Erosion and Sedimentation - Walter Scott, Jr. College of ...pierre/ce_old... · m s s m D s s v G g...
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1 Erosion and Sedimentation Dr. Pierre Y. Julien Dept. of Civil and Environmental Engineering Colorado State University, Fort Collins Short Course Gadjah Mada University Yogyakarta, Indonesia July 21, 2009 Objectives Erosion and Sedimentation: 1. Sediment Properties and Fall Velocity; 2. Flow Properties; 3. Incipient Motion; 4. Riprap Design; 5. Bed Load and Suspended Load; 6. Flow in Bends. 1. Sediment Properties and Fall Velocity
Transcript of Erosion and Sedimentation - Walter Scott, Jr. College of ...pierre/ce_old... · m s s m D s s v G g...
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Erosion and Sedimentation
Dr. Pierre Y. JulienDept. of Civil and Environmental Engineering
Colorado State University, Fort Collins
Short CourseGadjah Mada UniversityYogyakarta, Indonesia
July 21, 2009
ObjectivesErosion and Sedimentation:
1. Sediment Properties and Fall Velocity; 2. Flow Properties;3. Incipient Motion;4. Riprap Design;5. Bed Load and Suspended Load;6. Flow in Bends.
1. Sediment Properties and Fall Velocity
2
Los Corales
Sand Gravel Cobblesv.f. fine med. c. v.f. fine med. c.v.c. v.c. small large
100
90
80
70
60
50
40
30
20
10
0
% b
y w
eigh
t fin
er th
an
25612864321684210.50.250.1250.0625
d d d10 50 90Diameter (mm)
Vs
d d d16 50 84
Vv
φ
3
Fall Velocity( )
( )
( ) 31
2*
5.03*
2
1
172
18
&,134
&18
1
⎥⎦
⎤⎢⎣
⎡ −=
⎥⎥⎦
⎤
⎢⎢⎣
⎡−⎟⎟
⎠
⎞⎜⎜⎝
⎛+=
−=
→−
=
ms
s
m
D
s
s
vgGdd
diameterparticlesmensionlesdi
ddv
bouldescobblesgravelsforvalidC
dGg
clayssiltsforvalidLawStokesv
dGg
ω
ω
ω
2. Flow Properties
Logarithmic Velocity Profile
o
x
zz
uv ln1
* κ=
4
Open Channel Flow• Pressure Distribution
• Shear Stress
• Shear Velocity
( )zhgp
gdzdph
zp
−=
−= ∫∫ρ
ρ0
( )fo
fzx
ghSSzhg
ρτ
ρτ
=
−=
fo ghSu ==
ρτ
*
Sw
So
Datum
zo
h
SfV2/2g
g
g sin at o
t zxp
Q
x
z
Example - Shear Velocity
smu
msmghSu f
113.0
0001312.0*9.9*81.9
*
2*
=
==
Resistance to Flow
5
3. Incipient Motion
Incipient Motion
Angle of Repose Effects of Angularity
Motion occurs when the center of gravity (G), is inline with the point of contact (C). o60== φθ
6
Angle of ReposeGranular Material
Shields Parameter• Ratio of
Hydrodynamic Forces to Submerged Weight
( ) ( ) ss
m
ss
o
du
d γγρ
γγττ
−=
−=
2*
*
Beginning of Motion• Critical Shields Parameter(τ*c)
– beginning of motion (τo = τc) ( ) ss
cc dγγ
ττ−
=*
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Critical Shear Stress
4. Riprap Design
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CHANNEL PROTECTION - RIPRAP
Θβ
δλ
A
Au
F
F sin
F sinF a
FBed
Top of bank
Sideslope gradient
Streamline
View normal to sideslope
Horizontal
s θ1
s
D
s 1
s 0
F sins 1
F
F cos
F 1 - a cos
O'
OF a
1
2 3
4
2
s θ D δ
s βθ
LParticle P
Section A - A
1
3
F sinD δParticle P
OF 1 - a sin2
s βθ
Section normal to section A - A
Θ
ΘΘΘ
ΘDownstream
1Θ0Θ
δ βλ ΘDownstre
am
Streamline drag component
Particle pathline
Weight component
Q
l
l
l
l l
l
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Velocity Method
( )
φtan4log
12
⎟⎟⎠
⎞⎜⎜⎝
⎛=
−=
sc
scc
dhK
gdGKV
Riprap Design
Gradation of Riprap• Well graded riprap
scours less than uniform size riprap due to the process of armoring
• Suggested Riprap gradation from USACE is shown to the right
• Riprap with poor gradation may be used, but a “filter” layer is required
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Gravel Filters• Gravel filters should
not be less than 15 to 23 cm
• ½ thickness of Riprap layer is a good guideline
• Suggested gravel filter gradation equations are shown to the right
5)()(
40)()(5
40)()(
85
15
15
15
50
50
<
<<
<
bankdfilterd
bankdfilterd
bankdfilterd
CHANNEL PROTECTION - RIPRAP
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5. Bedload and Suspended Load
Incipient Motion
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Medición Transporte Sedimento 36 Prof. Em. Ing. J.J. Peters | ConsultorProf. Em. Ing. J.J. Peters | Consultor
Muestreador US BL-84
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1.5
*
*
*
*
τ
*q = 40 τ 3
– 0.391τ
1/τ
q
10 10 1 102 -1
2
-1
-2
-3
-4
10
10
1
10
10
10
10
310
10 10 1 10-1-2
bv*
bv*
*
bvq
=w
d os
q = 15 τ
q = 2.15 e
bv*
bv*
IsokineticIsokinetic DepthDepth--integrating Samplerintegrating Sampler
isokineticnozzle
14
Collapsible-bagsampler array
As used in:AmazonOrinocoMississippi
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10
10
1
1010 10 1 10 10 10
1
11
R = 0.63
oR = 0.49
o
Run 19 Vanoni, 1946 h = 0.236 ft d = 0.10mm κ = 0.33
Run 55 h = 0.590 ft d = 0.10mm κ = 0.34
Run S-16 Einstein & Chien, 1955 h = 0.390 ft d = 0.274mm κ = 0.18
R = 1.86
o
Hyper-conc.Suspension
2
-1-2 -1 2 3
Concentration C (g/ )
(h -
z)/z
50
5050
l
SEDIMENTRATINGCURVES
1.0
0.8
0.6
0.4
0.2
01 10
Bedload Suspended load
d = 190 µm d = 270 µm d = 280 µm d = 450 µm d = 930 µm
5050
50
50
50
Data Guy et al., 1966h = 0.1 - 0.3 m
Ratio shear velocity - fall velocity, u /ω*
st
Rat
io su
spen
ded
- tot
al lo
ad, q
/q
Mixed load
10 -1
Lowest incipient motion (gravel)
100010 000
100 000
100
h/d = 100s100010 000100 000
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AGU Hydrology days 2005 Flood Damages
6. Flow in Bends
τ tan λ τ
λoo
τ tan λ o
Thalweg
Sedimentation Erosion
λ = 10°SF
1
Thalweg
Lateral migration
Sedimentation Erosion
(a)
(b)
(c)
(d)
Fine Coarse
Equilibrium
Point bar
Fine sediment in suspension
Coarse sediment bedload
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Mississip
pi River
< - 20 ft below LWRP
> - 20 ft below LWRP
> - 30 ft below LWRP
Fine sand concentration
0 100 200 300 400 500 mg/L
250
750
30004000
Right bank Left bankWater surface12
10
8
6
4
2
00 100 200 300 400 500 600 700 800 900
Stationing across section (ft)
Dis
tanc
e ab
ove
stre
am b
ed (f
t)
= 31 600 ft /s = 4.9 ft/s = 838 ppm - sand = 0.20 mm - bed sediment = 1.5 x 10
Q V S
C d
m50 -4
3
3500
500
1000
15002000
2500
5000
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Old River Control Complex
Mississippi RiverMississippi River
Outflow ChannelOutflow Channel
Example 3-D Model Mississippi
Erosion and River Mechanics Textbooks
