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8/6/2019 GSCE Geography Rivers
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In the upper course therivers cross section is narrowand in a deep V shape,because erosion is mainly downwards as it is fastflowing because the gradientis high. The material carriedhere is large.
In the middle and lowercourse, the river becomes
wider and the river is slowermoving as the gradient isless. This means thaterosion is mainly lateralthan downwards. The rockscarried are smaller due toattrition and the fact thatthe river is slow and unableto move large rocks. More
deposition occurs here.
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Interlocking spurs: when the river winds around hard rock, it forms cliffs thatinterlock
When the water flows
over hardrock then
soft rock, it
will erodethe soft rock
faster by hydraulicpower andCorrasion,forming a waterfall.
The waterfall
willeventually
undercutthe softerrock and theoverhang of
the hardrock will
eventually collapse.
When the water hits
the plungepool, someof it retreatsupstream,forming a
gorge.
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Here, the gradient becomes lesssteep and erosion is more lateralthan downwards, so the rivertransports more material. It doesthis in four ways:
Traction: large boulders run alongthe river bed
Saltation: smaller pebbles arebounced along the river bed.
Suspension: the finer sand and siltlike material is carried in the water
Solution: minerals like limestoneare dissolve in the water and are
carried along.
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A meander is a bend in ariver.
The water is deeper and
flows faster on the outsidebend of the river.
The force of the watererodes the outside bend
forming a river cliff.
The water is shallower andflows more slowly on the
inside of the bend.
Sand and gravel that theriver no longer has the
energy to carry isdeposited on the inside of
the bend forming a slip off slope.
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H ydraulic power and Corrasionerode the OUTSIDE bends of a
meander, as the water flows fasterthere.
Deposition occurs on the SLIP OFFSLOPES, because the river flowsslower here.
This makes the neck of the meandernarrower and narrower until eventually it is broken through, normally when theriver is in flood as it has extra energy.
The river then flows along the straightpath as it is quicker. The meander is
sealed off by deposition to form an ox-bow lake.
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Definition: leveesare natural
embankments of silt along the banksof the river. Thereare many naturalones on the banksof the Mississippi.
When the river floodsit pours over the banks
and onto thefloodplain. The water isslowed by friction and
the larger coarser
material is depositedfirst but the finer
material travels furtheraway.
During dry weatherthe speed falls,
causing deposition.
The channelbecomes full of silt, which makes the
bed rise.
A fter many floodsthe river banks havelevees and the river
bed maybe raisedup so much that theriver rises above the
floodplain.
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A delta is a flat area of sand and silt builtout into the sea. It is found at the mouthof the river.The area around a delta is gradually filled in
with sediment and becomes dry land.
Deposition forces the river to split up into several
distributaries (a smaller river leaving a larger one).
This deposited sediment builds up over years,creating a delta.
A s the river reaches the sea the sea acts as a break and the riverslows down, dropping its sediment. The salt from the sea alsomakes the salt and sand particles stick together.
The river needs to be carrying a large load and the seaneeds to be sheltered without strong winds and
currents.
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The river tees is mainly used for
Forest fruits round trees:
Farming (mainly sheep farming)
Forestry Reservoirs. Tourism
Large towns
with:
Shops Offices Farmland IndustriesFlood
defences
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R un off: TR un off: The water that runs down hills into rivers.he water that runs down hills into rivers.Impermeable rocks:Impermeable rocks: Rocks that do not allow water to pass throughRocks that do not allow water to pass through
The causes of riverflooding:
Heavy rain overlong periods
Heavy snowfallsthat melt
Impermeable rocksmake the water run
off quicker
Rivers that have littleplant or tree cover
around are more likely to flood, because thesecan absorb some of the
rain.
Urban areas causeflooding, the concreteand tarmac cause therainwater to run off quicker into rivers.
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Wh y doesBangladesh
flood?
Deforestationmeans less
absorption of water
Heavy rainfalldue to monsoon
climate
Snow melts on theHimalayas, flowing
down to the rivers.
Cyclones (violentstorms)
frequently hit
Describe theeffects of a flood
in an LEDC.
Bangladesh 1998
1 million people were lefthomeless.
240 villages wereflooded.
Over 1000 people were killed.
Supplies of foodand water ran low
Diseases spread
1 billion dollars
worth of damagedone
How did it manage a flood disaster?
�Distribute food
�Provide fresh water and sanitation supplies
�The aid agencies provided boats to rescuepeople
Bangladeshsuffers fromflooding nearly every year, butthe floodwaterbring with themfertile silt, whichdoes make thearea good forfarming.
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Theeffects of a flood inan MEDC
TheMississippi river in
1993
28 peopledied
36,000peoplemade
homelessR oads and
railwaysunder water
Electricity lines
collapsed
Farmlandflooded
10 billiondollars
needed to
repairdamage.
The Mississippi river. (DA RTS)
D- dams andreservoirs
were built on
the tributary rivers
reducing thequantity of
waterreaching themain river
A -afforestation
to absorbmore water
R- reroutingthe river,
shorteningthe river andallowing the
water totravel away
quicker
T-tallerlevees
S-spillways-overflowchannels
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The building of levees or
embankments
Huge damsbuilt
Storage basinsto take in waterdiverted fromthe main river
A fforestation
Floodforecasting and
warningschemes
Improved floodshelters
Less technologies tofight floods in
LEDCs
No early warningsystems
Less medical andrescue services
They need the goodfarmland to growcrops to survive
Cannot afford tomove