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Uk Geographical Issues > River processes and pressures > Flashcards

River processes and pressures Flashcards

1
Q

Describe the Upper Course:

A
  • River starts as many tributaries, which are narrow and v-shaped
  • Each tributary doesn’t carry a lot of water, but together, they fill up the river channel below
  • The sides of the tributaries tend to be like a valley, with a large gradient either side
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2
Q

Describe the Middle Course:

A
  • Tributaries merge together to form a channel, which is rounder and deeper to compensate for the increase in water
  • The more water that passes by, the larger the energy of the water and so more erosion can take place to widen the channel
  • The area around the river channel is flat and low-lying, which is the floodplain if the river needs to flood
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3
Q

Describe the Lower Course:

A
  • Carries the largest volume of water in a very wide and very deep channel
  • Ridges either side of the bank called levees
  • Wider and flatter than the middle course
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4
Q

What is the speed of the water like in the Upper Course?

A
  • The channel is shallow and so most of the water passes the riverbed, which slows the rate of flow due to friction
  • As the river gets bigger, less water is in contact with the riverbed, meaning friction decreases
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5
Q

What is the speed of water like in the Lower Course?

A
  • Travels a lot faster than in the Upper Course as there is less friction from the riverbed
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6
Q

What are the four erosional processes?

A

Abrasion
Attrition
Hydraulic action
Solution

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7
Q

What is abrasion?

A
  • Where rocks carried by the water scrape and bang against the sides of the river and so gradually wear away the channel
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8
Q

What is attrition?

A
  • Rocks and pebbles hit against each other, wearing each other down and so becoming rounder and smaller
  • Doesn’t change river channel
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9
Q

What is hydraulic action?

A
  • Water under high pressure causes cracks to force apart and widen in any rocks along river banks
  • Over time this causes the rock to fracture and collapse into the river, expanding it
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10
Q

What is solution?

A
  • The river can gradually dissolve chemical compounds in rocks that it flows over
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11
Q

What are the transportation processes?

A

Solution
- Chemicals are dissolved in river water

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

Saltation
- Pebbles and rocks which are too heavy to be suspended bounce along the river channel

Traction
- Large rocks are rolled along the river bed

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12
Q

What is deposition?

A
  • The dropping of the river’s load when the water in a river decreases in speed
  • If the river travels slower, the water has less energy and can carry less material
  • Most deposition occurs in the lower course
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13
Q

What are landform characteristics of the Upper course?

A
  • Erosion is the predominant river process
  • Waterfalls
  • Interlocking spurs
  • V-shaped valley
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14
Q

What are landform characteristics of the Middle Course?

A
  • Mixture of erosional and depositional landforms
  • Gorges
  • Meanders
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15
Q

What are landform characteristics of the Lower Course?

A
  • Deposition is the predominant river process
  • Flood plains
  • Oxbow lakes
  • River estuary
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16
Q

What are interlocking spurs?

A
  • Found in the upper course as the low energy of the water means it can’t erode resistant rocks in the spur
  • Instead, the river re-routes and curls around them
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17
Q

Describe how waterfalls are formed:

A
  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, creating a step
  3. The soft rock continues to erode, undercutting the hard rock- which is left suspended in the air as an overhang. A plunge pool is created due to the rotational movement of the water which increases the rate of erosion
  4. Due to gravity, the unsupported overhang collapses. The rocks fall into the plunge pool and act as tools for erosion, further deepening it
  5. Erosion continues to undercut under the hard rock, creating an overhang again, further upstream
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18
Q

What is a gorge?

A
  • Formed from waterfalls
  • As the waterfall retreats upstream, it leaves behind a steep valley carved into the rock with the river running along the base
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19
Q

How are meanders formed?

A
  • 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
  • On the opposite side, the water travels slowly and changes direction sharply, so the water loses energy and deposits sediment
  • Hence, 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
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20
Q

What is the Thalweg?

A

The path of the fastest water

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21
Q

How do oxbow lakes form?

A
  1. In the beginning, the river has meanders that form depending on the speed of the water
  2. Erosion happens when the fastest water hits the side of the meander, whereas deposition happens on the inside of the bend
  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 a river 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 oxbow lake
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22
Q

What are floodplains and how are they formed?

A
  • When a river floods in the lower course, due to its many large meanders the water spills out onto land
  • The water loses velocity and deposits its load, and deposition of the finer sediment alluvium occurs
  • Floodplains are made from silts which make the land fertile
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23
Q

What are levees?

A
  • The banks of the river in the lower course
  • Every time the river floods, sediment is deposited on the top of the banks so levees grow in height
24
Q

What are estuaries?

A
  • Bodies of water where a river meets the sea
  • Rivers are affected by the tides, so river flow is disrupted, leading to lots of deposition. This can create mudflats and saltmarches

-

25
Q

What are human factors that increase the risk of flooding?

A

Urbanisation
Deforestation
River capacity

26
Q

How does urbanisation increase flood risk?

A
  • Increasing the amount of impermeable surfaces, such as concrete and tarmac, decreases the amount of time taken for water to flow into a river, so increasing the risk of flash flooding
27
Q

How does deforestation increase flood risk?

A
  • Trees intercept the rain, 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 water to enter a river
28
Q

How does river capacity increase flood risk?

A
  • If a river becomes filled with rubbish and debris, the channel’s size will decrease
  • This means the river can carry less water and so it’s more likely to flood
29
Q

What are physical factors that increase flood risk?

A

Rate and volume of rain
Geology
Topography

30
Q

How does rate and volume of rain increase flood risk?

A
  • If a large amount of water falls in a short amount of time, the amount of water running into a river is increased

-

31
Q

How does geology increase flood risk?

A
  • If the area has many impermeable rocks, the rainwater can’t run into soil or underground storage
32
Q

How does topography increase flood risk?

A
  • The shape of the land determines how quickly rainwater flows into the river
  • Steep hills with high gradients are more likely to have flash floods
33
Q

What are the features of a storm hydrograph

A

Peak precipitation
Rising limb
Peak flow
Lag time
Falling limb
Base flow

34
Q

What are the key characteristics of flashy flooding?

A

HYDROGRAPH
- Short lag time
- High Peak
- Steep rising limb

OTHER
- Caused by intense storm or rapid snow melt
- Impermeable rocks like granite
- High and steep slopes
- Usually small drainage basin
- Few plants

35
Q

What are the key characteristics of subdued flooding?

A

HYDROGRAPH:
- Long lag time
- Low peak
- Gently sloping rising limb

OTHER
- Caused by steady rainfall or snow melt
- Permeable rocks like limestone
- Low and gentle slopes
- Usually a large drainage basin
- High density of vegetation

36
Q

What are the risks of flooding?

A
  • Property damage and loss of belongings
  • Loss of crops or cattle drowning
  • If industries and factories are flooded, workers can lose their jobs
37
Q

What are economic values of land that should be considered when choosing a management strategy?

A
  • How many jobs depend on the river
  • Are there industries or business parks built in the floodplains at risk from flooding
  • What will the insurance cost be for a flood
  • How much does it cost the government to respond to a serious flood
38
Q

What are social values of land that should be considered when choosing a management strategy?

A
  • Is the river historic or a location of religious / cultural importance?
  • Do events or festivals happen here?
  • Are the river’s floodplains home to a village or town?
  • Is there a risk to life during flooding?
39
Q

What are environmental values of land that should be considered when choosing a management strategy?

A
  • Are there any rare or endangered species living in or around the river?
  • Would nature reserves be at risk if flooding continues?
  • Are there any farms at risk?
40
Q

What are soft engineering strategies for river management?

A

River Channel Restoration
Wetlands

41
Q

What are hard engineering strategies for river management?

A

Dams
Embankments and Flood Walls
Dredging
Channel Straightening and Flood Relief Channel

42
Q

What are dams?

A

Concrete blockades that store water in the upper course and can regulate river flow

43
Q

What are the pros and cons of dams?

A

PROS
- Valves can control and release the right amount of water to avoid flooding
- Can generate electricity (HEP)

CONS:
- Visually unappealing
- Villages can be flooded to create the reservoir

44
Q

What are embankments and flood walls?

A

Banks of a river are built up in brick and concrete to increase the channel capacity

45
Q

What are the pros and cons of embankments and flood walls?

A

PROS:
- Reduces lateral erosion, so the river doesn’t grow wider
- Protects valuable property on the river front

CONS:
- Looks unnatural and destroys habitats on the river banks

46
Q

What is dredging?

A

Rubbish and sediment are dug up from the bottom of a river

47
Q

What are the pros and cons of dredging?

A

PROS
- Widens the river channel and removes pollution from the area
- Doesn’t alter the look of a river
- Cheap hard engineering strategy

CONS:
- Takes time to complete, and dredging must be done regularly

48
Q

What is channel straightening and a flood relief channel?

A

The river is straightened and relief channels constructed to bypass the meanders to increase the speed of water flow

49
Q

What are the pros and cons of channel straightening and flood relief channels?

A

PROS:
- Reduces flooding risk since water flows faster downstream
- Protects urban villages by directing flood water away

CONS:
- Expensive and disruptive of natural habitats

50
Q

How can flood damage be minimised?

A
  • Putting sandbags in doorways to reduce flood water leaking into homes through doors
  • Temporary flood barriers can be put up, which act like temporary banks and increase the river’s capacity
  • Valuable possessions are moved upstairs and locals told to stay inside
  • Roads are closed that cross the river
51
Q

What can affect the lag time in a hydrograph?

A

Geology
Soil type
Slope
Drainage Basin shape
Antecedent conditions
Vegetation

52
Q

How does geology affect lag time?

A
  • If the rocks under the ground are impermeable and water cannot drain through the rock layer resulting in rapid overland flow and a shorter lag time
  • Permeable rocks encourage a slow transfer by groundwater flow, hence a longer lag time
53
Q

How does soil type affect lag time?

A
  • Clay soils don’t drain easily and become saturated very quickly. This results in rapid overland flow and shorter lag times
54
Q

How do slopes affect lag time?

A
  • Steep slopes lead to rapid water transfer and shorter lag times
55
Q

How does drainage basin shape affect lag time?

A

A high density basin has more streams and rivers which speeds up water transfer and shortens lag time

56
Q

How do antecedent conditions affect lag time?

A

Wet conditions before a storm causes the ground to become saturated. This speeds up overland flow and shortens lag flow.

Drier conditions mean the rainfall can infiltrate into the soil, slowing down lag time

Uk Geographical Issues (10 decks)

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