Rivers (4)

Question 1

What is the long profile of a river?

Answer 1

How the gradient changes over different courses of a river

Question 2

What is the cross-profile of a river?

Answer 2

What the cross-section of a river looks like

Question 3

How does the gradient change throughout the courses of a river?

Answer 3

Upper: steep

Middle: medium

Lower: gentle

Question 4

How does the valley and channel shape change throughout the courses of a river

Answer 4

Upper: V-shaped valley, steep sides. Narrow, shallow channel

Middle: Gently sloping valley sides. Wider, deeper channel

Lower: Very wide, almost flat valley. Very wide, deep channel

Question 5

What type of erosion happens in the Upper course of a river? + explain

Answer 5

VERTICAL erosion

• deepens the river valley (and channel), making it V-shaped
• high turbulence causes the rough, angular stones to be scraped along the river bed, causing intense downwards erosion

Question 6

What type of erosion happens in the Middle and Lower course?

Answer 6

LATERAL erosion

• widens the river valley (and channel) during the formation of meanders

Question 7

Describe the aspects and landscape of a river in the Upper course

Answer 7

• Typically, the source of a river is in areas with a high altitude and hard, resistant rock
• Valley is V-shaped and steep sided due to vertical erosion (steep gradient)
• River channel is narrow and shallow - low discharge (amount of water flowing)
• Low velocity due to high friction between the rough channel sides
• River carries large, angular stones

Question 8

Describe the aspects and landscape of a river in the Middle course

Answer 8

• Typically made from less-resistant rock, so the valley becomes wider due to lateral erosion
• Valley sides become gentle slopes and the gradient is less steep
• The river channel becomes wider and deeper, increasing discharge (more streams join river)
• Velocity increases as erosion makes the river bed smoother
• The sediment load is made up of smaller and more rounded rocks as erosion continues

Question 9

Describe the aspects and landscapes of a river in the Lower course

Answer 9

• Typically made from soft rock that is easily eroded (less-resistant)
• The valley is very wide and flat
• High velocity - very little friction from the channel’s smooth sides
• Large discharge because the channel holds more water (deeper) and other rivers can join
• The sediment load is fine and well-rounded

Question 10

Name the 4 processes of erosion and describe them

Answer 10

Hydraulic action: force of the water breaks rock particles away from the river channel

Abrasion: rocks scrape and rub against the channel, wearing it away

Attrition: rocks smash into each other and break into smaller fragments. Edges get rounded.

Solution: river water dissolves some type of rock eg. chalk and limestone

Question 11

Describe freeze-thaw Weathering (a type of mechanical weathering)

Answer 11

• Happens when temperatures fluctuates above and below 0C
• Water gets into the cracks of a rock. When the water freezes, it expands, putting pressure on the rock
• When the water thaws, it contracts, releasing the pressure on the rock
• Repeated freezing and thawing widens the cracks, causing the rock to break up

Question 12

Name and describe the 4 transportation processes

Answer 12

Traction: large boulders are rolled along the river bed by the force of the water

Saltation: pebble-sized particles are bounced along the river bed by the force of the water

Suspension: small particles are carried along by the water, suspended off the bed

Solution: soluble materials dissolved in the water are carried along

Question 13

What is deposition and when does it happen?

Answer 13

When a river drops the eroded material it’s transporting

It happens when a river loses velocity

Question 14

Why might the velocity of a river slow down?

Answer 14

• Volume of water in the river falls
• Amount of eroded material in the river increases
• Water is shallower (on the inside of a bend)
• The river reaches its mouth

Question 15

Which landforms would you find in the upper course of a river?

Answer 15

Waterfalls

Gorges

Interlocking Spurs

Question 16

How are Waterfalls formed?

Answer 16

(1) They form where a river flows over an area of hard rock, followed by an area of softer rock
(2) The softer rock is less resistant, so is eroded by hydraulic action and abrasion, creating a step in the river
(3) As water flows over, it erodes more and more of the rock
(4) A steep drop is eventually created, called a waterfall
(5) The hard rock is eventually undercut (becomes unsupported and collapses)
(6) Collapsed rocks are swirled around at the foot of the waterfall, eroding the softer rock by abrasion, creating a plunge pool
(7) Over time, the waterfall retreats, leaving a steep-sided gorge

Question 17

How are Interlocking Spurs formed?

Answer 17

(1) In the upper course of a river, vertical erosion creates V-shaped valleys
(2) The rivers aren’t powerful enough to erode laterally, so they wind around the hillsides
(3) The hillsides that interlock with each other as the river winds about them are called interlocking spurs

Question 18

How are Oxbow Lakes formed?

Answer 18

(1) Erosion causes the outside bends in the meander to get closer to each other
(2) Eventually, there will only be a small area of land between the bends (the neck)
(3) The river breaks through this land, typically during a flood
(4) The river will flow along the shortest course, ie. through the neck
(5) Deposition eventually cuts off the meander as it is slower here (less discharge)
(6) The Oxbow lake is formed

Question 19

How are Meanders formed?

Answer 19

(1) The current is faster on the outside of the bend as the channel is deeper (less friction)
(2) More erosion (hydraulic action + abrasion) happen at the bend, forming river cliffs
(3) The current is slower on the inside of the bend as the channel is shallower (more friction)
(4) More deposition happens on the inside of the bend, forming slip-off slopes

Question 20

Name some factors that Storm Hydrographs/Flooding risks affected by

Answer 20

• Geology: water can’t infiltrate through impermeable rock
• Drainage basin type: circular basins have a shorter lag time and higher discharge than narrow ones
• Antecedent conditions: previously wet conditions can increase runoff as soils are saturated
• Urbanisation: water can’t infiltrate through concrete/tarmac so there’s more runoff. Drains quickly take runoff to rivers, increasing discharge because water reaches the channel at the same time
• Deforestation: trees take up water from the ground and store it, reducing runoff. Loss of trees increases runoff and discharge

Question 21

Name the labels on a storm hydrograph

Answer 21

Peak discharge: highest discharge in the certain period of time
Lag time: delay between peak rainfall and peak discharge
Rising limb: increase in river discharge as rainwater flows into the river
Falling limb: decrease in river discharge as the river returns to its normal level
(Base flow)
(Peak rainfall)

Question 22

Why does lag time even happen?

Answer 22

Most rainwater doesn’t land directly into the river - there’s a delay as rainwater gets to the channel

Question 23

Why is the risk of flooding increasing in the UK (2 main factors)

Answer 23

Increased Storm Frequency
Land Use Change

Question 24

Why does Increased Storm Frequency lead to a higher risk of flooding in the UK?

Answer 24

(1) Frequency and intensity of storms is increasing, possibly due to global climate change
(2) More periods of wet weather makes the ground more saturated, making flooding more likely

Question 25

Why does Land Use Change increase the risk of flooding in the UK?

Answer 25

(1) As the population grows, the pressure to expand urban areas grows too (2) Leads to an increase in impermeable surfaces (eg concrete and tarmac) - more runoff (3) Removing vegetation means that water that would have been stored in the soil flows into the river

Question 26

State some examples as to how Flooding can threaten people

Answer 26

- People can be killed/injured by floodwater - Roads, bridges and rail lines can be destroyed - Floodwater is often contaminated (with sewage) which can lead to a lack of clean drinking water - People can be made homeless - Businesses may be forced to shut down due to flood damage, leading to a loss of livelihood

Question 27

Examples of how Flooding can threaten the Environment

Answer 27

- Farmland can be ruined by silt and sediment deposited after a flood - Floodwater contaminated with sewage can pollute rivers, damaging wildlife habitats - Force of floodwater can uproot trees - River banks are eroded, causing huge changes to the river landscape

Question 28

Name and explain the 2 types of Engineering used to reduce the effects of Flooding

Answer 28

Soft engineering: schemes set up using the knowledge of a river and its processes Hard engineering: man-made structures used to control river flow

Question 29

Name the 6 types of flood defences

Answer 29

Flood Walls Embankments Floodgates Flood barriers (demountable) Flood plain retention River restoration

Question 30

What are Flood Walls

Answer 30

Artificial barriers built along river banks, increasing their height, allowing the channel to hold more water However, they are very expensive and can be unsightly

Question 31

What are Embankments

Answer 31

High banks built along the river banks. They stop the river flowing into built-up areas. They can be made from earth or other natural materials. They are quite expensive and there is a risk of them breaking - leading to flooding

Question 32

What are Floodgates? (eg Thames Barrier)

Answer 32

Structures built on river estuaries to stop flooding from storm surges or high tides. They can be shut when there is a surge forecast to prevent flooding However, they are very expensive and need to maintained regularly

Question 33

What are Flood Barriers (demountable)?

Answer 33

Structures that provide temporary protection against flooding. The barriers are only put up when a flood forecast is put out, so there's a risk they may not even be put up in time. They are quite expensive, but do not ruin the aesthetics of an area

Question 34

What is Flood Plain Retention?

Answer 34

Involves maintaining the flood plain by not building on it. It helps slow floodwaters down by absorbing and storing the water. No money has to be spent, but it restricts development and can't be used in urban areas

Question 35

What is River Restoration?

Answer 35

Involves making the river more natural so that the flood plain can flood naturally. There's less risk of flooding downstream as discharge is reduced. Little maintenance required, however it can increase local flooding risk