The Blue Spot model: A key tool in assessing flood risks for the climate adaptation of national roads and highway systems

Description

The Blue Spots model is a method to identify flood sensitive areas in road networks. A blue spots is defined as a stretch of road where the likelihood of flooding is relatively high and where its consequences are significant. The Blue Spot methodology is applicable to any country if the required data are available.

The method is placed within a Geographical Information System (GIS) environment. The data employed in the Blue Spot analysis are: digital terrain models with hydrological adaptations, climate factors and precipitation statistics, soil morphology information, demography, and traffic loads. These date are combined to identify all blue spots within the network. The model is subdivided into three levels of analysis, with each subsequent level providing a more detailed assessment of the actual flood risk:

·         Level 1: Initial terrain screening of local depressions.

·         Level 2: Precipitation sensitivity analysis in regards of capacity depressions.

·         Level 3: In-depth hydrodynamic model of surface reservoirs and depressions.

The Blue Spot methodology was initially developed by the SWAMP project (see sources), and firstly applied to the Danish Road Network. The Swedish Transport Administration has applied this model to assess TEN-T road sections in Sweden vulnerable to extreme daily precipitation. In the Netherlands, Rijkswaterstaat Centre of Transport and Navigation has initiated the investigation of spots in the Dutch National Highway Network vulnerable to flooding.

·         Danish application: The Danish Road Directorate (DRD) was the first to apply the Blue Spot model. The main aim was to pinpoint sections of the Danish national road network which are particularly vulnerable to an increase in heavy rainfall. The Blue Spot model was not only used to identify existing vulnerablities under current weather conditions, but also to identify new potential blue spots, which could appear in the future, based on IPCC scenarios; therefore, calculations are also made for years 2050 and 2100, on the basis of future climate change scenarios.

·         Swedish application: The Swedish Transport Administration used the knowledge gained in the Blue Spot model, and conducted a pilot study to investigate blue spots in TEN-T road sections in the South of Sweden vulnerable to extreme daily precipitation, and also took future projections on precipitation in 2100 into account.

·         Dutch application: The Centre for Transport and Navigation commissioned Deltares to identify the vulnerable spots due to flooding in the Dutch National Infrastructure Network. They worked together with the Danish Road Institute (DRI) in accompanying this project, as DRI was responsible for the SWAMP project. Apart from blue spot identification, the probability of flooding (current and in 2050) was also assessed. 

Reference information