OCGC Seminar - Reginald Hermanns

Management of risk from unstable rock slopes in a Norwegian perspective

Dr. Reginald Hermanns 
Geological Survey of Norway 

Prospector on a cliff

Thursday, October 23rd, 2014
1:30 p.m. 

Please note that this lecture is not scheduled in the usual 11:30 timeslot.  

Room 0-23 (video-conference)
560 Rochester Street
Geological Survey of Canada  

Please be advised that this is a video of a lecture being delivered in Sidney, BC, to be streamed live. There will be a question and answer period with the speaker following the presentation. It will be just like being there in person. 

The steep glacially carved valleys and fjords in Norway are prone to many landslide types, i.e. large rockslides, rockfalls, and debris flows. These landslides and their secondary effects (rockslide-triggered displacement waves, landslide dams, lake formation and dam breach) pose a significant hazard to the population living in valleys and along fjord shorelines. The Geological Survey of Norway performs systematic mapping of unstable rock slopes in Norway and has detected more than 230 unstable slopes with significant postglacial deformation that is financed through the Norwegian Water and energy Directorate (NVE).

This large number necessitates prioritisation of follow-up activities, such as more detailed investigations, periodic displacement measurements, continuous monitoring and early-warning. This prioritisation is achieved through a hazard and risk classification system, which has been developed by a panel of international and Norwegian experts. The risk classification system combines a qualitative hazard assessment with a quantitative consequences assessment focusing on potential loss of life. The hazard assessment is based on a series of nine geomorphological, engineering geological and structural criteria, as well as displacement rates, past rock avalanche events and other signs of activity.

The mapping approach for unstable rock slopes is adjusted to this classification system and is iterative starting with simple assessments. However, the higher the hazard/risk level at a site, the larger the amount of geological information collected, and the more detailed the run-out, displacement wave models and consequence analyses will be carried out. This approach allows that mapping resources get focused on sites with higher risk level, delivering products with different levels of detail. Rock slope failures that would not result in any loss of life, , are mapped without a probability assessment. The mapping, however, is important in order to prevent that future development does not increase the risk level.

The method for consequences assessment includes four main modules: 1. computation of the volume of the unstable rock slope; 2. run-out assessment based on the volume-dependent angle of reach (Fahrböschung) or detailed numerical run-out modelling; 3. assessment of possible displacement wave propagation and run-up based on empirical relations or modelling in 2D or 3D; and 4. counting of the number of persons exposed to rock avalanches or displacement waves.

The combination of hazard and consequences analyses leads to a risk assessment within a risk matrix presented in the hazard and risk classification system. High risk sites are  followed up by continuous monitoring using multiple techniques and early warning practices, and potential  permanent evacuations are discussed. This task was carried out by Åknes/Tafjord Beredskap IKS in western Norway and the Nordnorsk Fjellovervåking in northern Norway. These companies will become part of NVE in 2015. Both research and mapping are carried out in collaboration with Norwegian universities through graduate studies projects. This collaboration has developed over two decades in Norway and showcases the importance of collaboration between the public sector, companies and the universities in which key roles such as data storage and collecting and handling of critical data fall into governmental responsibility while resources and knowledge from universities are used.