With a construction period until 2026, the spillway tunnel with inlet and outlet structure is the largest component of the entire Sarneraa Valley flood protection project. The tunnel runs along the right-hand side of the Sarneraa valley from the Seehof area in Sachseln (inlet structure) to just below the Wichelsee dam in Alpnach (outlet structure). There it flows into the Sarneraa.
Another milestone in the Sarneraa flood safety project has now been reached. After the first milestone - the breakthrough of the tunnel - was passed almost exactly two years ago, on 15 March 2023, the intake gate has now been installed at the intake structure and an emergency control system has been put into operation. With this combination of work from the disciplines of structural hydraulic engineering, hydraulic steel construction, electrical engineering and control technology, the water from Lake Sarnen can now be diverted under the village of Sarnen in the event of a flood more than a year before the final commissioning of the entire system. Although the construction site at the outlet structure would be affected in the event of flooding, the canton of Obwalden considers it appropriate to accept this damage to the construction site on the basis of a damage potential analysis in order to prevent the valley from being flooded as it was in 2005.
