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Traffic route construction convinces in hydraulic engineering

Flood protection measures in the Ahr valley

The damage caused by the severe storm in July 2021 continues to be serious and is clearly visible in many places in the Ahr valley. In order to be prepared against future flood events, the federal government, the federal states and the municipalities have begun to set up protective measures in the affected flood areas. Since 16 July 2021, the traffic route construction team from Düren has been in continuous operation to repair the flood damage in the severely affected Ahr valley. Elaborate protective measures are now also part of the task.

Protective measures for a listed railway viaduct © PORR Oevermann

Listed railway viaduct secured from sliding away

On behalf of the NRW state road construction company, Verkehrswegebau secured a listed railway viaduct from 1900 on the B258 near Ahrhütte, which was in danger of sliding away due to undercutting. In addition, road embankments and watercourse drains had to be secured and restored. For this purpose, the team used approx. 2,000 t of armourstones with a dead weight of 1 to 3 t per stone. The first layer of these armourstones was anchored to the rock to prevent the stones from slipping, especially in the embankment area. The heavy armourstones were also to serve as a weighting for the foundations of the viaduct in order to prevent floating.

Construction of an alternating wet zone

In order to protect the viaduct in the event of renewed flooding, an alternating wet zone was constructed using armourstones and backfilled topsoil. The alternating wet zone is only flooded during floods and is thus intended to keep the high water pressure safely away from the structure.

Looking into the darkness: uncertainty at a depth of 6 metres

Probably the greatest challenge of the work carried out was that the course of the stream had been washed out up to 6 metres in places. Step by step, the experts felt their way through the opaque water with the help of the excavator bucket. A safe footing for the excavator had to be created independently. A sorting grab set each stone individually in order to transport the tracked excavator along a safe path to the viaduct. Accurate visual judgement, high precision and flawless quality were the basic requirements.

Flood protection in harmony with nature and water protection

Responsibility for the planning and implementation of the measures was confidently transferred to the traffic route construction experts. From the very beginning, every step was coordinated down to the smallest detail with the lower landscape authority as well as the lower water authority, because both nature conservation and water protection were clearly in the foreground of the flood protection measures. Below the construction site, large bales of straw were placed in the course of the stream as a fine particle filter to maintain water quality and protect fish stocks. In addition, smaller biotopes were left untouched wherever possible to preserve biodiversity. No concrete was used during the entire construction project. Only natural building materials were used, because both Oevermann and the authorities saw a great advantage in the use of heavy armourstones to weigh down and secure the structures: the flow of water was still ensured and the endangerment of settled aquatic life could be ruled out. For this purpose, only machines operated with bio-oil were used to protect nature.

Convinced by high quality - follow-up orders guaranteed

After the contracted services had been largely completed, the NRW state road construction authority announced that further contracts would be awarded to the Düren branch. Oevermann had convinced with high quality and especially in flood protection quality is the basic requirement for a functioning result.


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