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LE2 Coastal > Sediment Transport > Flashcards

Sediment Transport Flashcards

1
Q

The process of eroding sediment from one place, transporting it in the flow and depositing it in another place.

A

Sediment Transport

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2
Q

Occurs when the shear stress applied on
the sediment bed exceeds the critical shear stress

A

Erosion

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3
Q

It takes place when the transport capacity of the flow is exceeded.

A

Deposition

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4
Q

(4) Basic sediment process

A

Resuspension
Transport
Settling
Consolidation & compaction

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5
Q

Sediment process is dependent on

A

1)Flow hydrodynamic conditions
2) Sediment Properties (size, shape, density, composition)

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6
Q

It is most fundamental property
governing the motion of the
sediment particles in water.

A

Particle Settling

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7
Q

Defined as the terminal velocity at which a single particle falls through quiescent water and depends on the particle’s size, shape, and density along with the water’s viscosity and density.

A

Settling Velocity

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8
Q

True/False

For Sediment Transport Modeling, the settling velocity of particles and their resistance to resuspension under shear
stress are the most significant.

A

True

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9
Q

True/False

PARTICLE SETTLING CHARACTERISTICS vary as they respond to hydrodynamic conditions in the water body.

A

True

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10
Q

True/False

Once near the bottom, DEPOSITION governs their removal from the water column.

A

True

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11
Q

2 major mechanisms for sediment transport

A

Currents & Wind waves

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12
Q

True/False

Sediment transport is significantly
influenced by the instability of the near-bed flows.

A

True

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13
Q

True/False

Sediment is moved either only suspended or bed load.

A

False (and/or)

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14
Q

Calculation of total sediment load

A

Suspended load + Bed load

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15
Q

It is the portion of the sediment load that is transported in suspension in the water column which includes:
sediments resuspended from the bed and wash load brought from upstream.

A

Suspended Load

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16
Q

It is used to analyze contaminant transport since contaminants are often attached to and transported by sediments in suspension.

A

Total Suspended Load

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17
Q

It has relatively fine material in near-permanent suspension
that is transported through the system without deposition.

A

Wash Load

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18
Q

It is comprised of particle sizes finer than those found in the
bed.

A

Wash Load

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19
Q

True/False
Cohesive sediments can be transported as suspend load and bed load.

A

False

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20
Q

True/False

Cohesive sediments can be transported as suspended and or bed load.

A

False (only as suspended load)

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21
Q

True/False

Cohesive sediments can be transported as suspended and or bed load.

A

False (only as suspended load)

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22
Q

True/False
Non-cohesive sediment can only be transported as bed load.

A

False (both suspended and bed load)

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23
Q

The 2 mechanism of transporting cohesive as suspend load:

A

Advection
Dispersion

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24
Q

It is a mechanism where the cohesive sediment is carried with the ambient water at the flow velocity.

A

Advection

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25
Q

It is a mechanism of transport where cohesive sediment is moved from an area of high to low sediment concentration.

A

Dispersion

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26
Q

It is a type of load where it is comprised of particles that move on/ near the bead by Saltation, rolling, or slid8ng in the bed layer.

A

Bed Load

27
Q

True/False

The bed load movement occurs intermittently in a thick layer; on or in close contact with the bed.

A

False (thin)

28
Q

It is a process by which individual
sediment grains make isolated or
serial jumps along the bed?

A

Saltation

29
Q

t provides a transition from bed-load
transport that takes place
immediately above the bed to
suspended-load transport that takes
place in the overlying water column.

A

Saltation

30
Q

It is defined as the frictional force per unit of bed area exerted on it by the flowing water.

A

Shear Stress

31
Q

It is an important factor in the movement of bed material and is a useful parameter in describing sediment transport as well as erosion and deposition.

A

Shear Stress

32
Q

True/False

Shear stress is exerted on the bed when water flows over it, as either steady flow or oscillatory flow under tides and waves.

A

True

33
Q

True/False

Shear stress moves bed particles in a sliding motion downstream.

A

False (rolling)

34
Q

True/False

If the shear stress is greater than the critical shear stress, only a fraction of the suspended material will be deposited.

A

True (higher shear stress-sediment go up)

35
Q

True/False

If the shear stress is less than the critical shear
stress, suspended sediment will be deposited on bed gradually.

A

True

36
Q

(3) bottom shear stress mechanism vary

A

Temperature
Topography
Salinity

37
Q

3 Bottom shear stress mechanism vary

A

Temperature
Topography
Salinity

38
Q

3 Bottom shear stress mechanism vary

A

Temperature
Topography
Salinity

39
Q

4 Sources of sediment transport

A

Point discharges
Land surface runoff
Bank erosion
Bed scour

40
Q

4 Predominant factors responsible for sediment transport

A

Currents
Winds
Inflows
Tides (in estuaries and coastal waters)

41
Q

Major Mechanism of sediment transport

A

Currents & Waves

42
Q

A major mechanism dominant in rivers.

A

Currents

43
Q

A major mechanism that is dominant in lakes, especially during storm.

A

Wind wave

44
Q

The two mechanism that is dominant estuaries.

A

Wind & tidal waves

45
Q

True/False

In Steps 1 and 2, the predominant mode of transport is sediment grains moving along the bottom in the form of bed load. Particle movement begins as a sliding or rolling motion.

A

True

46
Q

True/False

In Step 3, some particles also may move above the bed surface through saltation. These movements result in frequent contact of the moving particles with the bed and are transported as bed load.

A

True

47
Q

In Step 4, particles begin to be suspended and are subject to _______ forces as the flow velocity and shear stress increase. Particles are
thrown up into suspension and are transported as suspended load.

A

turbulent

48
Q

(2) Difficult to separately identify the phase of
resuspension and deposition in natural waterbodies

A

Resuspension &
Deposition

49
Q

It determined the critical shear stress for erosion as a function of depth and the erosion rate as a function of both shear stress and depth. (Designed by McNeil)

A

SEDflume

50
Q

It measures the erosion of sediments at high shear stresses and with sediment depth.

A

SEDflume

51
Q

It is controlled primarily by BOTTOM SHEAR STRESS and also SITE-SPECIFIC BED PROPERTIES for erosion rates and scour depths.

A

Sediment Resuspension

52
Q

True/False

Sediment on the bed will be eroded and transported when the bottom shear stress EXCEEDS A CRITICAL VALUE.

A

True

53
Q

[Sediment RESUSPENSION]

The Immersed particle weight is the main stabilizing force.

A

Non-cohesive sediment

54
Q

True/False

[Sediment RESUSPENSION]

For sediment with bulk density close to the water density, the main forces are interparticle adhesion and organic binding.

A

True

55
Q

True/False

[Sediment RESUSPENSION]

Beds are layered with density and shea strength decreasing downward.

A

False (increasing)

56
Q

True/False

Sediments move whenever the shear stress caused by water flow and wind waves REACHES A CRITICAL SHEAR STRESS FOR RESUSPENSION that is EQUAL TO THE SHEAR STRENGTH “HOLDING” the sediment to the bed.

A

True

57
Q

A process by which suspended sediments LEAVE the water column, either temporarily or permanently, and become part of the bottom sediments.

A

Sediment Deposition

58
Q

True/False

[Sediment DEPOSITION]

With non-cohesive sediment, the critical shear stress is only slightly less than that for erosion.

Particles settle to the bed almost as soon as the
shear stress is too small to erode it.

A

True

59
Q

True/False

[Sediment DEPOSITION]

With cohesive sediment, critical shear can be much greater than that for erosion.

A

False (smaller)

60
Q

It can be estimated as the
product of the settling velocity and the probability of deposition on contact with the bed, which is 0 for very turbulent systems and 1 for stagnant ponds.

A

Deposition Rate

61
Q

True/False

For depostion, particles must overcome
RESISTANCES due to:
Turbulence in the Water Column
Thin Viscous Sublayer at the Interface
Chemical or Biological Activity at the Bottom

A

True

62
Q

True/False

Probability of deposition depends on:
Bottom Shear Stress
Suspended Sediment Size
Cohesiveness of the Sediment

A

True

63
Q

True/False

Once in SUSPENSION, sediments will settle out at a rate determined by the sediment concentration, the settling velocity, and the turbulence intensity.

A

True

LE2 Coastal (3 decks)

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