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Croeso, welcome.
We're in Wales to look at flooding and river management on some of the country's most iconic rivers; the River Severn, River Rheidol and River Ystwyth.
Across the world, over a billion people live on river floodplains, that's over 16% of the world's population.
Most of the food we eat is grown or reared on these areas of flat, fertile land, alongside the middle and lower course of rivers.
Floodplains are also home to much of the world's manufacturing industries, meaning that flooding in one place can often have a global knock-on effect.
Floodplains are formed of river sediments being deposited during flood events.
Flooding on these areas is just as likely to happen today, as it was in the past.
In fact, in many parts of the world, floods are becoming more severe and happening more often, as climate change results in an increasing number of large storms.
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Because so much human activity takes place on river floodplains, this often means that flooding, erosion and deposition have to be carefully managed; in order to protect property, lives and infrastructure.
We're going to look at how river management was done in the past, the strengths and weaknesses of those approaches, and how river management is done today.
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Traditionally, hard engineering approaches were used to manage rivers.
Now, rivers flood when the amount of water flowing down the river, exceeds the capacity of the river channel, causing the river to overtop its banks.
On the River Severn, in mid-Wales, this happened in 1960 and again in 1964.
This caused significant flooding, here at Newtown, downstream at Welshpool and on the surrounding agricultural land, causing significant damage to property.
Following these events, several hard engineering techniques were put in place to try and prevent flooding in the future.
One way to prevent flooding is to control river discharge, or the amount of water flowing down the river every second.
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This is the Clywedog Dam on the River Clywedog, one of the tributaries of the River Severn.
The dam here is used to hold back water, following heavy rainfall, and this water can then be gradually released down the river channel, without flooding urban areas downstream, like Newtown.
During drought conditions the dam can also be used to maintain a steady flow of water down the river, which helps maintain river ecosystems.
Clywedog Dam is also used to generate hydroelectric power and provides a leisure facility for activities like fishing and sailing.
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Another way to try and prevent flooding is to increase the capacity of the river channel, so that it can hold more water during floods.
Downstream of the Clywedog Dam, back here at Newtown, this has been achieved in two ways.
The alluvial sediment, the gravels and the sand that the river transports, was dredged from the river and taken away, so that the river channel was deeper.
As a result of the dredging here, the cover of alluvial sediment, of gravel on the bed of the river, is actually quite thin, and in places you can actually see some of the underlying bedrock come to the surface.
Engineers have also built embankments, or artificial levees, along the banks of the river.
So the river channel is deeper, the river banks are higher, and this means that the river can carry more water before it begins to flood.
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Another hard engineering approach to preventing flooding is to help the water move downstream as quickly as possible and get the water away from urban areas like this.
This can be achieved by realigning, or straightening the river channel.
Either by removing gravel bars from the river channel, so that the water doesn't have to flow around them.
Or by mimicking the natural processes of river meander cut-off, by digging a channel between two meander bends.
This creates a shorter and a steeper river channel, that helps get the water out of the urban areas as quickly as possible.
Once again, this was done here at Newtown.
So the River Severn used to flow behind me here, round the back of this car-park, but during the channelisation works, it was moved about 200 metres to its present location.
And this means that the water can flow a bit more quickly through the slightly straighter reach and the water moves through a bit faster.
Removing other types of roughness from along the river channel, can also help with this.
Like getting rid of some of the riparian vegetation, so for example, some of the trees that grow along the riverbank.
Or by getting rid of the deep pools and shallow riffles that you would normally expect to see on the bed of a natural river, creating a smooth, graded riverbed profile.
All of these measures help the water flow more quickly through these sections and away from vulnerable areas.
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Erosion and flooding along riverbanks is also prevented by reinforcing the banks, using different hard engineering structures.
So this riprap is made up of large boulders, and it's resistant from erosion from the water.
It's been placed here to protect and strengthen the riverbanks.
Other hard engineering structures, such as block revetments and gabion baskets are also used in the same way, to prevent erosion and strengthen riverbanks.
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This concrete mattressing beneath my feet, has been engineered here, to strengthen and protect the riverbed.
So you can see behind me, that this mattressing extends up onto the side of the river, so it's not only protecting the bed of the river, but also its banks.
Groynes are also used along riverbanks, to divert water away from the banks and to encourage deposition.
Traditionally, hard engineering approaches are used in combination to fix the river channel in place and to prevent future flooding.
These different hard engineering approaches can be very effective in preventing river flooding and erosion.
However, they can be very expensive.
Based on recent Environment Agency reports, dredging a river channel can cost anywhere from £5 to £75 per cubic metre of sediment removed.
This can add up to over £50,000, just to dredge one kilometre of a river channel.
Artificial levees and embankments, generally cost thousands of pounds to build just one metre.
Gabions are reported to cost £1,216 per metre, and hard reinforcements of river beds and banks, is reported to cost £1,075 per metre.
All these structures have ongoing costs, as they require regular maintenance and repairs.
Towards the end of the 20th century, the negative impacts of these techniques began to be recognised too.
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