River landscapes and processes

Question 1

What are the three courses of a river?

Answer 1

1. Upper course
2. Middle course
3. Lower course

Question 2

Characteristics of upper course?

Answer 2

1. Steep gradient
2. V-shaped valley
3. Steep sides
4. Narrow, shallow channel

Question 3

Characteristics of middle course?

Answer 3

1. Medium gradient
2. Gently-sloping valley sides
3. Wider, deeper channel

Question 4

Characteristics of lower course?

Answer 4

1. Gentle gradient
2. Very wide, almost flat valley
3. Very wide, deep channel

Question 5

What is the long profile of a river?

Answer 5

1. Shows you how the gradient changes over the different courses.

Question 6

What is the cross profile of a river?

Answer 6

1. Shows you what a cross section of the river looks like.

Question 7

How does verticle erosion alter the cross profile of a river?

Answer 7

1. Verticle erosion deepens the river valley and channel, making it v-shaped.
2. Verticle erosion is dominant in the upper course of a river.
3. High turbulence causes the rough, angular particles to be scraped along the river bed, causing intense downward erosion.

Question 8

How does latural erosion alter the cross profile of a river.

Answer 8

1. This widens the river valley and channel during the formation of meanders.
2. It is dominant in the middle and lower courses.

Question 9

Why is the upper course the way it is?

Answer 9

1. The valley is steep-sided due to verticle erosion and the channel has a steep gradient.
2. The river channel is narrow and shallow - this means discharge is low. The velocity is low due to friction from the rough channel sides and bed.
3. The river carried large, angular stones.

Question 10

Why is the middle course the way it is?

Answer 10

1. The river valley becomes wider due to lateral erosion.
2. The valley sides become gentle slopes and the gradient of the channel is less steep.
3. The river channel becomes wider and deeper.
4. Discharge increases as more streams join the river.
5. The river has a higher velocity as the channel sides are smoother, which leads to less friction.
6. The river’s sediment load is made up of smaller and more rounded rocks as erosion continues.

Question 11

Why is the lower course the way it is?

Answer 11

1. In the lower course, the valley is very wide and flat.
2. The river has a high velocity because there is very little friction from the channel’s smooth sides.
3. It has a large discharge due to more tributaries joining it.
4. The river channel is very wide and deep.

Question 12

Difference between slides and slumps?

Answer 12

1. In slides, material shifts in a straight line.
2. In slumps, material shifts with a rotation.

Question 13

How does geology influence river landforms?

Answer 13

1. Rivers flowing through areas of hard rock have a slower rate of erosion because hard rocks are more resistant, whereas areas with softer rocks will experience more erosion.
2. Landscapes with more resistant rocks tend to have steeper valley sides, landscapes with less resistant rocks tend to have gentle sloping valley sides.

Question 14

How is a waterfall formed?

Answer 14

1. Waterfalls form where a river flows over an area of hard rock followed by an area of softer rock.
2. The softer rock is eroded by hydraulic action and abrasion more than the hard rock, creating a ‘step’ in the river.
3. As water goes over the step it erodes more and more of the softer rock.
4. A steep drop is eventually created, which is called a waterfall.
5. The hard rock is eventually undercut by erosion. It becomes unsupported and collapses.
6. The collapsed rocks are swirled around at the foot of the waterfall where they erode the softer rock by abrasion. This creates a deep plunge pool.

Question 15

How is a gorge formed from a waterfall?

Answer 15

1. Over time, more undercutting causes more collapses. The waterfall will retreat and leave behind a steep-sided gorge.

Question 16

How are interlocking spurs formed?

Answer 16

1. In the upper course of a river most of the erosion is vertically downwards. This creates steep sided V-shaped valleys.
2. The rivers aren’t powerful enough to erode laterally - they have to wind around the spurs that stick out into their paths on either side.
3. These hillsides are often made of a resistant rock which the river can’t erode, so the river erodes the less resistant rock between the spurs as it winds down the valley.
4. The hillsides that interlock with each other as the river winds around them are called interlocking spurs.

Question 17

What is deposition?

Answer 17

1. Deposition is when a river drops eroded material
2. It happens when a river slows down

Question 18

What are meanders?

Answer 18

1. Rivers develop large bends called meanders in their middle and lower course, in areas where there are both shallow and deep sections in the channel.

Question 19

How are meanders formed?

Answer 19

1. The current is faster on the outside of the bend because the river channel is deeper. (Less friction to slow the water down)
2. So the outside of the bend is a high-energy environment, meaning more erosion take splace there, forming steep sided river cliffs.
3. The inside of the bend is a low energy environment. The current is slower there because the river channel is shallower (more friction)
4. So eroded material is deposited on the inside of the bend.
5. Over time, this material builds up to form a point bar - a crescent shaped gentle slope made of sand or stones.

Question 20

How are ox-bow lakes formed?

Answer 20

1. Erosion caused the outside bends to get closer.
2. Eventually there’s only a small bit of land left between the bends called the neck.
3. The river breaks through this land, usually during a flood.
4. The river continues to flow along the shortest course.
5. Deposition eventually cuts off the meander.
6. This forms an ox-bow lake.

Question 21

What is a flood plain?

Answer 21

1. Thr flood plain is the wide valley floor on either side of a river which occasionally gets flooded.

Question 22

How is a flood plain made?

Answer 22

1. river floods onto the flood plain, the water slows down and deposits the eroded material that it’s transporting –> builds up flood plain
2. Meanders migrate across the flood plain, making it wider
3. Meanders also migrate downstream, flattening out the valley floo
4. Deposition that happens on the point bars of meanders -> builds up the flood plain.

Question 23

How are leeves formed?

Answer 23

1. Leeves are natural embankments along the edges of a river channel
2. During flood, eroded material deposited over whole flood plain
3. Heaviest material deposited closest to river channel because its dropped first when river slows down
4. Over time the deposited material builds up creating leeves along the edges of the channel.

Question 24

How does climate (rainfall) influence river landscapes?

Answer 24

1. higher discharge –> more water entering the channel
2. Higher discharge increases the rate of erosion - higher volume of water -> more power to erode river banks and beds -> adds material to the rivers load.
3. Shapes the landscape - forms V-shaped valleys in river’s upper course and wide, flat flood plain in the lower course
4. Transporation increases when river has higher discharge because more energy to carry material
5. Chemical weathering increases -> Carbonation and dissolution weathering can happen when rainwater comes into contact with minerals that make up the rocks in the river valley -> valley sides more unstable

Question 25

How does climate (temperature) influence river landscapes?

Answer 25

1. During winter temperatures often drop below freezing, especially at night -> more freeze-thaw weathering 2. In summer higher temperatures speed up the rate of chemical reactions -> chemical weathering increases 3. This can affect the shape of a river landscape as weathering means mass movements such as rockfalls become more likely, because it loosens material on the valley sides

Question 26

How can storms affect river processes and landscapes?

Answer 26

1. Storms bring heavy rainfall -> ground becomes saturated - makes it heavier and more unstable. Mass movement more likely, river banks my slide or slump into the river channel 2. Heavy rain flows quickly over the surface and into a river and the streams that feed into it -> volume of water increases rapidly 3. High volume of water increase transportation of material by the river -> more erosion by abrasion and hydraulic action - particularly in the upper course 4. Increased volume and velocity of the river can cause it to break through the neck of a meander -> eventually meander cut off forming an ox-bow lake 5. Floods caused by storms also build up the flood plain and form leeves

Question 27

How can droughts affect river processes and landscapes?

Answer 27

1. Water volume in river drops 2. Less erosion occurs -> lower discharge means less energy -> less able to pick up and transport material 3. Mass movement less likely to take place -> land is dry

Question 28

How are river processes affected by urbanisation?

Answer 28

1. Urban areas -> lots of impermeable surfaces - water can't infiltrate into these surfaces- so when it rains -> increased runoff -> gutters and drains quickly take runoff to rivers -> rapidly increases volume of water in river 2. more rainwater gets into a river in shorter time-> more energy -> increases erosion and transportation 3. In urban areas, rivers are often managed to reduce the risk of flooding - river defences can cause major changes to the rivers landscape

Question 29

How are river processes affected by agriculture?

Answer 29

1. Irrigation may involve taking water from a river. A reduction in the amount of water in a river decreases its ability to erode and transport material, and it may deposit material instead 2. Ploughing of farmland exposes soil, allowing it to be washed away into rivers when it rains. This gives rivers a larger sediment load, which leads to more deposition occurring downstream 3. Farmland may have drainage systems that remove water from the soil and move it into rivers. After heavy rainfall, these cause water to move more quickly into a river, increasing its discharge and temporarily causing higher rates of erosion

Question 30

How are river processes affected by industry?

Answer 30

1. Just like urbanisation, industry leads to move impermeable surfaces, which increases runoff into rivers 2. Air pollution from factories and vehicles can make rainwater more acidic, which results in more chemical weathering 3. Dredging for industry creates deeper channels, allowing large boats to fit. This means the river has a faster flow and higher energy for erosion. It also reduces the likelihood of flooding 4. Boats' motors disturb the water, which can lead to increased erosion

Question 31

How does prolonged rainfall increase the risk of flooding?

Answer 31

1. After a long period of rain -> soil becomes saturated 2. This means any further rainfall can't infiltrate, which increases runoff into rivers 3. This increases discharge, so flooding is more likely

Question 32

How does heavy rainfall increase the risk of flooding?

Answer 32

1. Heavy rainfall means the water arrives too rapidly for infiltration, so there's a lot of runoff 2. This increases discharge quickly, increasing the risk of a flood

Question 33

How does relief increase the risk of flooding?

Answer 33

1. Relief is the change in the height of the land 2. If a river is in a steep-sided valley, water will reach the river channel much quicker because water flows quicker on steeper slopes 3. Discharge increases rapidly, increasing the flood risk

Question 34

How does geology increase the risk of flooding?

Answer 34

1. Clay soils and some rocks are impermeable 2. This means they dont allow infiltration, so runoff is increased 3. When it rains, discharge increaes quickly, which can cause a flood

Question 35

How does building increase the risk of flooding?

Answer 35

1. Buildings are often made from impermeable materials and surrounded by impermeable roads 2. Impermeable surfaces increase runoff and drains quickly take runoff to rivers, quickly increasing discharge so there is a greater risk of flooding

Question 36

How does deforestation increase the risk of flooding?

Answer 36

1. Vegetation intercepts rainwater 2. Plants also take up water from the soil which allows more rainwater to infiltrate instead of surface runoff 3. When vegetation is removed, there is less interception and infiltration - more surface runoff 4. This increases discharge and makes flooding more likely

Question 37

How does flooding affect people?

Answer 37

1. People may be killed or injured 2. Floodwater is often contaminated with sewage, which can lead to a lack of clean drinking water 3. Posessions can be damaged or washed away 4. People can be made homeless as their properties are damaged 5. Electrical supplies can be cut off leaving homes and businesses without power for several days 6. Businesses may have to shut down leading to a loss of livelihood 7. Transport links can be affected

Question 38

How does flooding affect the environment?

Answer 38

1. Contaminated floodwater can pollute rivers, damaging wildlife habitats 2. Farmland can be ruined by silt and sediment 3. River banks are eroded, causing huge changes to the river landscape 4. The force of floodwater can uproot trees and plantsa, and standing floodwater may cause those that survive the initial wave of water to die

Question 39

What is lag time of a hydrograph?

Answer 39

1. The delay between peak rainfall and peak discharge

Question 40

Advantages and disadvantages of dams?

Answer 40

1. Reservoirs store water, especially during periods of pronlonged or heavy rain, reducing the risk of flooding. The water in the reservoir can be used as drinking water and to generate hydroelectric power 2. Dams are very expensive to build, and creating a reservoir can flood existing settlements. Eroded material is deposited in the reservoir and not along the rivers natural course. This means farmland down stream can become less fertile, and the formation of some depositional landforms may be slowed down or prevented

Question 41

Advantages and disadvantages of channelisation?

Answer 41

1. Channelisation reduces flood risk because deeper or wider channels can hold more water. With a straighter channel, watrer moves out the area more quickly. This is because it doesnt have to travel around meanders 2. Concrete beds and banks reduce the friction between the water and the channel, increasing the water velocity so water moves out of the area more quickly 3. Flooding may happen downstread instead, as water is carried their faster. The water is also flowing faster downstream, which may speed up the formation of erosional landforms

Question 42

Advantages and disadvantages of flood plain zoning?

Answer 42

1. It is a cheap strategy that reduces the risk of flooding - impermeable surfaces aren't created. The impact of flooding is also reduced as their arent and buildings to damage 2. However, the expansion of an urban area is limited if there are no other suitable building sites. Its no help in areas that have already been built on

Question 43

Advantages and disadvantages of washlands?

Answer 43

1. Washlands store more water when river discharge is high, which reduces the flood risk in areas wh ere floods could cause a lot of damage 2. Washlands can also provide a wetland habitat for many rare species, and they arent expensive 3. However, these areas can then not be used for anything else