Analyses of risk from natural hazards for early planning of new highways in Norway

On contract from a newly established road company in Norway, Nye Veier AS, a consortium of natural scientists and social scientists have carried out an early planning stage risk analysis from natural hazards for a series of new roads in Norway. An aim of the study was to establish methods and tools that the client could use relatively easily in their own premises and that could serve as a useful tool in design of the roads, including final selection of the route.

Firstly, a GIS-based tool was developed to perform a first screening of corridors around the proposed road. Hazards analysed included snow avalanches, rock falls, debris flows- and slides, landslides in sensitive ('quick') clays, floods, storm surges, strong winds and snow drift. In this phase we mainly used susceptibility maps and other data available on the internet. However, some of these are very conservative, and various methods of optimization have been performed in the analyses. After ground truthing of selected results of the GIS analyses, by field work, and by comparing with hazard maps based on previous field work, the GIS tool was installed in the client's premises and is currently being used by them.

Secondly, field work was carried out based on the results from the GIS screening. Identified higher-hazard segments were inspected, and key parameters, such as probability, length of closure in case of an event, type and cost of mitigation measure, and suggestions for potential re-routing were recorded in the field. Some of the hazard segments identified by the GIS analyses could also be called off from the field work. Results from the field work were standardized to the degree possible, e.g. in cost classes for mitigation measures, duration classes for closure time, etc.

Consequence and risk analyses were carried out based on the results of the combined GIS screening and field work. The consequences were estimated in two classes; a) Indirect Economic Consequence of a closed road, based on traffic density and type, the probable duration of closure, and the re-routing possibilities, and b) the consequences regarding emergency actions, i.e. the location of critical infrastructure (hospitals, fire stations, etc.) and the possibility for emergency vehicles to pass.

Climate change was considered mostly for the hazards that are directly connected to precipitation. For these a 'climate factor' was added based on the regional scenarios for 2100.

To ensure optimal communication of results to the client, the main delivery is a digital, GIS-based product. Hazard, consequence, and risk are marked in colours along the planned roads. By clicking on individual hazard segments, a comprehensive fact sheet appears with all available information, comments and numbers collected through the whole process. This includes also field comments, and a risk diagram, where also the estimated risk at year 2100 is indicated.

The work has been done in close interaction with the client, to ensure the most readily usable tool for them in present and future road projects.