They cannot be seen and yet the sewers deep beneath Hamburg are part of the city's important infrastructure. Every renovation is complex but necessary, as a current example shows. A visit deep down into Hamburg's sewage highway.
Hamburg Wasser has been preparing for the renovation of the large drains in the city center for years, testing techniques and materials to make the sewage pipes under the Hanseatic city, which are up to 4.70 meters wide, ready for the next decades. In many other places in the city, the municipal company is also enabling the wastewater infrastructure to withstand the challenges of the future.
There will probably be decades in which not only the amount of wastewater will increase due to more residents, but in which the city will also have to reckon with heavy rain events that will increasingly push the current sewer system to its capacity limits – and beyond.
Last week, the residents of Hausbruch in the south of the Hanseatic city experienced what happens when the city's underground veins cannot function as usual. It wasn't the sewers there, but a pumping station that was also part of the sewage system, which caused problems. Because there was major damage to the Süderebmarsch pumping station, the wastewater could not flow further north towards the sewage treatment plant. The dirty water built up and the drains overflowed. There were road closures and basement damage.
The fecal water stood at the Neuwiedenthaler Strasse underpass for several days. Until the middle of this week, experts checked whether the bridge structure had been damaged as a result. Sulfuric acid forms in the wastewater after a short time, which can severely damage concrete.
Photos from another sewer in the Hanseatic city show what what is technically called biogenic sulfuric acid corrosion looks like. In the southeast of the city, the wastewater is led to the Bergedorf secondary collector. Like the main drains in the inner city, the secondary collector is considered a large profile and is part of the backbone of wastewater disposal. The Bergedorfer Siel transports the feces of around 300,000 people towards the sewage treatment plant. Built in 1975, the first major renovation is currently underway.
As a construction engineer, Enrico Brandt is in charge of construction supervision for the project at Hamburg Wasser. In the construction container above the current construction phase, he shows photos that were taken during an inspection of the tubes. “The wastewater has a certain aggressiveness towards concrete,” says Brandt. Where it seeps into the concrete and where the sewage gases rise, the concrete becomes soft if it is not specifically protected against it.
Even a layperson can see that the concrete looks significantly different in the pictures. The gray has become a pale yellow-white, and the structure of the affected areas is more reminiscent of a loosely whipped mousse than of compressed concrete. Because the wastewater is so aggressive, Brandt explains, the concrete pipes that come into direct contact with the water are protected by other materials. PVC was primarily used in the Bergedorf underground. In other parts of the city, where a network of 6,000 kilometers of sewage pipes has gradually been built since 1842, other protective materials were used, such as epoxy resin.
Welds are a problem
“We are satisfied with the PVC coating,” says Brandt. The problem with the collector in Bergedorf arose in the shafts that are not protected with foil – and where the foils are welded together. “There is the damage.” And it is now being renovated – during ongoing operations. Wearing protective gear with a gas detector and oxygen cartridge for emergencies, you go down into the wastewater. The shafts are six meters deep. A rather short journey for the experienced wastewater and construction technician Brandt. In Altona, for example, the sewers are up to 21 meters underground.
Standing knee-deep in the sewage, only the headlamps illuminate the loudly rushing broth. Only the construction site itself has been drained. The company SMG from Lage in East Westphalia has developed a special technology that makes it possible to carry out the necessary repair work with running water and still keep the work area free of wastewater. The relevant construction section is cordoned off using bulkheads. The wastewater is carried through the construction site via pipes.
But the amenities end with dry feet. Because electricity is not allowed to be installed near water, the men work almost exclusively with the light from their head lamps. There are no electrical cables on the construction site. Nor for the hydraulic presses that the workers use to tension the metal sleeves that are necessary to repair the 50-year-old weld seams. This has to be done by hand. Approximately every three meters, the old interfaces of the film are reinforced with metal sleeves and new PVC rings.
A new sleeve is just coming in through the shaft. Everything on the construction site is designed to be brought down through the 60 centimeter wide shaft. And so, on its way down, the cuff is a long, curved metal beam that has to be lowered with great skill into the underground and only there becomes a ring. The men from SMG work their way 1200 meters through the Hamburg underground. 315 sleeves are stretched into the pipes. Minor damage to the PVC coating caused by driftwood, stones or other objects in the water is glued with glass fiber reinforced plastic.
Renovation only in 50 years
The damage was noticed during routine checks a few years ago. Since then, they have been monitored and the remediation plan has been developed. The shafts have already been renovated, now it's time for the concrete pipe. “This is not an emergency measure,” says Brandt – and it is not one that will be completed quickly. “We will be busy with this for the next seven years.” The new cuffs should then last a long time in the sewer. “We actually don’t want to go back there for 50 years,” says Brandt.
Hamburg Wasser will invest around one billion euros in wastewater disposal from 2023 to 2027. The renovation of the central pumping station on Hafenstrasse is expected to cost around 110 million euros. A failure of the pumping station like in Hausbruch would have much faster and more significant consequences in the central location of the city, where wastewater and rainwater are collected together.
A further three-digit million sum will be invested in the renovation of the main sewers in the city center. From October 2025, a 1.1 kilometer section of the 6.6 kilometer long Kuhmühlenstammsiel will initially be renovated. Like a total of 250 kilometers of Hamburg's sewers, it is still bricked up and largely in the same condition as it was in the 19th century.
The sluice will be renovated by installing new, smaller pipe elements. With this type of storage, called pipe lining, the pipes are put together along their entire length with sleeves when they are underground. The cavity created after the pipe-in-pipe system was inserted is then filled. The renovation work is expected to be completed at the end of 2027. Another main sewer – affectionately known as the “old giant” by Hamburg Wasser – that is being renovated is the Geest main sewer. 2.5 of the total 4.5 kilometers are to be renewed between 2026 and 2028. As with the Kuhmühlenstammsiels, the pipe lining process is used.
Repairs are made pipe by pipe
But so that the sluices can actually become a construction site, Hamburg Wasser has had two large new sluices built in recent years – the Isebek transport sluice and the Wallring transport sluice. They lie below the old sluices and will absorb their water while the “old giants” are being renovated.
Afterwards, however, they remain as additional storage. Such capacities are needed to minimize flooding, especially during heavy rain. The two sluices can hold 9,000 cubic meters, as much as 30,000 rain tons. Amounts that are not sufficient to replace concepts of a sponge city with many natural seepage areas. But capacities that help prevent worse things from happening.
Editor Julia Witte called Vedder works in the Hamburg editorial team of WELT and WELT AM SONNTAG. She has been reporting on since 2011 Hamburg. One of her focuses is the city's public infrastructure.
