Thread by @garius

Okay, this is a good opportunity to talk flood gates on the London Underground. The myths, the reality, and the known unknowns.

Spoiler: there are less than you think, and they were never there for the reasons you think. And the Thames Barrier is really, REALLY important. /1

https://twitter.com/mjattrill/status/1448036789130862592

So the first thing you need to think about here is what the Thames actually is, and what its relationship to London has always been:

It's been the city's lifeblood for centuries, but also its biggest divider. It's what protects us northerners from southerners, and vice-versa.

It was also a big barrier to the early railways. Because tunnelling under a river, particularly a tidal one, is pretty fucking hard.

So hard, in fact, that it took the combined brains of Marc, Isambard and Brunel to do it.

Indeed the Thames Tunnel, which the London Overground uses today, is the OLDEST tunnel bored under a tidal river anywhere in the world.

It almost killed both Marc and Isambard building it, and did killed a number of their workers.

SIDEBAR: At some point I need to do a thread about Sophie Brunel, Marc's daughter and Isambard's sister.

Both Marc and Isambard considered her easily their equal in the engineering brains department. If you want evidence of how women got screwed out of history: Hello Sophie.

Indeed it should probably be about both her and her mother, Sophia Kingdom, who was pretty bloody badass in her own right.

As Marc himself wrote to her when they finally broke through at Rotherhithe:

"Sans toi, ma chère Sophie, point de Tonnelle"

Anyway. I digress.

Pictures of Brunels tunnel flooding during construction, and a belief that it's a thing that can happen, linger in the consciousness. But it's not true.
Once you've managed to BUILD a tunnel, the chances of catastrophic flooding are tiny.

This why, despite the Underground crossing beneath the Thames about 18 times (including disused tunnels), NONE of those tunnels were built with flood protection.

There's no point. The bigger risk is surface flooding...

...unless the Germans are REALLY REALLY angry with you.

And THAT'S why you ended up with flood doors on the Underground. Not because anyone was worried about the tunnels spontaneously bursting open, but because in 1938 it was realised that the Luftwaffe might have a good chance of doing it, if they decided to pop over and say hello.

So William Halcrow (another threadworthy chap. Google him) oversaw the plugging of the Northern and Bakerloo tunnels with concrete, confining services to the north, until big floodgates could be built. These were in place by December 1939 and could be closed during air raids.

This logic for needing floodgates continued into the early Cold War era. Indeed at this point it expanded, because it became clear in the 1950s that an atomic bomb hitting London could not just cause river flooding, but utility flooding as well.

At this point, floodgates were added at TCR, Liverpool Street, Russell Square, Kennington, Moorgate, Green Park, Embankment, Waterloo, London Bridge, Bank and a lot more stations than I can fit in this Tweet.

Also: Holborn. The most visible remains of this exercise today.

These gates controlled by the secret London Underground emergency control centre (the "Special Works Project") built at the never-finished North End station on the Northern Line.

(The flood control centre was the only bit of that they finished. Opened in 1956, closed in 1984)

That closure date should provide you with a clue as to why almost all of the floodgates are decommissioned now:

Because by 1984 it was clear that if a nuke hit London, the Tube flooding was the LEAST of the city's problems.

And post-Cold War they became even more redundant.

Which is why you don't need to panic that most of the gates are out of action now. Because the risk of catastrophic flooding is tiny outside of an actual war.

And (back to the original Tweet) the risk of fluvial flooding hasn't been a thing since the Thames Barrier was built.

So what floodgates DO still work? Truth is: I don't know. Admittedly I've not tried to find out again for a few years, but that's mostly because ever since 7/7 it has (understandably) been seen as something TfL shouldn't really talk a lot about.

Instinctively, my suspicion is the only RIVER gates that still work aren't actually on the Thames. It's the ones at Tottenham Hale designed to deal with the river lea, which is a bit of a different situation (in terms of both river and station/tunnel setup) and thus riskier.

MAYBE the ones at Canning Town on the Jubbly. But I reckon that's probably doubtful post-signalling rework.

(It's the need to redo signalling and cabling that normally acted as their final decommissioning point).

But the important thing to remember is: It's fine. Don't panic.

But. BUT. This is why the Thames Barrier, and climate change, very much matters to London.

Because SURFACE flooding, as we're seeing, is the Underground's biggest flood risk. And you can't just slap some big gates on river tunnels to solve that.

It becomes a constant threat.

And that threat ISN'T hypothetical. You only have to look at recent incidents to see that.

As to fluvial flooding from the Thames? Well the Barrier is worthy of a thread of its own one day. It's an engineering masterpiece, one that is on track to protect London until about 2070.

Monitoring that life expectancy, and the rest of the Thames flood protection, is a critical part of the ongoing Thames Estuary 2100 project managed by the Environment Agency.

Most recent update here: gov.uk/government/pub…

So RIGHT NOW you don't need to stress about river flooding, or the lack of floodgates on the Underground. Unless the Barrier suddenly fails. Then we're looking at a 1953 scale disaster all over again.
en.wikipedia.org/wiki/North_Sea…

But you SHOULD worry about what climate change is doing to rainfall in London. To quote the Environment Agency:

Dealing with that problem is harder for TfL. There are no easy fixes. That'll reflect in taxes, fare prices and more.

And it's a problem that they're only just beginning to get a feel for how they tackle. Because floodgates are a solution to last century's problems. Not this one

(Apols for typos in the thread btw. Was a bit of a speedy throw out job as I'm quite busy today)