Post on 13-Jul-2020
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Sedimentation Engineering…Incipient Motion and Bedforms
Pierre Y. JulienProfessor of Civil and Environmental EngineeringColorado State University, Fort Collins, CO 80523
pierre@engr.colostate.edu
January 15, 2008UiTM, Shah Alam, Malaysia
Incipient Motion
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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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Calculating Critical Shear Stress
Bedforms and Resistance to Flow
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What are bedforms?Initiation of Bedforms on a flat bed
Wind Blown Ripples on Dunes
Antidunes
Ripples
Dunes
Lower Regime - Ripples• Small Grain Diameter
– d50 < 0. 6mm• Manning n
– 0.018 to 0.028• Concentration
– 10 to 200 mg/L• Small Features
– Less than 20 cm long – A few cm high
• Dominant Roughness– Form
Linguoid current ripples Kennetcook River
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Lower Regime - Dunes• Coarser Grain Diameter
– d50 < 2 mm• Manning n
– 0.02 to 0.04• Concentration
– 200 to 3000 mg/L• Large Features
– Up to tens of meters in height
• Dominant Roughness– Form
• Field Characteristic– Boils on the water surface
Transition - Washed Out Dunes
• Manning n– 0.014-0.025
• Concentration – 1,000 to 4,000 mg/L
• Water Surface Profile– Out of Phase
• Dominant Roughness– Form or Grain
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Upper Regime - Plane Bed• Manning n
– 0.010 to 0.013• Concentration
– 2,000 to 4,000 mg/L• Water Surface Profile
– Parallel• Dominant Roughness
– Grain
Upper Regime – Antidunes• Manning n
– 0.010 to 0.020• Concentration
– 2,000 to 5,000 mg/L• Water Surface Profile
– In Phase• Dominant Roughness
– Grain
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Upper Regime – Chutes and Pools
• Manning n– 0.018 to 0.035
• Concentration – 5,000 to 50,000 mg/L
• Water Surface Profile– In Phase
• Dominant Roughness– Variable
Bedform Classification• Bedforms are
classified based on:– Shape– Resistance to Flow
(Energy Dissipation)– Sediment Transport– Relationship between
the bed and water surface Forms of bed roughness in sand channels
(Simons and Richardson 1963, 1966)
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Based on Transport-Stage Parametervan Rijn, 1984b
Study Area of the Rhine River
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Field Surveys on the Rhine River
Bedform Profiles
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Dune Height during the Flood
Manning n during the Flood
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Resistance to Flow
Sedimentation Engineering
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Total rainfall of Typhoon Maemi from 9/8/2003 to 9/13/2003)
South Korea
Mangun mountain, South Korea
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Imha Reservoir, South Korea
Annual average: 3,450 tons/km2/year.
Soil loss maps
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CSU Watershed Model TREX
Flow Depth [ft] 100 yr Storm
Logarithmic Velocity Profile
o
x
zz
uv ln1
* κ=
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Turbulent Flow Equations
{{
4444 34444 2143421
3214444 34444 21nfluctuatioturbulent
zzzyzx
viscous
zm
gradientpressure
mnalgravitatioz
convective
zz
zy
zx
local
z
yzyyyxym
my
yz
yy
yx
y
xzxyxxxm
mx
xz
xy
xx
x
zvv
yvv
xvv
vzpg
zvv
yvv
xvv
tv
zvv
yvv
xvv
vypg
zv
vyv
vxv
vt
v
zvv
yvv
xvv
vxpg
zv
vyv
vxv
vt
v
⎥⎥⎦
⎤
⎢⎢⎣
⎡
∂∂
+∂
∂+
∂∂
−∇+∂∂
−=∂∂
+∂∂
+∂∂
+∂∂
⎥⎥⎦
⎤
⎢⎢⎣
⎡
∂
∂+
∂
∂+
∂
∂−∇+
∂∂
−=∂
∂+
∂
∂+
∂
∂+
∂
∂
⎥⎥⎦
⎤
⎢⎢⎣
⎡
∂∂
+∂
∂+
∂∂
−∇+∂∂
−=∂∂
+∂∂
+∂∂
+∂∂
++++++
++++++
++++++
2
2
2
1
1
1
υρ
υρ
υρ
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Riprap Design
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Hapcheon Re-regulation Dam
South Korea
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
time (hr)
wat
er d
epth
(m)
Degradation and armouring
40 km
37
39
41
43
45
47
49
0 100 200 300 400 500 600
width (m)
bed
elev
atio
n (m
)
19832003
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River changes below Hapcheon dam
2004
2007
1983
Before
After
Nakdong River and NREB Unsteady modeling for the upstream of NREB
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Nakdong River Estuary Barrage
Case-Study:Gupo Bridge during Typhoon Maemi in 2003
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Erosion and River Mechanics Textbooks
Acknowledgments• Dr. Sang Kil Park (PNU)• Dr. Un Ji (Myongji U. )• Hyeon Sik Kim (KOWACO)• Young Ho Shin (KOWACO)• Byungdal Kim (KOWACO)• A.F. Embi (DID-Malaysia)• Dr. N.A. Zakaria (USM)• Dr. A. Ab. Ghani (USM)• Dr. J.Ariffin (UiTM-Malaysia)• James Halgren (CSU)• Seema Shah (CSU)
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Terima Kasih!
pierre@engr.colostate.edu