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Geography Physical 2: rivers > Rivers > Flashcards

Rivers Flashcards

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1
Q

What is the definition of river discharge?

A

The volume of water flowing through a river channel at any given point

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2
Q

Draw a labelled diagram of a storm hydrograph

A 
Lag time
Discharge (cumecs)
Precipitation
Time
Peak discharge 
Bank fall discharge 
Rising limb
Falling limb
Stormflow
Baseflow
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3
Q

What is lag time?

A

The difference between peak rainfall and peak discharge

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4
Q

What are the factors influencing discharge?

A

Urbanisation (impermeable rock)- Water unable to percolate through impermeable rock + drainage direct to river, surface run off, short lag time, discharge high

Permeable rock- water able to percoulate through, taking longer to reach the river, ground water flow, long lag time, low discharge

Vegetation- Water flows and infiltrates to the plant roots, through flow, long lag time, low discharge

Farmland- soil is compact, increased forgave run off, through flow, short lag time, high discharge

Intense rainfall- soil becomes saturated, large surface storage, less infiltration, larger surface run off, surface run off/ through flow, short lag time, high discharge

Thin soils- Water able to infiltrate, low capacity, large saturation, more surface run off, through flow, short lag time, high discharge

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5
Q

Draw a sketch of a subdued and flashy discharge

A 
Subdued= large lag time
Flashy= short lag time
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6
Q

What are the 4 types of erosion and explain them

A

Hydraulic action: The force of air/water forcing into cracks

Attrition: Rocks break into smaller fragments after colliding with each other

Abrasion: Rocks erode by rubbing against the bed

Solution: Acidic water reacting with the rock making it dissolve

+(vertical and latteral erosion)
High energy conditions

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7
Q

What are the 4 types of transportation and explain them

A

Traction: large boulders rolling along the river bed

Saltation: small rocks bouncing along the river bed

Suspension: Light minerals held amongst the water

Solution: dissolved material carried by the river

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8
Q

What is the drainage basin hydrological cycle?

A

The cycle of water on a drainage basin scale, this is an open system with both inputs and outputs

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9
Q

What are the features of a drainage basin?

A 
Source 
Tributary 
Watershed
river channel
Confluence
Area within dotted line= catchment area
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10
Q

Hydrological cycle key terms:
Input:

What is precipitation?

A

When water/sleet/snow/hail droplets get heavy enough, gravity encourages them to fall to the ground

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11
Q

Hydrological cycle key terms:
Surface processes:

What is surface storage?
What is soil moisture?
What is groundwater flow?

A

When water accumulates on the surface of the land e.g. puddles

Water held within the soil layer

What stored in the rock layer

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12
Q

Hydrological cycle key terms:
Transfer processes:

What is infiltration?
What is through flow?
What is percolation?
What is groundwater flow?

A

What sinking in to soil/rock from the surface

What flowing through the soil layer parallel to the surface

What seeping deeper below the surface

What flowing through the rock layer parallel to the surface

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13
Q

Hydrological cycle key terms:
Outputs:

What is evaporation?

What is Transpiration?

What is evapotranspiration?

What is condensation?

A

Water changes state from liquid into a gas and rises into the air

The loss of water from plants through their leaves back into the atmosphere

The sum of transpiration and evaporation

When water vapour cools and changes its state from a gas to a liquid

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14
Q

What is dynamic equilibrium?

A

When inputs=outputs

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15
Q

True or False: The global hydrological cycle is a closed system.

A

True

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16
Q

What is the global hydrological cycle?

A

The continuous cycle of water between the oceans, the land and the atmosphere on a global scale. this is a closed system with no inputs or outputs

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17
Q

What is the drainage basin hydrological cycle?

A

The cycle of water on a drainage basin scale, open system with inputs and outputs

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18
Q

What is pipe flow?

A

Water that travels through holes left by root systems and animal burrows

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19
Q

What is through fall?

A

Where precipitation is not intercepted but falls straight to the ground

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20
Q

What is stem flow?

A

Where the precipitation flows along the stems of a plant to the ground

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21
Q

What is water balance?

What is it used for?

A

The balance between inputs and outputs as the river level rises and falls throughout the course of a year
Used to predict flooding

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22
Q

What is the river regime?

A

The annual pattern of river discharge

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23
Q

What is the water balance formula?

What does each symbol mean?

A

P=Q+E+/-S

P- Precipitation
Q- Streamflow
E- Evapotranspiration
S- Changes in storage

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24
Q

What is hydrostatic pressure?

A

Exerted by a fluid at equilibrium at a given point within the fluids. Increases the proportion to depth measured from the surface due to the increased weight exerting a downward force from above

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25
Q

Draw the water budget graph

A

See notes
Mean precipitation (mm)
Mean evapotranspiration (mm)
Months

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26
Q

What are the differences between a subdued and flashy hydrograph?

A

Flashy: Subdued:

  • Impermeable rock -Gentle sided basin
  • Steep sided basin -Freezing temperatures
  • Urban area -Long period of light rainfall
  • Chalk bedrock -Sandy soil
  • Intense rainfall
  • Thin soils
  • Deforested catchment
  • Clay soil (Barton)
  • Snow fall + warm spring
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27
Q

What is overland flow?

A

Rainwater flowing over the ground/surface

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28
Q

What is base flow?

A

Groundwater flow that feeds into rivers through river banks and river beds

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29
Q

What is antecedent discharge?

A

The level of discharge before the storm

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30
Q

What is GPE?

A

Potential energy (stored energy)- determined by the altitude of the source in relation to base level

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31
Q

What is the amount of kinetic determined by?

A

Gradient + Velocity

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32
Q

When does deposition occur?

A

Low energy environments
Lower course
When there is a sudden reduction in gradient
River enters a lake or sea
Discharge has been reduced following a period of low rainfall
Shallower water
Sudden increase in the calibre/volume of sediment

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33
Q

What is the wetted perimeter?

A

The part of the cross sectional area in contact with water

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34
Q

What is the cross sectional area?

A

The total area within the cross section of a river channel

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35
Q

What is the hydraulic radius?

A

Measures the efficiency of a river
Cross sectional area divided by the wetted perimeter
high value = efficient

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36
Q

What is channel efficiency?

A

The ability of a river to move water

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37
Q

What is channel roughness?

A

The S.A of a river bed e.g. angular rock

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38
Q

What are the 3 channel processes?

A

Transportation
Erosion
Deposition

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39
Q

What are the factors influencing channel efficiency?

A

Channel shape
Channel roughness
Channel slope

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40
Q

Sketch the Hjulstrom curve

A

see notes
X axis- river velocity (cm per sec)

Y axis- Size of particles (mm)

Mean or critical erosion velocity curve- Velocity needed to entrain sediment (pick up sediment) of various sizes

Mean fall or setting velocity curve- velocity at which particles start to become deposited

Particles transported
Particles eroded
Particles deposited

this velocity is required to erode and entrain the smallest material clay particles is highest as they tend to stick together

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41
Q

What are the characteristics of the upper course within the long profile?

A

Vertical erosion- high amounts of friction

Large bed load size- river doesn’t hold enough energy to move large fragments

Large gradient

High amounts of friction as the channel depth is very shallow

Large GPE- as the altitude is high in relation to the base level

Stones are very angular as there is less attrition/abrasion within the upper course

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42
Q

What are the characteristics of the middle course within the long profile?

A

Velocity increases due to the introduction of tributaries

High kinetic energy due to velocity + gradient

Stones become less angular due to abrasion

Discharge increases a both the velocity and volume increase, due to the widening and deepening of the channel

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43
Q

What are the characteristics of the lower course within the long profile?

A

Cross sectional area increases as depth/width become larger increasing the carrying capacity

Low friction as water ti deeper

Gentle gradient as the depth increases due to erosional processes

Smaller bed load size as sediment gets eroded by attrition

Increased width, chunks of the bank and are eroded through hydraulic action + solution

44
Q

What is the river capacity?

A

The total sediment load of a river at a particular point or location

45
Q

What is the river calibre?

A

The size of a particular pebble/particle

46
Q

What is the river competence?

A

The size of the largest sediment particle that can be carried by that river at a particular time or location

47
Q

What is the hjulstrom curve?

A

The graph shows the relationship between the velocity of a river and the particle sizes transported. It shows the velocity needed to erode, transport and deposit material of different sizes

48
Q

What is sediment entrainment?

A

The action of picking up sediment so that it can be transported

49
Q

What is meant by spatial variations in load?

A

The level of load a river can carry depending on the drainage basin size

50
Q

What are the landforms of erosion?

A 
Waterfalls
Gorges
Interlocking spurs
V-shaped valleys
Potholes
51
Q

What are the landforms of erosion and deposition?

A

Meander
Oxbow lakes
Floodplains
Braided channels

52
Q

What is name for the deepest and shallowest part of a river channel?

A 
Deepest= pool
Shallowest= riffle
53
Q

What is the thalweg?

A

Fastest flow of water in a channel, centripetal force swings the thalweg into the opposite bank

54
Q

Draw the 3 stages of meander initiation

A 
See notes,
Pool
Riffle
Thalweg
Centripetal force
55
Q

Draw a leader cross section

A 
See notes
Low efficiency
Thalweg 
Deposition
Erosion
Slip off slope
Undercut by lateral erosion
Small river cliff
56
Q

What is helicoidal flow?

A

Helicoidal flow is the cork-screw-like flow of water in a meander

57
Q

Explain the formation of meanders

A

1) alternating pools and riffles
2) pools are deeper and able to hold more energy than riffles due to less friction
3) as the river meets a riffle (low efficiency/low hydraulic radius) the thawed flows around it

58
Q

Erosional landforms:

Give a description of a V shaped valley and interlocking Spurs

Draw a labelled diagram

Explain the formation of both

A

V shaped valley- a steep sided valley within the upper course

Interlocking Spurs- river bends and winds around hard rock on the upper course

See notes

V shaped valleys form when erosion takes place which is predominantly vertical
Interlocking Spurs are formed when the river is forced to wind around a hill or ridge of land taking the path of least resistance, protrusions of land are called Spurs

59
Q

Erosional landforms:

Give a description of potholes

Draw a labelled diagram

Explain the formation of them

A

They are cylindrical holes drilled into the rocky bed of a river, by turbulent high velocity water loaded with pebbles
Upper/early middle course

See notes

Pebbles become trapped in slight hollows and vertical eddies in the water which are strong enough to cause sediment to grind a hole into the Rock by abrasion
Attrition smooths and rounds the pebbles caught in the hole to reduce the size of the bed load

60
Q

Erosional landforms:

Give a description of waterfalls and Rapids

Draw a labelled diagram

Explain the formation of both

A

Waterfalls -A waterfall is a place where water flows over a vertical drop or a series of drops in the course of a stream or river.
Rapids- a fast-flowing and turbulent part of the course of a river.

See notes

Waterfalls- Soft rock is undercut (1).
This leaves a layer of hard rock which overhangs the layer of soft rock (2).
The water flows over the overhang and creates a plunge pool in the soft rock below. As the water hits the plunge pool it will erode it by both hydraulic action (the force of the water against the bedrock) and by abrasion (where the material carried by the river acts like sand paper against the riverbed) (3).
Eventually the overhang will collapse due to the erosion of the soft rock beneath it. The waterfall then retreats up stream (4).
This creates a steep, gorge-like valley.

Rapids- They are caused by different resistance among various rocks, that leads to sudden drops and rises in the river bed, creating fast/turbulent flow of water

61
Q

Give a description of braided channels

Explain their formation

A

A river becomes braided as it sub divides into many smaller streams
In between, small islands form although streams are constantly shifting
made of loose sands and gravel

Braiding occurs as rivers made up of easily eroded material e.g. sands and gravel break down and variable discharge causes braiding to be common in the snout of glaciers and semi-arid regions. The river has a low carrying capacity due to it being broad and shallow (low hydraulic radius), this means that it constantly gets overloaded by water. As a result the river sub divides into smaller and faster streams. There is increased sediment deposition at times of high discharge.

62
Q

Draw a diagram of a braided channel

A

see notes

point bar

63
Q

Give a description of Floodplains and Levees
Explain their formation

Draw a diagram

A

A floodplain is a large area of flat land on either side of the river which constantly gets flooded
Levees- Larger, heavier sediment deposited at the top of a bank creating a larger natural embankment

Floodplains are caused as erosion on the outside of the meander (lateral) causes channel migration. The river alluvium then becomes deposited building up the level of the floodplain- through sediment accretion of fertile land
Levees- As a river overflows, friction increases, the coarsest sediment is deposited first

See notes

64
Q

What is a delta?

Draw a diagram of a delta

A

A delta is a land form created by deposition of sediment as the channel progresses from the mouth to slower moving/standing water
Occurs when rivers meet an ocean, sea estuary, lake or reservoir

see notes
low tidal range
delta growing into sea/lake
little or no currents
Deposition of silt fills in sea or lake forming a delta
Dis tributary
River water carrying large amounts of silt from upper parts of the valley

65
Q

Give an explanation for delta formation

A

When a river reaches a sea/lake mouth, the energy is absorbed by the sea/lake with a lower velocity. As a result the rate of deposition is greater than the rate of removal, a large quantity of sediment in still conditions causes it to build up rising above sea level.
Flocculation occurs as sea water meets fresh water, where particles on suspension E.g. Clay/silt react with the salt, becoming heavy enough to sink and become deposited. The river then braids in order to reach the sea, this increases the rate of sediment removal and the river gains more energy.

66
Q

What are top set beds?
What are Foreset beds?
What are Bottom set beds?

A

Larger and heavier particles are first to loose energy

Medium calibre particles travel a little further before deposited , they are deposited at more steep angled (wedges) of sediment

Finest particles which travel the furthest distance before low velocity and flocculation leads to their deposition

67
Q

What are the features of a Arculate delta?

A

Arcuate Deltas:
Most common deltas
Curving the shoreline, distinct pattern of drainage more gravelly deposits
E.g. Nile Delta
Longshore drift keeps the seaward edge relatively smooth in shape

68
Q

What are the features of a birds foot delta?

Draw a diagram

A

Deposited material divides the river into smaller distributaries
E.g. Mississippi River

See notes

69
Q

What are the features of a Estuarine Delta?

Draw a diagram

A

Deposited material divides the river into smaller distributaries
See notes

70
Q

What are the features of a lobate delta?

Draw a diagram

A

Formed when a river flows into a lake

See diagram

71
Q

What are the 5 landforms in the upper course?

A
  • V shaped valleys
  • Interlocking Spurs
  • Potholes
  • Waterfalls+Rapids
  • Gorges
72
Q

What are the 2 landforms in the middle course?

A
  • Meanders

- Oxbow lakes

73
Q

What are the 4 landforms in the lower course?

A
  • Floodplains
  • Deltas
  • Levees
  • Braided channels
74
Q

What is the base level of a river?

A

The lowest point a river can erode down to

75
Q

Which course is there the most erosion?

A

Upper course

76
Q

What happens to GPE as it moves into the lower course?

A

There is very little GPE as the distance to base level is very small, meaning vertical erosion is minimal. High kinetic energy used to erode banks not the beds, bed is smoother therefore less erosion.

77
Q

Draw the graph of a graded profile

A

See notes

The long profile is smoothened out by the river

78
Q

What conditions does river rejuvenation occur?

A
  • a fall in sea level relative to the level of land
  • a rise of the land relative to the sea

Enables a river to renew its capacity to erode as its potential energy is increased

79
Q

What are the landforms created by river rejuvenation

A
  • Knickpoints
  • River Terraces
  • Incised meanders
80
Q

What is river rejuvenation?

A

Decline in base level, increasing the rivers potential energy

81
Q

Explain why land can rise: (positive isostacy)

A

Positive isostacy occurs as an ice sheet weighing down the land melts, therefore the weight gets removed causing the land to rise after it has sunk
Collision/Destructive plate boundary

82
Q

Explain why sea levels fall: (negative Eustacy)

A

Occurs due to an ice age freezing the water

83
Q

What are the 7 natural causes of flooding? And give key words

A

Soil depth- (infiltration, capacity, saturation, overland flow, through flow)
Vegetation- (Interception, soil moisture extraction, transpiration, evapotranspiration)
Geology- (groundwater flow, impermeable, permeable, percolation
Slope angle- (Gradient, Overland flow, surface run off, steep/shallow)
Rainfall: excessive or intensive- (Precipitation, saturated/unsaturated, Baked ground)
Snow melt- (Saturated/unsaturated, rapid, frozen soil, surface run off, infiltration, capacity
Drainage density [total length of streams/total drainage basin area]- (impermeable, excessive, carrying capacity, runoff, increased discharge)

84
Q

What are the 6 Human causes of flooding?

Give key words

A

Urbanisation: Developing on flood plains- (Vulnerable, flat land, low lying)
Artificial conduits e.g. drains and sewers- (Lag time, infiltration, capacity)
Channel straightening- (Artificial, increased velocity, downstream flooding)
Deforestation- (Soil moisture extraction, interception, through flow, evapotranspiration)
Farmland: Overgrazing and ploughing- (Compact, Infiltration, capacity, run off)
Dam failure- (Artificial, rapid increase, discharge, hard engineering)

85
Q

What is the definition of flood?

A

An overflow of water breaching the warring capacity of a river

86
Q

What is meant by the primary causes of a flood?

A

Usually the result of climatic factors

87
Q

What is meant by the secondary causes of a flood?

A

Tend to be drainage basin specific e.g. topography/geology

88
Q

What are the 2 types of Incised meanders?

A

Entrenched Meanders - River wear- Durham

Ingrown meanders- River Wye, Tintern Abbey

89
Q

Comment on the cross section of an entrenched meander

What are the causes of entrenched meanders?

A

Entrenched meanders have a symmetrical cross section
Occur due to:
-Very rapid incision due to rapid uplift
-Sides being resistant to erosion

90
Q

Comment on the cross section of an ingrown meander

What are the causes of ingrown meanders?

A

Produce an asymmetrical cross profile
Ingrown meanders occur due to:
Uplift of land, or incision by the river is less rapid (erodes laterally)

91
Q

What are river terraces?

A

They are level/steps on the sides of rivers marking former floodplains which are caused by rejuvenation due to vertical erosion

92
Q

How are river terraces formed?

A

River creates a floodplain
River is rejuvenated
Incised GPE and vertical erosion so river incises downwards
Creates a new floodplain at a lower level, leaving marks of levels/steps of the former flood plain

93
Q

What are paired terraces?

A

Levels on either side of the floodplain which are the same height

94
Q

What are unpaired terraces?

A

Form when lateral migration is dominant compared to incision.

95
Q

What are the 3 causes of river rejuvenation?

A

Dynamic change
Eustatic change
Static change

96
Q

What is dynamic change?

A

Upwards movement of land, raising the height above sea level, increasing GPE

97
Q

What are knickpoints?

A

A knick point is a sudden break or irregualrity in the gradient along the long profile of a river.
shown by waterfalls/rapids etc.

98
Q

How are knickpoints formed?

A

Base level falls (positive isostasy/negative ecstasy)\
river begins to cut down to new base level with renewed energy due to more GDP, carrying out more vertical erosion

The prices begins at sea level and begins to cut back up the long profile (headward erosion), moving upstream in the rivers course until an equilibrium in terms of GPE is reached

The knickpoint represents where the old long profile meets the new/regraded one

99
Q

What is orogenesis?

A

plate movement, plate compression resulting in mountain building

100
Q

What is a case study for an ingrown meander?

A

River Gwash Rutland
Runs through the village of Braunstone in Rutland
Fall in discharge means river channel becomes meandered, downcutting was marked by the ingrown meander

101
Q

What is the flood magnitude?

A

The size/extent of the flood

102
Q

What is the flood frequency?

A

The occurrence of a flood

103
Q

What is the recurrence interval?

A

The interval at which particular levels of flooding will occur

104
Q

What 6 factors influence flood risk?

A 
Urbanisation
Preparation/defences
Economic development, infrastructure- better prep
Population density, more people at risk
Frequency of flooding 
Magnitude of flooding
105
Q

Comment on the frequency of large and small magnitude floodings

A

Large magnitude floodings don’t happen very often e.g. every 100 years
Small magnitude floodings are more frequent e.g. every 2 years

106
Q

What is the recurrence interval formula?

A

R= n+1
—–
m

m= rank

A longer recurrence interval = soft management instead of hard

107
Q

What is sustainable development?

A

Development now that does not compromise the needs of future generations. It must ensure that economies, society and environment are preserved and maintained now and in the future

Geography Physical 2: rivers (6 decks)

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