Download DEBRIS FLOW

DEBRIS
FLOW
TAMOTSU TAKAHASHI
Disaster Prevention Research Institute, Kyoto University
Publishedfor the lnternational Associationfor Hydraulic Research by
A.A.BALKEMA l ROTTERDAM l BROOKFIELD l 1991
Table of contents
PREFACE
IX
l THE NATURE OF DEBRIS FLOW OBSERVED IN SOME MOUNTAIN
TORRENTS
1.1 Observation at the gully Kamikamihorizawa of M t. Yakedake, Japan
1.1.1 Process of generation of debris fiow
(a) The situation of occurrence
(b) Rainfall condition for occurrence of debris ftow
1.1.2 Process of ftow
(a) Behavior of flow
(b) The translation ve1ocity of the forefront
(c) The origin of the ftow material
(d) Specific density and the pressure in the ftow
1.1.3 Process of deposition
(a) Stoppage of the debris ftow and the arrivai distance
(b) Characteristics of the debris lobes and their distribution on the debris fan
(c) Topographical change on the debris fan
1.2
1.2.1
1.2.2
1.2.3
Observation at some other basins in Japan
Observation at the Name River
Observation in the gullies on the Sakurajima Volcano
Observation in the experimental basi n of the Hodaka Sedimentation
Observatory
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1.3 Observation at Jiang-Jia Ravine, China
1.3.1 Process of occurrence of the debris flow
1.3.2 Particle size
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l .4
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Observation at Mt.Thomas, North Canterbury, New Zealand
2 MECHANICS OF FLOW
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2.1
Momentum conservation equations
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2.2
Constitutive relations
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2.3 Debris Oows in the incrtial range
2.3.1 Stony dcbris fl ow
(a) The first approximation
(b) The second approximation
(c) Comparison to the field data
2.3.2 Immature debris flow
(a) Definition and thickness of particle flowing layer
(b) Velocity distribution
(c) Resistance formula
(d) Sediment discharge
(e) Cross-sectional mean solids concentration
2.3.3 Turbulent mud ftow
(a) Modeling of the ftow
(b) Resistance law
(c) Karman constant
2.3.4 A hybrid of stony and muddy debris ftows
2.3.5 Existence criteria of various type ftows
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2.4
2.4.1
2.4.2
2.4.3
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Debris flow in the macro-viscous range
Mechanics of flow
Existing criteria of the flow in the viscous range
Solids concentration
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3 PROCESSES OF OCCURRENCE, DEVELOPMENT AND DECLINATION
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3.1 Mechanism of occurrence
3.1.1 Debris ftow produced by appearance of/increase in surface water fiow on the
gully bed
3.1.2 Liquefaction of landslide mass
3.1.3 Debris ftow generation due to natura! dam collapse
(a) Erosive destruction due to overtopping
(b) Abrupt sliding collapse
(c) Progressive failure
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3.2 Formation of hydrograph
3.2.1 Development of a debris flow on a varying slope bed
(a) Description of the process
(b) Fundarnemal equations
(c) Comparison of experimental results with calculated ones
3.2.2 Debris ftow due to landslide dam failure
(a) Debris fiow prediction mode! for the overtopping type failure
(b) Debris flow prediction mode! for the instantaneous slip failure type
(c) Debris flow prediction mode! for the progressive failure type
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3. 3 Deformation of hydrograph
3.3.1 Kinematic wave theory
3.3.2 The big mud flow in the Stava River, Italy
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4 CHARACTERISTICS OF FULLY DEVELOPED FLOW
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4.1
Model of quasi-steady ftow and the shape of the snout
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4 .2
Roll waves
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4.3 Mechanics of accumulation of boulders at front of debris fiow
4.3. 1 Mechanism of particle segregation in a stony debris ftow
4.3.2 A numerica! simulation of convergence of larger particles to the front
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4.4
Transportation of huge stones
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4.5
Debris flow around bend
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5 PROCESSES OF DEPOSITION
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5.1
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Stoppage of inertial stony debris flow
5.2 Analysis of deposition in the channel of constant width
5.2.1 Surface slope on the deposit of a stony debris flow
5.2.2 Longitudinal profile of the deposi t of stony debris tlow
(a) In the case of ed ~ y
(b) In the case of y <ed< ec
5.2.3 Numerica! simulation of the depositing process of a stony debris fiow
5.2.4 Analysis of deposition of turbulent muddy flow
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5.3 The debris eone formation process
5.3.1 Description of the experimental results
5.3.2 Numerica! simulation
(a) Fundamental equations
(b) Verification of the mathematical model by experiment
5.3.3 Particle size distribution in the debris eone
(a) Field and experimental data
(b) Mathematical mode1
5.3.4 Analyses of the actual debris fiow/mud flow deposition
(a) Horadani debris flow
(b) Armero mud fiow
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APPENDIX- NOTATIONS
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REFERENCES
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VII