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Whaley Bridge Evacuated

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3 hours ago, Woodlover said:

Eggs will prob know if its true but when I was laying drainage a few years ago I was told due to minimum fall levels n that...that pipes full of turds and wet wipes need the piss water to help move em along ...if you just flushed the solids and there was no rain then you may get problems? Also the water must dilute the raw sewage flowing around the system and help control gases and smells? 

 

There is a drain, I usually end up having to rod it once a year. Comes from a toilet in a shed so mainly used for jobbies.

Aside from possibly not being the best constructed, I think half the problem with it is lack of water going through to clean the pipe out.

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3 hours ago, Woodlover said:

If core drill samples of the spillway were taken then the lack of re-bar and voids beneath would have been discovered and it would never have been allowed to be used. 

 

 

A quick look at the plans and specs should tell you if it was supposed to have rebar . Wonder if corners were cut ?

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Chalgravesteve keeps referring to the extra amount of water, due to excessive rainfall, causing extra erosion, I imagine this is a bit of a red-herring, since any amount of water percolating through seam/joints/fissures, due to any overflow, would cause the same erosion beneath the slab, the inflow being limited more by the width of the defective joint, than the volume/depth of water flowing over it.

O.K.

The greater the volume, the greater the depth and hydrostatic pressure ensuing, and therefore forcing "more" water through the joint.

BUT?

How much water was eroding the soil beneath the concrete before the excessive rainfall.

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28 minutes ago, Stubby said:

A quick look at the plans and specs should tell you if it was supposed to have rebar . Wonder if corners were cut ?

I would think they used the mesh sheets in the concrete ,and then these slabs sat on some kind of support at the edges. No bar used at all as it was just built as a cap not a structure? is my guess.

Its like a roof for the soil, but built in the cheapest way with the least metal and concrete possible.

Edited by Woodlover
Had a few beers and seen the light

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1 hour ago, Woodlover said:

I would think they used the mesh sheets in the concrete ,and then these slabs sat on some kind of support at the edges. No bar used at all as it was just built as a cap not a structure? is my guess.

Its like a roof for the soil, but built in the cheapest way with the least metal and concrete possible.

 

Does look very poor, I was surprised to see the concrete laid on top of what is basically fill. Something with a bit of aggregate would of held up better irrespective of the concrete letting water through.

 

Bob

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10 hours ago, eggsarascal said:

Bloody foreigners coming over here ruining the cut.

Not really fair, mate. People in glass houses and all that.

dambusters.jpg

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15 hours ago, difflock said:

Chalgravesteve keeps referring to the extra amount of water, due to excessive rainfall, causing extra erosion, I imagine this is a bit of a red-herring, since any amount of water percolating through seam/joints/fissures, due to any overflow, would cause the same erosion beneath the slab, the inflow being limited more by the width of the defective joint, than the volume/depth of water flowing over it.

O.K.

The greater the volume, the greater the depth and hydrostatic pressure ensuing, and therefore forcing "more" water through the joint.

BUT?

How much water was eroding the soil beneath the concrete before the excessive rainfall.

Once one of those slabs moves or cracks or drops, that’s it done. The water will just tear it apart. 

 

I worked out earlier that I thought the reservoir has a surface area around 100,000 m3

 

If the water cascading over the spillway way was 30cm deep and it looked at least that, then there is a volume of 30,000m3 that’s coming over that spillway in the hours that follow. That’s 30,000 tonnes of water travelling at speed.  Once it’s through any weak point it will tear it apart. 

 

I wouldn’t call that a red herring. 

 

Hindsight is a wonderful thing. But they could have cleaned and polished that spillway and brought it caked for its birthday but in that extreme circumstance it might still have failed. 

 

The only way that the whole thing could have been avoided would have been for the inflow to have been diverted before the reservoir overtopped the spillway. 

 

Im not disagreeing with anyone that maintenance could have and should have been better. The owners/operators should have done a better job. The inspection engineers should be more stringent, especially in the light of other dam spillway failures. 

 

But people are also expecting them to predict the impossible. In the past 50 years since they built that spillway, how many times previously had it been overtopped by anything? 

Probably never or only a few inch deep trickle. The normal full level of the reservoir will be some distance below The spillway

 

That allows additional emergency capacity. I’d be amazed if it’s normally closer than 1m from max water to the spillway. That’s 100,000 m3 of extra water  from the infill before it’s full to maximum. 

 

Thats the equivalent of 1000mm of rainfall in a few hours. If you double the catchment area, that’s 500mm of rain in the same period. Double it again and it’s 250mm. The area had 10/15mm of rain predicted. 

 

So it’s just my view that the combination of circumstances created a scenario that no one could have foreseen. The spillway then couldn’t stand the forces involved and failed. 

 

Its clearly not fit for purpose and a repair is not viable, needs a complete new modern engineering solution that enables the reservoir and dam to withstand the same or worse circumstances, because you can predict it now. It’s happened once so clearly it could happen again. 

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On 08/08/2019 at 09:46, Chalgravesteve said:

This is exactly their problem. If they dumped 1/3rd of the reservoir capacity every time they had heavy thunderstorms predicted, they would get so much criticism! They were between a rock and a hard place (although if the spillway was there then they wouldn't have had the problem!!) that they need the reservoir full to meet their high level demand, in a period of time not usually associated with torrential and sustained downpours. Its taken them a week with emergency pumps going full blast to lower the level, you simply cannot shift that volume of water in a short time frame, so the likelihood is that they probably needed to start shifting water OUT of the reservoir a week or more ahead, before the bad weather was even forecast!! 

 

And if you search on youtube for the USA spillway destruction, you will see that however good and solid it looks, the destructive power of flowing water is staggering once its found a way into the structure. 

 

Its OK if you are like the Hoover Dam, with huge solid rock formations acting as buttresses to the dam. They bored tunnels through that rock so that they could release water if they needed to. If they open those gates for 24 hours, the only thing that's going to happen to the tunnels is that the rock walls will get a little bit smoother than they were before!

 

I'm not defending in anyway a lack of maintenance (perceived or real - there was a quote from a reservoir panel engineer saying that she couldn't see anything that caused her concern in the pictures taken prior to the problem). 

 

 

If they could discharge the water using pumps "going full blast" why couldn't they have started draining earlier?, we've already established the Goyt had only just gone into flood, please don't try to tell me the runoff from the previous downpour had subsided before they started pumping.

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5 hours ago, Chalgravesteve said:

I worked out earlier that I thought the reservoir has a surface area around 100,000 m3 [sic].

But that's not the catchment area, which may be several square miles. Or in EU money, dozens of square kilometres.

 

Ok, a quick Google has revealed that the catchment area for Toddbrook Reservoir is 17 million square metres. Or in JRM money 4,200 acres.

Edited by EdwardC

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