# Sediment Transport-2011

Mécanique

22 févr. 2014 (il y a 4 années et 2 mois)

104 vue(s)

Sediment Transport

Outline

1.
Incipient motion criteria for
unisize

and
mixed
-
size sediments

2.
Modes of sediment transport

3.

transport

4.

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

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

Suspended bed material:

D

0.063 mm

c

0
s
u
au

*
(Bridge, 2003)

Modes of sediment transport

c

0
s
u
au

*

D

0.063 mm

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

Helley
-
Smith sampler

Gravel
-
bed stream
(Cudden & Hoey, 2003)

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

f
i
b

Q
f
i
b

trap

HS

HS

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

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

(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

Suspended Sediment

Simple criterion for suspension:

s
u
au

*
(van Rijn, 1993)

DH48

DH59

Hand line Sampler

D74

Hand line Sampler

Others: Super
-
critical flumes, ISCO, OBS, Acoustics

Measuring suspended

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

Bedform
Stability

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

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