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Sediment Transport
Outline
1. Incipient motion criteria for unisize and mixed-size sediments
2. Modes of sediment transport
3. Bedload transport
4. Suspended load
5. Bedforms
(Middleton and Southard, 1984)
gDgD
D
F
F
G
D
0
3
20
Threshold of Motion
(Shields,1936; Julien, 1998)
Sample Calculation
What is c for D = 0.005 mm quartz-density particle?
Pa 6.3005.081.910002650045.0
gDcc
gDc
c
Threshold of Motion for a Stationary Grain (Unisize or Graded Sediment)
Wiberg and Smith (1987), Bridge and Bennett (1992), + many others
, :Mixtures Dy
DLDG
DG
G
D
FFll
ll
F
F
tan1
sincostan
Sample Calculation
What is c for 0.001 and 0.010 m quartz-density particles in a mixture with D50 = 0.005 m?
Pa 8.401.0005.081.910002650045.0
m 0.01For
Pa 9.1001.0005.081.910002650045.0
m 0.001For
4.06.0
4.06.0
4.06.050045.0 ici DDg
Using Shields for unisize sediment
0.7 Pa
7.3 Pa
Criteria for Sediment Transport Modes
• Bedload:
• Suspended bed material:
• Washload: D 0.063 mm
c 0
suau *
Bedload Transport EquationsMeyer-Peter and Muller (1948)
Bagnold (1966)
323 18 gDg
gq cb
ccb uua
q
0**tan
Bedload Transport Observations
Gravel-bed stream (Cudden & Hoey, 2003)
Gravel-bed streams (Bunte et al., 2004)
fib Qfib
trap
HS
HS
Bedload Transport EquationsWilcock & Crowe (2003)
Reference threshold condition
Hiding function
Reference dimensionless shear stress for median size base don fraction of sand
Transport rate based on t/tri
Bedload Transport Equations
Meyer-Peter and Muller (1948)
Bagnold (1966)
323 18 gDg
gq cb
ccb uua
q
0**tan
Barry et al. (2004)
Abrahams and Gao (2006;following Bagnold, 1966, 1973)
sss ddQ
qb
fq
QAq
50502,,*
257 56.3*45.241.3
TTG
U
Gi
g
b
2
4.3
Barry et al. (2004)
Abrahams and Gao (2006)following Bagnold (1966, 1973)
Predicting bedload transport
(c) Ackers and White [1973] equation by di
(a) Meyer-Peter and Müller [1948] equation by d50ss
(b) Meyer-Peter and Müller equation by di
(d) Bagnold equation by dmss
(e) Bagnold equation by dmqb
(e) Bagnold equation by dmqb
(g) Parker et al. [1982] equation by di (Parker et al. hiding function)
(h) Parker et al. [1982] equation by di (Andrews [1983] hiding function)
(Barry et al., 2004)
Predicting bedload transport
DH48 – Wading Sampler
DH59 – Hand line Sampler
D74 – Hand line Sampler
Others: Super-critical flumes, ISCO, OBS, Acoustics
Measuring suspended load transport
Suspended Sediment
• Sediment-diffusion balance (equilibrium):
downward settling + upward diffusion Total suspended load
• Rouse equation:
01 y
CCCu ss
C
C
d y
y
a
d aa
z
*u
uz s
h
adyuCqs
Suspended Load Observations
Mobile river dunes with acoustic probe, Wren et al. (2007)
Stochastic simulation, Man (2007)
Mobile orbital ripples with acoustic probes, P. Thorne
Sediment Transport and Stream Restoration
• Deficient or excessive sediment transport based on design discharge will result in erosion or deposition, which can redirect flow and threaten infrastructure and ecologic indices
• Sediment transport prediction depends on grain size, gradation, and bed topography
• Uncertainty can be large• Excludes bank erosion and wash load• Use multiple relationships
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