Two-dimensional morphological simulation in transcritical flow RCEM 2005 Urbana, October 5, 2005 ...
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Transcript of Two-dimensional morphological simulation in transcritical flow RCEM 2005 Urbana, October 5, 2005 ...
Two-dimensional Two-dimensional morphological simulation in morphological simulation in
transcritical flowtranscritical flow
RCEM 2005RCEM 2005Urbana, October 5, 2005Urbana, October 5, 2005
www.PepeVasquez.cwww.PepeVasquez.comom
José A. Vásquez (UBC)José A. Vásquez (UBC)Robert G. Millar (UBC)Robert G. Millar (UBC)Peter M. Steffler (UoA)Peter M. Steffler (UoA)
University of British Columbia (UBC), Vancouver, University of British Columbia (UBC), Vancouver, CanadaCanada
University of Alberta (UoA), Edmonton, CanadaUniversity of Alberta (UoA), Edmonton, Canada
• Previous applications:Previous applications:– Bed aggradation and degradationBed aggradation and degradation– Meander scour and deposition.Meander scour and deposition.– Alternate bars in straight channels.Alternate bars in straight channels.– Dam-break.Dam-break.
• Knickpoint migration:Knickpoint migration:– Importance Importance – Results of the modelResults of the model
2D FE morphodynamic 2D FE morphodynamic model model
www.www.River2DRiver2D..caca 2D Hydrodynamic model. 2D Hydrodynamic model. Computes Computes uu, , vv and and hh..Developed by U of Alberta.Developed by U of Alberta.Finite Elements.Finite Elements.Sub- and Sub- and supercriticalsupercritical flows. flows.Steady and unsteady flows.Steady and unsteady flows.
Freely available.Freely available.Very robust and stable.Very robust and stable.Handles partially wet areas.Handles partially wet areas.FIXED BED.FIXED BED.
The Exner EquationThe Exner Equation(bedload sediment continuity)(bedload sediment continuity)
porosityporosityzzbb bed elevation (m) bed elevation (m)
qqss sediment transport rate (m sediment transport rate (m22/s)/s)
0)1(
y
q
x
q
t
z sysxb
tx
qqz
OUTs
INs
b
1
1For a 1D reach of lengthFor a 1D reach of lengthxx in a time interval in a time interval tt: :
0
0
OUTs
INs
OUTs
INs
qq Aggradation (deposition)Aggradation (deposition)
Degradation (erosion)Degradation (erosion)
Bed aggradationBed aggradation due to sediment due to sediment over-loading (Soni over-loading (Soni et al. 1980)et al. 1980)
0.56
0.58
0.60
0.62
0.64
0.66
0.68
0.70
0.72
0.74
0 2 4 6 8 10 12 14 16 18 20 22
Channel distance (m)
Ele
vati
on
(cm
)
Original bed
Observed
Computed
0.15
0.17
0.19
0.21
0.23
0.25
0.27
0.29
0.31
0.33
0.35
0 2 4 6 8 10 12 14 16 18
Channel distance (m)
Ele
va
tio
n (
m)
Observed bed
Observed WSE
Computed bed
Computed WSE
Original bed
Bed Bed Degradation Degradation by shut-off of by shut-off of
sediment supplysediment supply
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 2 4 6 8 10
Distance / Width
Rel
ativ
e d
epth
Q = 170 L/sh = 20 cmS = 0.18 %
T6
BEND
b = 0.4fs = 2.0
Deposition
Scour
Computed
Measured
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 2 4 6 8 10
Distance / Width
Rel
ativ
e d
epth
Q = 170 L/sh = 20 cmS = 0.18 %
T6
BEND
b = 0.4fs = 2.0
Deposition
Scour
Computed
Measured
Bend scourBend scour
The Waal River (The Netherlands)
Deposition
Erosion
ErosionErosion
50 m from right bank-1969 SoundingsTransversal Bed Slope Shape Factor, fs
-7
-6
-5
-4
-3
-2
-1
0
0 1 2 3 4 5 6 7 8 9 10
Ce Distance (km))
Bed
Lev
el in
met
ers
bel
ow
OL
W62
-3.5
-2.5
-1.5
-0.5
0.5
1.5
2.5
3.5
Deposition
Deposition
Initiation of Alternate Bars in a straight flume
B/H = 34B/H = 34Fr = 0.69Fr = 0.69S = 0.452%S = 0.452%
Dam breakDam break
1 m
0.4 m
DAM
Q = 1 m3/s
0
0.1
0.2
0.3
0.4
0.5
0.6
-10 -7.5 -5 -2.5 0 2.5 5 7.5 10
0
0.1
0.2
0.3
0.4
0.5
0.6
-10 -7.5 -5 -2.5 0 2.5 5 7.5 10
0.40 m
0.12 m
INITIALLY WET INITIALLY DRY
Leal et al. 2003Leal et al. 2003
• Point of sudden change in the bed slope. Point of sudden change in the bed slope. Examples:Examples:
– Meander cut-offsMeander cut-offs– Dam removalDam removal– Bed dredgingBed dredging
Knickpoints Knickpoints
Cantelli et al. 2004Cantelli et al. 2004
Cui and Wilcock, in pressCui and Wilcock, in press
Knickpoint migration in tidal flatKnickpoint migration in tidal flat (Vancouver, (Vancouver, Canada)Canada)
19719700
19719799
20020022
20020044
Experiment of Experiment of Nickpoint Migration Nickpoint Migration (Brush and Wolman 1960)(Brush and Wolman 1960)
0.61
0.62
0.63
0.64
0.65
0.66
0.67
0.68
0.69
10 11 12
Channel distance (m)
Be
d E
lev
ati
on
(m
)
So =
10%
So = 0.125%
So = 0.125% Hydraulic Jump
Knickpoint
WSE
bed
Experiment of Experiment of Nickpoint Migration Nickpoint Migration (First 6 minutes...)(First 6 minutes...)
So =
10%
So = 0.125%
So = 0.125%Hydraulic Jump
Knickpoint
WSE
bed
0.62
0.63
0.64
0.65
0.66
0.67
0.68
8 9 10 11 12 13
0 min
1 min
6 min
Hydraulic jump
Knickpoint
WATER
BED
Experiment of Experiment of Nickpoint Migration Nickpoint Migration (Measurements at 160 minutes)(Measurements at 160 minutes)
0.61
0.62
0.63
0.64
0.65
0.66
0.67
0.68
0.69
0 2 4 6 8 10 12 14 16
Channel distance (m)
Be
d E
lev
ati
on
(m
)
Original
Computed
Measured
Knickpoint
WSE
bed
Qualitative Qualitative dyke-breach test dyke-breach test (Unsteady flow)(Unsteady flow)
0.62
0.63
0.64
0.65
0.66
0.67
10 10.5 11 11.5 12 12.5 13
Distance (m)
Ele
vati
on
(m
)Bed 0 s
Bed 10 s
Bed 60 s
W.S. 0 s
W.S. 10 s
W.S. 60 s
WSE
bed
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 60 120 180 240
Time (s)
Dis
char
ge
(L/s
)
x = 10 m
x = 13 m
DISCHARGE HYDROGRAPH
• River2D-MORphology is a 2D model River2D-MORphology is a 2D model based on triangular FE with capabilities for based on triangular FE with capabilities for transcritical flow morphology. transcritical flow morphology.
• The potential of the model in this field are:The potential of the model in this field are:– Dam removalDam removal– Dam-breakDam-break– Dyke breachDyke breach
• The model also have capabilities for The model also have capabilities for secondary flow in bends and transversal secondary flow in bends and transversal bed correction.bed correction.
In summaryIn summary
• In some problems of transcritical In some problems of transcritical morphology 2D effects such as sand bars, morphology 2D effects such as sand bars, meandering, channel widening might be meandering, channel widening might be important (e.g tidal flat, dam removal in important (e.g tidal flat, dam removal in meandering river) that do not warrant the meandering river) that do not warrant the application of a 1D model.application of a 1D model.
• Present limitations:Present limitations:– Uniform bed material sediment.Uniform bed material sediment.– Lack of numerical upwinding (not good for Lack of numerical upwinding (not good for
sediment waves).sediment waves).
...in summary...in summary