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Year 3 Rivers And Sediment > Lecture 8 Hyporheic > Flashcards

Lecture 8 Hyporheic Flashcards

1
Q

What is the hyporheic layer

A

Area below a river bed

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2
Q

What characteristic of bedforms makes the hyporheic zone possible

A

Porus bedload

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3
Q

What pressure regime causes water movement to the hyporheic zone

A

High bed pressures, often when flow constricts

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4
Q

Why is residence time important between grains in the HZ

A

Reactions with carbon dioxide and microbial activity governed by movement and replacement of water

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5
Q

What is the name for how flow gets into the river bed

A

Advective exchange

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6
Q

How does water get into the bed via advective exchange

A

flow pathways and channels

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7
Q

Which side of a ripple formation does a flow pathway enter the bed

A

stoss side

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8
Q

In meander channels, how can water move in the hyporheic zone

A

From one channel to another, same in braided rivers

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9
Q

What are OFG

A

Open framework gravels, high porosity

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10
Q

What does mixing of different grain sizes lead to

A

Less porosity as small grains fill in gaps

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11
Q

What is the role of darcy’s law

A

Way of describing subsurface water movement

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12
Q

When do we see a drop in permeability with sand fraction percentage

A

Over 18%

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13
Q

What is wrong about conventional velocity profiles with the addition of hyporheic flow

A

Inconsistency of bed flow understanding, gap

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14
Q

What flow is seen from the bed to the main flow channel

A

Return flow

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15
Q

What do interconnected pores lead to

A

Creation of flow networks and channels

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16
Q

What force is adjective exchange said to solve

A

Lift force

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17
Q

What areas of study does the hyporheic zone link to

A

Ecology and biogeochemisty

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18
Q

What species lay there eggs within gravel beds

A

Salmon, trout species

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19
Q

What cycle is the hypirheic zone important in

A

Carbon cycle

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20
Q

What is the name for the amount of time water spends in pores

A

Residence time

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21
Q

What is Greg’s view on the size of hyporheic sizes

A

Just several grains in diameter below bed

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22
Q

How quickly can chemical composition change over the bed boundary

A

Very significant contrast, quick

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23
Q

How does oxygen differ in the HZ

A

Much less

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24
Q

Where does flow come out of the bed

A

Low pressure zones

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25
Q

How has HZ movement been visualized

A

Tracer tests

26
Q

As well as bed forms, where can adjective exchange be found

A

Pool riffle

27
Q

Why may water move in the HZ across a meander

A

Pressure and height difference

28
Q

What is hydraulic conductivity

A

Ease at which water can move through a substrate

29
Q

What does dh stand for in darcys law

A

Change in head

30
Q

What is strange about Hyporheic flow

A

Occur across scales with incredible similarities

31
Q

What does grain size, particle sorting and packing in the river bed change

A

Heterogeneity of hydraulic conductivity

32
Q

In the natural world, How is ease of movement determined

A

The mosaic of different bed types

33
Q

How does sediment transport rates effect hydraulic conductivity

A

Sediment sorting, slow transport leads to avalanching and movement together leading to more mixed substrate

34
Q

What sand fractions are OFGs

A

Less than 18%

35
Q

What is the assumpted new layer between hyporheic and normal freeflow

A

Transition layer

36
Q

What is the name of the point where flow speed changes to go to the bed

A

Inflection point

37
Q

How think is the transition layer

A

2 grains

38
Q

What is the porosity of gravel bed rivers

A

Over 40%

39
Q

What does larger porosity give us

A

Larger amount of space which water can move through

40
Q

What can the lift force lead to

A

Sediment transport

41
Q

What is the dominant mechanism for HZ exchange

A

Advenctive exchange (pressure)

42
Q

Where are large shear stress events that move down towards the bed

A

Sweep events

43
Q

What happens when sweep pushes water into the bed

A

Forces water outof porespaces into the flow, ejection

44
Q

What does permeanke beds do to horseshoe ejection structure

A

Gets rid of legs, changes boil structure

45
Q

How can pollutants be effected by HF flow

A

Fine scale pollutants can be filtered out of the flow, pollutants in the bed

46
Q

Where do we get scour

A

In the trough

47
Q

What does dune erosion mean with pollutants at HZ

A

Larger flood events will take pollutants far down, if flow reduces scour will not be as deep and pollutants will stay there

48
Q

What does the Ren and Packman paper show

A

Chemical (pH) water composition can effect repulsion due to electrostatic nature of substrates, can allow more or less HZ flow, mostly with clay

49
Q

What is the Reaction significance factor

A

Determines what is more factors within the bed, what is more important, dune forms and bed forms, vs larger scales such as meander bend movement

50
Q

What is the RSF reaction

A

(Transit / reaction)×(reach / turnover)

Time × length

51
Q

In headwaters reaches, what rsf is more important

A

Small bed forms and dunes

52
Q

What was found with efficiency with HZ flow

A

More efficient round meanders and on larger scale than with smaller scale1

53
Q

How does the classic flow model change with added porosity

A

Recirc becomes squished into the bank, with zone coming back up

54
Q

What substrate is still comparable with impermeable beds

A

Sand beds

55
Q

What is RIM

A

Refractive index matched, allows objects to become see through

56
Q

What can be said about pores within substrates

A

Flow is turbulent

57
Q

How far were fine materials in hyporheic flow paths stores compared to solutes (Harvey et al)

A

two-thirds as deep as solutes

58
Q

Are fines or solutes more easily mobilized by bedform migration (Harvey et al)

A

Fines

59
Q

What did floods do to solute storage

A

drove them deeper below the bed, beneath 8cm

60
Q

What three timescales are important in hyporheic reactions

A

flood duration, relaxation time of bedforms and hyporheic residence times.

Year 3 Rivers And Sediment (12 decks)

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