Blackwater Coast

The Thames barrier is a direct result of the 1953 floods.

It's one of the largest and most expensive defences of all,

designed to protect London from surge tides until 2030.

It's absolutely gigantic.

That's what it takes to stop

the capital city drowning.

Beautiful too. It's easy to forget how utilitarian engineering can look absolutely stunning.

With the high tide mark creeping up by 60cms a century, even this has its limitations.

Engineers are looking at extending its use until 2100 by raising the estuary walls by half a metre.

And another option, for the distant future,

is an even bigger barrier further out into the estuary.

There'll always be pressure to defend the nation's capital.

But, outside London, the costs are less easy to justify.

Continuously replacing rock armour is like signing away a blank cheque to the sea.

So, in the Black Water Estuary, they're thinking about coastal defence in a whole new way.

I'm cutting across the fields at Abbotts Hall Farm in Essex

to look at an unconventional approach to coastal defence.

Just down here, on the edge of the estuary,

they're cutting holes in the sea wall.

Punching through the old defences seems like madness

but it's like opening a safety valve to take the pressure of erosion out of the estuary.

This allows the water inland to create inter-tidal salt marshes -

nature's defence against the power of the sea.

What these salt marshes do,

they take the energy out of the water. The currents slow down

as they move through creek networks and the plants jut into the water

and take the wave energy out of the wave.

Repairing old defences is a costly job.

In the long run, creating man-made salt marshes can be cheaper.

But acres of farmland have to be given over to the buffer zone, so the scheme's not without critics.

In people's minds it probably does feel like we're giving up.

But we're not. We're trying to work with nature,

so when we have another 1953-type event, we're prepared for it.

We have areas like this for water to be stored in terms of the flooding.

You're talking about a coastline that's changing all the time,

a map of the UK that could look quite different in 100 years.

It's interesting, the word "coastline".

I think what happened was, you know, we mapped our coastline

and put a line on it and it's a snapshot of what it looked like when that person mapped that coast.

So it's a very hard perception to change in people's minds

that it isn't fixed, it's a very dynamic place.

Coastlines are probably the most dynamic environments in the UK

and it's constantly changing.

It may be a bitter pill to swallow

but we can't realistically protect every inch of our coastline.

Concrete walls destroy the sense of wonder that draws us to the coast.

But, without them, we face a precarious future

in the face of advancing seas.