Tag Archives: flood

Managing the Shannon

Sometimes you have to wonder about politicians and their grasp of reality. Take, for instance, young Mr Adams, Sinn Féin TD for Louth. There he was in the Dáil the other day, talking about flooding on the Shannon, and saying (amongst other things):

No single agency is responsible for the management of the River Shannon. Will the Taoiseach give full responsibility to the OPW for management of the Shannon?

Can Mr Adams have forgotten that, under the Good Friday Agreement, a cross-border implementation body called Waterways Ireland, reporting jointly to the Minister for Fairytales in the republic and the Minister for Marching Bands [a Sinn Féin MLA] in Northern Ireland, is responsible for navigation on certain named waterways including the Shannon?

Giving the Office of Public Works full responsibility for the management of the Shannon would require renegotiation of the Good Friday Agreement [and perhaps some later agreements]. I gather that the members of HM Devolved Administration in Northern Ireland delight in doing that sort of thing, but reducing the powers of the largest of the cross-border implementation bodies might not be wise.

 

 

Limerick water levels 14 December 2015

The Abbey River

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Abbey Bridge

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Baal’s Bridge

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Mathew Bridge

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Current heading for Mathew Bridge

The Shannon in Limerick

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The weir

Plassey

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Lots of pumps running and equipment trundling about the place

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Trouble at t’mill

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T’millstream

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Cots on the bank

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The Black Bridge getting another hammering

Annacotty

I have been told that the Mulkear River rose very rapidly on Saturday night and that, at one time, it was feared that the (older) bridge would be swept away. I gather that folk working in other areas were called to Annacotty to deal with the emergency.

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The old bridge at Annacotty (downstream face)

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A tree in the water above the bridge

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There’s a weir in there somewhere

The Mill Bar in Annacotty was closed today after being flooded.

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The Mill Bar

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This, from a small garden beside the bridge, suggests that the Mulkear may have carried and deposited a lot of silt

The Park Canal

I gather that the Mulkear’s waters, added to those of the Shannon itself, raised the level of the Park Canal (the bottom section of the Limerick Navigation). A problem with opening the lock gates, to release the water, meant that a few houses in Corbally were flooded. A Sinn Féin councillor, whose party colleague has been responsible [with her southern counterpart] for slashing Waterways Ireland’s budget in recent years, is quoted as saying

I am in no doubt it was primarily caused by the ineptitude of Waterways Ireland.

Alas, the news story does not tell us the source of the councillor’s certainty.

The article also says that

[…] the force of this water meant it was not possible to open the lock gates by hand.

That is, I think, misleading: neither set of gates has gate beams, so they are not opened by hand.

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The upper gates in 2004, shortly after installation. Note the absence of gate beams. Note also the two sluices or paddles on each gate

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Control pedestal and gear

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The upper gates open today

I see no sign of the paddles or sluices. Perhaps the level is so high that they’re underwater. I must try to check next time I’m at the canal harbour.

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The upper gates in the floods of 2009

In the floods of 2009 the upper gates were held slightly open and all four sluices were discharging water. That would have lowered the level in the canal; it would also, I think, have made it easier to open the gates fully.

I am guessing, but I imagine that on Saturday night some sort of hydraulic machine was brought in this way …

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Two bollards have been moved from the gateway and stacked beside it

… and used to push or pull open the near-side upper gate. There seems to be some slight damage to the stone and iron work.

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Slight damage

One other possibility that struck me is that silt from the Mulkear might have built up behind the gates, making them difficult to open, but I have no evidence on the matter.

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The lower gates

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From the outside looking in

 

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.

Update 2018: the ESB has a new page with lots of interesting information here.

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.]

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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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Stormont

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Pump

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Sandbags

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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 this quotation from a former web page of the Shannon International River Basin District:

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].

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.

Cumec

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.

Floods

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.

Envoi

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

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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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Tuamgraney

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Killaloe: the flash lock

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Killaloe bridge from downstream

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O’Briensbridge

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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.

 

Limerick flooded again

The waves covered the quays in some places to a depth of three and four feet, and rolled in to the adjoining streets with resistless fury. Shannon-street, Charlotte’s Quay, and the Mall were completely inundated, and in the corn stores on Honan’s-quay, Harvey’s quay, &c, the water reached a height of four feet in some instances.

I already had a page about the floods in Limerick in November 2009; here is an account of the floods in Limerick in 1850.

A little rain goes a long way

Here are some water level readings from Athlone Weir. I’ve taken them from the OPW’s very useful water levels site, where you can monitor levels from the comfort of your own armchair. [If only there were a gauge at Killaloe ….]

At Athlone, staff gauge zero is 35.360m above Poolbeg datum (from 18 Oct 2003). I chopped the bottoms off the first two graphs. The first one shows the level for 35 days to 30 September 2014; I presume that the level of Lough Ree was being reduced to enable it to hold some of the autumn’s rainfall.

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Athlone Weir 35 days to 30 September 2014 (truncated)

Here’s the graph for the 35 days to 15 October 2014.

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Athlone Weir 35 days to 15 October 2014 (truncated)

Then, in October, the level began to rise again. By 30 October, it was back to about 2.1 metres, roughly the starting point on the first of the graphs above.

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Athlone Weir 35 days ro 30 October 2014

And since then it has continued to rise.

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Athlone Weir 35 days to 17 November 2014

Met Éireann’s weather summary for October 2014 [PDF] has this chart:

Met Eireann weather Oct 2014

Met Éireann rainfall October 2014

It says:

Rainfall: wet conditions nearly everywhere

Monthly rainfall totals were above-average nearly everywhere with the exception of stations in coastal areas in the Northwest and West and in parts of the Midlands. Percentage of Long-Term Average (LTA) values ranged from 81% at Gurteen to 161% at Johnstown Castle, which recorded it wettest October since 2002.

Fermoy (Moore Park) reported 135% of its LTA with 153.6 mm and its wettest October in 10 years. The wettest days were mainly the 3rd, 5th and 28th, with the month’s highest daily rainfall reported on the 5th at Cork Airport with 38.6 mm, its wettest October day in five years. Mullingar reported its wettest October day in 12 years on the 28th with 26.4 mm. The number of wet days (days with 1 mm or more rainfall) ranged from 12 at Casement Aerodrome to 24 at Valentia Observatory and Claremorris, with Claremorris reporting its highest number of October wet days since 1973.

Use of the OPW charts is licensed under Directive 2003/98/EC [PDF] of the European Parliament and of the Council on the re-use of public sector information. Met Éireann allows use of “the web pages, and the information contained within them, for private and non-commercial purposes, for teaching, and for research […] is allowed subject to the condition that the source of the information is always credited in connection with its use”.

 

 

A wet winter?

Today’s Irish Times reports on yesterday’s launch of a report called Ireland’s climate: the road ahead [92.9 Mb 103 page PDF here]. The report predicts:

  • Daytime summer temperatures to rise by up to 2°C
  • Lowest winter night-time temperatures to rise by 2-3°C
  • Milder winters to reduce cold-related mortality rates
  • Wetter winters and drier summers
  • Increase in frequency of heavy precipitation event.

Chapter 10 “Climate change and catchment hydrology” covers river flows.

Met Éireann’s report on summer 2013 [2 page PDF] is available here; rainfall was down [on the 1981–2010 average] at all stations except Valentia; temperature was up everywhere and so was sunshine. So perhaps we’ll have a wet winter to look forward to.

Saving the banks

The banks, the Fergus and the lost island of Islandavanna.