Saalach – River section along the Austrian-German border – Käferhamer weir

As a replacement for an old, partially destroyed weir, a new structure was developed in 1998, consisting of a wooden weir sill and a ramp that is passable for fish.

Current over the blockstone ramp, you can see a water profile laid out with large hydraulic construction stones. A small amount of water flows over it.
© BAW-IWB

The old weir system (wooden box weir) was partially destroyed during a flood and temporarily restored by a rip-rap cover. Further floods led to an increased erosion of the left (Bavarian) river bank and, finally, to the entire destruction of the weir.

Therefore, a complete reconstruction of the weir system was needed to ensure, on the one hand, the stability of the river bed and, on the other hand, the existing rights of water use on the right (Austrian) river side.

Due to the complex situation in the area of the Käferhamer weir (location at the state border, curved river morphology, existing right of water use) a physical model test was needed to assess the hydraulic and ecological requirements as well as legal aspects of the new weir.

Two different solutions were developed and optimized during the physical model test. Finally, the solution combining a wooden weir and a block ramp serving as a fish pass was implemented. The two weir components were separated by an elongated island.

Comparison of the project section in the physical model (left) and in nature during the flood on August 12, 2002 (right). On the left side of the figure you can see an overview of the physical model with the left-banked blockstone ramp, the right-banked wooden box weir made of red plastic material and a central elongated gravel island. On the right side is an aerial photograph of the project section in question during high tide, obtained from a flight. To the left and right of the renovated weir structure, which was overflowed by brown floods, is forest.
© Left picture: BAW-IWB; Picture right: Weinberger

Concerned river stretch in the physical mode (left) and in the nature during the flood 12th August 2002 (right)

Erection of the wooden box weir in nature (foundations), you can see an abundance of wooden piles driven into the ground. Two excavators stand next to them. On them the wooden box weir will be built later. The river was diverted for the construction of the weir. It will be built in the dry.
© BAW-IWB

Construction of the weir sill made of wood (foundations)

Current over the blockstone ramp, you can see a water profile laid out with large hydraulic construction stones. A small amount of water flows over it.
© BAW-IWB

Flow over the block ramp

Flow over the completed wooden box weir, you can see a view from undercurrent on the stepped and overflowed wooden box weir. This fills the entire width of the picture. In the background is dense forest.
© BAW-IWB

Flow over the wooden box weir