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Year 3 Rivers And Sediment > Lecture 11 > Flashcards

Lecture 11 Flashcards

1
Q

How does a system stay balanced

A

Sediment supply must be equal to stream power otherwise either aggregation or degradation will take place

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2
Q

What geological feature can lead to high amounts of sediment

A

Techtonic

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3
Q

What can increase stream power

A

Slope, depth, rainfall, stream order

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4
Q

How does climate impact sediment and water

A

Sea level rise, more rainfall then more sediment,

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5
Q

How can vegetation impact river systems

A

More stable banks, water control and uptake

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6
Q

Where do we get little records of what a river is doing

A

Little sediment with little aggregation, no new locations, channel belt is stable

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7
Q

Where will we get high rates of preservation and sediment movement

A

High sediment with high channel aggregation

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8
Q

What is a key aspect of channel change

A

Sediment supply

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9
Q

What is the channel belt

A

The whole channel shape which the river runs in

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10
Q

What is an avulsion

A

A abrupt shift of the entire channel belt to a new location, inter avulsion period can be 1000s years

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11
Q

How long does it take for an avulsion to complete

A

May be almost instant, but may take longer for the whole channel to fill in or move

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12
Q

What is the hop length

A

Distance that the new channel shifted

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13
Q

What is avulsion length

A

distance that the channel belt is before is rejoins the channel

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14
Q

what is the hop length

A

size of the channel movement

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15
Q

what was the relationship between channel belt width and distance it was moving

A

almost a 1 correlation. 2.5 times channel belt width is how much it is moving over.

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16
Q

What is the set up

A

what would make the channel belt [perfect for switching to a new location

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17
Q

What is the trigger

A

The chance of the river avulsing after it has been set up to do so

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18
Q

what are the two theory for set up

A

superelevation and gradient advantage

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19
Q

what is super elevation

A

levee’s build up either side of the channel, channel starts to become perched above the flood plain.

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20
Q

what happens when the depth of the channel is the height of the land cover

A

channel depth above floodplain, when spills out all old channel is lost

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21
Q

What is gradient advantage

A

is there a tilt in the flood plain itself, water will move on the gradient, cutting a new channel

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22
Q

What is a trigger event

A

large flood which starts the avulsion

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23
Q

what can happen in really big floods

A

avulsion can take place even without set up

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24
Q

what is a key control on the avulsion processes

A

sediment supply.

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25
Q

Where do we get heigher avulsion frequency

A

more sediment.

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26
Q

What does bed load do to channels

A

build the channel up creating more channel height and therefore more avulsion chance

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27
Q

what does suspended sediment do to banks

A

builds up levees

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28
Q

How do we get a perched channel

A

some suspended sediment for levees and some bedload to build channel height

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29
Q

If you had little coarse sediment but lots of fine sediment what would happen

A

hinder avulsion, larger levees shallower channel

30
Q

In south America what has seen to be linked with avulsions

A

la nina events cause avulsions, 51 in la nina only 5 with el nino

31
Q

When can avulsions be linked climatically

A

high rainfall events

32
Q

what were rivers like pre 450ma

A

no vegetation, braided rivers were much more avulsive with no vegetation growth

33
Q

When was the older rhine-meuse avulsions

A

8000ya, nearer to the coast

34
Q

what drives the original avulsions

A

sea level rise, reduce the slope, sediment deposition

35
Q

What was the second avulsion stage caused by

A

subsidence of the crust, more low lying area

36
Q

What is the rhine avulsion duration

A

325 years

37
Q

If sea levels wall what happens to the land

A

erosion and incision

38
Q

How was the bridge karssenberg

A

based on the rhine system, numerical system model

39
Q

what is sediment transport a function of

A

the discharge

40
Q

How will channel incision change river shape

A

more sediment released if more incsion

41
Q

What can happen to the original channel after evolution

A

single channels can create multiple channels

42
Q

what are the two probability factors that lead to channel avulsion

A

Ps, birfurcation, super elevation,

Pd, probability of a yearly flood discharge

43
Q

If you’ve had one avulsion what is the probability of another one happening

A

it drops

44
Q

What can happen to channel belt size

A

they can widen

45
Q

How does the model know which channel to give more water

A

slope

46
Q

What happens if we get lots of connected channels together

A

can find aquifers below the soil

47
Q

what is base level?

A

the lower limit to which a river can erode its valley (powell 1875)

48
Q

what are the 3 river planform types

A

straight, braided, meander

49
Q

what is the equation for stream power

A

water density x gravity x discharge x slope

50
Q

What is unit stream power

A

stream power divided by width

51
Q

What are the 5 basic degrees of freedom in a channel system

A

Slope, width, depth, platform, bed roughness

52
Q

What is the efficient transfer of water

A

Hydraulic efficiency

53
Q

What is the primary movement process of larger bed load

A

Saltation

54
Q

What is the typical longprofile of a river

A

Concave from source to mouth

55
Q

What does curved channel result in

A

Super elevation of the waters surface higher at the outside of the bend

56
Q

Other than a flood, how else can avulsions occur

A

water build up after downstream blockage

57
Q

How much has the po river in Italy moved in 3000 years

A

50km

58
Q

how much has the yellow river moved laterally over 4200 years

A

800km

59
Q

what happens when avulsive rivers stay separate and both channels filled over a large length of time

A

they are termed anastomosed

60
Q

when do inter avlusion periods decrease

A

when base sea level rises

61
Q

what is the average inter avulsion period of the river kosi

A

4-44 years

62
Q

how does the flow of the kosi river change

A

gradual transfer of flow form one channel to another

63
Q

how were some of the po’s avulsions created

A

man made movement of channels

64
Q

when does avulsion frequency increase

A

with increasing deposition rate in the channel belt

65
Q

how might tectonic activity effect avulsions

A

may occur as a response to an individual tectonic event., or gradual tectonic shift

66
Q

tectonically, where to avulsing channels concentrate

A

in areas of tectonic subsidence

67
Q

how are belts seen over time

A

seen to be stacked on top of each other laterally

68
Q

What must the diversion of a channel to a new system result in

A

channel incision

69
Q

what did some scientists use dune movement to estimate

A

bed load movement

70
Q

what did kostachuk find about lagging with river dunes structure

A

dune height and length lagged behind changes in channel velocity leading to a hysteresis effect

71
Q

in migrating dunes, how much trapped sediment was suspension

A

95%

Year 3 Rivers And Sediment (12 decks)

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