July 2021 flooding in Europe: lessons learned for better risk prevention


Europe is still reeling from the catastrophic and deadly flooding that occurred in July 2021. From record-breaking rainfall on the heels of an uncharacteristically wet summer to rivers and retention structures at maximum capacity, these exceptional circumstances will serve as a catalyst for future flood risk management measures. 

Record rainfall in Belgium, soil saturation, dam works: a perfect storm 

The extraordinary nature of the events leading to the flooding has been clearly demonstrated. The rains recorded over 48 hours in the eastern townships of Belgium, for example, were the highest in well over 100 years (271.5 mm of precipitation in Jalhay, in the Liège province, from July 13 to 15). Numerous rivers exceeded their warning levels and the water levels at many gauge stations reached unprecedented highs. 

The importance of the affected area is also to be emphasized. While in Wallonia, the Liège area was the most affected, all the southern provinces in Belgium without exception were impacted. Significant damage was also recorded in neighboring countries, particularly in the area bordering the Rhineland in Germany. 

Other factors also compounded the consequences of the overflows. The flooding was preceded by a very wet period, marked by persistent downpours that caused mudslides and soil saturation. This resulted in a reduced storage capacity of certain retention structures. To this must be added the work on certain dams on the Meuse river, which did not allow complete evacuation (the summer period is the ideal time for dam maintenance). 

The surprise was all the greater since the disaster occurred in summer and affected the entire hydrographic network as a whole, causing flooding both on small rivers such as the Orne at Mont Saint Guibert and the river Vesdre in Pepinster, as well as on large rivers like the Meuse in Liège. 

In hydrology, there is no magic solution. It is very difficult, if not physically and economically impossible, to guard against all events. Risk management and resilience vis-à-vis these phenomena must be taken into account. 


The 2021 floods: a benchmark for future modeling studies 

To minimize the impact of future climatic events, measures proposed in flood risk prevention studies supported by extensive modeling work are required by the European Flood Directive and must be updated periodically. The aim of these is to provide administrations with a technical analysis of the risk of flooding and other climatic hazards and objective assistance for land use planning.  

These studies are at the basis of the implementation of infrastructure on the ground: storm basins, temporary immersion areas, dynamic slowing structures, waterway improvements, protection structures, etc. They respond to events for which the flood return period is set according to the issues and the areas to be protected. Here too, it is likely that these criteria will have to be reassessed in light of the recent floods. The operations of the structures, the controlled flooding of less critical infrastructure and the risk assessment for exceptional occurrences will likely have to be considered for future studies. 


Next steps: flood forecasting and hydraulic network management 

The re-evaluation of the hydrology following the July 2021 floods and the associated risk protection measures is a first step which should lead to an increase in the periods of return to protection of urban environments (currently they are between 20 and 100 years). 

In Belgium’s northern region, Flanders has implemented an early warning system based on an operational flood forecasting model called Flood Early Warning System (FEWS) Flanders. This was developed and is maintained by Tractebel company International Marine and Dredging Consultants (IMDC). FEWS collects weather data several times a day and allows flood forecasting over several days. The results and alerts are made available to the public via waterinfo.be. This approach could be compared with the tools currently used in Wallonia, in order to improve the forecasts for future events and better warn the authorities and the population of imminent flooding. 

A third point of reflection lies in better management of the various structures of the hydraulic network. Wallonia is currently in the process of developing a management system for works and waterways, with the help of IMDC, which should make it possible to better anticipate and react to major events such as the floods of July 2021.  

Floods and droughts will intensify with global warming. Our Tractebel experts are constantly striving to help mitigate the risks for our future.   
 

  

 

For more information about this article, you can contact:
Erkan TEKIRDAGLIOGLU – Head of Business Line Water
erkan.tekirdagli@tractebel.engie.com

François FOBEOperations & Performance Director, Business Line Water, Belgium
francois.fobe@tractebel.engie.com
Bernard WERY - Senior Engineer, IMDC
bernard.wery@imdc.be