Flood protection in the Ahr valley: “Engineering skills are required here”


interview

Status: 08.08.2021 6:51 p.m.

After the heavy rain catastrophe, the Ahr valley will not stay as it was. In an interview with, the biologist Wolfgang Büchs explains what has to change so that people can continue to live on the river tagesschau.de.

tagesschau.de: In 2020, the State Office for the Environment in Rhineland-Palatinate published the last of three studies on the Ahr Valley that you were involved in. What is special about the area?

Wolfgang Büchs: The valley fascinated me because of its diversity: In addition to sun-exposed wine-growing areas with a sub-Mediterranean character, there is a short distance between continental, Atlantic and boreal climatic influences. The study recorded more than 4,300 animal species, mostly insects, and around 1,200 plant species.

To person

The biologist Wolfgang Büchs teaches as a visiting professor at the University of Hildesheim. He was one of the main authors of a three-volume monograph on the Ahr Valley, which was published on behalf of the State Office for the Environment in Rhineland-Palatinate. The volumes appeared in 1993, 2003 and 2020. Büchs was born in Bonn. As a student he participated in the biotope mapping of the Ahr valley.

tagesschau.de: What went through your head when you heard about the heavy rain catastrophe?

Rifle: I was amazed that such a catastrophic event could still happen there today. At the same time, I am astonished that appropriate flood protection measures have not been taken, although they have been in discussion for 100 years, because for centuries catastrophic floods have occurred every 100 years. In the 1920s, the already very specific plans were postponed in favor of building the Nürburgring. These include measures such as flood retention basins, which could have held back a total of 11.3 million cubic meters of water.

tagesschau.de: Why weren’t they built?

Rifle: The Nürburgring was very important for the structurally weak region back then. But why were the plans for flood protection no longer taken up in the period that followed? I don’t have a correct explanation for it. There is a very large nature conservation project on the upper Ahr that began in 2007 and is financed by the Federal Agency for Nature Conservation. Many good measures have been planned here, except that flood protection has not really been taken into account. The Ahr has been given more space in many areas of the upper reaches. So-called “sturgeon stones” were placed in the mouth areas of the tributaries and bank plantings were carried out, which ensure greater dynamism and flow diversity. The meadow areas were also enlarged. Nevertheless – based on the disaster of 1910 – the concrete calculations for the required flood protection are missing. In June 2016 there was another significant flood: That would have been a warning signal for me.

In my opinion, other nature conservation measures were rather counterproductive, such as the removal of small weirs in order to create permeability for fish and the entire aquatic fauna, which can also be reached via fish ladders. This increased the flow rate. The forestry interventions are also very important. Spruce cultures have been and are being cut down on a large scale. In the case of heavy rain, this promotes the drainage of the water. This is a huge problem, not just in the Eifel. The forest plays a crucial role. We need a natural mixed forest with tree species suitable for the location, such as red beech, oak or ash on the slopes, as well as black alder, poplar and willow in the floodplains.

High concrete walls instead of small terraces

tagesschau.de: In your opinion, who should have acted?

Rifle: The nature conservation project is the responsibility of the state and, of course, the federal government, which is funding this with twelve million euros. This entire project must now be redesigned under the primacy of “flood protection” as possible in accordance with nature conservation. It has to be extended to all tributaries of the Ahr. That will not cost twelve million, but maybe 200 million.

tagesschau.de: Can people live directly on the Ahr again in the future?

Rifle: That has to be calculated. In view of climate change, we must expect such heavy rain and floods to occur in shorter succession than before. You can only continue to live on the Ahr if protection from floods can be guaranteed. But there will be changes: For example, near Altenahr-Altenburg, a former oxbow lake extends around a rock. The area has been continuously settled and built over since the 1960s. In addition, the standards that are applied to the flood hazard maps of the country must be reconsidered. Because according to these maps, the residents of this place would have gotten wet feet in the event of an extreme flood, which statistically is only supposed to occur every 200 years. The houses there were now under water up to the skylight.

Nor should it happen that commercial enterprises are built in the Talaue that seal large areas. You also have to take countermeasures when it comes to viticulture. For example, the area between Rech and Dernau was reorganized in the 1970s – an ecological catastrophe par excellence. Very steep, large terraces have been created with very high, concrete walls. Steep drainage channels were created to drain the water away. The rows of vines are cultivated in the direction of the slope and the undergrowth in the vineyards is partly removed with herbicides. Countermeasures must be taken here. Originally, the Ahr was known for its small dry-stone terraces. These are much flatter and more graduated. This leads to a significantly slower water drainage.

Settlement is still possible under changed conditions

tagesschau.de: Does that mean that people can live on the Ahr if you use the appropriate money and know-how?

Rifle: Yes, in any case. This is possible with appropriate measures. The Ahr valley is beautiful. People don’t want to lose their home. However, the entire catalog of flood-reducing measures has to be implemented consistently. This applies to agriculture as well as the construction of paths and roads. We need less sealing and paths made of permeable materials. Every tree by the water helps to reduce the flow rate. The installation of drainage shafts, Riegrol cisterns or rainwater storage tanks that can be integrated into the streets is also helpful.

tagesschau.de: What are the most urgent steps now?

Rifle: First of all, the disaster has to be investigated and dealt with. You have to analyze where the heavy rain occurred, how did it come about that such a massive tidal wave was able to build up that even the gauge at Altenahr was torn down at 5.72 meters and, according to calculations, at seven meters – some even say nine meters – landed. You always have to assume that it can go beyond the current “worst case” in the future. Based on this, you have to plan the flood protection.

The key is to get the flood peaks of the Ahr tributaries under control so that they do not overlap and then accumulate into a very high tidal wave. We need an intelligent flood management system. That is a task, engineering skill is required here. The reporting system also needs to be improved. It wasn’t a sheet of fame either, what was delivered there. There were certainly flood scenarios. But they were evidently insufficient and good enough. So now we have to examine everything and draw the conclusion that such disasters will not happen again.

The interview was conducted by Iris Völlnagel, SWR.



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