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).
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]
Flora and fauna
Flora
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]
Recreation
Sihltal is a well-known recreation area and popular for hiking and biking tours along Sihl and in the surrounding hills between the chains of Höhronen, Albis-Felsenegg and Zimmerberg.
