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UNIT 2 The Natural Environment
SECTION A- The Physical World
RIVER LANDSCAPES
River processes produce distinctive landforms
What is a drainage basin?
Rivers begin in upland area and flow downhill to the sea.
SOURCE - where the river starts.
MOUTH- where it meets the sea.
As makes its way to the sea,
RIVER CHANNEL (area which a river flows) and VALLEY change
- River becomes WIDER and DEEPER as joined by smaller rivers
(TRIBUTARIES).
CONFLUENCE – point at which rivers meet.
-River valley - sides become less steep, gradient decreases
shape of valley changes from V-shaped
broader U
DRAINAGE BASIN - land drained by river system
WATERSHED – boundary of drainage basin (usually highland)
Activities
a) Define : WATERSHED, CONFLUENCE, TRIBUTARY, SOURCE.
MOUTH (5 marks)
(10 marks)
b) Draw a diagram of a drainage basin and label key features.
How do rivers erode?
Banks and bed of a river are continuously attacked by water within the channel(EROSION) and processes out
of the channel such as WEATHERING and MASS MOVEMENT.
PROCESSES OF RIVER EROSION (in river channel)
HYDRAULIC ACTION- pressure of water pushing against
bank and bed of river. Includes air compressing into
cracks
more pressure
rock breaks.
CORROSION (solution)- chemical reaction between
certain rock types and river water. Seen in limestone
as river eats through rock and flows underground.
CORRASION- particles (load) carried by river thrown
against banks with force.
ATTRITION- Rocks in the upper course roll around and
knock each other until smooth pebbles or sand are
formed.
What are the main types of weathering? (the breakdown of rock in situ- not moving)
Physical weathering
Chemical weathering
Biological weathering
Freeze thaw or frost action- water
gets into cracks
temperature
falls below freezing
water will
expand as turns to ice.
Expansion puts pressure on rocks
around it
fragments of rock
break off.
Common in highland areas. (above
freezing daytime, below freezing at
night)
Rainwater contains weak acids
which react with certain rocks.
Carbonates in limestone dissolved
by these weak acids break up or
disintegrate the rock.
Seen in limestone statues or
pavement eg. Malham
Action of plants and animals on
land.
Seeds fall into cracks
grow
with moisture. Roots of young
plant force through cracks and
break up rock over time.
Burrowing animals (rabbits) also
break up the rocks further.
(see figure 2 p64 textbook)
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What is mass movement?
It is when material moves down a slope due to the pull of GRAVITY. Two types are soil creep & slumping.
SOIL CREEP
-The slowest downhill movement of soil.
-Water in the soil is pulled down the slope by
GRAVITY so the soil will move downhill with the
water.
-This happens very SLOWLY so we can’t see it
happen but moves quicker after heavy rain.
The slope may appear rippled (TERRACETTES)
-see photo below and fig 3 p65
SLUMPING (rotational slipping)
-Common on river banks.
-Involves large area of land moving down a slope.
-Due to the nature of the slip, leaves curved surface
-Common on CLAY riverbanks:
i) during dry weather clay contracts and cracks.
ii) when rains, water gets into cracks where
absorbed until rock is saturated.
iii) weakens rock, due to gravity slips down on slip
plane. (figure 4 p65)
Activities
a) Define: weathering and erosion. (4 marks)
b) Outline the process of slumping. (2 marks)
c) State one impact of slumping. (1 mark)
d) Mass movement can occur in river valleys. Explain the process of mass movement. (3 marks)
How do the characteristics of a river and its valley change?
-As a river moves downstream its ENERGY changes.
-In an upland area the river is way above sea level so has the power to erode downwards (vertical erosion)
so forms a V-shaped valley.
-As gradient (slope) of valley decreases, river uses energy to transport material it has eroded.
-Due to lack of gradient, river erodes sideways (laterally).
- As river moves closer to the sea, gradient decreases further.
- Deposition becomes most important process so valley becomes wider and flatter.
-Change from erosion to deposition explains change in landforms and shape of river valley as move to sea.
-LONG PROFILE shows steep gradient at source, becomes more gentle towards the sea
- These changes show river split into UPPER, MIDDLE and LOWER course. (figure 5 p65, fig 6 p66)
Activities
a) Draw a long profile of a river on an A3 sheet
b) Add arrows to show how variables change downstream
c) Add photos of landforms found at the different stages
d) Annotate the A3 sheet to explain the changes
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-As river moves downstream DISCHARGE also changes:
DISCHARGE: amount of water passing a specific point at a given time and is measured in cubic metres (m³)
per second [cumecs]. Depends on the river’s velocity and volume.
Volume: is the amount of water in the river
Velocity: is the speed of the river.
DISCHARGE = VELOCITY x VOLUME
As rivers moves towards the sea, DISCHARGE increases as increased volume as more tributaries join.
VELOCITY determined by amount of water in contact with bed and banks. If deeper, less contact between
river and its banks and bed therefore less FRICTION  river velocity greater.
Describe and explain the changes in width, depth, discharge and gradient of a river valley as it
moves from its source to its mouth.
 Channel becomes wider and deeper
 River valley: sides less steep, gradient decreases, shape changes from a V to a broader shape, almost like a flatbottomed U.
Reasons for these changes:
Discharge increases as the river flows downhill to the sea because tributaries join the main river increased river energy.
Friction decreases from upper course to lower course increased power of erosion.
Upper: only vertical erosion as the river is small, most of the water is in contact with bed 95% of energy used to
overcome friction small velocity and small volume of water= lowest discharge. V-shaped valley
Middle: lower gradient lateral erosion[ higher discharge + transported material increase erosion; lower friction as
discharge is higher]
Lower: still lateral erosion. But low gradient, deposition most important process valley wider and flatter.
What landforms can be found in river valleys? River’s course split into 3 sections: UPPER, MIDDLE, LOWER.
UPPER COURSE
• Vertical erosion is the dominant process
• River channel narrow and shallow, often lined with large angular boulders
• Quite steep gradient
• Velocity quite low because so much energy used in overcoming friction with the rocky bed and banks
of the river FEATURES: V-shaped valleys, interlocking spurs and waterfalls
V-shaped valleys and interlocking spurs
-Upper course river is small, most water
contact bed and banks lots of friction
-95% energy used to overcome friction.
-River flows slowly. Rest of energy used
to erode downwards(vertical erosion)
V-shaped valley
- As river winds its way down between
barriers of more resistant rock, spurs
which interlock down the valley are
formed interlocking spurs.
(also fig. 9 & 10 p68)
Activities
a) Outline how river characteristics change. (4 marks)
b) Compare the characteristic features of a river in its upper and lower stages. (4 marks)
c) Activities 1 & 2 p67 (map work)
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WATERFALLS
-Form when river crosses a band of less resistant rock, after flowing over relatively hard, resistant rock.
-A waterfall is a steep, sudden drop in the course of a river.
(also fig 11 p68)
1) The softer rock is cut back more quickly
leaving an OVERHANG of harder rock.
2) In time collapses due to GRAVITY
3) PLUNGE POOL develops with
HYDRAULIC ACTION eroding the soft rock
of the back wall.
4) Over time the waterfall RETREATS up
valley forming a GORGE.
PLUNGE POOL: deeper, contains boulders
from overhang and back wall. River erodes
rocks by CORRASION.
ACTIVITY: Explain how a waterfall is
formed. (4 marks)
MIDDLE COURSE
• River is deeper as result of being joined by a number of tributaries.
• Gradient less steep
• Less water in contact less friction and river more power to erode.
• River continues to erode vertically but lateral erosion becomes more important as less gradient as
valley flatter and more gentle slopes.
• Begins to meander due to increase in lateral erosion.
• Erosion on the outside of meanders removes interlocking spurs and the valley becomes wider.
MEANDERS:
Cross-section of a meander (label using fig 14)
-Outside of bend-deepest water because greatest
erosion forms RIVER CLIFF.
-Moving fast and erodes bank by CORRASION.
Moves fast due to depth and lack of contact less
FRICTION.
-SLIP-OFF SLOPE forms inside due to DEPOSITION.
-Here water shallower, slower, more friction,
so river less powerful unable to carry LOAD
DEPOSITION.
ACTIVITY: a) Explain the formation of a meander(4 marks)
b) Complete activities 1-3 p69 (4,3,4 marks)
LOWER COURSE
• Channel is wide and deep, surrounded by wide valley floor
• River flows through a wide flat valley called the FLOOD PLAIN.
• Velocity greatest as less friction.
• Slopes of valley and gradient of channel very gentle.
• Deposition of sand and silt (alluvium) most important process as has large load of eroded material.
• However, still some lateral erosion. FEATURES: Ox-bow lakes, floodplains, levees and deltas.
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OX-BOW LAKES (Also fig 20 p70)
ACTIVITIES
a) Explain the formation of an ox-bow lake. (4 marks)
b) Activity 1 (1 mark), 2 (4 marks), 3 (3marks) p70
FLOOD PLAINS AND LEVEES
(also fig 21 p71)
Lower course= very large meanders.
Continual erosion of outside banks,
deposition on inside bank meander
neck narrower if flooding [high
discharge] river cuts through the gap and
forms a straight channel.
Old bend cut off and called OX BOW lake.
FLOOD PLAIN- low, flat area either side of river.
Found middle course but more usually lower.
Formation of a flood plain
-The river carries large quantities of load.
-As the water floods onto the flood plain there is
greater friction, the water is shallow and the
velocity falls so its load is deposited onto the flood
plain as alluvium. The migration of meander bends
across a valley also contributes to formation of a
floodplain.
Levees
-As a river floods, its channel width increases
increased friction as more water in contact with
land.
-River has less energy and drops the load it is
carrying.
-Largest material [heaviest] deposited first close to
the river channel after a number of floods
builds up to form levees.
ACTIVITIES
a) Explain the formation of levees (4 marks)
b) Question 2 p71 (4 marks)
c) Question 3 p71 (3marks)
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Flooding and flood prevention
What are the human and physical causes of river flooding?
Flooding occurs when a river gets more water than its channel can hold.
HUMAN CAUSES OF FLOODING
PHYSICAL CAUSES OF FLOODING
Dams may burst leading to excess water in channel.
Steep valley slopes  rainwater into channel quicker
If town on floodplain ,storm drains will move water
If large amount of rainfall  ground become
quicker into channel. Higher risk of flooding.
saturated and flow quicker into river channel
If vegetation removed, less interception and water
During cloudburst in thunderstorm, rain droplets so
move into river channel quicker.
big and fall so quickly no time to sink into ground 
water runs very quickly into river  flooding
Ploughing up and down slopes channels water into
River beds become silted make channel smaller and
river quicker.
more likely to flood.
Impermeable rocks not allow water to soak so flows
Activities: Explain how flooding can be caused by
quickly to river channel
physical factors. (6 marks)
Snow and ice thaw quickly, large amount of water in
river and unable to cope and risk of flood.
Dry period, ground becomes hard, unable to soak in,
runs off quickly into channel, risk of flooding
What are the effects of flooding on people and the environment? (MAP p74-75)
-Effects of flooding depend upon: area of flood + where flood happens. Effects greater in DENSELY pop.area.
MEXICO 2007
The River Grijaiva flooded in the state of Tabasco.
-Approx. 1 million people were affected by the flood.
-70% of the state was under water.
-All the crops were destroyed.
-Tabasco’s capital, Villahermosa, was turned into a brown lake with only tree tops and roofs visible.
-300,000 people trapped in their homes.
-Sandbags used to protect carvings at Tabasco’s ancient archaeological site.
KENYA 2007
The River Tana burst its banks.
-Much of the town of Garissa was under water, with houses near river submerged.
-Flood destroyed bridges and made roads impassable, so aid drops by plane only way deliver food to people.
INDIA 2008
The Kosi river burst its banks. 1600 villages affected.
-Thousands of people were stranded on rooftops and trees or marooned on thin strips of dry land.
-55 people were killed.
-Road linking Saharia village to the rest of the hard-hit Saharsa district was completely washed away.
USA 2006
Floods caused problems in a number of states.
-200,000 people evacuated from homes in Pennsylvania because of rising waters on Susquehanna River.
-State of emergency declared across large parts of New Jersey, New York and Pennsylvania states.
-Largest evacuation in Wilkes-Barre, Pennsylvania.
-A group of children ferried out of a tennis camp by raft in Philadelphia.
-Numerous roads and bridges closed.
-Nine people killed in eastern USA.
BOLIVIA 2007
Many rivers burst their banks.
-340,000 people were estimated to have been affected.
-About 100,000 people left homeless. Roads in Santa Cruz and Beni were blocked by mudslides.
-At least 19 people died as a result of flooding of the Rio Grande, tributary of the Amazon.
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Activity: Explain the effects of flooding on people and the environment. Use examples (6 marks)
How are the effects of river flooding reduced by prediction and prevention?
EDUCATION
FORECASTING
-Governments give advice to the general public via
-The Met Office predicts (forecasts) the likelihood of
the internet. The advice includes information on how a flood. The information gets to householders
to protect your home.
through weather forecasts and news broadcasts on
-On the Environmental Agency website there is
TV and radio.
information on the likelihood of a flood. This will be
-Also on their website.
identified by a system of warning codes: flood watch, -If there is the likelihood of flooding the Met Office
flood warning, severe flood warning and all clear.
advises householders to be proactive and either ring
These warning codes give people information on
a flood hotline number or go to the Environment
what to expect and how to react. In this way the
Agency’s website to check the likelihood of a flood in
government is helping the effects of floods by
their area.
providing an effective warning system.
BUILDING DESIGN
It can cost between GB£3000 and £10000 to protect
a house from flooding. Some techniques are:
-Moving electricity sockets higher up the wall.
-Replacing doors with ones that are lightweight and
can be moved upstairs if necessary.
-Concrete floors instead of wooden ones so they do
not rot if they are wet.
-Using yacht varnish on skirting boards to protect
from water.
-Waterproof MDF can be used instead of wood as a
door frame.
-Building on stilts
PLANNING
-Before houses can be built the local authority has to
give planning permission. Not granted in flood risk
areas unless flood-risk assessment is carried out.
-In 2010 the law requires all new housing in floodrisk areas to be flood resistant or resilient.
- Defra (department for the Environment, Food and
Rural Affairs) has the responsibility for deciding
which areas are going to be defended against the
risk of flooding. The Environment Agency then
organises for the defences to be built and
maintained. Defra provides the money for most of
the work that is completed.
Activity: Explain how planning and building design can reduce the effects of flooding. (6 marks)
Severe flooding UK –August 2008: Doncaster Council and St Leger homes implemented series of flood
resilient repairs to 138 council homes.
● Waterproof plaster and wall covering.
● Chemical waterproofing of concrete floors.
● Waterproof medium density fibreboard used instead of wood for skirting boards.
These measures will not stop flooding but mean homes can be habitable quicker after a flood in the future.
Hard and Soft Engineering Techniques
HARD ENGINEERING- method of river flood management which involves major construction work.
SOFT ENGINEERING – method of river flood management which works or attempts to work with natural river
processes. Does not involve major construction work.
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Advantages and Disadvantages of Hard and Soft Engineering (p77-79)
HARD ENGINEERING
TECHNIQUE
EMBANKMENTS
CHANNELISATION
FLOOD RELIEF
CHANNELS
DAMS
FLOOD WALLS
STORAGE AREAS
SOFT ENGINEERING
TECHNIQUE
FLOODPLAIN
ZONING
DESCRIPTION
ADVANTAGES
These are raised banks
along the river
-Can be used as a path for
pedestrians beside the river.
-Concrete embankments are
effective at stopping bank
erosion.
-Earth embankments provide
habitat for plants and animals.
-Effectively protects
immediate area because
water is moved away quicker.
-Long lasting.
River channel may be
widened or deepened
to carry more water.
May be straightened
to carry water faster.
DISADVANTAGES
-The banks are often not
built high enough.
-Concrete embankments
are ugly and spoil the
view.
-Altering the river channel
may lead to a greater risk
of flooding, as water is
carried there faster.
-Unnatural and visually
intrusive.
-Needs large area of land,
Difficult to buy if farmland.
-Very expensive.
Channel course of
river can also be
altered, diverting
floodwaters away.
Built along course of
river to control
amount of discharge.
Water held back by
dam and released in
controlled way.
-People close to channel safer
as flood water diverted to
relief channel.
-Used for water sports.
-Water usually stored in a
reservoir behind dam. Then
used to generate hydroelectric
power or recreation.
Vertical barrier usually
made from
prefabricated
concrete.
Large depression close
to the river that will fill
with water if the river
overflows and
therefore protecting
surrounding land.
DESCRIPTION
-Can be used in areas where
space is limited.
-Easily and quickly erected in
pre-constructed sections.
-Natural looking.
-Does not damage the
environment.
ADVANTAGES
DISADVANTAGES
Local authorities and
national government
introduce policies to
control urban
development close or
on floodplains.
-Very cheap way to reduce risk
of damage to property.
-Sustainable as reduces impact
of flooding and building
damage.
-Surface runoff less likely to
cause flooding as floodplain
not built on.
-Resistance to restrictions
in areas of shortage of
housing.
-Enforcing planning
controls difficult in LIC’s.
-Very expensive.
-Sediment trapped behind
wall of dam leading to
erosion further
downstream.
-Settlement and
agricultural land may be
lost when the river valley
is flooded to form a
reservoir.
They have to be
constructed very well so
no water leaks through.
-Need a large area of land
that is not being used.
-Only come into use when
the river is flooded.
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WASHLANDS
River allowed to flood
naturally in wasteland
areas to prevent
flooding in other
areas.
WARNING SYSTEMS
Sirens give warning of
possible flooding.
Environment Agency
use TV, Radio, fax,
text, email, phone to
inform people.
Trees planted in
catchment to increase
interception and slow
flow of water to river.
AFFORESTATION
-Very cost effective as nothing
built.
-potential wetland sites for
birds and plants.
-deposited silt may enrich the
soil turning it into agricultural
land.
-Very cheap system.
-Electronic communication
very effective.
-Can move valuable
belongings to safer location
with early warning.
-Relatively low cost system.
-Improves quality of the
environment.
-soil erosion avoided as trees
prevent rapid runoff after
heavy rainfall.
-Very sustainable.
- Large areas of land taken
over and cannot be built
on.
-productive land can be
turned into marshland.
-Sirens vandalised so
tested every year.
-Might not be enough
time for residents to
respond.
-Often conifers planted
which makes soil acidic.
-Dense tree plantations
spoil natural look of
landscape.
-Increase fire risk due to
leisure activities in forests.
Activities: a)Outline the advantages and disadvantages of soft engineering techniques. (4 marks)
b) Question 2, p79 (9 marks)
River Management Case Study: River Nene, Northampton,UK
Introduction
-April 9 1998 heavy rain caused R.Nene and Grand Union canal to overflow. Parts of town flooded. 2 dead.
-Decision made to manage River Nene against future flooding.
-By 2002, Environment Agency completed £6.8million project to protect areas of Northampton hardest hit
by past flooding.
-2003 and 2007 further defence works were carried out in town.
(refer to map p80-81)
Note: You need to DESCRIBE and EXPLAIN the management techniques.
Management Techniques:
A- In 2002 a flood embankment was built across the river valley at Weedon. £2million. (describe)
-This raised the level of the land by 10m.
- In times of flood, water can be stored behind the bank. (explain)
B-Built earth embankments setback 10m from river.
-Increased river channel capacity at Upton
C-In 2007, work began to build defences in the Upton area. These cost £8 million.
-Aim to create an area called a washland, where up to 1.2 million m³ of water can be stored during flooding.
-Major roads in this area such as Upton Way(A45) are on embankments up to 6m high.
-Means communications not disrupted if flooding occurs.
D-At Foot Meadow 4m high floodwalls have been installed to protect the railway station, housing, industry
and the Castle Inn.
-Has created an open area of land onto which the river can flood.
E-The areas at risk of flooding are covered by the Environment Agency’s flood warning service-aims to give
2 hours warning of possible flooding.
-Gives local people time to prepare and evacuate if need be. Flood warning system upgraded in 2003.
Testing of system took place in the Far Cotton area of Northampton.
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