Sediment Transport-2011

heehawultraMécanique

22 févr. 2014 (il y a 3 années et 3 mois)

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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

Incipient Motion

(Middleton and Southard, 1984)

Forces Acting on Stationary Grain

(Middleton and Southard, 1984)





gD
gD
D
F
F
G
D












0
3
2
0
Threshold of Motion

(Shields,1936; Julien, 1998)

(Miller et al., 1977)



gD
c
c






Motion

Smooth

Transitional

Rough

045
.
0

c

No Motion

Sample Calculation

What is

c

for
D

= 0.005 mm quartz
-
density
particle?









Pa

6
.
3
005
.
0
81
.
9
1000
2650
045
.
0






gD
c
c






gD
c
c






Entrainment of mixed
-
size sediment

Due to:

1.
Relative Protrusion

2.
Pivoting angle

Relative Protrusion

Pivoting Angle

Threshold of Motion for a Stationary
Grain (Unisize or Graded Sediment)

Wiberg and Smith (1987), Bridge and
Bennett (1992), + many others


,

:
Mixtures
D
y






D
L
D
G
D
G
G
D
F
F
l
l
l
l
F
F




tan
1
sin
cos
tan









4
.
0
6
.
0
50
045
.
0
i
ci
D
D
g





Entrainment of mixed
-
size sediment

Sample Calculation

What is

c

for 0.001 and 0.010 m quartz
-
density
particles in a mixture with
D
50

= 0.005 m?

















Pa

8
.
4
01
.
0
005
.
0
81
.
9
1000
2650
045
.
0
m

0.01
For
Pa

9
.
1
001
.
0
005
.
0
81
.
9
1000
2650
045
.
0
m

0.001
For
4
.
0
6
.
0
4
.
0
6
.
0














4
.
0
6
.
0
50
045
.
0
i
ci
D
D
g





Using Shields
for unisize
sediment


0.7 Pa



7.3 Pa

Sediment Transport

(Leeder, 1999)

Modes of sediment transport

Criteria for Sediment Transport
Modes


Bedload:



Suspended bed material:



Washload:
D



0.063 mm

c



0
s
u
au

*
(Bridge, 2003)

Modes of sediment transport

c



0
s
u
au

*
Washload:

D



0.063 mm

Bedload Transport Equations

Meyer
-
Peter and Muller (1948)

Bagnold (1966)



3
2
3
1
8
gD
g
g
q
c
b



















c
c
b
u
u
a
q






0
*
*
tan
Bedload traps (K. Bunte)

Helley
-
Smith sampler

Measuring bedload transport

Bedload Transport Observations

Gravel
-
bed stream
(Cudden & Hoey, 2003)

Gravel
-
bed streams
(Bunte et al., 2004)




f
i
b



Q
f
i
b

trap

HS

HS

Bedload Transport Equations

Wilcock & Crowe (2003)

Reference threshold condition

Hiding function

Reference dimensionless shear stress for
median size base don fraction of sand

Transport rate based on

/

ri

Bedload Transport Equations

Meyer
-
Peter and Muller (1948)

Bagnold (1966)



3
2
3
1
8
gD
g
g
q
c
b



















c
c
b
u
u
a
q






0
*
*
tan
Barry et al. (2004)

Abrahams and Gao (2006;

following Bagnold, 1966, 1973)



ss
s
d
d
Q
q
b
f
q
Q
A
q
50
50
2
,
,
*
257
56
.
3
*
45
.
2
41
.
3








T
T
G
U
G
i
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
d
i

(a)
Meyer
-
Peter
and Müller

[1948]
equation by
d
50
ss

(b) Meyer
-
Peter and
Müller equation by
d
i


(d) Bagnold
equation by
d
mss


(e) Bagnold
equation by
d
mqb

(e) Bagnold equation
by
d
mqb

(g)
Parker et al.

[1982]
equation by
d
i

(
Parker et
al
. hiding function)

(h)
Parker et al.

[1982]
equation by
d
i

(
Andrews

[1983] hiding function)

(Barry et al., 2004)

Predicting
bedload transport

Suspended Sediment


Simple criterion for suspension:




s
u
au

*
(van Rijn, 1993)

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:




0
1



y
C
C
C
u
s
s



C
C
d
y
y
a
d
a
a
z










*
u
u
z
s




h
a
d
y
uC
q
s
(van Rijn, 1993)

Suspended sediment profiles and Rouse equation

Z

Ripples

Dunes

Upper
-
stage plane beds

Bedload sheet

Bedform
Stability

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

Sediment Transport

Conclusions


Threshold conditions defined by Shields
criterion


Modes of sediment transport depend on
Shields criterion and grain size


Bedload and suspended load transport
treated separately


Load is modulated by bedforms