Sihl Valley

The area alongside Lake Zürich had been formed as the left moraine of the Ice Age glacier, the bed of which is now the Lake Zürich and the valley of the Sihl. Sihl valley is extensively wooded, but also cultivated and heavily populated in its lower parts. The Sihl (German pronunciation: [ˈsiːl]) is the name of a 68 km (42 mi) long river located in the cantons of Schwyz (SZ) and Zürich (ZH). The valley compromises parts of the districts of Einsiedeln (SZ) (upper Sihl valley), Horgen (ZH) and Zürich. The region of the valley comprises about 250 km² (97 sq mi).

Sihl rises at Drusberg near Hoch-Ybrig in the canton of Schwyz, passes the 8.5 km (5.3 mi) long Sihlsee near Einsiedeln, Sunnegg near Biberbrugg and Schindellegi.

Now it enters the canton of Zurich, nearby Samstagern passing Hütten and the rapid called Sihlsprung situated in Schönenberg, flowing through the valley between the Zimmerberg and Albis chains. Near Sihlbrugg, the rivers passes the Sihlwald,[1] the largest remaining deciduous forest of the Swiss Plateau, located between Sihlbrugg and Zürich-Leimbach. The Sihl flows in Zürich underneath Zürich Hauptbahnhof – parts of the train station are built below the Sihl – before joining the Limmat at Platzspitz park located at the Swiss National Museum.

The break of the concrete dam of the Sihlsee could lead, according to studies, to an 8 m (26 ft) high flood wave reaching the city of Zürich, the biggest city in Switzerland, within 1.5 hours (Leimbach), its inner city (2 hours) and Zürich-Altstetten within 3 hours.[2]

As part of a floristic mapping, the territory of the Sihl Valley between the city of Zürich and Höhronen was mapped by the Institute for the conservation of the Canton of Zürich on an area of 249 km2. The so-called report "Flora des Sihltals von der Stadt Zürich bis zum Höhronen" includes 2109 species, including 611 frequent crops and ornamental plants or accidentally introduced species which grow wild at most locally and in the short term. 1498 species are, or were at least 30 years during the last 160 years in stable populations exist. Of which 177 or 13% are now extinct, and 284 have been re-introduced and introduced. In all, the flora has become more species-ric, however, 42% of the previous species have decreased and only 30% show an increasing trend.[3]