Hazard and risk assessment for early phase road planning in Norway

Road construction in rugged terrain and variable, partly harsh climate is challenging. Proper assessment of natural hazards at an early planning stage can give large cost savings and safer roads. In assessing natural hazards along 720 km of planned roads in Norway, a GIS-based tool was developed to utilize publicly available data and dynamic runout models. The output is an outline of the most critical locations and serves to limit the extent of necessary field work. The Norwegian national susceptibility maps are generally conservative and using only these in the planning would give unrealistically high hazard levels. Various optimizing techniques were therefore implemented in the GIS tool and the outputs further calibrated against existing detailed hazard maps in selected locations and further validated during field work at the defined 'hotspots'. The field work comprised assessing return periods of unwanted events, probable road closure time, and relevant mitigation measures, all within sets of pre-defined ranges of values. The following consequence evaluation quantified the indirect economic consequences of closed road and assessed the consequence for emergency preparedness qualitatively. Other consequences were not considered in the study. Climate change was considered and evaluated to affect the probability for flooding and debris flows, whereas the link between climate change and the other assessed hazards was considered too uncertain to impact on the risk estimates. Results of the study were communicated through an interactive map solution, with key results presented as fact sheets activated in the map for each risk section of the roads.