Rivers are places to enjoy, where you can relax and appreciate the beauty of the natural world.
But rivers are also vital for mankind and always have been.
In Britain today we don't drink straight from rivers, but rivers still provide the majority of our water supply.
This is river water entering a massive treatment plant, where it's filtered and purified before being piped to our homes.
As well as water to drink, we need food to eat and rivers are a vital source of water used to irrigate crops.
Present industries were founded on rivers.
The electricity from this station powers industries once driven by water mills.
River water used in these giant cooling towers is a key element of the electricity generating process.
River water not only cools the plant but also offers transport for the fuel.
In this case, millions of tonnes of coal are shipped to the site every year by river barge.
No coal trucks clog up roads here!
To get away from the pressures of life, rivers offer the perfect answer.
Whether we use them for recreation, drink from them, use them for agriculture or transport,
they are a defining and positive feature of Britain.
But to ensure that future generations can benefit from them fully, they have to be managed properly.
To do that, we first need to understand how rivers work.
Rivers of many sizes occur in the UK and the volume of water carried, even in the smallest is astonishing.
This relatively small river transports a road tankers load of water every second.
In times of flood, that can become as much as five tankers every second.
Rain seems the obvious reason why rivers continue to flow day in day out,
but days or even weeks can go by without any rainfall.
So why do rivers flow during these times?
The answer lies back upstream.
The land that a river drains is called the catchment and a river of this size
could collect the rain that falls on an area of several hundred square kilometres.
The amount of rain that falls in Britain varies greatly from place to place.
From only half a meter a year in areas of Southeast England,
to as much as four meters a year in parts of Scotland.
The amount also varies throughout the year.
The fate of each drop of rain depends on where and when it lands.
Some of the rain evaporates back into the atmosphere from the surface of plants.
Water hitting the ground can also evaporate, as well as soak into the soil.
Once in the soil it can be used by plants before being passed back into the atmosphere.
Large plants, like fully grown oak trees can use as much as 400 litres a day.
Some of the rainfall will also move off downhill - this is known as runoff.
The amount of rainfall that becomes runoff depends on how much rain there is and when during the year it falls.
It also depends on the type of land on which it falls.
Plowing for example will reduce runoff by holding up the water, allowing it to soak into the ground.
Runoff will be greater on bare soil and greater still where land is built on.
In upland areas, where slopes are steeper and the soils are often thin,
a lot of the rain runs off straight into rivers and so these rivers rise and fall rapidly with every rainstorm.
When the amount of rain falling is more than the river can carry away, the inevitable happens.
Runoff is one way for water to reach the river, but if this was the only way, then rivers would dry up when the rain stopped.
This doesn't happen, so there must be some other source of water.
To understand, we need to follow the path of raindrops which reach the ground surface and pass into the soil.
If enough rain is falling, water will pass through the soil and reach the rock beneath.
We are used to the idea that soil absorbs water.
But what about rocks?
What happens when water hits rock depends on the nature of the rock.
If it's made up of grains like this sandstone, with spaces in between which are connected,
then water will pass through and the rock is said to be permeable.
It's not just sand stones that are permeable.
Chalk made up of the remains of countless tiny shells is also permeable, mainly because there are cracks in the rock
and water can move through even the tiniest crack.
The percentage of the rock that's made up of spaces is known as the rocks porosity.
The porosity of sandstone can be 20% or more,
which means that a cubic meter of rock, say the size of a large fridge can absorb 200 or more liters of water.
Water that has passed through the soil will continue to move down through the underlying rock, until it reaches a level where all the pore spaces are full.
This level is called the water table.
Water moving in the rock below the water table is called groundwater.
Layers of rock that are permeable and allow a significant amount of water to flow through them are called aquifers.
These are the principal aquifers of the UK.
Chalk and particular sandstones make up the two most important aquifers.
About one third of Britain's public water supplies come from aquifers, but in some regions of the country it's as much as three-quarters.
We've seen how some of the rain that falls on the land makes its way to the water table.
In a normal year, most of that water will do so as a result of the rains in winter.
Because of the time it takes for the water to reach the water table, any rise won't be seen until later in the winter or even early spring.
The water table tends to be at its highest in spring, falling to its lowest level in the summer or early autumn
The shape of the water table follows that of the ground surface.
Groundwater flows from areas where the water table is high, to areas where it's low.
When the water table meets the ground surface, water leaves the rock either as a spring or by seeping directly into rivers.
The time the groundwater takes to travel to the river will depend on how permeable the rock is
and on whether it follows a shallow or a deep path.
Either way it can be in the ground for a long time - from months up to centuries in some cases.
So now we see how groundwater helps to keep our rivers flowing.
This is particularly true in areas underlain by aquifers, which feed many of the country's river systems.
The birthplace of a river will be high up in its catchment.
Most rivers start as a small boggy seep like this.
Others start at springs.
These magical places occur where the rocks bring the groundwater to the surface.
Here water is clearly seen to emerge from the ground.
Part of the magic of springs is the purity of the groundwater they provide, after its long voyage through the rock.
This stream in the South of England is typical of those kept flowing for much of the year by groundwater.
The water is clear with little sediment as the rock has acted as a natural filter.
This clear, clean water nurtures a wide range of plant, insect and animal life, that's unique to this type of stream.
Streams like this flow energetically in winter and spring, but in summer the flow is often low
and particularly during long dry periods the upper reaches may even dry up altogether.
There are often misconceptions as to why this happens.
In this village there's been a well for centuries just a few metres away from the banks of the stream ensuring that the villagers had water all year round.
That's a sign that in the past the stream occasionally dried up and is evidence that this is a natural process and not just a present-day problem.
The reason the stream dries up is because the water table that feeds it with groundwater falls below the bed of the river during the summer.
As it drops, the point at which it cuts the ground surface moves down the valley.
Where slopes are gentle that might be kilometers away from the source of the stream.
Many people are puzzled why in summertime the streams don't simply reappear after rain showers
and become suspicious when the water companies talk of the wrong type of rain.
What do they mean?
We have the wrong type of rain when none of it reaches the water table.
Most of the water that reaches the water table does so as a result of the rains in autumn and winter.
When rain falls during the summer months it is much less likely to reach the water table.
The higher temperatures mean that more of the rain will be evaporated.
The soil will be dry so it will soak up more of the rainfall and as plants need more water as they are growing fast they will use up much of the remaining rain water.
So falling water tables and as a result declining river flows summer are part of a natural process that normally takes place each year.
However, man's exploitation of groundwater may also have an effect on river flow.
This is a modern borehole pumping high-quality water from the aquifer tens of meters below supplying over 20,000 local people.
It's not surprising that if millions of litres of water are being extracted daily from this borehole,
that the pumping will have an effect on the water table.
The greatest drawdown in the water table occurs around the borehole, but the effects may be seen kilometers away.
It's possible that the fall in the water table can reduce the amount of groundwater that feeds into nearby rivers and streams,
so reducing their flow.
However it's often difficult to say how much the reduced flows that occur at times in some rivers are due to pumping
and how much they are due to natural changes in the water table.
Where it is recognized that groundwater pumping is having a bad effect on particularly important stretches of river,
water companies are working together with the Environment regulators to find ways of improving the flow.
What are the problems linked to low flowing rivers?
Low flows could affect navigation for private and commercial boats.
Or just spoil the enjoyment of simply walking along the riverbank.
Low flows can also reduce a rivers capacity to dilute the effluent from sewage treatment plants that discharge into it,
and of course they can affect plants, fish, insects and animals that live in the river or on its banks.
Low flows in rivers are a major problem but rivers are also threatened by straightening and canalization
by urbanization and by industrialization.
Agriculture can also have an effect;
for example by increasing the sediment that gets into rivers as a result of growing crops too close to rivers
or by allowing cattle to damage riverbeds and by modern land drains that carry rain straight to the river
before it can soak into the soil and reach the water table.
These are only a few examples but they highlight the challenges that we face to meet the ever-increasing demands of society
while keeping the impacts on the environment to an acceptable level.
This is particularly important, given the impact that climate change is likely to have on the country's water resources.
Because of all these threats, we need to appreciate the processes that allow rivers to flow.
How rain that reaches the land finds its way into the rocks and moves through them to emerge,
often after a very long time through springs or the beds of rivers.
How this water sustains the flows of rivers in summer months,
and how man's actions and that of nature control the volumes of groundwater that reach rivers
and as a result the variation in river flows.
We can see that to protect rivers, we need to manage not only the river itself and its banks
but what we do in the whole of the rivers catchment actions that affect the quantity and quality
of water that reaches our rivers both as run off and as ground water.
Rivers will continue to play a vital role in the environment and for all of society.
Understanding how they work, and the role of groundwater is the first step to appreciating and protecting them.