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If New York and London are twinned as cities, then it is only a small leap to think of the London Underground and the New York Subway as sister networks. They may differ in many ways, but they are both ultimately large Underground networks of historic standing, and over the years there have been many exchanges of both staff and knowledge between TfL and New York’s MTA.

With this relationship in mind, the damage that the recent “frankenstorm” inflicted on the New York Subway system will have been uncomfortable watching to anyone familiar with the way metro systems work. Of all the dangers to such systems that freak natural disasters can pose, it is arguably flood that presents the greatest potential for wholesale damage. New York was warned, and the MTA had moved trains to high ground and put in flood protection where it could, but it was not enough.

Holding back the water at West Side Yard, via MTA

Holding back the water at West Side Yard, via the MTA.

“Our transportation system has never faced a disaster as devastating as Hurricane Sandy, which has caused an unparalleled level of damage.” MTA Chairman Joe Lhota announced in front of the media yesterday. “In 108 years, our employees have never faced a challenge like the one that confronts us now.”

With surface lines blocked by fallen trees and debris, power lines down, and the Subway’s tunnels beneath the East River flooded. There is no-one who will argue with him.

Boat on the tracks near Ossining Station, via the MTA

Boat on the tracks near Ossining Station, via the MTA

Flooding on the Hudson Line, via the MTA

Flooding on the Hudson Line, via the MTA

Washed out track supports, via the MTA

Washed out track supports, via the MTA

Damaged signals, via the MTA

Damaged signals, via the MTA

Beyond the serious damage to track and operating infrastructure, comes the damage to stations themselves. The images of stations underwater that began to surface as the storm progressed, and the video footage that the MTA themselves have released since highlight the enormity of the task that faces the MTA and its railwaymen and women as they struggle in the coming weeks to return their lines to service.

Platforms at South Ferry station, via MTA

Platforms at South Ferry station, via the MTA

An escalator box at South Ferry, via MTA

An escalator box at South Ferry, via the MTA

As the Subway’s workers and commuters begin their quest to return to normality, London’s own railway workers and commuters will no doubt be look on with empathy and understanding.

As the London’s media watches from a distance, it seems almost inevitable that someone will look to the City and ask “could it happen here?” There are key differences between New York’s relationship with its rivers and the Atlantic, and London’s relationship with the Thames and the North Sea, but it is a fair question nonetheless. This thus seems a good opportunity for us to turn to the subject, and look briefly at the Underground’s own uneasy relationship with water.

A City of Two Halves

The role that the River Thames has played in the history and development of London needs no repeating here. As an artery for trade, and as a permanent divider between north and south, the Thames casts an inescapable shadow over London. Yet for the early Underground, confined as it was to north of the river Thames, it was surface water, not fluvial flooding, that presented the greatest risk. Sudden, heavy rain was the greatest cause of unexpected flooding.

Storm flooding at Farringdon in 1915, via the LTM

Storm flooding at Farringdon in 1915, via the LTM

It is a problem that remains today, as any reading of the various flood plans and assessments put together by London’s various local government bodies and oversight groups makes abundantly clear. In both the GLA’s 2009 Flood Risk Assessment and the City of London’s Flood Risk Assessment, it is clear that it is rain that concerns London Underground more than any risk from the river.

This may seem a strange stance to take. Common sense would seem to dictate that the fast flowing tidal Thames would be worth keeping a careful eye on. The Thames is crossed, beneath its surface, 9 times in total by 5 lines (the Jubilee 4 times, Northern twice, Bakerloo, Victoria and Waterloo & City once each). That’s a total of 18 tunnels taking trains, plus the two disused City & South London tunnels to King William Street. Indeed if the Overground is included, another tunnel can be added as the East London Line uses Brunel’s original Thames Tunnel to pass beneath the river. As the the first ever tunnel successfully constructed beneath a tidal river, and one that flooded a number of times during construction costing a number of lives (and almost that of Isambard Kingdom Brunel himself), the Thames Tunnel would seem to be the ultimate warning that the River Thames is not to be trifled with.

The truth, however, is that tunnels, once built, have little to fear from the mere proximity of a river itself. As New York discovered to its cost, it is tides and tidal flooding that pose the greatest risk. Water entering the lowest lying areas of the Tube network via tunnel portals and stations, not breaks within the tunnels as they pass beneath the river bed, are the real danger.

In this regard, London found itself geographically blessed. Whilst the Thames is tidal, it stops being so at Teddington. On top of this, historically it has never proven particularly liable to flooding. Between the construction of the Bakerloo and Northern Lines, the two lines most likely to be susceptible to fluvial flooding, and the Second World War, only the Thames Flood of 1928 (which caused 14 deaths) overtopped the Embankment and caused serious damage. Afterwards the great North Sea flood of 1953, for all the devastation it caused, failed (albeit by mere inches) to top the Embankment.

On top of this, by the end of the Second World War, the Underground had gained an additional level of protection – floodgates.

A floodgate on the Underground, via Halcrow

A floodgate on the Underground, via Halcrow

In 1938, with war looming, it had become clear that, for the duration of the coming conflict at least, it was bombs – not tides – that would be the likeliest cause of flooding. With that in mind, it was decided that the danger of a bomb breaking open the sections of the Bakerloo and Northern line tunnels beneath the river needed to be addressed.

On the advice of William Halcrow, a “quick fix” was put in place. Underground services were curtailed and limited to north of the Thames, and the tunnels were blocked off with concrete plugs. This was not, however, a long term solution and so a more flexible system for closing off the tunnels was put in place. This consisted of a series of heavy steel floodgates, put in place at key points between September and December 1939. Upwards of 30cm thick, and weighing about 6 tons, these could be slid into place either electronically or manually when an air-raid began.

Floodgate instructions at Liverpool Street. Many more images can be found on the Embsay & Bolton Abbey website

Floodgate instructions at Liverpool Street. Many more images can be found on the Embsay & Bolton Abbey website

This was not a new idea – indeed the same thing had been mooted in World War One as the risk of air attack began to emerge – but it was certainly effective. It meant (with one key exception) that the concrete plugs could be removed and normal service patterns resumed, but also that upon commencement of an air raid, the tunnels could still quickly and effectively sealed.

The key exception to this was the old Northern Line loop which had already fallen into disuse. Here Halcrow’s original concrete plug was left in place, which turned out to be very fortunate indeed – the loop was the only section of sub-Thames tunnel that would be pierced by bombs and flooded during the War. Luckily Halcrow’s plug held long enough for the breach to be found and sealed, and a major flood was avoided. For those interested, an excellent overview of the loop and its flooding can be found on Ianvisits website.

Sadly, the network did not escape flooding completely. As became abundantly clear, wherever stations or tunnels passed beneath major water pipes or sewers, they were also vulnerable to flooding. This became tragically clear on October 14th 1940, when Balham Station suffered a direct hit. The north-bound tunnel partially collapsed and water mains and sewer pipes above the station were ripped open, sending earth and water flooding into the station tunnels. With no floodgates in place, the water poured through the connecting passages into the southbound tunnel as well and flooded the tunnels almost as far as Clapham South. Over 65 people were killed.

Closing the floodgates at Charing Cross, via the LTM

Closing the floodgates at Charing Cross, via the LTM

By the end of the War, floodgates were in place at all the key points on the network where flooding from either the river or from utility or sewage pipes was a major risk. Amongst others, South Kensington, Embankment, Charing Cross, Waterloo, London Road, London Bridge, Wapping, Bethnal Green and Bank all had floodgates and in some locations – such as at the top of the Piccadilly Line escalators at Holborn – these gates remain visible today.

As the Cold War developed, and the fear of bombardment switched from the standard munitions of Germany to the atomic munitions of Russia, a second wave of floodgate installation followed. Tottenham Court Road, Kennington, Moorgate, Liverpool Street, Green Park and Russell Square all gained floodgates in the 1950s, as further protection against ruptured waterworks was added. A new cross-over juntion was also added at Kings Cross on the Piccadilly to allow the line to operate between there and Cockfosters should the Russell Square gate ever need to be closed.

At the same time, a plan was put in place to create a control centre from which the Tube could be kept running as long as possible in the case of an atomic bomb attack, and from which the floodgates could be remotely operated if needs be.

The location chosen for this so-called “Special Works” project was the never-finished North End station on the Northern Line. Work had started on the station fifty years before but no sooner had the lift shafts been sunk and various sub-surface spaces excavated when Hampstead Heath was expanded around the site, rendering its existence unnecessary. Construction stopped soon after in 1907.

Blast Door into the Flood Control Centre, via Subbrit

Blast Door into the Flood Control Centre, via Subbrit

As a secure, already excavated site located 70m below the surface of the Heath, North End made a perfect location for the new control centre, and work on the floodgate control element of the facility was soon completed. The rest of the centre, however, would never be built. As the power of nuclear bombs increased, it became increasingly obvious that an attack on London would leave very little operational, and work on the rest of the facility was quietly abandoned. The floodgate control centre, however, was brought into service in 1956, and remained operational until 1984. Today it remains, disused, beneath Hampstead Heath. More information, and some excellent photos, can be found on Subbrit.

The disused control room, via Subbrit

The disused control room, via Subbrit

The fact that the centre is abandoned hints at a truth about the flood defences that remain active on the London Underground today. For though “Oh they have metal floodgates!” would likely be the answer that any general user of the network would give to the question “What stops the Underground from flooding?” today, the simple truth is the the majority, indeed perhaps all, of the floodgates on the Underground are now no longer functional. As stations have been improved and signalling systems changed (such as on the Bakerloo Line in the 1980s) one by one the doors have been welded in place, bypassed by wiring or in some places boxed into the platform walls during refurbishment works.

On the surface this may seem worrying, but the truth is the gates simply became obsolete. In a nuclear war, the risk of catastrophic flooding due to multiple utility fractures would be the least of London’s problems, and thus updating and maintaining the majority of the floodgates away from the Thames became far less important. Their fate was effectively confirmed when the Brixton extension of the Victoria Line opened in 1971 and became the first section of post-war Line to be built with no floodgates at all.

So what floodgates remain today? The truth is that in the post 7/7 world no-one, apart from London Underground themselves, knows for sure. It is tempting to suggest that none of the floodgates remain operational, at least if anecdotal evidence is any guide. If some do, then the likely candidates are those to be found on the Jubilee Line Extension at Canning Town, and those to be found at Tottenham Hale, which is at risk of flooding not from the Thames but from the river Lea. Whatever the truth of the matter, the simple fact is that these days the floodgates on the Underground are more placebo than protection.

The Jubilee Portal at Canning Town, via Tubeprune

The Jubilee Portal at Canning Town, via Tubeprune

If not in floodgates, then where does the Underground’s real fluvial flood protection lie? The simple answer to that question is hinted at in the year that the flood control centre closed, and in the visual design of the tunnel portal (and floodgates) at Canning Town shown above.

It lies in the Thames Barrier.

Prince of Tides

The Thames Barrier, stretching between Newham and Greenwich, the second largest moveable flood barrier in the world and, quite simply, a masterpiece of British engineering, is the reason why the Underground – and indeed London itself – has almost no risk of suffering the kind of flooding seen in New York.

The Thames Barrier, via Halcrow

The Thames Barrier, via Halcrow

Born, conceptually, in the aftermath of the great North Sea Flood, the Thames Barrier finally opened in 1984, designed to near-as-possible eliminate the risk of tidal flooding within London for the next 100 years.

In that regard it has so far been a complete success, with tidal flooding within the capital now largely a thing of the past. It is not a permanent solution, however, and climate change means that its expected effective life is now shorter than originally planned. According to current estimates (as mentioned in the TfL Environment plan and various flood reports by the London Assembly and central government) a new solution will need to be in place by 2070 in order to maintain the same minimal risk levels that exist today. It may not be a problem that the current Mayor needs to be concerned about, therefore, or even the next – but it will need to be addressed, in time.

Until then, however, the flooding risks to the Underground remain relatively clear. With the Thames Barrier providing protection downstream, and the risk of a renewed German bombing campaign relatively low in these friendlier times, the risk of serious flood damage to the network is incredibly small. The floodgates may be a comforting thought to some, but they are actually largely unnecessary and likely almost entirely disabled anyway.

Nonetheless, London can rest relatively easy. Isolated flash flooding due to rain or utility failure remains the primary risk today, although as Thames Water so impressively demonstrated when they accidentally dumped 2 million litres of water onto the Central Line back in June, those are still risks not to be taken too lightly…

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There are 72 comments on this article
  1. swirlythingy says:

    “Welded”, not “wielded”. And the Charing Cross LTM link doesn’t work.

    Also, when you say three lines pass beneath the river bed, are you referring specifically to pre-war lines? And is this in terms of operational divisions, or tunnels? (If the latter, the Northern line has about three-and-a-half alone, and if the former, don’t forget the Northern line was originally two lines.)

  2. John Bull says:

    Cheers – typos fixed (you missed the horrific misuse of “their” rather than “there” in the first para though).

    Yes, I’m actually open to suggestions as to how to best phrase the “lines beneath the river” bit. I was thinking operationally (and that was originally a much bigger paragraph) but it feels a bit clunky.

    Any ideas for a good way to make it nice and clear to readers appreciated…

  3. Anonymous says:

    Is it not FOUR Underground Lines that cross the Thames (plus Overground ELL)? Northern, Bakerloo, Victoria and the Jubilee extension (which goes back and forth several times between Canada Water and Canning Town).

    Also, references in the article to floodgates and tunnel portals at Canada Water should probably be Canning Town, as the caption to the photo provided so helpfully points out.

  4. Chris Constantine says:

    For years I wondered why the tunnel portals at Canning town paid homage to the Thames Barrier. I presumed it was an attempt at creating a local architectural movement that would crop up throughout East London. Maybe it will continue, but only when there’s a requirement to hold back the floods.

  5. Patrickov says:

    Isn’t LU having *four* lines crossing under the Thames even if ELL is excluded? Northern (both branches), Jubilee, Bakerloo and Waterloo & City.

  6. Patrickov says:

    Oops, forgot the Vic. FIVE then.

  7. Lazarus says:

    The Thames is crossed (beneath) 9 times in total by 5 lines (Jubilee 4 times, Northern twice, Bakerloo, Victoria and Waterloo & City once each. That’s a total of 18 tunnels taking trains, plus the two disused City & South London tunnels to King William Street.

  8. John Bull says:

    Yeah, I think I’m officially declaring that paragraph badly mauled.

    I’ve changed it so it now reflects current, operational lines. Which, as Patrickov says, should be five (rising to six). Seems the best thing to do.

  9. PhilD says:

    Top piece. Just to add, there’s a great article from Wired on US Army engineers are busy ‘dewatering’ (their phrase not mine) the various road and rail tunnels under NYC:
    http://www.wired.com/dangerroom/2012/11/sandy-unwatering-tunnels/

    Also, a quick glance at the Carte Metro map – http://carto.metro.free.fr/cartes/metro-tram-london/ – is instructive about river tunnels. Pre-war you have 4 different lines, the Waterloo & City, Northern, ELL and Bakerloo with two, seven, two and two tunnels respectively for a total of thirteen. (The Northern gets seven when you include the abandoned King William St crossing and the reversing loop at Charing Cross.) Post war it gets more complex. The Jubilee goes under the river in four separate places, but I’m not sure how you’d want to count it. In addition you have the DLR going under the river at two different points and not forgetting the Victoria Line and its two tunnels between Pimlico and Vauxhall.
    All this before we add Crossrail….
    cheers
    Phil

  10. John Bull says:

    Scratch that – Lazarus that’s perfect. Thanks. I’ve put that in.

  11. Alex says:

    Presumably there must be a risk from a widescale loss of power (as seen after Sandy) – don’t they pump thousands of cubic litres of water out of the deeper tunnels every day where the water table has risen? What if those pumps got knocked out? (Though, I guess, the solution would be pretty straightforward!)

  12. John Bull says:

    Alex, that’s a fair point to raise – I originally had some stuff in about rising water tables (in part thanks to the fact that we don’t brew in the Capital as much as we used to do!) and the increasing need to pump out various tunnels, but it was already quite long.

    I do wonder whether it might be worth doing a post at some point about the Underground’s power setup actually. Not least because it would give me an excuse to try and find out whether its actually true that they “accidentally forgot to change the name on the electricity bill” when they took over the Waterloo & City, and didn’t pay for power on it for donkeys years.

  13. Pedantic of Purley says:

    We were discussing this internally. Yes. One of the vital pumps is at Wapping to keep the Thames Tunnel less damp than it otherwise would be. If I recall correctly you can hear the constant background noise it makes when you stand at the end of the platform. But it is not just the deep level tunnels. One of the places where pumps are most needed is around Victoria on the Circle and District lines. When they introduced “cooling the tube” at Victoria they didn’t have to go looking for a source of water! And I believe that is why Victoria was done first. The previously-neglected Waterloo and City line used to be terrible for water ingress but I believe that is now fixed.

    Nowadays a significant part of the work in modernising the tube, especially on subsurface lines, is drainage work. Unglamorous but vital. Possibly it took PPP to realise the value in this as, amongst other things, damp conditions tend to lead to expensive signal failures.

    Whilst in one of my rare moments of singing the praises of PPP, one of the less publicised advantages of PPP was that one of the members of the Metronet consortium was Thames Water and Metronet seemed very keen on fixing water leaks. Indeed it must be one of the beneficial legacies of PPP.

  14. Anonymous says:

    Have you seen the quality of comment at the bottom of the page PhilD mentioned above. Mind you – someone asks a pertinent question. With all the flooding, what has become of the Men in Black – their secret base was down there!

  15. John Bull says:

    Blimey. That is indeed a SPECTACULAR comment derail. I’d missed that.

  16. Laughing Noam says:

    I’ve seen the Bakerloo line flood gates operating – in 1999 they were used to close the tunnels outside of operational hours – and the reason? I can’t quite remember but it was probably something to do with the Millenium footbridge works going on at that time. The Underground were concerned that there was an outside chance of a tunnel breach occuring so closed the tunnel. So I’m pretty sure the Bakerloo doors still work at least.

    I believe the closures were published in the engineering circular that comes out weekly – so if anyone has access to the archived circulars they’ll be able to check.

  17. Greg Tingey says:

    Correct
    The greatest & commonest threat to the tubes is surface flooding, especially at Farringdon, where it is close to the Fleet, & also not too far above river level as well.

  18. Guano says:

    In the 1970s, and up to the completion of the Thames Barrier, there were maps in the Underground showing which sections of line would be closed if there were flooding due to high tides and a storm surge. It was a serious concern.

  19. Alan Griffiths says:

    Isolated flash flooding due to rain or utility failure remains the primary risk today, although as Thames Water so impressively demonstrated when they accidentally dumped 2 million litres of water onto the Central Line back in June, those are still risks not to be taken too lightly…”

    That was no small matter. Now then children, write a risk assessment about lifting a rather rigid and large water pipe above a ventilation shaft of a railway tunnel. Don’t be inhibited about how much paper you use to explain why this is really not a very good idea.

  20. Robert Carroll says:

    If I recall correctly a large water main burst at Euston in the 1980s caused flooding of the Underground there.

  21. Anonymous says:

    I can remember that the Bakerloo Line suffered suspension, maybe happening throughout the 1980s, whenever there was heavy rain just north of Willesden Junction, because the tunnel flooded.
    Lack of investment, sadly.

  22. Steven Taylor says:

    About 25 years ago the Waterloo & City was flooded by a burst water main, that burst on Christmas Eve. The line was closed for about 3 months.

  23. swirlythingy says:

    Just noticed the Farringdon link is broken in the same way that the Charing Cross one was.[Now fixed. Ta. PoP]

    Could someone summarise the Wired comments for me? Whatever fancy ‘app’ they’re using doesn’t seem to work in my browser.

  24. Anonymous says:

    i would love to read about the undergrounds power set up. i know there is a station in greenwich witch used to be used for powering the underground, but is no longer. but i think it would be fasanting :3

  25. Fandroid says:

    JB – the threat from what was known at the time as ‘London’s Rising Groundwater’ was mostly sorted out around the Millenium. The simple answer was to make it a regulatory obligation on Thames Water to include use of deep groundwater in their Water Resources Plan, and for them to have the capital investment recognised in their price review. A lot of other folk (including Buckingham Palace!) jumped on the bandwagon but they were really only fiddling about on the fringes. Several old water supply sites were re-activated, but the main one that did the trick was at Brixton, where faults in the London Clay and the chalk beneath meant that the water was a lot easier to get at. Also, TW had a handy tunnel shaft there (on the Ring Main) so after treatment the water could easily be connected into the supply system.

    LUL were on the steering group that oversaw the research and the putting together of a programme of work. Their main worry was not so much water getting into the tunnels but rising water infiltrating the clay and changing its engineering properties. That would result in movement, and they felt the most vulnerable structures were escalator shafts, where a differential movement between bottom and top could cause the whole shebang to seize up! I remember the Piccadilly at Holborn being the place they worried about most. After that I always felt slightly odd when using that station!

    I remember them saying that Tooting was one of the worst places for that deep groundwater actually getting into tunnels. That’s not a surprise because roughly the same geological features are there at Tooting as are at Brixton.

    The groundwater at Victoria is from the gravel layers above the London Clay. That was considered for water supply use but it is more polluted than the deeper chalk based water and it would have been difficult to find a site for a treatment plant. The story at the time was that all that water was being pumped into TW’s sewers, but LUL were not being charged for what is known as a ‘trade discharge’. It might sound odd charging someone for pumping relatively clean water into a sewer, but it then has to be pumped several times before treatment and discharge, and treatment plant tank sizes have to be increased to cope with the greater hydraulic load. Also, once it’s in there it cannot be separated from the nasty foul stuff! Whether LUL get charged these days, I have no idea, but Metronet may have resolved that one!

  26. Anonymous says:

    If we’re fixing typos for posterity, there’s an extraneous apostrophe in “means that it’s expected effective life”.
    [Done. The Rogue Apostrophe Police]

  27. timbeau says:

    Anon 7:45

    As I understand it Greenwich Poweer Station was originally built by the London County Council to supply power for its tram network. Lots Road powered the Yerkes lines, and Neasden the Met.

  28. Greg Tingey says:

    To which one may add:
    Poole Street, Shoreditch, for the GN&CRly & Stockwell for the C&SLRly …..

  29. Tim says:

    Fantastic article. Kept an ill man interested all the way through :)

  30. Guru Gosling says:

    Super item. Top marks to the team at MTA for getting as much of the New York system up and running as they have.

    Not sure if they know about it but they – and their colleagues at LU – should be using ACF-50 or Corrosion Block. It comes from a Canadian outfit – Lear Cemicals I think – and is simply the most effective way of getting water out of electrical system. Use of that would see the items in picture 5 most likely return to service. I know it’s in use with the US military and our own RNLI and currently under test with our friends at Network Rail.

    Worth a thought.

  31. Anonymous says:

    Alex – I think we’ve conflated some units here. 1000 litres is the same as one cubic metre. If it’s water, it weighs about a tonne. The Underground infrastructure was mainly built in Imperial, but now operates in SI metric. The USA has its own system of measurements.
    Does the London Reconnections site have a consistent policy on units of measurement, I wonder?
    I’m sure that nobody under 60 has ever worked in chains!

  32. mdb says:

    There are some hefty looking doors at Baker Street just before the escalators down to the Jubilee/Bakerloo southbound platforms. Were these relating to flooding or are they just big doors?

  33. Greg Tingey says:

    Err “chains” are a wierdo – & the ex-BR lines still use them.
    80 chains to a mile – how very convenient, since a chain is … therefore … wait for it .. 20 metres!
    so 50 chains = 1 kilometre.
    And so it goes ….

  34. timbeau says:

    The most unusual unit in this thread is the one in Alex’s post on 2nd November – cubic litres: welcome to the ninth dimension! It seems to be becoming strangely common: a few years ago Saab made the same error in advertising the size of the boot of one of its products as 1273 cubic litres. Now Saab has disappeared, maybe into one of those extra dimensions. More recently, Citroen have claimed 504.98 cubic litres, which in adition to the extra six dimensions suggests a level of precision which required measurement with a pipette.

    Other strangely common units are the ever-popular kW per hour, mbit/s (millibits per second – i.e one bit every 16 minutes or so!) and the rather unappealling claim that a fuel saving system allowed a car to operate at 0mpg (presumably an unthinking translation from the metric litres/100km)

    a cubic metre of water weighs a tonne – A litre of water weighs a kilogram* -A cubic centimetre of water weighs a gramme
    a cubic metre of air weighs a kilogram – a litre of air weighs a gramme

    *original definition of the kilogram.

  35. Fandroid says:

    Wow Greg!

    I’ve learnt something new! A chain is as near as dammit 20 metres! My personal experience of them was limited to the length of cricket wickets, although I always thought ‘how quaint’ when seeing them on Network Rail asset markers. Having worked in SI units since 1970, I have lost the plot with many of the more obscure Imperial units (including weights above pounds). However, there was one good American one I learnt at the end of my education: Acre-feet, for the volume of an impounding reservoir.

  36. timbeau says:

    An acre is 4,840 sq yds – 1 chain times 1 furlong – a furlong being 220 yards or a surprisingly metric 10 chains!

    To help visualise – a standard running track lane is 4 feet (1.25 metres) so an eight-lane track is very close to half a chain wide. The circumference of an (Imperial) running rack is 440 yards, or two furlongs. So the actual area of the track (not including the infield) is about a acre. The dimensions required by FIFA require Association Football internationals to be played on pitches between 110 and 120 yards long and between 70 and 80 yards wide, meaning a maximum of just under 2 acres.

  37. Anonymous says:

    Great article!

    The pic labelled “Floodgate instructions at Liverpool Street” is somewhat mislabelled. The white on black instruction panel are old instructions regarding taking a release on a signal – and can be found in any signal cabin. The switch on the white plate is something to do with the flood gates obviously, but I suspect it is either: an illumination that affects the signal prior to the flood gate, making a controlled signal that a driver must obey (preventing them ‘applying the rule’ into a closed flood gate!) or – and more likely – simply an alarm bell that is the cabin’s way of knowing the flood gate has been deployed, that can be switched off. It’s very similar to traction current alarms that can still be found in cabins at Hammersmith, Whitechapel and elsewhere.

    Er, now I’ve typed all that your caption is still technically correct :) but I still think it’s somewhat misleading..

  38. Anonymous says:

    Also: There is (or was as a year ago) a relatively modern flooding alarm box on the wall in Edgware Road cabin, but no one knew what it sounded like or even where it was reporting about! :)

    Also 2: The elephant in the room seems to be danger of tunnel flooding via an internal explosion – i.e. a terrorist strike on a river tunnel. Admittedly not the cheeriest of topics..

  39. Littlejohn says:

    @timbeau 03:38PM, 5th November 2012. I have a vague idea that a tonne was originally a measure of volume, not weight. Is this right or am I having one more senior moment?

  40. ChrisMitch says:

    A tonne is not strictly an SI unit. 1 tonne = 1000kg, so it should really be called a megagram – Mg.
    I think it was introduced because it is roughly equivalent to an imperial ton. It is a convenience shortcut, introduced for real life.
    And it is definitely a unit of mass, not volume.

  41. answer=42 says:

    @Littlejohn
    The ‘net tonnage’ of a vessel is related to its volume:
    http://en.wikipedia.org/wiki/Net_tonnage

    Also from Wikipedia:
    A ship’s displacement or displacement tonnage is the weight of the water that a ship displaces when it is floating with its fuel tanks full and all stores aboard. … As a measurement of weight, displacement should not be confused with similarly named measurements of volume or capacity such as net tonnage, gross tonnage, or deadweight tonnage… Consider a 100-ton ship passing from a saltwater sea into a freshwater river. It always displaces exactly 100 tons of water, but it has to displace a greater volume of (less dense) fresh water to amount to 100 tons. Therefore it would sit slightly lower in the water in the freshwater river than it would in the saltwater sea.

    So you are not right but understandably so.

  42. Greg Tingey says:

    My Engineering MSc is in Measurement & systems – DON’T get me started!

  43. Fandroid says:

    We have deviated wildly off-topic here, but what fun it is.

    @Littlejohn

    you may or may not be having a senior moment, depending on how you define it. ‘Tun’ is an ‘antiquated measurement of volume’. So you are quite correct. (Allowing for spelling).

  44. timbeau says:

    Interestingly, the “tonnage” of a ship is a measure of volume (derived from “tun” rather than “ton”) – net or gross depending on whether non-payload carrying space is included: and there is some variation in net tonnage depending on whether the cargo is regularly shaped or a bulk commodity like grain.

    It is on the gross tonnage measure that the Titanic was claimed to be the largest ship in the world, despite being almost identical to her older sister the Olympic. On the Olympic the promenade deck (“A” deck) was open-sided, whereas in the light of experience the Titanic had weather screens fitted. These screens made that deck part of the internal volume of the ship, hence it had a greater gross tonnage, even though they had negligible effect on its weight (displacement). (They also made it harder to get to the lifeboats being lowered past that deck!)

    Displacement is of course measured in tons, as the volume of water displaced depends on its density (which varies with temperature and, particularly, salinity)

  45. Whiff says:

    Definitely an interesting and useful deviation as I’ve never been able to visualise an acre before!

  46. Anonymous says:

    Well, this sidetrack has provided more insight into the mindset of regular contributors than anything else I have read so far. I am truly humbled by Mr Tingey’s Master’s.

  47. John Bull says:

    It’s certainly been informative!

    Reminds me of a comment derail on another site I read years ago, which started on a post about glamour shots for women, and ended up being a huge debate about SQL Syntax.

  48. KentishTrack says:

    Surely a chain is 22 yards, i.e. a cricket pitch? So our railways are measured in cricket pitches.
    Something I like very much.

  49. Pedantic of Purley says:

    A chain is an old unit of surveying because, not surprisingly in the days before retractable tape measures, they surveyed distances using a standard length chain along with rods and other devices. A standard furlong (furrow long) was 10 chains long and one chain wide and a mile, by statutory definition, was eight furlongs.

    It is hardly surprising that the early railway engineers measured things in chains as it was the obvious measurement to use. There are 80 chains to the mile although it does sometimes appear that Network Rail doesn’t know this. Network Rail is under an inherited statutory obligation to measure and mark out distances in miles and as the original plans would have been in imperial measurements there is some logic to this.

    In contrast to Network Rail, London Underground has gone fully metric and, would you believe it, measures all track distances in kilometres from the buffer stops at Ongar.

    One could argue that imperial measurements are actually metric since the inch nowadays is defined as being exactly 25.4 mm. Since we are going well off-topic I may as well add that it could be argued that distance is no longer a fundamental unit of measurement. The reason for this is that the velocity of light is a constant and time can be measured much more accurately than distance so a metre is defined as the distance light travels in a certain amount of time.

  50. Twopenny Tube says:

    JB: “Since we are going well off-topic I may as well add that it could be argued that distance is no longer a fundamental unit of measurement. The reason for this is that the velocity of light is a constant and time can be measured much more accurately than distance so a metre is defined as the distance light travels in a certain amount of time.”

    So how long would it take for light to get from Ongar to say, Bank?

  51. Anonymous says:

    Twopenny Tube – 37.77 Km at 299,792,458 metres per second. I make it just under 126 microseconds, but this would entail bending light round corners!

  52. Greg Tingey says:

    Ongar to Bank along a light-pipe laid alongside the track, or in a straight line?

    my old copy of “Quail” says 37.77 km Ongar-Bank, & light travels at 2.99793*10^8 metres/second (approx)
    And that translates to 3.77*10^4 metres
    Doing the division gives you …approx 1.257*10^-4 seconds
    One-&-a-quarter ten-thousandths of a second, in other words!

    Remember what I said, above, & remembering that 1km = 5/8 mile, so a chain IS a cricket-pitch (because real, actual “chains” were easy to come by) but it is also 50 metres. However, there are certain truly “fundamental” units of measurement, irrespective of units, by which we can get a metric on the universe.
    They are (IIRC):
    Length, time, temperature (absolute), angle, light-flux, mass, current.
    Everything else can be derived from these.
    Hence a great deal of effort is made, at NPL in Teddington, & similar national laboratories to pin down values for these quantities, expressed, these days, of course in the International Metric System’s units.

    Ship “tonnage” is very confusing.
    Most merchant ships aree measured by Volume (length^3, remember) rather that their mass, how many “Tuns” can you stow in one – even passenger liners.
    But warships are always measured by displacement – actual mass of water shoved aside by the ship.

    Of course a “Tun” is also, & importantly a Beer/wine volume measure, not used much now-adays.
    Beer now comes in (doubling in volume at each step …Pipkin (pin), Kilderkin (kiln), Barrel = 36 gallons = 160.2 litres, Hogshead, Pipe (or Butt) & Tun,
    So a Tun is 8 barrels = 288 gallons = 1281 litres which is well over a Ton (or even a tonne ) in mass.

    Hic.

  53. timbeau says:

    It says here* that a tun was indeed 8 barrels, but a barrel was 26.25 imperial gallons (not 36). A tun was originally 256 gallons, later 252 and later still 210 gallons. 252 gallons of water weigh 1 ton.

    (*wikipedia)

  54. Taz says:

    A search of the LT Museum poster collection for the topic Flood and also for Flooding at:
    http://www.ltmcollection.org/posters/themes/themes-main.html?_IXSESSION_=3twcKGIFnuO
    brings items from the days when the city really was at risk. The maps have been mentioned already. The flood warning notices may not have been ever used, but only held in reserve.

  55. Greg Tingey says:

    timbeau
    A barrel is NOW 36 gallons & has been for all of my life, & since 1803, in fact (!)
    Try: http://en.wikipedia.org/wiki/English_brewery_cask_units HERE for better info.
    Yup, Wikipedia is contradicting itself.
    However, I can tell you that, these days, pins & kils are usually just called “9′s & 18′s” …..

    Taz
    As for flooding, reading Gerry Feinnes’ other reminiscences, gives a tale of 1953 in East London ….

  56. timbeau says:

    yes, but the derivation of ship tonnage is from when a tun of water weighed a ton

  57. Anonymous says:

    Curious – 1 US gallon is about 4/5 of a UK gallon, so a US tun would be about 1025 litres and weigh 2,260 pounds. Not very far from 2,240. It seems likely that the measure was consistent with the wine gallon, predecessor of the US gallon, rather than the Imperial gallon’s precursor, the ale gallon. This would resolve the discussion and allow us to go back to flooding. Does the Master of Measurement concur?

    So far as 1953 is concerned, central London escaped by the skin of its teeth. If the banks hadn’t failed in Canvey, the surge would have overtopped the embankments. This is why there was a very dangerous period between raising the banks as far as Woolwich and the eventual completion of the Thames Barrier. Did you know that the George Wimpey group took the threat so seriously in the late 1970′s that they built a bund wall with flood gates around their headquarters building in Hammersmith Grove?

  58. Long Branch Mike says:

    Now that we’ve been inondated with measurement, I’m happy to hear we can flood back on the rising tide of London rail transport comments…

  59. Anonymous says:

    One significant flash flooding risk has been identified by the City of London: if the dams containing the ponds on Hampstead Heath were to be overtopped or, even worse, fail, there is the potential for the water, having flooded some of the most expensive properties in the capital, to end up flowing into the Northern Line tunnels (presumably via Belsize Park station). But, luckily, this is only likely in the very worst case scenario, and the City is undertaking works to reduce the risk significantly, not just through engineering works on the dams themselves but also through landscape management such as reducing compaction on the Heath, the creation of swales, and tree planting and leaving grass areas longer to reduce the rate of surface run-off.

  60. Greg Tingey says:

    The US “gallon” is smaller than ours, because their Pint is smaller than ours!
    Beer drinkers please note.
    And this is because their pint is 16floz not 20
    So their pint weighs a pound, whereas ours weighs a pound-&-a-quarter …
    Amateur drinkers, you see!

  61. Fandroid says:

    @Anonymous

    Water tends to flow downhill (it has done since I was kid anyway), so Belsize Park station should be safe from Hampstead Heath ponds. The eponymous Hampstead Heath Overground station is a bit more in the firing line. Past there the water is likely to head down Fleet Road (a hint of a buried river there perhaps!) and Southampton Road, possibly heading towards Chalk Farm Northern Line station.

  62. PhilD says:

    Just as a follow up there’s a piece on the clean up operation from the New York Times here:
    http://www.nytimes.com/2012/11/09/nyregion/new-york-subways-find-magic-in-speedy-hurricane-recovery.html?pagewanted=1&_r=0
    (and no I haven’t read the comments. With the exception of this fine blog, reading the bottom half of the internet is rarely good for one’s sanity :) )

  63. Anonymous says:

    I love this blog!

    Next time I’m asked what it means to be English, I will direct the asker here.

  64. Ian says:

    “So what floodgates remain today? The truth is that in the post 7/7 world no-one, apart from London Underground themselves, knows for sure.”

    A few years ago, there was a TV programme on scenarios for a terrorist attack on London, complete with experts role-playing the responses.

    I knew that they weren’t testing them properly when the attack on the tube was ‘just’ a bomb at both ends of a train in a tunnel somewhere rather than causing the collapse in one of the tunnels just under the bed of the Thames between Embankment and Waterloo. (But I suppose people saying “Right, let’s give up and go home” doesn’t make good TV.)

    If the floodgates protecting against problems there don’t work, at some point someone is going to try to take advantage of this.

  65. Malcolm says:

    …err, do’t you mean “Let’s give up and not go home” ?

  66. Greg Tingey says:

    Ian
    Totally unrealistic
    A bomb powerful enough to not only destroy the train, but breach the tunnel would be much “better” employed elsewhere by the terrorists.
    It’s like the “security” checks @ St Pancras, Gare du Nord & Brussel Zuid – 150% pointless. If you’re really intending to bomb the chunnel, you put it on a lorry-shuttle & hope their security checks (note the absence of quotes?) don’t find it & you.

  67. SarahBell says:

    BBC Panorama: London Under Attack
    https://www.youtube.com/watch?v=x7uIjg9dtoI

    Is the drama

  68. stimarco says:

    If memory serves, most of the deep-level Tube tunnels are actually quite deep. As they’re designed to withstand the pressures acting on them already – London isn’t built on granite, but mostly on clay, gravel and sand – you’d need a seriously big bomb to actually blow out a deep level Tube tunnel.

    Even the shallower Thames Tunnel would be a tough ask for a bomb: it was built as a single bore, divided internally by brick arches to keep the expected vehicle traffic flows separated, so most of the blast energy would be dissipated along the tunnel, rather than outwards into the crown. You’d need a truly massive bomb to break it.

    The fact is, as various tunnel fires and explosions have proved over the years, tunnels are bloody difficult to seriously damage from the inside. The Channel Tunnel itself has seen three serious fires, but none managed to bring the English Channel down into the tunnels and flood the system. All the damage has been repairable, though not always cheaply.

    Have a read of this, if you don’t believe me. That’s proper Geordie engineering, that is.

  69. Graham H says:

    Can anyone explain what the previous post is for, or about. This seems to happen quite a lot and I really wonder why it happens – some sort of automated response?

  70. @Graham Feakins H,

    Actually it was the following post as they always appear at the bottom. They are a WordPress feature that is added when another WordPress blog mentions an article here. Ideally the site should be configured so we don’t get these. I don’t even know if WordPress allows this. Meanwhile I just delete them when I encounter them.

  71. Graham Feakins says:

    @ Graham H – And the one below yours, too? Or is that the one you mean, as it is timed before yours but appears below?

    Incidentally, stimarco might need to be reminded that one Bakerloo tunnel lies just 3 feet below the Thames river bed and hence the reason it was encased some years ago in concrete.

  72. Graham Feakins says:

    @ PoP – Yours crossed with mine and you meant to address Graham H.

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