Topic 4: Rivers

Question 1

Discharge

Answer 1

The volume of water flowing in a river, measured in cubic metres per second.

Question 2

Velocity

Answer 2

The speed of a river, measured in metres per second.

Question 3

Load

Answer 3

Material carried by the river.

Question 4

Upper course

Answer 4

• Resistant rocks
• Steep
• Narrow and allow
• Slow velocity and low energy
• Inefficient
• Low load
• Large load
• Traction and saltation in times of high flow (when energy increases)
• Narrow and V-shaped
• Waterfalls and V-shaped valleys

Question 5

Middle course

Answer 5

• Becoming less resistant rocks
• Becoming more gentle
• Getting wider and deeper
• Increasing velocity and energy
• Becoming more efficient
• Increasing load
• Smaller size of load
• Less saltation and traction. More suspensions and solution.
• Getting wider and flatter
• Meanders and floodplains develop

Question 6

Lower course

Answer 6

• Less resistant sedimentary rocks
• Almost flat land
• Wide and deep channel
• Very fast flowing (less friction)
• Very efficient
• Load is high
• Small size load
• Suspension
• Wide, flat floodplain
• Oxbow lakes, floodplains, levees, deltas

Question 7

Why velocity increases going downstream?

Answer 7

It is more efficient because there is less friction so energy increases.

Question 8

Named example: The River Seven

Answer 8

• The source is on the slopes of Plynlimon, Wales
• Runs through Shrewsbury and Gloucestershire
• Hard more resistant rock (sedimentary) to clay at the end
• The mouth is in the Bristol Channel.

Question 9

River landforms:
Upper course

Answer 9

1) Waterfalls
2) V-shaped valleys

Question 10

Waterfalls

Answer 10

• Bands of hard rock and soft rock, and overtime soft rock gets exposed to the water and eroded.
• The soft rock is being undercut and wears away.
• Overhang becomes unstable.
• Plunge pool is formed.
• Rock is eroded through hydraulic action and abrasion.
• This repeats and gets deeper.

Question 11

V-shaped valleys

Answer 11

• Valleys are formed by vertical erosion when the river is in bank full conditions.
• This means it has lots of energy due to high discharge and therefore efficiency.
• The bedload transported by traction and saltation causes abrasion on the channel bed.
• The valley sides are not vertical due to weathering and mass movements.

Question 12

Interlocking spurs

Answer 12

Fingers of land that potrude into the river and restrict the view down the valley. Forms when river doesn’t have enough energy to erode more resistant rocks so diverts around.

Question 13

Meanders

Answer 13

• River velocity varies in the river channel.
• Erosion will be happening on the outside of the bend through hydraulic action and abrasion where it’s fastest and deepest.
• Deposition will happen on the inside of the bend where it’s slowest and friction is highest.
• On the outside of the bend river cliffs will form.
• On the inside of the bend a slip of slope/river beach will form.
• Meanders continue to grow
• River increases its sinuosity (bends/curves)

Question 14

Oxbow lakes

Answer 14

• Meanders become so large and tight that they are nearly touching.
• In times of flood, the fast flowing water erodes a more efficient channel and breaks through the land between a meander.
• Sediment is then deposited between the new river channel and the meander.
• The meander is cut off and eventually drys up.

Question 15

Levees

Answer 15

• In times of flood eroded material is deposited.
• Thickest and heaviest sediments is deposited first closest to the river channel.
• Thin and fine sediments deposited after,
• Over time deposited material builds up creating levees along the edges of the channel after a flood.

Question 16

Deltas

Answer 16

• Rivers are forced to slow down when they meet the sea or a lake causing them to deposit material.
• This forms many channels (distributaries) if it’s not washed away.

Question 17

Transportation types

Answer 17

1) Traction
2) Saltation
3) Suspension
4) Solution

Question 18

Traction

Answer 18

Heavy boulders are rolled along the river bed.

Question 19

Saltation

Answer 19

Smaller rocks are bounced along the river bed.

Question 20

Suspension

Answer 20

Fine sediment is picked up, suspended (floating) and carried along the river course.

Question 21

Solution

Answer 21

The finer sediment is dissolved as it travels in the river.

Question 22

What factors increase surface runoff and mean a river is more likely to flood?

Answer 22

• Urban areas
• Deforestation
• Large amounts of rainfall
• Waterlogged soil and frozen soil
• Frozen ground
• Hard rock
• Steep mountains
• Narrow drainage basin

Question 23

What factors encourage more infiltration and mean a river is less likely to flood?

Answer 23

• Rural areas
• Forested areas
• Little rainfall
• Dry soil
• Mild conditions makes ground permeable
• Soft less resistant rock
• Flat land
• Circle drainage basin

Question 24

Hydrograph

Answer 24

Show how fast rainfall gets to the river.

Question 25

Flashy hydrograph

Answer 25

• Short lag time
• High peak discharge
• Steep rising limb
• Rainfall reached river quickly
• More likely to cause flooding

Question 26

Subdued hydrograph

Answer 26

• Long lag time
• Low peak discharge
• Gentle rising limb
• Rainfall reached river slowly
• Less likely to cause flooding

Question 27

River Wey Woking:
Significance of situation

Answer 27

• Confluence with the Thames
• River Wey at Old Woking
• Confluence at Tilford to form the main river Wey
• 2 sources. Alton and Haselmere

Question 28

Causing of flooding in Woking?

Answer 28

• Urbanisation
• Global climate change
• The Jet Stream moved, causing more rain (high level wind that blows west to east across Northern Hemisphere)
• Deforestation

Question 29

Impacts of flooding in Woking?

Answer 29

• Damaged homes
• Money needed to repair damage

Question 30

Why is flood risk increasing?

Answer 30

• Increase in storm frequency and severity
• Global warming - changes to weather patterns
• Urbanisation is causing urban sprawl which means less green space so more impermeable surfaces.

Question 31

Hard engineering techniques to mitigate flood risk?

Answer 31

• Flood walls
• Flood barriers
• Embankments

Question 32

Positives and negatives on flood walls?

Answer 32

+ One off cost
+ Increases channel capacity
- Disperse water quickly and so can cause flooding downstream
- Not natural looking

Question 33

Positives and negatives on flood barriers?

Answer 33

+ Can protect large areas
+ Gates can open and close when a storm surge is forecasted
- High cost and need regular maintenance

Question 34

Positives and negatives of embankments?

Answer 34

+ Stop flooding in places of high economic value
- Water may go over the top and get trapped

Question 35

Soft engineering techniques to migrate against flood risk?

Answer 35

• River channel restoration
• Flood plain retention

Question 36

Positives and negatives of river channel restoration?

Answer 36

+ More natural, improves ecology
+ Meanders being rebuilt, slows done water (reduces flooding)
+ Less risk of flooding downstream because discharge is reduced
- Can increase local flood risk

Question 37

Positives and negatives of flood plain retention?

Answer 37

+ Increased ability to store flood water
+ Restored to grassland, so retain and release water slowly
- Restricts development
- Can’t be used in urban areas