0:00:02 > 0:00:04Here in Britain, we love talking about the weather
0:00:04 > 0:00:07and over the past few months, there's been plenty to talk about.
0:00:07 > 0:00:11But stoical though we are about the wind and the rain, this last winter
0:00:11 > 0:00:16has been a powerful reminder of how water can wreak absolute havoc.
0:00:20 > 0:00:21It all began in December,
0:00:21 > 0:00:25when the British Isles were bombarded by storms.
0:00:25 > 0:00:29Waves battered the coast, gale force winds uprooted trees
0:00:29 > 0:00:33and torrential rain filled rivers to bursting point.
0:00:33 > 0:00:35We witnessed some of the worst flooding we'd ever seen.
0:00:35 > 0:00:39There's no wall, no defence - just nothing there.
0:00:39 > 0:00:41We saw the flood waters right up to our gate.
0:00:41 > 0:00:43We weren't prepared for this.
0:00:43 > 0:00:45And it didn't end there.
0:00:45 > 0:00:47Just when we thought we might get some respite,
0:00:47 > 0:00:48the storms struck again.
0:00:48 > 0:00:51The last 24 hours have seen the biggest waves
0:00:51 > 0:00:54ever recorded in British waters.
0:00:54 > 0:00:57We've never been flooded in 55 years and it's indoors now.
0:00:57 > 0:00:59The water's rising an inch an hour, they tell me.
0:00:59 > 0:01:02I'd have done anything to have saved my home.
0:01:02 > 0:01:06This week, Bang puts flooding under the spotlight,
0:01:06 > 0:01:10asking not only why does it happen and what can we do about it,
0:01:10 > 0:01:12but what can we expect in the future?
0:01:14 > 0:01:17Tonight, we'll be looking at what causes flooding,
0:01:17 > 0:01:21from the humble raindrop to an epic storm surge.
0:01:23 > 0:01:26'We'll look at what we can do to protect ourselves.'
0:01:26 > 0:01:28There's literally water logging going on.
0:01:28 > 0:01:32'And we'll see how technology can help us to deal with floods.'
0:01:32 > 0:01:35It's wonderful to see it in action in real time.
0:01:35 > 0:01:37- Fantastic.- We can see live telemetry.
0:01:37 > 0:01:40Files are being exchanged between the spacecraft and the ground.
0:01:45 > 0:01:47This winter, the British Isles were struck by at least
0:01:47 > 0:01:5112 major storms and some parts of the country received
0:01:51 > 0:01:54more than twice the average winter rainfall.
0:01:54 > 0:01:58This deluge provided us with some extraordinary scenes
0:01:58 > 0:02:03of Britain under water, but sadly around 6,500 homes were flooded.
0:02:04 > 0:02:07Back in January, I visited Rod and Holly
0:02:07 > 0:02:10in the village of Thorney, in Somerset.
0:02:10 > 0:02:12The flood water was so deep,
0:02:12 > 0:02:14I had to don waders to get to their house.
0:02:15 > 0:02:19- Hello.- Hi. This is just horrendous, isn't it?
0:02:19 > 0:02:23Just tell me how quickly the water came up.
0:02:23 > 0:02:26Well, it came up quite slowly to start with
0:02:26 > 0:02:28and we started to put all our furniture on bricks.
0:02:28 > 0:02:31Then another hour or so, two hours, and we had to put it on
0:02:31 > 0:02:33another brick and another brick and then some wood.
0:02:39 > 0:02:42- Wow! Gosh, it's coming through the floor, isn't it?- Yeah.
0:02:42 > 0:02:45Has it changed the way you're thinking about this house?
0:02:45 > 0:02:48Yes. Well, it has me. I feel very insecure.
0:02:48 > 0:02:51And the hard thing, really, is the not knowing -
0:02:51 > 0:02:53will it happen next year? Will it happen every year?
0:02:53 > 0:02:57Yeah, absolutely, absolutely right. This was ten days' rain.
0:02:57 > 0:02:59Am I going to be waking up every time I hear it raining, thinking,
0:02:59 > 0:03:03"Gosh, we've only got six days of rain before we're flooded again."
0:03:03 > 0:03:04It's completely untenable.
0:03:04 > 0:03:08Sadly, Rod and Holly were flooded again
0:03:08 > 0:03:10shortly after I left in January.
0:03:10 > 0:03:14And for weeks after, they had several inches of water in their home.
0:03:14 > 0:03:16It finally drained away at the beginning of March.
0:03:16 > 0:03:20It's been an extremely traumatic time - not only for them,
0:03:20 > 0:03:23but for people up and down the country.
0:03:23 > 0:03:24And you can completely understand
0:03:24 > 0:03:27that if you've been through all this,
0:03:27 > 0:03:30you'd like some reassurance that it's not going to happen again.
0:03:32 > 0:03:35So, what exactly is it that causes flooding?
0:03:35 > 0:03:37And what can we do about it?
0:03:39 > 0:03:42The total amount of water on earth remains fairly constant
0:03:42 > 0:03:45and it moves in a cycle around our planet.
0:03:45 > 0:03:48It's released by plants through transpiration
0:03:48 > 0:03:51and evaporates from oceans and rivers.
0:03:51 > 0:03:54And it returns to earth as precipitation.
0:03:54 > 0:03:57Around 96% of it is held by the oceans.
0:03:57 > 0:04:001.7% exists as ice.
0:04:01 > 0:04:06And 0.8% is ground water stored in rocks.
0:04:06 > 0:04:11A mere thousandth of a per cent exists as water vapour in the atmosphere.
0:04:11 > 0:04:13And while that may not sound like much,
0:04:13 > 0:04:15it's still five times more water
0:04:15 > 0:04:18than is held in all of the world's rivers.
0:04:18 > 0:04:22So when weather events combine to bring a lot of water to one place,
0:04:22 > 0:04:24our rivers, land and coastlines
0:04:24 > 0:04:28can be inundated with more water than they can cope with.
0:04:30 > 0:04:32But the weather isn't the only factor.
0:04:32 > 0:04:35We also have to consider how that excess water
0:04:35 > 0:04:37interacts with the land.
0:04:44 > 0:04:49This is a model of a river in its catchment area or drainage basin.
0:04:49 > 0:04:51You've got a natural landscape here upstream,
0:04:51 > 0:04:53you've got trees and grass,
0:04:53 > 0:04:57a town here and a village further downstream.
0:04:57 > 0:04:59And, obviously, all the water is running to the sea in this
0:04:59 > 0:05:02direction, so let's take a look at what happens if you get
0:05:02 > 0:05:03heavy rainfall in this area.
0:05:14 > 0:05:16So, take a look at what's happening.
0:05:16 > 0:05:19Because this is natural landscape, a lot of water has been
0:05:19 > 0:05:21absorbed by the soil.
0:05:21 > 0:05:25But here, the river has still flooded in the flood plain.
0:05:25 > 0:05:27But the thing is, this is supposed to happen.
0:05:27 > 0:05:31A river and its flood plain are actually one natural single
0:05:31 > 0:05:33highway of moving water.
0:05:33 > 0:05:36As the water levels eventually decrease again, the flood plain
0:05:36 > 0:05:40drains back into the river and all of the water goes towards the sea.
0:05:42 > 0:05:44OK, so now let's look at what happens
0:05:44 > 0:05:47if we alter the landscape in some way.
0:05:47 > 0:05:51Imagine we've decided to build a big city in this nice
0:05:51 > 0:05:54bit of land upstream of the town and village.
0:05:54 > 0:05:58We're talking car parks, supermarkets, schools, roads etc.
0:05:58 > 0:06:02So there's a lot of concrete covering up a lot of the soil.
0:06:02 > 0:06:05And then we have a rainstorm.
0:06:07 > 0:06:09I'm pouring the same amount of water,
0:06:09 > 0:06:12but hardly any of it is being absorbed.
0:06:13 > 0:06:16So what happens downstream of this city
0:06:16 > 0:06:20is that this town gets completely flooded.
0:06:20 > 0:06:23And what's clear is that it's not just about the amount
0:06:23 > 0:06:25of rainfall at any given time -
0:06:25 > 0:06:28it's about how the landscape is able to cope with that rain.
0:06:29 > 0:06:32To make matters worse, building on flood plains has
0:06:32 > 0:06:35increased by 12% in the last decade.
0:06:35 > 0:06:39This town wants to be protected from floods and so they go ahead
0:06:39 > 0:06:42and they build a big flood defence around their town.
0:06:42 > 0:06:43So let's take a look at what happens
0:06:43 > 0:06:47the next time a big rainstorm comes along.
0:06:54 > 0:06:59Fairly quickly, it's evident what happens as a result.
0:06:59 > 0:07:01The town is now protected because it's gone ahead
0:07:01 > 0:07:03and built a big flood defence
0:07:03 > 0:07:05but take a look what's happened downstream.
0:07:05 > 0:07:07The village that was fine before
0:07:07 > 0:07:10is completely flooded - and that's the crux of the problem.
0:07:10 > 0:07:12The water has to go somewhere.
0:07:14 > 0:07:17If you go ahead and make a change in one place,
0:07:17 > 0:07:20that will inevitably impact somewhere else.
0:07:21 > 0:07:25And you don't have to live next to a river for this to be a problem.
0:07:25 > 0:07:29In our towns and cities, green gardens are disappearing
0:07:29 > 0:07:32to make way for paving, decking and patios.
0:07:32 > 0:07:35In London alone, seven Hyde Parks' worth of garden
0:07:35 > 0:07:38have been paved over in the last ten years.
0:07:38 > 0:07:42I've been responsible for a fair few garden revamps in my time
0:07:42 > 0:07:45and paving and decking have indeed featured in them,
0:07:45 > 0:07:50but it doesn't take a scientist to work out that paving will
0:07:50 > 0:07:54absorb a lot less rain and water than a grassy surface.
0:07:56 > 0:07:59But can paving over a small front garden like this one
0:07:59 > 0:08:02really have an impact on flooding?
0:08:02 > 0:08:05Well, according to the experts, yes.
0:08:05 > 0:08:09In an hour's downpour, up to three bathtubs' worth of rain
0:08:09 > 0:08:12could fall on this small driveway,
0:08:12 > 0:08:15of which 5% will make its way into the ground.
0:08:15 > 0:08:20The other 95% whooshes off as surface run off.
0:08:23 > 0:08:26This can lead to more water than our drains can cope with.
0:08:26 > 0:08:29And to make matters worse, this run off sweeps
0:08:29 > 0:08:32pollution along with it, which ends up in our rivers.
0:08:32 > 0:08:35But there are things we can do about it.
0:08:35 > 0:08:39This front garden has been covered with a special porous paving,
0:08:39 > 0:08:41which, they tell me,
0:08:41 > 0:08:44lets the water naturally seep through to the ground below.
0:08:44 > 0:08:47But we're not going to just sprinkle a little bit of water -
0:08:47 > 0:08:49we're going to flood it.
0:08:53 > 0:08:56The joints of the paving are filled with crushed stone,
0:08:56 > 0:08:57as is the base layer beneath,
0:08:57 > 0:09:00allowing the water to flow down to the bedrock.
0:09:05 > 0:09:07Paving like this can make a difference
0:09:07 > 0:09:10but it doesn't beat a real garden.
0:09:13 > 0:09:16Here at the Susi Earnshaw Theatre School in London,
0:09:16 > 0:09:18flooding was a regular occurrence -
0:09:18 > 0:09:23until a scheme run by the Wildfowl and Wetlands Trust solved the problem.
0:09:23 > 0:09:25Now rain water is caught at source,
0:09:25 > 0:09:30channelled down this tarmac river and dealt with sustainably.
0:09:30 > 0:09:32Andy, explain this project.
0:09:32 > 0:09:35When it rains, the water overflows from the water butt,
0:09:35 > 0:09:39and it ends up down here in our sustainable drainage system
0:09:39 > 0:09:42and it spreads along this gutter that you can see in front of you -
0:09:42 > 0:09:46you can see the water now from the recent rain - over the grassy strip.
0:09:46 > 0:09:50All the sediments and big bits of pollution are trapped by the grass.
0:09:50 > 0:09:54The grass turns the petrol and diesel into plant nutrients and then
0:09:54 > 0:09:57any overflow makes its way into our Mediterranean gravel garden,
0:09:57 > 0:10:01which is, essentially, a big storage feature for those big rainfall events.
0:10:01 > 0:10:05So, not only are you solving the problem of the rain puddling up
0:10:05 > 0:10:08in the parking area, you end up with a nice garden,
0:10:08 > 0:10:13an educational facility and I'm glad to see you've got a pond there, as well.
0:10:13 > 0:10:14Yeah, it's fantastic, isn't it?
0:10:14 > 0:10:17Any overflow from the bog garden makes it into the pond,
0:10:17 > 0:10:20overflow from there going into this rain garden there.
0:10:20 > 0:10:23So what can this cope with in the way of rainfall?
0:10:23 > 0:10:25We've designed this to deal with
0:10:25 > 0:10:30all rainfall that a one-in-ten-year event will throw at the system.
0:10:30 > 0:10:32That's quite a lot of rain.
0:10:32 > 0:10:36One garden may not seem like much, but this scheme now involves
0:10:36 > 0:10:38ten schools across the catchment.
0:10:38 > 0:10:40And if businesses and home owners get involved too,
0:10:40 > 0:10:43then these small things can start to have a big impact.
0:10:45 > 0:10:49This will help us in our cities, but some of the worst flooding
0:10:49 > 0:10:52this winter struck rural areas like the Somerset Levels.
0:10:52 > 0:10:54And the question of what should be done there
0:10:54 > 0:10:58brings us to the controversial subject of dredging.
0:10:58 > 0:11:02Why was this not done ages ago? Why are you only doing this now?
0:11:02 > 0:11:05Dredging is where the river beds are cleared of sediment.
0:11:05 > 0:11:08The idea is that this creates more room in the river for excess water
0:11:08 > 0:11:11and gets it to the oceans more quickly.
0:11:11 > 0:11:14But it's not quite as simple as that.
0:11:14 > 0:11:16So, imagine this is our flooded flood plain
0:11:16 > 0:11:19with a river running through the middle of it.
0:11:19 > 0:11:21And, as you can see, there's quite a lot of sediment
0:11:21 > 0:11:23at the bottom of the river.
0:11:23 > 0:11:27What would happen if we dredged the river and removed the sediment?
0:11:28 > 0:11:33Well, if we do that, you can see that the water levels do drop a bit,
0:11:33 > 0:11:35but it doesn't solve the problem.
0:11:35 > 0:11:38And that's because the volume of water across the flood plain
0:11:38 > 0:11:42is so much greater than the volume we've made available
0:11:42 > 0:11:44by dredging the river.
0:11:44 > 0:11:47Dredging couldn't have prevented the floods,
0:11:47 > 0:11:50but increased capacity also means water can be moved more quickly.
0:11:50 > 0:11:53And while we have to be wary of pushing the problem downstream,
0:11:53 > 0:11:56research suggests dredging in Somerset could have
0:11:56 > 0:12:00reduced the duration of the floods by draining the Levels faster.
0:12:03 > 0:12:07But experts now believe that instead of focusing solely on rivers,
0:12:07 > 0:12:10we should be looking at the entire catchment.
0:12:12 > 0:12:15And here in Yorkshire is a scheme that's doing just that.
0:12:17 > 0:12:22This is the town of Pickering, on the southern edge of the North York Moors.
0:12:22 > 0:12:26And this river below me, running right through the centre of the town, is Pickering Beck.
0:12:28 > 0:12:31Pickering sits in a catchment that begins in the steep hills
0:12:31 > 0:12:32to the north of the town.
0:12:32 > 0:12:36When the area gets a lot of rain, the water runs off the land
0:12:36 > 0:12:39and into the rivers, which rush the water downstream.
0:12:40 > 0:12:43By the time the water arrives here,
0:12:43 > 0:12:45this river could already be at bursting point -
0:12:45 > 0:12:47and when it meets an obstacle like this bridge,
0:12:47 > 0:12:50it'll spill out, flooding the surrounding area.
0:12:51 > 0:12:55Pickering has flooded four times in the last 15 years,
0:12:55 > 0:12:58with the worst floods occurring in 2007.
0:12:58 > 0:13:02To protect the town in future, a new project has been launched
0:13:02 > 0:13:04using a combination of natural measures
0:13:04 > 0:13:08and targeted engineering to hold excess water upstream.
0:13:15 > 0:13:18What we're trying to do is bring that water back upstream
0:13:18 > 0:13:20and the more we can hold it back in the upper parts
0:13:20 > 0:13:23of the catchment, the smaller the flow hopefully will be
0:13:23 > 0:13:25when it comes to the towns and the cities.
0:13:25 > 0:13:28So, this is what we call a debris dam?
0:13:28 > 0:13:31Yes, we refer to it as a large woody debris dam.
0:13:31 > 0:13:33A porous dam. It's not sealed.
0:13:33 > 0:13:37So, the fact there are gaps in it is absolutely crucial?
0:13:37 > 0:13:39Very much so. We only want these to function
0:13:39 > 0:13:41under high flow conditions.
0:13:41 > 0:13:45It's when we get the heavy rainfall - that's when we want it to hold back that water.
0:13:45 > 0:13:48So you're talking about holding water back -
0:13:48 > 0:13:52is that in any way detrimental to the natural way the waterways flow?
0:13:52 > 0:13:55No, we're recognising that the way we've managed
0:13:55 > 0:13:59the land in the past has sped that flow of water off the land.
0:13:59 > 0:14:02We've lost a lot of our natural wooded river systems.
0:14:02 > 0:14:05These debris dams are a natural feature,
0:14:05 > 0:14:06so we're trying to recreate that.
0:14:06 > 0:14:09So, how much of the geology of this landscape
0:14:09 > 0:14:13do you need to understand in order to know where to put the dams,
0:14:13 > 0:14:15and that you're not causing more harm than good?
0:14:15 > 0:14:18I worked with Durham University in applying models to see
0:14:18 > 0:14:20what sort of difference this might make.
0:14:20 > 0:14:23That sufficiently encouraged us to then go ahead,
0:14:23 > 0:14:25with the understanding of the catchment, the hydrology
0:14:25 > 0:14:28and the geology, to determine where we put these.
0:14:28 > 0:14:30Although they only hold, individually,
0:14:30 > 0:14:32a small amount of water, if you total that up over
0:14:32 > 0:14:35hundreds of dams over the whole catchment, that's a lot of water.
0:14:36 > 0:14:40There are 180 debris dams like this in the area
0:14:40 > 0:14:42but that's just the beginning.
0:14:42 > 0:14:43As well as slowing the rivers,
0:14:43 > 0:14:47this scheme is also helping to hold water on the land.
0:14:53 > 0:14:56Tom, we are in the catchment now, aren't we?
0:14:56 > 0:14:59Yes, we're in the catchment of the Vale of Pickering.
0:14:59 > 0:15:02The river's down there in the background just in the corner.
0:15:02 > 0:15:05What are we looking at here, then? What are they planting?
0:15:05 > 0:15:08This is an example of one of the other measures we're trying,
0:15:08 > 0:15:11which is to plant woodland on farmland.
0:15:11 > 0:15:15Not just anywhere, but targeting soils that we believe have
0:15:15 > 0:15:17a high propensity to generate rapid run off.
0:15:17 > 0:15:20Trees will help because they store water
0:15:20 > 0:15:22and release it through transpiration,
0:15:22 > 0:15:25but they can also have a positive impact on the soil.
0:15:25 > 0:15:29On the left, this is land covered in forest.
0:15:29 > 0:15:32Imagine each tree has a long, complex system of roots
0:15:32 > 0:15:36and all of those roots are increasing the porosity of the soil.
0:15:36 > 0:15:38You're also going to have lots of organic material -
0:15:38 > 0:15:40dead, decaying plant material -
0:15:40 > 0:15:43that's going to also increase the porosity of the ground,
0:15:43 > 0:15:47and that means this soil is going to absorb a lot of water,
0:15:47 > 0:15:52hold it for longer and also direct it deeper, down as far as the bedrock.
0:15:52 > 0:15:56Now on the right, imagine this is farmed land
0:15:56 > 0:15:58and imagine you're grazing this land so you've got
0:15:58 > 0:16:00sheep constantly trampling on the ground here.
0:16:00 > 0:16:03creating a compact layer at the surface.
0:16:03 > 0:16:08That means that this soil is going to increase the risk of surface run off.
0:16:10 > 0:16:16If I pour my coloured liquid in one position in our porous soil,
0:16:16 > 0:16:19immediately you can see it permeating the soil
0:16:19 > 0:16:22all the way down to quite a good depth.
0:16:22 > 0:16:28Now, if I pour my coloured liquid on to the land
0:16:28 > 0:16:33that's been farmed so you've got this thick compact layer of soil,
0:16:33 > 0:16:37you can see immediately how much slower it travels
0:16:37 > 0:16:39through that compact layer.
0:16:39 > 0:16:43There is literally coloured water logging going on.
0:16:43 > 0:16:45You get all of this water
0:16:45 > 0:16:47having to go somewhere on the surface instead -
0:16:47 > 0:16:49and that's when you get problems.
0:16:54 > 0:16:57The final piece of the puzzle here at Pickering
0:16:57 > 0:16:59lies further downstream.
0:16:59 > 0:17:02Here, the Environment Agency are implementing a flood storage scheme
0:17:02 > 0:17:06which will temporarily divert flood waters at high flow,
0:17:06 > 0:17:09holding the excess back in these fields,
0:17:09 > 0:17:12and preventing it from flowing down the river to the town.
0:17:12 > 0:17:15The thing that impresses me most about this project
0:17:15 > 0:17:18is that it looks at the whole catchment and its unique geology
0:17:18 > 0:17:22and hydrology to come up with well-thought-out,
0:17:22 > 0:17:25long-term solutions that are centred around working
0:17:25 > 0:17:27with nature and not against it.
0:17:27 > 0:17:31And it's projected this is going to reduce the flooding risk
0:17:31 > 0:17:35in Pickering in any given year from 25% down to 4%.
0:17:35 > 0:17:39Now, it's not going to solve extreme events,
0:17:39 > 0:17:43but it is going to make a huge difference.
0:17:46 > 0:17:49This winter, the river levels in Pickering did rise,
0:17:49 > 0:17:51but the town didn't flood.
0:17:53 > 0:17:56But, sadly, it's not just rain we have to contend with
0:17:56 > 0:17:58when it comes to flooding.
0:17:58 > 0:18:02There's another deadly source of water that threatens our islands -
0:18:02 > 0:18:04storm surge.
0:18:04 > 0:18:08'Another defence overwhelmed as the forecasts remain bad.'
0:18:10 > 0:18:11On 31 January 1953,
0:18:11 > 0:18:16Britain learned just how devastating storm surge could be.
0:18:16 > 0:18:21The Great North Sea Flood inundated thousands of miles of coastline
0:18:21 > 0:18:24in Britain, the Netherlands and Belgium,
0:18:24 > 0:18:26claiming over 300 British lives.
0:18:26 > 0:18:28There were virtually no warnings.
0:18:28 > 0:18:31And many of those killed were drowned in their beds.
0:18:35 > 0:18:38But what is storm surge and why is it such a threat?
0:18:41 > 0:18:44A storm surge is a localised rise in sea level
0:18:44 > 0:18:46which happens during storms
0:18:46 > 0:18:51and one of the factors that causes this is low atmospheric pressure.
0:18:51 > 0:18:54The atmosphere is constantly exerting pressure on earth
0:18:54 > 0:18:58and here in the UK, we measure that pressure in millibars,
0:18:58 > 0:19:02so, on average, at sea level, it's around 1013mb.
0:19:02 > 0:19:08But that can vary depending on whether air is rising or falling.
0:19:08 > 0:19:10In a storm, warm air rises
0:19:10 > 0:19:14and, as it rises, it condenses and turns into clouds and rain.
0:19:14 > 0:19:18But as it rises, it creates an area underneath it of low pressure.
0:19:18 > 0:19:22That low pressure is exerting a weaker force on the sea below.
0:19:22 > 0:19:26And we can see what effect that might have on the sea
0:19:26 > 0:19:28by creating our own area of low pressure.
0:19:28 > 0:19:31So, the water level
0:19:31 > 0:19:33in this container and tube, at the moment,
0:19:33 > 0:19:35is absolutely the same and that's because
0:19:35 > 0:19:37the pressure on it is exactly the same.
0:19:37 > 0:19:41But if we change that by sucking some of the air
0:19:41 > 0:19:43out of the tube, you can see what happens.
0:19:45 > 0:19:51As the pressure on that water changes, so the water level rises.
0:19:51 > 0:19:55A one-millibar change in air pressure can lead to
0:19:55 > 0:19:57a 1cm change in sea level.
0:19:57 > 0:20:02So when air pressure dropped below 970 millibars in the North Sea last December,
0:20:02 > 0:20:08that alone created the potential for a rise of up to 40cm.
0:20:08 > 0:20:12In a storm, that rise in sea level, combined with strong winds,
0:20:12 > 0:20:14can cause a dangerous storm surge.
0:20:14 > 0:20:17And if that coincides with high tide,
0:20:17 > 0:20:20the storm surge is even bigger.
0:20:20 > 0:20:23It can become worse still when driven by north winds
0:20:23 > 0:20:27into the smaller, shallower parts of the North Sea.
0:20:27 > 0:20:32This caused the disaster of 1953 and threatened us again this winter.
0:20:32 > 0:20:35But this time, we were ready.
0:20:35 > 0:20:38The Thames Barrier was part of a range of flood defences
0:20:38 > 0:20:41built in response to what happened in '53.
0:20:41 > 0:20:45Its gates rotate to create a solid steel wall across the river,
0:20:45 > 0:20:49each holding back up to 9,000 tonnes of water.
0:20:49 > 0:20:52Just one of these central gates is the same width as Tower Bridge.
0:20:52 > 0:20:56Just talk us through what's been happening here over the past few months.
0:20:56 > 0:20:59I suppose the story really started on 6th December.
0:20:59 > 0:21:03We saw a surge coming down the east coast of about three metres.
0:21:03 > 0:21:06This is the highest level we'd actually seen for about 60 years
0:21:06 > 0:21:08and as far as the barrier's concerned,
0:21:08 > 0:21:11the largest tide in its 30 years' operational history.
0:21:11 > 0:21:15Normally, we'd be closing about three to four times per year,
0:21:15 > 0:21:20but we're up to about 50 closures so far in the last couple of months.
0:21:20 > 0:21:22How do you make the decision to close the barrier?
0:21:22 > 0:21:25We link in and work very closely with the Met Office, so we're able
0:21:25 > 0:21:29to plot what actually is happening down the North Sea coast.
0:21:29 > 0:21:32We also need to take account of rainfall
0:21:32 > 0:21:35because the Thames catchment - the Readings, the Oxfords -
0:21:35 > 0:21:38if it rains there, at some point, we're going to see that rainfall
0:21:38 > 0:21:41pass us here in Woolwich on its way out to the sea.
0:21:41 > 0:21:44We need to compute all of that in our computers here
0:21:44 > 0:21:47and literally, if we're seeing that by closing the barrier
0:21:47 > 0:21:52we can safeguard properties and people, than that is what we'll do.
0:21:52 > 0:21:55We don't play Russian roulette with that. You have to get it right.
0:21:55 > 0:21:59Without the barrier and its associated defences,
0:21:59 > 0:22:03around 125 square kilometres of central London could be at risk
0:22:03 > 0:22:06from flooding, an area that includes landmarks
0:22:06 > 0:22:08like the Houses of Parliament and the London Eye
0:22:08 > 0:22:12as well as 16 hospitals and 400 schools.
0:22:12 > 0:22:16It makes you realise how vulnerable the city really is.
0:22:17 > 0:22:19But the barrier also provides reassurance
0:22:19 > 0:22:22that with the right knowledge, the right planning
0:22:22 > 0:22:25and the right engineering, we can protect ourselves.
0:22:27 > 0:22:31But decisions about how we should direct our resources
0:22:31 > 0:22:35are being made harder by the uncertainty surrounding our future climate.
0:22:35 > 0:22:38What we do know is that our planet is warming,
0:22:38 > 0:22:41so I asked the Met Office Chief Scientist
0:22:41 > 0:22:43how this might affect flooding.
0:22:43 > 0:22:47There's a very simple link and it all goes back to basic physics -
0:22:47 > 0:22:51that the warmer the air, the more moisture it can hold.
0:22:51 > 0:22:53Then we take the weather systems that we've had
0:22:53 > 0:22:56and those storms are now carrying that air that's holding
0:22:56 > 0:22:58that little bit more moisture,
0:22:58 > 0:23:01and when the storms arrive they wring out that moisture.
0:23:01 > 0:23:05That means that the rainfall that we get from that system today
0:23:05 > 0:23:07will be that little bit heavier.
0:23:07 > 0:23:12So that's where we think climate change has made a real contribution
0:23:12 > 0:23:15to the severity of the flooding that we've seen this winter.
0:23:15 > 0:23:19What do you see as the biggest challenges that lie ahead for us?
0:23:19 > 0:23:24We do need to get to grips with how often we're going to see
0:23:24 > 0:23:28these sorts of events, because the investments that we
0:23:28 > 0:23:31as a country need to make to protect our citizens
0:23:31 > 0:23:34and our infrastructure is huge,
0:23:34 > 0:23:36and we need to make that wisely.
0:23:36 > 0:23:41More accurate data and better forecasting will be vital
0:23:41 > 0:23:43for dealing with floods in future.
0:23:43 > 0:23:47That's why I want to see how satellite technology can help.
0:23:47 > 0:23:51During the recent flooding, we were able to gather vital information
0:23:51 > 0:23:52from earth observation satellites,
0:23:52 > 0:23:56which were built here at Surrey Satellite Technology.
0:23:56 > 0:24:01One such satellite called upon in the recent floods was UKDMC2.
0:24:01 > 0:24:04So, UKDMC2 is how above the horizon. We're tracking this pass.
0:24:04 > 0:24:07It's a near overhead pass. You can see the red track.
0:24:07 > 0:24:09The red line is where it's going to pass over.
0:24:09 > 0:24:12And our ground station here down in Hampshire is now tracking the satellite.
0:24:12 > 0:24:16It's moved into position to track UKDMC2
0:24:16 > 0:24:18and it's receiving that information.
0:24:18 > 0:24:20That's right. You can see on this screen here, this is all
0:24:20 > 0:24:22- the information coming down. - Fantastic.
0:24:22 > 0:24:24We can see live telemetry.
0:24:24 > 0:24:27Files are being exchanged between the spacecraft and the ground.
0:24:27 > 0:24:30It's wonderful to see it in action in real-time.
0:24:30 > 0:24:33And how long will it spend over any one particular spot?
0:24:33 > 0:24:35When it's over the UK and we're getting data down,
0:24:35 > 0:24:38it can be over us for a maximum of about 12 minutes.
0:24:38 > 0:24:40You could be imaging for up to four to five minutes.
0:24:40 > 0:24:43So, James, with the recent floods, how do you go about telling
0:24:43 > 0:24:47the satellite to take images of the floods in question?
0:24:47 > 0:24:50The mission planning system will produce a schedule file.
0:24:50 > 0:24:52That tells the satellite where to take an image,
0:24:52 > 0:24:54so it'll go over its target, it'll capture the image.
0:24:54 > 0:24:58When it's back over our ground station, it'll download the image.
0:24:58 > 0:25:01Nearby at DMC International Imaging,
0:25:01 > 0:25:04a team of analysts are ready to process the images.
0:25:04 > 0:25:07What are these blue lines around the globe, then?
0:25:07 > 0:25:12Here, we've got the satellite passes for UKDMC2 in a 24-hour period.
0:25:12 > 0:25:15So what are these orange dots representing?
0:25:15 > 0:25:18These are the areas of interest to focus on for the flooding.
0:25:18 > 0:25:20Can we have a look at one of the images?
0:25:20 > 0:25:22Yeah, so here we've got the Oxford/Reading area.
0:25:22 > 0:25:27Over here, we have a before picture and here we show
0:25:27 > 0:25:31the image we got on 8th Feb, which shows the extent of the flooding.
0:25:31 > 0:25:32That's desperate.
0:25:32 > 0:25:37It really shows the extent of the flooding from these tributaries.
0:25:37 > 0:25:42Claire, how do we use these satellite images to understand flooding better?
0:25:42 > 0:25:44Here, we have the information products
0:25:44 > 0:25:46created by the Environment Agency.
0:25:46 > 0:25:50Here, they've got layers of satellite imagery, topography
0:25:50 > 0:25:53and the Ordnance Survey map, and on top of that,
0:25:53 > 0:25:56they have classified the flood from the satellite imagery.
0:25:56 > 0:25:58And what's this image?
0:25:58 > 0:26:00So this is also a DMCii satellite image.
0:26:00 > 0:26:04It's on a different scale, so you can see
0:26:04 > 0:26:07all of the Thames Valley, you can see the Somerset flooding.
0:26:07 > 0:26:09It provides the bigger picture here.
0:26:09 > 0:26:12It tells people how everything is actually linked up.
0:26:12 > 0:26:16When it comes to flood mitigation, how can this data help us?
0:26:16 > 0:26:18This will basically inform the decisions that are being made
0:26:18 > 0:26:21about how to deal with these floods at the moment,
0:26:21 > 0:26:23and all the risk areas can be identified.
0:26:23 > 0:26:27By looking at this alongside previous satellite images,
0:26:27 > 0:26:29you can see how things are changing over time
0:26:29 > 0:26:31and then you can use that picture
0:26:31 > 0:26:34to inform what may happen in the future.
0:26:36 > 0:26:40And it's not just satellite images that are filling the gaps in our knowledge.
0:26:40 > 0:26:44Satellites orbiting our planet at this very moment
0:26:44 > 0:26:47are gathering vital information about the earth's natural systems.
0:26:47 > 0:26:51Now this in NASA's Jason 2 satellite
0:26:51 > 0:26:54and it uses a radar altimeter to bounce microwave pulses
0:26:54 > 0:26:58off the surface of the earth, and by measuring how long it takes
0:26:58 > 0:27:02for the pulses to come back, it can measure differences in sea level.
0:27:02 > 0:27:06Satellites are also improving our knowledge of rainfall patterns.
0:27:06 > 0:27:11In February 2014, an international satellite mission called
0:27:11 > 0:27:14Global Precipitation Measurement was launched, and it can tell us
0:27:14 > 0:27:19how much rain and snow falls around the globe every three hours.
0:27:19 > 0:27:23This kind of data can be fed into models to help us monitor
0:27:23 > 0:27:27and predict climate change and it can also lead to more accurate forecasting
0:27:27 > 0:27:30of the conditions that lead to flooding.
0:27:34 > 0:27:38I think it's safe to say that we haven't seen the last of flooding.
0:27:38 > 0:27:41The storms will come again, the water will be back
0:27:41 > 0:27:45and the defences and our ingenuity will be put to the test.
0:27:46 > 0:27:49And what's clear is that there's no one solution.
0:27:49 > 0:27:52We need to combat flooding with a combination of tools
0:27:52 > 0:27:55from natural measures to engineering,
0:27:55 > 0:27:59and we need to widen our gaze to look at entire catchments.
0:27:59 > 0:28:01We also need to take responsibility
0:28:01 > 0:28:03for the changes we've made to the landscape.
0:28:03 > 0:28:07Some tough decisions with a long-term view lie ahead -
0:28:07 > 0:28:10but armed with an ever-growing understanding of the nature of floods,
0:28:10 > 0:28:14we can learn how to better prepare ourselves and mitigate their effects.
0:28:24 > 0:28:27Bang is back in two weeks' time, looking at the railways
0:28:27 > 0:28:29and how they'll cope as passenger numbers rise.
0:28:35 > 0:28:37In the meantime, if you want to find out more about satellites,
0:28:37 > 0:28:41check out the website at /bang for our careers guide.
0:28:41 > 0:28:43And to learn more about flooding, follow the links
0:28:43 > 0:28:45to the Open University.