The Horlachgraben is part of a former arm of the Main River and serves as a receiving watercourse for stormwater from the sewer system. This channel has no natural inflow and is divided into 13 basins. In 2024, only the first three basins were treated. Basin 1 is 1,013 meters long and 25 meters wide. Basin 2 is divided into two sections, each approximately 180 meters long; one is 19 meters wide, the other 7 meters wide. Basin 3 is 1,020 meters long and also 25 meters wide. Th