Arno

File:Arno watershed.png

The river originates on Monte Falterona{{cite report |author=Parco Nazionale delle Foreste Casentinesi |date=1999-01-01 |title=Environmental restoration of the area of the river Arno offsprings |url=https://webgate.ec.europa.eu/life/publicWebsite/project/LIFE98-NAT-IT-005075/environmental-restoration-of-the-area-of-the-river-arno-offsprings# |publisher=European Climate, Infrastructure and Environment Executive Agency |access-date=2024-02-16 |quote="...on the southern slopes of Mount Falterona... the springs of the Arno River, described by the great poet Dante Alighieri, and the Etruscan archaeological site Lago degli Idoli are both located here.}} in the Casentino area of the Apennines, and initially takes a southward curve. The river turns to the west near Arezzo passing through Florence, Empoli and Pisa,{{cite web | title=Arno River | website=Encyclopedia Britannica | date=July 20, 1998 | url=https://www.britannica.com/place/Arno-River | access-date=February 16, 2024}} flowing into the Ligurian Sea{{cite web | last1=Magazine | first1=Smithsonian | last2=Solly | first2=Meilan | title=Like a Reverse Atlantis, This Legendary Harbor Ended When Its Sea Route Dried Up | website=Smithsonian Magazine | date=August 24, 2018 | url=https://www.smithsonianmag.com/smart-news/rising-sea-levels-changing-environment-doomed-legendary-pisan-harbor-180970132/ | access-date=February 16, 2024}}{{cite web | title=Interesting facts about the Arno River | website=Encyclopedia Britannica | date=March 12, 1965 | url=https://www.britannica.com/summary/Arno-River | access-date=February 16, 2024}} at Marina di Pisa.{{cite web | title=Marina di Pisa, la mareggiata si porta via lo storico retone di Bocca d'Arno | website=La Nazione | date=November 3, 2023 | url=https://www.lanazione.it/pisa/cronaca/retone-boccadarno-mareggiata-sb48sb4d | language=it | access-date=February 16, 2024}}{{cite web | title=Mareggiata Marina di Pisa | website=PisaToday | date=November 3, 2023 | url=https://www.pisatoday.it/cronaca/allagamenti-marina-pisa-mareggiata-3-novembre-2023.html | language=it | access-date=February 16, 2024}}

With a length of {{convert|241|km}}, it is the largest river in the region. It has many tributaries: Sieve at {{convert|60|km|mi}} long, Bisenzio at {{convert|49|km}}, Ombrone Pistoiese at {{convert|47|km}}, and the Era, Elsa, Pesa, and Pescia. The drainage basin amounts to more than {{convert|8200|sqkm}} and drains the waters of the following subbasins:

• The Casentino, in the province of Arezzo, formed by the upper course of the river until its confluence with the Maestro della Chiana channel.
• The Val di Chiana, a plain drained in the 18th century, which until then had been a marshy area tributary of the Tiber.
• The upper Valdarno, a long valley bordered on the east by the Pratomagno massif and on the west by the hills around Siena.
• The Sieve's basin, which flows into the Arno immediately before Florence.
• The middle Valdarno, with the plain including Florence, Sesto Fiorentino, Prato, and Pistoia.
• 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 about {{convert|6|m3/s|cuft/s}} to more than {{convert|2000|m3/s|cuft/s}}. The mouth of the river was once near Pisa but is now several kilometres westwards.

File:Ponte Vecchio.jpg

File:View From the Ponte Vecchio of the River Arno.jpg]]

It crosses Florence, where it passes below the Ponte Vecchio and the Santa Trinita bridge (built by Bartolomeo Ammannati but inspired by Michelangelo). The river flooded this city regularly in historical times, most recently in 1966, with {{convert|4500|m3/s|cuft/s}} after rainfall of {{convert|437.2|mm}} in Badia Agnano and {{convert|190|mm}} in Florence, in only 24 hours.{{Citation needed|date=January 2024}}

Before Pisa, the Arno is crossed by the Imperial Canal at La Botte. This water channel passes under the Arno through a tunnel, and serves to drain the former area of the Lago di Bientina, which was once the largest lake in Tuscany before its reclamation.

The flow rate of the Arno is irregular. It is sometimes described as having a torrentlike 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 {{convert|0.56|and|4100 |m3/s|cuft/s}}. New dams built upstream of Florence have greatly alleviated the problem in recent years.{{Citation needed|date=February 2023}}

File:FirenzeArno1547.jpgs of Arno river floods on August 13, 1547 (left) and November 3, 1844 (metal plate on the right). Photographed in Via delle Casine.]]

The 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 decades later hundreds of works still await restoration.{{cite journal | author = Alison McLean |date=November 2006 | title = This Month in History | journal = Smithsonian | volume = 37 | issue = 8 | pages = 34 }}

From Latin Arnus (Pliny, Natural History 3.50). The philologist Hans Krahe related this toponym on a paleo-European basis *Ar-n-, derived from the Proto-Indo-European root *er-, "flow, move".Edelmiro Bascuas, Hidronimia y léxico de origen paleoeuropeo en Galicia (page 41). The hydronym is closely akin to another nearby hydronym, for the Reno (river).

The Arno river has been strongly affected by non-native species: over 90% of fish species and 70% of macroinvertebrate species in the area around Florence are alien species.{{Cite journal|last1=Haubrock|first1=Phillip J.|last2=Pilotto|first2=Francesca|last3=Innocenti|first3=Gianna|last4=Cianfanelli|first4=Simone|last5=Haase|first5=Peter|date=2021|title=Two centuries for an almost complete community turnover from native to non-native species in a riverine ecosystem|journal=Global Change Biology|language=en|volume=27|issue=3|pages=606–623|doi=10.1111/gcb.15442|pmid=33159701 |bibcode=2021GCBio..27..606H |s2cid=226274730 |issn=1365-2486|doi-access=free}} These include the European catfish,{{Cite journal|last1=Haubrock|first1=Phillip Joschka|last2=Azzini|first2=Martina|last3=Balzani|first3=Paride|last4=Inghilesi|first4=Alberto Francesco|last5=Tricarico|first5=Elena|date=2020|title=When alien catfish meet—Resource overlap between the North American Ictalurus punctatus and immature European Silurus glanis in the Arno River (Italy)|journal=Ecology of Freshwater Fish|language=en|volume=29|issue=1|pages=4–17|doi=10.1111/eff.12481|s2cid=149848379 |issn=1600-0633|doi-access=free|bibcode=2020EcoFF..29....4H |hdl=2158/1262515|hdl-access=free}} channel catfish, Crucian carp, common bleak,{{Cite journal|last1=Balzani|first1=Paride|last2=Gozlan|first2=Rodolphe E.|last3=Haubrock|first3=Phillip J.|date=2020|title=Overlapping niches between two co-occurring invasive fish: the topmouth gudgeon Pseudorasbora parva and the common bleak Alburnus alburnus|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/jfb.14499|journal=Journal of Fish Biology|language=en|volume=97|issue=5|pages=1385–1392|doi=10.1111/jfb.14499|pmid=33460088 |bibcode=2020JFBio..97.1385B |s2cid=224936178 |issn=1095-8649|url-access=subscription}} topmouth gudgeon, New Zealand mud snail, and killer shrimp. The mud crab has been found in the river near Pisa.{{Cite journal|last1=Langeneck|first1=J.|last2=Barbieri|first2=M.|last3=Maltagliati|first3=F.|last4=Castelli|first4=A.|date=2015-11-18|title=The low basin of the Arno River (Tuscany, Italy) as alien species hotspot: first data about Rhithropanopeus harrisii (Crustacea, Panopeidae)|url=http://siba-ese.unisalento.it/index.php/twb/article/view/15385|journal=Transitional Waters Bulletin|volume=9|issue=1|pages=1–10|doi=10.1285/i1825229Xv9n1p1|issn=1825-229X}}

Water from the Arno drainage basin is used for drinking water, irrigation, and firefighting.{{Cite journal|last1=Pacetti|first1=T.|last2=Castelli|first2=G.|last3=Bresci|first3=E.|last4=Caporali|first4=E.|date=2020-11-01|title=Water Values: Participatory Water Ecosystem Services Assessment in the Arno River Basin, Italy|journal=Water Resources Management|language=en|volume=34|issue=14|pages=4527–4544|doi=10.1007/s11269-020-02684-4|s2cid=222279681 |issn=1573-1650|doi-access=free|bibcode=2020WatRM..34.4527P |hdl=2158/1209763|hdl-access=free}} Citizens in the central part of the drainage basin also identified flood control, support for biodiversity, fisheries, and cultural value as other services that the river provides. There is the risk that flooding will jeopardize these ecosystem services, as 9% of wastewater treatment plants, 10% of landfills or other waste sites, and 4.5% of contaminated sites are at high risk of flooding, which would produce hotspots of pollution.{{Cite journal|last1=Arrighi|first1=Chiara|last2=Masi|first2=Matteo|last3=Iannelli|first3=Renato|date=2018-02-01|title=Flood risk assessment of environmental pollution hotspots|url=https://www.sciencedirect.com/science/article/pii/S1364815217305169|journal=Environmental Modelling & Software|language=en|volume=100|pages=1–10|doi=10.1016/j.envsoft.2017.11.014|bibcode=2018EnvMS.100....1A |hdl=11568/877149 |issn=1364-8152|hdl-access=free}}

File:Arno_river.jpg|The Arno in Florence

File:Arno River in Pisa.honeydew.jpg|The Arno in Pisa, near the Ponte della Fortezza (Fortress Bridge)

File:Firenze.Arno.jpg|Banks of the Arno, seen from the Ponte Vecchio (Old Bridge), Florence

File:Arno_Mouth_Italy_aerial_view.jpg|Mouth of the Arno in Marina di Pisa

File:Florence Arno 180.jpg|The Arno in Florence, 180 degree view: the Uffizi Gallery is straight across and the Ponte Vecchio is to the left

File:Florence at night.jpg|The Arno in Florence at night

File:Ponte amerigo vespucci.JPG|The Ponte Amerigo Vespucci (Amerigo Vespucci Bridge)

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• [http://www.adbarno.it/cont/testo.php?id=1 Basin Authority of the Arno] {{in lang|it}}

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Category:Rivers of Italy

Category:Rivers of Tuscany

Category:Geography of Florence

Category:Geography of Pisa

Category:Rivers of the Province of Arezzo

Category:Rivers of the Metropolitan City of Florence

Category:Rivers of the Province of Pisa

Category:Rivers of the Province of Prato

Category:Rivers of the Apennines

Category:Drainage basins of the Tyrrhenian Sea