Work is under way on the concrete canal on the Sihl-Lake Zurich flood relief tunnel.
The canal is being constructed in a 12m-deep excavation pit on the edge of the Swiss lake. Preparations involved pumps working for three days to remove more than 13 million litres of water from the pit.
The canal, which will channel extreme flood peaks in the Sihl River into the lake, is the last major construction stage of the relief tunnel.
Marti Tunnel AG broke through on the bored flood relief tunnel in November 2024.
The 6.6m-diameter, 2km-long tunnel is designed to protect the city of Zurich and the lower Sihl valley from flooding by diverting the Sihl River into Lake Zurich during heavy rain.
The relief tunnel is scheduled to come into operation next year.
