thumb|250px|left|Arno in FlorenceThe
Arno is a
river in the
Tuscany region of
Italy. It is the most important river of central Italy after the
Tiber.
Source and route
The river originates on
Mount Falterona in the
Casentino area of the
Apennines, and takes initially a southward curve. The river turns to the west near
Arezzo passing through
Florence,
Empoli and
Pisa, flowing into the
Ligurian Sea at
Marina di Pisa. With a length of 241 kilometers, it is the largest river in the region. Its main tributaries are: the
Sieve (60 kilometers),
Bisenzio (49 kilometers),
Ombrone,
Era,
Elsa,
Pesa and
Pescia. The drainage basin amounts to more than 8,200 km² and drains the waters of the following sub-basins:
- The Casentino, in the province of Arezzo, formed by the upper course of the river until the confluence with the Maestro della Chiana channel.
- The Val di Chiana, a plain dried in the 18th century, which, until the 18th century, was a marshy area tributary of the Tiber.
- The upper Valdarno, a long valley bordered from East by the Pratomagno massif and from West by the hills around Siena.
- The Sieve's basin, which flows in the Arno immediately before Florence.
- The lower Valdarno, with the valley of important tributaries such as the Pesa, Elsa and Era and in which, after Pontedera, the Arno flows into the Ligurian Sea. The river has a very variable discharge, ranging from minimum values such as 6 m³/s to more than 2,000. The mouth of the river was once near Pisa, but is now several kilometres westwards.
It crosses
Florence, where it passes below the
Ponte Vecchio and the
Santa Trìnita bridge (built by
Bartolomeo Ammanati, but inspired by
Michelangelo). The river
flooded this city regularly in historical times, the last occasion being the
famous flood of 1966, with 4,500 m³/s after a rain of 437.2 mm in Badia Agnano and 190 millimetres in Florence, in only 24 hours.
The flow rate of the Arno is irregular. It is sometimes described as having a torrent-like behaviour, because it can easily go from almost dry to near-flood in a few days. At the point where the Arno leaves the Apennines, flow measurements can vary between 0.56 m³/s and 3,540 m³/s. New
dams built upstream of Florence have greatly alleviated the problem in recent years.
A
flood on November 4, 1966 collapsed the embankment in Florence, killing at least 40 people and damaging or destroying millions of works of art and rare books. New conservation techniques were inspired by the disaster, but even 40 years later hundreds of works still await restoration.
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