NAB Revision Hydrosphere

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NAB Revision Hydrosphere
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Today we are going to look at the four main parts
of the hydrosphere unit

• 1 Hydrological cycle
• ? components of the global hydrological cycle
• ? movement of water within drainage basins
  inputs, storage, outputs
• 2 Fluvial landforms and landscapes
• ? effects of flowing water in terms of erosion,
  transportation and deposition and the resultant
  landforms upper, middle and lower sections of
  river basins
• ? characteristic landscape features within a
  drainage basin explanation of formation of such
  features and identification of river features
  from OS maps

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Hydrological Cycle

• The diagram for this should now be engraved in
  your brains!

You should also be familiar with the earths
water balance.
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Flood Hydrographs

• It is more common for you to be asked to
  analyse a hydrograph rather than construct one in
  an exam.

Remember Storm Hydrographs show the change in
river discharge (the level of water flowing down
a river channel) caused by a period of rainfall.
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The discharge of the river is measured in cumecs
- this stands for cubic metres per second
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Rainfall shown in mm, as a bar graph
3
2
mm
Discharge (m3/s)
4
1
3
2
0 12 24 36 48 30 72
Hours from start of rain storm
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Discharge in m3/s, as a line graph
3
2
mm
Discharge (m3/s)
4
1
3
2
0 12 24 36 48 30 72
Hours from start of rain storm
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Rising limb
The normal (base) flow of the river starts to
rise when run-off, ground and soil water reaches
the river.
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Rising limb
2
mm
Discharge (m3/s)
4
1
3
2
0 12 24 36 48 30 72
Hours from start of rain storm
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Peak flow
Peak flow
Maximum discharge in the river, the time when the
river reaches its highest flow
3
Rising limb
2
mm
Discharge (m3/s)
4
1
3
2
0 12 24 36 48 30 72
Hours from start of rain storm
10
Recession limb
Peak flow
shows that water is still reaching the river but
in decreasing amounts
3
Rising limb
Recession limb
2
mm
Discharge (m3/s)
4
1
3
2
0 12 24 36 48 30 72
Hours from start of rain storm
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Basin lag time
Basin lag time
Peak flow
The time it takes for the water to find its way
to the river
3
Rising limb
Recession limb
2
mm
Discharge (m3/s)
4
1
3
2
0 12 24 36 48 30 72
Hours from start of rain storm
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Interpretation of Storm Hydrographs
Basin lag time
You need to refer to
Peak flow
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• Rising Limb

Rising limb
2
Recession limb
mm

• Recession Limb

Discharge (m3/s)
4
1
3

• Lag time

2

• Rainfall Intensity

0 12 24 36 48 30
72
Hours from start of rain storm

• Peak flow compared to Base flow

• Recovery rate, back to Base flow

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Task 1 Answer the hydrograph question from
2000.
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• Points could include
• Low steady discharge (approx 4 cummecs) until
  first fall of rain which shows up as a gradual
  increase in discharge levels some 4 hours later.
• Continued heavier rainfall contributes to a
  steeping of the (rising limb) hydrograph which
  reaches a peak of 75 cummecs.
• The river continues to flow at a high level for
  several hours before falling steeply (falling
  limb).
• A later period of (reduced) rainfall during the
  evening-night of the 18th December explains the
  secondary peak in discharge (40 cummecs) in the
  early hours of the 19th December.
• It stopped raining around midnight on the
  18th/19th. This is reflecting in the gradual
  lowering of water levels which eventually even
  off and almost return to the level they were at
  before the rain started.
• Explanation might include reference to basin lag
  the time taken for the rain water to infiltrate
  the soil and reach the river.

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Effects of flowing water and the resultant
landforms
Within the river basin, water erosion,
transportation and deposition create the
distinctive valley and channel characteristics.

• Main erosion processes
• Hydraulic. The sheer force of the water causes an
  increase in pressure, resulting in material being
  dragged from the beds and the banks for the
  river.
• Corrasion. The sandpaper effect where sediment
  scours and wears away the river bed and river
  banks.
• Corrosion/solution. Where rocks lining the river
  bed and banks slowly get dissolved in the weak
  acidic waters.
• Attrition. The weathering away of rock fragments
  already in the river as they collide with each
  other.

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• Main transportation processes
• The dissolved load of the river can be carried in
  solution.
• Fine-grained, light-weight material can be
  carried in suspension.
• Debris can be bounced (saltation) along the river
  bed, pushed, or rolled (traction).

Main deposition processes. Transported load is
dumped when

• Rivers reach their base level, the sea/ a loch.
• The river overflows onto a floodplain.
• At low energy points such as the inside of a
  meander.
• A general drop in the level of a river, e.g. a
  drought.
• Where there is decrease in gradient, e.g. below a
  waterfall.

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You should be able to explain the characteristics
(i.e. sediment type, gradient, speed) of each the
upper, middle and lower courses of a river. The
hydrosphere q. in the 1996 paper asked just that.
You are also expected to be able to describe and
explain the formation of various river features.
These features can come from the upper, middle
and lower course of a river.
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Upper Course Features
Waterfalls are the most commonly tested upper
course feature and are relatively easy to explain.
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Middle Course Features
Meanders are the most commonly tested lower
course feature but often poorly answered.
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Lower Course Features
Ox-bow lakes are the most commonly tested middle
course features.
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Task 2 Create a model answer for the formation
of a waterfall.
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Last but not least- you may be given a map and
simply asked to describe the course of a river on
that map.These are the things you should be
looking to include in your answer
- The direction the river is flowing in,- The
shape of the valley the river flows through,-
Features such as meanders, tributaries,-
Drainage, - Does the river widen, get narrower
at any point?