STUDYING RIVER VALLEYS

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STUDYING RIVER VALLEYS

• We will look at-
• General characteristics of rivers.
• Upper stages- waterfalls.
• Middle stages- meanders and oxbow lakes.
• Lower stages levees and deltas
• Rejuvenation

At Standard Grade, you learned about the three
stages of a typical river, and about the
characteristics of each stage. We will be
re-visiting this material and adding more depth-
excuse the pun- to our studies of rivers.
These slide-shows are all on the Prepwork folder
if you wish to copy any notes from them we will
not be stopping in class for you to do this
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GENERAL CHARACTERISTICS
A river LONG PROFILE is a sideways look at a
river valley from source to mouth. It can also
be called a LONG SECTION. In an ideal river, it
looks like this-
Notice the three stages we studied in S4.
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The key to understanding how a river creates its
landforms is to look at the energy
needed to move the material around
it. Large sized material needs high
energy. Large amounts of material needs high
energy. Tiny particles need only low amounts of
energy. Small amounts of material need little
energy.
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Where does the energy come from?

• The volume of water, which varies with
  precipitation.
• The speed of the flow, which varies with gradient
  of the river bed.

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As the diagram on the handout shows, energy
values determine whether the river erodes,
transports or deposits a particle. (Note the
scale isnt the more familiar cumecs- cubic
metres per second- but a more sensitive mms per
second! ) This means that you can predict for
any river in any conditions how the river will
deal with material at a given speed- discharge.
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So it is obvious that erosion is greatest in the
upper stage and deposition in the lower stage.
EROSION
DEPOSITION
SOURCE
MOUTH
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TRANSPORT TYPES
Make a copy of the diagram at the foot of page
262 of Wider World.
This shows the four main methods that a river
uses to move material of different sizes.
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UPPER STAGES- WATERFALLS
3. Why does the rock layer collapse?
Study factzone 10 about this in the
booklet. Answer the questions.
4. What two-word landform is created by these
processes?
1. Describe simply the rock-type layout of a
typical waterfall.
5. Name and locate two examples of this feature.
2. Describe where and how the plunge pool is
created.
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ANSWERS
1.A layer of hard rock lies over softer rock.
3. The rock layer collapses as a result of the
weight of the hard rock and gravity.
2.The plunge pool is created by water eroding
vertically and laterally below the hard rock.
4.This creates a river gorge.
5.Thornton Force on the River Twiss, Ingleton.
High Force on the River Tees.(examples only! )
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High Force on the Tees
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Note this is a river gorge !
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MIDDLE STAGES- MEANDERS
These are found initially in the middle stage,
although they get well developed in the lower
stage too. There are a few new terms about
meanders for you to learn, beyond the Standard
Grade ones.
Read section 11 in the booklet and use the
diagram on page 19 to help define-
SINUOSITY
WAVELENGTH
POINTS OF INFLEXION
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The first stages in the formation of meanders is
believed to be the development of riffles and
pools.
These are zones of alternating deposition and
erosion that cause the channel of the river to
alter course, thus creating the meander.
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Meanders should be familiar to you from Standard
Grade, and their features are shown as a reminder
on the handout diagram. Use Wider World page 284
to label and colour your handout, and stick it
into your jotter.
Can you identify each feature lettered ?
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Remember that meanders are a developing feature,
changing with time and moving both across the
flood plain and down-stream! Remind yourself how
they do this- what are the PROCESSES?
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The photograph here and the diagram on the next
slide shows the processes going on below the
water.
Notice how the inner bank is being built up into
a point bar deposit /river beach/ slip-off slope,
and the outer bank is being eroded into a river
cliff.
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The finale of the process is for an ox-bow lake
to form.
Read the notes in the booklet page 22 and look at
the diagrams here.
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An ox-bow lake on the Endrick valley floodplain.
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The meanders and ox-bow lakes of the Mississippi
River from the air.
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The movement of the meanders create the wide
floodplain and bluffs of the mature lower stage
of the river.
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LOWER STAGE
Here the gradient is low and energy levels are
also low. As a result..
there is much deposition and high sinuosity
the flood plain is wide.
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LEVEES
Levees are either natural or man-made raised
banks.
Read about them in the booklet, page 23. You
need to be able to explain them as well as this
in an answer!
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Read also the sections about BRAIDING and DELTAS.
Answer the following questions firstly about
BRAIDING.
1.Why are there sometimes greater than usual
amounts of load in the channel?
2. What causes this load to be deposited?
3. Explain why these mounds of material are
unstable?
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ANSWERS
1. Increased discharge in the river will bring
down more (and larger) load from upstream.
2. If the discharge drops quickly, reducing the
volume in the channel, the material will be
dropped in the bed.
Sometimes debris remains long enough to be
colonised with vegetation which stabilises it
more!
3. The material is poorly consolidated and is
likely to be re-eroded with further increased
discharge.
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Answer these DELTA questions-
1.Why does a delta not form if there are tides or
currents?
2. Why are the beds/ sets graded by size?
3. Why do distributaries form?
4. Name a big river in Europe that has a delta.
Say where it is.
flow
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ANSWERS
1. Currents would wash away the deposits before
they could gather.
2. As the material reaches the still water, the
river flow almost stops. The heavier material
drops and rolls down the slope offshore, and the
medium particles fall on top of them. The
lightest particles are carried further out to sea
and deposited, to be covered much later by more
heavy deposits.
3. Distributaries form as the water has trouble
flowing over the deposited material.
4.The Rhine delta is in Netherlands at Rotterdam,
and the Rhone delta is in France, beside
Marseilles.
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Summary-handouts
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REJUVENATION
This is the name given to when a river gets a new
rush of energy. This is due to ISOSTATIC UPLIFT-
remember what that is?
This is when the land rises up after the weight
of the glaciers has been removed. It is seldom
even across the land.
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As the land rises, there is now more falling for
the river to do to get to sea- level. It starts
to flow faster with the renewed energy, and
vertical erosion starts to increase. The results
are the channel of the river eats downwards into
the floodplain and creates river terraces and
incised/ entrenched meanders.
Now watch video 86 number 3, second half
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THIS IS THE END OF THIS TOPIC.
YOU NOW ONLY NEED TO LEARN THIS TOPIC FOR THE
EXAM AND THE NAB!