A man-made canal that once powered a spinning mill. Unused for decades. Until now. Thanks to the renovations carried out by WALO on behalf of the City of Zurich. A project that combines civil engineering, preservation of listed structures and conservation of nature.
1857: A spinning mill, a canal, a city in transition
The Manegg spinning mill in Zurich-Wollishofen was built in 1857 in the Sihl Valley, where hydropower fuelled early industry in the canton of Zurich. The mill canal, an artificial side canal of the Sihl, supplied the energy for the machinery. Although it lost its original purpose after the power station was decommissioned, it was preserved. Between 2016 and 2018, the listed spinning mill building was converted into a modern residential and commercial complex. The canal was then renovated in 2024/2025, which was ecologically upgraded and transformed into a local recreation area for an entire neighbourhood.
Four kilometres, ten structures, one divided neighbourhood
The scope of the project presented significant challenges from the outset. There are ten structures spread out over around four kilometres and separated by a densely populated residential area. Many of these were barely developed. Electricity and water supplies had to be brought in via long pipelines. Added to this were three tunnels dating back to the 19th century, in which up to one metre of mud had accumulated over the decades, covering the channel bottom.
“No two structures are alike. The axis radius of the inlet tunnel continuously changes, the cut-and-cover tunnel follows a slight S-shape and the underwater tunnel runs under busy roads. The project demanded technical adaptability and a willingness to think outside the box,” says Christoph Annen, Project Manager Civil Engineering Zurich.
Precision underground
The inlet tunnel (75 m) and the cut-and-cover tunnel (210 m) were given a new inner shell made of in-situ concrete. The formwork was specially adapted to the varying geometry of the historic structures. Shotcrete was used for the underwater tunnel (250 m) instead of in-situ concrete. The goal was the same for all three tunnels: to strengthen the existing structure in the long term without altering its historic appearance.
“The cut-and-cover tunnel was renovated in 52 stages – all completed to the same standard, even though the geometry was never the same. This requires excellent preparation and a well-coordinated team,” says Sven Eckert, Construction Manager Civil Engineering Zurich.
Benefit for Zurich
Renovating the canal has provided Zurich with another recreational area. A place where water can be heard and experienced once again, right in the centre of an urban neighbourhood. Walkers and families have just as much to be happy about as nature conservation organisations, who see the restored body of water as an ecologically valuable corridor for small animals, insects and aquatic plants. Not to mention, anyone with an interest in industrial history will find a rare example from the days of Switzerland’s spinning era here.
Construction under the gaze of generations
It’s not often that a construction project has to be structurally sound, adhere to the principles of heritage conservation and be environmentally sustainable all at the same time. What’s more: “It encompasses practically every construction discipline: tunnelling, specialist civil engineering, hydraulic engineering, concrete construction. You don’t come across this combination every day,” says Claudio Räss, Construction Manager Civil Engineering Zurich.
At WALO, we call this responsibility that spans generations. The Manegg mill canal is a perfect example of this: a 19th-century structure that was restored to its intended purpose in 2025.
