river system - source to estuary
river has a ‘source’, a place where the river begins.
The sources of many rivers in Cornwall, for example the Fowey and
the Lynher, are to be found on Bodmin moor. Rain falling on high
ground drains off the moor to form small channels, and the beginnings
of these rivers.
Withybrook on Bodmin
As a river flows across the land
it grows in size, smaller channels and streams, known as tributaries,
join it. This increases the size of the river as rainwater from
a larger area is able to enter the river through these tributaries.
As the amount and speed of water
in a river increases so does the river’s ability to transport
materials. The more water it has the more energy it has to erode
and carry sediment, carry leaves and wood – branches and even
whole trees. Rivers can be very powerful, they move a lot of material
on their journey from source to sea.
River Lynher aftera
rainstorm, evidence of cattle erosion on the far bank
The type of terrain (land) over
which a river travels and its gradient (G1)
will make a difference to the appearance of the river. Rivers on
steep gradients will try and cut down into the terrain rather than
widen out over an area when the amount of water entering a river
increases. This is because it creates a faster pathway by cutting
down. When, however, there is a sudden increase in water through
heavy rain or a thunderstorm, the river will not have time to cut
down into the land and alter its shape to accommodate the extra
water. Instead the river will flood over nearby land, especially
in the lower part of the river where the land is usually much flatter.
Land either side of a river is called the floodplain because of
De Lank in flood
at Delphi Bridge
At different stages on its journey a river will offer a home to
different plants and animals, creating a variety of habitats from
source to sea. As the energy of a river increases the things it
can carry and its ability to create different features e.g. overhanging
banks (see Fisheries
F01 – point 6), gravel islands (F01
– point 7) is increased. The amount of places for plants
and animals to live is then increased, so the habitat has more variety
and different places suitable for different creatures.
Salt Marshes on
the Lynher estuary
When a river nears the sea it usually becomes much flatter, loses
energy and the heavier materials settle on the river bed. Where
it meets the sea it is called an estuary or the ‘mouth‘
of the river. At this point the river will drop its sediment for
a last time as it loses the rest of its energy when joining a bigger
mass of water. The freshwater of the river will then mix with the
saltwater of the sea.