Rivers AS geography

what happens the the water balance in wet seasons
precipitation exceeds evapotranspiration creating a water surplus.
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what happens to the water balance in the dry seasons
precipitation is lower than evapotranspiration so there is a water deficit
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what is peak dishcharge
when the river discharge is at its greatest
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what is lag time
`the delay between peak rainfall and peak discharge
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what is the rising limb
when the river discharge is increasing as rain water flows into the river channel
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what is the falling limb
discharge is decreasing because of less water in the channel
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what physical factors affect river discharge
relief // size of the drainage basin // previous rainfall // rock type // vegetation // intensity of the precipitation // temperature
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what human factors affect river discharge
deforestation // urbanisation // drainage systems
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what are the 5 erosional processes in a river
hydraulic action // abrasion // attrition // cavitation // corrosion
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what is hydraulic action
the pressure of the water breaks rock particles away from the bed and the banks of the river channel it is strongest in rapids and waterfalls
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what is abrasion
eroded pieces of rock in the water scrape and rub against the bed and banks removing material. most common form of erosion
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what is attrition
eroded rocks smash into each other and break into smaller fragments rounding off the edges. it does not erode the bed and the banks
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what is corrosion or solution
the dissolving of rock by chemical processes.
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what are the 4 methods of transportation in a river
solution // suspension // saltation // traction
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what is solution (transportation)
substances that can dissolve are carried along in the water
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what is suspension
very fine material such as silt or clay particles are whipped up by the turbulence and carried along in the water
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what is saltation
pebbles and geravel are too heavy to be carried so instead the force of the water causes them to bounce along the river bed
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what is traciton
very large particles e.g. boulders are pushed along the river bed by the force of the water
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what is the long profile
it shows the gradient of the channel from the source to the mouth by showing the height of the river bed above base level.
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what is the long profile of the upper stage
steep gradient // high above sea level // lots of potential energy
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what is the long profile of the middle stage of a river
gradient decreases // potential energy is converted to kinetic energy // river gains velocity
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what is the long profile of the lower stage of a river
little potential energy // lots of kinetic energy // shallow gradient // closer to sea level
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what are the processes in the upper course of the river in terms of erosion, transportation and deposition
mainly vertical erosion and abrasion // mainly large material are carried by traction or saltation // little deposition
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what are the processes in the middle course of the river in terms of erosion, transportation and deposition
mainly lateral erosion with abrasion and some attrition of larger particles that decrease in size // more material carried by suspension some larger particles move by saltation // sand and gravel are deposited across the floodplain when rivers flood
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what are the processes in the lower course of the river in terms of erosion, transportation and deposition
less erosion though mostly lateral // mainly smaller particles are transported carried by suspension or solution // smaller particles such as sand are deposited on the floodplains and in the mouth
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what is the cross profile of the upper course
steep V shape // narrow valley floor // steep sided slopes
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what is the cross profile of the middle course of the river
wider valley // deposition created floodplains on the valley shore // gentle sloping valley
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what is the cross profile of the lower course of the river
very wide valley // gently sloping sides // much wider floodplain
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how do waterfalls form
there a band of hard then soft rock / the soft rock is eroded quicker causing a step / the water speed up due to lack of friction eroding the soft rock more to undercut the hard rock / a deep pool is made by abrasion / the hard rock collapses /
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what are pot holes
small circular hollows in the river bed.
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how are potholes formed
they are due to abraision when the turbulence swirls a river's bedload round in a circular motion causing them to rub and scrape out potholes
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what are rapid and how are they formed
relatively steep sections of river with turbulent flow where there are several sections of hard rock.
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what is braiding and how is it formed
when rivers are carrying a lot of eroded sediment / if the velocity drops sediment is deposited in the channel / causing the river to divide up into small winding channels and then return together
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what are levees and how are they formed
natural raised embankments formed when the river overflows its banks / during a flood material is deposited across the whole floodplain due to increased friction / the heaviest material deposited closest to the channel / it' the build up on the banks
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what are deltas and how are they formed
when the river reaches the sea it loses energy / the river deposits its load / this partly blocks the mouth of the river / the river has to braid into several distributaries to reach the sea
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what is rejuvination
when the base level is lowered, this can be caused by either the ground level rising or the sea level dropping
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physical factors that increase the risk of flooding
sparse vegetation / time of year (deciduous trees) / large drainage basin / steep relief / previous rainfall / rock type
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human factors that increase the risk of flooding
urbanisation / deforestation / flood management strategies failing eg dam failure / agriculture / climate change
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what is magnitude frequency analysis
refers to the size of the flood and how often it will occur in order to predict the return period of a flood event on a particular scales by looking at past occurrences
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physical causes of the south asia flood
monsoon climate - a lot of rainfall within a short time period / melting snow on the himalayas / 90% of land in bangladesh is less than 10m above sea level / saturated soil
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what are the human causes of the south asia floods
deforestation in nepal / increased urban areas / collapsed old earth dams
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social impacts of south asia floods
over 2000 people died / 25 million made homeless / 100,000 people caught waterborne diseases / 4000 schools affected 44 destroyed / 112,000 homes destroyed
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economic impacts of the south asia floods
$1 billion worth of damage / debt increased individually and nationally / loss of livestock / increased unemployment due to destroyed factories
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environmental impacts of the south asia floods
deposited fertile silt into floodplains / rivers polluted with sewage and rubbish
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what are the physical causes of the carlisle floods
lots of rainfall on january 6th meant ground was already saturated / large drainage basin / steep relief
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human cause of the carise floods
urbanisation leading to impermeable surfaces / drains overflowed leading to 25% of the problems
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social impacts of the carlisle floods
3 people died / 44 schools damaged / increased stress related ilness/ over 3000 made homeless for up to a year
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economic impacts of the carlisle floods
cost £100 million / 70,000 addresses without power inc. the police and fire station / 350 businesses had to close / united biscuits had £5 million of damage and had to fire 33 employees / 80 buses destroyed
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environmental impacts of the carlisle floods
increased river bank erosion / rivers polluted with sewage and rubbish
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positives of the 3 gorges dam
reduced flooding from once every 10 years to onces every 100 years , produces 3% of china's power / creates a renewable energy source / safer to navigate up the yangtze increasing shipping
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negatives of the 3 gorges dam
2 million had to relocate / 1300 sites of cultural interest lost / habitats lost e.g. baiji dolphin / increased flooding along tributaries / traps sediment
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soft engineering strategies at abingdon
gravel soakaways along the A34, low value land is allowed to flood / permeable tarmac in tesco car park / new housing developments have to have improved drains / flood warning system and flood wardens / planting trees along the thames and ock
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what is channel straightening
meanders are removed by building artificial cut throughs making the water flow faster reducing flooding as it moves quickly downstream
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what are diversion spillways
channels that take the water elsewhere if the water levels are too high usually to divert around an important area.
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Other cards in this set

Card 2

Front

what happens to the water balance in the dry seasons

Back

precipitation is lower than evapotranspiration so there is a water deficit

Card 3

Front

what is peak dishcharge

Back

Preview of the front of card 3

Card 4

Front

what is lag time

Back

Preview of the front of card 4

Card 5

Front

what is the rising limb

Back

Preview of the front of card 5
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