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Core Physical Geography > Hydrology and fluvial geomorphology > Flashcards

Hydrology and fluvial geomorphology Flashcards

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1
Q

What are the processes (flows) of the drainage basin system?

A

Infiltration, surface run-off, stem flow, throughflow, percolation, groundwater flow.

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2
Q

What are the outputs of the drainage basin system?

A

Evaporation, transpiration, evapotranspiration, condensation, river discharge.

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3
Q

What is an example of storage in the drainage basin system?

A

Interception (via trees and plants), groundwater storage

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4
Q

What is an example of input in the drainage basin system?

A

Precipitation

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5
Q

What is the Hydrological cycle?

A

The way that water moves from the sea, through the air, onto (and into) the land, and back into the sea.

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6
Q

What is a system?

A

A set of interrelated components, working together towards some kind of process.

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7
Q

What is a closed system?

A

Energy is transferred into and out of the system. All matter is enclosed. e.g. the hydrological system.

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8
Q

What is an open system?

A

Matter and energy can be transferred from the system into the surrounding environment.

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9
Q

What is an example of an open system?

A

The drainage basin system as part of the cycle operates on land.

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10
Q

What factors lead to a faster route through the drainage basin?

A

Impermeable surfaces (urbanisation), saturated soil, less vegetation. steep relief (more overland flow), more tributaries, higher/more intense population.

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11
Q

What factors lead to a slower rate through the drainage basin?

A

Permeable surfaces (type of soil and rock), more vegetation (increased interception and stem flow), flat/gentle relief (increases interception), fewer tributaries (lower drainage density, less channel flow), lower precipitation.

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12
Q

How does agriculture affect infiltration?

A

Tractors and livestock compress soil, ploughs create indents for water.

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13
Q

What is infiltration capacity?

A

the rate at which water can infiltrate the soil

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14
Q

What is porosity?

A

The amount of pores in the soil. Particles with larger pores will allow water to infiltrate faster, as there is more space available for water to enter.

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15
Q

What are two types of soil?

A
  • Clay soil: has very small pores and does not let water pass through it easily- increased overland flow
  • Sandy soil: has large pores so lets water past easily- increased throughflow.
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16
Q

What is the water table?

A

The level of saturation in the soil/rock/surface- water sits on top of the bedrock most of the time.

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17
Q

What are Artesian springs?

A

They are springs which typically occur at the lowest point in a given area.

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18
Q

How are Artesian springs created?

A

They are created when the pressure of the groundwater becomes greater than the pressure from the atmosphere. In this case water is pushed straight up out of the ground

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19
Q

What are non-artesian springs?

A

They are springs that may simply flow from a higher elevation through the earth to a lower elevation and exit in the form of a spring, using the ground like a drainage pipe.

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20
Q

What is the Water Budget?

A

The amount of water in the soil and the rocks which depends on the balance between precipitation and potential evapotranspiration.

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21
Q

What is the general water balance equation?

A

P = Q + E + ΔS

Where:

  • P = Precipitation
  • Q = Runoff (including surface runoff and groundwater flow)
  • E = Evapotranspiration
  • ΔS = Change in water storage (in surface water, soil moisture, and groundwater)
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22
Q

Why is the water balance equation useful?

A
  • Plan and manage water supply
  • Suggest possible periods of shortage in advance
  • Plan to implement measures such as hosepipe bans
  • Guidance for agriculture- which crops to grow, amount of water for irrigation, etc
  • Flooding management
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23
Q

What is soil moisture recharge?

A

the refilling of stores of water during warmer months when evapotranspiration has exceeded precipitation.

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24
Q

What is water surplus?

A

When precipitation exceeds evapotranspiration.

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25
Q

What is ground store depletion?

A

When evapotranspiration exceeds precipitation.

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26
Q

What is river discharge?

A

The amount of water flowing past one point in the river at any one time is called the discharge of the river

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27
Q

What is discharge measured in?

A

Measured in cubic metres of water per second (cumecs)

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28
Q

What is a hydrograph?

A

A graph showing the rate of flow (discharge) versus time past a specific point in a river.

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29
Q

What is an annual hydrograph?

A

Represents the long-term average flow in a river over the course of a year. It shows how long-term discharge varies from season to season.

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30
Q

What is a storm hydrograph?

A

Shows the change in discharge of a river or stream in response to a specific rainfall event.

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31
Q

What does a storm hydrograph show?

A

How quickly the river responds to rainfall, peak discharge, lag time and how long it takes the river to return to its normal discharge.

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32
Q

What is peak rainfall?

A

The highest point of rainfall intensity during the storm event.

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33
Q

What is peak discharge?

A

The maximum rate of water flow in the river channel, typically occurring after the peak rainfall.

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34
Q

What is baseflow?

A

Groundwater flow before and after the storm event.

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35
Q

What is storm flow/ runoff?

A

The additional water added to the river channel directly from the rainfall event causing the rise in discharge above the groundwater flow.

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36
Q

What is the approach segment?

A

The initial part of hydrograph, showing the river’s discharge before the storm’s impact becomes evident.

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37
Q

What is the rising limb?

A

The part of the hydrograph showing the rapid increase in river discharge as the storm runoff reaches the channel.

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38
Q

What is the falling/ receding limb?

A

The section of the hydrograph depicting the gradual decrease in river discharge as the storm runoff subsides.

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39
Q

What is lag time?

A

The time difference between the peak rainfall and peak discharge.

40
Q

What is Bankfull discharge?

A

The discharge at which water fills the river channel without spilling over the banks.

41
Q

What are the characteristics of a lag/ subdued hydrograph?

A

Long lag time, gradually rising and falling limb, lower flood risk and low peak discharge.

42
Q

What are the characteristics of a flashy hydrograph?

A

Short lag time, steep rising and falling limb, higher flood risk and high peak discharge.

43
Q

What is the river channel?

A

The ‘trench’ in which the river flows. It is defined by the river bed and the river banks.

44
Q

What does a long profile diagram show?

A

It is a line drawn from the source to the mouth of a river. It shows how gradient of a river channel changes as it flows downhill. The typical long profile is concave.

45
Q

What is a knickpoint?

A

A sharp break of slope in the smooth, concave long profile of a river. It is formed by the influence of tectonics, glacial activity and/or lithology (rock structure).

46
Q

What is the potential energy of the river determined by?

A

The altitude of the source in relation to base level.

47
Q

What is the amount of kinetic potential energy determined by?

A

Gradient which determines velocity.

48
Q

What are all channel processes dependent on?

A

The amount of energy available.

49
Q

How does the river use energy?

A
  • The river uses energy to TRANSPORT load
  • If it still has some left it will ERODE as well
  • If it loses energy it will DEPOSIT
50
Q

What is the capacity of a river?

A

The total amount of load that it is carrying

51
Q

What is the competence of a river?

A

The maximum size of particle that the river is capable of transporting.

52
Q

What does total energy of the river depend on?

A

-Weight of the water (more water = more energy due to gravity)
-Height above base level
-Steepness of channel

53
Q

What is vertical erosion?

A

Erosion of the river bed.

54
Q

What is horizontal erosion?

A

Erosion of the river banks.

55
Q

What is abrasion?

A

When a river uses its load of sediment to wear away its bed and banks.

56
Q

How and when do potholes form?

A

They form in the uplands where pebbles get caught in hallows in the river bed; as they swirl abrasion makes a hole.

57
Q

What is attrition?

A

When sediment bumps into each other and wear each other away becoming rounder and smaller.

58
Q

What is hydraulic action?

A

The direct force of the flowing river water which can break material from the bed an the banks.

59
Q

What is cavitation?

A

The force of exploding air.

60
Q

How does cavitation occur?

A

Powerful eddies compress and decompress water in cracks forming air bubbles which explode weakening the crack, breaking off sediment.

61
Q

What are Eddies?

A

Sections of river that move against the current.

62
Q

How do eddies form?

A

When the current flows around an obstruction and some water breaks on itself to refill the space.

63
Q

What is solution?

A

Natural river water is often slightly acidic and can dissolve rocks such as chalk and limestone.

64
Q

What is Suspension?

A

Lighter material held by turbulent eddies.

65
Q

What is Solution?

A

Dissolved load derived from soluble rock such as limestone and chalk.

66
Q

What is Saltation?

A

Smaller pebbles bouncing along the river bed carried by eddies until the water current slows them down.

67
Q

What is traction?

A

Larger particles rolled along by the force of the flowing water.

68
Q

What are the processes occurring in the upper course and lower course?

A

Vertical erosion, high velocity=less deposition, higher bed load size due to less time for attrition. Lower discharge. Transportation.
and vice versa for lower course.

69
Q

Why do these river characteristics exist at different parts of the river?

A

In the upper course due to a steeper relief and gradient. But in the lower course due to shallower relief and gradient + higher discharge and velocity.

70
Q

When does a river deposit its load?

A

When its energy drops i.e. when it is no longer competent enough to transport it.

71
Q

How are the particles deposited?

A

The particles are deposited in order of size, the larger the particle to more energy required to transport it. This creates a pattern of deposition along a river.

72
Q

What are some of the specific circumstances when deposition occurs?

A
  • During a period of low discharge after a dry spell- shallow more friction
  • Slip off slope of a meander bend
  • When a river bursts its bank and floods due to a reduction in the hydraulic radius
  • When the load is increased e.g. after deforestation or landslide
  • At the mouth of a river where it meets the sea
  • Behind human intervention such as bridges or dams
73
Q

When does sedimentation occur?

A

When river sediment is deposited from still water. The process is common on floodplains and on the sea bed.

74
Q

What is the process of flocculation?

A

It is the way that charged ions in sea water allow clay particles to coagulate together and settle out of suspension.

75
Q

What does Bradshaw’s Model show?

A
  • how different characteristics increase or decrease from upstream to downstream.
  • Size of triangles show extent of changes
76
Q

What does the Hjolstrum curve show?

A

the relationship between velocity of the river and the size of the particles it can carry

77
Q

What are the characteristics of the Hjulstrom curve?

A
  • It has two lines- the top curve is the critical erosion velocity curve and the bottom curve is the mean settling velocity curve.
  • Graph uses a logarithmic scales (Axis multiplied by 10) to allow a wide range of data to be shown on a relatively small graph.
78
Q

What is the relationship between velocity of the river and the size of the particles it can carry?

A

As discharge rises, velocity increases and the river has more energy to pick up particles. As velocity reduces it deposits particles in order of size.

79
Q

What is the mean settling velocity?

A

The velocity which particles can no longer be carried.

80
Q

What is the critical erosion velocity?

A

The speed a particle must be reached to be picked up.

81
Q

What is roughness measured by?

A

Manning’s Roughness coefficient

82
Q

What does hydraulic radius compare?

A

The friction caused by the bed and banks with the amount of discharge flowing down a river.

The higher the value the more efficient the river is.

83
Q

What is the hydraulic radius formula?

A

Hydraulic radius= channel cross sectional area (CSA) / wetted perimeter (WP)
where:
- CSA = channel depth x channel depth
- WP = length of the bed and banks in direct contact with the water in the river channel.

84
Q

How does laminar flow form/what does it cause?

A

When water flows downwards with minimal friction over a smooth surface

85
Q

How does turbulent flow form/ what does it cause?

A

Forms when water flows with a large amount of friction. The bed and banks cause friction slowing the water at the edge of the bank and the other water overtakes it.

86
Q

How does helicoidal flow form/ what does it cause?

A

A depression occurs in the banks of the river which allows water to travel into it. From this is will rebound and corkscrew to the other side of the bank further down the channel. It will result in the formation of pools, riffles and meanders.

87
Q

What are the three main types of river channel?

A
  • Straight channel
  • Meandering channel
  • Braided channel
88
Q

What is sinuosity?

A

A measure of how ‘bendy’ the river is.

89
Q

What is considered a low, medium and high sinuosity?

A
  • Straight 1 to 1.05
  • Low sinuosity 1.06 to 1.3
  • Sinuous 1.3 to 3
90
Q

Where do braided channels occur?

A

In the lower course in areas where the discharge fluctuates throughout the year, where large amount of sediment are found.

91
Q

How do braided river channels form?

A

Sediment will be transported and then deposited particularly when there is a sudden change of slope leading to a loss of energy. This creates islands (eyots) and bars that see the level of deposition increase further. Over time they become large enough to cause a channel to split.

92
Q

What are the features of a braided river channel?

A
  • Islands/ eyots (vegetated or not)
  • Gravel/ sand bars
  • Several river channels
93
Q

When does flooding occur?

A

When the discharge exceeds the capacity of its channel to carry that discharge and the river overflows its bank.

94
Q

What is a recurrence interval?

A

The average number of years between floods of a certain size is the recurrence interval or return period.

95
Q
A

Core Physical Geography (2 decks)

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