Jump to content
Sign in to follow this  
JohnD

Damned, or not?

Recommended Posts

I see that the RAF is using Chinook helcopters to lift tons of giant sandbags onto the damaged spillway of the dam above Whaley Bridge, to try and stop it collapsing.

They show extraordinary flying skill, dropping tons at a time, precisely on the right sport, but is this a real, if temporary, repair job?     Not just a "quick, get busy, do something to look as if we know what we're doing!" ploy, to satisfy the madia?    The overflowing water washed away concrete slabs.   If it overtops the dam again, surely it will wash those sand bags away?

John

 

Edited by JohnD

Share this post


Link to post
Share on other sites
4 minutes ago, JohnD said:

I see that the RAF is using Chinook helcopters to lift tons of giant sandbags onto the damaged spillway of the dam above Whaley Bridge, to try and stop it collapsing.

They show extraordinary flying skill, dropping tons at a time, precisely on the right sport, but is this a real, if temporary, repair job?     Not just a "quick, get busy, do something to look as if we know what we're doing!" ploy, to satisfy the madia?    The overflowing water washed away concrete slabs.   If it overtops the dam again, surely it will wash those sand bags away?

John

 

Yes, overtopping water will wash out the earth behind the bags. I'm puzzled why a geotextile wasnt draped over the soil and then bags of stone dropped to hold it in place. Also why not use bags of stone to raise the crest of the dam above the damage so overtopping there is reduced.  A resoundingly amateur effort.   Peter

Share this post


Link to post
Share on other sites

I expect the idea is just to add weight to stabilise the wall where it is now short of mass. They are pumping out to prevent over-topping.

Share this post


Link to post
Share on other sites
1 minute ago, DeTRacted said:

I expect the idea is just to add weight to stabilise the wall where it is now short of mass. They are pumping out to prevent over-topping.

Ah, yes, to stop the wet side of the dam buckling and then leaking below the waterline, I can see that now. But as the damage was due to overtopping and more heavy rain might fall, how much time has pumping-down bought before water spills over again ?  Looking closely at the photo there is what appears to be a row of sandbags along the crest.  

Peter

 

Share this post


Link to post
Share on other sites

Come on chaps give them some credit.

The bags are there to help reduce the effects of rain. To stop the infill, under the panels, being washed away.

Who is to say that when all the bags are in place they will not put a plastic covering over it.

 

Every news broadcast spouts out some more rubbish. I don;t know where the BBC get their info from but it is fantasy.

 

Roger

 

 

Share this post


Link to post
Share on other sites

I thought the bags of ballast is the first stage. Think I heard somewhere they are then going to fill with quick acting cement to seal and bind the bags together.

Mark

Share this post


Link to post
Share on other sites

My only experience of amateur civil engineering for water control has worked a treat. https://supertrarged.wordpress.com/2015/11/12/concrete-canvas-ditch-lining/

But further upstream there are dams of loose stones held with dead tree trunks..compacted leaves and silt. And a 2 meter long erratic boulder, nice and rounded, ready to roll as the stream undercuts it. The TRs live downhill. And all inaccesssible to diggers except maybe the spider type.  Answers please......

Peter

 

Share this post


Link to post
Share on other sites

Fascinating series of pics, Peter!

But when a influx of pigeons threatened the visitors to the Crystal Palace with fouling, and for obvious reasons they could not be shot, Prince Albertbwas stumped.  The Queen asked the wisest man she knew, thevDuke of Wellington, who replied, "Try sparrowhawk's, ma'am!".     I don't pretentbto be the wisest, but I say, try Beavers, Peter!

John

Share this post


Link to post
Share on other sites
57 minutes ago, JohnD said:

Fascinating series of pics, Peter!

But when a influx of pigeons threatened the visitors to the Crystal Palace with fouling, and for obvious reasons they could not be shot, Prince Albertbwas stumped.  The Queen asked the wisest man she knew, thevDuke of Wellington, who replied, "Try sparrowhawk's, ma'am!".     I don't pretentbto be the wisest, but I say, try Beavers, Peter!

John

Good idea John, except the trees are falling across the stream without beaver-assist.  Like beaver dams the rock+silt dams are good at slowing the torrent. What I need to do is stabilise them, as a sudden collapse could bring several tons of rock and even more water onto the garage roof.   Dont ya love climate change.

Peter

 

Share this post


Link to post
Share on other sites
10 hours ago, JohnD said:

I see that the RAF is using Chinook helcopters to lift tons of giant sandbags onto the damaged spillway of the dam above Whaley Bridge, to try and stop it collapsing.

 

They show extraordinary flying skill, dropping tons at a time, precisely on the right sport, but is this a real, if temporary, repair job?     Not just a "quick, get busy, do something to look as if we know what we're doing!" ploy, to satisfy the madia?    The overflowing water washed away concrete slabs.   If it overtops the dam again, surely it will wash those sand bags away?

John

 

John

They're not bags of sand

According to the guy who supplied 157 (or was it 153, can't remember) of the bags, they contain what he described as 'rocks'

Will they wash away?

I guess so, if the water flow is great enough, but, they will certainly survive where sand will wash away

John

Share this post


Link to post
Share on other sites

Chaps

Received wisdom seems to be that the emergency bolstering of the dam, pumping and the precautionary evacuation are the best solutions.

The dam is about 180 years old and is, fundamentally, a big lump of earth which provides enough critical mass to offset the weight of water pressing on it, with a core of clay to maintain a waterproof lining.  The spillway ostensibly prevents the pressure of water getting anywhere near the limit of the dam’s ability to restrain it.

The erosion of the spillway risks reducing the critical mass of the dam and increasing the waterlogging of the dam structure, both of which undermine its ability to retain the body of water behind it.  The priority is therefore to add stable critical mass to the body of the dam, which the ballast sacks will achieve, and to reduce the volume of water in the reservoir, which the high-capacity pumps are aiming to do.  At this point, adding geotextile would only add complexity and delay.

There is a long history of repairs to the Toddbrook reservoir, including a partial draining about ten years ago.  The spillway was severely damaged fifty-odd years ago and the increased rainfall in recent years – and the prospect of more in the future as a result of CC – mean that a more fundamental solution to Toddbrook is needed.  Like Oroville dam last year, it may be that a key part of the problem is that the design of the spillway is fundamentally flawed.

There is no precedent for the complete collapse of a clay retaining dam and several respected engineers have offered opinions that it wouldn’t happen at Toddbrook, even without the emergency stabilising works.

  Heaven forbid that there should be a first time.

Paul

Share this post


Link to post
Share on other sites

 

32 minutes ago, PaulAA said:

Heaven forbid that there should be a first time

Lets hope that they don't get any significant rain before they've got their repairs sealed and the level down further.  Pumping is a very poor substitute for a spillway.....

Share this post


Link to post
Share on other sites
3 hours ago, PeterC said:

Good idea John, except the trees are falling across the stream without beaver-assist.  Like beaver dams the rock+silt dams are good at slowing the torrent. What I need to do is stabilise them, as a sudden collapse could bring several tons of rock and even more water onto the garage roof.   Dont ya love climate change.

Peter

 

But, Peter, the beavers will.do.that for you!  And routine maintenance.  J.

Share this post


Link to post
Share on other sites
1 hour ago, Janner said:

John

They're not bags of sand

According to the guy who supplied 157 (or was it 153, can't remember) of the bags, they contain what he described as 'rocks'

Will they wash away?

I guess so, if the water flow is great enough, but, they will certainly survive where sand will wash away

John

The water shifted concrete blocks that were yards wife and high.   Rocks or sand in those bags they'll wash away too if it comes back surely.   But I like Pauls made addition theory coupled with pumping out the reservojr.  Let's hope the predicted heavy r ain on Sunday does fall.in that catchment.

J.

Share this post


Link to post
Share on other sites
9 hours ago, JohnD said:

The water shifted concrete blocks that were yards wife and high.   Rocks or sand in those bags they'll wash away too if it comes back surely.   But I like Pauls made addition theory coupled with pumping out the reservojr.  Let's hope the predicted heavy r ain on Sunday does fall.in that catchment.

J.

John

Mother Nature remains firmly in control of our planet.

All we do is piss her off.

To be living in Whaley Bridge right now must be a nightmare.

You are right, be it sand, rock, or mans greatest ever construction, water will move it, it's just a matter of volume.

I'm just keeping my fingers crossed for all the residents up there.

John

Share this post


Link to post
Share on other sites

A few years ago we were walking up a river valley in southern France, inland from Frejus. We started coming across massive blocks of concrete, clearly smashed off a huge structure. Over a few hundred metres these went from car sized to house sized, then to apartment block sized. Then finally, the remains of a concrete dam wall. Still attached the valley side on one side, utterly gone on the other.

There was no memorial or info-boards explaining it which is perhaps surprising as it turned out to be this

https://en.m.wikipedia.org/wiki/Malpasset_Dam

423 dead......

Share this post


Link to post
Share on other sites

I read in my newspaper that concrete is being poured over the dropped ballast.  Let's hope it sets by tonight (??)

Interesting link, Nick.    I was puzzled by one of the reasons given for the Malpasset disaster, "the water pressure was aimed diagonally towards the dam wall".

Pressure has no direction, or rather acts in all directions.   Or do I misunderstand?

John

Share this post


Link to post
Share on other sites
2 hours ago, Nick Jones said:

A few years ago we were walking up a river valley in southern France, inland from Frejus. We started coming across massive blocks of concrete, clearly smashed off a huge structure. Over a few hundred metres these went from car sized to house sized, then to apartment block sized. Then finally, the remains of a concrete dam wall. Still attached the valley side on one side, utterly gone on the other.

There was no memorial or info-boards explaining it which is perhaps surprising as it turned out to be this

https://en.m.wikipedia.org/wiki/Malpasset_Dam

423 dead......

Nick

Similar experience upon discovering the area of the Vajont Dam disaster, just north of Venice, which resulted from a substantial portion of the mountain above the reservoir sliding into it:

https://en.wikipedia.org/wiki/Vajont_Dam

Paul

 

Share this post


Link to post
Share on other sites
1 hour ago, JohnD said:

I read in my newspaper that concrete is being poured over the dropped ballast.  Let's hope it sets by tonight (??)

Interesting link, Nick.    I was puzzled by one of the reasons given for the Malpasset disaster, "the water pressure was aimed diagonally towards the dam wall".

Pressure has no direction, or rather acts in all directions.   Or do I misunderstand?

John

I understood that the reason for the collapse was that the geological survey was insufficiently thorough and missed cracking/ faulting that was present. I think the pressure comment is a mistranslation. Water leaked into the cracks and faults and led to further weakening.

Paul,

There was a good documentary on Vajont dam disaster which was fascinating, if grim viewing. At least the current problems are in plain sight and the people safely out of the way.

Share this post


Link to post
Share on other sites

I'm surprised that the Fire Brigade pumps are still being used, obviously good as a start but surely they are low volume - high pressure pumps and I would have expected that a high volume pump would be more suitable such as used in mines.

Always providing that downstream can handle the volume of water needed to be dumped.

Alan

Share this post


Link to post
Share on other sites
14 hours ago, JohnD said:

But, Peter, the beavers will.do.that for you!  And routine maintenance.  J.

John,  Plenty of badgers here, but beavers in short supply, and I suspect they would prefer to dam the river rather than a precipitous stream.

Decided to terrace the slope below the stream with sloping berms to try to direct any flood sideways away from the property. Contractor with a mini excavator reckons he can do it safely .  The  rock dams are indeed beyond access by excavator...... and Chinook. They formed during a deluge and are stable in normal storms. But at some point an even bigger deluge will shift them.  Am wondering if planting fast-growing willows might help anchor the dams.................back to Google to find out.

Peter

Share this post


Link to post
Share on other sites
15 hours ago, JohnD said:

The water shifted concrete blocks that were yards wife and high.   Rocks or sand in those bags they'll wash away too if it comes back surely.   But I like Pauls made addition theory coupled with pumping out the reservojr.  Let's hope the predicted heavy r ain on Sunday does fall.in that catchment.

J.

Damn autocomplete on a tablet.   Hope my intent was clear, certainly "doesn't fall"!   J.

Share this post


Link to post
Share on other sites
3 hours ago, AB|W said:

I'm surprised that the Fire Brigade pumps are still being used, obviously good as a start but surely they are low volume - high pressure pumps and I would have expected that a high volume pump would be more suitable such as used in mines.

Always providing that downstream can handle the volume of water needed to be dumped.

Alan

Nah, the fire brigade have high volume pumps these days, what with all the flooding that has been occuring.

However I am slightly bemused that they haven't called for the big pumps from Holland again which would be far quicker.

Given I understood the reservoir provides water for the local canal system, pumping rate should be a major issue? Get as many pumps as possible, and simply open all the lock gates, that'll get the water shifted.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...