rivers

1. RiversIGCSE
M Ralph

2. Topic Outline
• Explain the main hydrological characteristics and processes which
operate within rivers and drainage basins
• Demonstrate an understanding of the work of a river in eroding,
transporting and depositing
• Describe and explain the formation of the land forms associated
with these processes.
• Demonstrate and understanding that rivers present hazards and
offer opportunities for people.
• Explain what can be done to manage the impacts of river flooding
• Know a case study of the opportunities presented by a river, the
hazards associated with it and their management.

3. STARTER
Are there any rivers
in the UAE? explain
your answer!

4. Learning Objectives
•All – identify the different
features of a river
•Most – can discuss the
journey of a river from source
to mouth
•Some – can define what each
key feature is.

6. Common River Terms
•Source – The place where a river begins.
•Course – The route the river takes to the sea
•Tributary – A small river that joins a larger
river.
•Confluence – The point where the tributary
joins the river.

7. Common River Terms
•Mouth – The point where the river enters the
sea.
•Estuary – The part of the mouth that is tidal.
•Basin – The area of land drained by a river.
•Watershed – The high ground separating one
river basin from another.

8. The River’s Journey
• Rivers usually begin in the mountains.
• They flow downhill onto flat land and into the sea.

9. The Stages of a River’s Journey
As the river flows from it’s
source to the sea it goes
through 3 stages. These
are:
1. The Upper or Youthful
Stage
2. The Middle or Mature
Stage
3. The Lower or Old Stage

10. 4 Processes of River Erosion
•Hydraulic Action – The force of the moving
water wears away the banks and bed of
the river.
•Abrasion – Small stones carried by the river
wear away at the banks and bed of the
river.

11. 4 Processes of River Erosion
•Attrition – The small stones in the river are
worn down and broken up as they hit off
each other.
•Solution – Rocks and soil are dissolved by
acids in the water.

12. The Youthful River
•The youthful river has a small amount of water
but it travels very quickly down the steep
mountain slope.
•Most of its energy is used to erode (wear away)
the landscape.
•This erosion (wearing away) occurs in 4 ways.

13. Landforms of the Youthful Stage
• All of the erosion by the river creates features or
landforms on the landscape.
Three features created in the youthful stage are,
1. V-shaped Valleys
2. Interlocking Spurs
3. Waterfalls

14. V-Shaped Valleys
• V-shaped valleys get their name from their shape.
The river erodes the landscape and creates a valley
in the shape of a V.
• This occurs because of Vertical Erosion. The river cuts
down into the river bed, making it deeper. It creates
a narrow deep valley. Mechanical weathering and
mass movement create the V shape. See Diagram.

15. V-Shaped Valleys

16. Interlocking Spurs
•As the rivers flows it
meets areas of hard
rock. It cannot erode
these so it flows
around them.
•This creates a zigzag
course.

17. Waterfalls
• Waterfalls are formed when
rivers flow over areas of hard and
soft rock.
• The river erodes the soft rock but
cannot erode the hard rock. This
creates a step which the water
starts to fall over.
• The falling water erodes deeper
into the bed. The rivers load
creates a Plunge Pool as it falls.
See Diagram.

18. Video clip
• https://www.youtube.com/
watch?v=fOI7aKvrFn4
Write down 5 facts
you learned from the
video clip!

19. Starter
List the 4 types of
river erosion
…write it down!

20. Learning Objectives
•All – can identify features
at the middle course of the
river
•Most – Can explain how the
river transports its load
•Some – can describe what
the rivers load consists of.

21. The Mature Stage
• We now know that during the youthful stage the
river is mainly eroding the landscape.
• Erosion breaks off particles of rock and soil from the
bed and banks of the river. They are carried along by
the river and are known as the Load.
• The load is carried from upland to lowland areas.
This process is called River Transportation.

22. River Transportation
• All rivers carry material in them. This material is carried by
• the river as it flows along.
• Rivers can carry large stones, small stones, sand, and
• other dissolved minerals.
• All of this material in the river is called the river’s Load
• When the river moves its load we call this River
Transportation

23. River Transportation
•Transportation occurs in 4 ways.
•1. Rolling
•2. Bouncing
•3. Suspension
•4. Solution

24. Rolling
The large stones are rolled along
the bed of the river.
Rolling

25. Bouncing
The smaller pebbles are bounced
along the bed of the river.
Bouncing

26. Suspension
Light material like sand and silt are
carried along (floating) in the water.

27. Solution
Dissolved materials are carried along by the river.
Solution

28. Starter
What is a Wadi?
Where is the closest
one to the school?
…Write it down!

29. Learning Objectives
•All – can identify all features at
the mature and old stage of
the river
•Most – can explain with the aid
of a diagram how meanders
form
•Some – can discuss how ox-
bow lakes, levees and deltas
form.

30. Landforms of the Mature Stage
In the Mature Stage the river begins to slow down,
and so it begins to deposit some of its load. It
creates the following features.
1. Wide river valley
2. Meanders
3. Flood plain

31. Wider River Valley
• In the mature stage the river
moves from side to side and
the valley becomes wide and
flat.
• Weathering and Mass
Movement continue to wear
away at the sides of the valley.

32. Meanders
Meanders are bends or
curves along the river.
They are formed by
erosion and deposition.
Erosion occurs on one
side of the river while
deposition occurs on
the opposite side. This
continues, making the
bends sharper. See
diagrams.

34. Flood Plain
A flood plain is the flat area of
land on either side of the river.
After heavy rain the river
sometimes floods. The water
spreads out over the land on
either side of the river. When
the river retreats it leaves
behind a thin layer of
alluvium. After many floods a
thick layer of alluvium is
created. This is very fertile soil.

35. The Old Stage
• In the Old Stage the river is
carrying lots of sand and silt. It
is now flowing over flat land
and so it is moving slowly.
Therefore it begins to drop off
its load. This is called
deposition. Like erosion in the
Youthful Stage, deposition also
creates many features or
landforms.

36. Landforms of the Old Stage
The following features or landforms are
created by river deposition in the Old Stage.
1. Ox-Bow Lakes
2. Levees
3. Delta

37. Ox-Bow Lakes
An ox-bow lake is a horseshoe
shaped lake found beside a
river. Ox-bow lakes are formed
when continued erosion and
deposition create very
pronounced meanders.
Eventually the river cuts through
the neck of the meander.
Deposition then occurs which
leaves the ox-bow lake
separated from the river.

38. How an Ox-Bow Lake is Made

39. Levees
Levees are raised banks of deposited
material found along the banks of
the river. When the river floods and
spreads out over the floodplain, the
heaviest material is deposited close
to the river.
Over time and after many periods of
flooding this deposited material
forms levees along the banks of the
river.

40. Delta• A Delta is a triangular shaped piece of
land which is formed at the mouth of the
river.
• As the river enters the sea it drops off all
the
• remaining material it is carrying.
• This material builds up to form new land.
• The river is forced to break up into smaller
channels called distributaries.

41. StarterLast year we
experienced some
flooding at school
what was the main
cause of it?
... Write it down

42. Learning Objectives
•All – identify the main causes
of flooding
•Most - can explain the
impacts of flooding in an area
•Some – can describe how the
flood was responded to
•Extension – what are the long
and short term effects?

43. Causes of Flooding• Heavy Rainfall
• Loss of Trees
• Tributaries
• Flat Land
• Impermeable Rock
• Steep Slopes
• Soggy Soil
• Built Up Areas
• Snow Melt
What is a flash flood?

44. Boscastle Flood MEDC
Background
• Boscastle is situated on the
northwest coast of Cornwall,
near Bude
• It is situated at the confluence
of the River Valency and its
tributaries
• It happened on Monday 16th
August 2004

46. What were the Causes?
• The day had been very warm, drawing
in sea breezes along the coast. When
they joined forces with a wet
southerly air flow they shot upwards
with a dangerous mix of warm, moist,
highly unstable air.
• The thunderclouds grew so tall that
they created intense rain leading to
more than 5 inches falling around
Boscastle in just a few hours.
• With the ground already saturated
from recent rains, the storm waters
were funneled down steep river
valleys and burst

47. Video clip
• http://www.bbc.co.uk/lear
ningzone/clips/why-did-
boscastle-flood/14072.html
Write down 5 facts
you learned from the
video clip!

48. Reasons For Flooding in Boscastle
• Heavy rainfall - is less likely to infiltrate into the soil and will reach the river
quickly. This will result in a rapid increase in river discharge.
• Relief of the surrounding area - Boscastle is in a valley, flanked on either side
by high ground. The slopes of the valley are very steep and the river
becomes narrower in the approach to the mouth.
• Impermeable ground - The underlying strata are mostly shales and slate,
with some sandstone beds which break down in weathering to give clay-rich
soils.
• Confluence of two rivers - Boscastle stands where two valleys meet, formed
by the rivers Valency and Jordan. A third river, Paradise, also flows through
the village.
• Bridge - This constricted the flow of the water through the village, forcing
the river to burst its banks.

49. What were the effects?
• 90% of Boscastle’s economy is dependent on tourism.
• After the flood, more than 20 accommodation providers were
forced to shut
• Seven helicopters from the Coastguard, the Royal Navy and the
Royal Air Force hovered overhead, winching people to safety
• Cars, boulders and uprooted trees were strewn through the streets.
• Cars were swept out to sea, bridges were washed away and people
clung to rooftops and trees
• Work has started on new £4.5m flood defences to protect the
Cornish village of Boscastle from flooding.

50. Video clip
https://www.youtube.
com/watch?v=xrb0Ea0
OkKU
What do you think the
immediate impacts of
the Boscastle floods
were?

51. Mozambique LEDC Flooding
Background
• 9th Feb – 27th Feb 2000
• 40 million population
• Zambezi was 2.5 m over
flood level

52. Mozambique LEDC Flooding
Hazards
•Destroy infrastructure
•Death
•Destroy services
•Disease
•Damage to field
•Damage to communication

53. Mozambique LEDC Flooding
Opportunities
• Fertile land (alluvium)
• LEDCs make money from
subsistence farming
• Water for irrigation
• Transport - Travel by boat
along river
• Flat land for building
• River source of fish (food)

54. Mozambique LEDC Flooding
Impacts
• Social – 180,000 fled, 81
dead, 150,000 in danger from
starvation, 23,000 lost
everything they had
• Economic – Roads and
bridges destroyed, transport
links cut off
• Environmental – 7,000
trapped in trees