Tag Archives: Ardnacrusha

Ardnacrusha by train

Here’s an event.

I think that Heuston Station means Kingsbridge.

Ardnacrusha tours

From 26 June through 1 September 2017, ESB will be providing guided tours of Ardnacrusha hydroelectric power station. It’s not usually open to the public and, if you haven’t seen it, it’s well worth a visit. Go here to book.

I have some information about the site here, here and here, but you should try to see it for yourself.

Building Ardnacrusha

I had a page with photos of the construction of Ardnacrusha in 1930; I have expanded that page to include

  • photos taken in the 1920s by Eyre Chatterton and kindly supplied by Tony and Blair Chatterton
  • links to the ESB Archive’s reports made by Siemens during construction; h/t Carthach O’Maonaigh for drawing them to my attention.


Building Ireland

There is a television series called Building Ireland, about “Ireland’s building and engineering heritage”. A series of six programmes will begin on Friday 30 September 2016 at 8.30pm on RTÉ One, which is a television station.

The third programme, on 14 October, covers Ardnacrusha and the sixth, on 4 November, is entitled “Galway’s Corrib Canal” and covers canals in Galway and, I believe, may have some material about the Cong Canal.

Here is a PDF describing the series.



Oberkommando der Wehrmacht and O’Briensbridge

Boogie on over to the splendid David Rumsey Historical Map Collection and put

ireland shannon

in the search box. All going well, you’ll get a set of 14 pages published by Generalstab des Heeres (the German Military High Command) in 1940, with drawings, maps, photos and a page of text about the Shannon. The set includes Clonmacnoise (no doubt because the Wehrmacht intended to go there on pilgrimage), Foynes and, in particular, Ardnacrusha, O’Briensbridge, Parteen Villa and Killaloe.

Industrial railway enthusiasts may also be interested.

And the collection includes many photos of British ports and other installations.

ESB water discharge info

Here is the ESB’s Notifications page, with info on the rate of discharge from its hydroelectric dams and weirs. Today (14 December 2015) Parteen Villa Weir is discharging 440 cumecs (cubic metres per second or, roughly, ton[ne]s per second down the original course of the Shannon. That’s 44 times the 10 cumec usually discharged and more than replaces the 400 cumec diverted through the headrace to the Ardnacrusha power station. The Shannon is therefore running at its pre-Ardnacrusha levels and the Falls of Doonass have regained their power.

Of course if Ardnacrusha didn’t exist, its 400 cumec would be coming down the original course of the Shannon on top of the 440 cumec already there, which would make for interesting levels of flooding.

That ESB page has a link to this infographic, which shows the sort of information I was trying to get across here. I usually start from Leitrim [village]; the ESB starts slightly further upstream at Lough Allen. Note that the Shannon’s few locks are concentrated upstream of Lough Ree: between them and Killaloe are only two locks, at Athlone and Meelick, so the river’s fall is very slight.


What’s a cumec, Daddy?

I don’t know, but here’s a picture of 415 of them flowing through Castleconnell. [Update 13 December: that may be only 405 cumec.]

Castleconnell 20151212 10_resize

415 cumecs on 12 December 2015

Actually, a cumec is one cubic metre of water per second, which is roughly one ton per second, which is a lot of water. And 415 cumec is the amount that, according to the blatts, the ESB is currently letting down the original course of the Shannon from Parteen Villa Weir; the minimum flow in that channel, as seen in summer, is 10 cumec.

Castleconnell 12 December 2015

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Younger trees getting their feet wet

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Who’d have guessed?

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Below the bridge

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Above the bridge

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Sandbag Central

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Sandbags filled here for distribution

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Army engineers

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More equipment arriving

Clonlara 11 December 2015

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Ardnacrusha headrace, said to take 400 cumec

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Errina bridge on the Plassey-Errina Canal

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The stop planks seem to be quite effective …

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… as there is little water getting down the canal to Clonlara bridge

Park Canal 9 December 2015

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Depth gauge at Park Lock

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Lock chamber

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Full canal upstream


Why the Shannon floods

From the search terms used, it seems that many people are visiting this site with questions about Parteen Villa Weir, water levels, Shannon floods and so on. They are not this site’s primary focus, but some non-technical information might be of interest.

The best place to start is with a map of the Shannon International River Basin District. As the Shannon RBD site says,

The Shannon International River Basin District is the largest in Ireland at more than 18,000 km2 in area. It covers the natural drainage basin of the Shannon river itself, stretching from the source of the River Shannon in the Cuilcagh mountains in Counties Cavan and Fermanagh to the tip of the Dingle peninsula in north Kerry. It also includes coastal parts of Kerry and Clare which drain to the sea. It flows through 18 local authority areas and is also an international RBD as a small portion of County Fermanagh in Northern Ireland drains underground to the Shannon Pot.

The district is about one fifth of the area of the island, one quarter the area of the state. Rain that falls on that area of land ends up in the Shannon (or in a few small rivers in Clare and Kerry that flow to the sea). Some goes to the Shannon estuary or its tributaries; most flows into the non-tidal Shannon, which means the river upstream of Limerick.

The nature of the Shannon

Ireland has been described as saucer-like, with a high rim and a low flat centre. It’s not entirely true, but there certainly is a very large central plain, and the Shannon flows down through the middle of that. And, because the land it flows through is flat, the river falls very little.

In 113 miles from Leitrim to Killaloe, the Shannon falls just over 30 feet; the navigation channel needs only five locks. [By way of contrast, the Thames has 45 locks over 135 miles; the Trent has 12 locks over 42 miles.] So extra rainwater allows the Shannon to spread out, covering a much wider area, and it takes time for that water to drain away downstream. But many of the rivers that flow into the Shannon have been subjected to drainage schemes, so they can get rid of their flood waters quickly … into the Shannon.

Why don’t they open [or close] the weirs?

There are some weirs on the Shannon, designed to keep a minimum depth in the river for navigation; there are also some natural obstacles that hold water back. But once the level has risen high enough, water simply flows over the top of the weir, and there is nothing useful anybody can do — apart, of course, from farmers’ representatives and politicians, who can always make use of a photo opportunity.

The bottleneck

Almost all the water that enters the non-tidal Shannon will eventually flow through Killaloe, the town at the southern end of Lough Derg [it’s on the west bank, in Co Clare; the east bank is Ballina, in Co Tipperary].

As James Robinson Kilroe wrote in 1907,

[…] we have the formidable barrier at Killaloe, naturally damming up a considerable depth of water in Lough Derg, and the river falling away southward by a series of rapids which correspond with drops in the canal, south of O’Briensbridge […], along an alternative course, possibly one used by a branch of the Shannon.

The diagrams with that article are worth a look.

In the twelve Irish (fifteen statute) miles between Killaloe and the tidewater at Limerick, the river falls about 100 feet: more than three times its fall from Leitrim to Killaloe. In the nineteenth century, the water level at Killaloe used to change by about eleven feet between summer and winter — even without storms.  The old Limerick Navigation, including the canal Kilroe mentioned, could drain only a small amount of water (which could put the navigation out of action); the rest went down the river’s original course through the Falls of Doonass.

The relief channel

Nowadays, the Falls of Doonass are a shadow of their former selves, and the water level through O’Briensbridge, Castleconnell and Plassey is much below its previous levels. I suspect that the older, larger trees along the river show the original level, with the newer, smaller trees having grown since the 1920s.

The cause was the construction of a relief drainage channel in the 1920s. This channel is controlled by a weir at Parteen Villa [not to be confused with Parteen]. Switch between the modern Street Map and the Historic views here to see what has happened.

Actually, of course, it’s not a relief drainage channel. The weir [sometimes referred to as the Hydro Dam] controls the flow of water to the original course of the Shannon [the right-hand or eastern channel, which gets the first 10 cubic metres of water per second] and the headrace for the hydroelectric power station at Ardnacrusha [the left-hand or western channel, which gets the next 400 cubic metres of water per second, 100 for each of its turbines]. The power station was built to use that 100-foot fall of the Shannon, concentrated between Killaloe and Limerick, to generate electricity.

But one effect of the construction of Ardnacrusha was to provide a channel, the power station headrace, capable of taking [at least] 400 cubic metres of water per second away from the original river channel, thus reducing the likelihood of flooding.


Water experts talk about cumecs: a cumec is a flow of one cubic metre, or 1000 litres, of water per second. And a cubic metre of water weighs about one [metric] tonne, which is roughly the same as an imperial ton. So one cumec is one ton of water per second, which is a lot.

It was said, on 8 December 2015, that the ESB, using Parteen Villa Weir, had released 315 cumec down the original course of the Shannon on the previous day and had increased that to 375 cumec. If the Ardnacrusha headrace was getting 400 cumec, then the amount of water being discharged from Lough Derg and the upper Shannon had doubled.


As far as I can see, the Shannon has always flooded. The 2009 floods affected some nineteenth century houses, which I guess would have been flooded even worse before Ardnacrusha was constructed. However, I suspect that more houses have been built on the flood plain since then. But I don’t see that there is any way to prevent Shannon floods.


There is a good article in the Irish Times of 9 December 2015; it will no doubt disappear behind a paywall at some stage.

Here is an ESB infographic about the Shannon.

Shannon water levels 8 December 2015

North to south (more or less)

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Shannonbridge upstream

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Shannonbridge downstream

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Shannon Harbour: 36th lock

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Shannon Harbour: below the 36th

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Shannon Harbour: road to Banagher closed

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Banagher: the harbour above the bridge

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Banagher: the harbour’s sole inhabitant

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Banagher: work goes on

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Portumna Bridge: Hawthorn moving

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Portumna Bridge

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Below Portumna Bridge

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Above Portumna Bridge

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Portumna Bridge: Waterways Ireland yard

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Mountshannon: the main quay

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Scarriff: the river in flood

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Scarriff: the river flowing on to the road to the harbour

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Scarriff: sandbags blocking the road …

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… to the Waterways Ireland Shannon HQ. Anyone in the building must have waded there

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Killaloe: the flash lock

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Killaloe bridge from downstream

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Water level with the quay at O’Briensbridge

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Flooded fields at O’Briensbridge

O’Briensbridge is on the original course of the Shannon, downstream of Parteen Villa Weir, which controls how much water goes via the original course and how much goes to the hydroelectric power station at Ardnacrusha.

Normally, the original course gets the first 10 cubic metres per second (10 cumec, they say) of water and Ardnacrusha gets the next 400, 100 for each of its four turbines. In floods, any excess is sent down the original course, through O’Briensbridge, Castleconnell and Plassey. One newspaper today said that, on Monday 7 December 2015, 315 cumec had been sent down the original course and, on Tuesday 8 December, 375 cumec.

The water levels are still below the peak achieved in November 2009, but there is more to come: as the Shannon drains a very large amount of Ireland, and as it is falls very little in its upper reaches, it takes a long time for the runoff to reach Killaloe and Parteen Villa. It may be that the ESB, which controls Ardnacrusha and Parteen Villa, is now running down the level of Lough Derg to make room for the water that has yet to arrive from the upper Shannon.


Hard sums on Lough Derg

According to the Clare Champion, a Clare county councillor called Pat Hayes, who is a member of Fianna Fáil [an excitable lot, Fianna Fáil], is boycotting something or other for some reason that is not clear to me [and, to be honest, is probably entirely unimportant]. Mr Hayes thinks that water from Lough Derg should be sent to the Atlantic, where it is wasted, rather than to Dublin, where it might be used, and the newspaper cites the River Shannon Protection Alliance as estimating that

… up to 350 million litres of water could be taken from Lough Derg by 2030.

The River Shannon Protection Alliance itself doesn’t agree with those figures. It says:

The central principal and immediate purpose of the organisation is to prevent the proposal of Dublin City Council to abstract in excess of 350 million litres of water on a daily basis from Lough Ree on the river Shannon, and to oppose any action that may be harmful to the well being of the river Shannon system. Since then, the abstraction options have been considered and the current recommended proposal is to abstract upwards 500 million litres of water from Lough Derg and store it in a depleted bog hole to be developed by Bord na Móna at Garryhinch bog, (near Portarlington) where the water will then be treated and pumped on to Dublin.

Eek. That’s a bignum: a lot of litres. Let’s all panic.

On the other hand, 500 000 000 litres is 500 000 cubic metres. Each of Ardnacrusha’s four turbines uses 100 cubic metres per second. So the amount of water to be sent to Dublin every day is less than Ardnacrusha uses in 21 minutes.

If the Alliance wants to save the Shannon, shouldn’t it be trying to get Ardnacrusha closed down first?