Development of a screening method to assess flood risk on Danish national roads and highway systems

摘要

A method to assess flood risk on Danish national roads in a large area in the middle and southernnpart of Jutland, Denmark, was developed for the Danish Road Directorate. Flood risk has gainednrenewed focus due to the climate changes in recent years and extreme rain events are expected tonbecome more frequent in the future. The assessment was primarily based on a digital terrain modeln(DTM) covering 7,500 km2nin a 1.6 × 1.6 m grid. The high-resolution terrain model was chosen in ordernto get an accurate estimation of the potential flooding in the road area and in the immediate vicinity,nbut also put a high requirement on the methods, hardware and software applied. The outcome of thenanalysis was detailed maps (as GIS layers) illustrating the location of depressions with depths,nsurface area and volume data for each depression. Furthermore, preferential flow paths, catchmentnboundaries and ranking of each depression were calculated. The ranking was based on volume ofndepressions compared with upstream catchment and a sensitivity analysis of the runoff coefficient.nFinally, a method for assessing flood risk at a more advanced level (hydrodynamic simulation ofnsurface and drainage) was developed and used on a specific blue spot as an example. The case studynshows that upstream catchment, depressions, drainage system, and use of hydrodynamicncalculations have a great influence on the result. Upstream catchments can contribute greatly to thenflooding.