The River Shannon ( or archaic ') is the major river on the island of Ireland, and at in length, is the longest river in the British Isles. It drains the Shannon River Basin, which has an area of , – approximately one fifth of the area of Ireland.

Known as an important waterway since antiquity, the Shannon first appeared in maps by the Graeco-Egyptian geographer Ptolemy ( 100 –  170 AD). The river flows generally southwards 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. The Shannon 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-five crossing points between the village of Dowra in the north and Limerick city in the south.

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 Mountain in County Cavan, Republic of Ireland, from where the young river appears as a small trout stream. Surveys have defined a immediate pot catchment area covering the slopes of Cuilcagh. This area includes Garvah Lough, Cavan, to the northeast, drained by Pollnaowen. 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.

From the Shannon Pot, the river subsumes a number of tributaries before replenishing Lough Allen at its head. 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.

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 . An official Irish source gives a total length of (being fresh and tidal). 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 off the distance.) The 280 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 , it is the longest river in Ireland. and the Boyle River, total length with its source in County Mayo.

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 tidal estuary from its total length of , if one also excludes the lakes (L. Derg , L. Ree , L. Allen plus L. Boderg, L. Bofin, L. Forbes, L. Corry) from the Shannon's freshwater flow of , the Shannon, as a freshwater river, is only about long.

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 (at Limerick). This is double the flow rate of Ireland's second highest-volume river, the short River Corrib (. If the discharges from all of the rivers and streams into the Shannon Estuary (including the rivers Feale , Maigue , Fergus , and Deel ) are added to the discharge at Limerick, the total discharge of the River Shannon at its mouth at Loop Head reaches . Indeed, the Shannon is a major river by the time it leaves Lough Ree with an average flow rate (at Athlone weir) of , larger than any of the other Irish rivers' total flow (apart from the River Corrib at 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 flows around the northeastern, eastern, and southern shores of King's Island, Limerick before rejoining the Shannon at Hellsgate Island.

Protected areas

The Shannon Callows, areas of lowland along the river, are classified as a Special Area of Conservation.

Settlements

Settlements along the river (going upriver) include Kilrush, Tarbert, Glin, Foynes, Askeaton, Shannon Town, Limerick, Castletroy, Castleconnell, O'Briensbridge, Montpelier, Killaloe, Ballina, Portumna, Banagher, Athlone, Lanesborough, Carrick-on-Shannon, Leitrim village and Dowra.

Historical aspects

thumb|left|River Shannon at [[Clonmacnoise, County Offaly]]The river began flowing along its present course after the end of the last glacial period.

Ptolemy's Geography (2nd century AD) described a river called Σηνος (Sēnos) from PIE *sai-/sei- 'to bind', the root of English sinew and Irish sin ‘collar’, referring to the long and sinuous estuary leading up to Limerick.

Vikings settled in the region in the 10th century and used the river to raid the rich monasteries deep inland. In 937 the Limerick Vikings clashed with those of Dublin on Lough Ree and were defeated.

In the 17th century, the Shannon was of major strategic importance in military campaigns in Ireland, as it formed a physical boundary between the east and west of the country. In the Irish Confederate Wars of 1641–53, the Irish retreated behind the Shannon in 1650 and held out for two further years against English Parliamentarian forces. In preparing a land settlement, or plantation after his conquest of Ireland Oliver Cromwell reputedly said the remaining Irish landowners would go to "Hell or Connacht", referring to their choice of forced migration west across the river Shannon, or death, thus freeing up the eastern landholdings for the incoming English settlers.

In the Williamite War in Ireland (1689–91), the Jacobites also retreated behind the Shannon after their defeat at the Battle of the Boyne in 1690. Athlone and Limerick, cities commanding bridges over the river, saw bloody sieges (see Sieges of Limerick and Siege of Athlone).

As late as 1916, the leaders of the Easter Rising planned to have their forces in the west "hold the line of the Shannon". However, in the event, the rebels were neither well enough armed nor equipped to attempt such an ambitious policy.

thumb|right|Course of River Shannon

1755 to 1820

Though the Shannon has always been important for navigation in Ireland, there is a fall of only in its first . Consequently, it has always been shallow, with depths in various places. The first serious attempt to improve navigability came in 1755 when the Commissioners of Inland Navigation ordered Thomas Omer, a new immigrant from England, possibly of Dutch origin, to commence work. He worked at four places between Lough Derg and Lough Ree where natural navigation was obstructed, by installing lateral canals and either pound locks or flash locks. He then continued north of Lough Ree and made several similar improvements, most notably by creating the first Jamestown Canal which cut out a loop of the river between Jamestown and Drumsna, as well as lateral canals at Roosky and Lanesborough. She went to Connla's Well to find wisdom, despite having been warned not to approach it. In some sources she, like Fionn mac Cumhaill, caught and ate the Salmon of Wisdom who swam there, becoming the wisest being on Earth, in others, she merely drank from the well. At any rate, the waters of the well are said to have burst forth, drowning Sionann, and carrying her out to sea. Notably, a similar tale is told of Boann and the River Boyne. It is said that Sionann thus became the goddess of the river. Patricia Monaghan notes that "The drowning of a goddess in a river is common in Irish mythology and typically represents the dissolving of her divine power into the water, which then gives life to the land".

A small myth about Sionann tells that the legendary hunter-warrior Fionn mac Cumhaill was attacked by a number of other warriors at Ballyleague, near north Lough Ree. It is said that when Fionn was near to defeat, Sionnan rescued him, and he arrived with the Stone of Sionann, threw the stone, and the warriors were immediately killed. It further says that Fionn was afraid of the power of the stone and threw it into the river, where it remains at a low ford, and that if a woman named Be Thuinne finds it, then the world's end is near. Cata is described as a large creature with a horse's mane, gleaming eyes, thick feet, nails of iron, and a whale's tail. Another story has an oilliphéist flee its home in the Shannon, upon hearing that Saint Patrick has arrived to remove its kind from Ireland.

Economics

thumb|left|[[Shannonbridge, County Offaly]]

Despite being long, it rises only above sea level, so the river is easily navigable, with only a few locks along its length. There is a hydroelectric generation plant at Ardnacrusha belonging to the ESB.

Shipping in the Shannon estuary was developed extensively during the 1980s, with over IR£2 billion (€2.5 billion) investment. A tanker terminal at Foynes and an oil jetty at Shannon Airport were built. In 1982 a large-scale alumina extraction plant was built at Aughinish. 60,000-tonne cargo vessels now carry raw bauxite from West African mines to the plant, where it is refined to alumina. This is then exported to Canada where it is further refined to aluminium. 1985 saw the opening of a 915 MW coal-fired electricity plant at Moneypoint, fed by regular visits by 150,000-tonne bulk carriers.

Flora and fauna

Shannon eel management programme

A trap and transport scheme is in force on the Shannon as part of an eel management programme following the discovery of a reduced eel population. This scheme ensures safe passage for young eels between Lough Derg and the Shannon estuary.

Fishing

Though the Shannon estuary fishing industry is now depleted, at one time it employed hundreds of men along its length. At Limerick, fishermen based on Clancy's Strand used the Gandelow to catch Salmon. The Abbey Fishermen used a net and a boat type known as a Breacaun to fish between Limerick City and Plassey until 1929. In 1929, the construction of a dam at Ardnacrusha severely impacted salmon breeding and that, and the introduction of quotas, had by the 1950s caused salmon fishing to cease. However, recreational fishing still goes on. Further down the Shannon Estuary at Kilrush the Currach was used to catch herring as well as drift netting for salmon.

Water extraction

thumb|[[Athlone, County Westmeath]]

Dublin City Council published a plan in 2011 to supply up to 350 million litres of water a day from Lough Derg to Dublin city and region. In 2016 the Parteen Basin to the south of lough was chosen as the proposed site of extraction. Water would be pumped to a break pressure tank Knockanacree near Cloughjordan in County Tipperary and gravity fed from there by pipeline to Dublin.

See also

  • Rivers of Ireland
  • List of loughs of Ireland

Notes

References

  • Information, maps, etc. on The Shannon Navigation (from Inland Waterways Association of Ireland)
  • Ireland's Wild River (2014 "Nature" episode on the River Shannon by wildlife cameraman Colin Stafford-Johnson)