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Year 3 Rivers And Sediment > Lecture 4 > Flashcards

Lecture 4 Flashcards

1
Q

What is the law for fine suspended sediment

A

Stokes law, only for fine gravels and clay

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2
Q

How does turbulence influence travel within the flow

A

Can cause higher retention depending on sweep burst ect, also caused shear stress to pick up grains

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3
Q

What is the name of the process of a particle falling to the bed

A

Settling, particle settling time

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4
Q

What is the stokes law equation

A

Vg=((o-p)gDsquared)/18

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5
Q

What is the name for the Greek symbol used to represent sediment density

A

Sigma o

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6
Q

What is the name of the Greek symbol used to represent water density

A

Rho p

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7
Q

What is the symbol used to show viscosity

A

u

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8
Q

What is the settling velocity a function of

A

Particle size square

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9
Q

What is the common value we use for sediment density

A

The value of quartz 2650kg per cubic meter

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10
Q

What is the normally value of water density

A

A thousand kg for cubic meter

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11
Q

What is the value of gravity

A

9.81

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12
Q

What is fluid viscosity

A

The ability for the liquid to move eg lava vs water

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13
Q

Why might some particles behave differently to other particles and fall faster

A

Cohesion with other particles, flocculation

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14
Q

How does a particle remain in suspension

A

If the positive verticals fluctuations are greater than the negative ones and Settling velocity

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15
Q

What material can stay in the flow for a long time

A

Very fine material

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16
Q

What happens if the positive v fluctuations are not greater then Vg and negative v

A

Particle will fall out of suspension

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17
Q

Where is the concentration of larger sediments

A

Near the bed

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18
Q

What does stokes law only hold for

A

Smooth spheres falling through a still fluid at low Re

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19
Q

In what law is fall velocity proportional to root of Diamater

A

Impact law

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20
Q

With small particals what is unique in the way they move in the flow

A

They move through the liquid as if the flow is laminar

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21
Q

With larger particles how do they behave in the water

A

They have more mass so they create turbulent Wakes

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22
Q

At what particle size of most common for stokes law

A

Less than 0.01cm

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23
Q

What is it called when particles join together

A

Aggregation, flocculation

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24
Q

At what sizes particle is viscous drag dominant

A

Less than 0.1mm

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25
Q

What size partical is form drag dominant

A

Larger than 0.1mm

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26
Q

When is the viscosity of the water changed

A

When there is a huge amount of suspended sediment

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27
Q

What happens with sediment density in the case of the Rio bermejo

A

The denser bermejo sinks under the Paraguay

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28
Q

At what sizes do particles start becoming more common at the bottom of the river

A

0.062-0.125 mm

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29
Q

What particle size is only found at the bottom of the river depth

A

Over 0.25 mm

30
Q

What is the highest concentration of upper river sediment by size of grain

A

Less than 0.002 mm

31
Q

What is the method to calculate sediment concentration at depth

A

Rouse equation

32
Q

What is k in the rouse equation

A

Von karman constant

33
Q

What is the rouse equation based on

A

Th fall velocity of the different particles

34
Q

What is the section of the rouse number called that is fall velocity divided by shear velocity x Von Karmans constant

A

Rouse coefficient

35
Q

If the rouse number shows a low value, what does this mean?

A

Fine particles and high turbulence and velocity, uniform distribution of suspended sediment

36
Q

What do high rouse numbers show

A

Coarse particles, low velocity and turbulence, strong vertical sediment distribution

37
Q

What are some other factors that control suspended load

A

Precipitation intensity, run off amount, site area sampled, differences in transport rates, amount of sediment already in the channel and the depletion is easily erodible debris

38
Q

Who created the idea of hysteresis graphs with river sediment suspended load

A

Williams 1989

39
Q

If there is an even level of sediment with discharge what will the graph look like

A

Straight

40
Q

What is the name of the straight type of graph seen in Williams 1989

A

Class 1

41
Q

What creates curving in a Williams class 1 graph

A

C/Q reach the same peak at the same time but are spaced differently

42
Q

What causes a Williams 1989 class 2 graph and what is it called

A

Clockwise loop, caused by when concentration change rises faster on the rising limb then discharge

43
Q

How is a counter clockwise loop created (class 3)

A

Discharge (Q) rises faster than C with Q dropping on the way back

44
Q

What conditions are associated with a class 1 graph

A

Uninterrupted sediment supply throughout the flood, but increased and decreased at the same rate

45
Q

What conditions create a class 2 clockwise loop

A

Either a depletion of available sediment before discharge has peaked or flushing out of sediment as discharge builds, common in the early part of a storm

46
Q

What conditions can cause a class 5 figure 8 loop

A

Ice break up or another peak which causes the hydrograph to show two distinct peaks between sediment and discharge

47
Q

What causes grains to accelerate towards the bed

A

Gravity

48
Q

When does a grain reach terminal settling velocity

A

When the fluid drag on the accelerating grain becomes equal to the weight of the grain

49
Q

What are the separation forces detached from each side of the falling grain

A

Karmen Vortex

50
Q

What do rotating grains experience that is different to a non oscillating grain

A

Magnus effect

51
Q

If the stokes number is less than 1 what path do particles follow

A

Follow the motion of turbulence eddies

52
Q

What is the vertical velocity profile sometimes called

A

Law of the wall

53
Q

What conditions can cause a type 3 graph

A

Flood waves move faster than sediment flux, high soil erodability throughout flood event

54
Q

What happens as a large amount of sediment is added to river systems

A

Can enhance turbulence especially near the bed for example shear stress

55
Q

Why is turbulence enhanced under thicker flows

A

As there is more viscosity it is harder for water to move past each other and more resistance is created

56
Q

What happens when more sediment is put into an already turbulence enhanced flow setting

A

Turbulence is dampened and there is a chance that a laminar plug flow can occur at the top of the flow

57
Q

Who showed the idea of turbulence enhanced flow and turbulence plug flows

A

Bass et al 2009

58
Q

What causes the turbulence to damped in high sediment systems

A

Greatly increased viscosity

59
Q

At a dune level, what features are present in an Baas turbulent enhanced flow

A

More turbulence in the seperation zone, maximum turbulence at reattachment point, packages of low velocity upwards shed, low turbulence near surface due to plug development

60
Q

At what area of the dune are boils created

A

Reattachment point, area of highest shear stress

61
Q

When can boils mic suspended sediment

A

All the way from the bed to the surface

62
Q

What is the name of the bursting structure that can be created by dunes

A

Dune generated vortex m, horseshoe vortex

63
Q

What is the name of the zone where the boil is present on the waters surface

A

Upwelling zone

64
Q

What is the symbol for settling velocity

A

Vg

65
Q

What is the symbol for sediment transport rate

A

i

66
Q

What are the 4 categories of grain shape

A

disc, sphere, tabulate. rod

67
Q

what is the predominate size of sediment grains in river systems

A

1/2 - 1/4 of a mm

68
Q

Why will a grain sink

A

if the weight if the grain exceeds buoyancy force

69
Q

What is the immersed weight of a sediment grain

A

gravity force minus the buoyancy force

70
Q

What is the resistance to motion acting on sediment particles

A

drag

71
Q

What type of drag is caused by fluid pressure

A

form drag

72
Q

What is the name given where the drag on an accelerating grain becomes equal to the immersed weight of the grain

A

terminal settling velocity

Year 3 Rivers And Sediment (12 decks)

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