Shannon river basin flooding and the ESB

probe wrote: »

I’ve been reading the report on the Shannon flood of December 1999 – early 2000.

I must take serious issue with you on this post its old IFA/farmers claptrap, that has been bebunked both professionally and by informed observation.

The water draining out of the Shannon River system is constrained at Parteen / Ardnacrusha, where the ESB operates a “tap” (a weir / sluce gates) to restrict the flow. Effectively, the ESB appears to be using the Shannon lake system (Lough Derg upstream to Lough Allen + the river itself and its tributaries) as a reservoir to store water for the Ardnacrusha hydro generation system!

no thats a simplistic description, The primary restriction on the flow is the natural geography of the river sections, shallow and flat. coupled with some restrictions due to river crossings like athlone banagher etc. the lakes respond to the flow in and out and go up and down as that varies, they dont in general restrict the river flow in normal or flood conditions.

Lets also debunk the ESB/storage system. The ESB made a policy decision in the 90's that ardnacrusha was no longer of any significant strategic importance as it now contributes less then 5% of irelans total electricity generation. They do not "store" water for electricity generation, they merely use whatever flow rate is available and generate accordingly, running one two three or four turbines are the rate allows. This is completely evident in summer months. water is not held back. The ESB controls Parteen weir, Athlone and Lough Allen sluices, all others are controlled by Waterways Ireland. The ESB did agree to reduce the wide variations of levels in Lough Allen to facilitate boating, but the effect is minimal.

The design of the Ardnacrusha system appears to be inefficient from an electricity generation perspective, because less than half the water flowing down the Shannon at that point is routed via the generation turbines. They created a canal to take water off the main Shannon to feed the turbines. In any other country, I would have thought that the canal would be created to carry boats through a system of locks to conserve water, and they would put the hydro turbines on the main river, capturing the considerable energy in Ireland’s largest river flow.

this is the most incredably uniformed statement I have ever read. The shannon hydroelectric system was designed to take a average of what the river generates . in summer flows, there is actually hardly enough water to spin even one turbine and lots of the time the turbines arnt running at all., a minimum flow is always maintained over parteen weir to maintain the downstream river ecosystem, hence the station can be starved of water. IN winter, the characteristics of the river basin is that far too much water is available in flood times, it would have made no economic sense whatever to build a monster 10-12 turbine system , merely on the off chance that the flow might be available.

Also you are wrong in your understanding of the purpose of the head race ( the so called canal you mention). The head race is designed to smooth and control the flow of water to the turbines and secondly to maximise the height of water as the land drops away quickly here at its not possible to expand the lake to the power station directly. putting the station at the original end of teh lake at killaloe, would have lost valuable height and hence energy. This feature is extremely common in the siemens designs of the time.

by the way the headrace is also a canal carrying boats through two locks (to conservse water) so its there despite your critism of its non-existence, perhaps a visit to the station and a chat to the engineers might inform you rather then listening to IFA nonsense.

I’ve read many reports on the current flooding problem in the Shannon river basin affecting numerous areas – Athlone, Banagher, Ballinasloe and numerous other communities, basically from the Border down including parts or most of counties Leitrim, Roscommon, Westmeath, Galway, Mayo, Offaly, Tipperary, Clare and Limerick are at risk.

Aside from Limerick, these areas are in the reverse situation of Cork city last week – because they are upstream of the ESB dam (whereas Cork is downstream), and their farms, towns and villages are unwittingly becoming part of the reservoir system due to bad medium and long term water level management by the ESB at the Ardnacrusha/Parteen system.

name or produce these "many" reports, they dont exist, are they by recognised exports, the only comprehensive report was done in the fifties by a US army core of engineer with experience of US levies along the missisippi. he debunked the lower the levels issue and suggested that any engineering work to expand the capacity of the river would require expenditure on a truely enormous level that couldnt be justified, and his only possible suggestion was to reverse the River suck, and drain it to the western seaboard to act as an additional exit point. The ESB does not "hold water back", if fact in dry summers the lake levels have fallen considerably, theres noboby closing sluices to raise the levels

The solution to the problem is partially the same as for Cork*, enforce a “new normal” where maximum permitted water levels in the lake and river system are reduced by a figure of 1, 2 or 3 meters or whatever it takes to create spare capacity in the lakes to deal with prolonged periods of heavy rain.

No hydrologist agrees with you, this is the claptrap IFA nonsense that spouted by people who would like to grap the land so revealed by lowering the lakes. All professional opinion debunks the IFA "drain the shannon" nonsense.


not to mention the enormous environmental damage that would be done to the surrounding wetlands, massive loss of habitat, etc. of course farmers are the worst offenders when its comes to protecting habitat. this leaves aside the visual damage to places like athlone where the lowering would turn the river into a trickle in dry summers. and explain how you would lower say LOugh Ree by 2 metres given that the weir is 4 feet , youd have to remove the river bed all the way from athlone to banagher.- nonsense, rubbish

The quantities of water to be managed are enormous – 1,035 tonnes a second fell on the Shannon catchment on 27.1.1995. The maximum discharge rate through the Ardnacrusha /Parteen system is 700 tonnes per second. This implies that the Shannon system has to be kept low enough in terms of water level to be able to store a 300 tonnes per second build-up of water over a prolonged period of rainfall.

Lough Allen, Ree and Derg have a total surface area of 262 km2. For every 1 m reduction in maximum permitted water levels in these three lakes, one would buy 10 days of storage capacity for torrential rain pouring 24 hours each day at 300 tonnes per second faster than the existing Ardnacrusha / Parteen system could discharge.

theres a simple flaw in this logic and it has been pointed out many times, you can only lower a lake if you can get the water OUT OF IT. The situation that occurred in december was not caused soley by december rainfall. it was caused by the whole summers worth. the fact is that all summer the lakes were rising , especially lough Ree, By late august the levels were approaching winter levels, the water simply could not be got down the river fast enough. No body was "HOLDING BACK" water , how could they , it was over the sluice gates, ardnacrusha was running 4 turbines almost the whole summer and still discharging over parteen weir. Ree rose 4 feet over the normal summer levels.

The simple fact is that downstream river sections are incapable of handling significant increased flows due to the flat gradient and shallow nature, their solution is to spread widthways and take the strain thatways, tahts what the creator intended.

again consider what happened this year , a wet summer ( following a wet winter ) had meant that the systems was already approaching winter conditions at the end of the summer. All sluices were open, yet the levels still went up.

When the increased rainfall appeared, it merely further over whelemed an already swollen system, your mythical 10 days of storage was long since used up by late august, then youd need another 10 or maybe 20 days storage to cope with teh demember rains. Not possible

Look at where most of the flooding was generated, Around the major lakes NO, there was little additional flooding around most of lough Allen, Ree and Derg ( and I know this river extremely well). ( and where it did happen was a direct result of bad planning. Most of the flodding occured in the slow river sections, namely around Carrick, below the lock in AThlone and Banagher /ballinasloe. Firstly even with the floods we had the lakes remained "below" these river levels, hence they were not a serious restriction on them. Its the river geometry in these sections that causes problem, flat shallow, constricted by towns. ( and other housing and planning horrors). The level in the Lakes had no real effect on the flooding on the river sections. The levels dropped in these sections when the input flow into these sections went below the output sections. The level of the Lakes is and always basically irrelevant.

Deciding the level of reduction is more complex compared with the River Lee, because of the numerous lakes and tributaries and intermediary sluce gate systems which form this massive reservoir. To cater for new normal increased rainfall peaks, it may be necessary to widen and deepen the Shannon between Killaloe and Limerick city. Looking at the satellite imagery there are numerous islands of trees in the river around Castletroy and Castleconnell which may be inhibiting peak flow rates.

absolute balderdash, the fact is that even with a massive engineering program in the lower shannon, and the river bed here is all rock and very shallow in places, also massive works would be neccessary to reengineer the abbey river, the fact is this would do NOTHING to reduce upstream flooding especially the areas most vunerable , to Banagher to Athlone, remember Dedrg didnt rise above meelick weir, so was not constrsining this section, Ree would have to rise 9 metres to oppose drainage from the Carrick area, (I suspest Ree would flood Dublin first). Hence its levels have no effect on that flooding.

THe simple fact is that as the fifties study show, unless you are preapred to effectively re-engineer the whole shannon, from the top to the bottom and effectively turn a wide slow moving flood prone river into a fast deep non flooding river that gets water quickly to the sea, you will not solve the problems by so called lowering of the lakes, (nor the othe IFA baby , the silt)

This massive task would (a) bankrupt the country, (b) cause the riverside towns to be effectivly removed from thr planet and (c) reck untold environmental damage. and anyway cause the people who are currently flooded to be moved off their land anyway.

The decision and implementation of the decision to reduce the maximum permitted water levels in the lakes is urgently required to minimise the risk of a repeat of the flooding. Other measures will obviously take time to engineer and implement. The cost of a water level reduction is minimal.

no its not , johnn gormly does agree with you, all the hydrologists dont agree with you and significant lowering is not physically possible, nor is it hrdraulically possible in any sort of wet summer, ( This is proved this summer). lowering the lake only works in the case of a kind of flash fllood that appears in a couple of days and then stops, thats not what we get in this country, its sustained rain over a relatively long period, somtimes months.

There is no excuse for inaction on this front.... it has been a problem for decades.

your right about that , the farmers, the biggest vested interest in the whole area would love to reduce levels and remove flooding, they love to turn flood plains in development land and grap extra lakeshore land that would be revealed.

The first thing thats need to be done is to accept that short of engineering on a massive scale, the shannon is what it has always been, a slow flat river feed by a very large catchment area, whose area can generate a lot of extra water in wet times.

Secondly the only solution to this is to allow it access to its flood plains ,as far as it needs. Poor planing that let people build on this floodplains needs to be rectified, buy back the land and houses, resettle people and return the land to the river. completely halt all extended flood plain development.

and finally lets ignorethe IFA claptrap and the "drain the shannon nonsense" and lets see it for what it is --greed.


*http://www.boards.ie/vbulletin/showthread.php?t=2055751080

Report on Shannon flood of 1999-2000: https://sites.google.com/site/probeinfosite/docs/shannonfloodreport19992000.pdf?attredirects=0&d=1

Picture of Parteen weir: http://www.flickr.com/photos/m_j_g/106333779/in/photostream/[/quote]

how exactly can you confirm these things, when your request to see the evidence which would be required for such confirmation was denied?

Also...just for clarification...when you refer to "the top management of the power station", who are you referring to? The station manager?

Sorry was asleep on this one.
I can confirm because I was there.
The "evidence" is in the "control room log" and "hydrometric log sheets" and "regulations book" as stated. My request to the OPW was an attempt to see what "spin" was put on that report, not an attempt to gather evidence re the actual event, more so, the aftermath of the event.
Top management at that time would have been the Station manager and the Civil Engineer, both comfortably retired now.
There have been changes since with a lot of the control transferred to a remote station, Turlough Hill. But some staff remain in the control room in Ardna, thumb twiddling till retirement.