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Year 3 Rivers And Sediment > Lecture 10 > Flashcards

Lecture 10 Flashcards

1
Q

What’s the main thing that discriminates a braided and a meander river

A

Multiple mid channel bars in a braided channel

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2
Q

What sides does a singular central unit bar deflect water to

A

Both sides, erosion on both banks

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3
Q

What happens to a single unit bar when flow goes either side of it

A

Can turn into a compound bar

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4
Q

Why are cross bar channels Important in braided systems

A

Can become the dominant channels due to widening and scouring of the channel

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5
Q

Barr migration is faster in meander or braided rivers

A

Braided

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6
Q

Can bars migrate even in flow with no flood events

A

Yes

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7
Q

How did the bar move on the jamuna river

A

Bar appeard, and doubled insize over the space of 2 years

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8
Q

What is one way that bars can grow

A

Accumulates other unitbars

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9
Q

Where do bars form

A

At a confluence site between multiple channels, creates scour

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10
Q

What does the scour zone create downstream

A

A supply of sediment

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11
Q

Is the flow on either sides of the bar normally even

A

No, one side normally sees more flow, creating a lopsided bar

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12
Q

How will flow be concentrated around a bar

A

In one channel

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13
Q

What does eneven channel flow cause around the bar

A

Elongation of one bar side

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14
Q

In parker et al how many bars could be tracked over 4 years

A

1

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15
Q

Do bars tracks from one year to the next, parker et al

A

No not in all cases, dynamic system

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16
Q

What is channel cut

A

Creation of new channels

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17
Q

Whag is channel fill

A

Abandonment of channels

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18
Q

When bars are moving how will that effect flow

A

Moving bars deflect flow differently

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19
Q

What can cause channel cut and fill

A

Bar shape, can stall and stop flows

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20
Q

When 2 under water bars merge together what do you get

A

A larger compound bar that sticks out of the water

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21
Q

What can happen with large compound bars with uni bar growth

A

Smaller unit bars can pile on the the compound bar side, adding sediment and size to the compound bar

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22
Q

Where can abandoned channels form

A

In the middle of bars, caused by abandoned cross bar channels

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23
Q

Where may cross bar channels also form

A

In the topographic low point between bar and compound bar

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24
Q

In the south Saskatchewan what bar formed in low flow

A

Large attached bar, simplified the channel down

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25
Q

What happens to braided systems during high flows

A

Channel cutting and new channels formed, many unit bars

26
Q

In normal flow conditions what does the topography of braided rivers look like

A

Bell shaped curve, even

27
Q

In a flood event what shape does the topographical chart represent

A

Uneven, sporadic

28
Q

In rivers with strong banks, what does the system look like

A

Narrow with less unit bars due to less sediment entering the system and less width to move

29
Q

Bars with weak vegetation growth are stable or unstable

A

Unstable

30
Q

So with strong banks but weak vegetation growth what does the system look like

A

Dynamic and quick, unit bars always moving, compound bars do not survive for long

31
Q

What are the key characteristics of a weak bank with low vegetation growth

A

Wide and unstable channel, many channels, with heavily divided flow

32
Q

In a heavily venerated channel what is common

A

Fairly stable bars with the main channel acting like a meander system

33
Q

What is laterally accretion

A

Bars can grow on the side of larger channels

34
Q

What radar is used to see unit bar structure below the bed

A

Ground penetrating radar

35
Q

How can we see bar movement in ground penetrating radar

A

Slip face movement

36
Q

How can we see larger scale unit bar migration

A

Whole strands of sediment diagonally twisted together

37
Q

How can high angle reflections show us bar migration

A

Can show movement and channel fill due to slip face accretion

38
Q

How can gpr who channel truncation

A

Up down meander like shapes show channels that have cut through at different orientations

39
Q

Do we get fining up in meander and braided channels

A

Yes

40
Q

Do we only find lateral accretion surfaces in meander rivers

A

No, also on the side of braid bars

41
Q

How do braided channels show lateral accretion

A

Braided channels are sinuous therefore they grow by sediment aggrading laterally

42
Q

Is the process in meander fill and channel filling similar

A

Yes, toonen et al

43
Q

What is the difference between braid bars and islands (Brice 1964)

A

Islands are not submerged at bankfull stage

44
Q

Why do bars look different at different flow stages

A

different river depths produce different erosional characteristics

45
Q

What is the difference between an anastomosing and braided channel

A

anastomosing channels are a lot longer, and are split of from the main river belt.

46
Q

What is channel diversion associated with

A

high stage scouring of thalwegs

47
Q

How does a channel become filled in

A

channel filled with sediment from the upstream end, downstream end blocked by moving channel bars

48
Q

How will despositional unit scale vary

A

with the scale of the alluvial feature

49
Q

What feature can be seen in a sandstone conglomerate body

A

complete channel belt

50
Q

What feature can be seen in sets of inclined strata (storeys)

A

Individual channel bars and channel fills

51
Q

What is depositional imprication

A

when deposits are aligned or orientated the same way

52
Q

What is a paleocurrent

A

A geological indicator of flow direction

53
Q

What does paleocurrent depend on

A

orientation of bedforms and sedimentary structure, what part of the channel bar fill is preserved

54
Q

How do rivers self organise their planform pattern

A

feedback from bars, channels, floodplain and vegetation

55
Q

What determins bar pattern

A

width-depth ratio

56
Q

what 3 bar types can form in a point bar (Kleinhaus)

A

chute, tail and scroll

57
Q

what 4 stages did kleinhaus create for braided rivers

A

highly braided, braided and meandering, meandering with scroll bars, laterally immobile no bars

58
Q

what does vegetation affect (kleinhaus)

A

channel mobility

59
Q

What can cause high sinuosity with vegetation in braided rivers

A

vegetation can stop the erosion of the point bar leading to outer bank erosion

60
Q

according to carson, what 3 groups can river channels be separated in

A

bed load. mixed load and suspended load

Year 3 Rivers And Sediment (12 decks)

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