2. Content Revised?
Rivers
The units and links in the hydrological cycle.
The storm hydrograph and how it responds to changes.
The river basin as a system of inputs, flows, stores and
outputs.
Physical causes of river flooding.
The activities of people that can cause river flooding.
Use of GIS, new technologies, satellite images, aerial
photographs and data in a variety of contexts to
highlight flood management schemes and their
effectiveness.
How weathering, erosion, transport and deposition
operate in a river basin.
The formation of fluvial landforms, including meanders,
interlocking spurs, floodplains, river cliffs, valleys,
waterfalls with appropriate examples.
Case study Named example
Theme 1 Rivers and Coasts
A MEDC case study to illustrate the causes, effects and
management of river flooding.
A LEDC case study to illustrate the causes, effects and
management of river flooding.
A case study of one river valley and its landforms.
3. The River System/ Water Cycle
Fill in the boxes using these words:
Air Condensation Clouds Precipitation
Transpiration Percolation Groundwater Ocean
Run-off Evaporation
Drainage Basin Terminology
4. EXAM PRACTICE
1 Study the diagram which shows part of the hydrological cycle.
(a)(i) Name the processes labelled 1 and 2 in the diagram. (2 marks)
(ii) Describe the difference between processes A and B. (2 marks)
(b) Describe how the water vapour shown in the diagram becomes water on the
land at the point labelled 4. (3marks)
(c) Describe two stores of water in the hydrological cycle that are not labelled
in the diagram. (4 marks)
(d)(i) Name the process labelled 6 in the diagram. (1 mark)
(ii) Suggest how the water moved by process 6 could end up in the sea.
(4 marks)
5. Match Up these Definitions
(use the diagram on the previous page to help you if necessary)
Drainage basin a stream or smaller river which
joins a larger stream or river
Catchment area the edge of highland surrounding
a drainage basin. It marks the
boundary between two drainage
basins
Watershed the area of land drained by a
river
Source the point where the river comes
to the end, usually when entering
a sea
Confluence - The beginning or start of a
river
Tributary the area within the drainage
basin
Mouth the point at which two rivers or
streams join
River Profiles
A river changes shape as it flows from its source
(where a river starts) to its mouth (where a river
flows into a sea or lake).
The shape of
both the long
profile (a slice
through the
river from
source to
mouth) and
the cross
profile (a slice
across the
river)
changes.
6. Spot Test!
A slice through a river from source to mouth is called what?
Long profile
Cross profile
Cross section
Steep profile
A typical cross profile in the upper course will be:
wide and deep.
narrow and shallow.
narrow and deep.
wide and shallow.
Erosion
Erosion involves the wearing away of rock and soil found along the river bed and banks. Erosion also
involves the breaking down of the rock particles being carried downstream by the river.
Match up the four main forms of river erosion
Hydraulic action rocks carried along by the river wear down the river
bed and banks
Abrasion soluble particles are dissolved into the river
Attrition rocks being carried by the river smash together and
break into smaller, smoother and rounder particles
Solution the force of the river against the banks can cause
air to be trapped in cracks and crevices. The
pressure weakens the banks and gradually wears it
away
Match up the four different river transport processes (use diagram on following page
only if you NEED to).
Solution small pebbles and stones are bounced along the
river bed
Suspension fine light material is carried along in the water
Saltation large boulders and rocks are rolled along the river
bed
Traction minerals are dissolved in the water and carried
along in solution
7. TRANSPORTATAION
Rivers need energy to transport material, and levels of energy change as the river moves from source
to mouth.
When energy levels are very high, large rocks and boulders can be transported. Energy levels
are usually higher near a river's source, when its course is steep and its valley narrow. Energy
levels rise even higher in times of flood.
When energy levels are low, only small particles can be transported (if any). Energy levels are
lowest when velocity drops as a river enters a lake or sea (at the mouth).
River Processes Test - Underline the correct answer
1. Which of the following is NOT a type of river erosion?
Solution or corrosion Abrasion Percolation Hydraulic action Attrition
2. When rocks and pebbles being carried by the river knock together and are broken
down to form smaller particles this is called:
Corrosion Abrasion Percolation Hydraulic action Attrition
3. When the force of the water being carried by the river wears away the bed and banks
this is called:
solution or corrosion abrasion percolation hydraulic action attrition
8. 4. Which of the following statements about deposition is NOT correct?
Deposition is more common at the source of the river.
Deposition occurs when a river loses energy.
Deposition may occur when the river is shallow.
Deposition may occur when the volume of water decreases.
5. Erosion is vertical or downwards:
at the source of a river
at the mouth of a river
6. A wide river channel is formed:
at the source of a river
at the mouth of a river
River Landforms
Upper-course river features include steep-sided V-shaped valleys, interlocking spurs, rapids,
waterfalls and gorges.
Middle-course river features include wider, shallower valleys, meanders, and oxbow lakes.
Lower-course river features include wide flat-bottomed valleys, floodplains and deltas.
Upper Course Features
As the river moves through the upper course it cuts
downwards. The gradient here is steep and the river
channel is narrow. Vertical erosion in this highland part of
the river helps to create steep-sided V-shaped valleys,
interlocking spurs, rapids, waterfalls and gorges.
As the river erodes the landscape in the upper course,
it winds and bends to avoid areas of hard rock. This
creates interlocking spurs, which look a bit like the
interlocking parts of a zip.
When a river runs over alternating layers of hard and
soft rock, rapids and waterfalls may form
9. Middle course features
Meanders
In the middle course the river has more energy and a high
volume of water. The gradient here is gentle and lateral
(sideways) erosion has widened the river channel. The river
channel has also deepened. A larger river channel means
there is less friction, so the water flows faster:
As the river erodes laterally, to the right side then the left
side, it forms large bends, and then horseshoe-like loops
called meanders.
The formation of meanders is due to both deposition and erosion and meanders gradually migrate
downstream.
The force of the water erodes and undercuts the river bank on the outside of the bend where water
flow has most energy due to decreased friction.
On the inside of the bend, where the river flow is slower, material is deposited, as there is more
friction.
Over time the horseshoe become tighter, until the ends become very close together. As the river
breaks through, eg during a flood when the river has a higher discharge and more energy, and the
ends join, the loop is cut-off from the main channel. The cut-off loop is called an oxbow lake.
Lower course features
In the lower course, the river has a high volume and a large discharge. The river channel is now deep
and wide and the landscape around it is flat. However, as a river reaches the end of its journey, energy
levels are low and deposition takes place.
Floodplains
The river now has a wide floodplain. A floodplain is the area around a river that is covered in
times of flood. A floodplain is a very fertile area due to the rich alluvium deposited by
floodwaters. This makes floodplains a good place for agriculture. A build up of alluvium on the
banks of a river can create levees, which raise the river bank.
Deltas
Deltas are found at the mouth of large rivers - for example, the Mississippi. A delta is formed
when the river deposits its material faster than the sea can remove it. There are three main
types of delta, named after the shape they create:
11. Case Study – MEDC Case Study to illustrate the causes, effects and
management of river flooding
BOSCASTLE - The Boscastle Flood (Cornwall) on 16th August 2004
Why the flood risk?
Human Factors
A bridge caused a blocking point until it gave way.
Physical Factors
The cause was torrential rain, as over 1 months worth fell in just 3 hours.
Warm moist air had moved in from the Atlantic and condensed into thunder clouds.
The catchment area of Bodmin Moor was already saturated through earlier rainfall, so run-off was
immediate.
3 tributaries all converge above the village, and the steep slopes created a raging torrent.
Impacts
Social
Whilst no people died, the flood caused serious problems in the small town.
Bridges were washed away and over 80 cars were swept along, many of them were tourist’s cars who
were parked at the head of the village.
Economic
The unique witchcraft museum was totally lost.
As many locals ran bed and breakfast businesses, their summer was ruined as it was over a year before
they could re-open. Some had no insurance and never re-opened.
The emergency services were over stretched and subsequently, the local council have had to spend huge
sums of money introducing flood prevention schemes such as channel straightening and building holding
dams (also called check dams).
Over 20 houses were badly damage, with many being beyond repair.
Managing the flood risks
1. Channel modification – River Valency – widened and deepened so it can carry higher flows of water.
Lower river bed by an average 0.75m. Widen river channel next to the Riverside Hotel; move back the
patio and replace and extend the footbridge.
2. Removal of large bridge that acted as a block for debris and the fast flowing water
3. Encourage landowners to maintain vegetation cover on valley sides and remove any dead trees
4. Form wide river channel upstream of the car park to create an area of slower flow where larger
sediment will deposit and the river can spread out
12. Case Study – LEDC Case Study to illustrate the causes, effects and
management of river flooding
Bangladesh is a low lying country most of which lies on the delta of Ganges, Brahmaputra and Meghna.
Why the flood risk?
Physical factors:
Sources of rivers are in Himalayas so snowmelt adds to the discharge during spring.
S Asia has a monsoon climate and experiences a wet season between May and September when low pressure and
winds blowing from SW across Bay of Bengal bring heavy rain to coastal regions.
Bangladesh also suffers from cyclones that bring high winds, heavy rainfall and storm surges.
Human Factors:
Urbanisation - the capital city Dhaka now has a population of more than 1 million people
Rapid deforestation in Himalayas has had a negative effect on rates of interception and evapotranspiration
resulting in more water reaching the rivers.
River management is difficult to implement in LEDCs. Average GDP per capita is around $300.
Population rely on subsistence agriculture to survive growing rice on rented plots of land so there is little
income from taxation for Government and Bangladesh relies heavily on foreign aid to finance large scale
development project which might help prevent floods.
In 2004 the monsoon season brought more rainfall than usual.
Impacts
Social impacts:
36 million people were made homeless
By mid September the death toll had risen to 800. People died as a result of disease because they had no
access to clean water.
Landless labourers and small farmers were the most severely affected in rural areas and in the urban areas it
was typically the slum dwellers squatting on poorly drained land who suffered the most.
Economic impacts:
Flood also caused serious damage to infrastructure – roads, bridges, embankments, railway lines, irrigation
systems
13. All domestic and internal flights had to be suspended during July
Road and rail links into Dhaka were severely affected
Value of damage was assessed as being in region of $2.2 billion of 4% of total GDP for 2004
Environmental impacts:
During July and August approximately 38% of the total land area was flooded including 800,000 ha of
agricultural land and Dhaka
Floods caused river bank erosion especially on embankment areas close to the main channels, soil erosion, water-
logging, water contamination
Responses
Short term responses
The government working with non-governmental organisations provided emergency relief: rice, clothing,
medicines, blankets and towels
In July the United Nations activated a disaster management team to coordinate the activities of the various
UN agencies. They supplied critical emergency supplies and conducted a ‘damage and needs assessment’ in
affected areas.
Bilateral aid from individual countries was directed to the UN team.
Self help schemes – local people worked together to rebuild their properties and communities.
Long – term responses
Long term responses to major floods are largely dependent on foreign aid from both official and unofficial
sources. Previous river management schemes implemented by foreigners and funded by aid have proved to be
inadequate. These schemes paid little attention to knowledge of rivers and many attempts at river management
failed
Recent small scale community based projects have resulted in lives being saved. Food shelters and early warning
systems have been successfully put in place.
Following the 2004 floods additional financial aid was granted for a period of 5 years. This was mainly in the
form of a loan from the World Bank to pay for repairs to infrastructure, water resource management and
education.
And the future?
Disaster preparedness is a key priority for the future. This includes flood management and improved water
resources. It is also planned that flood-resistant designs should be used in all social and economic
infrastructure projects
14. Why are the effects of river flooding usually greater in an LEDC than in an MEDC?
1. Less money to spend on tackling problems so less flood protection measures to prevent the same
effects happening again.
2. Difficult to get to affected area due to lack of transport links which would require plenty of money to
improve road networks and other transport links
3. People are attracted to living on fertile flood plains in LEDCs because farming is an important part of
their economy and the alluvium (silt) deposited on the floodplain during floods is a very good and cheap
fertiliser for crops.