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Geography A Paper 1 Flashcards > River Landscapes > Flashcards

River Landscapes Flashcards

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1
Q

Physical Processes 1

A

Two of the physical processes that shape a river landscape are weathering and mass movement.

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2
Q

Weathering Processes

A

Weathering is the wearing away in situ of the river valley sides. There are three weathering processes common to river valleys. Mechanical, Chemical and Biological.

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3
Q

Mechanical (freeze-thaw) Weathering

A
  1. Water fills a crack or joint in the rock
  2. Water freezes and the crack is widened
  3. Repeated freeze-thaw action increases the size of the crack until the block of rock breaks off.
  4. Loose block of rock are called scree.
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4
Q

Chemical (acid rain) Weathering

A

Rainwater is slightly acidic. The acid reacts with minerals in the rocks and dissolves them. For example, granite contains feldspar, which is converted into soft clay minerals as a result of a chemical reaction with water.

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5
Q

Biological Weathering

A

Roots grow into cracks and split rocks apart.
Acids released by vegetation speed up chemical weathering.

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6
Q

Mass Movement

A

Over time, the sides of a river valley become less steep as material is moved from the top to the bottom. 2 types of mass movement is sliding and slumping.

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7
Q

Sliding

A

Where rock, weathered or eroded material or Earth moves down on a slope. Gravity pulls the weakened material quickly downwards.

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8
Q

Slumping

A

Where the river erodes the bottom of the valley slope, making it steeper. Material above slides downwards, particularly if it is saturated with rainwater.

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9
Q

Physical Processes 2

A

Erosion, transport and deposition are also physical processes that shape a river landscape.

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10
Q

Erosion

A

Hydraulic action - the force of the water on the bed and banks of the river removes material.
Attrition - the load that is carried by the river bumps together and wears down into smaller, smoother pieces.
Solution - some rock minerals dissolve in river water (e.g. calcium carbonate in limestone).
Abrasion - material carried by the river rubs against the bed and banks and wears them away.

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11
Q

Transport

A

Transport is the way in which the river carries eroded material or load.
There are four main types of transportation: traction, saltation, suspension and solution.

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12
Q

Traction

A

Large boulders are rolled along the sea bed.

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13
Q

Saltation

A

Smaller pebbles are bounced along the river bed, picked up then dropped as the river flow changes.

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14
Q

Suspension

A

Finer sand and silt particles are carried along in the flow, giving the river a brown appearance.

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15
Q

Solution

A

Some minerals, such as chalk, are dissolved in the water and carried along in the glow, although they cannot be seen.

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16
Q

Explain how a river will transport eroded material.
(2 marks)

A

One way a river can transport eroded material is through traction. This is where the river’s flow rolls large boulders along the river bed.

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17
Q

River Valley Changes

A

Rivers, and the valleys they flow in, change in different ways between their source (where they start) and their mouth (where they join the sea).

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18
Q

River Profile

A

A river’s long profile shows the height and distance downstream from the river’s source to its mouth. It is a curved shape, steeper near the source and flatter near the mouth.

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19
Q

Upper Course

A

Gradient - steep
Discharge - small
Depth - shallow
Channel shape - narrow, steep sides
Velocity - quite fast
Valley profile - steep sides
Features - waterfalls, interlocking spurs
Sediment size and shape - angular bolders

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20
Q

Middle Course

A

Gradient - less steep
Discharge - large
Depth - deeper
Channel shape - flat, steep sides
Velocity - fast
Valley profile - flat with steep sides
Features - meanders, floodplain
Sediment size and shape - more rounded rocks

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21
Q

Lower Course

A

Gradient - shallow gradient
Discharge - very large
Depth - deep
Channel shape - flat floor, gently sloping sides
Velocity - very fast
Valley profile - flat with gently sloping sides
Features - meanders, floodplain, levees, ox-bow lakes
Sediment size and shape - smooth, rounded pebbles

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22
Q

Explain one difference between the shape of a river valley in its upper and lower course.

A

In the upper course, the river valley has steep sides due to the river eroding downwards, whereas in the lower course, the valley is flatter, with gently sloping sides, as the river erodes horizontally.

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23
Q

Weather and Climate Challenges

A

The UK’s weather and climate have an effect on river processes, causing changes to landforms and landscapes.

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24
Q

Impacts of climate on river landforms and landscapes

A
  • Erosion rate will be higher with greater discharge, so rivers in wet climates will erode more material than those in dry climates, widening and deepening river valleys and increasing the amount of eroded sediment.
  • Transport rate will be greater where the energy of the water is greater, so rivers in wet climates will transport more material than those in dry climates.
  • Weathering of rocks will be greater in some climates: for example, freeze-thaw weathering increases where temperatures range from just above to just below freezing.
  • Amount of discharge is affected by climate. Wetter climates mean greater discharge. Hotter temperatures mean greater evaporation so less discharge. The greater the discharge, the higher the velocity of the river.
25
Q

Changing Weather

A

The UK has experienced some extreme weather in recent years. This can increase the risk of river flooding due to:
- Increasing frequency of storms - more periods of heavy, intense rainfall meaning more water flowing into rivers, which then overflow
- Increasing periods of hot, dry weather - bakes the upper soil so when it does rain, the water runs off the surface, it can’t soak in, reaching rivers and rapidly increasing discharge
- Soil becoming impermeable during cold conditions - snowmelt cannot infiltrate and flows rapidly into rivers, increasing flood risk.

26
Q

Explain the impact that storms can have on river landforms.

A

Storms can cause a sudden increase in river discharge and velocity. This increases the rate of erosion and sediment transport and means that landforms (for example, river valleys) will be widened and deepened by increased hydraulic action and abrasion. The river can flood and sediment is deposited on the floodplain. This raises the height of the floodplain and the levees, which are immediately parallel to the river.

27
Q

Upper Course Landscape

A

Interlocking spurs, waterfalls, gorges and river cliffs are formed by erosion processes and the influence of geology in the upper course of the river.

28
Q

Landforms (Upper Course)

A

In the upper course, the river erodes vertically (downwards). The gradient is steep and the channel is narrow.

29
Q

Interlocking Spurs

A

The river at its source is small and has limited energy. It flows naturally from side to side, around ridges in the valley sides, called spurs. The spurs become interlocking with those on the other side of the valley.

30
Q

Waterfalls

A

Waterfalls are a common feature in the upper course of a river, where there is an increase in vertical erosion. They form where there is a layer of hard, resistant rock overlying a softer, less resistant rock.
- Hard, resistant rock on top
- Soft, less resistant rock, eroded by hydraulic action
- Waterfall retreats upstream, leaving a steep-sided
gorge
- Plunge pool formed by hydraulic action and abrasion
- Overhand gradually collapses

31
Q

Gorges

A

Over a long time, the process of undercutting and collapse is repeated, and the waterfall retreats, forming a steep-sided gorge.

32
Q

Explain how river cliffs form.

A

River cliffs form on the outer side of the meander, when the faster water velocity laterally erodes the riverbank. They are usually almost vertical.

33
Q

Lower Course Landscape 1

A

Depositional processes in the lower course of the river produce distinctive landforms - floodplains, levees and point bars.

34
Q

Floodplains

A

A floodplain is the wide, flat area of land either side of a river and experiences floods when the river tops its banks.
- In the lower course, the river is nearing the sea and
carries a huge amount of sediment.
- When the river floods, excess water spills over the
surrounding area.
- During flooding, the velocity of the river is reduced, it
loses energy, and deposits sediment, forming the
floodplain.
- The floodplain is shaped by the lateral erosion of meanders as they gradually migrate downstream and by deposition of material on the inner bends.

35
Q

How Levees Develop

A

The depositional process, which takes place during flooding, continues until eventually embankments, made of larger, heavier sediment, are created beside the river. These are called levees.

36
Q

Explain how a point bar is formed.

A

Point bars are formed by deposition. On the inside bends of meanders, the river current is relatively slow and therefore low energy. This means that the river is not able to transport its load due to low velocity and the load is deposited on the inside bend. Over time the deposits of sand, silt and pebbles build up to form a point bar.

37
Q

Lower Course Landscape 2

A

Meanders and ox-bow lakes are landforms created by the interaction of deposition and erosion processes in the middle and lower courses of a river.

38
Q

Meanders

A

In the middle course, the width, depth and velocity of the river all increase. The river erodes laterally and starts to form large bends. The bends get bigger and wider, and eventually develop into a horseshoe shape called a meander.
- On the outer bend of a meander, where the current is faster, there is greater erosion. This wears away the bank creating a river cliff.
- On the inner bend of a meander, where the current is slower, there is greater deposition creating a point bar.

39
Q

Ox-bow Lakes

A
  1. Narrow neck of meander is gradually being eroded.
  2. Water now takes the quickest route.
  3. Deposition takes place, sealing off the old meander.
  4. Meander neck has been cut through completely.
  5. Ox-bow lake left behind when meander completely
    cut off.
40
Q

Human Activity

A

Human activities and changes in land use - urbanisation, agriculture and industry - can affect rivers and change river landscapes.

41
Q

Urbanisation

A
  • Urbanisation has caused towns to grow, meaning there are fewer permeable surfaces. Water flows into the rivers, increasing discharge.
  • Increasing demand for housing has led to new houses being built on floodplains. This changes the natural landscape.
  • Rivers may be channelised or made to flow underground to make room for urban developments. If this happens, erosion and deposition cannot take place.
42
Q

Agriculture

A
  • Field drains can improve farmland, but quickly move water into streams and rivers, and can destroy natural wetland landscapes.
  • Forests can be felled to make way for farmland. Trees intercept rainfall, helping to reduce surface run-ff. Removing trees means water reaches rivers more quickly.
  • Abstracting water for irrigation reduces the flow and velocity of a river so deposition occurs rather than erosion.
  • Ploughing fields up and down a slope can increase the amount of sediment in rivers and increase deposition.
43
Q

Industry

A
  • Industry is a big user of water, so can reduce the amount of water in rivers, leading to less erosion.
  • Industrial processes can pollute rivers if chemicals or waste are spilled or dumped into them. This can destroy plants and animals and change the natural landscape.
44
Q

Explain how land-use change can affect rivers.

A

Land-use change can affect rivers in several ways. Changing land from soil to artificial surfaces, such as paving over gardens to create parking spaces on previously green spaces, increases the amount of impermeable surfaces. This means less water can infiltrate into the ground and increases the speed and amount of run-off, so more water reaches the river faster, and increases discharge. Deforestation, another type of land-use change, reduces the amount of interception so rain reaches the ground faster and surface run-off increases. Building on floodplains removes one way that rivers can flood without causing damages, and increases the risk of flooding as the amount of impermeable surfaces increase.

45
Q

Causes and Effects of Flooding

A

River flooding is caused by a combination of physical and human factors, and has a range of physical and human effects.

46
Q

Physical Causes

A
  • Rainfall Intensity - a lot of rainfall over a short period of time prevents soil infiltration.
  • Geology - rocks like granite are impermeable, so water is unable to percolate from the tin soil above.
  • Snowmelt - at spring time, warmer temperatures will melt snow creating more water.
  • Drainage Basin - steep-sided valleys or a lot of tributaries means the water enters the river system quicker.

Excess water will flow towards the river as surface run-off or groundwater.
Water will reach the river channel more quickly and force the level of river to rise above the bank level. Flooding can then occur.

47
Q

Effects of Floods

A
  • Physical effects include landslides, soil erosion, loss of natural habitats, contamination of water supplies.
  • Human effects include death, disease, damage to property, insurance claims, loss of livelihoods, loss of crops and farm animals, disruption to transport.
48
Q

River Management

A

Hard and soft engineering are used to help protect river landscapes from flooding, but each has its advantages and disadvantages.

49
Q

Hard Engineering

A

Hard engineering involves building structures as a defence against flooding.

50
Q

Dams and Reservoirs

A

Barriers constructed to hold back water in artificial lakes:

Pros
- Store large volumes of water until needed
- Long-lasting; can be used to generate hydro-electric power (HEP)

Cons
- Expensive to build
- Sediment can build up in reservoirs

Landscape impact - the natural river valley landscape is flooded

51
Q

Channelisation

A

Deepening or widening the river channel:

Pros
- Allows water to flow more quickly away from areas of flood risk

Cons
- Visually unattractive
- More water is taken downstream, increasing the flood risk to other settlements

Landscape impact - replaces the natural meanders and floodplain with an artificial channel

52
Q

Soft Engineering

A

Soft engineering uses natural processes to reduce the impacts of river flooding.

53
Q

Floodplain Zoning

A

Prevents development in areas most prone to flooding next to rivers.

Pros
- Reduces the number of homes at risk of flooding
- Allows infiltration so surface run-off takes place and flooding is reduced

Cons
- Restricts the growth of settlements

Landscape impact - preserves the natural floodplain

54
Q

Washlands

A

Areas next to rivers that are deliberately flooded to avoid flooding residential or important agricultural areas.

Pros
- Create an area for floodwater to go
- Allow natural river processes such as deposition

Cons
- Might limit the use of land

Landscape impact - preserves the natural floodplain landscapes in the mid and lower river courses

55
Q

Explain one advantage and one disadvantage of channelisation of a river.

A

One advantage of channelisation is that the friction between the water and the channel sides is reduced. This means that water moves rapidly away from areas that could otherwise flood.
One disadvantage is that this rapid increase in water velocity will erode and flood areas downstream from the channelised section of the river.

56
Q

River Dee, Wales

A

You need to know a located example of the significance of an upland or lowland river landscape.

57
Q

How the River Dee landscape was formed

A
  • The source of the River dee is Dduallt, an upland area in Snowdonia, North Wales.
  • Here, annual precipitation is very high.
  • The Dee flows south-easterly, eroding this heavily glaciated upland landscape formed of igneous and metamorphic rocks.
  • Near Chester, the river meanders across a wide floodplain, eroding softer sedimentary rocks and depositing sediment.
  • A section is artificially straightened, giving a man-made landscape.
  • Further deposition occurs to form the Wirral estuarine landscape.
58
Q

Human factors causing change

A
  • 1732-1736 - channelisation of 8 km improved navigation, increasing discharge and velocity and creating an artificial landscape.
  • Under the River Dee Regulation Scheme, a series of reservoirs was built, e.g. Llyn Celyn.
  • Earth embankments were built along the middle course to protect agricultural land and properties, preventing further development of the floodplain landscape.
59
Q

Physical factors causing change

A
  • Floodplain landscape between Holt and Worthenbury with meanders formed by active erosion and deposition, causing the river to change its course over time.
  • If sea levels rise by 1 m by the year 2100, coastal landscapes will replace salt - and freshwater marsh landscapes.
  • In the Dee Estuary, rises in sea level will destroy the estuary landscape.

Geography A Paper 1 Flashcards (4 decks)

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