cuckoo
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Posts posted by cuckoo
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Better but need the limpet low to head SE
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8 hours ago, SevernTrent said:
Just to confirm that we only discharge when asked to by the Environment Agency and we haven't had such a request since early October. We didn't release any water before or during the weekend floods and, in fact, we haven't operated the valves for well over a month.
Thank you for coming on to explain the upside down graphs and to clarify that no valves were opened to release extra water before or during the weekend floods.
However a lot of water was still released into the Derwent from Ladybower through the plugholes (as you confirmed this occurs when the level is at a negative number). The response of the Derwent (rising to all time records in a number of locations) was out of step with other nearby rivers (e.g. Wye, which stayed below levels where property was at risk) suggesting that the water coming through the Ladybower plugholes was making a big difference.on the Derwent.
You said you didn't release any water before the floods but wouldn't it have made sense to do so?
Releasing water before the well forecast rain event and taking the reservoir level to a positive number would have left Ladybower in a position to absorb a lot more water prior to the level exceeding the plughole height and starting to overflow. I don't have access to the Environment Agencys river level prediction models but prior to Thursday I would have thought the Derwent was at a level where it could cope with some extra flow and would only flood low lying land.
I understand that it might have been the Environment Agency's call but it looks like the level is not being very actively managed and doing nothing prior to the weather warning may have been a missed opportunity to mitigate the level of impact of the floods.
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Looking at the historical data, I've been reading your graph the wrong way round. At the time Ashopton was visible, late summer/autumn 2018, the level is given as +13.01 mBDAT, which shows the positive numbers correspond to low reservoir levels and the negative numbers are when the reservoir is full.
Reinterpreting the recent graph that you posted it now looks very different. With all the rain on 07th the reservoir begins to fill and goes from +0.0 to -0.5. The normal operating level at -0.21 has been exceeded. Allow an embankment dam to overtop would be dangerous so water starts to be released into the river moving the level back towards -0.3 and the normal level.
Maybe there's no conspiracy after all!
If they were prepared to let it fill to -0.5 though couldn't they have held it for longer at that level before gradually releasing back to -0.2 rather than the sudden release at the worst time?
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above link about dam safety. The section that caught my attention about embankment dams like Ladybower
"If the downstream face of the reservoir is saturated with water, for example after very heavy rain or due to a leak from the reservoir, it will be weaker and more prone to failure by slipping along a plane of weakness within the embankment. The strength of the embankment can also be reduced over time. This reduction in strength can be caused by: • natural weathering • tree roots • burrowing animals"
Maybe there are some concerns about slope instability at Ladybower which triggered the water dump? Doubt I'll find out without working there.
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Very interesting post. Not sure, but I think something similar happened on the Derwent for the 2007 event.
As many people on this site posted the 24-hr rainfall totals for Thursday were typically below 50mm for a lot of the catchment areas surrounding Matlock. A wet day during a very wet autumn but still well below 2007 totals and well below the 100mm amounts that fell around the Don catchment area and onto the Derwent moors further North.
The response of nearby rivers like the Wye were nothing exceptional with levels presenting a flood risk to low lying areas only. Yet the Derwent exceeded all time records at Chatsworth and in Derby.
Looking at your graph I believe mBDAT stands for metres below datum. According to Google "the normal level of the Ladybower Reservoir at Ladybower Reservoir LVL in average weather conditions is between -0.21m and 13.03m".
Yet it is clear looking at your medium-term data that the reservoir level is being managed to keep the reservoir at or below the datum. When the level starts to exceed the 0.0 datum there is a discharge event to move it back. As anyone who goes there regularly will know Howden and Derwent dams often fill to full capacity and brim over the dam walls but Ladybower appears to be managed differently.
Maybe, as you say, there are safety concerns letting about letting Ladybower fill up and given the rainfall totals on the moors they visualised the mBDAT going strongly positive so preemptively dumped the water. Looking at the graph it looks like a big overreaction as even now the levels are still well down compared to the datum.
The timing and quantity of the water dump for some of those downstream was disastrous, turning a minor flooding scenario into an all-time record breaking event. Someone should be asking Severn Trent serious questions about what happened, but as you say, a few smoke-screen stories about the plugs, Boris Johnson in town with a mop and it should soon blow over.
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3 hours ago, matty40s said:
This is what happened at Ladybower reservoir yesterday, that's why the Derwent valley is having so many problems.
Why would they do that at that time?
Are there structural concerns about the dam when the reservoir is full?
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4 minutes ago, matty40s said:
only because they are dumping water out of Ladybower as fast as possible!!
Ah that explains why its so much higher than average compared to other nearby rivers e.g. Wye & Amber. Makes sense I guess, empty it now to make space to hold back as much as possible over the next few days. I remember in 2007 when the dam was overwhelmed the levels became very high downstream.
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Looks like the river Derwent is pretty high at Chatsworth (highest recorded level)
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The gulf stream continues up towards the arctic hindering ice formation. Therefore the northerlies heading toward the UK are soon being warmed over the ocean. As others have said areas of the mid-Atlantic / north east Pacific are much closer to frigid continental land masses e.g. Greenland and Northerly flows are subject to less modification prior to reaching the low latitudes.
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Fascinating conditions in the Netherlands, thanks for posting Vorticity.
I can certainly verify that freezing rain is dangerous as I have discovered (painfully) on my cycle commute before.
Looks like increasing possibilities for a UK cold shot now.
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Looking good for The Netherlands and West / South Germany tomorrow.
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This website shows lightning maps
http://www.lightningmaps.org/realtime
Invading the Peak District?? Sounds like a rise in Mercian nationalism happening around Birmingham!
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Lightening in Matlock.......
Could it have been power lines going down? The wet snow is really accumulating on telegraph wires & tree branches
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The last time we had 30cm of lying snow in January was 1987 so the next occasion is long overdue.
Surprised at that. I remember being near Buxton in Jan 2010 and there was just over 40cm. In December 2010 there was over 40cm near Chesterfield, so both west and east of the peak district did well, you must have been a bit unlucky on those occasions.
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Synopsis for Horizon tonight in case anybody might be interested.
Nobel Prize winner Sir Paul Nurse examines why science appears to be under attack, and why public trust in key scientific theories has been eroded - from the theory that man-made climate change is warming our planet, to the safety of GM food, or that HIV causes AIDS.He interviews scientists and campaigners from both sides of the climate change debate, and travels to New York to meet Tony, who has HIV but doesn't believe that that the virus is responsible for AIDS.This is a passionate defence of the importance of scientific evidence and the power of experiment, and a look at what scientists themselves need to do to earn trust in controversial areas of science in the 21st century.
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Nice pictures. It seems like the west of the pennines has seen more valley fogs whilst the east has been largely sunny and clear.
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Fantastic pictures :-)
How much snow on the table? Over 1 metre would be my guess
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I was watching the Arctic programme by Bruce Parry last night and a couple of remarks he made really hit home as to the scale of some of the changes taking place up there.
He was on Disko Island in Greenland with a geologist who was prospecting the mineral deposits. The geologist said that just a few decades ago the huge mountain sides of rock they were flying over were under ice 60 metres thick. Nowadays the bare rock is exposed and with the ice long gone the mining companies are moving in to extract the billion dollar deposits of zinc that were contained in the virgin hillsides.
I am sure many on here are fully aware of these changes having read the relevant research papers but as someone who only picks up limited information from the media I found the scale of changes quite shocking and the fact the minimg companies were already there blowing up the hillsides kind of shattered my preconceptions about Greenland still being a place virtually untouched by man.
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29 Nov-3 December 2010
Relentless snow showers over much of the North and East giving 20-30 cm of lying snow in South Yorkshire and around 40 cm in Lincolnshire.
Well there was 38cm even in the centre of Sheffield and many places had in excess of 40cm e.g. Chesterfield and I heard reports of Dronfield having in excess of 50cm.
I think they got the general areas affected well forecasted but underestimated the amount of snow that fell. A bit generous giving themselves a tick on that one.
26-27 December 2010A marked change to milder weather pushed across the UK from the west preceeded by rain falling on frozen surfaces.
That certainly wasn't what was forecast for my area (even with the rain band about 1 hour away the BBC 10:30pm forecast still went for snow). Maybe the person who scored the Metoffice performance could also do my performance review at work.
On the whole I think the MetOffice did well, especially with the cold snap predictions, but in this article they overestimate their local snowfall performance IMO.
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Interesting data thank you for posting it. Some impressive statistics, as you say, for a medium sized low-lying country.
I read also that Sweden has had a record cold setting December.
It seems you are well positioned for receiving cold shots, the latest northerly blast from the Baltic low (which skimmed Britain) semmed to hit you head on and I remember a number of northerly blasts last winter, that were initially programmed by the models to hit the UK, later slipped east and hit Denmark / Germany / Poland instead.
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What do you understand by a SD with regards to Artic ice ??
I understand it as the standard deviation of the dataset measuring arctic ice levels.
The validity of the dataset is another question entirely.
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I have no idea what your on about. The Met O removed the warnings from many areas including my own location way before the front arrived. The only warnings that existed were for high ground and even then they downplayed the amounts suggesting 2-5cm.
Fair enough about the inital caution but the 10:30pm weather forecast was still predicting snow for my region even though there were reports of mild temperatures and heavy rain approaching. It looked to me like they were too inflexible and went down like a captain with a sinking ship continuing to predict snow. Local councils and gritters have to make decisions based on the forecasts and in this instance a lot of taxpayers money could have been wasted.
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Assuming a normal distribution Students 2-tailed t-test would give less than 0.5% probability that 3 standard deviations of difference has occured by chance.
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Firstly I should say I am a weather layman and frequent the forum to ascertain the likely upcoming weather patterns, mainly through observing the model thread.
Many of the forum members on netweather were giving a list of things that needed to happen for the precipitation to fall as snow, e.g. front aligned NW / SE, the flow to change to include an Easterly component instead of straight Southerly etc..
As a laymen watching the event I did not see any of these things occuring yet the Met-office were predicting snow for my region so I was interested to observe the outcome. As the evening wore on some surprisingly mild temperatures were being reported in the regional threads where the 2nd precipitation band was passing over and some of the areas in the midlands where the BBC graphics had shown rain starting to turn to sleet / snow were only reporting heavy rain and significantly posiiive temperatures.
I was interested to view the BBC Look North forecast as it was aparent to me by now that this would likely be rain for my area but the local evening (after 10pm) forecast by Keeley Donovan continued to show rain turning to snow for my region although she did mention that the amount of snow expected had been downgraded slightly.
I was surprised at this forecast, given the weather reports coming in from further south, and after watching a few more reports coming in I concluded this event was 100% rain and didn't bother to stay up to see the band arrive as I had originally intended. Sure enough I was awoken in the night by heavy rain and wind lashing the windows.
I understand what people mean when they say they were "playing it safe" but if the council reacted to the late night forecast they would have sent gritters out wasting a lot of taxpayers money and a lot of dwindling salt stocks.
I think the forecasts have been largely very good in the recent cold snaps but last night was their second poor one for my region. If even an amateur like me could pick up enough information to conclude it was highly likely going to be rain why didn't they and why didn't their late evening forecast change?
Model output discussion - is the beast awakening?
in Forecast Model Discussion
Posted
Hoping these 'outlier' Ops don't prove to be trendsetters. Massive 12z's later.