river processes

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What do rainstorms do to a river?

-increase the rivers energy

-allow it to carry large boulders

-these wear away the rivers channel. which is why erosion is done during periods of wet weather

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how a river carries its load?

-suspension=tiny particles of sediment carried along the river bed

-soulotion=dissolved chemicals carried along the river bed

-saltation=smaller stone and pebbles are picked up then dropped down again in a skipping motion

-traction- large boulders are carried along by the river

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how does a river erode its channel

abrasion- sand and pebbles are dragged along by the river bed, which wear it away

attrition- pebbles and stones knock into one another which wear eachother away

soulotion- alkaline rocks such as limestone are weared away by acidic rain

-hydraulic aciton- where fast flowing water gets into cracks and break away the bank over time

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why do water falls form at the upper course

this is because here most erosion is done vertically downwards, so when the river meets hard ro resistant rock a step is formed and this eventually becomes a water fall. the river gains a great deal of energy as it goes over the lip of the water fall, allowing it to erode rapidly

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how are waterfalls formed?

1 when a river meets less resitant rock, it erodes and is a continuous process. The rivers enerfy creates a plunge pool

2less resistant rocks underneath is redoed by abrasion and hydraulic action creating a ledge and collapses

3 the water fall continues this process and takes up a new postition leaving behind a gorge

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how are v shaped valleys formed

- the river cuts between two steep sides, causing interlocking spurs


-once rock is broken up it falls down the steep sides,some move quickly.

LAND SLIDES- do not happen much in uk, but have happened on rail way tracks and along cliffs

SOIL creep- 2cm a year, slow process


biological weathering- small cracks in the rocks allow plants roots to get in as are trying to dearch for water. As they grow the rocks break

physical weathering- when its cold, the cracks within the rocks freexe, which expand the rocks and make them break; this is known as freeze thaw. These pieces then become scree at the bottom of the cliff

chemical weathering- rain water mixes with c02 to form weak acids which dissolve alkaline rocks

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what affects the shape of a valley?

-speed of weathering

-speed of mass movement

-how quickly a river can remove material from mass movement


- the river will take material away and erode the valley, making it steeper


-it can not cope with the material so therefore weathered rock collects at the bottom of the slope making valley gentler and flatter

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what happens to a river at its middle course

- several streams have joined it making it wider and deeper

-gradient is more gentle but rivers discharge has increase (amount of water flowing in a river)

-velocity has increased due to less friction, meaning it erodes laterally which creates meanders

- this changes the shape of the valley to a u shape not a v

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what happens at a flood plain?

-food plain is an area designed to flood

-when the flooding has dried up, fine sands and clay are brought down by the river stream, which then create ALLUVIUM layers, which farmers love because ALLUVIUM creates fertile soils

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HOW do meanders change the valley?

MEANDER- river bend, they are natural rivers in the middle courde which do not travel in a straight line. the water flows in a roller coaster loop pattern called helical flow

the helical flow makes the river erode laterally, the fast current uner cuts the bank producing a river cliff which collapses.  This continues making it change position

The helicial flow moves sediment across the channel which it deposits it here. Which makes the river channel get bigger forming a flood plain

continued erosiom happens amd creates a narrow neck between two meanders, eventually the neck becomes breeched creating a oxbow lake

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what are leeves

-form beside a river bank, where it first floods. This is where clay and sand build up and for alluvium

- they also have man made rivers which are built by engineers to protect farms and towns from flooding

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how does surface run off happen

trees intercept rain water and some water drips of leaves into soil called infiltration. Eventually the soil becomes saturated and can no longer take in anymore water. So the rain flows over land as surface run off. This happens if

-rain is heavy

-impermable soil and rocks are presenet

-how much rain has fallen recently


-some is taken up by plans and transpired through leaves in the atmosphere

-some continues into solid rock and saturates it. This water then seeps slowly towards the river and keeps it flowing when there is no rain

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what caused the flooding in sheffield

1 prolonged rain- 190 mm of rain fell in 2 days

2 soil was saturated after the rain fall, all drains were overwhelmed, so water ran off to river as ground flow

3 the river joins many other rivers such as river loxely which increased the volume making flooding more likely

4 steep hills, caused many water run offs


- drains blocked due to surface run off

- fallen trees blocked river channells

-football stadium flooded

-families had to be moved into caravans, people were ill because of raw sewage

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impacts on sheffield

- meadown shopping centre flooded causing millions of pounds of stock damage

-m1 was closed fro two days

-20 people air lifted

-two people drowned

-1200 homes flooded

-13,000 people without power

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soft scheme management

planting trees, which intercept water

flooding proofing new building by changing design or creating new buidlings, which can be expensive

flood plain zoining- not building on flood plains which can phase out development

flood prediction and warning- monitor rivers to help reduce flood damage by working out whee it will flood

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