Flooded river Sihl should flow into Lake Zurich
A relief tunnel between Langnau am Albis and Thalwil is intended to direct the floodwaters of the Sihl into Lake Zurich. The ground-breaking ceremony for the project took place on March 18th. The construction work for the underground tunnel, which is around 2 kilometers long, is scheduled to be completed in 2026.
From 2026, extreme flood peaks in the Sihl are to be channeled into Lake Zurich via a relief tunnel, according to a statement from the Canton of Zurich ‘s building department. For this purpose, a 2 km long underground tunnel with a diameter of 6.6 m is planned between Langnau am Albis and Thalwil. The start of construction for the project took place on March 18th with the groundbreaking ceremony.
Extreme flooding of the Sihl could cause severe flooding in the lower Sihl valley and in the city of Zurich, the statement said. The possible damage for the city of Zurich alone is estimated at up to 6.7 billion Swiss francs. They should be averted by the relief tunnel.
The costs for the planning and construction of the tunnel as well as for the ecological replacement measures on the Sihl and on Lake Zurich are estimated at around 175 million francs. They are largely borne by the canton of Zurich. In addition, the federal government, the city of Zurich, the SBB and the Sihltal Zurich Uetliberg Bahn SZU AG share in the costs. The Canton of Zurich is making further information on the project available on the internet .