Editing River Shannon (section)

==Course==
By tradition the Shannon is said to rise in the [[Shannon Pot]], a small pool in the townland of [[Derrylahan]] on the slopes of [[Cuilcagh|Cuilcagh Mountain]] in [[County Cavan]], [[Republic of Ireland]], from where the young river appears as a small trout stream. Surveys have defined a {{convert|12.8|km2|abbr=on}} immediate pot catchment area covering the slopes of Cuilcagh. This area includes Garvah Lough, Cavan, {{convert|2.2|km|abbr=on}} to the northeast, drained by ''Pollnaowen''.<ref group="n">Note '''Poll nm1:''' hole, pit, sink, leak, aperture (''The Pocket Oxford Irish Dictionary – Irish-English'')</ref> Further sinks that source the pot include Pollboy and, through [[Shannon Cave]], Pollahune in Cavan and Polltullyard and Tullynakeeragh in [[County Fermanagh]], [[Northern Ireland]]. The highest point in the catchment is a spring at Tiltinbane on the western end of the Cuilcagh mountain ridge.<ref name="SBW">Philip Elmer et al. ''Springs and Bottled Waters of the World'' Springer {{ISBN|3-540-61841-4}}</ref>

From the Shannon Pot, the river subsumes a number of tributaries before replenishing [[Lough Allen]] at its head.<ref>{{cite web|url=http://www.iwai.ie/maps/shannon/guide/17.php3|archive-url=https://web.archive.org/web/20150319000141/http://www.iwai.ie/maps/shannon/guide/17.php3|url-status=dead|title=The Shannon Guide|archive-date=19 March 2015}}</ref> The river runs through or between 11 of Ireland's [[Counties of Ireland|counties]], subsuming the tributary rivers [[Boyle River (Ireland)|Boyle]], [[River Inny, Westmeath|Inny]], [[River Suck|Suck]], [[Mulkear River|Mulkear]] and [[River Brosna|Brosna]], among others, before reaching the Shannon Estuary at [[Limerick]].

[[File:Shannon Pot (474383119).jpg|thumb|left|The [[Shannon Pot]], the traditional source of the river]]
Many different values have been given for the length of the Shannon. A traditional value is {{Convert|390|km|mi|abbr=on}}.<ref>{{cite EB1911|wstitle= Shannon |volume= 24 | pages = 819–820; see page 819, line two |quote= ...with a length of about 240 m....}}</ref> An official Irish source gives a total length of {{Convert|360.5|km|mi|abbr=on}} (being {{convert|258.1|km|abbr=on|disp=sqbr}} fresh and {{convert|102.1|km|abbr=on|disp=sqbr}} tidal).<ref name="Facts"/> Some Irish guides now give {{Convert|344|km|mi|abbr=on}}.<ref>{{cite book|first=Ruth|last=Delaney|title=Shell Guide to the River Shannon|year=1996|url=http://www.iwai.ie/maps/shannon/guide/1.php3|access-date=8 September 2014|archive-url=https://web.archive.org/web/20160303165644/http://www.iwai.ie/maps/shannon/guide/1.php3|archive-date=3 March 2016|url-status=live}}</ref><ref>{{cite web|title=Cruising on the Shannon|publisher=Fodor|url=http://www.fodors.com/world/europe/ireland/the-midlands/feature_30012.html|url-status=dead|archive-url=https://web.archive.org/web/20140908224458/http://www.fodors.com/world/europe/ireland/the-midlands/feature_30012.html|archive-date=8 September 2014}}</ref><ref name="Discover Ireland">{{cite web|url=http://www.discoverireland.com/gb/about-ireland/nature/|title=Nature & Scenery|publisher=Discover Ireland|archive-url=https://web.archive.org/web/20130520121337/http://www.discoverireland.com/gb/about-ireland/nature/|archive-date=20 May 2013}}</ref> Some academic sources give {{Convert|280|km|mi|abbr=on}},<ref name="Environmental Geology">{{cite journal|title=Source of the River Shannon, Ireland|journal=Environmental Geology|volume=27|number=2|pages=110–112|date=31 January 2005|doi=10.1007/BF01061681|last1=Gunn|first1=J.|s2cid=129442165}}{{dead link|date=February 2020|bot=medic}}{{cbignore|bot=medic}}</ref> although most will refuse to give a number. The reason is that there is no particular end to a river that empties into an estuary. The 344&nbsp;km length relates to the distance between Shannon Pot and a line between [[Kerry Head]] and [[Loop Head]], the furthest reaches of the land. (It also assumes the current shipping route via Ardnacrusha, which takes {{convert|7|km|abbr=on}} off the distance.) The 280&nbsp;km distance finishes where the Shannon estuary joins the estuary of the [[River Fergus]], close to [[Shannon Airport]]. Longer claimed lengths emerged before the use of modern surveying instruments.

At a total length of {{convert|360.5|km|mi|0|abbr=in}}, it is the longest river in Ireland.<ref name="Discover Ireland"/> That the Shannon is the longest river in the British Isles was evidently known in the 12th century, although a map of the time showed this river as flowing out of the south of Ireland.<ref name=BI1 />

There are some tributaries within the [[Shannon River Basin]] which have headwaters that are further in length (from source to mouth) than the [[Shannon Pot]] source's length of {{convert|360.5|km|mi|0|abbr=in}}, such as the [[Owenmore River (County Cavan)|Owenmore River]], total length {{Convert|372|km||abbr=on}} in County Cavan<ref>{{cite book|title=Atlas and Cyclopedia of Ireland|author=P. W. Joyce|chapter=Cavan|chapter-url=http://www.libraryireland.com/Atlas/Cavan.php|year=1900|publisher=Murphy & McCarthy|access-date=8 October 2011|archive-date=11 April 2012|archive-url=https://web.archive.org/web/20120411192148/http://www.libraryireland.com/Atlas/Cavan.php|url-status=live}}</ref> and the [[Boyle River (Ireland)|Boyle River]], total length {{Convert|392.1|km||abbr=on}} with its source in [[County Mayo]].<ref>{{cite web|url=http://archive.org/details/notesonriverbas00willgoog|title=Notes on river basins|date=3 January 1872|via=Internet Archive|access-date=3 January 2020|archive-url=https://web.archive.org/web/20160325205428/https://archive.org/details/notesonriverbas00willgoog|archive-date=25 March 2016|url-status=live}}</ref>

[[File:Upper Shannon catchment.jpg|thumb|left|Upper Shannon catchment (with Shannon source, Owenmore River and Boyle River Basin)]]

The River Shannon is a traditional freshwater river for about 45% of its total length. Excluding the {{convert|63+1/2|mi|0|order=flip|abbr=on}} tidal estuary from its total length of {{convert|224|mi|order=flip|abbr=on}}, if one also excludes the lakes ([[Lough Derg (Shannon)|L. Derg]] {{convert|24|mi|order=flip|abbr=on}}, [[Lough Ree|L. Ree]] {{convert|18|mi|order=flip|abbr=on}}, [[Lough Allen|L. Allen]] {{convert|7|mi|order=flip|abbr=on}}<ref>{{cite web|url=http://www.askaboutireland.ie/|title=Home|website=askaboutireland.ie|access-date=3 January 2020|archive-url=https://web.archive.org/web/20200110054610/http://askaboutireland.ie/|archive-date=10 January 2020|url-status=live}}</ref> plus [[Lough Boderg|L. Boderg]], [[Lough Bofin (River Shannon)|L. Bofin]], [[Lough Forbes|L. Forbes]], [[Lough Corry|L. Corry]]) from the Shannon's freshwater flow of {{convert|160+1/2|mi|0|order=flip|abbr=on}}, the Shannon, as a freshwater river, is only about {{convert|100|mi|0|order=flip|abbr=on}} long.

Apart from being Ireland's longest river, the Shannon is also, by far, Ireland's largest river by [[streamflow|flow]]. It has a long-term average flow rate of {{convert|208.1|m3/s|abbr=on}} (at [[Limerick]]). This is double the flow rate of Ireland's second highest-volume river, the short [[River Corrib]] ({{convert|104.8|m3/s|abbr=on|disp=sqbr}}.<ref>{{cite web|url=http://www.serbd.com/MultiDownloads/Creport/Chapters/Physical%20Description%20Ch3.pdf|archive-url=https://web.archive.org/web/20160303222354/http://www.serbd.com/MultiDownloads/Creport/Chapters/Physical%20Description%20Ch3.pdf|url-status=dead|title=South Eastern River Basin Management: Page 38|archive-date=3 March 2016}}</ref> If the discharges from all of the rivers and streams into the Shannon Estuary (including the rivers [[River Feale|Feale]] {{convert|34.6|m3/s|abbr=on|disp=sqbr}}, [[River Maigue|Maigue]] {{convert|15.6|m3/s|abbr=on|disp=sqbr}}, [[River Fergus|Fergus]] {{convert|25.7|m3/s|abbr=on|disp=sqbr}}, and [[River Deel|Deel]] {{convert|7.4|m3/s|abbr=on|disp=sqbr}})<ref>{{cite web|url=http://www.nuigalway.ie/faculties_departments/zoology/mccarthy/documents/mccarthy_et_al_2008.pdf|title=Long-term effects of hydropower installations and associated river regulation on River Shannon eel populations: mitigation and management|website=nuigalway.ie|access-date=2020-01-03|url-status=live|archive-url=https://web.archive.org/web/20160304191259/http://www.nuigalway.ie/faculties_departments/zoology/mccarthy/documents/mccarthy_et_al_2008.pdf|archive-date=4 March 2016}}</ref><ref>{{cite web|url=http://www.environ.ie/en/Publications/DevelopmentandHousing/Foreshore/FileDownLoad,30279,en.pdf|title=SFPC Maintenance Dredging Application: Table 3-7|access-date=14 April 2015|archive-url=https://web.archive.org/web/20141208233846/http://www.environ.ie/en/Publications/DevelopmentandHousing/Foreshore/FileDownLoad,30279,en.pdf|archive-date=8 December 2014|url-status=dead}}</ref> are added to the discharge at Limerick, the total discharge of the River Shannon at its mouth at Loop Head reaches {{convert|300|m3/s|abbr=on}}. Indeed, the Shannon is a major river by the time it leaves [[Lough Ree]] with an average flow rate (at [[Athlone]] weir) of {{convert|98|m3/s|abbr=on}},<ref>{{cite web|url=http://shannoncframstudy.ie/docs/River%20Shannon%20Level%20Operation%20Review%20Report.pdf|title=Shannon Catchment-based Flood Risk Assessment and Management (CFRAM) Study|page=6|url-status=dead|archive-url=https://web.archive.org/web/20180805113034/http://shannoncframstudy.ie/docs/River%20Shannon%20Level%20Operation%20Review%20Report.pdf|archive-date=2018-08-05}}</ref> larger than any of the other Irish rivers' total flow (apart from the [[River Corrib]] at [[Galway City|Galway]]).

===Distributaries===
The main flow of the river is affected by some [[distributaries]] along its course, many of which rejoin it downstream. The [[Abbey River, Limerick|Abbey River]] flows around the northeastern, eastern, and southern shores of [[King's Island, Limerick|King's Island]], [[Limerick]] before rejoining the Shannon at ''Hellsgate Island''.<ref>{{cite book|last=Simms|first=J.G.|date=1986|title=War and Politics in Ireland, 1649-1730|url=https://archive.org/details/warpoliticsinire0000simm|url-access=registration|page=[https://archive.org/details/warpoliticsinire0000simm/page/22 22]|location=London|publisher=Hambledon Press|isbn=978-0907628729|access-date=23 October 2013|quote=The Shannon divides at Limerick; a branch, called the Abbey river, makes an island which was called the King's Island.}}</ref><ref>{{cite web|url=http://www.geographic.org/geographic_names/name.php?uni=-2141679&fid=1641&c=ireland|title=Abbey River, Ireland|date=5 May 1998|website=Geographical Names|publisher=National Geospatial-Intelligence Agency, Bethesda, Maryland, US|access-date=23 October 2013|archive-url=https://web.archive.org/web/20131029193202/http://www.geographic.org/geographic_names/name.php?uni=-2141679&fid=1641&c=ireland|archive-date=29 October 2013|url-status=live}}</ref>