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Cork City flood -again

Level 42

https://twitter.com/CorkSafetyAlert/status/1318462555703181312

https://twitter.com/NeilRedFM/status/1318462491685433344

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saabsaab

alanucc wrote: »

It's more like 0.5mm/year. Sorry don't have a source to hand

Fair enough, 1cm every 20 years.

alanucc

saabsaab wrote: »

Added to that is the fact that Cork is sinking into the ocean, I could be wrong but the rate is 1 cm every ten years!

It's more like 0.5mm/year. Sorry don't have a source to hand

fonzy951

saabsaab wrote: »

Flooding in Cork city is likely to continue every year from now on. Sea levels are rising and a 0.5M rise is likely by the end of the century. Added to that is the fact that Cork is sinking into the ocean, I could be wrong but the rate is 1 cm every ten years!

Is it time to move and rebuild further inland and leave certain areas to the inevitable?

The Dutch have much greater issues with sea level rise than Cork and seem to have no problem in solving them, even reclaiming land from the sea. Every part of Cork city can be very easily protected, the Dutch would have no bother with it, that's for sure. They would probably get a fit of laughing if they saw the state of the existing quays, especially on Morrison's Island.

Mefistofelino

blindsider wrote: »

I'm certainly not discounting major fluvial events, but I am concerned about events such as yesterday which seem all too regular.

I'd be interested to know how many of the previous flood events were tidal v fluvial

I appreciate the fact-based arguments (from e.g. AlanUCC) and I'll happily declare my lack of knowledge in this area.

I do have significant concerns that the OPW seem wedded to a scheme which is unsightly, potentially expensive (even compared to a tidal barrier), difficult to implement and maintain and less effective than another proposal.

Separately, I've seen no mention of dredging apart from a couple of short comments here.

Whatever about the OPW costs for their scheme, the idea that the tidal barrier can be constructed for €170 million seems utter mince. The shortest the barrier can be is approximately 1km which, coincidently, is about the same length as the tidal barrier in Cardiff which consists of a long stone barrage with a number of navigable gates in the middle. Twenty years ago, the Cardiff project ended up around £220 million (and has had quite a deleterious impact on the bay). Even the relatively piddley Bridgwater tidal barrier is now looking like costing more over £100 million (and it hasn't started yet).

Perhaps a tidal barrier is a better solution than the OPW proposal but we need to be going into it with our eyes fully open.

alanucc

blindsider wrote: »

I'd be interested to know how many of the previous flood events were tidal v fluvial

Have a look at figure 2-1 on page 4 here

saabsaab

Flooding in Cork city is likely to continue every year from now on. Sea levels are rising and a 0.5M rise is likely by the end of the century. Added to that is the fact that Cork is sinking into the ocean, I could be wrong but the rate is 1 cm every ten years!

Is it time to move and rebuild further inland and leave certain areas to the inevitable?

blindsider

alanucc wrote: »

The channel capacity in the western half of the city centre gets exceeded at much lower flows than 2009. See this map for an idea - the 10%AEP (i.e. small flood) still floods out

I don't want to get into debating 2009 either, but would note that fluvial flood risk on the Lee is very real and "natural" - similar events to 2009 occurred in 1853, 1875 and 1916, all before the dams were built and before climate change started to bite. I think it would be foolish to think that similar events will never happen again (whether they will in our lifetime is another matter)

I'm certainly not discounting major fluvial events, but I am concerned about events such as yesterday which seem all too regular.

I'd be interested to know how many of the previous flood events were tidal v fluvial

I appreciate the fact-based arguments (from e.g. AlanUCC) and I'll happily declare my lack of knowledge in this area.

I do have significant concerns that the OPW seem wedded to a scheme which is unsightly, potentially expensive (even compared to a tidal barrier), difficult to implement and maintain and less effective than another proposal.

Separately, I've seen no mention of dredging apart from a couple of short comments here.

jetfiremuck

Dredging for the most part is the least intrusive and quickest method of seeing results. tidal barriers cost wise will end like the childrens hospital....overruns, not even thinking about eco analysis etc.

TheChizler

Nerdlingr wrote: »

Clonmel's flood defence barriers

Grand if you want to pretend the river doesn't exist

Nerdlingr

Clonmel's flood defence barriers :

c69cba76c12c491087f86ad2899894ce.jpg--the_mountable_barriers_on_the_flood_defence_walls_in_clonmel_that_were_erected_this_week_in_anticipation_of_rising_water_levels_in_the_river_suir_.jpg

Padraig Mor

corkgsxr wrote: »

No need for barriers. Go back to dredging the river. Simple solution

It was dredged literally last month - dredger was around for a month.

alanucc

blindsider wrote: »

But wasn't 2009 an 'artificial' flood? The ESB added to the issue by opening Inniscarra. (I'm not getting into why, when, how etc - just a statement of fact.)

...

Am I missing something?

The channel capacity in the western half of the city centre gets exceeded at much lower flows than 2009. See this map for an idea - the 10%AEP (i.e. small flood) still floods out

I don't want to get into debating 2009 either, but would note that fluvial flood risk on the Lee is very real and "natural" - similar events to 2009 occurred in 1853, 1875 and 1916, all before the dams were built and before climate change started to bite. I think it would be foolish to think that similar events will never happen again (whether they will in our lifetime is another matter)

AugustusMinimus

corkgsxr wrote: »

Yes it will. The winds stop the river from draining effectively. Lower base height means lower flood water height.

Funny how dredging stopped and as the years go by we have worse issues with flooding.

If the tide is held at say 2 meters below peak, there is no way any amount of conceivable discharge or wind could result in the city centre flooding.

corkgsxr

Outkast_IRE wrote: »

I think dredging would have no effect on what occurred yesterday. As it was primarily due to a very high tide coinciding exactly with very low atmospheric pressure and a wind directly pushing water into the harbour. A combination of factors that dredging does not alleviate as you are literally fighting against sea level.

Yes it will. The winds stop the river from draining effectively. Lower base height means lower flood water height.

Funny how dredging stopped and as the years go by we have worse issues with flooding.

blindsider

alanucc wrote: »

There is an element of truth in your comment, but it's not the whole story. Keeping water levels in Lough Mahon low with a tidal barrier would help to reduce fluvial flood levels in the eastern part of the city centre. However for the really big fluvial floods like the 100 year event, the flow would still exceed the channel capacity and spill out regardless of the tide - particularly upstream of the Mercy.

To demonstrate this you only need to look at the 2009 event. I attached a water level graph taken from the river gauge which used to operate at Tyndall. The markups in red are mine, just trying to clarify what's shown.

You'll see that the flood actually rose on the falling tide, due to the magnitude of the flow coming from upstream. The gauge died during the peak of the event so not all of the river level data is there, but for sure the subsequent high tide prolonged/exacerbated the flood. However my point is that water had already spilled out and caused damage at Victoria Cross, UCC, Mardyke etc while the tide was down.

But wasn't 2009 an 'artificial' flood? The ESB added to the issue by opening Inniscarra. (I'm not getting into why, when, how etc - just a statement of fact.)

I am assuming that the dam won't be opened in a similar fashion again - therefore any future scenario will be different.

Also, if a tidal barrier is used properly, won't it be possible to create an 'artificial' temporary reservoir? Closing the tidal barrier at 'low water' would leave an empty Lough Mahon etc - plenty of room for the ebbing tide carrying the upstream water, and once the tide turns again, 12 hrs later, the barrier could be opened again? Couldn't this be done on successive days until the flood threat has passed?

2 Scenarios cause flooding:

1 - heavy and prolonged rainfall: Close the flood barrier at the end of 'low water'. Open it 12 hrs later at the start of the next 'Low water' cycle. 2-3 days later, the threat has passed...

2 - Tidal Surge - Spring tides are exacerbated by SE winds/gales: Close the tidal barrier until the start of 'low water' and the open it for 12 hrs.

Am I missing something?

wally1990

I look forward to this thread again next year
Thanks goverment, council and whoever else
And every year afterwards

alanucc

AugustusMinimus wrote: »

I’ve read others saying that a tidal barrier cannot stop fluvial flooding in the city. Absolute nonsense.

The tidal barriers can close before high tide leaving the water level in Lough Mahon and upstream well below the quay walls. The river can then discharge into Lough Mahon which would likely take weeks to fill with just the Lee alone. There’s no way the river could flood the city if the tidal barrier is used correctly.

There is an element of truth in your comment, but it's not the whole story. Keeping water levels in Lough Mahon low with a tidal barrier would help to reduce fluvial flood levels in the eastern part of the city centre. However for the really big fluvial floods like the 100 year event, the flow would still exceed the channel capacity and spill out regardless of the tide - particularly upstream of the Mercy.

To demonstrate this you only need to look at the 2009 event. I attached a water level graph taken from the river gauge which used to operate at Tyndall. The markups in red are mine, just trying to clarify what's shown.

You'll see that the flood actually rose on the falling tide, due to the magnitude of the flow coming from upstream. The gauge died during the peak of the event so not all of the river level data is there, but for sure the subsequent high tide prolonged/exacerbated the flood. However my point is that water had already spilled out and caused damage at Victoria Cross, UCC, Mardyke etc while the tide was down.

blindsider

@The Chizler - thanks for the link to the EcoEye video!

The OPW chap said that talk of a 2m - 2.5m sea-level rise is extreme. But the walls they propose are only sufficient for a 0.5m rise. Surely, if 2.5m is extreme on one hand, then 0.5m is extreme on the other!

The cost of the walls scheme is between €100m and €200m (2017 prices) and the tidal barrier is €140m (2017).

HR Wallingford, who were commissioned by Save Cork City to examine the issue also said:

The Dutch say that when considering flood walls it is better to choose the shortest form of
defence as it is easier to predict the outcome, more economical to construct and to maintain and significantly it is less likely to fail. We refer you to Edgecombe in New Zealand which flooded extensively in April 2017 due to a small breach in a walls based flood protection system. We also refer to New Orleans in 2017 which flooded due to its own pump system not starting when required.

https://data.oireachtas.ie/ie/oireachtas/committee/dail/32/joint_committee_on_culture_heritage_and_the_gaeltacht/submissions/2017/2017-10-18_opening-statement-save-cork-city-mr-john-hegarty_en.pdf

It's never been cheaper to borrow money than it is is now. The ECB is 'giving' money away.

https://www.irishtimes.com/business/economy/banks-rush-to-borrow-record-1-3tn-at-negative-rates-from-ecb-1.4282382
Banks have rushed to borrow a record €1.3 trillion from the European Central Bank at deeply negative interest rates in the latest monetary policy drive to boost liquidity in the euro zone’s pandemic-stricken economy.

It is the first time that a major central bank has offered multiyear loans to banks at an interest rate below its main deposit rate, introducing a so-called dual-rate system.

I understand that the country is in a parlous state with Covid as well as everything else. It seems to me that the OPW are entrenched and won't admit they got it wrong. Time for people to stand up and call them out on this!

(I have absolutely no connection to Save our City - or any other interested party.)

AugustusMinimus

I’ve read others saying that a tidal barrier cannot stop fluvial flooding in the city. Absolute nonsense.

The tidal barriers can close before high tide leaving the water level in Lough Mahon and upstream well below the quay walls. The river can then discharge into Lough Mahon which would likely take weeks to fill with just the Lee alone. There’s no way the river could flood the city if the tidal barrier is used correctly.

TheChizler

cantalach wrote: »

I fully agree that defining an objective measure of "directly affected" would be challenging but there needs to be some limit because you otherwise get ludicrous stuff, e.g. the Port of Waterford objected to the Port of Cork's new container port in Ringaskiddy, SuperValu objected to the new Aldi/Lidl in Bantry, etc.

I'd agree if the act of objecting alone counted against a development, effectively turning it into a popularity contest, but it's not; an objection has to point out an objective legal argument against it which the planners or judge consider in it's own right regardless of the location of the complainant. If they can't do that it's given the same weight as someone posting on boards. It's unfortunate that a judical review adds time the planning process that an earlier objection doesn't but if ABP have erred in their procedures it's worth getting to the bottom of IMO. It's added a few months to a multi-year construction project, people were quoted as saying it would be half built by now were it not for savecorkcity which is ridiculous, was there any chance of it even starting this year? Would a contractor been selected yet?

Because people commonly misread or misinterpret statements like you made, and would be under the impression that most businesses and residents supported Save Cork City. I was just clarifying what you wrote without disagreeing with it in the slightest.

I'm not sure how anyone but the most careless of readers would interpret "most X are Y" as "most Y are X" but I'll take you at face value here.

cantalach

TheChizler wrote: »

1. Anyone living in Cork is directly affected, whether by flooding or the destruction of the historic connection to the river. The importance you assign to either is subjective. If you can arbitrarily block people from objecting based on some subjective measure of how directly affected they are you might as well throw away the whole planning appeals system and let people do what they like.

I fully agree that defining an objective measure of "directly affected" would be challenging but there needs to be some limit because you otherwise get ludicrous stuff, e.g. the Port of Waterford objected to the Port of Cork's new container port in Ringaskiddy, SuperValu objected to the new Aldi/Lidl in Bantry, etc.

2. I never said most did, don't know, so I'm not sure why you'd make that point.

Because people commonly misread or misinterpret statements like you made, and would be under the impression that most businesses and residents supported Save Cork City. I was just clarifying what you wrote without disagreeing with it in the slightest.

TheChizler

True there are some fluvial flooding events that will need engineering work upstream of the city, but nothing to do with what happened yesterday. In theory the ESB should be preventing those kind of events but I'm not sure that can be relied on. No the tidal barrier isn't perfect either, but something has to be done and the full long term benefits, complications, and value of both schemes need to be weighed up. As admitted in that video the OPW are only focused on the short term low-to-medium 'worst' case predictions, and if they go ahead with it we'll be having the same conversation in a few short years.

Outkast_IRE

Ultimately i think both schemes are needed , just at different points along our timeline.

A tidal barrier is not without its problems, in some scenarios the ecological impacts can be appreciable.

Outkast_IRE

corkgsxr wrote: »

No need for barriers. Go back to dredging the river. Simple solution

I think dredging would have no effect on what occurred yesterday. As it was primarily due to a very high tide coinciding exactly with very low atmospheric pressure and a wind directly pushing water into the harbour. A combination of factors that dredging does not alleviate as you are literally fighting against sea level.

hans aus dtschl

TheChizler wrote: »

Eco eye did a program on this last year for anyone interested. I'm possibly biased but the OPW guy at the end didn't inspire confidence. Basically admitted that the plans were a bandage on the current problem.

But but but....

"A tidal barrier won't be economically viable for Cork until we have more than half a meter of sea level rise".

It's such a solid argument against building the tidal barrier, right?

Basically, it's the best long-term solution but the OPW say that it'll cost so much that they won't consider it.

PreCocious

The OPW plan is quite complex and has a lot of moving parts - many valves, multiple pumping stations and what have you.

Twice in the last few years a single, simple flap valve has failed leading to seawater flooding in to the Atlantic Pond causing serious damage to the area including the heronry.

On each occasion it has taken the city council many weeks to repair this simple flap valve.

This is the same council which can't maintain automatic bollards on Oliver Plunkett and Maylor Streets.

It doesn't inspire confidence.

TheChizler

Eco eye did a program on this last year for anyone interested. I'm possibly biased but the OPW guy at the end didn't inspire confidence. Basically admitted that the plans were a bandage on the current problem.

https://www.youtube.com/watch?v=y3_pIZLJvRk

TheChizler

cantalach wrote: »

Two points:

1. Unless you are *directly* affected, you are a third party.
2. Most Save Cork City member may well be businesses and residents, but that doesn’t mean that most businesses and residents support Save Cork City.

1. Anyone living in Cork is directly affected, whether by flooding or the destruction of the historic connection to the river. The importance you assign to either is subjective. If you can arbitrarily block people from objecting based on some subjective measure of how directly affected they are you might as well throw away the whole planning appeals system and let people do what they like.
2. I never said most did, don't know, so I'm not sure why you'd make that point.

Savecorkcity are commonly misrepresented as being against flood defenses full stop, they're not, many of their members are professionals in civil and environmental engineering and have pointed out the flaws in the current plans and a suitable alternative which the council and OPW have constantly failed to engage with. The current plans involve a complex interdependent system of walls, detachable barriers, pumping stations, and valves to protect a limited area of the city. If all of the above work at best they protect a portion of the city against flooding for a few years before rising sea levels overflow the walls during flood events. If any of those links fails (or water just seeps up through basements through the silty substrate under the city) they protect against nothing.

The council can't even organise sandbags with plenty warning of high tide, or temporarily improve cycle and pedestrian facilities when government are throwing money at them, do you honestly expect they'll be capable of maintaining that complex system and activating all the components when needed?

The tidal barrier, though probably more expensive, will protect everything from Lough Mahon upstream, have a longer lifespan, would be simpler to maintain with less single points of failure, and have next to no disruption to the city while constructing unlike the current plans which involve around 6 years of constant disruption as every quay and bridge connecting the city to the rest of the world is dug up, something traders in favour of walls seem to be forgetting.

I'm sure there's a few inaccuracies in that rant as it's been a while since I've looked into it but that's basically why I think walls are an inferior solution.

cantalach

TheChizler wrote: »

I'm fully with SaveCorkCity on this one. Most of their members are businesses and residents in the city so no third party argument.

Two points:

1. Unless you are *directly* affected, you are a third party.
2. Most Save Cork City member may well be businesses and residents, but that doesn’t mean that most businesses and residents support Save Cork City.

corkgsxr

No need for barriers. Go back to dredging the river. Simple solution