7. How do rivers erode?
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/solution
This is the chemical action of river water. The acids in the
water slowly dissolve the bed and the banks.
8. How do rivers transport their load?
Bedload/
Saltation
Solution
Bedload/
Traction
Suspension
Boulders and pebbles are rolled
along the river bed at times of high
discharge.
Sand sized particles are bounced
along the river bed by the flow of
water.
Fine clay and sand particles are
carried along within the water
even at low discharges.
Some minerals dissolve in water
such as calcium carbonate. This
requires very little energy.
14. Interlocking spurs
In the upper course the river does not have a huge amount of
energy to erode as it does not have a high discharge and it has to
transport large pieces of sediment.
When the river meets areas of harder rock that are difficult to
erode it winds around them. A series of hills form on either side
of the river called spurs. As the river flows around these hills
they become interlocked. So, a series of interlocking spurs are
often found in the upper course of a river valley.
29. Floodplains and leveés are formed by deposition in
times of river flood. The river‟s load is composed of
different sized particles. When a river floods it deposits
the heaviest of these particles first. The larger particles,
often pebble-sized, form the leveés. The sands, silts and
clays are similarly sorted with the sands being
deposited next, then the silts and finally the lightest
clays. Every time the river floods deposition builds up
the floodplain.
Floodplain formation
30. What types of delta are there?
arcuate - the land around
the river mouth arches out
into the sea, the river
splits many times on the
way to the sea, creating a
fan effect.
cuspate - the land around
the mouth of the river juts
out arrow-like into the
sea.
bird's foot - the river splits
on the way to the
sea, each part of the river
juts out into the
sea, rather like a bird's
foot.
31. Rivers flood for many reasons. The main reasons are:
Precipitation:
Frequent cause of flooding = heavy rainfall over days
Ground becomes saturated and water runs over surface
Most serious flooding usually after short intense storms.
Flash floods usually occur after hot summer when ground dry so water can‟t infiltrate the
surface.
Water held as snow also can cause floods when melts as temp‟ rises
Soil/underlying rock:
Rocks that let water through – Permeable
Rocks that don‟t let water through – Impermeable
Surface run-off and flood risk greater when river basin has impermeable soil and
underlying rock.
Land use:
River basins with little vegetation cover = high flood risk
Forested basins = low flood risk
Human activity:
Deforestation (cutting down trees) and urban growth increasing flood risk
Bangladesh = increased flood risk due to deforestation in Himalayas
Impermeable tarmac surfaces and concrete surfaces are replacing fields and woodland –
surface run-off increased
The reasons why some
rivers flood
32. The discharge of a river at any point can be plotted on a
STORM HYDROGRPH. This shows the rivers response to
a single rainfall eventThe soil
becomes
saturated and
overland flow
and through
flow reach the
river and
discharge
increases.
Overland flow
arrives first.
The time from peak rainfall to
peak discharge is the LAG
TIME.
The discharge
starts to fall slowly
as water is added
from through flow
and groundwater
flows which are
much slower.
The base flow
supplies the river
with water between
storms and keeps it
flowing in summer.Rainfall is intercepted
or infiltrated into the
soil moisture store
Start of the storm
there is a slow rise in
discharge, as only a
small amount of water
falls into the channel
33. FACTORS WHICH
INFLUENCE
STORM
HYDROGRAPHS
VEGETATION COVER
This varies seasonally. The type
and amount will affect
interception and
stemflow/throughfall. Overland
flow is reduced. Lag time will be
increased.
ROCK TYPE
Impermeable rocks prevent
groundwater flow and encourage
through flow and overland flow.
These rocks will decrease lag time.
Permeable rock will have the
opposite effect.
LAKES & RESERVOIRS
These will store floodwater
and thus reduce lag time and
control river response to
heavy rainfall.
SOIL TYPE & DEPTH
Deep soils store more
water, pipes in the
soil encourage
through flow. Soils
with small pore
spaces will reduce
infiltration and
increase overland
flow.
LAND USE
Impermeable surfaces
created by urbanisation
will reduce infiltration
and encourage overland
flow.
Different types of crops
affect interception rates
e.g. cereals 7-15%.
RAINFALL INTENSITY &
DURATION
Intense rain will increase
overland flow and reduce lag
times. Gentle rain over a
longer time will allow more
infiltration.
SLOPES
Steep slopes will
encourage overland flow
and gentle slope will
slow run off down.
CLIMATE
The distribution of rainfall over the
year and the temperatures will
affect the lag times.
34. Boscastle Floods 2004
•It has been estimated that the Boscastle valley‟s catchment area exceeds 23
km2, spanning inland to Bodmin Moor where many small rivers spring.
•The steep sided valleys that converge down to the sea, known as “flashy
catchments”, act as huge funnels and can produce true flash floods after a
sudden cloudburst or prolonged heavy rainfall.
•During the afternoon of the 16th, an incredible amount of rainwater fell,
conservatively estimated to have been over 1422 million litres of rain in just 2
hours, that‟s over 197500 litres falling per second. At its peak, nearly 25mm
had been recorded in a 15 minute time span, that‟s over 632000 litres falling
per second, the equivalent of 100 tonnes or 21 petrol tanker loads flowing
through Boscastle every second!
•Consultants HR Wallingford concluded in their technical study that land use
changes would have had little impact on the severity of the flooding in the
centre of Boscastle.
37. Longshore drift
Longshore drift is the movement of sediments, usually sand,
along a coast parallel to the shoreline.
Waves approaching the shore break in a region called the
surf zone. They carry sediment up the shore in a white,
frothy surge called the swash, and down again in the
backwash. When the swash approaches the shore at an
angle, it will carry and deposit sediment both up and along
the beach, but the backwash, acting under gravity, will
always carry and deposit its sediment perpendicular to the
shoreline, following the line of the steepest gradient. This
produces a zig-zag movement of sediment along the beach
known as longshore drift. Generally, the largest particles of
beach sediment are found updrift, closer to the sediment
source. The smallest sediment particles, those which are
most easily picked up and suspended by wave action, are
transported further downdrift before again being deposited.
38. The formation of a coastal spit
Spits are long narrow ridges of sand and shingle which project from the coastline into
the sea.
The formation of a spit begins due to a change in the direction of a coastline - the main
source of material building up a spit is from longshore drift which brings material from
further down the coast.
Where there is a break in the coastline and a slight drop in energy, longshore drift will
deposit material at a faster rate than it can be removed and gradually a ridge is built
up, projecting outwards into the sea - this continues to grow by the process of
longshore drift and the deposition of material.
A change in prevailing wind direction often causes the end of spits to become hooked.
On the spit itself, sand dunes often form and vegetation colonises (for example
Blakeney Point - North Norfolk)
Water is trapped behind the spit, creating a low energy zone, as the water begins to
stagnate, mud and marshland begins to develop behind the spit.
Spits may continue to grow until deposition can no longer occur, for example due to
increased depth, or the spit begins to cross the mouth of a river and the water removes
the material faster than it can deposited - preventing further build up.
41. Holderness
Location and Background
What processes are operating at Holderness?
What are the reasons why Holderness is subject to such a
rapid rate of erosion?
What management strategies have been
employed to protect the coastline?
Use the
video to
help fill
this in...
45. Development means improving the
economic and social conditions in a
country and the quality of life of the
people living there. It is more than wealth
as it includes such things as happiness
and the state of the environment.
55. Human Development Index
(HDI)
HDI is a way of combining different
indicators to come up with a more
rounded development level for each
country. It comprises:
• Life expectancy
• Education
• GDP
57. Types of Aid
• Bilateral aid
This is aid given from one country to another, in the form of
money, goods or services.
• Multilateral aid
This is aid which comes from several different countries - often
through international agencies such as the World Bank.
• Tied aid
is gifts of money, goods or services that come with conditions
attached. For example, the recipient country may have to agree to
spend the money in particular ways introduce specific economic
reforms allow companies from the donor country to set up or sell
goods in the recipient country spend the money on goods and
services from the donor country.
Both bilateral and multilateral aid may be tied in this way.
• Non-governmental aid
This comes from NGOs such as Save the Children, UNICEF and
Oxfam, which provide money and professional support paid for by
donations from members of the public across the world. This type of
aid is less likely to come with any conditions attached.
Tied aid is now illegal in the
UK following the UK funding
of a hydroelectric dam on the
Pergau River in Malaysia in
1991. The Malaysian
government bought around £1
billion worth of arms from the
UK at the same time.
58. Short-term or long-term aid?
Aid can also be either short-term or long-term.
Short-term aid deals with emergencies such as the tsunami that
devastated parts of Asia on Boxing Day 2004. Other disasters requiring
short-term aid are earthquakes, hurricanes, flooding, drought, and wars.
This type of aid brings immediate help to people - flying in food to prevent
starvation, tending the injured and sick, and trying to prevent the spread
of disease.
Long-term aid is required where problems are deep-rooted or cyclical.
For example, the climate in some parts of Africa means that drought
commonly occurs. This requires long term development to try to prevent
water shortages - for example sinking a well and providing a village with a
water pump so it can have permanent access to underground water.
Of course, many disasters that require short-term aid also need long-term
aid - for example, to rebuild houses and work-places that have been
destroyed, or to provide seeds to farmers so that food can be grown the
following year.
60. The Pergau
Dam, Malaysi
a
Tied aid is now illegal in the
UK following the UK funding
of a hydroelectric dam on the
Pergau River in Malaysia in
1991. The Malaysian
government bought around £1
billion worth of arms from the
UK at the same time.
64. Computers (Kenya)
Computers for Schools Kenya
Computers for Schools Kenya was established as a non-profit
organisation to facilitate the productive and sustainable use of
computers in education on a national level in Kenya's secondary
schools.
Since August 2002 Computers for Schools Kenya has installed over
3,000 high-quality, fully refurbished PCs into Kenyan state secondary
schools. Computers for Schools Kenya also advises upon and assess
the preparedness of each school's infrastructure and provides
ongoing timely technical support to recipient schools.
Who benefits?
The project will ensure an equitable balance of distribution between
rural and urban schools, girls and boys institutions and ensure the
inclusion of marginalised sectors, and schools for children with
disabilities.
Over the coming months Computer Aid International (through the
generous financial support of a UK trust) will provide 450
professionally refurbished Pentium 4 computers needed for this
project.
70. How do population structures differ within
countries?
The economically active are those people
in the 15 to 64 year age group. It is this
group of people who usually earn most
of the wealth for a region or town. Those
outside of this group are referred to as
the dependant population.
age
= 3 years
81. China‟s
one child
policy
History of the policy?
Incentives for having one
child
Where is China?
Penalties for having more than one
child
Success? Future of
the policy
Why does China need a
one child policy?
82. Western Europe –
Pronatalist policies
Much of western
Europe is
entering stage 5
of the
demographic
transition model
and there are
concerns about
ageing populations
or underpopulated
places.
85. Push and pull
Push Pull
Crime rates are high Low crime rates
No green spaces Open space
Poor quality schools Good quality schools
Difficult political
regime
Democracy
High unemployment Good jobs and wages
86. Mexico to USA
Why leave Mexico?
• Low standard of living
• Lack of skilled, well-paid
employment
• Few opportunities
• Lack of education
• Poor quality housing
• Poor health service
Why migrate to the USA?
• Many opportunities
• High standard of living (one of
highest in the world)
• Many job opportunities (well-paid
jobs)
• Education
• Excellent health care
• Search for the „American Dream‟
• Some characteristics of Mexico
and the USA
USA Mexico
Unemployment 7% 17%
People per
doctor
400 1800
GDP per capita $52,000 $10,000
School
attendance
99% 55%
87.
88. Factsheet
for Counter-
urbanisation
in the Chew
Valley
In the past part of the population worked in
coal mining, although there are no working
mines in the area now. There is still a fairly
large agricultural workforce and in light
industry or service industries, although
many people commute to surrounding cities
for work.
Chew Valley
School 5 A*-C =
70%
Bristol Schools 5
A*- C = 35.4%
Winford business park
takes advantage of the
space, access, attractive
working environment and
the local labour force.
Nearby Bristol
airport offers
easy access to
Europe and the
US for
business and
pleasure
Ashton Gate
park and ride
offers easy
access to
Bristol for
commuters
94. Greenwich
Millenium
Village
(GMV)
How is this development
sustainable?
Future of GMV – can we
learn from it?
Context statement/
Viewpoints
Positives Negatives
Basic facts of the
development
How has land use helped
make GMV ecological?
95. The recent history of
shopping in Bristol
Local
shops
The
Galleries
Cribbs
Causeway
Cabot
Circus
96. Low order goods
(convenience) don‟t
travel far, e.g. The Co-op
High order goods
(consumer) travel
further, e.g. The apple
shop
