ICG project 2: Vulnerability and risk assessment for geohazards. Case studies: Risk associated with avalanches.

This report documents an approach for the probabilistic risk assessment for avalanches. It presents two case studies: 1) A case regarding the risk to a building in an avalanche path: 2) A study concerningtherisk to traffic on a major mountain road. Estimates of hazard, vulnerability and risk are given. The methodology adopted in the present case study refers to the general risk terminology from ICG (2004). The report summarizes vulnerability values due to avalanche impacts retrieved from the literature. In the first case study of a farm in an avalanche path, a combination of empirical meteorological data (extreme snow precipitation data), a slide release model, and a runout model employing Monte-Carlo simulations in both cases are used to quantify hazard and risk. The second case study considers traffic along a road stretch in avalanche-prone area and reveals high risk to individuals. A comparison between the risk with and without å mitigation measure (i.e. with and without a protection gallery) shows the beneficial effect of the mitigation measure. However, waiting traffic increase significantly the risk, which implies that after an avalanche event immediate action is needed to avoid waiting traffic. The case studies illustrate the methods, but do not claim to be generally valid. A main challenge for the proposed methodsis the choice of realistic distribution functions and their parameters. Not enough knowledge is available on this subject. To fill those gaps, expert judgment needs to be applied, more data should be gathered, and more research should be carried out. Deterministic models support the probabilistic approach for the choice of parameters.Norges Forskningsråd (NFR

The use of a numerical snow-drift model as a decision making tool in the planning of avalanche protection measures.

Blowing and' drifting snow is not only a major factor in the assessment of the acute avalanche danger, its contribution to the snow distribution also influences land-use planning. In many parts of alpine terrain end an ge red areas are secured by expensive avalanche protection measures. The effidency of these measures can be affected by the redistribution of snow due to wind. Numerical snow-drift simulation could providc useful information at the planning state of protection measure to increase their effidency and so to reduce costs

Avalanche studies and model validation in Europe, SATSIE. Ryggfonn measurements. Winter 2002 / 2003 and 2003 / 2004

This report presents data collected from the full-scale Ryggfonn project during the Winters 2002/2003 and 2003/2004. The weather and snow conditions described and when possible, the avalanches have been characterized according to the IAHS avalanche code and the deposit boundaries have been mapped. Measurements obtained from the avalanche path include pressure readings from two load cells at a steel tower, as well as avalanche pressure on three load cells fixed to a concrete structure. In addition, normal stress and shear stress were measured on two locations at a 16 high dam. Six geophones, placed on the ground in the runout zone, have detected vibrations from some of the passing avalanches. When possible, for each avalanche the front speeds have been estimated. The estimates are based on continuous-cave Doppler radar measurements, seismic measurements, and the timing between impacts on the constructions.The measurements obtained are briefly discussed and presented in graphs.European Commissio

Cross-comparison of Selected Avalanche Observations

In many mountainous regions, snow avalanches are severe threats to the population and their infrastructure. Delineation of avalanche endangered areas or the design of suffcient mitigation measures require in-depth understanding on the avalanche phenomenon. Measurements and observation constitute the basis for this understanding

CPT 3 – Quantitative risk assessment: Remarks on the uncertainty in the delimitation of hazard zones based on historical observations

The Norwegian building code regulates the societal acceptable risk from avalanches for three building classes (S1, S1, and S3). The corresponding highest allowed nominal annual probabilities of avalanches reaching the building for these classes are set as 1/100, 1/1000 and 1/5000 respectively (TEK17, 2017). That is, avalanches should not reach a building, or the accompanying outdoor area and cause (considerable) damage more often than the building class permits. These hazard classes are used for delineation of avalanche hazard zones for land use planning (TEK17, 2017). For the assessment of the quantitative risk of avalanches reaching existing settlements only limited methods are available. Thus, historical observations can be of special importance, as they may be direct indicators for the real hazard in the area of interest. To a certain degree, they can also provide an indication of a possible change of hazard over time due to environmental changes. However, historical observations are affected by inherent uncertainties and many questions remain open. Here, we aim to combine results from several work packages to develop a more consistent method of using historical observations that may help improve quantitative hazard assessments and evaluation of the uncertainties involved.NVE (Norges vassdrags- og energidirektorat

Exploring the significance of the fluidized flow regime for avalanche hazard mapping.

Observational and experimental evidence suggests that it is important to explicitly account for the fluidized flow regime in avalanche hazard mapping due to its high mobility, intermediate density and high velocity. We explore the differences from conventional runout modelling by implementing an extension of the Norem–Irgens–Schieldrop (NIS) rheology in a simple mass-point model. When the dispersive stresses and the excess pore pressure equal the overburden pressure, the flow height increases and the density diminishes until a new equilibrium is reached, determined by the different density dependencies of the two parameters of the dispersive stresses. Fluidization requires sufficiently steep terrain; when it occurs it leads to substantially higher velocities than compared to the dense-flow regime. The model parameters are strongly constrained by their physical meaning and vary little between widely different avalanches. However, in all test cases we obtained better agreement between simulated and observed runout distances and pressure effects than with conventional models

WP 2 – Full-scale experiments at Ryggfonn Ryggfonn avalanche observations 2019/2020

NGI is operating the avalanche test site at Ryggfonn in Stryn municipality, Vestland county, western Norway (61.969°N, 7.275°E) since early 1980s. In addition to the field work and data collection in frame work of WP2, necessary repairs and updating of the data acquisition system at the Ryggfonn avalanche test site were carried out under this task. This is to ensure that the site is ready for the winter season 2020/2021.NVE (Norges vassdrags- og energidirektorat

The influence of drifting snow on the location of glaciers on western Spitsbergen, Svalbard

On western Spitsbergen, Svalbard, the amount of winter precipitation is insufficient to maintain the present-day mass balance of the local glaciers. Additional snow mass must be added to the precipitation to reach the observed accumulation rates of the glaciers. It was assumed in previous work that this additional mass is transported onto the glaciers by drifting snow and snow avalanches. This study is a first attempt to quantify the amount of snow mass added to the glacier mass balance by wind-transported snow. The wind field over an area of 60 × 50 km2 on western Spitsbergen was simulated for 24 idealized weather types by a mesoscale meteorological model on a 750 m grid. The resulting wind velocities and directions were coupled to a two-level snowdrift model. The model output clearly shows erosion and accumulation areas in the terrain. Comparison with the present glacier locations suggests that the glacier accumulation areas coincide with low wind speeds. Moreover, exposed areas with high wind speeds are mostly glacier-free in reality. Thus, the wind field and corresponding snowdrift gives an indication of the location of the present glaciers on western Spitsbergen