Paper 2: River Processes and Pressures

Question 1

What are the 3 sections of a river?

Answer 1

Upper course, middle course, lower course

Question 2

What are some key features of the upper course of a river?

Answer 2

• The source of the river
• Lots of little tributaries
• Thin and shallow
• Lowest volume of water
• Slow rate of water travelling due to friction
• Not much erosion due to slow water

Question 3

What are some key features of the middle course of a river?

Answer 3

• Rounder in shape and deeper
• Higher volume of water
• The area around it is often a floodplain

Question 4

What are some key features of the lower course of a river?

Answer 4

• The mouth of the river
• Deep and wide
• Has levees (build up of sediment on its banks)
• Less friction and so faster rate of water travelling
• More erosion due to fast water
• The most deposition happens here

Question 5

What are the 4 river transportation processes?

Answer 5

• Solution
• Suspension
• Saltation
• Traction

Question 6

What is solution?

Answer 6

Chemicals are dissolved in the river water

Question 7

What is suspension?

Answer 7

Particles and small rocks are light enough to float within the water

Question 8

What is saltation?

Answer 8

Pebbles and small rocks which are too heavy to be suspended bounce along the river bed

Question 9

What is traction?

Answer 9

Large rocks are rolled along the river bed

Question 10

What is river deposition?

Answer 10

The dropping of the river’s load when the water decreases in speed

Question 11

What landforms are found in the upper course of the river?

Answer 11

Erosion is the predominant river process
- Waterfalls
- Interlocking spurs
- V-shaped valleys

Question 12

What landforms are found in the middle course of the river?

Answer 12

Mixture of erosional and depositional landforms
- Gorges
- Meanders

Question 13

What landforms are found in the lower course of the river?

Answer 13

Deposition is the predominant river process
- Floodplains
- Ox-bow lakes
- Estuary

Question 14

How are interlocking spurs formed?

Answer 14

These are found in the upper course of the river where the water doesn’t have a lot of energy so isn’t very powerful. The low energy means the water isn’t strong enough to erode resistant rocks in the spur. Instead, the river re-routes and curls around them.

Question 15

How are waterfalls formed?

Answer 15

1. In an area where a river flows over an area of hard rock and soft rock, the soft rock erodes more quickly
2. The soft rock erodes away around
   the hard rock over time
3. The soft rock continues to erode, undercutting the hard rock - The hard rock is left suspended in the air as an overhang - The rotational movement of the water quickens erosion, creating a deep plunge pool.
4. Due to the force of gravity, the unsupported overhang collapses - The broken up rocks fall into the plunge pool, which act as tools for erosion and further deepens the plunge pool
5. This repeats, causing the waterfall to retreat upstream

Question 16

What is a gorge?

Answer 16

As the waterfall retreats upstream, it leaves a steep valley carved into the rock with the river running along the base

Question 17

How are meanders formed?

Answer 17

1. Water travels faster on the outside of the bend which means lateral erosion takes place here - This leaves a river cliff, as material falls into the river and gets transported downstream
2. On the opposite side the water travels slowly and changes direction sharply and so the water loses energy and deposits sediment
3. Erosion wears away a cliff on the outer edge of a bend and deposition creates a
   slip-off slope on the inside of the bend

Question 18

What is the thalweg?

Answer 18

The path of fastest water in the river

Question 19

How is an ox-bow lake formed?

Answer 19

1. The river has meanders that form depending on the speed of the water
2. Erosion happens when the fastest water hits the sides of the meander, whereas deposition occurs on the inside of the bend, where the water is slowest
3. Gradually, erosion bends the river so that the meanders travel towards each other
4. The neck of the meander will eventually break (normally due to a flood), creating a straight river and a bend where water is slow if not stationary
5. The old meander becomes separated from the main river as material gets deposited at the top, creating the separate ox-bow lake

Question 20

What’s a levee?

Answer 20

A ridge of sediment naturally deposited on the bank of the river

Question 21

What is an estuary?

Answer 21

The open mouth of the river where it meets the sea

Question 22

What are the human factors that increase the flood risk?

Answer 22

• Urbanisation - Increasing the amount of
  impermeable surfaces (concrete and tarmac, for example) decreases the time taken for water to flow into the river, and so increases the risk of flash flooding
• Deforestation - Trees intercept the rain and so it takes longer for the rain to travel through the leaves into the river - Therefore, cutting down trees will speed up the time taken for rainwater to flow into the river, increasing the risk of flash flooding
• The capacity of the river - If the river becomes filled with rubbish and debris, the channel’s size will decrease - This means the river can carry less water and so is more likely to flood

Question 23

What are the physical factors that increase the flood risk?

Answer 23

• The rate and volume of rain (precipitation) falling - If there is a storm, and a large amount of rain falls in a short amount of time, the amount of water running into the river is increased - This increases the risk of flash
  flooding downstream
• Geology - If the area has many impermeable rocks, the rainwater can’t run into the soil and into underground storage - The rainwater runs straight into the river, increasing the risk of flash flooding on bad weather days
• Topography - The shape of the land will
  determine how quickly rainwater flows into the river - Steep hills with high gradients are more likely to have flash floods than gradual gradient

Question 24

What’s a storm hydrograph?

Answer 24

They represent the variation in the river’s discharge (volume of water) within a short period

Question 25

What are the features of a storm hydrograph?

Answer 25

• Peak Precipitation - The maximum rainfall that occurs, shown as bar charts at the start of the graph
• Rising limb – The increase of river discharge, not necessarily straight after precipitation
• Peak flow - The maximum discharge, delayed after maximum precipitation has occurred
• Lag time – The time delay between peak rainfall and peak river discharge
• Falling limb – As the storm precipitation levels decrease, river discharge will in turn decrease over time
• Base flow – Eventually, the discharge returns to its normal level

Question 26

What happens if a drainage basin isn’t managed?

Answer 26

There is a risk of flooding
- Damaged properties
- Farmers could lose crops or livestock
- Industries may become flooded so people lose their jobs

Question 27

What are the soft engineering strategies for rivers?

Answer 27

• River channel restoration (Concrete structures are replaced with natural sediment)
• Wetlands (Vegetation is planted)

Question 28

What are the hard engineering strategies for rivers?

Answer 28

• Dams (Concrete blockades in the river can regulate river pressure)
• Embankments and flood walls (Banks of the river are built up in concrete to increase the channel capacity)
• Dredging (Rubbish and sediment are dug up from the river bed)
• Channel straightening and flood relief channel (The river is straightened)

Question 29

What are some positives of river channel restoration?

Answer 29

• More natural resources and concrete discouraged
• The natural environment benefits

Question 30

What are some negatives of river channel restoration?

Answer 30

• Land will still flood

Question 31

What are some positives of wetlands?

Answer 31

• Store river water and can flood when needed
• Creates habitats for river life

Question 32

What are some negatives of wetlands?

Answer 32

• Takes a long time for them to grow

Question 33

What are some positives of dams?

Answer 33

• Valves can control water and release the right amount to avoid flooding
• Can generate electricity

Question 34

What are some negatives of wetlands?

Answer 34

• Not visually appealing
• Villages can be flooded to create the reservoir

Question 35

What are some positives of embankments and flood walls?

Answer 35

• Reduces lateral erosion so the river doesn’t grow wider
• Protects properties on the river front

Question 36

What are some negatives of embankments and flood walls?

Answer 36

• Looks unatrual and destroys habitats along the river bank

Question 37

What are some positives of dredging?

Answer 37

• Widens the river channel and removes pollution
• Doesn’t alter the look of the river
• Cheap

Question 38

What are some negatives of dredging?

Answer 38

• Takes time to complete
• Must be done regularly

Question 39

What are some positives of channel straightening and flood relief channel?

Answer 39

• Reduces flooding risk since water flows downstream
• Protects villages by directing water away

Question 40

What are some negatives of channel straightening and flood relief channel?

Answer 40

• Expensive
• Disruptive of natural habitats

Question 41

What can people/the local council to to try and prepare for flooding?

Answer 41

• Putting sandbags in doorways
• Temporary flood barriers can be put up
• Valuable possessions moved upstairs
• Roads can be closed