Flooding on the Ahr, Swist and Erft rivers Smaller rivers and streams were not in view so far
Bonn · In flood protection, smaller rivers have not been (in) the focus so far. That has to change, experts say. As should the risk perception of local residents. The consequences are serious.
Alongside the storm surge in Hamburg in 1962, the Elbe floods of 2002 and 2013 are generally regarded as catastrophic flood events that have burned themselves into the collective consciousness. From a future perspective, the current floods in the Ahr Valley, the Voreifel, the Bergisches Land and the Eifel will also fall into a similar category in terms of the number of victims, the amount of damage and the extent of the devastation - except that this time it was hardly larger rivers that burst their banks, but smaller bodies of water such as the Ahr, Swist or Erft. Flood protection and flood risk management have so far focused primarily on large rivers such as the Rhine, Elbe and Weser. Behavioral plans exist for their flooding, and scenarios are played out.
"The risk potential of small rivers will have to be reassessed," says Holger Schüttrumpf, professor of hydraulic engineering and water management at the RWTH Aachen University. "That goes all the way to the question of whether it's even possible to live in certain areas." Small bodies of water are definitely on the radar, Schüttrumpf says: "The only question is whether that also applies to those affected." It's not a matter of assigning blame. After all, the fact that the houses in the cities with their narrow valleys are mostly grouped along the river is historically so, says the scientist.
People have been settling along rivers for centuries, living and working there, using the water. "Today we have to ask ourselves whether this is still in keeping with the times, whether we don't need larger open spaces instead of building up everything," says Schüttrumpf. In doing so, the Dutch provide the model of what flood protection is all about, among other things: giving the river space. Says Schüttrumpf, "But in the low mountain places, that's exactly the kind of space that's missing for waterways."
So in certain areas now affected, he says, it will be necessary to consider whether it makes sense to stick with existing structures or try to find a compromise. Flood protection always reaches its limits when it comes to extreme cases, he said. "We can handle smaller and medium flood events quite well," says Schüttrumpf, "that works. However, we will never be able to completely control catastrophic floods." This is often not technically possible and does not necessarily make economic sense; the more protection is expanded, the more money has to be spent. Nevertheless, there is always a residual risk because the next flood could be higher than the last one.
Schüttrumpf: "In addition, it must be taken into account that we are permanently in a conflict of different, sometimes opposing interests. We want to live and work somewhere, we need nature, agriculture, forests. That makes it complicated to implement flood protection as deemed necessary."
For the SPD parliamentary group in the state parliament, it is clear that after this catastrophe, the water bodies must be subjected to more examination and better adapted to heavy rainfall. It is undisputed that rivers and streams that have plenty of space and follow a natural course are better equipped to withstand heavy rain than canalized streams and rivers, he said. "Their connection to former floodplains, their interconnection with groundwater, and new floodplains also make the watercourses safer," said deputy parliamentary group chairman André Stinka. Therefore, building on these areas should be avoided. "At the same time, we must increasingly support the municipalities and river associations in their renaturation measures.“
That something absolutely must be done is a broad consensus across party and state lines. For example, NRW Environment Minister Ursula Heinen-Esser (CDU) explained that it is now necessary to analyze in detail how municipalities can prepare even better for such extreme events. Concepts for adapting to climate change or integrated climate protection and adaptation concepts already exist in many places; in addition, climate precautions must play a central role in planning procedures.
The NRW Greens see the main element of preventive flood protection as being a significant increase in water storage in settlement areas and in the open countryside in order to slow down runoff. The environmental spokesman Norwich Rüße said that unsealing surfaces, green roofs and the creation of large flood areas, so-called retention areas, and the consistent protection of open spaces could be important building blocks in this regard.
Already after the flood events of 2013, Schüttrumpf and 15 other professors from the chairs of hydraulic engineering and engineering hydrology drafted a resolution on flood protection. The goal was to draw attention to the complexity of the problem situation, to point out possibilities for improvement and to appeal to those in positions of responsibility to make use of the existing expertise at the universities. "However, this requires the awareness that flood protection is not a task that recurs from time to time, but is part of the provision of public services in large areas of our country," the resolution states.
In the view of the scientists, the situation has improved only to a limited extent since then. There are many approaches to improving precautions in such cases. According to Schüttrumpf, for example, the use of risk warnings in advance, where many things could have been done more effectively and more precisely. "The alarm must not be spread too widely, but must reach those who are affected," he says. With the help of rain radar systems and the use of artificial intelligence, much could be optimized in this regard. In addition, preventive flood protection measures would have to be implemented consistently. "You can't compromise on that," says Schüttrumpf. "How are you supposed to explain to the affected citizens after the fact that a dike wasn't built, for example?“
It would also be good if more people were insured against such damage, if that is possible, he adds. Flood hazards and risk maps would show whether you live in a region at risk, the expert said. "Of course, we're talking about rare scenarios," Schüttrumpf says, "and it's just human nature to say, 'This won't affect me.'" However, the probability of this happening is increasing enormously, water managers, as well as meteorologists and climate researchers, agree. Flood protection is a permanent task, says Schüttrumpf: "It shouldn't only be on the agenda when we have floods."
Original text: Jörg Isringhaus and Christian Schwerdtfeger
Translation: Mareike Graepel