River Lee levels at 5m this morning - ESB in deep slumber after the Christmas binge

Impetus

River levels at the UCC Maltings site reached 5m this morning – please see chart:

http://77.74.50.157/cfw/

High tide was 4.2m at 07h08 on Monday morning 28.12.2015 – which implies about 80 cm of water height at the Maltaings was due to river pressure of flow (ie 4.2 tidal + .8 river = 5m total height).

The river height is down to about 3 m and falling just now, and likely to hit a low of about 2.5 m in a few hours, before the tides start pushing it up again. The river should be flowing past the Maltings around at least 4.7 m height all day and all night – ie the sluice gates should be almost fully shut at high tide, and opened to make maximum use of the ebbing tide. If this was being done, the chart at http://77.74.50.157/cfw/ would be almost a straight line at 4.7m level, or thereabouts.

The river catchment basin has about 70 mm of rain forecast between now and Wednesday afternoon. There is always a fallibility range in forecasting – it could be wetter or less wet than forecast. For planning purposes one has to assume the worst end of the forecast range.

The catchment area of the Lee is 1’253 km2 which is 1,253,000,000 m2 of land collecting rainfall, most of which ends up flowing into the river system.

Given the forecast rainfall of 70 mm over about 48h, that means an additional 87,710,000 tonnes of extra water flowing into the river. Call it 87 million. The normal long term flow of the Lee is about 3.45 million tonnes every 24h. While some of this rainfall will end up underground, and evaporating (not a lot of that with 93% humidity), much will be dumped in and on the city area, putting pressure on the river system to deal with such large water movements over a short period. There are also other rivers flowing into the Lee, which can’t be controlled by the dam system. Depending on where the rain falls, these tributaries could use up river capacity downstream.

This dumping must be managed by storage in the reservoir system, and making the most of tidal variations to dump water as quickly as possible.

The chart shows that this opportunistic discharge of water is not being carried out. This is putting low lying property at risk. Needlessly.

Add to that the strong southerly winds forecast for tomorrow (Tuesday) 16 m/s – southerly winds tend to maximise tide levels. Met.ie have assigned Orange to this wind risk. Perhaps it should be status Red is low lying areas….

TheChizler

I'd be interested to know how long it takes for high tide to propagate up to the maltings. And also what the levels are measured relative to. I presume it's height above the river bed in the river but relative to some statistical mean elsewhere. Might look into it when I'm on the PC later.

As mentioned in another thread if you were to keep the level at the maltings at 4.7 m at low tide it would involve basically washing away communities upstream.

Impetus

TheChizler wrote: »

As mentioned in another thread if you were to keep the level at the maltings at 4.7 m at low tide it would involve basically washing away communities upstream.

Why? Link please? Your posting is gloriously vague and without detail on the factors as you see them.

It seems to me that if they can handle 4.7 m without flooding upstream, at high tide, they should be able to handle the same height during the 24h cycle. It may require additional water level gauges to fine tune the discharge -but so what?

There are water gauges all over the country on https://waterlevel.ie but none in Cork city centre, or at any point in on the city side of the dam system or at any point along the reservoir itself. These need to be published in real-time (as well as putting them into the sluice gate feedback/control loop). People can't rely on ESB or any other government agency to accurately manage the flood risk, and at the very least should be provided with accurate, high resolution (relative to their local risk source) data so that they can take their own action to preserve life and property.

Ideally the gauge data should be combined on a dash board with forecast rainfall data, tide, windspeed and direction forecast etc. Something like: http://smartgriddashboard.eirgrid.com/#all which is used for the power grid.

TheChizler

I'll try to get my hands on figures later but as you say, during high tide most of the level is not due to the flow from the dam, only a small percentage is. The greater percentage is from the tide. Areas upstream closer to the dam are totally unaffected by the tide, their level is mainly dictated by the flow from the dam.

Therefore during low tide, when the level by the maltings is least affected by the tide, and you want the level to be the same as at high tide, the majority of the height will have to be provided by the flow from the dam. Portions of the river upstream which would have in general a fairly consistent level would become hugely variable, tidal even, under the proposal. The high level upstream would be much greater than its current level. I presume those living around Carrigodrohid wouldn't be fans of this proposal.

Tldr; in order to make a consistent level downstream in tidally affected areas, the flow upstream will have to be increased massively from current rates in advance of times of low tide.

TheChizler

Thinking a bit more about this it could be devastating for the city too. There's several meters difference between 4.7 m at the maltings and low tide where the river joins back together by the Port of Cork sign. Taking this as (very roughly) the point where river flow no longer has an effect on the level, i.e. purely tidal as it has the volume of the estuary and Cork Harbour behind it, you would have this difference of x meters over a mile or two. This would equate to a massive flow rate being necessary in order to maintain that level. In electrical terms, that's a short circuit.

I imagine this would have consequences for the areas around the Carrigrohane Road, the Mercy and Western Road, never mind further upstream where the river bends.

The good news is that I don't think the dam has the capability of maintaining this necessary flow, short of blowing it up.

Impetus

TheChizler wrote: »

Therefore during low tide, when the level by the maltings is least affected by the tide, and you want the level to be the same as at high tide, the majority of the height will have to be provided by the flow from the dam. Portions of the river upstream which would have in general a fairly consistent level would become hugely variable, tidal even, under the proposal. The high level upstream would be much greater than its current level. I presume those living around Carrigodrohid wouldn't be fans of this proposal.

The only reason I picked the Maltings river level is that it is the sole city centre river level meter on the internet. It is not a question of do I flood Carridodrohid or the city centre. Which is why I suggest that waterlevel.ie (i.e. OPW) should have online water level meters at that side of the river too. Aside from that, there is far more life and property at stake in the city centre than points west upstream.

TheChizler wrote: »

Tldr; in order to make a consistent level downstream in tidally affected areas, the flow upstream will have to be increased massively from current rates in advance of times of low tide.

Exactly my point. During periods of tidal ebbing, turn up the volume. During high tide, turn the tap off (i.e. water flowing out of the dam system). One could use an algo based control system, fed from multiple water level meters to manage the system. As of lunchtime Maltings is only showing 2.5 m of water. Another lost opportunity to make space in the reservoir for the deluge forecast for early tomorrow morning + high wind impact on tides.

This and other river systems in Ireland are 'managed' with breathless incompetence.

The latest model run on http://www.wunderground.com/q/zmw:00000.1.03955?sp=ICORKCOR19 is forecasting 111 mm of rainfall overnight for Cork, on Tuesday night. This mornings model run was showing just under half that figure. This is based on 14 stations in the Cork city area - which is far higher in data resolution accuracy than met.ie whose only stations are at Cork Airport and Roche's Point.

Impetus

TheChizler wrote: »

Thinking a bit more about this it could be devastating for the city too. There's several meters difference between 4.7 m at the maltings and low tide where the river joins back together by the Port of Cork sign. Taking this as (very roughly) the point where river flow no longer has an effect on the level, i.e. purely tidal as it has the volume of the estuary and Cork Harbour behind it, you would have this difference of x meters over a mile or two. This would equate to a massive flow rate being necessary in order to maintain that level. In electrical terms, that's a short circuit.

I imagine this would have consequences for the areas around the Carrigrohane Road, the Mercy and Western Road, never mind further upstream where the river bends.

The good news is that I don't think the dam has the capability of maintaining this necessary flow, short of blowing it up.

Again, at the expense of repeating myself, OPW or whoever should put water level meters along both channels of the Lee, all around the downtown island - map : https://www.google.ie/maps/@51.8996992,-8.4644125,17z and use the data collected as part of a feedback loop to control the sluice gates. The tide is out at the moment, The river is relatively low all around the city. There is no excuse for not increasing the flow rate from the dam. It is as bog simple as that.

Your sort of thinking is not part of the solution - it seems to me to be part of the problem!

Graham

Impetus wrote: »

Again, at the expense of repeating myself, OPW or whoever should put water level meters along both channels of the Lee, all around the downtown island - map : https://www.google.ie/maps/@51.8996992,-8.4644125,17z and use the data collected as part of a feedback loop to control the sluice gates. The tide is out at the moment, The river is relatively low all around the city. There is no excuse for not increasing the flow rate from the dam. It is as bog simple as that.

Your sort of thinking is not part of the solution - it seems to me to be part of the problem!

This I think was answered a week ago when you posted it last:

http://www.boards.ie/vbulletin/showthread.php?t=2057536054&page=3

Impetus

Graham wrote: »

I think was answered a week ago when you posted it last:

http://www.boards.ie/vbulletin/showthread.php?t=2057536054&page=3

Yet another gloriously vague comment that simply poinrs to another page of comments. Is it impossible for certain people to express themselves precisely?

TheChizler

Just because it's not publicly available doesn't mean the ESB doesn't have access to that data, or aren't able to infer fairly accurately the levels in between via data modelling.

Impetus

TheChizler wrote: »

Just because it's not publicly available doesn't mean the ESB doesn't have access to that data, or aren't able to infer fairly accurately the levels in between via data modelling.

Transparency please. Why bother with a vague coverage on the OPW website? What river gauge data does ESB have not on waterlevel.ie?

The public should have access to these data first hand.

The public has to pay for flooding screw-ups.

It is incredible that the second city has no public river level data. It points to a dysfunctional state.

Impetus

I have driven along the North and South channels of the Lee this afternoon and there is an obvious imbalance between the higher carrying capacity of the North channel and that of the South. The South channel is narrower in most places, which causes the river to flow at higher levels, for a given amount of water, than the North channel.

The river splits into two channels here
Satellite map: https://www.google.ie/maps/@51.894899,-8.506496,461m/data=!3m1!1e3

There are a series of weirs, which appear to be connected with the water works water extraction facility.

There is a second weir at 51.894305, -8.507156, and an island with trees (51.894576, -8.506410) which seem to me to be restraining the flow into the North channel. This channel could take more flow, relative to the South channel. Perhaps part of the solution would be to have an electromechanical floodgate system to regulate the flow of water into the North channel to maximize its carrying capacity. The movement of this floodgate would have to be based on detailed water level readings fed in real time from various points along the North and South channels.

The North Channel is at its widest at the Maltings (51.898723, -8.483903).

The lower end of the gardens along Sunday’s Well act as a natural flood plain, without risk to the houses themselves (with the odd exception), which are on much higher ground. UCC is the landowner most at risk, if something is not done to better manage water flows. Much of the main campus lies on the banks of the South channel. Ditto for the Mardyke arena and the Maltings/Tyndall Institute, also UCC property.

There are few opportunities to make the river wider, aside from removing islands of trees, which block flow into the North Channel.

Suggestions:

1. Install higher resolution measurement and real-time data collection on river heights taken from various points along both channels of the river in the centre, as well as data on reservoir height levels. Flow rates and river heights should also be available for tributaries.


2. Remove the ‘artificial blockage’ at the point where the North and South Channels form to allow more water to flow into the North channel, ideally using controllable electromechanical floodgates.


3. Keep more of the water upstream, by paying farmers whose land bounds the reservoir system to store water during the peak wet periods. It may be necessary to increase the height of the walls of the Iniscarra dam, and perhaps buttress the walls with steel to increase their stability during periods of peak stress from water pressure.


4. Install a water traffic management system which is capable of taking in the variables (river and reservoir heights, rainfall forecast, and tidal heights).


5. Construct higher walls at critical points along river banks to prevent overflow.

The increasing number of climate extremes, which will involve higher rainfall outbursts for Ireland, make the need for action more urgent.

Impetus

Some images taken this evening of where the River Lee splits into two channels – the North and the South.
It is easy to see the weir which forces much of the water into the South channel – despite its low carrying capacity compared with the North channel on the right.
These images were taken just after 16h00 UTC – 2015.12.29.
The weir is causing a high flow into the left branch (looking downstream) which is the South (skinny) channel of the Lee compared with the right wideband (North channel).
https://s3-eu-west-1.amazonaws.com/repstore101/DSC03421.JPG
https://s3-eu-west-1.amazonaws.com/repstore101/DSC03419.JPG
At Wellington Bridge, the North channel could take perhaps 80 to 100 cm of higher water level without a problem.
https://s3-eu-west-1.amazonaws.com/repstore101/DSC03423.JPG
Add to that the obstructions to the free flow of water along the North Channel, forcing it along the South channel – a recipe for disaster.
https://www.google.ie/maps/@51.894616,-8.5065041,271m/data=!3m1!1e3
http://www.openstreetmap.org/search?query=Cork%20city#map=17/51.89441/-8.50700

Impetus

I had a further look at relative North/South channel river levels this afternoon around 13h30.

While the bridges around Wandesford Q were running at about 95 to 98% water flow capacity, the North Mall bridges were only carrying about 70% of their total water capacity.

This takes me again back to the weirs a few hundred m to the west of R846 Wellington Bridge, where the river splits into two channels. One of those weirs is causing excess gravitational flow into the South channel –v- the North Channel. The other weir is sprouting vegetation and the ‘island’ in the river is reducing North channel flow rates. A further consideration is the city water treatment plant.

Nothing was done since the 2009 disaster, aside from repair work to re-instate walls etc. No provision was made for the next 1 in x year major flood event to control the river’s contribution to same. This is gross negligence on the part of the authorities responsible.

It seems to me that multiple defence levels are necessary upstream, where more water is temporarily stored on ‘rented land’ in times of impending crisis. This water could be trapped upstream using mechanical floodgates or sluice gates. They might even be used to generate some electricity and provide road crossings over the river. You can store a large quantity of water in a flood plain – far more than in a skinny river. By way of example turn the R619 bridge into a water flow control device (eg type of sluice gate). Allow an amount of flooding to occur to land upstream of this bridge in the event of an emergency, and pay the landowners affected a per Ha compensation rent for the period in question. After a survey other points of control may be determined, which may well be more suitable The R619 is only a suggestion.

As a last element in the chain of defences, install mechanical floodgates at the entrance to the North and South channels which would allow independent controls for either channel, and the holding back of water – forcing it to flood the Lee Fields (rather than in downtown Cork). This would allow each channel to take their full burden of water independent of the other channel. Management of the process could be computer controlled based on an algorithm collecting real-time data from water level and flow rate meters situated at various points up and downstream.