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Geography > River Processes And Pressures > Flashcards

River Processes And Pressures Flashcards

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1
Q

What characteristics would you find in the upper course of a river?

A
  • gradient- steep
  • discharge- small
  • depth- shallow
  • channel shape- narrow/steep sides
  • velocity- quite fast
  • valley shape- steep sides
  • features- waterfalls, interlocking spurs
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2
Q

What characteristics would you find in the middle course of a river?

A
  • gradient- less steep
  • discharge- large
  • depth- deeper
  • channel shape- flat, steep sides
  • velocity- fast
  • valley shape- flat with steep sides
  • features- meanders, floodpains
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3
Q

What characteristics would you find in the lower course of a river?

A
  • gradient- shallow
  • discharge- very large
  • depth- deep
  • channel shape- flat floor, gently sloping sides
  • velocity-very fast
  • valley shape- flat with gently sloping sides
  • features- meanders, floodplain, levees, ox-bow lakes
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4
Q

What is a ‘long profile’ of a river?

A

A river long profile shows the shape of the river’s course from source to sea. It shows the changing width, depth and gradient of the channel downstream.

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5
Q

what is corrosion?

A

rocks forming the banks and bed of a river are dissolved by acids in the water

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6
Q

what is hydraulic action?

A

the sheer force of water hitting the banks of the river and breaking it up

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7
Q

what is attrition?

A

material is moved along the bed of a river, collides with other material and breaks up into smaller pieces

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8
Q

what is abrasion?

A

rocks carried by the river, smashing into the river bed and banks, wearing them down

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9
Q

what are the 3 main types of weathering that shape river valleys?

A
  • Freeze-thaw - In the cold winter months, when rain water enters a crack in a rock and freezes, the freezing process exerts pressure on the rock eventually causing it to break into smaller pieces.
  • Biological - Tree roots can penetrate cracks in rocks and split them apart
  • Chemical - All rainwater is slightly acidic and this can dissolve some rocks, especially limestone and chalk.
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10
Q

what are the main forms of mass movement? How do they affect valley sides?

A
  • Soil creep - Particles of soil slowly move down the sides of valleys due to gravity
  • Slumping - The river erodes the valley sides making them steeper and increasing the downward movement of material. Heavy rainfall can trigger this movement.
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11
Q

how is a waterfall formed?

A

1) where rivers flow over bands of rocks with different resistance, the softer rocks will be eroded more quickly, creating a step which gradually becomes deeper.
2) eventually the overhanging resistant rock will collapse, making the waterfall steeper. If this happens repeatedly, the position of the waterfall moves upstream, known as retreat.
3) The water flows down over the resistant rock but when it reaches less resistant rock underneath, it erodes it, cutting back into the rock and creating the overhang above.
4) At the foot of the waterfall is a plunge pool(area of deeper water that has been created by the rapid erosion of the soft rock as the waters plunge down) The higher the waterfall, the greater the speed of erosion due to the higher speed the water is travelling at.

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12
Q

how are ‘river cliffs’ formed?

A

in a meander, the river swings from side to side and the force of it doing so directs the fastest current and greatest force of water against the outside of the meander, forming a steep bank called a river cliff.

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13
Q

how is a ‘slip off slope’ formed?

A

On the inside edge of the meander, the current is slower and deposition of sand takes place, creating a gently sloping bank called a slip-off slope.

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14
Q

how is an ‘ox-bow lake’ formed?

A

1) narrow neck of land is eroded
2) narrow neck of land is cut through and water takes quickest route.
3) an ox-bow lake is formed.
4) deposition seals off old meander and ox-bow lake begins to dry up.

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15
Q

what are causes of river flooding?

A
  • heavy rainfall
  • impermeable rocks
  • snow melt
  • deforestation
  • urbanisation
  • climate change
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16
Q

what were the effects of the flooding in Boscastle?

A
  • 90% of economy dependent on tourism
  • more than 20 accommodation providers shut down
  • people had to be winched to safety from helicopters
  • cards, boulders + trees strewn around streets
  • cars swept to sea, bridges washed away
  • 4.5million pounds spent on new flood defences
17
Q

what is lag time?

A

the time between the heaviest rainfall and maximum level of the river on a hydro-graph

18
Q

what are some factors that cause rivers to flood?

A
  • a steep-sided channel - a river channel surrounded by steep slopes causes fast surface run-off.
  • a lack of vegetation or woodland - trees and plants intercept precipitation (ie they catch or drink water). If there is little vegetation in the drainage basin then surface run-off will be high.
  • a drainage basin, consisting of mainly impermeable rock - this will mean that water cannot percolate through the rock layer, and so will run faster over the surface.
  • a drainage basin in an urban area - these consist largely of impermeable concrete, which encourages overland flow. Drains and sewers take water quickly and directly to the river channel. Houses with sloping roofs further increase the amount of run-off.
19
Q

how can human activities increase flood risk?

A
  • laying down large amounts of cement for channels, paths, and roads, cement stops the rain from being absorbed into the ground so it runs off
  • deforestation-trees are vital in prevent flooding because of evaportranspiration
20
Q

what are hard engineering options to control floods?

A
  • embankment or levee: stops flood water from spreading, expensive, may burst or may go over
  • deepening and/or straightening of the river(dredging), water flows away more quickly, delays flooding, may be a scar on the landscape(unattractive)
  • dam built upstream: able to regulate and control the flow of water, expensive, can burst
  • Relief channel: takes overflow water, expensive, disruptive and complex to build
21
Q

what are soft engineering options to control floods?

A
  • washlands: cheap, water can go somewhere without causing much damage, can be used for special habitats
  • plant trees (afforestation): the trees reduce the amount of water reaching the river and the time it takes to do so, provides wildlife habitats, land cannot be used for anything else
  • planning: building restricted to areas with a low risk of any flooding, may cause planning problems elsewhere
  • flood warning system: prepare people, sometimes it is not possible to give people enough warning

Geography (18 decks)

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