Draft:Avisio

(Avisio, translating from the Italian article)

Avisio
The Avisio at Soraga di Fassa
Location
Country	Italy
Region	Trentino-Alto Adige
Province	Trento
Physical characteristics
Source	Fedaia Lake, Marmolada
• coordinates	46.46065°N 11.86419°E / 46.46065; 11.86419
• elevation	2057 m
Mouth	Adige River, near Lavis
• coordinates	46.126°N 11.084°E / 46.126; 11.084
Basin features
Tributaries
• left	Ruf d'Antermont, Ruf de Duron], Ruf de Dona, Ruf de Udai, Ruf de Soal, Rio San Pellegrino, Rio Costalunga, Travignolo, Pozze, Sadole, Cavelonte,Lagorai River, Val Moena, Cadino, Rio Brusago, Rio Regnana
• right	Ruf de Contrin, Rio di San Nicolò, Rio Gardoné, Rio di Valaverta, Rio Bianco, Rio Stava, Rio Predaia, Rio Molino, Rio Scorzai

The Avisio (Ladin: La Veisc, German: Laifserbach) is an 89.4-kilometre-long (55.6 mi) Italian stream (torrente), a left tributary of the Adige, which flows in Trentino.

It rises from Marmolada and runs through the Fassa Valley, the Fiemme Valley, and the Cembra Valley before joining the Adige in Lavis, a small town 8 km (5 mi) north of Trento.

The Avisio's watershed covers 940 km² (360 sq mi). It powers four hydroelectric power plants with a total nominal power of 106.18 megawatts.

Etymology

The name "Avisio" first appears ca. 1050 ("supra fluvium qui vocatur Auis"), then in 1200 ("ponte Avisi"). It is likely derived from Gaulish abisijo, "watercourse", which in turn comes from the Proto-Indo-European root abì, "water".

Source and route

The river rises on Marmolada, then crosses the Fassa Valley, Fiemme Valley, and the Cembra Valley.

Fassa Valley

The Avisio in Moena

The first stretch of the Avisio is in the Fassa Valley (Val di Fassa). It originates there at Passo Fedaia (elev. 2,054 metres (6,739 ft)) as an outflow of Fedaia Lake, formed by the melting waters of the Marmolada Glacier. It flows immediately into the Fedaia reservoir, which diverts part of the water into the Cordevole basin for hydroelectric use.

The stream flows quickly and steeply down to the village of Penia, where it joins its first tributary, the ruf de Contrin from the Contrin Valley. After Penia, the valley widens suddenly into a wide southward curve, whose shallower slope slows and widens the stream.

In Canazei it joins the ruf d'Antermont from the Sella group. In the Campitello di Fassa stretch its flow rate increases considerably thanks to the ruf de Duron, and subsequently with the inflows of the ruf de Dona, the ruf de Udai, and the ruf de Soal, all coming from the Rosengarden group. At Pozza di Fassa, the San Nicolò River also joins the watercourse, arriving from the San Nicolò Valley. After Soraga di Fassa the stream forms the Soraga Lake behind the Pezzé dam, a pipeline from which feeds the Predazzo hydroelectric power station. At Moena the Rio San Pellegrino and the Rio Costalunga, both from the Latemar, flow into the Avisio.

After Moena, the Avisio enters the Fiemme valley.

Fiemme Valley

The Avisio near Ischiazza, Valfloriana

In the Fiemme Valley, the stream flows roughly east-west. Here its watershed extends to its maximum width as it receives the copious contribution of numerous streams, especially from the left, from the Lagorai. The main left-side tributaries include, in upstream-to-downstream order:

• the Travignolo, the main tributary of the Avisio, which originates from the Travignolo glacier (located in the Pala group) and runs through the Venegia valley. Its course is dammed downstream of Paneveggio, creating Lake Paneveggio, which conveys its waters into the Cismon basin and thence the Brenta River. It flows into the Avisio near Predazzo;
• the Pozze downstream of Predazzo, famous for its waterfall;
• the Sadole near Ziano di Fiemme;
• the Cavelonte near Panchià;
• the Lagorai River, coming from Lake Lagorai, near Tesero;
• the Val Moena, which forms a picturesque waterfall in the last stretch, near Cavalese;
• the Cadino from Manghen Pass, near Castello-Molina di Fiemme.

The right-side tributaries are generally shorter and more irregular in character. They include the Valsorda stream at Forno, the Gardoné stream at Predazzo, the Valaverta stream in Ziano, the Bianco stream in Panchià, the Stava in Tesero (famous for the 1985 Val di Stava dam collapse), the Gambìs stream near Cavalese and the Predaia River in Molina di Fiemme. Downstream of Molina, the stream is impounded by the Stramentizzo dam, creating Lake Stramentizzo; part of the water is conveyed to the hydroelectric power plant at San Floriano di Egna (BZ) and then released into the Adige.

In the Fiemme Valley, the Avisio intially flows on permeable, calcareous dolomitic rocks, but gradually moves onto the Adige porphyritic platform, where the rocks are impermeable and siliceous. This changes its hydrology.

Cembra Valley

The Avisio at the Cantilaga bridge, below Prà di Segonzano

The Avisio below the hydroelectric dam at Pozzolago (Lona-Lases)

In the Cembra Valley, just below Lake Stramentizzo, the stream's flow reduces substantially due to hydroelectric withdrawals, drops into a distinctive, tortuous canyon carved from porphyritic rock, and bends again to the southwest. Here it flows in an environment virtually unchanged from the past and is visible only in brief stretches from the villages in the upper part of the valley.

The largest left-bank tributaries in this stretch of the river are those coming from the Lagorai, including the Brusago stream near Sover and the Regnana near Piazzo di Segonzano. The shorter, swifter-flowing right-bank tributaries include the Molino near Grauno and the Scorzai near Cembra.

Between the comuni of Giovo, Lavis, and Meanto (Trento), after joining the "Vai dei Molini" (Verla) and "Rio Valalta" (Meano) streams, the river passes through the Serra di San Giorgio, a large weir built at the end of the nineteenth century. After passing Lavis, it flows into the Adige; its wide mouth, 1 km (0.62 mi) across, forms a marshy area that has been protected since 1994 as the Biotopo Foci dell'Avisio.

This area's steeps slopes and impermeable rocks give the Avisio a torrential character, with normal minimum flows of 5 cubic metres per second (180 cu ft/s) and floods of over 1,000 m³/s (35,000 cu ft/s). Historically, Lavis has been noted for episodes in which the river dried up completely due to excessive water withdrawals during droughts, but also for disastrous floods carrying significant amounts of debris, such as the floods of 1882 and 1966 with flow rates of 1,200 m³/s (42,000 cu ft/s) and 1,100 m³/s (39,000 cu ft/s) respectively. The 1966 flow rate is particularly significant when compared to the Adige's 2,500 m³/s (88,000 cu ft/s) flow at Trento, downstream of the Avisio's mouth.

Bibliography

• Vittorio Bassetti, ed. (April 2013). Val di Fassa. Documenti e Studi.
• Società degli alpinisti tridentini e Commissione per la tutela dell'ambiente montano (2012). Alessio Bertolli (ed.). Naturalmente Trentino: i paesaggi, la natura, i luoghi. Trento: Curcu & Genovese. ISBN 978-88-96737-55-2. OCLC 898546419.