In 1908 a larger sewage association, in the ruhrarea, acquired land along the river to regulate it. This feeds itself from three springs in the south of the city.
In 1911 the river was then partially canalized at three points and placed underground. For more than a hundred years, it was used for the sewer discharge of the city and a steelworks, until it was completely renatured in 2018. Today only groundwater flows through the tunnels. The actual river has been branched off in the first section since the renaturation and feeds the new main collection sewer.
There is also a branch, in dilapidated condition, which is the oldest part of the city's sewer system. Built by a steelwork in 1889 and was also connected to their service tunnels. The river also connected, underground, two of the separate parts of the steelwork.

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Kick ass drain/sewer, tons of shape changes. Thanks for sharing. I imagine some of the brick portions photographed are part of the 1889 construction?