Many of the longer Irish rivers flow, for at least part of their journey to the sea, along courses where the gradient is quite limited. As a result, they are quite sluggish. When there is prolonged rainfall in their upper reaches, they may overflow downstream, flooding adjacent areas. The longest Irish river is the Shannon, which rises on Cuilcagh mountain, Co. Cavan. With its tributaries, notably the Rivers Suck, Inny and Brosna, and the Rivers Fergus and Maigue, which flow into its estuary, it drains over 15700 square kilometres of central Ireland. Its total length is 360.5km including some 102.2 km of tidal water.

Over its first ten kilometres to Lough Allen, the Shannon descends some 500 metres, but along a middle section of some 120km, between Lough Boderg and Lough Derg, the river falls less than nine metres, while at the same time receiving the input of the Suck, Inny and Brosna. Not surprisingly, perhaps this part of the Shannon, which includes the famous Shannon Callows, south of Athlone, and the ancient monastic site of Clonmacnoise, is liable to serious winter flooding, on a scale which so far has proven difficult to control.

All other rivers are under 200km in length, the longest being the Rivers Barrow

Barrow Navigation

(192km), Suir (184km), (Munster) Blackwater (168km), Erne

Map showing Shannon-Erne Waterway

A map of the canals and waterways of Ireland showing the Shannon- Erne waterway, the Ballinamore and Ulster Canals

Courtesy of John B Cunningham

 (120 km) and Bann (129 km). Along with the Rivers Main and (Ulster) Blackwater, the Bann drains an area of over 5800 square kilometres in the north-east. In the south-east, the Barrow

River Barrow at Leighlinbridge

The River Barrow at Leighlinbridge, County Carlow. It was an important river crossing as early as the 10th Century. The first stone bridge here was built by Maurice Jakis in c1319. the present bridge which was altered in the 18th Century, dates originally from circa 1650.

Courtesy of Carlow County Library

 , Nore and Suir each drain areas of over 5000 square kilometres. The Erne has a drainage or catchment area of 4400 sq.km. By comparison, the rivers feeding into the largest cities drain much smaller areas: the Liffey (126km in length), Lagan (60 km) and Lee (90km) all have catchments under 1,500 sq.km.


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