16 may 2002spinewine - impact workshop 1 - wallingford1 geomorphic dam-break floods: near-field and...
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16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 1
Geomorphic dam-break Geomorphic dam-break
floods:floods:Near-field and far-field Near-field and far-field
perspectivesperspectives
Benoit Spinewine, Yves ZechUniversité catholique de Louvain
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 2
Presentation outlinePresentation outline
• Introduction and motivation• Near-field perspective
Key aspectsKey aspects: inertial effects, coupled description, vertical movements
Experimental workExperimental work: dam-break & breaching; past, present & future…
Theoretical frameworksTheoretical frameworks: strengths & limitations
• Far-field perspective Key aspectsKey aspects: 2D-H, bank erosion, frictional resistance, debulking Experimental workExperimental work: channels with erodible bed & banks Numerical modelNumerical model: bank failure mechanism, 1D & 2D-H models
• Conclusions
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 3
IntroductionIntroduction
• Problems to be solved Geomorphic changes induced by rapid flood waves Mobilised sediments affect wave dynamics
• Motivation Lessons from the past: real cases of catastrophic
failures Increased risks in the future
• Approaches Near-field vs. far-field Theoretical, experimental and numerical Collection of data from real cases
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 4
IntroductionIntroduction
• Real cases Lawn Lake dam failure (1982)
U.S. Geological Survey
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 5
IntroductionIntroduction
• Real cases Lawn Lake dam failure (1982) Lake Ha!Ha! Break-out flood (1996)
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 6
Presentation outlinePresentation outline
• Introduction and motivation• Near-field perspective
Key aspectsKey aspects: inertial effects, coupled description, vertical movements
Experimental workExperimental work: dam-break & breaching; past, present & future…
Theoretical frameworksTheoretical frameworks: strengths & limitations
• Far-field perspective Key aspectsKey aspects: 2D-H, bank erosion, frictional resistance, debulking Experimental workExperimental work: channels with erodible bed & banks Numerical modelNumerical model: bank failure mechanism, 1D & 2D-H models
• Conclusions
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 7
Near-field perspectiveNear-field perspective
• Introduction Phenomenological descriptionPhenomenological description
• Complex initiation of movement, including vertical and pressure-related effects
• Intense scouring of the sediment bed• Bulking of sediments into the flow• Remobilisation of sediments trapped in reservoir
Key aspects of near-field modellingKey aspects of near-field modelling• Account for sediment inertia• Multi-phase approach• Debris-flow-like rheology• Erosion viewed as a phase change• Vertical movements and non-hydrostatic pressures
2D-V model ??
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 8
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments
• Chen & Simons (CSU, 1979) Sudden removal of a
submerged barrage
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 9
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments
• Chen & Simons (CSU, 1979)• Capart & Young (NTU, 1998)
Sudden dam-break wave Flat sediment bed Light pearls (s = 1.048) Particle tracking
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 10
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments
• Chen & Simons (CSU, 1979)• Capart & Young (NTU, 1998)• Spinewine, Zech & Capart (UCL, 2000)
Heavier PVC pellets(s = 1.54)
Flat bed Upward-moving gate
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 11
Near-field perspectiveNear-field perspective
• Louvain experiments 10 cm of water Mosaics assembled from different runs
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 12
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments
• Chen & Simons (CSU, 1979)• Capart & Young (NTU, 1998)• Spinewine, Zech & Capart (UCL, 2000)• Fraccarollo & Larcher (UDT, 2000)
PVC pellets (s = 1.54) Downward-moving gate
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 13
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments
• Chen & Simons (CSU, 1979)• Capart & Young (NTU, 1998)• Spinewine, Zech & Capart (UCL, 2000)• Fraccarollo & Larcher (UDT, 2000)• Leal, Ferreira et al. (IST, 2000)
Natural sand (d50 = 1 mm) Various water and sediment levels
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 14
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments Future work during IMPACT project
• Explore various water and sediment levels Preliminary results obtained at UCL laboratory (hs= 6; hw=
10 cm)
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 15
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments Future work during IMPACT project
• Explore various water and sediment levels• Explore extended grain size distributions (multimodal,
graded)
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 16
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments Future work during IMPACT project
• Explore various water and sediment levels• Explore extended grain size distributions (multimodal,
graded)• Explore changes in geometry
Widening, contraction, chute, sloping channel
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 17
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments Future work during IMPACT project
• Explore various water and sediment levels• Explore extended grain size distributions (multimodal,
graded)• Explore changes in geometry• Improve quantitative measurements
Velocity profiles within water and sediment phases 3D imaging (concentration estimate, flow topography)
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 18
Near-field perspectiveNear-field perspective
• Experimental work Idealised dam-break experiments Future work during IMPACT project
• Explore various water and sediment levels• Explore extended grain size distributions (multimodal,
graded)• Explore changes in geometry• Improve quantitative measurements• Other types of ‘near filed’ fast transients involving
intense sediment movements Dike-breaching experiments
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 19
Near-field perspectiveNear-field perspective
• Experimental work Dike-breaching experiments
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 20
Near-field perspectiveNear-field perspective
• Experimental work Dike-breaching experiments
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 21
Near-field perspectiveNear-field perspective
• Theoretical frameworks
Traditional alluvial hydraulics & why it fails…• Slowly evolving alluvial flows• Solid transport as a passive phase
Key features for geomorphic flood routing :• Transients shock-capturing schemes (also
sediments!)• Bulking of sediments couple water and sediment
flows
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 22
Near-field perspectiveNear-field perspective
• Extended shallow water framework (Capart, 2000)
Layered flow description Basic assumptions on velocities & concentrations Erosion & deposition viewed as a phase change of
bed material (transition from solid-like to fluid-like behaviour)
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 23
Near-field perspectiveNear-field perspective
• Extended shallow water framework (Capart, 2000)
Two continuity equations
One momentum equation
euhxt
h
euh
xt
hs
s
bws cr 1
w
b
bssss
uee
r
x
zhrhghgrhguhrh
xuhrh
t
21
2212
212
w
b
bssss
uee
r
x
zhrhghgrhguhrh
xuhrh
t
21
2212
212
et
zb
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 24
Near-field perspectiveNear-field perspective
• Extended shallow water framework (Capart, 2000)
Semi-empirical closure relation for the erosion rate
• Sediment mobility parameter m• Relaxation time tr
Physically-based relation expressing a shear-stress imbalance across the bed interface (Fraccarollo-Capart 2002)
• in the flow region, s is given by a Chezy-type relation
• In the bed region, b derives from a Coulomb yield criterion
)(1 2
smr
b humtt
ze
)()1(
1bs
mwb ure
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 25
Near-field perspectiveNear-field perspective
• Extended shallow water framework (Capart, 2000)
Numerical results• Finite volumes• Roe method for evaluation of convective fluxes
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 26
Near-field perspectiveNear-field perspective
• Extended shallow water framework (Capart, 2000)
Limitations• Equal velocities in the clear water and slurry layer
Pure water
transport layer
dep
th
velocity
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 27
Near-field perspectiveNear-field perspective
• Extended shallow water framework (Capart, 2000)
Limitations• Equal velocities in the clear water and slurry layer
Let the two moving layers flowing at different velocities uw & us
Unlocked, but still coupled velocities (not independent)
One more momentum equation for the slurry layer
h w
h s
z b
u w
u s
w
s
b
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 28
Near-field perspectiveNear-field perspective
• Extended shallow water framework (Capart, 2000)
Limitations• Equal velocities in the clear water and slurry layer• Equal concentration in the slurry layer and static bed
???
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 29
Near-field perspectiveNear-field perspective
• Extended shallow water framework (Capart, 2000)
Limitations• Equal velocities in the clear water and slurry layer• Equal concentration in the slurry layer and static bed• Inherently limited by shallow-water assumptions
2D-V model ???
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 30
Presentation outlinePresentation outline
• Introduction and motivation• Near-field perspective
Key aspectsKey aspects: inertial effects, coupled description, vertical movements
Experimental workExperimental work: dam-break & breaching; past, present & future…
Theoretical frameworksTheoretical frameworks: strengths & limitations
• Far-field perspective Key aspectsKey aspects: 2D-H, bank erosion, frictional resistance, debulking Experimental workExperimental work: channels with erodible bed & banks Numerical modelNumerical model: bank failure mechanism, 1D & 2D-H models
• Conclusions
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 31
Far-field perspectiveFar-field perspective
• Introduction Phenomenological descriptionPhenomenological description
• Lateral effetcts: bank failures and channel widening• Progressive debulking of the sediment phase• Deposition in downstream reaches• Formation of alluvial fans• Blocking of tributaries, formation of natural dams
Key aspects of far-field modellingKey aspects of far-field modelling• 2D-H modelling for reproducing actual valley
topography• Geometrical singularities (bends, widening, chutes, …)• Discrete bank failure criterion
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 32
Far-field perspectiveFar-field perspective
• Erodible channel dam-break wave experiments
Gate
erodible channel
rigid bank
Gate
erodible channel
(a) (b )
h = 0.2 m0
1 60
6 0
2 00 1 60
4 5°1 60
6 0
2 56 1 34 1 05
5 0°
h = 0.14 m0
(a) (b )
Gate
erodible channel
rigid bank
Gate
erodible channel
(a) (b )
h = 0.2 m0
1 60
6 0
2 00 1 60
4 5°1 60
6 0
2 56 1 34 1 05
5 0°
h = 0.14 m0
(a) (b )
• Le Grelle & Jonard (UCL, 2001)
Half-channel experiments Top-view and side-view Time evolution
• Paquier & Poncin (UCL, 2000) Full-channel experiments Post-flood valley topography
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 33
Far-field perspectiveFar-field perspective
• Erodible channel dam-break wave experiments• Paquier & Poncin (UCL, 2000)
Full-channel experiments Post-flood valley topography
« Panel » digital imaging initial post-flood
Flow
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 34
Far-field perspectiveFar-field perspective
• Erodible channel dam-break wave experiments
• Le Grelle & Jonard (UCL, 2001)
Half-channel experiments Top-view and side-view Time evolution
(b )
(a)
side
top
Flow
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 35
Far-field perspectiveFar-field perspective
• Numerical modelling Bank failure mechanisms
• Traditional models: continuous process, excess bank shear stress
• Not applic. to sudden surges with abrupt changes of water levels !
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 36
Far-field perspectiveFar-field perspective
• Numerical modelling Simple model accounting for discrete mass failure events
• Distinct angles of repose for submerged and emerged banks• Failure triggered whenever and wherever critical angles
exceeded• Easily extended to 2D by invoking conic failure surfaces
8 5 °
3 7 °
5 0 °
q s
c e
c s h
i
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 37
Far-field perspectiveFar-field perspective
• Numerical modelling Simple model accounting for discrete mass failure
events• Distinct angles of repose for submerged and emerged
banks• Failure triggered whenever and wherever critical angles
exceeded• Easily extended to 2D by invoking conic failure surfaces• Extension: distinguish between critical and residual angles
Failure triggered when critical failure is exceeded Residual angle is adopted after failure
z z s 0
u n s t a b l e m e t a s t a b l e s t a b l e
s u b m e r g e de m e r g e dh w 0
( )( ) + ( )x x y y 0 0
2 2 1 / 2
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 38
Far-field perspectiveFar-field perspective
• Numerical modelling 1D model with separate hydr. and sed. routines (Spinewine
et al 2002)
• Hydrodynamic: finite volume, Roe• Sediment transport: non-equilibrium, bed and submerged
banks• Bank failure
Two angles of repose (emerged and submerged) Failed material uniformly distributed over wetted cross-section
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 39
Far-field perspectiveFar-field perspective
• Numerical modelling 2D-H model, coupled phases (Capart & Young 2002)
• 2D extension of the set of extended shallow water equations
Two layers, two velocities
• Bank failure Distinct failure and residual angles Biconic failure surfaces Failed material assumed to
liquefy instantaneously After failure, the flow operator
simply takes over
( a )
( b )
( c )
( d )
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 40
Far-field perspectiveFar-field perspective
• Numerical modelling Comparisons of 1D simulations with half-channel
experiments• (blue = experimental, red = numerical)• Elevation profiles at successive times
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 41
Far-field perspectiveFar-field perspective
• Numerical modelling Comparisons of 1D simulations with half-channel
experiments• (blue = experimental, red = numerical)• Width evolutions in time at a given x-section
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 42
Presentation outlinePresentation outline
• Introduction and motivation• Near-field perspective
Key aspectsKey aspects: inertial effects, coupled description, vertical movements
Experimental workExperimental work: dam-break & breaching; past, present & future…
Theoretical frameworksTheoretical frameworks: strengths & limitations
• Far-field perspective Key aspectsKey aspects: 2D-H, bank erosion, frictional resistance, debulking Experimental workExperimental work: channels with erodible bed & banks Numerical modelNumerical model: bank failure mechanism, 1D & 2D-H models
• Conclusions
16 May 2002 Spinewine - IMPACT Workshop 1 - Wallingford 43
ConclusionsConclusions
• Conclusions Geomorphic impacts divided in near-field and far-field
features Near-field: bulking of sediments, inertia, vertical effects,
… Far-field: decreasing velocities, lateral effects,
debulking Modelling
• Near-field : extended shallow water framework, 2DV• Far-field : 2DH extension, bank failures
Experiments
• Perspectives