Dam Solution?

DMB,

Not quite.

There are possible geological deficiencies below and around the dam. - like coal mining activities. Solid structures tend to crack and fail catastrophically. The surrounding geology is the first thing they looked at, I’m sure.

SDL,

Your sentence should have been two? Rutland Water dam, constructed in the 1970s, is of a puddled clay construction. What they should, perhaps, have done years ago was to incorporate some form of hydro-generation to take water off at a much lower level....

Funny you should mention coal mining because old maps show a number old coal shafts in the area around the dam. Worse, the 1898 OS Map shows 'Wharf Pit' about 500 feet away from the dam. Very likely coal was extracted from underneath the dam long after it was built...

Subsidence due to coal mining can be 'quite interesting'. Most modern coal mines extract all the coal in a strip and allow the roof to collapse safely behind as the coal face moves forward. Depending how deep the seam is there will be subsidence on the surface but it could be small and take a long time to appear. Or rapid and and obvious. Older coal miners left large pillars to support the roof and, when the mine was exhausted, would rob coal from the pillars as they retreated back towards the shaft. Dangerous work that left the mine in a dangerous condition; after the mine is abandoned the weakened pillars are likely to collapse causing trouble above, perhaps several decades later. There was an incident at Lindal in 1945 were a steam locomotive and driver both disappeared entirely into a coal mine closed in 1919 when the workings gave way...

Dave

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In light of the present speculation, I am wondering if anyone followed that link ^^^

The box-out, which briefly covers Historic problems, might inform the discussion.

MichaelG.

Dams built like this one ?

The Sorpe springs to mind and it is still standing, lot more water too.

The dam owners had to buy the coal seams below the dam, to prevent it being removed!

As an aside, similarly, there are about a milion(?) tonnes of coal that was never extracted below Bolsover Castle - although I don’t think anyone had to buy those seams.

Each seam was extracted by modern machinery that cut very little extra, with the roof collapsing in very close behind. I am(was!) 1.75m tall and could just stoop low enough (not to have to crawl) along the ~250m coal face supported by hydraulic supports a few metres behind the face (just sufficient space for the cutting machine to pass by) - that was when I was fit! Several of our visiting group (of about twenty) had to crawl on hands and knees along the whole face! I think we were about a mile and a half from the winding shaft and had a high speed ride from the face back to the shaft on a conveyor belt. A day out to remember.

There seems to be some disagreement about the opening date. But given how long such things take from design to implementation, the engineering appears to be late Georgian. Don't blame them either

Georgian or Victorian, I bet they had it built more quickly using picks and shovels than we could nowadays, we'd still be on the planning and impact assessment phase. Anyone remember £53 million spent on a Garden Bridge that never got started?

Any cynic assumes that's largesse for the mates - why there's always a vanity project..

Indeed I did, along with the stuff about the Buxworth canal basin etc. and the American chap on youtube, who'd also covered the Oroville dam problem. (Top of Page 4 on this thread)

I also spoke to a neighbour yesterday who's been rather involved with it all on a professional level, though not as an engineer. He and his colleagues were initially briefed that there was an estimated 70% chance of the dam breaching catastrophically.
My partner Jane was watching some of the earlier coverage, when everyone on top of the dam immediately evacuated; I assume they felt something move, maybe one of the spillway slabs shifting??

Bill

Edited By peak4 on 08/08/2019 20:45:05

Properly built earth dams are actually very good, and there does not appear to be anything wrong with the basic construction of the dam itself here. Earth dams have the advantage of being able to absorb a bit of movement in the underlying material, whether from natural faults of mining subsidence. However they are vulnerable if water is able to overtop them, and the situation with this dam where the spillway concrete had failed would have much the same effect. Water running over the dam is quite capable of eroding the dam quite quickly and catastrophically.

At Oroville, the failed emergency spillway was not built over the dam itself, so there was natural rock under the vanished concrete. There was some concern about the nature of the rock and its ability to withstand the erosion from the overflowing water for very long, and of course if they had not spilled water fast enough the dam might have overtopped at the earth dam itself, which would be bad news. They did have the advantage of being able to pass as much water as possible through the hydro electric plant there. But mainly they had to keep using the emergency spillway despite the damage it was doing to itself and the surroundings.

John

Definition of evacuate [Merriam-Webster]

intransitive verb

In both senses possibly! Being somewhat ancient my immediate reading was def 2 and an unpleasant image came to mind.

I'm not making an English usage point, it was just an amusing ambiguity when I realised what was intended (I assume!)

Robin

The good old USA is the place for failing earth dams, many of which were built at a time when 'can do' mattered more than Health and Safety and high death rates were all part of the pioneer spirit.

I recommend the book 'Why Buildings Fall Down' by Levi & Salvadori (1994), which is a good example of making technicalities readable. A chapter entitled 'Valley of Tears' covers dam failures and starts with an account of the 1889 USA Johnstown disaster in which about 3000 people died and 35000 were left homeless. The introduction mentions that of 1764 dams built in the US before 1959, one in fifty has failed.

Johnstown lay 14 miles downstream of the South Fork Dam. Started in 1839 to provide water for the Pennsylvania Canal but not finished until 1853 by which time railways were rapidly making the canal redundant. In 1880 the dam was sold to the South Fork Hunting and Fishing Club of Pittsburgh, a top-persons facility. The new owners removed the outlet pipes, reduced the size of the spillway, and added a trestle bridge and wooden screen that reduced the flow over the spillway to about one third of design capacity. The screen was to stop fish escaping. Then came a period of heavy rain...

Despite the cause being 100% due to negligent modifications designed to improve the pleasure of millionaire sportsmen, a court deemed the cause to be a 'providential visitation'.

Dave

Interesting fact to come out of all this, generating electricity from hydro power causes more deaths per unit of electricity than either nuclear or gas.

**LINK**

I hope the feared storms do not materialise, having seen the pictures of the water cascading over that relief weir before the end part failed. That amount of water flow would undoubtedly overwhelm the small channel which runs alongside the north side of the dam. Having reduced the water level has hopefully bought enough time for any flash floods to stop before another overtopping.

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It's looking rather threatening at the moment

I went over to Whaley this morning, and took a few photos [will start a new album sometime]

The reservoir looks nearly empty now, so I think it will stay safe.

Had a chat with one of the Kier guys, who confirmed my presumption that the concrete 'tiles' on the spillway are no more than about 150mm thick.

MichaelG

Hullo everyone,

Not familiar with the area, but if the dam is for making up the canal where locking down can mean a big loss of water, such that further operations are delayed until more water is available, which could have made the canal uneconomic at the time, then a possible modern way would be to back pump from lower down so recapturing the lock discharge. Dead easy....... but not quite! Big pumps, ducts, track excavations, a basin, and all that. An interesting problem. What to do with the old dam? Dead easy.......but not quite! Perhaps let it grow into an attractive ruin. Sailing club and an SSSI could be very expensive. You can see the lawyers circling already as there will be much to be had. The residents fear ....it won't go away. A few sleepless night for some people in charge.

Best wishes to all and happy modeling.

I believe Combs reservoir will feed the canal system.

I'm interested to know how the 70% failure probability mentioned earlier was calculated. Probabalistic structural integrity assessment is possible, but it is difficult and requires a vast amount of data. I suspect the error bounds on that figure are approximately +29%/ -69%.

Eric

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Eric

Estimated [not Calculated] was the word that Bill used ...

From something [as yet uncorroborated] that I was told today; that estimate was a 'gut feel' based on one of the very early videos of the spillway event. ... These are probably worth a second look.

MichaelG.

Interesting 'background' piece here: **LINK**

https://notalotofpeopleknowthat.wordpress.com/2019/08/04/the-whaley-bridge-flood-of-1872/

And a lovely video of the location: 

https://m.youtube.com/watch?v=2dQKvMYnj2k

MichaelG.

Edited By Michael Gilligan on 09/08/2019 18:46:52

Not that big for the pumps. Rochdale canal has locks 14ft wide, 70ft long, 10ft rise. This is 179712 lbs of water, but if you are prepared to wait 10 minutes whilst it fills the flow rate is 300 lb/sec, so the power is 3000 ft.lb/sec = 5.5 hp. Add a bit for inefficiency and call it 7 hp, not that big. 7 hp for 10 minutes is less than 1 kWh. This calc is a bit simplistic as the flow would depend on the head, but I've based it on all the water having to be lifted 10ft, in reality all the water through 5 ft gives you the energy required. Narrow canals would be less. Might be cheaper to re-equip all the locks with pumps than to repair the dam.

A better scheme might be to have a little pump running continuously filling the top pound from the bottom one, more total energy but a quicker lock operation.

Edited By duncan webster on 09/08/2019 18:54:15

Edited By duncan webster on 09/08/2019 18:54:59