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Whaley Bridge Evacuated


furnessvale
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11 hours ago, Cheshire cat said:

Just spotted you have responded to me Dave. I was under the impression that it was the low levels at Sutton last summer that caused Bosley to be closed for a few months. 

 

Does Toddbrook need to be so big? I presume it was built to serve the needs of the quarrying industry which must have involved many more movements than the leisure industry generates today. 

 

I assume your last statement is a reference to the frequency with which the banks above Bollington fail

Sutton was low last summer, when we took a look, and the locks were closed, but that doesn't indicate exclusive causation.

 

Bosley was shut because all the reservoirs were low, and yes my comment was a reference to the utter failure to maintain the canal at Bollington.

 

Does Toddbrook need to be so big? Well, there are many things they could do that would reduce the demand;

 

  • Fix the leaks at bollington
  • Fix the leaks through Bosley
  • Dredge all the reservoirs
  • Restore the side ponds at bosley
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9 hours ago, matty40s said:

There are experts and there are experts who know what they are talking about.

A weed has roots, which growing on the join of a concrete spillway will be growing through the mortar, grout, sealant etc which is supposed to stop water ingress. The roots will have weakened this. Some of those concrete joins had large weeds over the whole length of the joints....meaning the whole join was compromised....over its whole length. 

Go figure.

Well, the expert who saw no problem is a reservoir panel engineer, and therefor qualified to inspect a reservoir in the UK. Various other experts trotted out by the media are NOT qualified to inspect reservoirs in the UK.

 

Until we know the failure mode, it is difficult to say whether the vegetation is an issue.

 

One theory is that the concrete spillway had made it impossible to tell what the condition of the earth bank below was, and that it is entirely possible that the earth beneath the spillway had been undermined for some considerable time, and that the hydraulic forces acting on unsupported panels caused deformation and allowed water ingress.

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5 minutes ago, mayalld said:

Well, the expert who saw no problem is a reservoir panel engineer, and therefor qualified to inspect a reservoir in the UK. Various other experts trotted out by the media are NOT qualified to inspect reservoirs in the UK.

 

Until we know the failure mode, it is difficult to say whether the vegetation is an issue.

 

One theory is that the concrete spillway had made it impossible to tell what the condition of the earth bank below was, and that it is entirely possible that the earth beneath the spillway had been undermined for some considerable time, and that the hydraulic forces acting on unsupported panels caused deformation and allowed water ingress.

But the panel engineer does have a vested interest in proving the other panel engineer wasn't at fault? The university experts are impartial. 

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2 minutes ago, mayalld said:

One theory is that the concrete spillway had made it impossible to tell what the condition of the earth bank below was, and that it is entirely possible that the earth beneath the spillway had been undermined for some considerable time, and that the hydraulic forces acting on unsupported panels caused deformation and allowed water ingress.

 

I was wondering about this too, and such a fear that there was not much left underneath the rest of the spillway either was probably the reason they were so keen to get the water level down so fast. If they knew the only erosion was the visible bit, then stabilising it with the helicoptered-in bags of aggregate would probably have sufficed and peeps let back into their homes.

 

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Something that I don't understand and don't think has been explained in the thread:

 

Why are they using pumps?  Won't the draw down valves do that job and not use any energy?

 

 

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5 minutes ago, Theo said:

Something that I don't understand and don't think has been explained in the thread:

 

Why are they using pumps?  Won't the draw down valves do that job and not use any energy?

 

 

Probably they have lost the 'andle what works 'em. ;)

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6 minutes ago, Theo said:

Something that I don't understand and don't think has been explained in the thread:

 

Why are they using pumps?  Won't the draw down valves do that job and not use any energy?

 

 

The draw down valves will do ths job, eventually.  Pumps, which are really only needed to prime a syphon so don't use all that much energy, will speed things up because they provide extra capacity over that of the valves.

The limiting factor is where you can  put the water.  In this case the Goyt valley and the Upper Peak Forest.

N

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7 minutes ago, BEngo said:

The draw down valves will do ths job, eventually.  Pumps, which are really only needed to prime a syphon so don't use all that much energy, will speed things up because they provide extra capacity over that of the valves.

The limiting factor is where you can  put the water.  In this case the Goyt valley and the Upper Peak Forest.

N

New laws were brought in about ten years ago covering draw down of reservoirs.  New valves were fitted at Combs and Toddbrook to comply with these laws.

 

I stand to be corrected on the detail but the law requires something like one third or one half of capacity to be dropped in three days if an emergency like the present one occurs.  Given the elapsed time, the valves alone could have done the job without pumps, not forgetting the pumps are discharging into the same river as the valves would.

 

I hate conjecture, but are the valves working?  No doubt the inquest will reveal all in due course.

 

George

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Probably because the valve is near the bottom of the reservoir; and its all silted up. So, turn the valve (with great force) and you 1) snap something in the base of the reservoir, underneath metres of mud; 2) get a flowrate of about 3 litres/minute of water (but loads of silt/mud too). I guess if it were 'excercised', say weekly, a channel would remain to the valve and it would be fairly clear. But I bet that didn't (and doesn't elsewhere) happen!

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28 minutes ago, furnessvale said:

New laws were brought in about ten years ago covering draw down of reservoirs.  New valves were fitted at Combs and Toddbrook to comply with these laws.

 

I stand to be corrected on the detail but the law requires something like one third or one half of capacity to be dropped in three days if an emergency like the present one occurs.  Given the elapsed time, the valves alone could have done the job without pumps, not forgetting the pumps are discharging into the same river as the valves would.

 

I hate conjecture, but are the valves working?  No doubt the inquest will reveal all in due course.

 

George

Thank God it will be an enquiry and not an "inquest".

 

It is a near miss that could have been a major disaster except for the faultless response by the emergency services.

 

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5 minutes ago, PaulD said:

Thank God  Let us be happy that it will be an enquiry and not an "inquest".

 

It is a near miss that could have been a major disaster except for the faultless response by the emergency services.

 

 

I am in full agreement with you, subject to the minor modification shown. Unless, of course, your expression of gratitude to an imaginary deity was purely figurative!

 

It was the emergency services wot did it.

 

 

 

Edited by Machpoint005
sp.
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14 minutes ago, Paul C said:

Probably because the valve is near the bottom of the reservoir; and its all silted up. So, turn the valve (with great force) and you 1) snap something in the base of the reservoir, underneath metres of mud; 2) get a flowrate of about 3 litres/minute of water (but loads of silt/mud too). I guess if it were 'excercised', say weekly, a channel would remain to the valve and it would be fairly clear. But I bet that didn't (and doesn't elsewhere) happen!

I suspect it's because of where the sluice comes out in relation to the collapsed spillway - they might be trying very hard not to undercut the collapsed bit any further!

 

https://www.google.co.uk/maps/@53.3267792,-1.9897661,136m/data=!3m1!1e3

 

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12 hours ago, matty40s said:

There are experts and there are experts who know what they are talking about.

A weed has roots, which growing on the join of a concrete spillway will be growing through the mortar, grout, sealant etc which is supposed to stop water ingress. The roots will have weakened this. Some of those concrete joins had large weeds over the whole length of the joints....meaning the whole join was compromised....over its whole length. 

Go figure.

Well to 'go figure' perhaps you can offer an answer to the question raised, which was " If the plants were the problem why has the right hand side remained undamaged? " 

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4 minutes ago, Wanderer Vagabond said:

" If the plants were the problem why has the right hand side remained undamaged? " 

 

I'm not the right flavour of engineer, but my stock answer to the question "What's causing it?" was always "That's what I'm here to find out. When I have found out, I'll tell you".

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37 minutes ago, Wanderer Vagabond said:

Well to 'go figure' perhaps you can offer an answer to the question raised, which was " If the plants were the problem why has the right hand side remained undamaged? " 

Isn't it that the plants weren't the initial problem, the water hitting the side wall was the problem.  That caused excessive turbulence in that particular area, and then add in the fact that the plants had weakened the structure enough to allow the water to batter it's way through, though they may of course have added to the turbulence too.  For the rest of the spill, the water might have been belted down at unprecedented rates, but it didn't have the turbulence or drilling effect of the side wall area.

Whatever the cause, I'd lay odds that we'll never hear the results of any investigation - it'll be kept secret "for commercial reasons" or simply to avoid frightening the natives.

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1 hour ago, PaulD said:

Thank God it will be an enquiry and not an "inquest".

 

It is a near miss that could have been a major disaster except for the faultless response by the emergency services.

 

My use of the word was deliberate.  Heads will roll! ?

 

George

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The plant life could be kept in check if the spillway thing was used for surfing when wet or as a dry ski slope or skateboard slope. If a part of it was curved upwards at the bottom Halfpipe practice looping the loop could be done.

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Emergency crews pumping water from a damaged dam above Whaley Bridge have reached their target.

The Canal and River Trust said it needed to drop the water level by eight metres and confirmed the level was now down 8.4m.

More than 1,500 people were evacuated from their homes on Thursday amid fears the 300-million-gallon Toddbrook Reservoir could flood the town.

They hope to find out later when they can return.

The Canal and River Trust, which owns the dam, said it carried out an annual inspection of the structure in November and it was "absolutely fine".

The government has said it is considering a national review into the structural safety of dams across the country.

https://www.bbc.co.uk/news/uk-england-derbyshire-49247226

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Roger Meredith was a construction engineer at Tarbela dam in Pakistan. This is an earth-filled dam like the one at Toddbrook Reservoir but is much bigger - 2,743 (1.7 miles) long compared with Toddbrook's 200m (0.12 miles) length.

He thinks the presence of vegetation on the spillway is not a good sign.

"It isn't good because whatever vegetation is there, its roots are going through the joint of the slabs or where the slabs are cracked," he said.

"There has to be some sort of ingress of water there somehow."

He said concrete slabs on water-retaining structures should have "water bars" in between the joints to stop water being able to get through. However, he was not able to see any bars in photos of the collapsed spillway.

"It looks like the slabs are not reinforced with steel," he said. "There has been ingress of water either through cracks or through the joints between the slabs.

"Somehow water has got in under the slabs and popped the slabs off."

Mr Meredith also thinks there is a problem with the design of the auxiliary spillway.

"When you look at the spillway the side kicks in, it's not straight. So you are increasing the amount of water trying to get down that side," he said.

This is the same side of the spillway where residents have seen water flowing down and pooling in the past. It is also the same side that collapsed.

He added: "Vegetation in itself is not a major concern. It does obviously demonstrate that water could penetrate the spillway slab. Water penetrating the spillway slab is the reason the slab failed."

 

 

Dr Panagiotis Michalis has been researching dams since 2010 and has assessed several in the UK as part of consultancy work through the University of Strathclyde.

He believes dams are a "ticking bomb" because of their ageing infrastructure and thinks incidents like the one at Whaley Bridge will become more common.

"In the UK the majority of the dams are more than 100 years old. That means they've exceeded their design lifespan," he said.

"Back then their design standards didn't take into account future climatic conditions that are happening now, so they have an outdated design."

He described the vegetation in the photos as a "yellow flag".

"Vegetation is an issue in dams, especially if this vegetation is coming out of concrete panels like the ones of this particular dam," he said.

"The vegetation might have opened ways inside the concrete, allowing water to infiltrate inside its clay core that has led to erosion."

However, he said the vegetation "does not look to be so extensive" and the collapse of the dam "cannot be attributed just to vegetation, but probably a matter of factors".

One of these factors, he believes, was the dry weather followed by heavy rainfall.

"The problem is we are passing from extreme dry periods where the reservoir is very low, to extreme rainfall events and flooding which fills the reservoir very quickly," he said.

"The water level fluctuations of the reservoir have a significant impact on the deformation of these dams."

 

 

The BBC spoke to two people who live near the dam, both of whom said they had been concerned for years about the condition of the structure.

One said: "Everybody has been concentrating on it [the collapse] being global warming, but I think the biggest factor in all of this is the absolute lack of maintenance of the dam".

One resident said the spillway was not level and water pooled in the area which has now failed.

"You would always see water in that part of the dam," he said.

 

 

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2 hours ago, Theo said:

Something that I don't understand and don't think has been explained in the thread:

 

Why are they using pumps?  Won't the draw down valves do that job and not use any energy?

 

 

 

Its a very good question, and the answer could possibly be political and nothing more. 

 

Boris may well have demanded a show of lots of pumps being delivered for the TV cameras.

 

I've not seen any photos or footage yet of any of the extra pumps actually running. Has anyone?

 

 

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2 hours ago, Theo said:

Something that I don't understand and don't think has been explained in the thread:

 

Why are they using pumps?  Won't the draw down valves do that job and not use any energy?

 

 

The pumps are being used to supplement the draw down valves. See the report from "New Civil Engineer"

 

https://www.newcivilengineer.com/latest/whaley-bridge-dam-engineers-reduce-reservoir-target-level-06-08-2019/?eea=SHFEcFNZN2c1RDVaaXBlSHFNUmxGRm0xaFIvYldLajdGWVdEcXlRODh1WT0=&n_hash=63&mkt_tok=eyJpIjoiTkdZMk1URXpNREV4Tm1WaiIsInQiOiJma3RKclhoT3BqTHhqVU9Ed2c0VmhlQUdsdWZ2WWhRcEo3ODBEdGRVS0cxZTVtNVRKZ3FwVFRYRU03ZU8rUnBVUG5oMTNyRWt1MmhzM1ppa3hKMDhsZTU2eFBwd0ZnbDZ2RHlqenVwTEp2XC9xQVhXcXpCN2VjTkpKSXI4WVRUck0ifQ%3D%3D

 

"We opened the emergency values and sandbagged the top of the weir. Once we had done that and started to get pumps on site, we actually broke the crest of the auxiliary spillway weir to try and increase the flow down that direction. Doing this brought the water down below the primary weir level.”

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1 hour ago, Arthur Marshall said:

Isn't it that the plants weren't the initial problem, the water hitting the side wall was the problem.  That caused excessive turbulence in that particular area, and then add in the fact that the plants had weakened the structure enough to allow the water to batter it's way through, though they may of course have added to the turbulence too.  For the rest of the spill, the water might have been belted down at unprecedented rates, but it didn't have the turbulence or drilling effect of the side wall area.

Whatever the cause, I'd lay odds that we'll never hear the results of any investigation - it'll be kept secret "for commercial reasons" or simply to avoid frightening the natives.

I think that you are probably right about the turbulence effects, but that is just an opinion. You are undoubtedly right about the results of the investigation, but this goes back to 'where there's a blame there's a claim' culture we now have. Why would you release information to those who want to sue you, logic says that if they want the information they should commission their own assessors and then the two sets of assessors can argue the toss between themselves at Court (for considerable expense). On the other hand an enquiry solely to find out what happened, why it happened and what we can do to stop it happening again, without looking for someone to blame (in the style of aviation enquiries)..................

Edited by Wanderer Vagabond
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