The ESB lock at Ardnacrusha

Update 2019: ESB tours of Ardnacrusha are available again this year. Public tours run from 1 July to 13 September 2019.

Update 2017: the ESB is offering free tours to school groups and to the public in 2017. Tours for the public are available from 26 June through 1 September 2017; go here to book.

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One of the earliest acts of the newly-independent Irish Free State was to harness the power of the River Shannon to generate electricity. The fall of the Shannon is concentrated in its lower reaches: it drops only 12m in the 185km from Battlebridge to Killaloe, but a further 30m between there and Killaloe. That drop made the construction of the eighteenth-century Limerick Navigation difficult: it linked Limerick, at the head of the Shannon Estuary, to Killaloe, at the foot of Lough Derg, using two locks on the Park Canal, a river section to Plassey, a canal with six locks to Errina, another river section up through O’Briensbridge and a final canal section with three locks through Killaloe itself. When the hydroelectric power station at Ardnacrusha was opened in 1929, that navigation became disused, with a new route provided through a lock at the power station.

Just to give an idea of why this lock is interesting, here is a photo taken from the top of the upper chamber, looking down at a 60-foot barge and a cruiser in the bottom of the lower chamber.

A very long way down (2003)

And for British readers, here is a 59′ narrowboat in the bottom chamber.

A narrowboat in the lower chamber (2007)

The total drop in this lock is about 100 feet or 30 metres: 60 feet in the upper chamber and about 40 in the lower. It’s “about 40” because the water below the lock is tidal so its level varies; the drop in the upper chamber can change too, as the level of water in the headrace varies with the number of turbines running.

Ardnacrusha is the deepest lock in These Islands. The lock is actually quite small, which enhances the effect when you’re looking up from the bottom.

The  power station is supplied with water from a headrace canal: a new weir at Parteen Villa allows the first 10 cubic metres of water per second down the river’s original course through O’Briensbridge and Castleconnell, but sends the next 400 cumec down the headrace. Anything left over after that is sent down the original course.

The headrace is a large, deep canal, spanned by three bridges; it leads to the power station, where a “double lock” (on Irish waterways, a staircase pair counts as one lock) drops boats down to sea level via a short canal that soon merges with the power station’s tailrace. It rejoins the Shannon’s original course near Corbally. After a short period, the navigation leaves the main course of the river and passes through the Abbey River, from which there is access to the old canal harbour at the foot of the Park Canal.

This page concentrates on the lock at Ardnacrusha; it does not cover the headrace, the tailrace or the navigation through Limerick in any detail. Suffice it to say that there are four turbines at Ardnacrusha; each one adds one knot to the current, which can also be swelled by rainfall upstream and by an ebb tide: peak flows of 10.6 knots were recorded under  Mathew Bridge in Limerick. Anyone proposing to use this route should plan the journey, time  it properly and take local advice.

Above the power station

We skip the first several miles of the headrace canal and begin at Blackwater Bridge, the closest to the power station at Ardnacrusha.

The power station seen through Blackwater Bridge (2001)

The power station seen from Blackwater Bridge (2007)

You can see that there is a considerable flow as the turbines draw water into the power station.

The power station from just past the bridge (2001)

The tall part on the left houses the guillotine gates for the upper chamber of the lock.

The lock is operated by the Electricity Supply Board (ESB). It has a wonderful machine for clearing blockages from the intakes to the turbines.

The wonderful machine 1 (2007)

The wonderful machine 2 (2007)

There is a small waiting jetty above the lock.

The waiting jetty (2007)

Power station

Before we examine the locks, let’s have a quick look at the power station itself.

Looking down from the upper level (2001)

The tall building on the left houses the bottom gates; just in front of it is the lower chamber, which is full. To the right of that is the spillway through which the chambers are emptied into the same area as the outflow from the turbines. The turbine hall is the large building on the right, with its copper control room, which won an architectural award in 1996.

The control room (2007)

I understand (if I’ve got this wrong, please correct me) that nobody works on the generation side at Ardnacrusha any more; the turbines are switched on and off from the ESB pumped storage facility at Turlough Hill.

Here are the penstocks feeding the water from the headrace to the turbines. Ardnacrusha was originally designed to have six turbines but it was found that there was only enough water for four. Three were installed ab initio and a fourth in the 1930s.

The penstocks (2007)

I’m not sure how many turbines are operating to produce the outflow shown in this next photo, but I imagine only one or two.

Outflow (2003)

One of the unused penstock bays was later adapted to provide a large fish-pass, intended to let salmon get upstream through the power station. It is in effect a large vertical cylinder; fish swim up and pass out at the top through the dam into the headrace. If you have more details on its innards or workings, do please leave a Comment below. The cylinder is the part with the grey boxes on top; the fish then swim towards the viewer.

The fish-pass (2007)

You can explore the links between salmon, choirs, evolutionary algorithms and Ardnacrusha here. There are some photos of the turbine hall under Images.

Here is the space between the dam and the turbine hall, over the top of the penstocks. I’d love to know what that track is ….

The mysterious track (2007)

Upper chamber

Here’s the top gate from the outside. A cruiser has just gone in and the gate is being closed.

The top gate from outside the lock (2001)

The gate (2007)

The upper works (2007)

The sides of this chamber are quite high, even when the lock is full, so boats usually pay their tolls in the lower chamber, where it’s easier to get on and off the boat. If you give some notice, and the  lock isn’t too busy, the keeper is usually happy to give you time to look around and take photographs.It is possible to get on or off by ladder in the upper chamber.

The high sides of the upper chamber (2007)

Here is the top gate, with its cill, while the chamber is being emptied.

Top gate and cill (2007)

While cables have been added in recent years, the traditional method of holding on is to use the hooks in the side walls. Note also the ladders (which I would hate to have to climb). As there are no gate racks (paddles), there is very little turbulence in the lock.

Hooks and a ladder (2007)

Hooks and a ladder from below (2001)

There are zebra mussels on the walls of the upper chamber but not in the lower, perhaps (as Mike Miller suggests in the Comments below) because it is kept empty.

Here are the upper gates rising.

Upper gate rising 1 (2007)

Upper gate rising 2 (2007)

Finally, here are the two banks of the upper chamber. Note the large bollards, now no longer accessible, in both photos.

Land-side bank of upper chamber (2007)

Dam-side bank of upper chamber (2007)

Passing through the upper chamber

For some reason, I have more pics of boats coming up from Limerick than of those descending thereto. Here’s one, though.

Cruiser descending in the upper chamber (2001)

Barge and cruiser entering upper chamber from lower (2003)

The following photos show NB Earnest in 2007; you can get an Earnest-eye view here (going down) and here (back up).

NB Earnest rising in the upper chamber 1 (2007)

NB Earnest rising in the upper chamber 2 (2007)

NB Earnest rising in the upper chamber 3 (2007)

NB Earnest rising in the upper chamber 4 (2007)

NB Earnest rising in the upper chamber 5 (2007)

NB Earnest leaving the upper chamber heading upstream (2007)

Meanwhile, going in the other direction ….

Passing from the upper to the lower chamber 1 (2001)

Passing from the upper to the lower chamber 2 (2001)

The lower chamber

All my photos show boats rising, not descending, in the chamber. The first shows a barge and a cruiser in the lower chamber.

Barge and cruiser in lower lock (2003)

That photo was taken from the lower control room, which is shown in the next photo.

Lower control room (2007)

The next photo was taken from the deck of a sailing-boat in the lower chamber, looking up at the gate dividing it from the upper chamber.

Looking up from the lower chamber (2004)

The curved wall at the top of that photo is what is holding back the contents of the upper chamber. You can see the lockkeeper near the top and a bar across the lock below him.

The wall of the upper chamber (2007)

Here’s the same bar, seen from above (from the lockkeeper’s platform) with the bow of the barge below it.

Barge bow (2003)

And here are some views of NB Earnest rising in the lower chamber (all in July 2007).

Note the small bollard

Note the old and new (large and small) bollards as well as the safety fencing installed some years ago

NB Earnest using the wall hooks. Note the spillway on the right

Openings to spillway. I’m not clear on how the system works, though (2003)

The middle gate has lifted and the boat enters the upper chamber

Below the lock

The short canal below the lock is itself usually fairly calm, but it soon joins the tailrace, where the current reflects the number of turbines in operation. And more turbines may be turned on at any time while you’re in the stretch between Ardnacrusha and Limerick; no account will be taken of the presence of any boat in the navigation.

This photo shows the short canal and, coming in on the right, the tailrace; they meet just behind the clump of trees in the middle.

The short canal and the tailrace (2007)

Here’s a view under the bottom gate and down the canal. Some pontoons have since been installed as a waiting jetty; before then, you had to hang on to chains along the sloping wall on the right.

Looking under the gate down the canal (2001)

The next photo shows the old chains; the barge is moored to the new pontoon.

Chains and pontoon (2003)

I know that the architecture isn’t really as enchanting as that of the castles of the Loire, say, or even of Lismore, but Ardnacrusha in the distance is still pretty impressive. The next photo, taken from Parteen Bridge, also gives an idea of the current in the tailrace …

Battling upstream to the enchanted, er, power station (2007)

… as does this one.

Full steam ahead (2007)

Finally, this next photo, taken from a boat that has just left going downstream, shows all the levels of the lock.

The lock from below (2001)

Operation and equipment

Unlike the other locks on the Shannon, which are controlled by Waterways Ireland, this one is operated by the ESB (Electricity Supply Board), which has spent a considerable amount of money on maintenance, upgrading and improved safety in recent years.

Update February 2012

The gates are now interlocked, which means that the upper chamber can not be filled until the lower has been emptied. As a result, the cycle time is now about 90 minutes: in other words, if there are more boats than will fit in a single locking, some of them will have to wait for 90 minutes to be admitted to the chamber.

The chamber is 105′ X 20′ (slightly narrower in one place). It can accommodate a Grand Canal size barge and a cruiser, or two 36′ cruisers at a time.

The water level in the headrace varies with the number of turbines running; in consequence, the headroom (air draught) under the top gates can vary from 12′ to 16′. The middle gate has 13′ 2″ of headroom and the bottom gate headroom ranges from 11′ to 20′, depending on the state of the tide.

The lock should be booked at least two days in advance. No toll is now charged. The lock passage itself takes about an hour and uses (someone once told me) about a million gallons of water.

Let us finish with a few photos of aspects of the operation of the lock. The first set shows the old control system, which was replaced during the winter of 2008/9; these photos show machinery that no longer exists.

The upper chamber is controlled from this room between the two chambers (2007)

Old equipment 1 (2007)

The lower chamber is controlled from a similar room over the bottom gates. For some reason, this had black equipment.

Old equipment 2 (2007)

There were clear instructions for the lockkeeper.

Old equipment 3 (2007)

Then there are the spillways.

Spillways 1 (2007)

Spillways 2 (2007)

Spillways 3 (2007)

Spillways 4 (2007)

Spillways 5 (2007)

Finally, there is provision for stop planks below the lower chamber, with an overhead railway to carry them into position.

Stop planks 1 (2007)

Stop planks 2 (2007)

Stop planks 3 (2007)

As usual, if you can correct, clarify or amplify anything on this page, do please leave a Comment below.

Visiting Ardnacrusha

The ESB offered tours in 2017 and 2018; here is the information for 2018.

More info

Some more photos of Ardnacrusha here. Some photos, from the 1920s and 1930, of Parteen Villa Weir here and an account by Siemens here with an interesting list of the plant used in construction, including 31 barges, tugs, launches and pontoons. Clare County Library has much material, including here and here. The ESB archives site has the 39 reports made by Siemens during construction here.

Here is a kayaker‘s account of a passage through Ardnacrusha and here are photos of the IARU expedition along the headrace and through Ardnacrusha lock in May 2011 (click on a photo to see a larger version).

If you have some time to spare, you might like my slide show of a trip on a barge from Killaloe through Ardnacrusha to Limerick. It has about 300 photos, taken from the barge, so you get to see what the whole trip is like. You can let the slide show run by itself or click through faster if you prefer. All 300 photos have to be loaded on the page before the slide show starts running, so don’t panic if it takes a while to get ready.

If you would like to be kept informed of updates to this site, subscribe to the RSS feed on the front page.  That way, you’ll get a brief notification of any updates or additions, and can decide for yourself whether you want to go and look at them.

Here is a page about the bleach mill at Doonass and here is another about the bleach mill at Clareville: they both made use of the Shannon’s horsepower before Ardnacrusha was built.

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