| Grabenbach | |
| Mouth Coordinates: | 47.7538°N 12.91°W |
| Subdivision Type1: | Country |
| Subdivision Type2: | States |
Grabenbach is a small river located in Bavaria, Germany.
The Grabenbach is a tributary of the Saalach. It is about long. For the first the river flows in an underground channel under the city of Bad Reichenhall. The deepest part of it flows below the surface.
thumb|Course of streams and Grabenbach in Bad Reichenhall around 1900. The red squares are places where hydropower was used, e.g. mills.
The tunnel was built after plans of Erasmus Grasser from about 1524 to 1538. After the route has been determined in 1522, the construction was started in 1524 under the direction of master builder Fabian Zehentner and the supervision of the Salzmaier (supervisor of the saline) Hans Humbs. The tunnel was dug from north to south, towards the higher saline. Therefore, with progressing work one had to dug deeper and deeper; a gradient of had to be compensated. During length, the canal was walled high and wide, vaulted and then filled with soil again. In 1534, the well shaft was reached and in 1538 the construction work was finished.
The Grabenbach begins in the old saline and reaches the surface again near the street Gewerkenstraße. On the nearly long line, there are five air shafts. Then it flows for another through the Marzoller Au to the Saalach. At the Kurstraße street, one of the shafts was renovated. Through a glass plate one now can see the Grabenbach flowing in the deep. The river is passable by boat, at irregular intervals guided tours through the tunnel are offered for small groups.
The Grabenbach leads intruding fresh water and water driving the wheels out of the galleries, so that it does not mix with the salty water. Today a part of the water is used for a water-treading basin in the pedestrian zone. Additionally, there are pipes in the canal that carry the brine to the graduation tower and the spa pump room. Also, rainwater of the pedestrian zone is led into the Grabenbach.