Whaley Bridge pumps...

[The Natural Philosopher]

It probably WAS absolutely fine until the heavy rain

I bet you the work hasnt cost even one useless wind turbine yet

[Roland Perry]

In message <qi8t9f$8vj$ [e-mail]>, at 10:35:43 on Mon, 5 Aug

2019, Martin Brown <'''newspam'''@nezumi.demon.co.uk> remarked:

True, but...

... just because they are designed to be as water-efficient as possible doesn't mean you can't open the paddles at both ends of a lock and quite safely result in a significant flow. Every now and again a boater does that by accident, but it's routine to do it to drain a pound for maintenance, or to bring water through to fill up a drained pound.

[Roland Perry]

In message <qi95f4$u7s$ [e-mail], at 12:54:36 on Mon, 5 Aug 2019, NY [e-mail] remarked:

Depends on the size of the paddle-gear. But one lock every five minutes is about the fastest one would normally achieve.

However, you don't do it like that - the correct method is to open the paddles both ends, which will at least double the flow compared to a lock full ever five minutes.

[Roland Perry]

In message <qi9dc5$als$ [e-mail], at 15:09:59 on Mon, 5 Aug 2019, Gareth's was W7 now W10 Downstairs Computer [e-mail] remarked:

That includes all the gate closing and opening, as well as the possibility that the lock has to be prepared first (which doubles the water-flowing time). And the time taken to manoeuvre the boat in and out.

Flights are usually quicker for all these reasons.

But to make water (rather than boats) flow, you don't do it a lock at a time; you simply open all the paddles simultaneously.

[Roland Perry]

There are many canals which are mainly water-feeders. I expect the first few miles of the canal at Whaley Bridge are (for the Ashton and Macclesfield canals).

[Roland Perry]

In message [e-mail], at

04:30:31 on Mon, 5 Aug 2019, Cynic [e-mail] remarked:

This dam was last drained in order to maintain that very facility. The question is: why aren't they using it?

Or perhaps it is being used and the civilians writing in the press haven't noticed.

[Roland Perry]

In message [e-mail]>, at 12:53:39 on Mon, 5 Aug 2019, charles [e-mail]> remarked:

Actually, the locks have paddles at both ends which are specifically designed to promote the flow of water. It's just that normally you don't open both ends at once.

[NY]

Ah yes, I was forgetting about the paddles (I, too, would have called them sluice gates, but I stand corrected) which would be needed anyway to fill the pound before the upper gates could be opened.

So if you needed to transfer a lot of water in the shortest time, how long could you leave the paddles of all the locks open without damaging the sides/bottom of the canal by scouring? I wonder if that is being done in parallel with pumping water directly out of the reservoir into non-canal waterways?

450,000 litres every 5 minutes by the lock paddles is a hell of a lot more water than 7000 litres every minute by the pumps. But that is making the big assumption that it is OK to drain a lock's worth of water every five minutes as a sustained rate over many hours, rather than just a burst rate with gaps in between.

[charles]

Doubt it. From the photos of the concrete break up, the earth underneath had been washed away for weeks beforehand.

[Martin Brown]

Maybe. Certainly the heavy rain stressed one edge of the spillway to a point where it failed catastrophically. There may well have been a latent fault that allowed water to get behind one of the panels.

I dunno. The flying time of the Chinnooks must be mounting up by now. £24k an hour of flying time according to defence minister Bob Ainsworth:

And that was about a decade ago - Hansard entry:

Military aircraft operating costs. Apache is nearly double that!

[Gareth's was W7 now W10 Downst]

The Pontcysyllte Aqueduct is famous on that canal.

[Martin Brown]

He is basically right at least when the pipe size becomes large enough that the water in free fall near the middle allows bubbles of air to get back up the top side where friction slows the water to a crawl.

Talking large diameter pipes here not thin hose pipes. It doesn't take much to prevent air going back up the outlet but it does require a bit of care or bubbles of air will rise up the top side of the pipe and accumulate at the top of the syphon.

[Gareth's was W7 now W10 Downst]

Actually, that was an interpretation that I had not considered.

[NY]

I presume if the outlet pipe is kept vertical, there is less chance of air bubbles getting in at the bottom and rising to the top of the loop, breaking the siphon.

I imagine few of us have ever used a very fat pipe for siphoning - normally it is something about the diameter of a hosepipe.

Is it purely the diameter that causes air to bubble back up, or is it the ratio of the diameter to the length? In other words, is a short fat pipe more likely to do it than a longer pipe of the same diameter?

[Tim+]

I don?t see how you can possibly infer that. It?s *possible* but given the speed with which fast moving water can erode riverbanks etc, it seems equally likely that this was an ?acute? event.

Tim

[NY]

The BBC article about the dam yesterday or the day before had comments by various dam experts who were alarmed by the amount of vegetation that had been growing in the cracks between the concrete slabs in the weeks/months before. They said that this suggested that water had been getting through the spillway concrete into the earth fill below. So it's possible that the problem had been going on for a while. I presume it's a lot worse when the spillway is actually carrying water than when the only water is rainwater falling on the slabs.

[charles]

If the water had been going over the slipway, then I'd agree with your suggestion. But it wasn't.

[NY]

I thought on the day that the news first broke about Whaley Bridge there was a video which showed a lot of water cascading over the full width of the spillway. I got the impression that this was a recent video dating from a day or so earlier, with the implication that it was after this that they slabs were found to be cracking.

Interesting that

shows them taking the outlet of the pumps over the lower part of the spillway on the opposite side to the collapse. I'd have thought they'd want to avoid any more water flowing over the spillway in case of undermining of the earth fill beneath the concrete.

[Tim+]

It had been going over the spillway though.

It only needed the grouting to fail between the slabs for erosion of the soil beneath to begin.

Tim

[Robin]

Indeed. The spillway was being asked to do its job. But ISTM as yet unclear if the problem was lack of maintenance, poor design, or more water than it was designed to handle.

Some rather more than averagely informed comments are at