RISK VIP: Evaluation of Flood Risk on the French Railway Network Using an Innovative GIS Approach

Abstract

Flooding can have significant direct and indirect negative effects on a railway network affecting both infrastructure and rail operations. Such impacts include the delaying or cancelling of train services, damage to railway structures or the implementation of costly maintenance and monitoring programs to ensure the safety and performance of the railway system. Identifying sections of railway line at risk from flooding allows appropriate actions to be targeted at specific areas and contributes to an effective asset management plan. Flooding of railway infrastructure can have numerous sources including surface water run-off, insufficient capacity of hydraulic structures or the inundation of embankments located in floodplains. Consequences of flooding include the destabilisation of structures (surface erosion of embankments or the undermining of bridge foundations), differential settlement of structures and damage to the track structure. This paper details an innovative approach developed at the SNCF using a Geographic Information System (GIS) model to identify zones of the railway network at risk of different types of flooding. The GIS model RiskVIP has been constructed through the assessment of three distinct components of risk: "Vulnerability" (assessment of the susceptibility of the railway infrastructure to flood conditions), Intensity' (capacity of a catchment to generate a flood flow), Probability' (probability of a rainfall event).Through the application of decision trees, the component 'Intensity' has been characterised in the model by the physical properties of the catchment intercepted by the railway line (surface area of the catchment, slope and land cover characteristics) and "Vulnerability" by the infrastructure itself (type, geometry and the presence of hydraulic structures). In order to evaluate its efficiency at identifying sites at risk of flooding, the model has been tested in the region of Languedoc-Roussillon in France on a reach of over 380km of railway line. In order to characterise the component "probability", data relating to important historic rainfall events have been used in the model against which known incidents on the railway line have been subsequently analysed. Initial results are very positive with a high level of capture of known incidents by the model in relation to the type of flooding recorded. The model RiskVIP allows the evaluation of flood risk to be undertaken at different scales and will aid in targeting precise reaches of railway line to be studied in more detail. It is a tool which can aid in the management of flood risk on the railway network, optimising for example the maintenance program of drainage structures, ensuring monitoring and inspections are targeted at problem reaches, identifying areas where civil works are necessary and improving the overall resilience of the railway system.