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🌄 > 4c Rivers > Flashcards

4c Rivers Flashcards

1
Q

What is a drainage basin?

A

An area of land drained by a river and its tributaries

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2
Q

What is weathering and what are the three types?

A

Breakdown of rock by natural processes

- Biological, chemical and physical

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3
Q

What is physical weathering

A

free-thaw

- rainwater enters cracks and freezes, water expands and breaks rocks into the soil

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4
Q

What is chemical weathering

A

Acid rain reacts with the weak minerals and decays the rocks causing it to dissolve

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5
Q

What is biological weathering

A

Plant roots grow into the rock cracks and cause them to split apart

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6
Q

What is mass movement

A

Downward movement due to gravity

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7
Q

What is soil creep

A

Individual soil particles move slowly down the slope under the force of gravity and collect at the bottom of the valley
The river may erode this

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8
Q

What is slumping

A

Bottom of the valley is eroded by the river and the slopes become steeper and the material above slides downwards, rotating as it does so
- triggered by heavy rain and saturates overlying rock and makes it heavy and liable to slide

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9
Q

What is river erosion?

A

Water wearing away rocks and soils on the valley bottoms and causes it to slide

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10
Q

What is hydraulic action

A

When high velocity flows causes it to hit the riverbed and wears it away

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11
Q

What is abrasion

A

Material carried in the river rubs against the bed and banks of the channels and causes it to wear away
- abrasion causes the most erosion

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12
Q

What is solution

A

River water can dissolve some rocks and minerals

- limestone and chalk are the most affected

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13
Q

What is attrition

A

Sediment particles collide with each other

- become rounder and smaller downstream

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14
Q

What are the 4 transportation of load?

A

Deposition

  • river discharge decreases and heaviest material is deposited first
  • needs the least energy
  • traction, saltation, suspension, solution
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15
Q

What is traction?

A

Rolling of stones over the river bed

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16
Q

What is saltation?

A

Particles the size of sand grains bounce over each other

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17
Q

What is suspension

A

Silt sized particles carried in the river

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18
Q

What is solution

A

DIssolved minerals in the water

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19
Q

How do interlocking spurs form?

A
  • near the source the rivers are small so low power and mainly erode downwards
  • flow around the valley side slopes, called spurs
  • spurs left interlock
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20
Q

How do waterfalls and gorges form?

A
  • formed along the river when the band of hard, more resistant rock lies above the less resistant rock
  • river erodes less resistant rock at a faster rate and gradually undercutting more resistant rock
  • continued erosion of soft rock by abrasion and hydraulic action causes an overhang of hard rock
  • eventually, hard rock collapses due to gravity and abrasion erodes the river bed creating a plunge pool
  • soft rock keeps eroding and hard rock collapses and forms a steep sided gorge
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21
Q

Where to gorges mainly form?

A
  • hard rocks where vertical erosion by rivers in dominant
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22
Q

How do meanders form?

A
  • found in a river’s floodplain
  • water flow swings side to side - max. velocity and force of water is on the outside of the bend which causes lateral erosion by undercutting and forms an outer steepbank creating a river cliff
  • inside of the river bend has less velocity which leads of deposition and formation of gently sloping bank creating a slop off slope and the material deposited creates a point bar
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23
Q

Why is the cross section of a meander asymmterical?

A

The outisde is steep and the inside is gentle

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24
Q

How do oxbow lakes form?

A
  • meander bends more and the neck becomes narrower as the river erodes
  • deposition at the end of the neck seals off the bend
  • leaves a horse shoe shaped lake called an oxbow lake
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25
Q

How do flood plains form

A
  • flat area of land on either side of the river = formed
  • lateral erosion on the outside bends means they erode into the valley sides which are wide and flat and with less energy so the river deposits fine sediment
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26
Q

How do levees form?

A

They are natural embankments of sediment on both sides of the river bank which carry load and occasionally flood

  • flood water causes the sediment to come out as the river flows
  • overflows = the river loses velocity and energy and deposits larger and heavier sediment first on its banks
  • repeated flooding causes the banks to get even higher creating levees
27
Q

How are deltas formed

A

River reaches another body of water which causes it to lose its velocity and deposit sediment

  • river deposits cause coastal processes to erode it causing sediment to build up in layers called deltas
  • river splits into distributaries and creates large wetland areas
28
Q

What is a river’s long profile include?

A

The height and the distance downstream from the source of the mouth –> is in a curved shape and steeper near the source and flatter near the mouth

29
Q

What is the upper course of a river like?

A
  • steep gradient and mainly vertical erosion
  • V shaped valleys so steep slopes so lots of soil creep and mass movement
  • narrow channel and shallow
  • high turbulence so low river velocity
  • full of angular stones
30
Q

What is the middle course of a river like?

A
  • wider and deeper channel
  • lateral and vertical erosion
  • wide and flat valleys with gentle slopes creating floodplains
  • medium velocity
  • some deposition as less energy
  • softer rocks
31
Q

What is the lower course of a river like?

A
  • wide and deep river channel
  • highest river velocity due to low friction with the river bed
  • lateral erosion and transportation as high sediment load
  • very wide and almost a flat valley
32
Q

What is vertical erosion?

A

It deepens the valley making it more V shaped

  • dom in the upper course
  • more turbulence as it has rough angular particles which scrape along the river bed
33
Q

What is lateral erosion?

A

It widens the river valley/ channel and forms meanders

- dom in the lower and middle course

34
Q

How do you identify the upper course of a river in OS maps?

A
  • high nearby land
  • lots of contour lines crossed in a short distance
  • close contour lines
  • narrow valley floor and waterfalls and cliff marked nearby
35
Q

How do you identify the lower course of a river in OS maps?

A
  • low nearby land
  • river doesn’t cross many contour lines so gently sloping
  • meanders across a large flat area = floodplain
  • thick wide blue lines
  • large meanders so oxbow lake may be formed
36
Q

How does climate impact river landscape?

A
  • wetter so more discharge
  • more rate of erosion as more power
  • more load so V shaped valleys in upper course
  • wide flat floodplain so more transportation then more energy and weathering for sediment load
37
Q

How does geology impact river landscape?

A
  • rivers through resistant rock so less rate of erosion and as more resistant means there is low sediment load = steep valley sides
  • softer rock = more erosion and sediment load (gently sloping valley sides)
  • waterfalls = hard rock on top of softer rock
  • interlocking spurs = softer rock eroded first leaving areas of hard rock sticking out
38
Q

How do slope processes impact river landscape?

A
  • vertical erosion means that steep valleys means there are more mass movement
  • mass movement means that there is more material (more likely in cold due to freeze thaw) and more rainfall makes the ground less stable
  • soil creep = cause by expansion and contraction of soil (water adds weight to soil)= adds fine material to load
39
Q

What do hydrographs show?

A
  • peak discharge = highest (in cumecs)
  • lag time = delay between peak rainfall and discharge
  • rising limb = increases in discharge
  • falling limb = decrease in discharge as river returns to normal
40
Q

How can precipitation affect flooding?

A
  • more rain

- more discharge and lower lag time

41
Q

How can geology affect flooding?

A
  • impermeable rocks can’t absorb water

- there is more run off

42
Q

How can drainage basin type affect flooding?

A
  • small then rainfall reaches quicker and narrow basin water takes a long time to reach the channel
  • circular basins have more discharge and shorter lag time
43
Q

How can soil affect flooding?

A
  • more impermeable soil (clays) can’t absrob much
  • more run off
  • thin soil so saturated quicker or as if frozen soil so holds a little water
44
Q

How can sloped affect flooding?

A
  • if the soil is sleep = rapid run off as less infiltration
45
Q

How can vegetation affect flooding?

A
  • less vegetation means that there is run off as less interception to infiltrate water into soil
  • more flood if more deforestation
46
Q

How can urbanisation affect flooding?

A
  • water can infiltrate into the tarmac

- more runoff and gutters which drains quickly run off into rivers so there is more discharge

47
Q

How can antedecent conditions affect flooding?

A
  • wet/cold weather means mroe run off as frozen soil

- saturated soils?

48
Q

How long is the river Severn?

A

Longest river in the UK

- 354 km long

49
Q

What is the upper course of the river severn like?

A
  • source from the Welsh mountains
  • avg rainfall is 2500mm = high runoff
  • Mountains have hard impermeable shales and grits
  • narrow, shallow channel, angular stones, slow velocity, vertical erosion = V-shaped valleys with steep sided slopes
  • soil creep and mass movement happen
50
Q

What is the middle course of the river severn like?

A
  • towards Shrewbury
  • rainfall of avg 700mm
  • softer rocks have more permeable - sandstones, conlomerates and marts
  • wide and deep channel with vertical and lateral erosion = floodplain
  • deposition on the inside bends of meanders and flood plain when flooding
  • rounded and smaller sediments and more tributaries causes more discharge
51
Q

What is the lower course of the river severn like?

A
  • soft geology - mudstones and lias
  • wide channels in Tewsbury = 70m wide and deep
  • less friction and high velocity
  • more discharge and more sediment load means that there is more deposition as the river mouth
52
Q

Why did the river severn flooding happen?

A
  • settlements around such as Shrewsbury, Bewdley and Gloucester and resistant Welsh Mountains
  • July 2017 - highest rainfall in 100 yrs - 140mm in a few hours
  • series of depression across the UK due to the strong jet stream –> went south
  • confluence so lots of tributaries and more discharge and lots of V-shaped valleys
53
Q

How were bridging point settlemtns affected?

A
  • damage of £140,000 of local council
  • £20-£30,000 for each house
  • 48000 houses affected
  • £3.2bn in total taken
  • more population means there is more building ons the floodplain therefore more impereable surface
54
Q

Why is the flood risk increasing?

A
  • more population, land use change, climate change (changing weather patterns and jet steam bought more intense storms)
  • environment agency = reduces flood chance = land use, controlling development in flood plains and defences/ reduces impact = preparation and flood warning
55
Q

How is flood risk figured out in the river severn?

A
  • 1% annual probablity that flood puts 60,000 people and 29,000 businesses at risk
  • rural areas reduce run off by increasing floodwater storage
  • middle and lower = unsuitable development
  • urban areas = improve defence and protect buildings
56
Q

What are some ways of hard engineering?

A
  • Hard engineering involves building artificial structures which try to control natural processes
  • embankments (levees)
  • floodwalls
  • demountable
  • flood barriers/ storm surge barriers
57
Q

What are the advantages and disadvantages of Embankments?

A
  • high banks on river banks (low cost)
  • stop water spreading into settlements
  • earth and grass banks (blend w environment)
  • BUT - floodwater goes over top and is trapped behind and bursts under Pa = even more damage
58
Q

What are the advantages and disadvantages of Floodwalls?

A
  • artifical barriers to raise height of river banks to gold more water (more cost)
  • stops water from spreading into high impact areas
  • BUT expensive, may cause flooding downstream, not natural and may spoil the view
59
Q

What are the advantages and disadvantages of Demoutable flood barriers (temp)?

A
  • used where a permanent flood wall could act ugly and costs less
  • only used in specific locations and may be risks if not installed on time
60
Q

What are the advantages and disadvantages of Flood barriers or storm surge barriers?

A
  • floodgates near the mouth to prevent storm surge
  • closed in tide/ surge in a forecast
  • protects like areas from conditions of storm surges
  • high cost and regular maintenance
61
Q

What is soft engineering?

A
  • Soft engineering does not involve building artificial structures, but takes a more sustainable and natural approach to manage the coast
  • Flood plain retention and river restoration
62
Q

What are the advantages and disadvantages of flood plain retention?

A
  • restores the original floodplain (low cost)
  • restores soil structure floodplain
    BUT change of land use (farmland)
63
Q

What are the advantages and disadvantages of river restoration?

A
  • using a variety of strategies to restore the original course
  • more attractive and creates natural habitats and benefits the wildlife
  • BUT floodbanks are still needed but change in land use causes disadvantages

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