- If the Thames Barrier were
to fail when it was needed, the damage would be almost
impossible to calculate. The best estimates I've found say that
the financial cost of London flooding would be somewhere between
£20 billion and £100 billion. The Houses of Parliament, every skyscraper in the city of London, every building near the river
would be unusable for weeks. The central parts of
the London Underground would be out of action
for months, possibly more. That's before you get to the human costs. Worst case, perhaps hundreds
of thousands of people who'd be forced out of their homes. Which is why this barrier
is designed to not fail. To be clear, that still means it can
have occasional glitches or scheduled maintenance, or even
have parts of it break entirely. But if any of those things happen,
it must still protect London. And there's a whole team
who work here full time to make sure that it does. - We aim to move each of
the ten individual gates at least twice a month to exercise them. Today is one of our monthly test closures. For test closures, we close just as
the tide is finishing going out. And that way, we can
wait until the tide turns and then we get equilibrium
on both sides of the Barrier, and therefore, we can reopen. That avoids us having to be
closed for the full tidal cycle. - A couple of months ago, the Barrier had a full
high-tide test closure and it is dramatic. Normally, the gates
just sit out of the way on the bottom of the river, but when they're needed,
they're rotated up into place. - Well, for the annual test closure, because we're trying to
maximise the differential, the water levels on each
side of the barrier, we like to close early in the tidal cycle to allow that differential
level to build up to a maximum of 4½ metres. On a flood defence closure, we close much later in the tidal cycle, because we just want to stop
the danger element of the tide going up into Central London. We try and be gentle with the river. So, we start by closing
the outer smaller gates. And then, we slowly work
across into the middle. And sometimes, we'll bring
the two 61-metre gates in the centre of the river
up a couple of metres below the surface, before we finally bring them
into the closed position. And that avoids a
reflective wave of the water that's coming in and being stopped, being pushed back downstream. So, during a flood defence closure, we don't have to stop the whole tide
going into Central London. We just need to stop the part of that tide that would overtop the linear defences. Normal spring tides that
go into London each day do not overtop the embankment
walls, for example. But if you've got a surge
element on top of that, that is what would go over the top
of the walls in London, and that's the element that we
need to stop with the Barrier. Once we've stopped the
danger element of the tide and got a differential, we've effectively created a reservoir
upstream of the Barrier. We can then over-rotate the large gates and allow a controlled
flow of water upstream into the reservoir that we've created. And again, that reduces the amount of time before we get equilibrium on both sides
of the barrier and can reopen. - The barrier cannot be allowed
to fail when it's needed. So, each gate can be moved by
one of four separate motors. That service tunnel I was in?
There are two of them, a few metres apart, identical, with completely independent
power and control systems. The barrier has three connections
to the UK power grid, for both the north and south of the river. And if the entire British
national power grid fails, which has never happened, but if it does, the barrier has three
separate diesel generators, any one of which could
operate the entire thing. - We have a number of modes of operation, so that if, when we're
using Mode 1 operation, we have a problem of a technical nature,
we go to Mode 2. Problem with Mode 2,
we go to Mode 3. We don't necessarily have time
to sort out any technical issues, but we've got other modes of operation
that we can fall back on. The barrier has to close
when we need it to. I always say that if the Prime Minister was stood in the House of
Commons in his wellingtons and we said, "Sorry, PM,
we'll get it right next tide," that would probably be
fairly career-limiting(!) - So, that's the technical resilience. What about the physical construction? Well, these piers are
made of Portland cement, so, they'll stand for a
couple of centuries at least. The steel gates are protected by
what's called a sacrificial anode. Corrosion in water like this
is an electrochemical process. So, if you connect a chunk of metal that's more easily corroded
to something like the gate, that chunk of metal will take
the corrosion damage instead, and you can replace it fairly
easily whenever you need to. So, the gates will also be
fine for a century or so. What if a ship hits the Barrier? Well, ships are designed to float. Relatively speaking,
they're not that solid. These piers are thick concrete, and each of the main gates
is 3,000 tonnes of steel. So, the ship's going to come off worse. Collisions have actually
happened several times. In 1997, a ship called the
Sand Kite hit one of the piers. The only damage to the Barrier
was some scratched paint and a broken ladder, but the ship sank. The trouble was that it sank where it hit and sat broken on top of
one of the open gates. That would've blocked that
part of the Barrier from closing. The contingency plan,
if there had been a flood tide, would have been to close
all the other gates and use the force of the
water trying to get through to blast the wrecked ship clear. But also, even if one gate
was completely broken somehow, the Barrier would still
not technically fail. The margin for error would be gone,
but that's why the margin's there. It would still hold back enough
water to keep London safe. - We have a series of forecast models and we run what we call
an ensemble forecast that looks many tides ahead. With any models,
particularly forecast models, you will always get a degree of error. So, the forecaster here will make
an adjustment to the forecast and that data will be
passed to the controller from which to make a decision
as to whether to close or not. - So, the barrier is
highly reliable and strong. What if there's a really high tide, a storm surge that's too
much for this to cope with? Well, the design odds of that
are one in a thousand per year. Not technically failure, just not
being specified high enough. The barrier was designed
in 1970 for a 60-year life, which would be 2030, which must've seemed a
very long way away then. The good news is that with
modern simulations and modelling, the team here are confident that
it'll last another 40 years at least. But part of the reason for that is
because those 1970s engineers built in a huge margin of safety. They didn't cut corners then, and
that's given us breathing space now. - The gates themselves, with inspections and remedial works, will probably be good to go until 2070, but a lot of the
supporting infrastructure, the fire systems, the security systems,
even the cranes on the piers will all have to be updated
in the years to come. - But what if the tide went high enough
to actually overtop the barrier? Well, those gates are built strong enough
that any water they can't hold back can flow under into the
low water on the other side. Remember, they close the barrier early,
when the river's at its lowest point, so, yes, if some apocalyptic
storm comes along, the barrier should still work well enough. If this was almost anything else, you could say the redundancy
was over-specified, that requirements like
this were ridiculous, but with so much at stake, the Thames Barrier is a marvel
not just of engineering, but of how you have to build when
something cannot be allowed to fail.
That was incredibly interesting. Thanks for sharing!
Interesting, he renamed the video to "The Thames Barrier must never fail. Here's why it doesn't."
I didn’t realize it was that close to London. For some reason I assumed it was much further downstream.
This gives me a couple of questions.
First, how do they prevent the river from going around the barrier? If the area around London is low enough to be flooded I would assume that there would be an easy path for the excess water pushing up the river to simply go around the barrier. Are there dikes and levees? Is the topology such that the area around the barrier is not as low as the threatened portions of London? Is that area simply sacrificed as part of the protection of London?
Bloody hell, I remember when that thing was built!
Fascinating. Always enjoy these videos.
Were the computers running Windows 7? I suppose mechanically it has a crazy amount of redundant systems in place
Interesting he didn’t mention cyber attacks at all. If anything is critical infrastructure, this is, and I hope they have some good firewalls to protect them from one hacker bypassing their system and giving orders from a distance.
$20 billion doesn't really sound like that incredible of a disaster to me, not on the scale of modern cities.
Based on the thumbnail, I hope the next video on TomScottPlus is where Tom discovers a set of dumbbells.