River Lee flooding/Inniscara dam query?

sporina · 18-02-2021 07:33PM #1

Pardon my ignorance... query about how the Inniscarra dam works and it effect on flooding in the city...

So The Lee Fields are v flooded today.. along with all the rain we have been having, how does the dam affect flooding of the river? Is it when water is released from that dam that flooding is more severe or water not being released?

who_me · 18-02-2021 10:33PM

Presumably it's when the water is released it's more dangerous, particularly if it coincides with high tides downriver. Likely depends on how much, and how fast it's released too.

corkgsxr · 18-02-2021 10:35PM

If they want they can rise the water level 1-1.2 metres in 10-15 mins.

Rows Grower · 18-02-2021 10:40PM

sporina wrote: »

Pardon my ignorance... query about how the Inniscarra dam works and it effect on flooding in the city...

So The Lee Fields are v flooded today.. along with all the rain we have been having, how does the dam affect flooding of the river? Is it when water is released from that dam that flooding is more severe or water not being released?

Down river of the dam will be higher when the dam is opened, sometimes there is so much water being held behind the dam that it has to let some go even if the river downstream is already high.

sporina · 18-02-2021 10:42PM

thanks all - got it now..

blindsider · 18-02-2021 11:41PM

I was expecting a flood of responses.....

cantalach · 19-02-2021 02:56AM

I was holding back........

lalababa · 19-02-2021 03:04AM

Dam you

sharingan · 19-02-2021 08:56AM

Rows Grower wrote: »

Down river of the dam will be higher when the dam is opened, sometimes there is so much water being held behind the dam that it has to let some go even if the river downstream is already high.

It should be on a schedule, but I cant find a link to where that schedule is posted.

However once the levels behind the dam become dangerously high, they have to release it.

Limerick residents had the same problem with ardnacrusha a few years back, when they had to open up parteen and let Lough Derg down into the city.

Corkladddd!! · 19-02-2021 12:00PM

Wasn't the severe flooding in '09 due to them releasing from the Dam to prevent it breaching, they were something like 100mm from the top. IIRC they were holding back as much as they could due to an incident downstream and released significant amounts once they could. Over the last 24 hours the peak flowrate was 150m3/s or to put it into context enough water to fill 75000 2L milk cartons a second.

Rows Grower · 19-02-2021 12:05PM

Corkladddd!! wrote: »

Wasn't the severe flooding in '09 due to them releasing from the Dam to prevent it breaching, they were something like 100mm from the top. IIRC they were holding back as much as they could due to an incident downstream and released significant amounts once they could. Over the last 24 hours the peak flowrate was 150m3/s or to put it into context enough water to fill 75000 2L milk cartons a second.

Makes total sense.

19-02-2021 12:07PM

Corkladddd!! wrote: »

Wasn't the severe flooding in '09 due to them releasing from the Dam to prevent it breaching, they were something like 100mm from the top. IIRC they were holding back as much as they could due to an incident downstream.............

They were indeed a contributory factor in that.

"The ESB could face a huge damages bill after the Supreme Court ruled it was guilty of negligence concerning extensive flood damage to buildings on the campus of University College Cork (UCC) in 2009.

UCC’s action over the damage against the semi-State company is among about 400 sets of proceedings initiated against the ESB arising from the flooding in Cork"

https://www.irishtimes.com/news/crime-and-law/courts/supreme-court/esb-could-face-huge-bill-over-ucc-flood-damage-1.4299119

Holding water back due to the downstream incident in a sort of gentleman's agreement / common sense approach between them and the various emergency services but I reckon they should have well thought out procedures to follow that look at the bigger picture.......

"The second was, by releasing water earlier to cope with very heavy rain forecast, the ESB may well have flooded UCC and Cork city to some degree which, on the evidence, would have been less than the major flood ultimately caused. Any future damages would be assessed on the difference in the damage of the two floods, he said"

Corkladddd!! · 19-02-2021 01:26PM

Augeo wrote: »

Holding water back due to the downstream incident in a sort of gentleman's agreement / common sense approach between them and the various emergency services but I reckon they should have well thought out procedures to follow that look at the bigger picture.......

Completely agree, having the procedures in place takes the emotion out of these things; a very bad combination of events (Iniscarra going on full release, heavy rains and high tides)that to pardon the pun was a perfect storm that led to the flooding we saw.

One would hope that UCC learned a very basic lesson that storing Art and IT equipment in the basement of buildings built on flood planes was not a great idea, to quote my father...I wouldn't need to go to UCC to learn that...

the beer revolu · 19-02-2021 03:16PM

Corkladddd!! wrote: »

Completely agree, having the procedures in place takes the emotion out of these things; a very bad combination of events (Iniscarra going on full release, heavy rains and high tides)that to pardon the pun was a perfect storm that led to the flooding we saw.

One would hope that UCC learned a very basic lesson that storing Art and IT equipment in the basement of buildings built on flood planes was not a great idea, to quote my father...I wouldn't need to go to UCC to learn that...

The Glug,glug, Glucksman!

who_me · 19-02-2021 03:47PM

I remember being up late that night, and seeing the flow as they released the water; the river was like the white-water rapids you'd see people rafting down; without having any idea what caused it. And by the time I went to work the next day the floods had already done down, so I was wondering why the city streets were so dirty...

I don't know if there was a safety concern about the decision to open the spillway gates. It might not make much difference to those downriver whether they're inundated by overtopping water or water being released through the gates; but there might be a safety/stability issue with maintaining the water level so high behind the dam for an extended period of time?

Corkladddd!! · 19-02-2021 05:25PM

who_me wrote: »

I don't know if there was a safety concern about the decision to open the spillway gates. It might not make much difference to those downriver whether they're inundated by overtopping water or water being released through the gates; but there might be a safety/stability issue with maintaining the water level so high behind the dam for an extended period of time?

I gather at the time there was; very much a fear of the unknown and once the gates are no longer in control of the flow it's essentially completely at the mercy of the water behind it. It was all to help the rescue efforts down stream, consensus at the time was given the volume released there would be no chance of any conclusion to the efforts being undertaken by the various search and rescue teams.

A bit of googling tells me the peak flow was 547m3/s and that they had enough water enter Inniscarra in 3 days to fill the reservoir 5 times.

the beer revolu · 19-02-2021 06:44PM

Corkladddd!! wrote: »

I gather at the time there was; very much a fear of the unknown and once the gates are no longer in control of the flow it's essentially completely at the mercy of the water behind it. It was all to help the rescue efforts down stream, consensus at the time was given the volume released there would be no chance of any conclusion to the efforts being undertaken by the various search and rescue teams.

A bit of googling tells me the peak flow was 547m3/s and that they had enough water enter Inniscarra in 3 days to fill the reservoir 5 times.

While everyone would have huge sympathy for the loved ones of missing people, it was insane to endanger the city the way it was to facilitate the search for bodies. It wasn't to save a life.

I guess lessons have been learned.

opus · 20-02-2021 07:17PM

Corkladddd!! wrote: »

Completely agree, having the procedures in place takes the emotion out of these things; a very bad combination of events (Iniscarra going on full release, heavy rains and high tides)that to pardon the pun was a perfect storm that led to the flooding we saw.

One would hope that UCC learned a very basic lesson that storing Art and IT equipment in the basement of buildings built on flood planes was not a great idea, to quote my father...I wouldn't need to go to UCC to learn that...

There's good write up on the verdict here, doesn't hold back on UCC's lack of care in building the WGB & the Glucksman in known flood plains.

20-02-2021 08:07PM

opus wrote: »

There's good write up on the verdict here, doesn't hold back on UCC's lack of care in building the WGB & the Glucksman in known flood plains.

Good read.

blindsider · 21-02-2021 03:20PM

A very good read indeed and thanks for posting Opus!

- No mention there at all of the ESB delaying the release of water to allow for a river search - I always thought that was suspect. (I believe that there had been 1-2 incidents, but I'm sceptical that the ESB delayed the release because of them. I've never seen that reason given officially...only hearsay.)

- The dam (Iniscarra and Carrigadrohid combined) produces only 27MW of the ESB's total of 4800MW....that's 0.562%!!!!!!

I imagine the dam is almost loss-making at that level of production!

opus · 21-02-2021 07:07PM

I heard that as well about the ESB delaying but have never seen it written down anywhere so unsure if it's just rumour & hearsay.

TheChizler · 21-02-2021 07:35PM

opus wrote: »

I heard that as well about the ESB delaying but have never seen it written down anywhere so unsure if it's just rumour & hearsay.

There was definitely an ongoing search for a UCC student at the time, he was a couple of years below me in my course. I heard they were holding back the flow for that reason before there was any flooding but yeah never saw it officially written down.

Victor · 21-02-2021 07:39PM

blindsider wrote: »

- The dam (Iniscarra and Carrigadrohid combined) produces only 27MW of the ESB's total of 4800MW....that's 0.562%!!!!!!

I imagine the dam is almost loss-making at that level of production!

1. The capital costs are the main costs at a hydro power plant. Running costs are quite low.
2. The capital costs have been incurred already. Not using it would be a waste.

21-02-2021 08:57PM

Dont know how right this is, but I recall from somewhere, that its kept as some kind of emergency power start up , that they don't need any electricity to start it up if the grid is ever knocked out.
Or something.

Once saw a good local documentary about its disastrous effect on salmon migration.

https://www.youtube.com/watch?v=5eyNX6JEGN4

Maybe there's merit in getting rid of it

blindsider · 21-02-2021 10:06PM

Victor wrote: »

1. The capital costs are the main costs at a hydro power plant. Running costs are quite low.
2. The capital costs have been incurred already. Not using it would be a waste.

I would wonder about e.g. maintenance, inspections, parts etc especially over e.g. a 10 yr period and all for 0.5% ...... but I haven't a clue (vaguely interested amateur) so I'll go with the experts.

It seems a shame that hydro produces so little electricity. I presume wind will play an increasingly important role.

Anyway, don't want to de-rail the thread into Energy.

opus · 22-02-2021 05:13PM

Coincidentally this is part of an email just went round at work.

As you may be aware the City Council have issued a number of Weather Warning for the Cork area. The ESB have also been in contact to let us know that they have considerably increased the discharge level at the Inniscarra Dam.

22-02-2021 07:07PM

Co.Hall have flood balloon looking things around it, and Lee fields are flooded already.

Shot of water on the way...

Pen Rua · 22-02-2021 09:46PM

https://twitter.com/OSullivanJennie/status/1363951899662315525

the beer revolu · 23-02-2021 09:05AM

Luckily, the tides are quite moderate today.

23-02-2021 09:18AM

Yes, warnings are for areas prone to river flooding.

River Lee flooding/Inniscara dam query?

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