River Processes Flashcards

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1
Q

effect of headward erosion

A

makes the river longer.
happens near a rivers source as throughflow and surface runoff causes erosion at the point the water enters the river channel (the valley head)

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2
Q

effect of vertical erosion

A

deepens river channels

happens in the upper stages of a river

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3
Q

effect of lateral erosion

A

makes the river wider

happens in the middle and lower stages of a river

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4
Q

5 ways in which erosion can occur

A
hydraulic action
abrasion/corrasion
attrition
cavitation
corrosion/solution
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5
Q

what is hydraulic action

A

pressure of water breaks rock particles away from the bed and banks - its strongest in rapids and waterfalls and during floods

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6
Q

what is abrasion

A

eroded pieces of rock in the water scrape and rub against the bed and banks, removing material. most erosion of river beds and banks happens by abrasion

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7
Q

what is attrition

A

eroded rocks smash into each other and break into smaller fragments
their edges also get rounded off as they rub together
attrition doesn’t erode the bed and banks - it just makes the particles of rock in the river smaller and more rounded

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8
Q

what is cavitation

A

air bubbles in turbulent stretches of water implode causing shockwaves that break pieces of rock off the banks and bed

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9
Q

what is corrosion/solution

A

the dissolving of rocks by chemical processes
carbon dioxide dissolves in water to form a weak acid which reacts with rocks like limestone and chalk, breaking them down

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10
Q

4 types of transportation

A

solution
suspension
saltation
traction

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11
Q

what is solution

A

substances that dissolve are carried along in the water - e.g limestone is dissolved in water thats slightly acidic

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12
Q

what is suspension

A

very fine material, like silt/clay particles, is whipped up by turbulence (erratic swirling of water) and carried along in the water. most eroded material is transported this way

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13
Q

what is saltation

A

larger particles, like pebbles/gravel, are too heavy to be carried in suspension. instead the force of the water causes them to bounce along the river bed

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14
Q

what is traction

A

very large particles, e.g boulders, are pushed along the river bed by the force of the water

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15
Q

material transported by traction/saltation is called

A

the rivers bedload

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16
Q

how can the speed and energy of a river be reduced (5)

A
  1. reduced rainfall causes lower discharge, which means the river slows down and has less energy
  2. increased evaporation or abstraction also causes lower discharge
  3. friction e.g in shallow areas close to the banks, reduces speed of river, reducing energy
  4. when the river is forced to slow down, e.g before a narrow section of the channel, it loses energy
  5. a lot of energy is lost when the river meets the sea (the sea absorbs the energy)
17
Q

what is the capacity of a river

A

the total load (measured in volume, weight or mass) that a river can transport at a given point
the load of a river can be divided into diff categories according to particle size - sizes range from fine silt/clay (less than 0.1mm diameter) to big boulders

18
Q

what does the competence describe

A

the maximum particle size that a river is capable of transporting at a given point

19
Q

what does the Hjulstrom curve show

A

relationship between river velocity and competence

also shows how processes of erosion, deposition and transportation vary with river velocity

20
Q

what is the critical erosion velocity curve

A

shows the minimum velocity needed for the river to put up (erode) and transport particles of diff sizes
it takes a higher velocity to erode material than it does to just transport material

21
Q

what does mean settling velocity curve show

A

the velocities at which particles of diff sizes are deposited. i.e it shows the competence of the river at diff velocities