What is the path of a river as it flows downhill called?
course
What are the three sections of any river
upper, middle, lower courses
What do rivers form as they flow downhill?
channels, valleys
How do rivers change the shape of the landscape?
Erosion, followed by deposition of eroded sediment
What is the changing shape of the valley/channel dependent on?
whether erosion/deposition is prevalent
What does the long profile of a river tell you?
The changing gradient of the river
What does the cross profile of a river tell you/
The cross-section of that particular point in the river
Describe the characteristics of a river in its upper course.
steep gradient, v-shaped valley, steep sides, narrow, shallow channel
Describe the characteristics of a river in its middle course.
medium gradient, gently sloping valley sides, wider, deeper channel
Describe the characteristics of a river in its lower course.
gentle gradient, very wide, almost flat valley, very wide, deep channel
What does vertical erosion do?
deepens the river valley and channel
Where is vertical erosion dominant?
upper course
What does lateral erosion do?
widens river valley and channel
Where is lateral erosion dominant?
middle/lower courses
What are the four processes of erosion?
hydraulic action, abrasion, attrition, solution
What is hydraulic action?
force of water breaks rock away from the river channel
What is abrasion?
eroded rocks in river load rub away the channel
What is attrition?
rocks in river load smash against each other and break
What is solution?
river water dissolves certain types of rock e.g. chalk, limestone
When does erosion happen more?
when the river flows faster
What are the four processes of transportation?
traction, saltation, suspension, solution
What is traction?
large rocks are pushed along river bed by force of water
What is saltation?
smaller rocks are bounced along river bed by force of water
What is suspension?
small particles are carried along suspended by the water
What is solution?
soluble particles are dissolved and carried along by the water
What is deposition?
when a river drops some of its load (eroded material it's transporting)
Why does deposition happen?
because the river slows down
What are four reasons a river may slow down?
1. volume of water falls
2. load increases
3. shallower water (e.g. inside of bend)
4. river reaches mouth
What are meanders?
bends in river
Where are there lots of meanders?
Mississippi River
How are meanders formed?
deeper water on outside bend- faster current: erosion forms river cliffs
shallower water on inside bend- slower current: deposition forms slip-off slopes
How are oxbow lakes formed?
meander becomes more pronounced until the neck between two bends is very small- swan's neck meander
river breaks through in flood and follows shortest course
deposition cuts off meander
Where are waterfalls formed?
Where a river flows over hard rock followed by soft rock
How are waterfalls formed?
soft rock erodes more than hard rock- a 'step' is created in river
over time, soft rock eroded even more and step becomes very big- waterfall
How are gorges formed?
hard rock from waterfall is eventually undercut by erosion- collapses
hard rock swirls around under waterfall and erodes river bed- forming plunge pool
more undercutting->more collapses: waterfall retreats- steep gorge formed
How is a flood plain formed?
when rivers flood they deposit material- flood plain built up
meanders migrate across floodplain and make it wider
deposition on meander slip-off slopes also builds up flood plain
How is a levee formed?
during flood, eroded material is deposited over whole flood plain
heaviest material deposited closest to the river as it's dropped first when river slows down
deposited material builds up
Where are there lots of natural levees?
Yellow River, China
What is river discharge
volume of water flowing in a river: the amount of water to pass a given point per second
What is river discharge measured in?
cumecs: cubic meters per second
What does a hydrograph show?
the changing discharge of a river over a given timespan
What is the highest discharge called?
peak discharge
What is the delay between peak rainfall and peak discharge called?
lag time
What is the time when river discharge is increasing called?
rising limb
What is the time when river discharge is decreasing called?
falling limb
What is surface run-off?
water flows quickly overland to reach river channel
What is infiltration?
water soaking into the ground and flowing slowly into the river
What are the six ways river discharge can be affected?
amount and type of rainfall, temperature, previous weather conditions, rock type, land use, relief
How does the amount and type of rainfall affect river discharge?
lots of rain/short heavy rain = more run-off
lag time is decreased so discharge increased
How does temperature affect river discharge?
hot/dry conditions and cold/freezing conditions cause hard ground
increases run-off: lag time decreased so discharge increased
How does previous weather conditions affect river discharge?
lots of rain, ground becomes saturated
rain cannot infiltrate
lag time decreased so discharge increased
How does rock type affect river discharge?
PERMEABLE ROCK- water can infiltrate: lag time increased, discharge decreased
IMPERMEABLE ROCK- water cannot infiltrate: lag time decreased, discharge increased
How does land use affect river discharge?
Impermeable materials+drainage systems= more run-off: decreased lag time, increased discharge
How does relief affect river discharge?
lots of run-off occurs on steep slope: lag time decreased, discharge increased
What is a flood?
when the river level gets so high, that the water spills over the banks
What is a flash-flood?
a flood that happens without warning
What are four physical factors that lead to flooding?
prolonged rainfall, heavy rainfall, snowmelt, relief
How does prolonged rainfall lead to flooding?
prolonged period of rain, soil becomes saturated
further rainfall cannot infiltrate, increased run-off
lag-time reduced, discharge increases quickly, FLOOD
How does heavy rainfall lead to flooding?
lots of run-off, lag-time reduced, discharge increases quickly, FLOOD
How does snowmelt lead to flooding?
snow/ice melts, lots of water into river in little time
discharge increased quickly, FLOOD
How does relief lead to flooding?
steep-sided valley, water reaches river faster
increases discharge quickly, FLOOD
What are two human factors that cause flooding?
deforestation, building construction
How does deforestation cause flooding?
trees intercept rainwater which evaporates
trees take up water in roots and store
cutting down trees increases amount of water reaching river channel
How does building construction cause flooding?
impermeable materials increase run-off, reducing lag time and increasing discharge
Name and date a flood wwhich took place in a rich part of the world.
Carlisle, England
8th Jan 2005
River Eden
Name and date a flood which took place in a poor part of the world.
South Asia (Bangladesh/India)
July/Aug 2007
Rivers Brahmaputra and Ganges
What were the causes of the Carlisle flood?
heavy rainfall- 200mm 36 hours
urban area- impermeable ground
discharge reached 1520 cumecs (usually 52 cumecs)
What were the primary effects of the Carlisle flood?
3 deaths
3000 people made homeless
4 schools severely flooded
350 businesses shut down
70,000 addresses lost power
some roads/bridges damaged
rivers polluted with rubbish/sewage
What were the secondary effects of the Carlisle flood?
children lost out on education- school closed for months
stress-related illnesses
3000 jobs at risk as businesses were affected by floods
What were the immediate responses to the Carlisle floods?
evacuation from flooded areas
reception centres set up with food/drink for evacuees
temporary accommodation
What were the long-term responses to the Carlisle floods?
community groups set up for emotional/practical support
flood defence scheme- build up river banks of Eden
What were the causes of the floods in South-East Asia?
heavy/continuous rainfall- 900mm in July
melting snow from Himalayas into Brahmaputra
peak discharge of two rivers happened at the same time, increased discharge downstream
What were the primary affects of the floods in South East Asia?
over 2000 deaths
25 million made homeless
44 schools totally destroyed
factories closed, livestock killed
112,000 houses destroyed in India
10,000 kilometres of road destroyed
rivers polluted with rubbish/sewage
What were the secondary effects of the floods in South East Asia?
children lost out on education- 4000 schools affected
100,000 people caught water-borne diseases
flooded fields reduced rice crop- prices rose by 10%
farmers and factory workers unemployed
What were the immediate responses to the floods in South East Asia?
people didn't evacuate- flooded/blocked transport slowed any evacuation
international governments/charities distributed food/water/medical aid
boats sent to rescue those stranded
What were the long-term responses to the floods in South East Asia?
international charities funded rebuilding of homes+agriculture/fishing industries
some homes rebuilt on stilts
What is hard engineering?
man-made structures built to control the flow of rivers and reduce flooding
What is soft engineering?
schemes set up using knowledge of a river and its processes to reduce the effects of flooding
Which areas of the UK have lots of rain?
North and West
Which areas in the UK have high population densities?
South East and Midlands
Where in the UK is there a water deficit?
South East and Midlands
What is water deficit?
demand higher than supply
What is water surplus?
supply higher than demand
Where in the UK is there a water surplus?
North and West
Why is demand for water in the UK increasing?
water usage has gone up by 50%
predicted population increase- 10 million over next 20 years
What is a way of managing a water supply?
transfer water from an area of surplus to an area of deficit
What is an example of transferring water from an area of surplus to an area of deficit?
Wales->Birmingham
What are the disadvantages of water transferal?
dams/aqueducts are expensive
could affect wildlife (fish migration patterns)
political issues (people don't want their water given to another country)
How do you increase water supplies?
build reservoirs to store water
What are the disadvantages of reservoirs?
building can involve flooding settlements/relocating people
How could you ensure that less water is lost through transfer?
fix leaky pipes
How can people reduce the demand for water at home?
showers instead of baths
running washing machines only when full
not using hoses
How can water companies reduce the demand for water?
install water metres so that people are more aware of the water they use
Where is Rutland reservoir?
East Midlands, near Peterborough
When was Rutland reservoir built?
1970s
How big is Rutland reservoir?
12km squared
How is Rutland reservoir filled?
River Welland, River Nene
Why was Rutland reservoir built?
to supply East Midlands with enough water to combat population growth in towns such as Peterborough
What are areas around the reservoir used for?
nature reserve, recreation
What are the economic impacts of the reservoir?
boosts local economy as tourist attraction
6km squared of land flooded to create- farmland destroyed, farmers lost their livelihood
What are the social impacts of the reservoir?
recreational activities for locals
jobs created
schools can use for visits
two villages demolished
What are the environmental impacts of the reservoir?
it is an SSSI (site of special scientific interest) for wildlife protection
provides habitat for birds- Ospreys have been reintroduced there
provides variety of habitats for many different organisms
large area had to be flooded- destroyed many habitats
What is a sustainable water supply?
having the water you need today without stopping people from the future from having enough
How can a reservoir be used in a sustainable way?
only take as much water out as the river puts in