illustrating the benefits of the risk-based, probabilistic approach. Source


Vilajosana I.,Worldsensing | Vilajosana I.,University of Barcelona | Llosa J.,Applied Technology Internet | Schaefer M.,Swiss Federal Institute for Snow and Avalanche Research SLF | And 2 more authors.
Cold Regions Science and Technology | Year: 2011

Specially designed wireless accelerometers units were used in a series of experiments at the snow chute operated by the SLF at Weissflühjoch (Switzerland) during 2008-2009 winter. The purpose of the experiment was to evaluate the best design and the performance of these innovative instruments to provide information on the internal dynamics of flowing snow. The wireless accelerometers were placed in the snow chute starting zone prior to the experiments and traveled within the flow when the avalanche was released. The characteristics of the units (size and density) allow them to evolve like active particle tracers. Acceleration measurements obtained at 85. Hz in the different experiments were analyzed. The analysis methods used include Empirical Mode Decomposition and Kalman filtering techniques. The developed methodologies were used to obtain reliable speed and position values from the single 2D acceleration measurements. The obtained results were compared to independent speed and position measurements. The results show to be in agreement with that obtained from independent speed measurements from optoelectronic sensor arrays and video images and open a new perspective for future avalanche research. The extracted information could provide valuable data related to internal dynamics of the avalanche. Small-scale chutes are the ideal scenario to test these new technologies. Moreover, we consider these sites essential to develop and test new instrumentation (to be deployed), in the future, in full-scale experiments. In addition, the experiments performed show for the first time the potential of the wireless technologies and wireless sensors to study snow avalanches. © 2010 Elsevier B.V. Source

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