Risk assessment for rail freight traffic using the example of river floods | Umweltbundesamt

Flooding caused financial damages of millions of euros in Germany in the last years. In early 2013 Regions in Southern and Eastern Germany were affected by momentous floods which damages are estimated to be about 12 billion Euros stated by the MunichRE. Solely 2,4 Mrd. Euro were insured. Partially, flooding caused serious traffic disruption with interruptions of passenger and freight traffic. Particularly affected was the rail link between North and West Germany and Berlin, which mainly serves on the high-speed line Hannover-Berlin.

As a result of the flood of the Elbe, the strategically important bridge near Hämerten (Saxony-Anhalt) had to be closed in June 2013. Although the bridge was not damaged by the flood itself, the regular rail service resumed only about five months later due to the flooding of the surrounding section. Traffic had to be diverted and trains were cancelled. Due to these reasons the Deutsche Bahn needed to set up a replacement timetable.
Emergences of floods are caused by a series of meteorological factors. These include the emergence and trend of weather conditions, rain intensity, spatial and temporal rainfall distribution as well as the spread of rain events. However, the extent of the damage caused by river floods is not only dependent on the intensity and distribution of extreme rainfall or moisture penetration of the catchment area due to pre-rain, but is also influenced by anthropogenic factors. In particular, factors such as the sealing of the surrounding landscape and the expansion of settlement areas into the floodplains have indirect influence. In addition, soil structure, processing and vegetation play an essential role. A degraded vegetation cover, saturated soil structure or impermeability and thus limited absorption and retention capacity of the soil can contribute to rapid and uncontrolled surface runoff. If river valleys are still characterized by steep slopes, the risk of flash floods is particularly high. However, flash floods are not dealt within this publication. As a result of local floods, landslides and mudflows can also be used, which further increase the damage potential for the traffic infrastructure and other structures.

Usually for river floods, mudflows or landslides local phenomena occur. Exemplarily relevant dangers or hazard processes for affected structures (eg bridges) affect their use. These include, for example, stoppages (pressure build-up and stress on the structure due to the accumulation of large quantities of loose material), impacts (collision of loose material with bridge whippers or superstructures) or softening, d. H. the "stiffness loss" of surrounding soils as a result of prolonged periods of heavy water exposure.

Since river floods are very likely to be directly influenced by the expected climatic changes, in particular the more frequent occurrence of rainy low-pressure areas over Central Europe in winter, it is estimated that doubling will occur by the end of the 21st century until tripling of the river floods is possible compared to today's occurrence of such events. If this happens, the negative consequences for the transport sector and other socio-technical sectors will also increase.

Goal of the project is for estimate the risk for rail freight traffic in Germany considering flood hazards. As input data traffic demand data as well as the Transport Stream Visualisation Model (TraViMo), created by the BBSR and Geographic Information Systems are used. Information is being added to existing analyses in which the climate impacts or dangers often solely relate to the transport infrastructure, but not to their actual use.

Potential impacts of river floods on rail freight traffic are estimated by comparing the river flood risk faced by districts and cities in the year 2030 with the predicted traffic importance of these areas during the same period. For the traffic importance the indicator "traffic performance" is used. At the same time, traffic infrastructural and logistic transport flows are addressed which form a conceptual link between rail infrastructures in the districts and their actual use. In addition, the transport performance of one region outstrips its two-dimensional connection function more than the other two indicators.

In rail freight transport, the risk assessment identifies a sub area of the transport system whose specific vulnerability to the dangers of climate change must be estimated to be higher than, for example, road traffic. Although the responsiveness of the (German) rail sector to weather-related damage is generally considered to be high, the comparably coarse network makes it difficult, for example, to redirect freight demand in the short term.

Although changing to other routes during track interruptions is not impossible but exemplarily the blockage of the Rhine Valley at Rastatt in the summer of 2017 has shown that the use of parallel infrastructure such as the route through Alsace or the Gäubahn between Stuttgart and Singen is limited due to alternating international approval standards, capacity restrictions, ongoing remedial measures of redundant routes is restricted.

Due to economic and technical necessities as well as the historically grown infrastructure, rail corridors with partly high intensity of use by passenger and freight traffic often run in the valleys of large rivers. Thus, the infrastructure is often located in close proximity to or even in the middle of potential flood plains of rivers. In Germany, this is the case in the valleys of many large and small rivers, for example along the Rhine and the rivers Danube, Elbe and Weser.

In extreme flooding event following infrastructure elements can be affected:

• Track (subsoil and substructure, superstructure and overhead lines)
• bridges and tunnels
• Signal Box
• (train station-) Building
• Transhipment facilities such as transhipment terminals or combined transport terminals (KLV)
• substations

These facilities and machinery usually have a high financial value and are essential for the smooth operation of rail transport. However, railway operations are dependent not only on the functioning of the railway infrastructure itself, but on the interplay of a number of public and private actors directly involved in transport, such as railway undertakings or train safety. In addition, there is a strong dependency on the functionality of other infrastructure and service sectors such as external power supply or telecommunications, which complicates the coordination of possible emergency and preparedness and adaptation measures against risks as a whole and contributes to a higher systemic vulnerability of the transport mode rail. Finally, (structural) measures to reduce the vulnerability or to adapt the system to climate change are often focused on strategically important network sections and new construction measures for economic reasons. However, it cannot be ruled out that the functionality of the overall rail system in the event of a disaster is dependant on the vulnerability of subordinate infrastructure elements or sections of the existing network that have not been taken into account by the infrastructure manager or if they require a different approach.

Methodology used to estimate the sensitivity of regional transport system  towards flood hazards due to aggregated metrics were following:

• Usage of traffic demand data and Transport Stream Visualization Model (TraViMo) by the BBSR and Geographic Information Systems
• Sensitivity of traffic system with importance for counties and county-level cities for the rail freight traffic: Operationalizing with the help of rail freight infrastructure and transport flows data
•  Relative extent of regional flood risk (potential floodplain) is related to traffic importance: 3 indicators with importance for traffic: Level of traffic structural facilities in counties and cities based on track length in km in respective district; Freight traffic in tonnes, length of the rail route in a room in tonne-kilometers
• Estimation for the year 2030
• Risk assessment by comparison of river flood risk and traffic significance

Rail freight traffic is impacted differently by flood hazard depending on the Region. Results of the analysis show that not all counties and cities with high river flood risk are counties and cities with a large traffic importance are. However, it also shows that river floods in some very significant parts of Germany can lead to major disruptions of rail freight traffic, the effects of which would significantly exceed the directly affected areas. These and other regions threatened by river floods along the major river systems Elbe, Weser, Rhine and Danube will continue to perform important logistics, connection and transit functions in the railway sector in the near future. The effects of temporary disruptions of rail links in these regions will also have impacts in other regions of Germany because of the diverse traffic links.

It should be noted that a potentially strong climate impact, ie the combination of high spatial exposure and sensitivity, indicates that it should be verified in the affected regions whether sufficient measures have already been implemented or planned to adapt the transport infrastructure to possible flood events.