Inn

Inn, River, in Tirol and Upper Austria, (Celtic "Ine" = flowing; Latin "Aenus"; Romansh "En"), largest tributary of the upper reaches of River Danube, 510 km long (183 km in Austria), catchment area 25,700 km². The water of the River Inn is only moderately polluted upstream of Innsbruck (576 m). Near Schärding River Inn has an average flow rate of 731 m³/sec. The Austrian Inn Valley consists of the narrow Upper Inn Valley and the wide Lower Inn Valley (downstream of Innsbruck). Morphologically, the Inn Valley, shaped by glaciers during the Ice Age, is a U-shaped valley with steep slopes (e.g. Martinswand); the valley bottom was later filled with young sedimentary deposits. Major tributaries: Ötztaler Ache, Sill and Ziller in the south; Sanna in the northwest; Gurgl and Brandenberger Ache streams in the north. Electric power stations sited on River Inn: Prutz, Imst, Sellrain-Silz, Mühlau I, Voldertal, Jenbach, Kirchbichl, Oberaudorf-Ebbs, Nußdorf-Innstufe, Braunau-Simbach, Ering, Obernberg, Schärding-Neuhaus and Passau-Ingling. The Inn has its source at the Maloja Pass south of St. Moritz in Switzerland and enters Austrian territory near Finstermünz Pass/Nauders (alt. 1,394 m). In Austria, the river first enters the narrow Upper Inn Valley down to its confluence with River Sanna (called "Oberes Gericht" in Austrian vernacular); broadens below Landeck downstream of Telfs (634 m); fertile terraces ("Tiroler Mittelgebirge", 300-400 metres above the valley bottom). The Inn is joined by the Sill river (Wipptal valley) at Innsbruck, the capital of Tirol. Below Innsbruck is the fertile Lower Inn Valley, which was formed by glaciers during the Ice Age. Frequent warm foehn winds that blow down the mountain slopes cause discomfort in the local population but favours wheat, maize, fruit and even wine-growing. Annual precipitation increases further downstream. Whereas the northern slopes of the Inn Valley are steep and only sparsely forested, the gentler slopes on the southern side of the slate mountains are densely wooded. Major economic factors in the Lower Inn Valley are glass and paper manufacturing; machine construction (vehicle construction, railways and cable-cars); building construction and civil engineering. South of Kufstein (499 m) the Inn breaks through the northern Limestone Alps and enters Bavarian territory. North of Burghausen (Germany), at its confluence with the River Salzach, it forms the natural border between Upper Austria and Bavaria, and finally merges into the Danube near Passau (313 m); it contributes more than half the water carried by the River Danube.

Literature: G. Pfaundler, Tirol-Lexikon, 1983.