The screws at Landquart – 2

Continuing the series, just across the outlet mall in Landquart there is a pumping station that is open to the air but protected by a fence:

Interestingly, there is a small creek just behind this installation, but the screws go down much, much lower (probably a good 15 m) lower than the level of the river:

Things like this really confuse me. It smelled a bit like sewage, so I assume it was somehow for dealing with sewage water. But only one of the huge screws was turning, and in fact the tiniest one.  Does it receive a higher volume in the rain? Does it pump more than just sewer water? Sadly, these things are never documented anywhere that the public can easily read about them!