Norwegian demands on avalanche safety - legislation, quality policy and judicial practice

Avalanche Workshop, Davos 13-17 May 1990The Building and Planning Act and the Working Environment Act both have demands concerning avalanche safety. The legal demands concerning avalanche safety were first established in the Building Act of 1924. The act was put into force for the whole country in January 1966

A contribution to the prediction of slush avalanches

Symposium on Snow and Ice Processes at the Earth's Surface. Sapporo 1984Slush avalanches, primarily known from uninhabited arctic and mountainous regions, every year cause damage to man and property in Norway. Seeking objective criteria to identify their hazard zones, and methods for their prediction and control, the Norwegian Geotechnical In stitute (NGI) has started a research program on these topics. Thirty-four slush avalanches with known loca tions of crown surface have been investigated with regard to geomorphic and climatic characteristics. Starting zones, crown surfaces and tracks were classified according to geomorphic conditions important to avalanche release and motion. Weak cohesionless snowpacks of coarse grain s, and hard la yers or crusts of ice in snow cover or on the ground, are cr itica l conditions for slush avalanche release. Intense rain, falling on cohesionless new snow on these substrata, is the most striking feature of current weather sit uations. The main starting zones were drainage channels, sloping bogs, depressions and open fields. Channel-like, scar-like or bowl-like features appeared in the snow cover due to avalanche release. Three main types of release were identified: I) Sudden release from crown surface, 2) drainage of snow-emba nked , water-satu rated snowfields through narrow outlets and 3) rapid head ward growth from first point of release. En largements and confinements along Ihe avalanche tracks were caused by distinctly defined features in the tracks

Impact of rapid mass movement and drifting snow on the infrastructure and development of Longyearbyen, Svalbard

The thermal regime and hydrological conditions in arctic regions are a threat and a challenge to human activity. In the Longyearbyen area, Svalbard, snow avalanches, slushflows, debris flows , creep and drifting snow interfere with the location and design of construction works - buildings, roads, ditches, pipes, masts etc., and during winter and spring, popular skiing areas and routes for snowcats can in periods be hazardous. Svalbard Samfunnsdrift AIS has sought professional help from the Norwegian Geotechnical Institute, to evaluate risks and safety measures for existing housing and reduce operational problems caused by drifting snow. Future development will take place in areas which fulfill the safety requirements of the Norwegian Building and Planning Act. A review of problems and recommendations is presented. Limited time-series of relevant meteorological data from Longyearbyen, as weIl as sparse knowledge of the processes influencing mass stability in permafrost areas, have proved to complicate both risk analysis and accomplishment of mitigative measures. Better knowledge of local wind direction and speed are the key to improve the location and design of roads, production areas and buildings with regard to drifting snow. Research projects within these fields of arctic hydrology are proposed.publishedVersio

Slushflow hazard - where, why and when? 25 years of experience with slushflow consulting and research.

Slushflows — flowing mixtures of water and snow — are a major natural hazard in Norway. Knowledge gathered by the Norwegian Geotechnical Institute during 25 years of slushflow consulting and research is presented. The variation in regional occurrence is described and related to climatic premises and ground conditions. The principal ideas about slushflow release, down-slope propagation and run-out are outlined. They are closely related to the rate and duration of water supply, snowpack properties and geomorphic factors. Slushflow release is caused by basal shear failure aided by water pressure to cause loss of basal support and finally tensile failure through the snowpack. Our methods of hazard evaluation and acute hazard prediction and warning are summarized, including the estimation of water supply based on meteorological data. The results of a worldwide questionnaire on slushflows, literature studies and scientific contacts, indicate that slushflows occur in all countries having a seasonal snow cover and that the results of our studies in Norway have a general validity

Prediction of slushflow hazard based on data from local meteorological stations.

Seeking objective criteria for slushflow prediction and warning, meteorological data has been recorded at two slushflow sites in Rana District, North Norway, during a 10 years period. The two starting zones were equipped with standard meteorological devices. In addition, the fluctuation of water level in snowpack was monitored by pressure transmitters. The measurements were performed automatically every ten minutes. Within a distance of 20 km from the slushflow sites there are one standard climatological station and two precipitation stations. One of the main topics of the research project is to evaluate the possibility of using neighbouring meteorological stations in the prediction of current slushflow hazard and slushflow releases. Correlation of in situ measurements with records from the local meteorological stations is the basic input to the evaluation. The analysis has documented that observations at the meteorological stations can be used as a base for predicting slushflow hazard in the Rana District. The temperature and humidity are well correlated in slushflow situations while the wind speed and precipitation measurements had to be adjusted by simple models taking into account topographic characteristics, distance and elevation differences. Generally, the result indicates that slushflow prediction might be based on observations at local meteorological stations if the necessary models for parameter transformation are established

Slushflow hazard prediction and warning

Parameters critical to slushflow release have been studied during 11 winters in Rana, North Norway. Slushflows occurred during 16 periods within the research areas and during another 13 in the district. A noticeable rise of water in snowpack was registered 49 times. Field predictors of acute-hazard and critical water influxes related to different snowpack conditions are identified. Threshold values for acute-hazard prediction based on five main combinations of winter snowpack and current rise of water in snowpack were identified and checked against the registered slushflows, with promising results. Cohesionless new snow and coarse-grained snow are most liable to start flowing. A snowpack reinforced by layers of crust and ice is normally the most stable. An automatic system for supervising slushflow hazard based on the defined criteria is presented. The system can be tailored for any location and problem owner

Slushflow questionnaire

Questionnaires concerning slushflows were distributed globally. The purpose of the questionnaire was to determine the geographic distribution of slushflow activity as well as to collect information concerning most common nomenclature, release conditions, period of occurrence, type of terrain upon which they occur, the characteristics of starting zones, paths and run out zones, geomorphic activity, type of damage and hazard control

Sheet pile walls - a space-saving avalanche defense structure.

Steel sheet piles, primarily used as retaining walls when excavating soft ground and for stabilizing fills, are introduced as flexible components for a variety of effective and space-saving avalanche defense structures. Where ground conditions are favourable sheet piles can be arranged in any actual pattern and may have fixed spacing for any given snow depth and slope-angel. Both catching and deflecting dams and methods of energy dissipation, is presented. The design and layout, and choice of pile profile, dimension and quality of steel, are based on the dimensioning load and actual purpose of the measure. Single and double steel sheet walls and barriers are space-saving and more flexible than alternative mitigative measures of comparable efficiency. They are also much faster and normally cheaper to construct than structures erected by concrete, stonewall, geo-textiles or steel fabrics given the actual ground conditions. Examples applied for protection of rural highways in Iceland are exhibited