IGCSE River Processes

1. River Processes & Landforms
Chapter 5

2. River Processes
• Erosion removes material
from a river bed making it
deeper/wider
• These pebbles, sand, silt,
etc. get transported
downstream (river’s load)
• Deposition occurs after a
river no longer has enough
energy to carry the load
and drops it on the river
bed-boulders first, silt &
mud last

3. How a River Transports

4. WORKSHEET

5. Factors Affecting River Work
• Velocity/energy-the
faster the river the
larger the material able
to be transported
• After rain rivers may
look brown due to
suspension

6. Factors Affecting River Work
• Volume-the more water
the greater the volume
of the load
• Bedrock-harder rocks-
i.e. granite- erode
slowly, soft rocks-shale-
erode easily & some
rocks- i.e. limestone-
can be dissolved
completely

7. Deposition
• Occurs when rivers lose
velocity
– Decrease in the gradient
– Decrease in river flow as
water drains after a
heavy rain
– River meets the sea/lake
– River flows slower on
the inside of bends

8. The River Channel

9. Upper Course of a River
Source
• Where the river starts in a
highland or mountainous
area
• Vertical erosion can be
great in some areas and
create gorges, canyons,
potholes
• Potholes-smooth rounded
hollows formed by stones
trapped in the hollows of a
river bed

10. Upper Course of a River
Rapids
• Form where the water is
shallow and the river bed is
rocky & irregular making
the water rough
• Usually in steeper areas
• Can make river travel
difficult unless white water
rafting/kayaking

11. Upper Course of a River
Waterfalls & Gorges

12. Victoria Falls Zambia & Zimbabwe

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14. Waterfalls & Gorges
Positives
• Brings in tourists
• Hydroelectricity
Negatives
• Can cause navigation
problems, makes the river
difficult to cross

15. Upper Course
Interlocking Spurs
• Narrow valleys force the
river to create a winding
path

16. Middle and Lower Courses
• As the river valley
begins to widen and
become less steep
• Begin to see more
lateral (sideways)
erosion
• Vertical erosion may
stop completely by the
time we reach the
lower course

17. Meanders & Oxbows

18. Meanders & Oxbow Lakes

19. Floodplains & Levèes
• Flat land next to a river
liable to flood
• Occasionally the river
flows above the level of
the surrounding plain
but is enclosed by
raised embankments
called levèes

20. Floodplains & Levèes

22. Deltas
• Low-lying flat marshy
land where a river
meets a sea/lake
• Formed from a river
with carrying a lot of
sediments that meets a
still sea/lake and the
sediments build up
• May cause
distributaries

23. Mississippi Delta, USA

24. Mahakam River, Borneo

25. The Long Profile of a River
• A line drawn from the
source of the river to
the mouth showing
how the gradient
changes
• Typically steep in the
upper course and more
gentle and smooth in
the lower course
• Erosion & deposition
remove irregularities in
the profile making it
smooth and concave

26. Long Profile

27. ACTIVITY

28. Living in River Flood Plains & Deltas
• Often densely populated
• Offer flat land (easy to
build)
• Fertile soils
• River valleys are natural
route ways
• Navigable rivers allow
transport & trade
• Provide drinking water
and food source

29. Living in River Flood Plains & Deltas
• Tropics can suffer from diseases
carried by insects i.e. malaria
(mosquitoes) & sleeping
sickness (tsetse flies)

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32. Flooding
• Discharge-the volume of
water flowing down the
river at any one time
• When the discharge can no
longer be contained within
the channel & overflows to
the surrounding area it
floods
• Dense population can
make flooding severe
• When it rains, very little of
it actually falls into the
river, so where does the
water come from?

33. Flooding

34. Activity

35. Factors Affecting Discharge
• Rainfall
• Relief
– Rainwater runs over steep slopes
vs. infiltration on gentle
• Land Use
• Weather Conditions
– Hi-temps reduce discharge
• Rock & Soil Type
– Permeable vs. impermeable

37. Hydrographs
• Graph showing how a
river responds to a
storm
• Shows rainfall and
discharge

38. Flood Prevention
Planting Vegetation
• Planting vegetation (trees)
allows rainwater to be taken
in by roots & go out through
transpiration
• Acts like a sponge that
releases water slowly so
flood peaks are reduced

39. Flood Prevention
• Reservoirs can trap
water and release it
slowly

40. Flood Prevention
Straightening the Channel
• Shortens the river and gets the water away faster.

41. Kissimmee River, Florida USA

42. Flood Prevention
Artificial Levèes
• Increase the capacity of the channel
• Usually banks are strengthened with concrete or stone so less
likely to break

44. Flood Prevention
Dredging the Channel
• By making it deeper this
increases the capacity and
makes it less likely to
overflow

45. Flood Prevention
Bridge Design
• Bridges with wide pillars and
walls on top act like dams which
hold back water; modern bridges
are slim and prevent this from
happening

46. Flood Prevention
Wash Lands
• Control land on flood plains
areas for recreation instead of
residential to minimize
damage

47. CAUSE & EFFECTS

48. Textbook Pg. 132-137 #7