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AS Geography (physical) > Rivers, Floods Management- Notes 1 content > Flashcards

Rivers, Floods Management- Notes 1 content Flashcards

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1
Q

What separates one drainage basin from the next?

A

The watershed

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2
Q

Where does a river get its water from?

A

The drainage basin which is its catchment area

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3
Q

Is the drainage system considered to be open or closed and why?

A

It is considered to be an open system with inputs, outputs of energy and stores and transfers of water, it is open as it has inputs and outputs

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4
Q

What cycle is the drainage basin part of?

A

The hydrological cycle

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5
Q

Give a basic sequence of events for the hydrological cycle

A

Input: precipitation- lands on the surface
Outputs: evapotranspiration and runoff

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6
Q

What knock on effect will drainage basin deforestation have?

A

There will be less interception and transpiration, leading to an eventual increase in channel flow

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7
Q

What effect will a drought have on a drainage basin?

A

This may cause a reduction in soil run off and a decrease in other stores and transfers such as infiltration and soil water storage

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8
Q

Name all stores in a drainage basin?

A
  1. Interception
  2. Surface storage
  3. Vegetation storage
  4. Soil storage
  5. Groundwater storage
  6. Channel storage
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9
Q

Name the flows and transfers in a drainage basin?

A
  1. Stemflow
  2. Infiltration
  3. Transpiration
  4. Throughflow
  5. Percolation
  6. Groundwater flow
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10
Q

What are the three outputs from drainage basins?

A
  1. Transpiration
  2. Runoff
  3. Evaporation
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11
Q

What does evaporation and transpiration combine to produce?

A

Evapotranspiration

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12
Q

Between when does the water balance change?

A

Between seasons

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13
Q

In the U.K. When is there a water surplus and why?

A

In the winter and early spring. Evaporation is greater than transpiration, resulting in high run off

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14
Q

In what season is there a soil moisture deficit in the U.K.?

A

In the summer, when the temperature rises and vegetation grows quickly, groundwater stores from springs may be needed to keep rivers flowing

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15
Q

What is the water balance equation?

A

Precipitation=runoff+evapotranspiration+change in storage

P=Q+E+(triangle)/\s

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16
Q

Water budget graphs can help people manage water supplies, give examples of how this can be done

A
  1. They can show periods where there’s likely to be drought
  2. Periods when flooding is most likely to occur
  3. The best time for irrigation
  4. Or the need for a water transfer system
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17
Q

How does vegetation and land use influence flows within a drainage basin?

A

The more vegetation there’s the less the overland flow but bare ground as well as urban development with impermeable surfaces will increase it and impermeable surfaces especially will reduce infiltration. Vegetation levels will also affect levels of interception storage and throughfall and stemflow

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18
Q

How will rainfall affect water flows within a drainage basin?

A

Intense rainfall=increase in overland flows= sudden rise in river discharge. Gentle rainfall over a period of time allows for more infiltration

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19
Q

How does the soil type and depth affect water flows in a drainage basin?

A

Deeper soil will be able to store more water, in some soils there are pipers created as water flows along the lines of roots and burrows, thus increasing throughflow rates. Soils with smaller pores such as clays will help reduce infiltration.

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20
Q

How will bedrock affect water flows in a drainage basin?

A

Impermeable bedrock e.g. Granite and slate will prevent groundwater flow and encourage throughflow and overland flow. Rocks w/ air spaces and cracks can let water through but if these rocks become saturated they will act as if they’re impermeable

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21
Q

How will the shape of the land affect water flows within a drainage basin?

A

Steep slopes will encourage overland flow, while many surface stores such as lakes and ponds will reduce river flows.

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22
Q

How will conditions in a drainage basin affect water flows within a drainage basin?

A

Frozen or baked ground can reduce infiltration and increase surface runoff, in the same vein if the ground was already wet then overland flow will occur sooner

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23
Q

How will climate affect the water flows within a drainage basin?

A

This affects the distribution of rainfall e.g. Some areas only have rain in one season. Temp conditions are also important as they’ll affect evapotranspiration and may determine if water is stored as ice or snow

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24
Q

How will the size and shape of a drainage basin affect water flows within it?

A

The larger the basin, the more the run off. The shape of the basin can affect the time taken for water to reach a river channel. A high density of tributaries can produce high flows

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25
Q

What does a storm hydrograph show?

A

How a river’s discharge changes as a result of a period of heavy rain

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26
Q

Only a small proportion of rainfall goes directly into a river channel, where does most of the rainwater fall?

A

On the valley slopes, it then takes time to reach the river channel.

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27
Q

What does the rising limb of the storm hydrograph show?

A

Water entering the river channel and increasing its discharge

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28
Q

Flow increases to a specific level, what is this?

A

Peak discharge

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29
Q

What does the receding limb show?

A

The amount of water reaching the river after the storm decreases, so the river level forms

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30
Q

What is the starting and finishing level of river discharge called on the storm hydrograph?

A

Base flow

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31
Q

What is the time delay between peak rainfall and peak discharge called?

A

Lag time

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32
Q

What’s the pattern of seasonal variation in the flow of a river called?

A

The river’s regime

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33
Q

What does a river regime hydrograph show?

A

Monthly discharge figures and variations that result from its response to the regions climate- e.g. Rainfall amount and distribution and the amount of evaporation and snow melt

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34
Q

What happens to the rising limb of a storm hydrograph if there’s a high intensity, long storm?

A

It is steep

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35
Q

If soil is already saturated by previous rainfall, what is the name for this previous rainfall?

A

Antecedent rainfall

36
Q

What kind of soil (to do with rainfall) can contribute to an increase in discharge if heavy rain falls on it?

A

Saturated soil

37
Q

What types of soil and rock produce less flashy storm hydrographs and why?

A

Porous soil and permeable rocks as they allow water to be regulated more slowly through natural systems

38
Q

Does a small drainage basin increase or decrease lag time?

A

Decrease as they respond more rapidly to rainfall

39
Q

What do deciduous trees do in terms of discharge?

A

In summer they reduce peak discharge as there’s more interception

40
Q

Does coniferous vegetation have more or less of a variable effect on discharge than deciduous vegetation?

A

Less they don’t lose their leaves

41
Q

What human practices can have an affect on river discharge levels?

A

Impermeable surfaces especially in urban areas as well as cattle grazing which have similar effects

42
Q

What does the long profile show?

A

The change in altitude by a river from source to mouth

43
Q

What shape would the rivers long profile be in theory but what irregularities stop it being like this?

A

A smooth concave curve with the steepest gradient at the source becoming less steep as the river approaches the sea, but irregularities such as lakes, waterfalls and Rapids stop this

44
Q

What is endogenic material?

A

Eroded material from the bed and bank

45
Q

What is exogenic material?

A

Material that has entered the river via mass movement and weathering of the valley sides

46
Q

What are the four processes of river erosion?

A
  1. Hydraulic action
  2. Abrasion
  3. Solution
  4. Attrition
47
Q

What are the four processes of transportation?

A
  1. Traction
  2. Saltation
  3. Suspension
  4. Solution
48
Q

The higher the velocity and discharge, the more or less material will the river be able to carry?

A

Less …… jk more

49
Q

What two factors generally increase downstream?

A

Velocity and discharge

50
Q

What’s the general rule of the Hjulström curve?

A

As the velocity of the river increases, its able to erode and transport bigger particles, the velocity needed to carry a particle is slightly less than that needed to erode it. As velocity falls, particles are deposited with the largest particles first.

51
Q

What are the exceptions to the general rule of the Hjulström curve?

A
  1. Larger sand particles take a lower velocity to pick up than smaller clays and silts as the clays are cohesive and hard to entrain
  2. Once entrained fine particles can be carried at much lower velocities than those required to pick them up. For larger particles there’s only a small difference between erosion and fall velocities
52
Q

When does deposition occur in a river?

A

When a river loses energy and is no longer competent, nor has the capacity to transport its entire load, this happens when velocity and discharge decreases

53
Q

What are the reasons for deposition?

A
  1. A sudden reduction in gradient
  2. Less precipitation leading to a reduction in discharge
  3. The river entering a body of water
  4. A sudden increase in load (due to a tributary bringing in high calibre material, increased erosion or a landslide)
  5. Shallow water within a river channel e.g. Riffles or the inside of a meander bend
  6. As the river floods onto a flood plain
54
Q

What is type of material is deposited first?

A

Large, coarse particles

55
Q

What type of material are mountain streams filled with?

A

Large boulders

56
Q

What type of material dominates river load in the lower courses?

A

Finer sediments

57
Q

What causes significant deposition of even the finest material at the river mouth?

A

There’s a sudden reduction in velocity

58
Q

What process which creates an electrical charge between clay particles causes them to coagulate and become deposited?

A

Flocculation

59
Q

What does the dissolved load consist of?

A

Soluble materials carried as chemical ions so there are no measurable particles

60
Q

What is one of the reasons why particles become smaller and rounded as they travel downstream?

A

Attrition

61
Q

Does total sediment load increase or decrease downstream and why?

A

It increases because of increases in both average discharge and velocity in the lower reaches of a river, here the river has a greater capacity

62
Q

What is the equation for total sediment load?

A

Total sediment load= dissolved load + suspended load + bed load (+flocculation load)

63
Q

What does the type, course and character of a river’s load depend on?

A

They depend upon the nature of the drainage basin, its location and more and more on human activity

64
Q

What do larger drainage basins with more tributaries have?

A

A greater potential for transporting sediment than smaller drainage basins with a lower tributary density

65
Q

How does the type of underlying geology affect river load?

A
  1. If it is soft e.g. Sandstones and clays the sediment transported will consist mainly of these
  2. If it is limestone, then the load will largely consist of dissolved material as it is a soluble rock
  3. If it’s a resistant rock e.g. Granite then there’ll be little total load
66
Q

How does drainage basin relief affect the rivers load?

A

The less the difference between the river’s source and base level then there’ll be a lower amount of sediment as the energy available for erosion and transportation is limited compared to that of rivers with upper reaches with high relief

67
Q

Do low precipitation rates cause high or low sediment yields?

A

It causes low yields as less water is available for runoff. Locations with great seasonal variation in precipitation can have highly variable levels of sediment load

68
Q

How can human activity affect sediment load?

A

It can both increase and decrease sediment load

69
Q

How does deforestation affect sediment load?

A

It leads to soil erosion which in turn leads to increased sediment load

70
Q

How can chemical fertilisers affect river load?

A

It increases the dissolved load especially with nitrates and phosphates

71
Q

How do dams affect sediment levels?

A

They trap sediment and cause lowered sediment levels downstream

72
Q

On the rivers journey from source to mouth what generally increases in a river?

A

Velocity, discharge, load amount and efficiency

73
Q

What decreases for a river from source to mouth?

A

Roughness, friction, turbulence and load size

74
Q

Describe the valley cross profile of the upper course of the river?

A

The valley is narrow and steep sided and the river occupies the entire valley floor, vertical erosion is the dominant process

75
Q

Describe the valley cross profile of the middle course of the river

A

The valley is wider with distinct bluffs and a flat flood plain, which is the result of lateral erosion

76
Q

Describe the valley cross profile of the lower course of a river

A

There’s a wide, flat floodplain where the valley sides are difficult to locate, there’s a lack of erosion and reduced competence, resulting in large scale deposition

77
Q

Why is the velocity of a river channel lower in the upper course?

A

Due to the roughness of the river bed

78
Q

Where is the gravitational potential energy of a river at its highest?

A

In the upper course of the river due to its height above its base level

79
Q

What type of energy does the river have in the middle and lower courses?

A

Kinetic energy

80
Q

What’s the equation for kinetic energy?

A

KE=1/2mv^2

81
Q

What state is the river in when it has achieved a smooth graded profile?

A

Dynamic equilibrium

82
Q

Describe how factors are in balance in dynamic equilibrium

A

An example is of kinetic energy where it is used to transport the water and sediment load, however there’s no excess for erosion of deficit for deposition

83
Q

If the volume and load change, what will happen to the channel morphology?

A

It will also change

84
Q

What is the river like if the hydraulic radius is higher?

A

It is more efficient as less energy is used overcoming friction on the river bed and banks

85
Q

What is greater if there’s a greater channel roughness?

A

There’s a greater wetted perimeter, often due to boulders in the channel

86
Q

In the Bradshaw model, what increases downstream?

A
  1. Discharge
  2. Occupied channel width
  3. Channel depth
  4. Average velocity
  5. Load quantity
87
Q

In the Bradshaw model, what decreases downstream?

A
  1. Load particle size
  2. Channel bed roughness
  3. Slope angle (gradient)

AS Geography (physical) (19 decks)

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