♪♪♪

-Summer 2016, Canning Town, East London.

-I was sitting here, just working away,

and it was raining, so I went outside

and opened the door, had a look.

I thought, "My God, this is tropical."

It was a lot of rain. [ Rain pouring ]

You know, you just don't see

that kind of rain here in London,

and the water just started coming in.

It was crazy.

In over two hours, there was almost a meter of water in here,

sewage everywhere.

Drum kits were floating about in the water.

Amps was just under the water.

Things that survived were things that are on tables.

The roads were impassable because the roads flooded.

The trains couldn't run because it was basically a stream.

The amount of water that was falling filled all the sewers,

and the water is going to find its lowest point

below ground level here.

At the end of the day, how can you cope?

-The world's great cities face threats

they have never before encountered.

New York,

Tokyo,

London,

Miami --

the threats come from the sea,

from above and from below.

These are the problems and their solutions...

♪♪♪

...for when the water comes.

[ Waves crashing ]

-So, underneath here is

the pump chamber with the pumps.

I know for a fact it's going to happen again.

It will happen again.

It's just a matter of when.

Rebuilding it took a good 10 months.

God forbid it should happen like that again

and for some reason the pumps don't work.

If it happened again, I would just pack up.

-Flash flooding has become commonplace in London.

In 2007, one incident left 1,400 properties in the city flooded.

-There's so much regeneration going on in London

at the moment where any kind of open space has been built on,

so where does all that rainwater go?

It's not being soaked into the ground anymore.

-London faces three challenges.

Summertime rainfall in the UK

has increased 20% in the past decade.

The city is densely developed

along the Thames River floodplain,

meaning all that rain has no place to go,

and the legendary Thames is handling more water than ever

as sea levels rise all around the island nation.

The Thames has always been at the heart

of London's prosperity,

linking the city to the outside world,

but it has also posed a threat.

-London probably has one of the longest flood histories

of anywhere in the world.

There's records of events going back thousands of years.

I mean, there's hundreds of major storms that have occurred

that have killed several thousands of people.

-London has a population of eight million people,

and the initial city was designed

for four million people,

so it's actually doubled over the course of,

we could say, 125 years.

If London stops functioning and London is flooded,

this country, as far as you know it, will stop functioning.

-While the Thames is widely thought of as London's river,

it's actually part of a 215-mile-long series

of tributaries and wetlands throughout southeastern England.

The Thames flows east from Greater London

into the North Sea 50 miles away.

Robert Muir-Wood is a resiliency scientist in the private sector.

-So what we're looking at here is a map

of the Greater London area,

and at the western end here, we have the river,

which comes in from the countryside

to the west of London, comes in,

and the river is getting wider now.

You can see it's also getting a bit muddier

because the tides are very strong.

They're carrying a lot of mud with them,

swings around here and passes into the Westminster area

so the center of government quite close to Hyde Park.

Up here, we get to the city of London, the old center,

which is actually on a slight hill,

so it's actually protected from flood risk.

In the aftermath of every flood or near-miss flood,

the walls in Central London,

which protect Central London from the river,

have been raised.

-As oceans rise, the Thames is affected

because its estuary flows into the North Sea,

and that poses further challenges for London.

-The North Sea has been described

as the perfect storm-surge basin.

It's very shallow.

The shallower it is, the more effect the wind

can have on raising up sea levels,

but the North Sea also funnels as well.

-When wind and storms make the waters of the North Sea rise,

they funnel west into the Thames Estuary

and up the river to London.

-And that wall of water has only one place to go,

and we know what's at the end of this big corridor --

London.

-These storm surges have flooded London

throughout history.

-1928 in the middle of the night,

there was high flow on the Thames

coming into London on the river, and also,

there was a storm surge came in from the North Sea.

In fact, the term "storm surge" was coined

in the aftermath of what happened

because people didn't have a word at the time

to describe what kind of flood this was,

but it actually flooded the areas of Central London,

of Westminster, in particular, drowned, I think, 14 people,

caused several thousand to lose their homes.

-The storm that was London's wake-up call hit the city

with a massive blow in January 1953.

-People went to bed that night

with no idea they were going to flood.

Some people unfortunately didn't wake up the next day.

-The storm began with high winds over the North Sea

battering its shores from Scotland to the Netherlands.

Combining with the rising spring tide,

a mammoth surge powered up the Thames.

-The country was different in those times.

There wasn't any warning system.

There weren't really any defenses, per se.

-At the mouth of the Thames,

the people of Canvey Island had no idea what was coming.

Only 11 years old at the time,

Ray Howard remembers being woken in the middle of the night.

-We were upstairs tucked in bed when,

all of a sudden, my sister came into the bedroom and said,

"Quick, there's water gushing down the street."

-Hundreds of millions of gallons of water

swept through the town.

-People were clinging to their roofs

and just hanging on because of the force of the breach

and the force of the tide and the heights of the tide.

-The storm tide reached London around midnight.

As water rose higher in the Thames,

the BBC issued a warning,

and cars equipped with loudspeakers

were dispatched to rouse the sleeping city.

The east end of the city was flooded

from the Royal Docks into Canning Town.

At London Bridge,

the water reached its highest level ever recorded,

threatening to breach the embankment

and inundate Central London.

-In fact, in center of London, the river was actually brimful.

It was a major event.

-Then the wind turned unexpectedly,

and the surge receded.

The center of London was spared,

but still, the destruction was immense.

-Helicopters, too, have played their part,

flying in supplies for the survivors

and helping to maintain the central services in areas

not yet evacuated.

-Poor people just had no chance.

59 people lost their lives on Canvey Island

in that terrible, terrible evening

but 309 people along the whole east coast of the UK.

-160,000 acres of land

were inundated across the UK.

The damage was the equivalent of nearly $2 billion today,

but it could've been even worse for London,

and the city decided to act.

-That was the foundation as to why London should be protected.

The flood was quite severe, and they realized

that if we carry on in this fashion in the future,

we won't be able to protect ourselves

from this ongoing problem of a tidal surge

leading to the riverbanks,

overtopping and actually flooding the floodplain

all the way down to Central London.

-The options considered were, "Do we do nothing?

Do we move London because the risk is too great?"

Or the third, "Do you build a barrier?"

-London set about bolstering its flood defenses

with nearly 200 miles of embankments,

gates and barriers along the Thames and its tributaries...

...but it would take $2 billion and nearly 30 years

to create the crown jewel of their new system,

the Thames Barrier.

A 600-yard-long floodgate

that runs from New Charlton to Silvertown

across the Thames was finished in 1982.

-Tower Bridge, the last major bridge,

and then the river, still getting wider,

swings around again past the old docks going south

and then north again in a big meander.

This is where Canary Wharf,

big new high-rise financial center, is.

Further towards the east,

the river is getting still wider.

We're heading more out to sea, and then, finally,

we come to the line of the Thames Barrier itself,

so everywhere to the west of that is actually protected

by the Thames Barrier

from the storm surges coming in from the sea.

-Normally, the barrier remains open so boat traffic

can reach the Port of London,

but when a storm surge approaches from the North Sea,

10 curved steel gates rotate up from the riverbed.

This forms a solid wall against millions of tons of water

that would inundate London.

♪♪♪

Since its installation, it's been used 182 times,

and London has not been flooded once.

Andy Batchelor has been the manager of this marvel

of flood engineering for nearly 20 years.

-The barrier is referred to as the sleeping giant

because if we do our job well,

no one needs to know because London is protected,

so the tides can come and go, the barrier close,

and they don't get their feet wet.

That is the art of good flood risk management.

-For three decades, the barrier has kept the city safe

from storm surges.

-The Thames Barrier has been designed

for a 1-in-a-1,000-year event.

What that means is that there's a 0.1% chance of London

being flooded as a result of that barrier.

That is why it works.

-But while it's been doing its job of keeping London dry,

the climate has been changing,

so now the Thames Barrier faces a new challenge.

-The barrier was designed in the '60s.

Climate change, global warming weren't phrases

in the dictionary then.

-The designers of the barrier had planned

for higher sea levels, not because of rising seas

but because southeast England is literally sinking

at a rate of 1.5 millimeters,

or a 1/16 inch, per year.

-The designers and engineers who crafted the barrier

made their best estimation and calculations to factor in

sea level rise in the future, not thinking of it

in the context of climate change or adaptation

but recognizing that the geological formation

underneath the southeast in London is sinking.

Their appreciation of geology

more than the appreciation of climate change

is what led them to put, in effect,

an 8-millimeter factor of safety every year

into the design of the Thames Barrier.

If you have a rising sea level in addition to a landmass

that is sinking,

that's a quite interesting combination.

-Climate change is now seen clearly

as a present and future threat.

In London, a dramatic 2013 weather event

exposed vulnerability

in the celebrated Thames Barrier system.

On December 5, 2013,

Cyclone Xaver smashed into Britain's east coast,

churning up the North Sea higher than in decades.

-In the northern parts of the UK,

the 5th and 6th of December

actually had higher sea levels than in 1953.

-The storm surge rushed up the Thames.

The barrier held strong and did its usual job.

-And that really was the most significant event

we've had since 1953, so that was a good test

of the sort of protective capabilities of the barrier.

-But in that storm, something new happened.

[ Rain pouring ]

Torrential rain filled the length of the Thames

with an unprecedented volume of water.

-The rainfall flow just didn't stop for 3 months.

-We have storm after storm tracking across the Atlantic

dumping hundreds of millimeters of rain on the UK,

so large regions experienced levels of rainfall

that we've not got in the observational record.

-The UK had more rain that winter than in any year

since records began in 1910,

and all that rain...

had to go somewhere.

-The River Thames is big, one of the UK's biggest rivers.

It's a catchment that we call it.

Any rain that's falling around that area

always goes down into the River Thames.

-By January, England was seeing a new kind

of flooding called fluvial.

The Thames was flooding, not draining, the land.

Now the barrier is put into action

in a way its designers never intended,

not to keep storm surge out of the Thames

but to use the river above the barrier

as a reservoir for excess rain.

At low tide, the barrier is closed,

leaving the Thames nearly empty to take on

flooding from heavy rainfall upstream.

-We've got two factors, rainfall going one way,

tide going the other,

and what we're able to do is close the barrier

and stop the surge tide from going into London.

If we close the Thames Barrier very shortly after low water,

what we end up in the center of London

is like an empty reservoir,

so the rainfall is able to come in and not cause any problems,

and the barrier is shut,

and with all the other defenses being closed as well,

they're able to contain that surge tide

and thereby stop from going into London

and therefore also not overflow, so we've done a double act

of the reservoirs contain the rainfall,

and the defenses and the barriers contain the surge,

so it's that act of looking after both sides, shall we say.

-Without the barrier's use, Central London

would've suffered catastrophic flooding,

♪♪♪

and there was a limit to how far the barrier

did work that winter.

In places like Sunbury on the Thames

just south of Heathrow Airport,

the water had no outlet, so it overflowed its banks.

[ Indistinct conversation ]

-We watch it coming up,

creeping up the bank slowly and steadily,

and once it breaks this bank, you know it's going to --

It goes very fast because once it's over this brow,

it starts to take the part very quickly,

and the you know you're going to be watching it

for quite a few days.

-In a matter of days, the Kirbys' home is underwater.

Tina, her husband, Adrian, and daughters

Sujata and Sujaza decide to stand their ground

as the waters rise right to their front door.

-Three weeks to a month, it was here.

It was around the house. We were --

We would have to wear waders to leave the house.

-Use a boat. -Then we started using a boat

to leave the house.

-It's creating a lot of mess and not going anywhere.

-We would take the children out in the boat,

you know, and sail them down the road.

You would try and make fun where you could.

-Yeah, because if you, you know, didn't have a laugh,

then you'd probably cry, but it was better to be at home

than to find yourself alternative accommodation.

-After nearly a month,

the Kirbys thought they had won the battle.

-Towards the end of January,

it started to recede, and so we thought,

"Okay. The worst of it's over, and things would be better."

It then started to rain again really heavily.

[ Rain pouring ]

The second time it came,

it came a lot faster.

-Now the water came higher and higher into the house.

-Probably about -- Was it about that high?

-Yeah, I'd say about nine inches --

-Nine inches... -...sort of maximum.

-...that, so it cleared the skirting

and was into the plaster.

-For more than a month, the Kirbys lived

with water nine inches deep in their house.

-And we thought, "It will be one night.

It'll go away, and we'll dry it out.

We'll get dryers, and it'll be fine,"

but, you know, wearing Wellington boots

in your house, you put them down,

and they float away the minute you put them down,

so every time you took your shoe off to go up the stairs,

you had to make sure you held onto it.

Otherwise, it would be gone,

and you'd be left standing there with nothing.

-That is the moment that you evacuate,

when you get a cold Wellington boot.

There's no way of drying it.

It's so cold.

That's when you go.

-Across southwest London,

families were flooded out of their homes.

In total, over 10,000 properties in the UK

were flooded that winter.

Even in Central London, which escaped flooding,

the defense systems were stretched to their limits.

-It was absolutely unprecedented in that

we actually had 50 closures of the Thames Barrier.

41 of those were as a consequence of the rainfall

with the remaining nine as a consequence of the tides.

Now, to put that into context, the normal operation

is of the order of about one to two per year,

so at that time,

we'd only closed about 160 times in 30 years,

so we saw a third of our closures roughly in three months

by comparison to 30 years.

-With their prized barrier working far more

often than it was intended to,

London's future against the rising Thames

is once again uncertain.

-The flood barriers have made a difference,

both the permanent ones and the temporary ones,

but it's clear, in some cases, they've been overtopped.

They've been overrun, and so, of course, we should look again

about whether there's more we can do.

-London has been here for many centuries.

Currently, we have a population of eight million.

By 2100, that could almost double,

and yet everybody wants to live in the center,

so we're building taller.

We're densifying, and we're building more subways,

more tube systems, and we're going down,

so when the rain falls, where does it go?

So we need space for water.

We need space for it soak to be able to be stored.

-With heavier and more frequent rainfall,

there is nowhere for all the water to go.

What's happening has as much to do with urbanization

as climate change.

Governments and public utilities are searching for solutions,

large and small.

-Things like gardens and parks

have been paved over for a variety of reasons.

There's more runoff, and it's more likely to cause

flooding than perhaps a generation ago

when there was just more greenery around to soak it up.

-15% of Greater London is considered

to be the floodplain,

most of it in the low-lying areas alongside the Thames

where approximately 1.5 million people live,

and more are still coming.

About 75% of this massive urban area

is completely paved over.

With so much of the absorbent green space

covered with asphalt and concrete,

the runoff is directed into sewers and drains,

which can't handle that excess water.

-It's running off into very old sewers that were built back

in Victorian times for a whole different population,

but they're too small, simple.

I feel we have been put to the test.

I know that this area is a floodplain, for instance.

They're still building many flats.

You know, people need accommodation.

I don't know what they're doing when it comes to the flood risk.

The Thames Barrier is not that far away from here.

I have this place because it's affordable.

The end of the day, it is in a floodplain,

and I know it's in a floodplain.

What do you do?

-London needs new solutions against the increase in rain.

The first challenge is better prediction of future rainstorms

like those of 2013-2014.

-When '13-'14 came along

and we had such unprecedented levels of rainfall,

then the immediate question arises, where did it comes from?

-Professor Adam Scaife is the head

of long-range prediction at the Met Office,

the UK's national weather service.

He says climate scientists have long known

that global warming will lead to increased rainfall.

-Something called the Clausius-Clapeyron Equation,

it's a really simple equation.

People study it at school, tells you that,

the warmer the air, the more moisture it will hold,

and therefore, when that moisture comes out,

which it must do somewhere, then you will have heavier,

more frequent downpours

and more mean rainfall, so that's really clear.

We know that.

The big question is, where?

Where is the rainfall going to come out?

And that, of course, is much more difficult.

-Traditional weather-prediction tools like satellites

provide part of the picture,

but long-term forecasting has to account for additional factors.

-You better take into account the increasing CO2

because the temperature is going to be that much different.

However, if you want to forecast very long range beyond,

say, a week, the ocean starts to play a really big role,

and so we have something called Argo floats.

There are thousands of these things all over the globe.

It's an international project.

We put them all together, collect all the data,

and that tells us what the temperature and salinity

of the ocean is throughout its depth worldwide.

The ocean is a bit like a pacemaker for the atmosphere.

The atmosphere is jumping around

with its weather storms and things,

but the slow guiding force of the ocean

can steer that chaotic variability one way or another.

-All of that data is compiled

onto one of the biggest supercomputers in the country.

-It allows us to split the globe

into tinier and tinier pixels,

and the more pixels we have and the more layers

we represent the ocean and the atmosphere over

and the more accurate we can get the forecast.

-That allows Scaife to narrow down

how the rainfall will affect the specific area.

What the computer's results show is bad news for London.

-We are very confident that, in winter,

we're going to see more rainfall, more heavy rainfall

and more average rainfall and hence more flooding.

There is, every single winter,

between 5% and 10% chance of a new record.

Then, after a few decades,

what is now an unprecedent event will become the norm.

-The Thames Barrier was designed to be used

just a few times a year.

If it's needed 50 or more times as it was in the winter of 2013,

it will wear out.

That is a mechanical certainty.

-You know, similar to your car, if you're always driving

your car, you're never going to be able

to put it in the garage to maintain it,

so there's got to be an optimum figure,

and notionally, just for now, we've put that as 50,

so we're working towards when we hit that maximum of 50 per year,

we would need to have a new barrier.

-And that's without factoring in the next big problem --

sea-level rise.

London has to plan for how much sea level

will rise by the end of the century.

One estimate predicts that could be from 10 to 35 inches.

-Based on the acceleration rates we're seeing

at the moment, we think it's going to be

at least 50 centimeters if not higher,

but we're expecting with an acceleration in ice melt

that, that will gradually increase,

so for London, the maximum we think it could be

by the end of the century is about 2 1/2 meters.

That's the physically plausible upper, upper rate.

-That's 8 feet of sea-level rise.

The UK Environment Agency,

the government body tasked with flood protection,

recommended the barrier's life expectancy

be extended from 2030 until 2070 to buy time.

-Within the original design criteria for the barrier,

there was enough allowance to actually mean

that we've got another 40 years

of that high degree of protection

but ease more life out of it.

-But that was before the winter floods of 2013

increased the barrier's workload so much.

More rain and rising seas

will put still more strain on London's infrastructure.

-You could get such a severe weather event

that we've never seen before in this country.

It could overwhelm our defenses.

-Even the best-designed engineering solutions

can't last forever.

All of London's current defenses

will soon need upgrading or replacing.

-Whether it's the barrier, all the walls

in the center of London or out to the estuary,

you're daft if you don't think things have a life.

You're daft when you don't plan for all them coming to an end.

-Increased and more intense rainfall,

a massive mostly concrete city surface,

an aging, overused barrier system

for the mighty but dangerous Thames River and rising seas

increasing the destructive power of storm surges.

The UK is bracing itself for the 21st century

with an array of solutions,

some low-tech, some among the most advanced in the world.

♪♪♪

This is the state-of-the-art Flood Forecasting Centre.

Senior Team Leader Brian Vinall

and his group are armed with satellites,

radar and coastal gauges

that give them up-to-the-minute information.

-We have a lot of data,

and we have some very, very highly trained staff.

They're the ones that have that decision

as to whether to ring me

and wake me up at 3:00 in the morning to say,

"We need to start briefing government."

It's up to them to decide what the response is.

We tell them what the risk could be.

We try and say how many properties might flood.

We try and put it into context about,

"This could be as bad as 1953."

-The prime goal of Vinall and the Flood Forecasting Centre

is to make sure evacuation orders

are given early enough to save lives.

-We're not going to be able to tell an individual house

whether they're going to flood in four, five days' time.

What we can do is tell the emergency responders

that there's probably going to be a community

affected in this area.

Now, you do get accused of cry wolf with that.

You do get people who could potentially by evacuated

and have no flooding happen.

I'd much rather have that on my conscience.

-Water is hitting London from all sides.

The problem here is getting it out.

-An awful lot of flood risk management

is about moving water around to places or holding water up

in places where it won't harm people and property.

Where everywhere is under the water,

then you start to have quite limitations

on what you can do about it.

-The government has a massive plan

to tackle climate change this century.

TE2100 is the blueprint for keeping London

from going underwater.

The Thames Tideway Tunnel is one of London's

most ambitious and expensive plans.

It's a massive initiative designed to channel the water

from overflowing sewers before it gets to the river.

200 feet below the Thames

and running along roughly the same path,

it's a £4-billion project that will take seven years to finish.

-At the turn of the century here in London,

the Victorian civil engineers

were some of the earliest pioneers

in providing fresh water and sanitation

below the heart of our city.

Now, that envisaged a certain quantum of population,

but that has grown tenfold, twentyfold.

-Managing the sewage network for 15 million people

is obviously a massive challenge.

-Rob Sainsbury and Pascal Lang are with Thames Water.

The sewer system they oversee, run end to end,

would stretch halfway around the world at the equator.

-We're trying to make it as resilient as possible,

but obviously there are times when we have extremely

heavy rainfall where the system can't cope.

-Many of the sewer lines carry channels

for both sewage and storm water, which is now a serious problem.

-If we have a combination of rainwater and sewage,

our sewage reaches capacity,

and then that sewage then spills out of the manhole.

If people are coming into contact with that sewage,

that's obviously a public health concern.

-The current sewer system was constructed

in the late 19th century.

It was designed principally to service 4 million people,

and because of the way sewer systems are built,

it's very difficult to retrofit them and upgrade them over time.

-A fail-safe is a backup mechanism

for when a system doesn't work,

and in the case of London's flooding sewers,

the fail-safe was overflow into the Thames.

This unsanitary solution of the Victorian era

still happens today,

and it's a major health problem London urgently needs to fix.

-So you have sewage going directly into the Thames.

You have water quality going down.

At the same time, you have all the water runoff in order for it

not to flood or it to be backed up in the system

actually going down into the River Thames.

So that happens 50 times a year.

-One goal of the Tideway Tunnel

is to upgrade this antiquated system

and ensure raw sewage no longer gets into the Thames

by diverting the contaminated overflow

to upgraded treatment facilities.

-The Tideway Tunnel is London now getting its act together

and trying to find a way to deal with this old sewer system.

It's a tunnel 25 kilometers long,

which lies across the London Basin of the Thames.

Its function is to allow for all the water runoff

that comes from the draining systems,

in addition to the sewage, to be discharged into the sea.

It's so expensive now to dig underground in London.

People are put off because of the price tag.

So in the future, unfortunately we'll be forced to use it,

whether we like it or not,

whether we like the price of it or not.

-The Tideway Tunnel

is projected to be finished in 2023.

Meanwhile, London has other mega projects

planned for the Thames.

-The T2100 is looking at improving all the flood

defenses along the Thames estuary

to improve both the riverbank,

the embankment, the floodwalls and the seawalls

and the coastal defenses that are in the estuary itself

to then allow the barrier to carry on functioning

until 2080 where the idea is

that they will want to build a second Thames barrier.

-Rather than building a new barrier now

that's going to cost billions,

they said, "Let's delay the procedure."

There's some things that they can do

to extend the lifetime of the barrier.

They can slightly overclock the gates.

They can build and use sort of defense schemes

in and around the barrier.

If sea level rise starts to accelerate

and gets much higher than that,

then obviously we've got to go down a different pathway.

Now, the problem with this approach is

it assumes that you can detect

when sea levels are accelerating,

and certainly with the original Thames barrier,

it took 30 years to build,

so there's a very long lead-in time.

-Considering that lead time, the Environment Agency needs to

make sure they have a clear picture of sea level rise.

They've enlisted researchers like Dr. Ivan Haigh

to make sure they have the most accurate data.

He observes fluctuations in sea level rise

that may not be related to climate change.

Some are part of natural annual patterns in the North Sea.

-Sea level doesn't just rise smoothly and gently.

Every year, sea levels rise as the ocean warms up

in the summer, falls as the ocean cools down,

so we can see every year its rising-falling.

-He collects data on other factors involved

in that fluctuation like temperature,

salinity, wind and atmospheric pressure.

He has to work out what is caused by climate change

and what isn't.

-The way I tend to picture it is,

imagine you're at a party.

There's 10 people in the room.

Everyone is talking.

Some people are talking very loud.

So sea level is very noisy.

The acceleration component is a small, quiet voice.

So what we found is, when we're able to remove

90% of the noise, we do now see a very clear

statistically significant acceleration signal.

Over the 20th century, we saw about 1.7 millimeters per year.

Now, in the last few decades, we're starting to see double

that rate -- about 3 millimeters per year.

For the first time in the UK now,

we are detecting that the rate is getting faster.

-London's TE2100 plan is tackling rising seas

and increased rainfall

with multi-billion-dollar infrastructure projects

and with small-scale solutions.

This project is called Sustainable Drainage Systems

or SuDS.

Kevin Barton is a landscape architect working on SuDS,

a localized approach to drainage becoming popular in London.

-The problem in London, much like many cities

around the world, is, over the centuries,

we have paved over large parts of our landscape.

We've created this impermeable barrier over our landscape,

which means that when it rains,

what we see is much larger volumes of water

entering our sewer systems and eventually into our rivers.

Plus there's none of the slowing of that water that nature gives.

-The problem when the rainwater falls

is that sewers reach capacity.

Then they overflow into basements or onto street level,

and of course with sewerage, it's foul waste,

so it's contaminated, which is even worse.

-Jessica Bastock is the flood risk manager

for Hammersmith and Fulham, a riverside district in London

that is almost entirely paved over and prone to flooding.

-So what we're trying to do here

is to stop that from happening

by relieving the pressure in the sewer

and actually dealing with water,

the rainwater that falls on the ground, sustainably.

-SuDS offers a range of drainage solutions

depending on the site. -This is Mendora Road,

and along Mendora Road, what we try to do

is use permeable-block paving to deal with water.

All that is, is block paving,

but instead of it being butted together,

it's actually open, so water can flow between the blocks,

and that means that when water falls,

it runs through the block paving and gets stored underneath.

We're on Bridget Joyce Square.

Along this stretch of road now,

there are multiple SuDS features.

On this side of Bridget Joyce Square,

we have permeable-block paving.

In between the blocks, there are little gaps,

and rainwater that falls on the surface

actually moves through these gaps

and then into a detention basin.

♪♪♪

When the basin starts to fill up during the intense rainfall

event, there is an overflow point,

so it will go back into the sewer system,

but it will go at a really slow rate,

so it will be a trickle.

On this side of Bridget Joyce Square,

we have a local school.

To incorporate this school into the design,

what we've done is, we've taken the rainwater

from the school building, on the roof,

and we've disconnected the downpipes,

which would normally have fed into the sewer system,

and we just channel it across, and then through little holes,

that actually feeds straight, directly into the basin.

-Another SuDS scheme has been implemented

about a mile away on Goldhawk Road.

-This road, it's very, very busy,

so in this kind of situation, what we've had to do

is to have a sustainable drainage measure

which can fit in this landscape.

Engineered tree pits were thought

to be the best way forward.

They collect water from the carriageway,

and then they feed into the drain here,

and then this is like a lateral drain, so a flat drain,

and it feeds straight into the base of the tree pit here,

and then underneath this tree pit

is lots of box-crate storage, which holds water.

-Kevin Barton believes SuDS

will be commonplace across London by 2100,

incremental steps with a big result.

-Feels like we're on a steep curve at the moment

where more and more people are coupling onto SuDS.

When you understand it saves money,

it's good for developers as well as the environment

and as well as flooding.

From everyone's perspective, SuDS is a no-brainer.

-SuDS are good, but they're a soft solution.

The difficulties in Thames is that,

if you have a flash flood incident,

and it rains, and there's a large amount of rain

in a short period of time,

that in itself becomes an impervious surface.

SuDS aren't able to deal with that type of water runoff

whereas a sewer system can, specifically the Tideway Tunnel.

-As London looks to the future,

it also looks to the past for overlooked options.

-By the mid-19th century, most of the tributary rivers

would become effectively open sewers,

and they were heavily polluted,

and they were faced with a public health crisis.

Their response was to bury those rivers,

pipe them up and build over the top of them.

It also created more space

because they could be built on top of,

so it made way for development.

-The project, run by David Harding,

revolves around a network of lost rivers

that lie beneath London.

-London lost about 26 of its major tributaries,

rivers like the Fleet and the Tyburn and the Walbrook.

There were lots of cases where we were investigating

flooding in the urban area

where we couldn't really account for where all the flow came from

because those rivers still do function

as rivers when it rains.

-And that's at the heart of many of today's

flooding problems in London

and other global cities built over rivers.

-So what we've got to do now is to start to restore

some of the more natural drainage of London.

Rather than wait for these water courses

to reveal themselves when they flooded,

go out and look for them proactively to understand

where all the rivers have disappeared to.

We start off from the LIDAR mapping,

the digital terrain mapping, to look for telltale signs.

The blue is the highest ground going down to the yellow,

which is the lowest ground,

and you start to see what looks like a floodplain

or a river valley with networks of tributaries coming off of it.

We then start to refer to the historical mapping.

So taking one of those potential

flow pathways from the LIDAR data

and referencing it to a map from 1846,

you can start to see that the Salmons Brook is actually mapped

when it coincides very well with the LIDAR data,

and at this stage in the urbanization,

the river was still on the surface.

-Guided by high-tech data,

he takes the search from the office to the field.

Harding is in a suburb of London where he hopes to find traces

of the city's Victorian shape and structure.

-So we're on Nestor Avenue now where we believe

that the Houndsden Gutter,

a lost watercourse, flows to my left.

If you put a river in a pipe or a channel,

it's got a finite capacity,

and when that capacity is reached,

then that's when you start to get flooding

coming out of things like manholes,

flooding into properties and gardens and roads

as opposed to the natural watercourses,

which could flood out on the floodplains,

which, in many cases, are still there.

So if we could daylight some of these watercourses in the areas

where they can be allowed to safely flood,

then that reduces the flood risk to the built-up area.

-Daylighting means opening the river back up

to its natural state,

giving the water more room to flow,

but since they've long been covered over,

these rivers have disappeared from modern maps.

-Okay, so the map has led us to the open section

of the watercourse that's to my left,

and there should be a pipe or a tunnel linking that

to the next visible open section of watercourse,

so we're just going to go down into the river now

and walk the river and look for the existence of the tunnel.

♪♪♪

-Harding discovers that his software correctly identified

the existence of a buried section of river.

-This conduit that was built when the road was built,

when the houses were built,

this was just a way of putting it in a nice,

straight line that was out of people's way,

and it's typical of thousands of kilometers of ordinary

watercourses across London.

-Most of the people who live and work in these shops

and cafes have no idea a river once ran through their community

and may soon be flowing again.

-There's no reason why they couldn't be restored

to a more natural river corridor.

Now that we know it's here,

we can understand any upstream flood risk that's caused

by the throttling effect of this tunnel,

and we can then look for opportunities to allow the river

to spread out into safe open areas.

-So far, over 11 miles of lost rivers in London

have been daylighted.

♪♪♪

One of the best examples uses landscaping with earth

bunds or embankments here

at the Firs Farms Wetlands in Enfield in north London.

♪♪♪

♪♪♪

-We identified that using Firs Farm as a flood storage area,

we could protect quite a significant number

of people living downstream.

We realized that instead of building a concrete wall,

we could build a natural earth bund as a defense

and to generate the spoil that we needed to build that bund,

we could carve out a channel,

and that channel has now become the restored river.

-Though the wetland is about 12 miles from the center of London,

the project is already having an impact,

reducing the amount of rainwater flowing into the Thames' system.

-And we realized that using wetland planting,

we could mitigate the urban pollution.

You can actually clean that water by passing it

through a filter bed system.

We've ended up with a combined wetland

and flood storage area here,

and by combining those two things,

you get multiple benefits.

You've got the permanent habitat, which is always here --

the wetlands and the plants and the wildlife and so on.

You've got an area that local residents can come and visit

and enjoy on a day-to-day basis,

but you've also got a functional landscape

which actually stores tens of thousands of cubic meters

of water during intense rainfall

and protects people living downstream.

-Harding sees this kind of organic approach

to flood prevention as a necessary complement

to large infrastructure like the Barrier.

-The scale of hard engineering that's needed

to start to address flood risk through climate change now

is becoming unfeasible, you know?

We can't go for the big-tunnel solutions forever,

so we need to start sort of rolling back

some of the urbanization and sort of managing flood risk

in a more natural way like this project does.

♪♪♪

-Another more radical solution is not to battle the rising sea

but to work with it.

Richard Coutts is an architect and urbanist

specializing in floating architecture.

-London is particularly under threat through climate change.

We have sea level rise, and we're seeing more rainfall.

We are building more, and the upshot of that is

there's just not enough capacity in the system

for this rainfall to go.

To meet those challenges, we need to use the water space.

We need to inhabit.

We need to optimize our resources.

Casting our minds forward to the next 50, next hundred years,

one could imagine London thriving at the water's edge,

new communities just growing, inhabiting the water space,

the parks, new homes, businesses right in the heart of cities.

-And Richard's secret weapon?

-And we're looking at floating communities.

We've actually coined the phrase "aquatecture,"

which is essentially architecture on water.

So we're currently located in the Royal Docks of London.

We are in a floating hotel.

This was constructed in the turn of the 19th century.

The Good Hotel is unique in terms of its thinking.

It's a traditional industrial unit on a floating base.

This was formerly a prison building

that was birthed in Amsterdam.

It was no longer fit for purpose,

and this is one of the wonderful things

with floating architecture -- it has flexibility.

You take it somewhere else.

You give it a fresh lease of life,

and from a building which previously people

were fighting not to get in, we're now in a situation

where people are paying a premium to dwell,

to rest right on the water's edge.

-Aquatecture is design that combines with water

rather than resisting it.

It's something Coutts believes

is a solution in London's future.

-And we're looking at the existing communities

and how to make those resilient.

We're looking at stilted houses and amphibious dwellings,

and then at the other end of the scale,

we're looking at floating and flood-resilient communities.

This is the UK's first amphibious house,

and it's built 8 meters from the River Thames

and is a house which is designed to rise and fall with the water.

This is more of a practical approach,

which allows the people who live here to be within their garden

and to be low,

but in the event of a flood, the house is more responsive.

The benefits of an amphibious house are,

in the event of a flood, the house can float.

It can literally move up and down.

The garden is designed as an early-warning system,

and what we've got is a series of tiered plains

almost like buckets.

When the first two fill,

it actually triggers the buoyancy of the house.

-Architecture that works with rather than against the water

is an idea being considered

by designers and engineers worldwide.

Coutts believes that floating structures will be embraced

by the world's most powerful players.

-Floating cities, those cities which really grow,

those which are at the forefront will be those that utilize water

in that adaptable fashion to bring in a floating Olympics,

to bring in those floating expos,

to providing housing, to meet the needs of their workforce

in the middle of the city,

and water provides that opportunity.

-For decades, London trusted the Thames Barrier

would keep it safe from water.

Now, that sleeping giant can no longer be relied upon

as rainfall increases and sea levels rise.

-You know, the risk to London is huge --

1.25 million people, £375 billion worth of infrastructure.

You know, there is 400,000 properties.

You can just keep on going with the stats.

We can't fail.

We've got to get this right.

-Still, the people of London aren't feeling

as safe as they once did.

-I think, if it rains for more than three days in a row,

I start thinking,

"Is this going to be another one of those winters

where we start getting rain after rain after rain?"

-The city's search for multiple solutions continues.

-I think that sort of the approach

that the Victorians took,

that, you know, you could always throw enough technology

and enough concrete at a problem,

and you could overcome it,

but, you know, there's an acceptance

that that's not appropriate in all circumstances,

and a more natural approach to flood risk management

is the only one that's going to be sustainable

in the face of more severe weather,

rising sea levels, you know, more prolonged wet periods.

-We need clever architects,

designers that can build cities that can cope with sea levels

and almost make that part of the future design of the city.

-The challenges are immense, as are the stakes,

but London is ready for the battle.

-In London, we need to make a few decisions.

You can see we have some wonderful heritage,

and we need to protect and defend that,

so maybe in these areas, we maintain our flood defenses,

but in other areas of the city,

we need the capacity in the system for this volume of water,

and we may have to consider retreating,

taking down some of those buildings,

creating parks to provide additional storage.

We can still use those as recreation,

but we need to think more intelligently.

We need our policy makers to keep up,

to be with us on this journey

as we deliver this very innovative infrastructure

and new ways of living to enable our cities to grow.

-So right now, the biggest challenge

is to let planners, policy makers,

the people who make decisions understand

that we have to actually streamline these systems

so they can function as one, and I think that alone

is a big challenge of what London needs to do

to move into the 21st century in its foremost.

So adaptation challenges our current way of thinking.

It challenges everything we think we do and say

and based not in the name of sustainability

but in the name of resilience.

-Well, even for wealthy cities, this is going to be a challenge.

They're going to have to watch this very carefully.

It's going to require

a significant amount of investment.

That investment will be an increasing proportion

of the economic activity in that city,

and this is going to be the issue for the 21st century

around a number of coastal cities.

♪♪♪

Narrator: Next time, Miami is considered the most at-risk city worldwide

due to rising sea level and storm-related flooding.

We're gonna get probably 2 feet of sea-level rise by 2060.

Then, by 2100, we might get 6 feet of water.

The water is coming.

We already see 20 days a year

that, just high tide, the water is higher than the land.

Man: Water is coming from the side, from below, from above.

Miami is at that point where they've got to decide,

"How do we solve the issues of sea-level rise?"

♪♪♪

-To order "Sinking Cities" on DVD,

visit Shop PBS or call 1-800-PLAY-PBS.

This program is also available on Amazon Prime Video.

♪♪♪