Water
Use this PowerPoint to complete the brainstorm on the topic of ‘Water’
Processes
• What three main process operate on a river?
Video http://www.bbc.co.uk/schools/gcsebitesize/geography/water_rivers/river_proce
sses_video.shtml
Erosion (4 types)
Hydraulic Action
• This process involves the force of water against the bed and banks.
Abrasion (Corrasion)
• This is the process by which the bed and banks are worn down by
the river’s load. The river throws these particles against the bed and
banks, sometimes at high velocity.
Attrition
• Material (the load) carried by the river bump into each other and so
are smoothed and broken down into smaller particles.
Corrosion
• This is the chemical action of river water. The acids in the water
slowly dissolve the bed and the banks.
Can you remember the Kung Fu moves?
(these will help you to remember the meaning of each word)
Do you know your processes of erosion?
Transportation (4 types)
Material floats in the water and are
carried by the flowing water
Material is rolled along the river
bed by the flowing water
Some materials dissolve in water (e.g.
Limestone and are carried by the
flowing water
Material bounces along the river
bed by the flow of the water
How is material transported downstream?
The Drainage Basin
Source
Tributary
Confluence
Watershed
Mouth
Landforms
• Landforms found along the course of a river can be created
by either erosion, deposition or a combination of both.
• Video http://www.bbc.co.uk/schools/gcsebitesize/geography/wat
er_rivers/river_landforms_video.shtml
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Waterfalls
Delta
Meanders
Levees
V-shaped valleys
Only learn two
landforms in detail
Waterfalls
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A waterfall is usually found in the upper course of a river
It occurs when a layer of hard rock overlies a layers of softer rock
The hard rock is less easily eroded creating a steep slope and rapids.
Eventually a drop develops over which the water falls
Waterfall formation
Waterfalls
Delta
• A delta is found at the mouth of a river.
• When a river enters the sea, it loses energy
and can no longer carry as much material. Its
load it deposited. If this happens at a fasters
rate than at which the sea can remove the
material, a delta is formed
• Deltas can provide rich farm lands but often
suffer flooding e.g. Bangladesh
Delta
Distributaries
Meanders and oxbow lakes
• A meander is a bend in a river formed by
lateral erosion (sideways)
• Meanders are found in the lower course of a
river
• Created through erosion and deposition
A cross section through a meander
Outside bend – Fastest Flow (erosion)
Inside bend - slowest flow (deposition)
This causes the bend to migrate (lateral
erosion)
Oxbow lakes
V-shaped valley
Vertical erosion
Interlocking
spurs
V-shaped valley
Floodplains and Levees
• These are found in the lower course of a river
close to the mouth
• As a river nears the mouth it has a large discharge
and the river channel is deep and wide. The valley
is also wide with an extensive flood plain.
• Each time the river floods, silt is deposited on the
floodplain. Creating fertile soils.
• Natural levees are raised banks of deposited
material found either side of the river channel.
Floodplains
Flooding
Flooding is an important issue relating to rivers.
• You will need to understand how water moves
through a drainage basin.
• You will also need to be able to explain how humans
change the flow of water in a drainage basin and
therefore can increase the risk of flooding
Videos
1. http://www.bbc.co.uk/schools/gcsebitesize/geography/water_rivers/river_floodin
g_management_video.shtml
2. http://www.bbc.co.uk/learningzone/clips/river-flooding-in-britain-causes-andeffects/5865.html
Movement of water in the drainage
precipitation
basin
interception
evapotranspiration
infiltration
percolation
water table
river
Key words - explained
Infiltration – down ward movement of water through the soil
Percolation – downward movement through the ground (rocks)
Surface runoff – when water flows over the surface of the soil
Through flow – when water flows through the soil
Ground water flow – when water flows through the ground (rocks)
Saturation – this happens to the soil when no more water can infiltrate the
soil (leads to surface runoff)
Interception – trees and vegetation intercept water by catching rain in their
leaves
Transpiration – trees breathing out water as a gas
Evapotranspiration – water that evaporates off the surface of tree leaves
Causes of flooding
Human causes
Deforestation
Reduces water stored, water lost to the
atmosphere in transportation and
evapotranspiration
Removing trees increases infiltration into the
soil and increases discharge in rivers
Building on the floodplain
Surfaces like tarmac can decreases infiltration
and increases surface runoff. Resulting in more
water getting into a river faster increasing the
risk of flooding.
Climate change
Global warming has resulted in sea level rise
and more incidents of extreme weather
making flooding more likely and more sever in
the future
Physical causes
Heavy rainfall
Increase the amount of discharge in a river.
Steep valley sides
Water travels at a faster velocity (speed) in the
drainage basin and gets into the river channel
faster causing river levels to rise faster
Rock type
Some rocks do not absorb water and therefore
less water will be stored into the rocks.
Resulting in increased water in the river
channel
Number of tributaries
Less tributaries means that the river has less
capacity to hold water and therefore more
likely to flood.
Hydrographs
Peak discharge
Rising
limb
I = Lagtime
Falling
limb
storm flow
normal (base) flow
Peak rainfall
Write a definition of lagtime.
Calculate the lagtime shown on this hydrograph.
Hydrographs
Geology and soil
Gradient of the valley sides
What affects the shape of a
hydrograph?
Land use
Drainage density
Type and amount of precipitation
Flood management
• Flooding can be managed in a variety of ways,
these can be divided into hard engineering
and soft engineering approaches
Remember in the exam to give examples of
where these things have been done.
See Boscastle casestudy
Hard Engineering
Soft Engineering
For flood management
• Some people argue flooding should be
managed. This is because: – Flooding can result in thousands of pounds worth of
damage
– It can threaten peoples lives
– Business and peoples livelihood can be damaged. Local
economy will lose money.
– Floods can affect large numbers of people in urban areas
– Flooding can last weeks and the effects can last months
even years
– Disruption to schools, roads, and businesses
Against flood management
• Some people argue flooding should not be
managed. This is because: – Flood defences are expensive and can result in
council tax being increased. This might mean
someone who is not affected by flooding having to
pay for flood defences.
– Flood defences are only put on one small part of a
river channel (too expensive to put all along a
river)
– Some flood defences can result in greater risk of
flooding further downstream.
How do the rivers affect people
lives?
Learn two casesudies for this question.
1. Tourism – Niagara Falls
2. Flooding – Boscastle
Tourism – Niagara Falls
Benefits Tourism
• Jobs created
• Boosted local economy
• Local facilities improved
Costs Tourism
• Congestion on roads
• Littering
• Crime rate increases (pick
pockets)
• River pollution (boats)
Flooding – Boscastle
Video - http://www.bbc.co.uk/learningzone/clips/why-did-boscastle-flood/14072.html
What factors increased the risk of flood in Boscastle ?
What factors increased the flood risk?
Effects of the Boscastle flood
Management of flooding in
Boscastle
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Low bridges where raised
The river channel was made deeper
The river was straightened in parts
Small amounts of afforestation in Boscastle
and surrounding area
How do the rivers affect people
lives? - The floodplain
• Provide ideal land for farming. The soil tends
to be very fertile so crops can be grown Or if
flooding is frequent the land can be used for
pastoral animals.
• Provide flat land that can easily be built on.
Many homes in the UK are built on the
floodplain of rivers.