The place where a river begins is called its source.
Rivers begin high in the mountains, where melting snow
gathers in small streams. The water winds its ways through
alpine meadows and begins its downward journey.
A river's long course goes
from high in the mountains
down to sea level.
About 90% of the downward
part is traveled in
the first 10% of its
route. The river
begins by rushing downward,
forming waterfalls and fast
rapids when stones block the
rush of water. Later
on, as more tributaries join
the river, the wide expanse
of water flows more smoothly
This picture shows a young river flowing in
its stony bed. You can see why people call this "white water".
The water twists this way and that around the rocks.
The young river flows swiftly, with many
rapids and waterfalls. It erodes its bed and cuts a narrow, V-shaped
valley with steep sides. Notice the very steep sides of this
valley and the powerful waterfall.
As the river flows, it is joined by other
steams, its tributaries. The river has a greater flow
of water now, and the river's bed is not so steep. The tributaries
are also eroding the sides of the valley. The valleys become
wider, and the walls of the valleys slope more gradually.
The valley floor becomes almost flat, and
the water can spread out when the snows melt. In the mountains
the streams form meadows where aspens and willows begin to grow.
Further down the river's course the valley becomes a flood plain.
When there is a lot of water catastrophic flooding can destroy
This lovely mountain meadow shows a stream
flowing in a very gently sloping bed.
In the last part of a river's journey,
it flows through a gently sloping flood plain. Because the plain
is nearly level, the river can wander across it in a winding,
snaking pattern. These loops and turns are called meanders.
A meandering river flowing through a floodplain is called a mature
This picture shows the beginning of a meander
pattern that this river formed when the green terraces in the
picture were the floor of the floodplain. It has started cutting
a V shaped valley again.
A mature river carries a heavy load of sediment.
When the flow of water slows, the sediment settles to the bottom.
Sand bars begin to appear.
The final stage in the life of a river is
its joining with the sea. By now the river is traveling smoothly
and carrying a lot of sand and clay. Merging with the sea slows
the water flow even more, and the sediment drops out. This often
leads to the formation of a delta, a broad, triangular river
mouth with many sand bars and water channels. The delta becomes
an estuary, an area with sheltered waters and a constant stream
of nutrients from the land.
The sand bars become islands
with grass and trees that
provide cover and nesting
sites for birds. Estuaries are important nurseries
for the young of aquatic animals.
They are highly productive
because they provide
nutrients washed down from
the land in an environment
that is sheltered, and
shallow enough to encourage
the growth of water plants.
Photographs from Corel CD-ROM
s: for viewing only, not for downloading.
Heading photograph from
NASA, Earth from Space.
1996,1997, 1998, 1999,
2000, 2002, 2003.
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