TIGRA. The integrated geological risk assessment. Hazard zoning methods of snow avalanches, debris flow and rock falls. Final report

Abstract

The present report describes natural hazard zoning methods for snow avalanches in Norway and in some other countries were avalanches are a serious threat to the society. In addition methods for rock-fall and debris slide zoning in Norway are discussed. The main problem in hazard zoning of avalanches and other kind of natural hazards in steep terrain, is the prediction of the runout distance for a given frequency. To day much effort is put into modelling of avalanche dynamics as the physical processes in avalanches and slides are not fully understood. More research and developmentis needed to make the models more precise, and to verify the different models towards Nature. Different kinds of runout models are described in the present report, both empirical/statistical - and dynamical methods. Hazard mapping legalisation, and mapping procedures are described. The countries included in this overview have all developed national regulations concerning avalanche risk levels. The accepted risk levels differs for all of the countries, as the return periods of the design avalanches ranges from about 150 to 5000 years. Hazard zoning in Norway is examplified by a description of a case study in a hazard prone village. The use of a Norwegian GIS system for this purposeis described.