dynamic characteristics of break debris flow and its numerical simulation state key laboratory of...

Dynamic Characteristics of Break Debris Dynamic Characteristics of Break Debris

Flow Flow

and its Numerical Simulationand its Numerical Simulation

State Key Laboratory of Geohazard Prevention and Geoenvironment ProtectionState Key Laboratory of Geohazard Prevention and Geoenvironment ProtectionChengdu UniversityChengdu University of Technology

Le MaohuaLe Maohua

((Environmental Geology))

Le MaohuaLe Maohua

((Environmental Geology))

Jan. 10, 2014Jan. 10, 2014

Supervisor: Professor Tang ChuanSupervisor: Professor Tang ChuanSupervisor: Professor Tang ChuanSupervisor: Professor Tang Chuan

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IntroductionIntroduction

Case StudyCase Study

Discharge ProcessDischarge Process

Simulation MethodsSimulation Methods

Further WorksFurther Works


1.1. A lot of collapses and landslides induced by the Wenchuan A lot of collapses and landslides induced by the Wenchuan

Earthquake have Earthquake have formed a lot of barrier damsformed a lot of barrier dams. When these . When these

dams outburst, it tend to form Break Debris Flow.dams outburst, it tend to form Break Debris Flow.

2.2. Owing to the serious blockage in the gully, The flow discharge Owing to the serious blockage in the gully, The flow discharge

calculated by the flood method was obviously smaller than that calculated by the flood method was obviously smaller than that

calculated by morphology investigation method.calculated by morphology investigation method.

3.3. If an incoming mountain torrent collapses a series of landslide If an incoming mountain torrent collapses a series of landslide

dams, large debris flows can form in a very short period. dams, large debris flows can form in a very short period.

Moreover, the torrent can Moreover, the torrent can amplify the scale amplify the scale of the debris flow in of the debris flow in

the flow direction.the flow direction.

4.4. The Break Debris Flow is The Break Debris Flow is highly destructivehighly destructive, such as Hongchun , such as Hongchun

gully debris flow, Qipan gully debris flow.gully debris flow, Qipan gully debris flow.

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Case :The Zhouqu debris flows, Aug. 8,2010Ⅰ

Ref: P. Cui, et al. Geomorphology,2013

Six obvious debris-flow scale amplification phases between point LG and A’


erosion of the channel bed

The cascading failure of landslides dams in the gully


Four stages of debris-flow scale amplification can be seen in the above figure

The cascading failure of landslides dams in the gullyerosion of the channel bed

Case :The Qipan gully debris flow, Jul. 10,2013Ⅱ

Case :The Qipan gully debris flow, Jul. 10,2013Ⅱ

UpstreamDownstream

Case :The Hongchun gully debris flow, Aug. 14,2010Ⅲ

Ref: Chuan Tang, et al. Landslides,2011

Case :The Hongchun gully debris flow, Aug. 14,2010Ⅲ

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Dam-break induced Dam-break induced debris flowdebris flow

A dam-break wave starting out as clear water is likely to A dam-break wave starting out as clear water is likely to

rapidly pick up sediment both from the dam body and rapidly pick up sediment both from the dam body and

from the valley floorfrom the valley floor. In many instances, it is possible for . In many instances, it is possible for

the wave to entrain enough sediment to turn into a fully the wave to entrain enough sediment to turn into a fully

developed debris flow. (Costa, et al.1988)developed debris flow. (Costa, et al.1988)

Dam-break waves can in many instances entrain and Dam-break waves can in many instances entrain and

deposit large volumes of sediment. deposit large volumes of sediment. This bulking and This bulking and

debulking process can significantly affect debulking process can significantly affect (i) the flow (i) the flow

rheology, (ii) the wave hydrodynamics, (iii) the valley rheology, (ii) the wave hydrodynamics, (iii) the valley

morphology. (H. Capart et al., 2001)morphology. (H. Capart et al., 2001)

Discharge Discharge ProcessProcess

Prediction of potential peak discharge and resulting hydrograph is Prediction of potential peak discharge and resulting hydrograph is

necessary for the management of dam-break flood hazards and to necessary for the management of dam-break flood hazards and to

decide appropriate mitigation measures including evacuation. decide appropriate mitigation measures including evacuation.

Basically, there are two methods to predict probable discharge from Basically, there are two methods to predict probable discharge from

potential failure of landslide dam. potential failure of landslide dam. One method One method relies on regression relies on regression

equations that relate observed peak discharge of landslide dam equations that relate observed peak discharge of landslide dam

failure to some measure of impounded water volume. failure to some measure of impounded water volume. The other The other

methodmethod employs computer implementation of a physically based employs computer implementation of a physically based

mathematical model. (Walder and O’Connor, 1997)mathematical model. (Walder and O’Connor, 1997)

The final purpose of research on dam break wave is: Calculate the The final purpose of research on dam break wave is: Calculate the

process of the wave propagation speed, water level and flow process of the wave propagation speed, water level and flow

characteristics with time in the detention basin and downstream characteristics with time in the detention basin and downstream

areas.areas.

Discharge Discharge ProcessProcess

Ref: X. Q. Chen, et al. Iranian Journal of Science & Technology, April 2007

Overall failure and Partial failure

Sudden failure and gradual failure

Flood/Debris flow hydrograph due to landslide dam failure

Governing Equations

ˆˆˆ 0

ˆ ˆh

uht x

ˆˆ ˆ

ˆ cos sinˆ ˆ ˆu u hu g g

t x x

0 cos , 0q uA gH x

Neglecting the effects of friction Considering the slope angle

0 0 0 0

ˆˆ ˆcos ˆ, , ,cos

x g h ux t t h u

H H H gH

0

h h uu h

t x x

tanu u hu

t x x

argFlood disch e q t

1 d w

s d

k

dq t k q t

At the outlet of the failed dam

Initial and Boundary conditions for the dam-break problem

Ref:1.C. Ancey, et al. Water resources research,2008. 2.X. Q. Chen, et al. Iranian Journal of Science & Technology,2007

Note: k is a coefficient of debris flow discharge

The wave propagation in the downstream areas

Governing Equations

ˆˆˆ 0

ˆ ˆh

uht x

ˆˆ ˆ

ˆ cos sinˆ ˆ ˆu u hu g g

t x x

0 cos , 0q uA gH x

0 0 0 0

ˆˆ ˆcos ˆ, , ,cos

x g h ux t t h u

H H H gH

0

h h uu h

t x x

tanu u hu

t x x

arg ,Flood disch e q x t

1 d w

s d

k

, ,d

Gq x t k k q x t

The flow below the dam

Initial and Boundary conditions for the dam-break problem

Note: kG is a parameter related to gully shape

1/2

0

xG

Bk

B

Ref:1.C. Ancey, et al. Water resources research,2008. 2.X. Q. Chen, et al. Iranian Journal of Science & Technology,2007

Neglecting the effects of friction Considering the slope angle

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Simulation Simulation MethodsMethods

Understanding the breaching process and the possible distribution Understanding the breaching process and the possible distribution

of debris deposition is crucial to effective hazard mitigation and of debris deposition is crucial to effective hazard mitigation and

timely emergency response.timely emergency response.

To reasonably facilitate the simulation of debris flows induced by the To reasonably facilitate the simulation of debris flows induced by the

landslide dam breach, The CFD software landslide dam breach, The CFD software FLUENTFLUENT will be applied to will be applied to

generate the landslide dam break hydrograph which is then used as generate the landslide dam break hydrograph which is then used as

input to drive the input to drive the FLO-2DFLO-2D model. A systematic integrated numerical model. A systematic integrated numerical

approach is proposed.approach is proposed.

Dam break routing and overland flood routing

Flowcharts of the integrated models approach

Model of seepage flow Model of slope stability Model of dam surface erosion and flow

Failure?Failure?

Dam break routing and overland flood routing

The FLUENT model provides comprehensive modeling capabilities for a The FLUENT model provides comprehensive modeling capabilities for a

wide range of incompressible and compressible, laminar and turbulent wide range of incompressible and compressible, laminar and turbulent

fluid flow problems. Steady-state or transient analyses can be fluid flow problems. Steady-state or transient analyses can be

performed. It also provides the volume-of-fluid, mixture and Eulerian performed. It also provides the volume-of-fluid, mixture and Eulerian

models, as well as the discrete phases, including coupling with the models, as well as the discrete phases, including coupling with the

continuous phase.continuous phase.

Ref: Ansys Fluent 12.0 DocumentationRef: Ansys Fluent 12.0 Documentation The FLO-2D model is a physically based, distributed flood-routing model The FLO-2D model is a physically based, distributed flood-routing model

using the fully dynamic wave momentum equation and a central finite-using the fully dynamic wave momentum equation and a central finite-

difference routing scheme. It also provides modules to simulate two-difference routing scheme. It also provides modules to simulate two-

dimensional sediment transport, hyperconcentrated debris and mud flow.dimensional sediment transport, hyperconcentrated debris and mud flow.

Ref: Flo-2D reference manualRef: Flo-2D reference manual

Part : Dam break routing simulationⅠ

Case: Partial breach modeling with FLUENT

↑ Computational domain

Initial conditions ↓

Part : Dam break routing simulationⅠ

↑ Water surface profile at t = 7.2 s

Velocity vectors ↓

Part : Overland flood routing simulationⅡ

1.1. Digital elevation dataDigital elevation data

2.2. Hydrograph at the outlet Hydrograph at the outlet

of the failed damof the failed dam

3.3. Rheology parameterRheology parameter

4.4. Resistance parameterResistance parameter

5.5. Manning’s roughness Manning’s roughness

coefficient.coefficient.

Note: Field investigationNote: Field investigation

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1.1. Calculate Calculate the impact force the impact force of the typical cases.of the typical cases.

2.2. Considering the model of dam surface erosion and flow, The Considering the model of dam surface erosion and flow, The

dissertation dissertation will put forward the calculation methods of k, kwill put forward the calculation methods of k, kGG. k can be . k can be

estimated from the size of grains remaining along the debris flow estimated from the size of grains remaining along the debris flow

path, and kpath, and kG G can be estimated from the channel shape. In other can be estimated from the channel shape. In other

words, the attention will turn into the changes in debris flow density words, the attention will turn into the changes in debris flow density

along the flow path. kalong the flow path. kG G depends on the geometry of the cross-section depends on the geometry of the cross-section

below the dam. Deposition will occur where the channel is wide (kbelow the dam. Deposition will occur where the channel is wide (kG G is is

small), and temporary damming may occur at a bend or where the small), and temporary damming may occur at a bend or where the

channel narrows (kchannel narrows (kG G is large).is large).

3.3. The systematic integrated numerical approach The systematic integrated numerical approach will be validated will be validated in the in the

typical cases.typical cases.

Thanks for Your Attention.

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