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The River Shannon ((アイルランド語:Abha na Sionainne / an tSionainn / an tSionna)) is the longest river in Ireland at .〔(【引用サイトリンク】publisher=Ordnance Survey Ireland )〕 The River Shannon drains the Shannon River Basin which has an area of 16,865 km2 (6,512 ml2),〔Biology and Management of European Eel (Anguilla anguilla, L) in the Shannon Estuary, Ireland ()〕 one fifth of the area of Ireland. It divides the west of Ireland (principally the province of Connacht) from the east and south (Leinster and most of Munster). County Clare, being west of the Shannon but part of the province of Munster, is the major exception. The river represents a major physical barrier between east and west, with fewer than thirty crossing-points between Limerick city in the south and the village of Dowra in the north. The river is named after ''Sionna'', a Celtic goddess. The Shannon has been an important waterway since antiquity, having first been mapped by the Graeco-Egyptian geographer Ptolemy. The river flows generally southward from the Shannon Pot in County Cavan before turning west and emptying into the Atlantic Ocean through the long Shannon Estuary. Limerick city stands at the point where the river water meets the sea water of the estuary. The Shannon is tidal east of Limerick as far as the base of the Ardnacrusha dam. ==Geography== By tradition the Shannon is said to rise in the Shannon Pot, a small pool on the slopes of Cuilcagh Mountain in County Cavan, from where the young river appears as a small trout stream. Surveys have defined a 12.8 km2 immediate pot catchment area covering the slopes of Cuilcagh. This area includes Garvah Lough, Cavan, 2.2 km to the northeast, drained by ''Pollnaowen''.〔Note Poll nm1: hole, pit, sink, leak, aperture (''The Pocket Oxford Irish Dictionary - Irish-English'')〕 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.〔Philip Elmer et al. ''Springs and Bottled Waters of the World'' Springer ISBN 3-540-61841-4〕 From the Shannon Pot, the river subsumes a number of tributaries before replenishing Lough Allen at its head.〔(The Shannon Guide )〕 The river runs through or between 11 of Ireland's counties, subsuming the tributary rivers Boyle, Inny, Suck, Mulkear and Brosna, among others, before reaching the Shannon Estuary at Limerick. Many different values have been given for the length of the Shannon. A traditional value is . An official Irish source gives a total length of (=258.1 km fresh + 102.1 km tidal).〔 Most Irish guides now give .〔(【引用サイトリンク】publisher=Fodor )〕 Some academic sources give , 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 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 7km off the distance〕) The 280 km distance finishes where the Shannon estuary joins the estuary of the River Fergus, close to Shannon Airport. Longer distances emerged before the use of modern surveying instruments. At a total length of , this means it is the longest river in Ireland.〔(【引用サイトリンク】title=Nature & Scenery )〕 That the Shannon is the longest river in the wider 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. The River Shannon is a traditional freshwater river for just about 45% of its total length. Excluding the 63.5 mile tidal estuary from its total length of 224 miles, if one also excludes the lakes (L. Derg 24 miles, L. Ree 18 miles, L. Allen 7 miles〔(Ask about Ireland )〕 plus L. Boderg, L. Bofin, L. Forbes, L. Corry) from the Shannon's freshwater flow of 160.5 miles, the Shannon, as a freshwater river, is only about 100 miles long. 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, such as the Owenmore River in County Cavan and the Boyle River with its source in Mayo.〔(Notes on River Basins: Page 64 )〕 Apart from being Ireland's longest river, the Shannon is also, by far, Ireland's largest river by flow. It has a long term average flow rate of 208.1 m3/s (at Limerick city). This is double the flow rate of Ireland's second largest river, the River Corrib (104.8 m3/s).〔(South Eastern River Basin Management: Page 38 )〕 If the discharges from all of the rivers and streams into the Shannon Estuary (including the rivers Feale 34.6 m3/s, Maigue 15.6 m3/s, Fergus 25.7 m3/s, and Deel 7.4 m3/s)〔Long-term effects of hydropower installations and associated river regulation on River Shannon eel populations: mitigation and management ()〕〔(SFPC Maintenance Dredging Application: Table 3-7 )〕 are added to the discharge at Limerick, the total discharge of the River Shannon at its mouth at Loop Head reaches 300m3/s. Indeed, the Shannon is a major river by the time it leaves Lough Ree with an average flow rate (at Athlone weir) of 98m3/s,〔Shannon Catchment-based Flood Risk Assessment and Management (CFRAM) Study P. 6 ()〕 larger than any of the other Irish river's total flow (apart from the River Corrib at Galway). Lakes on the Shannon include Lough Allen, Lough Ree and Lough Derg. The Shannon Callows, areas of lowland along the river, are classified as a Special Area of Conservation. Settlements: Settlements along th river include Kilrush, Tarbert, Shannon Town, Limerick, Castleconnell, Killaloe, Ballina, Portumna, Banagher, Athlone, Lanesborough, Carrick-on-Shannon and Ballinamore. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「River Shannon」の詳細全文を読む スポンサード リンク
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