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Heavy rain in Devon - flooding on the railways


Captain Kernow
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  • RMweb Gold

Its good to see these pictures of how hard the Captain and his colleagues are working to restore services. Not sure it was a good idea to show my wife these pictures considering we're going down to Exeter by train on the 9th!

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  • RMweb Gold

The one fortunate thing, I can think of, is that the 2nd flood hit quite soon after the first one. Given the extended damage of the signalling, and CK's explanation, I suspect the S&E engineers hadn't replaced all damaged parts yet, so at least some of the replacement equipment wouldn't be in place when the 2nd flood hit. Still, one must but feel sorry for all the hard work already done and swept away overnight. Certainly a morale buster :(

Yes, we had a feeling that the second flood was going to happen, and the S&T recovery was planned with this in mind, although with the work concentrating on the PW aspects, it is possible that not much could have been done by then anyway. Plans now being implemented to raise S&T location cabinets 'on stilts' to keep them up above future floods...

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Guest Belgian

I see from another site that there is a suspicion that damage to the old Teign Valley line to Teigngrace is such that the line will never reopen. Is there any substance to this, Cap'n?

 

JE

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Its good to see you are dealing with it. I wonder if long term we are going to suffer more frequently from floods. If so some places may need a re-think. A number of small culverts built in to provide paths for the water could reduce washouts. Almost like a mini viaducts for some places. Raising the S&T as you mention is also a good idea.

Don

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  • RMweb Gold

I see from another site that there is a suspicion that damage to the old Teign Valley line to Teigngrace is such that the line will never reopen. Is there any substance to this, Cap'n?

 

JE

Well, the PW re-opened the Heathfield branch a few days ago, and I believe that Colas Rail are planning a train down there on Wednesday, so looks like that's just an unsupported rumour, thankfully! :)

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Raised glasses to those who work night and day in arduous circumstances to restore service. cheers2.gifcheers2.gifcheers2.gif

 

Isn't it time the river was grade-separated at Cowley Bridge by putting it on a flyover? ;) staff_muttley.gif

Edited by Gwiwer
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  • RMweb Gold

Its good to see you are dealing with it. I wonder if long term we are going to suffer more frequently from floods. If so some places may need a re-think. A number of small culverts built in to provide paths for the water could reduce washouts. Almost like a mini viaducts for some places. Raising the S&T as you mention is also a good idea.

Don

 

The sheer volume of water means - in bad flooding - that the river level rises above the level of the railway upstream of Cowley Bridge. AS I said before the only sensible answer is a large bore pipe to divert the river away but you are still faced with the fact that the river is very nearly at sea level (especially at high tide) all the way down past Exeter although things are not as bad as they used to be downstream opposite Riverside Yard and beyond St Davids due to river widening etc.

 

The only realistic answer is either some way of holding more of thh water above Cowley Bridge (where it in any case already fills the flood plain in times of flooding) and/or some means of pumping it away from there or, probably, to elevate the railway several feet on new bridges and arches (which then poses other problems). A lot of flood relief work was done at Cowley Bridge some years ago and it has undoubtedly reduced the impact of 'normal' seasonal flooding - which used to close the railway in most years. The next step, to handle floods this bad, is going to be very expensive even if a practicable scheme could be devised.

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Without an understanding the full dynamics of the Exe in flood I would venture to suggest that if that were thought workable it would have been done before now.

 

The problem which exists is that the river is almost at sea level and therefore tends to "pond" when in flood despite appearing to flow quite fast. All the water running off the large region of hills around has nowhere else to go. The river level rises and the railway (and adjacent roads) goes under. Building a wall may not create enough force to restrain the ballast and will not prevent the river flooding nor water running over the tracks. If anything it may worsen the problem by creating a narrower channel through which water will flow more quickly and do more, not less, damage. Ballast will still be washed out, signalling still inundated and debris still be strewn across the tracks so where is the saving?

 

I don't have an answer. If I did I might be selling my services as a consultant rather than typing a post on a model railway forum ;)

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  • RMweb Gold

Would, perhaps, a thick retaining wall help by reducing the tendency for the ballast to get washed away? It would still get flooded but if the ballast is in effect 'restrained' by the wall then it can't go anywhere?

But the water would then pond even faster, and potentially to the depth of the height of the wall, so much worse for the railway. Any sluices etc in the wall would quickly become blocked by detritus in the floodwater, so be of little help.
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But the water would then pond even faster, and potentially to the depth of the height of the wall, so much worse for the railway. Any sluices etc in the wall would quickly become blocked by detritus in the floodwater, so be of little help.

 

Not saying it would work - just an idea.. but drainage sluices below the level of the ballast shouldn't get blocked because the ballast would act as a filter. Also the sleepers would probably help retain ballast - but hey probably is a crazy idea.. but no harm in at least thinking them up :)

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  • RMweb Gold

Not saying it would work - just an idea.. but drainage sluices below the level of the ballast shouldn't get blocked because the ballast would act as a filter. Also the sleepers would probably help retain ballast - but hey probably is a crazy idea.. but no harm in at least thinking them up :)

 

Having seen some of the trees which come down when the river is in flood I think drainage sluices wouldn't be much help - and after all there are already bridges taking the rivers under the railway and they can clear water a lot faster than any sluices. The problem is much more basic than that - the confluence of several rivers all of which are very shallow graded, are near to sea level, and which meander for a considerable way back upstream from the bridges (=shallow graded over some miles) and, as Rick said above, drain a very large area. Net result very large quantities of water which pond on the flood plains until they overflow.

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As someone whose track building experience is restricted to EM gauge, and a little bit of work on the full size Lynton and Barnstaple (mostly cutting sleepers in half with a chainsaw!), is it possible to build a waterproof trackbed, in concrete or something, that still floods, but remains undamaged and can be used as soon as the water recedes?

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  • RMweb Gold

As someone whose track building experience is restricted to EM gauge, and a little bit of work on the full size Lynton and Barnstaple (mostly cutting sleepers in half with a chainsaw!), is it possible to build a waterproof trackbed, in concrete or something, that still floods, but remains undamaged and can be used as soon as the water recedes?

 

Even if it was done like that (and I have an idea it would require very deep foundations in view of the ground conditions and the fact that the ground acts like a sponge) the signalling system would still have to be 'dried out' and tested before trains could run. And if you were to spend the money on paved track with deep foundations I reckon it wouldn't necessarily cost that much more to lift the track a few feet higher - but installing either would shut the railway for several weeks and involve other, very expensive, engineering work beyond the flooding area. And as long as a potential diversionary route is available (which it is of course - but time consuming & not entirely convenient) then I think that NR might possibly have other things in which to invest (unless it gets some of the rumoured £40 billion and some Parliamentary seats west of Taunton are 'at risk').

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is it possible to build a waterproof trackbed, in concrete or something, that still floods, but remains undamaged and can be used as soon as the water recedes?

Even if it was done like that (and I have an idea it would require very deep foundations in view of the ground conditions and the fact that the ground acts like a sponge) the signalling system would still have to be 'dried out' and tested before trains could run. And if you were to spend the money on paved track with deep foundations I reckon it wouldn't necessarily cost that much more to lift the track a few feet higher

Certainly waterproofing the ballast not the problem. Washouts are caused by the sub-roadbed being eroded by adjacent water intrusion and the ballast goes with it.

 

It is completely possible to build a flood resistant foundation to the railway as you suggest in concrete. This would essentially be a concrete bridge sitting in the ground, but structurally resting on pylons attached to the bedrock. Anything that 'floats' on the ground - even a concrete pad - would be vulnerable to washout of the ground beneath it. As Mike says, these solutions are very expensive and logistically difficult.

 

Ballast only maintains its structural integrity when water can seep through it. This has been evident with coaldust fouled ballast in the Powder River. When deep snow buried the line, with meltwater slowly seeping into the fouled ballast but could not drain, and the shear strength of the ballast was reduced and caused derailments.

 

There is an interesting study on this phenomenon by the University of Illinois. This link can be cranky. (Clicking it twice worked for me.) Google "University of Illinois, ballast, coal dust, derailment powder river" to alternatively find it.

Edited by Ozexpatriate
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Ozexpatriate wrote>

 

It is completely possible to build a flood resistant foundation to the railway as you suggest in concrete. This would essentially be a concrete bridge sitting in the ground, but structurally resting on pylons attached to the bedrock. Anything that 'floats' on the ground - even a concrete pad - would be vulnerable to washout of the ground beneath it. As Mike says, these solutions are very expensive and logistically difficult.

 

That sounds the sort of thing that would be needed. It all depends on how frequent the floods become. Probably too expensive but how often do we realise the seemly more expensive option would have been cheaper than keep repairing things.

Don

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