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IJEGE-11_BS-Nakatani-et-alii

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Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
735
DOI: 10.4408/IJEGE.2011-03.B-080
DEVELOPMENT AND APPLICATION OF GUI EQUIPPED 1-D AND 2-D
DEBRIS FLOW SIMULATOR, APPLIED TO MIXED-SIZE GRAINS
k
ana
NAKATANI
(*)
, t
akasHi
WADA
(**)
, n
aoki
MATSUMOTO
(***)
,
y
osHifumi
SATOFUKA
(****)
& t
akaHisa
MIZUYAMA
(*****)
(*)
JSPS Research Fellow, Graduate School of Agriculture, Kyoto University, Japan
(**)
Affiliation River Engineering Group, Engineering Consultants NEWJEC Inc., Japan
(***)
Himekawa Sabo Office, Nagano Prefecture, Japan
(****)
Ritsumeikan University, Dept. of Civil Engineering, Japan
(*****)
Graduate School of Agriculture, Kyoto University, Japan
system enabled the user to input the data easily and to
understand the results instinctively from the animated
graphical results. Thus, the interface enables users to
run high-quality debris-flow simulations easily and
leads them to better solutions for sabo engineering.
K
ey
words
: debris flow, numerical simulation, mixed-size
grains, sediment sorting, two-layer model, GUI, Miyajima area
INTRODUCTION
Debris flows often cause substantial losses to hu-
man life and the economy. The amount of damage can
be effectively reduced using numerical simulation
models, which can describe the debris-flow process
(e.g., e
GasHiRa
et alii, 1997; t
akaHasHi
, 2007) and
determine the possible effects of sabo dams (e.g.,
s
atofuaka
& m
izuyama
, 2005, 2006). Although vari-
ous models have been developed, many existing de-
bris-flow numerical simulations do not have efficient
graphical user interfaces (GUIs). Therefore, we devel-
oped KANAKO and KANAKO 2D (n
akatani
et alii,
2007, 2008), general-purpose debris-flow simulation
packages equipped with efficient GUIs, and applied
them to real disasters and debris-flow torrents (n
aka
-
tani
et alii, 2009, 2010). However, actual debris flows
are composed of mixed grain-size sediment, which
causes sediment sorting (t
akaHasHi
et alii, 2001).
Some researchers have studied this phenomenon (e.g.,
d
avid
, 1990; i
veRson
, 2003), while many simulation
models have been developed only for uniform-sized.
ABSTRACT
Debris flows often cause substantial losses to hu-
man life and the economy. The amount of damage can
be effectively reduced using numerical simulation
models, which can describe the debris-flow process and
determine the possible effects of sabo dams or erosion
and sediment control dams. Although various models
have been developed, many existing debris-flow nu-
merical simulations do not have efficient graphical
user interfaces (GUIs). In addition, actual debris flows
are composed of mixed grain-size sediment, which
causes sediment sorting, while many simulation mod-
els have been developed only for uniform-sized gravel.
Here, we report the development of a GUI-equipped
oneand two-dimensional (1D and 2D, respectively)
debris-flow simulation system for mixed-size gravel.
The model uses two layers in 1D simulations to ac-
count for debris-flow sediment sorting, and can also
examine the effect of closed, slit, and grid sabo dams.
The model can incorporate multiple dams and combi-
nations of different types of sabo dams. We simulated
a debris-flow disaster that occurred on September 6,
2005, in Miyajima, Hiroshima Prefecture. Although
two sabo dams were present along the torrent, a large
amount of damage was caused in the nearby residential
area. We considered these existing dams in our simula-
tion. Our results demonstrated that applying the mixed
grain-size sediment model provided a more realistic
description of the debris-flow deposition than uniform-
sized gravel models. Furthermore, our GUIequipped
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k. NAkATANI, T. wADA, N. MATSUMOTO, Y. SATOFUkA & T. MIZUYAMA
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
TwO-LAYER MODEL FOR 1D SIMULATION AREAS
In 1D simulation areas, we applied a two-layer
model as a simple means of representing the sorting
phenomena. This model uses the basic equations for a
one-layer debris-flow model with mixed materials, but
the vertical change in the sediment concentration is also
considered. The flow is divided into two vertical layers
(see Fig. 1), and the proportion of each grain-size cat-
egory of flowing sediment at each point is considered.
Inverse gradient or sediment sorting is modeled by ex-
changing particles between layers. The process is calcu-
lated using parameters obtained from laboratory experi-
ment results (see details from s
atofuaka
et alii, 2007).
We use the subscript k to indicate the k
th
grain-size
category. Therefore, d
k
and C
k
are the particle diameter
and concentration, respectively, of the k
th
grain size.
The average particle diameter d
m
in a debris flow that
consists of mixed materials can be expressed as
where ke is the largest grain-size category. Here, C
k
,
d
k
, and d
m
represent the values of the total flow depth.
The vertical change in sediment concentration is
considered using a new variable p
k
, as shown in Fig.
2, that indicates the proportion of each grain-size
category of flowing particles. Given the exchange of
particles between the two layers, this proportion will
Here, we report the development of a GUI-
equipped one- and two-dimensional (1D and 2D,
respectively) debris-flow simulation system “KANA-
KO 2D Ver. 2.1” for mixed grain-size sediment. The
model uses two layers in 1D simulations to account
for debrisflow sediment sorting, and it can also exam-
ine the effect of sabo dams. We used the developed
software package to simulate the debris-flow disaster
that occurred on September 6, 2005, in Miyajima, Hi-
roshima Prefecture, and compared the results obtained
using mixed and uniform grain-size sediment.
METHODS
We developed our system using MS Visual Basic.
NET (VB.NET). Our resulting software package con-
tains two parts: a user interface that manages the data
input and displays the output, and a simulation model.
For the user interface, we applied and extended KANA-
KO 2D, which can simulate uniform-sized gravel. For
the simulation model, we applied and modified an inte-
grated model (w
ada
et alii, 2008) so that we could ob-
tain more accurate results in the boundary area between
1D simulation areas, such as gullies, and 2D simulation
areas, such as alluvial fans. We also modified a mixed
grain-size gravel model (m
atsumoto
et alii, 2008).
By integrating and improving existing simulation
models (s
atofuaka
& m
izuyama
, 2005, 2006), users
can easily simulate and examine the effect of closed,
slit, and grid sabo dams.
1D AND 2D DEBRIS-FLOW SIMULATION
MODEL APPLIED TO MIXED GRAIN-SI-
ZE SEDIMENT
Our proposed model is based on an integration
model for uniformsized gravel for 1D and 2D simula-
tion areas. In 1D simulation areas, we applied a mixed
grain-size gravel erosion/deposition process, and also
considered sediment sorting and the concentration of
coarse particles at the front of the debris flow (s
ato
-
fuaka
et alii, 2007). In 2D simulation areas, the vertical
slope becomes gradual and the stress is distributed in
the cross-flow direction. Therefore, since the exchange
of particles in the vertical direction decreases, we ex-
cluded the process of sediment sorting and the concen-
tration of coarse particles at the front of the debris flow.
The governing equations for the proposed model
are given separately for 1D and 2D simulation areas in
the following sections.
Fig. 1 - Velocity distribution in the debris flow (u
0
: aver-
age flow velocity for the total flow depth)
Fig. 2 - Outline of particle proportion p
k
in the upper layer
(1)
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DEVELOPMENT AND APPLICATION OF GUI EQUIPPED 1-D AND 2-D DEBRIS FLOW SIMULATOR, APPLIED TO MIXED-SIZE GRAINS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
737
where k
3
is a coefficient.
From the results of laboratory experiments examining
the size distribution of debris flow in the vertical di-
rection, we set k
1
= 0.75 and k
2
= 0.01.
GOVERNING EQUATIONS FOR 1D SIMULA-
TION AREAS
The governing equations for 1D simulation areas
are as follows. First, the continuity equation for the
entire debris-flow volume is:
The continuity equation for the k
th
grain-size cat-
egory sediment volume for the entire flow is:
The continuity equation for the k
th
grain-size cat-
egory sediment volume of the upper layer is:
The momentum equation for the debris flow in the
flow direction (xaxis) can be expressed as:
Finally, the equation used to determine the change
in the bed surface elevation is:
In Eqs (7)-(10), i
k
is the erosion/deposition velocity
for the k
th
grainsize category, u is the x-axis flow velocity,
z is the bed elevation, t is time, g is the acceleration due
to gravity, H is the flow surface elevation (H = h + z), ρ
is the interstitial fluid density, C
*
is the sediment concen-
tration by volume in the movable bed layer, and τ
x
is the
riverbed shearing stresses in the x-axis direction.
change with time, and is determined using
Here, the subscripts U and L indicate the upper
and lower layers, respectively.
The total unit sediment discharge for the k
th
grain-
size category in entire layer q
bk
is calculated as following;
Since the value of p
k
ranges between 0 and 1, q
bk
is affected by a change in concentration ranging from
0.5 to 1.5 times that of the uniform case. When we
use Eq. (3) to solve the continuity equations for each
grain-size category instead of the standard sediment
flux formula, we can reproduce the concentration of
larger particles at the front of the flow.
If a particle in the upper layer is sufficiently small-
er than the average opening space in the lower layer
R
m
, it can move into the lower layer. However, a larger
particle cannot enter the same opening, as shown in
Fig. 3. m
iddleton
(1970) inferred that large particles
are pushed upward when small particles fall into the
openings between large particles (dynamic sieving).
We considered that this is the main factor producing
vertical sediment sorting. The average opening size of
the lower layer can be expressed as follows using the
average particle diameter in the lower layer:
where d
Lm
is average particle diameter of the lower
layer and k
1
is a coefficient.
The rate at which particles fall into openings in the lower
layer is thought to increase when the proportion of small
particles in the upper layer is large and the velocity is
high. Therefore, the rate r
k
can be expressed as follows:
where k
2
is a coefficient. Equation (5) can be applied
to smaller particle categories, d
k
< R
m
. Larger particle
categories, d
k
R
m
, must move upward to compensate
for the downward movement of the smaller particles
because of the assumption that the sediment is distrib-
uted homogeneously over the entire flow.
These movements cause the exchange of particles
and vertical sorting in the debris flow. The rate r'
k
can be expressed as:
(2)
(3)
Fig. 3 - Settling condition of small particles and large
particles, depending on the opening space in
the lower layer
(4)
(5)
(6)
(7)
(8a)
(8b)
(9)
(10)
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k. NAkATANI, T. wADA, N. MATSUMOTO, Y. SATOFUkA & T. MIZUYAMA
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
If C > C
and i > 0, the erosion velocity is:
where δ
e
is the erosion coefficient and d
mbed
is the aver-
age particle diameter of the bed surface.
Whether particles of diameter d
k
are movable can
be judged depending on the sediment transport move-
ment. The deposition velocity for the k
th
grain-size
category i
k
is as follows.
For debris flow and sediment sheet flow:
For bed load transport, whether particles of diam-
eter d
k
are movable can be judged by using a modified
Egiazaroff’s critical shear stress concept:
where f
bk
is the volume ratio of the k
th
grain-size cat-
egory particles to all the particles on the bed surface,
u
*
is the shear stress
(= , where θ
w
is the
slope of the water surface), and u
*ck
is the critical fric-
tion velocity of a k
th
grain-size category particle.
EQUILIBRIUM SEDIMENT CONCENTRATION
AND RIVERBED SHEARING STRESS
The equations for equilibrium sediment concen-
tration and riverbed shearing stress are based on pre-
vious research (n
akaGawa
& t
akaHasHi
, 1991a). The
sediment transportation is classified as debris flow,
sediment sheet flow, or bed load transport based on the
slope gradient and sediment concentration of the flow.
GRAIN SIZE DISTRIBUTION ON A RIVERBED
SURFACE
To calculate the erosion/deposition process for
mixed grain-size sediment, we need to consider
how the grain-size distribution of a riverbed sur-
face varies with time. Therefore, we define a par-
ticleexchange layer δ
m
above the riverbed surface,
as shown in Fig. 4 (the layer thickness is constant),
and consider that the grain-size distribution changes
only in this layer. When erosion/deposition occurs
and the riverbed surface changes, the particle-ex-
change layer will also change. On the upper surface
of the particle-exchange layer, particle exchanges
will occur through the fluid-phase erosion/deposi-
tion volume. On the lower surface of the particleex-
change layer, particle exchange will occur through
When considering the continuity equation for the
k
th
grain-size category sediment volume, we first cal-
culate the continuity equation for the entire flow, and
then we calculate the continuity equation for the upper
layer. We determine the lower layer volume from the
difference between the entire flow and the upper layer
volumes. When sediment sorting does not occur, we
set the falling rate and rising rate to 0; thus, we don’t
need to consider the continuity equation for the upper
layer, and just model one layer of flow. Such a situation
can occur when applying this model to uniform-sized
grains or to bed load transport in mild-slope areas.
We apply the two-layer model to represent the
sediment sorting phenomena. However, we do not
calculate the flow motion of the upper and lower lay-
ers separately. Instead, we assume that the sediment
concentration is distributed homogeneously in the
flow depth direction, and we use the entire flow sedi-
ment concentration when calculating the momentum
equation and the erosion/deposition process.
EROSION / DEPOSITON VELOCITY
The erosion and deposition process is related to
the difference between the equilibrium sediment con-
centration C
and the actual sediment concentration
C (t
akaHasHi
et alii, 1991a). If C < C
, and i < 0, the
deposition velocity is
where q is a unit sediment discharge, C
is the equilib-
rium sediment concentration, C is the sediment con-
centration of all the grain sizes in the flow, and δ
d
is a
deposition coefficient. The deposition velocity for the
k
th
grain-size category i
k
is as follows:
However, in Eq. (12), once erosion occurs and sedi-
ment is taken into the flow, the deposition due to particle
settling is neglected, even in low gradient and velocity
areas, such as the mouth of a river or upstream of a dam.
Therefore, when the sediment diameter (k
th
grain-size
number) is small and the flow reaches a low-velocity sec-
tion so that the friction velocity u
*ck
is less than the settling
velocity w
0k
, we consider deposition due to the settling by
adding the Rubey’s settling velocity w
0k
as follows:
(11)
(12)
(13)
(14)
(15a)
(15b)
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DEVELOPMENT AND APPLICATION OF GUI EQUIPPED 1-D AND 2-D DEBRIS FLOW SIMULATOR, APPLIED TO MIXED-SIZE GRAINS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
739
the lower layer, depending on how much the parti-
cle-exchange layer elevations have moved.
The time variation of the volume ratio of the k
th
grain-size category particles to all the particles on the
bed surface, or the riverbed surface ratio f
bk
, is as follows:
where f
0k
is the volume ratio of the k
th
grain-size cate-
gory particles to all the particles on the lower bed layer.
EFFECT OF A SABO DAM
As in the existing versions of KANAKO and
KANAKO 2D, the user can prescribe three types of
sabo dams for a 1D simulation area: closed, slit, or
grid. For detail information of deposition process up-
stream to the sabo dam, see the following references
(s
atofuka
& m
izuyama
2005, 2006; n
akatani
et alii,
2008). For a grid sabo dam, the sediment material is
composed of several grain-size classes, but we only
consider the largest class of sediment, which blocks the
grid dam opening and increases the dam height. In the
future, we may divide the grain-size classes into two
groups for grid sabo dams, and consider that the mean
diameter of the larger group affects the dam blockage.
2D SIMULATION AREAS
In a 2D simulation area, the vertical slope is more
gradual and the stress is distributed in the cross-flow
direction. Therefore, since the exchange of particles
in the vertical direction decreases, we excluded the
process of sediment sorting and the concentration of
coarse particles at the front of the debris flow. We ap-
ply the particle-number conservation law (t
akaHasHi
et alii, 1991b) to calculate the change in time and
space of the mean particle size d
m
in the flow, and then
calculate the other variables assuming a uniform grain
size and making use of the calculated d
m
:
The governing equations for 2D simulation ar-
eas are same as those for 1D simulation areas, but
they consider the cross (y-axis) direction as well as
the flow (x-axis) direction. We only modeled uniform
grain-size and one layer flow in 2D simulation areas,
calculated using Eq. (17).
KANAKO 2D VER. 2.10: A GUI-EQUIPPED
1D AND 2D DEBRIS-FLOW SIMULATOR AP-
PLIED TO MIXED GRAIN-SIZE SEDIMENT
As in the existing version of KANAKO 2D for
uniform grain-size sediment simulations, a longitudinal
figure representing the 1D riverbed profile, and a plane
figure displaying the 1D river width and 2D landform
plane appears. The debris flow first passes through the
1D simulation area, and then through the 2D simulations
area. The KANAKO 2D GUI system is also easy to use
for beginners because the required simulation data sets
can be input using a mouse and viewed on a monitor. A
new function for mixed grain-size sediment is the grain-
size detail-setting screen, which is used to set the grain-
size classifications, grain diameter, and concentration of
particles in the supplied hydrograph. A data file is used
to set the volume ratio of riverbed particles.
During simulations, users can view real-time im-
ages of the simulation results on the main screen and the
2D landform screen. On the main screen, the user can
see real-time images of the flow depth and riverbed vari-
ation in the longitudinal and plane plots. Users can also
visualize the flow and sediment discharge at each calcu-
lation point. The new mixed grain-size sediment func-
tion allows the user to visualize the discharge of each
grain-size classification of sediment along with the entire
sediment discharge. Users can also view real-time im-
ages of the average particle diameter on the 2D landform
screen during the simulations, as it is shown in Figs. 8.
Other functions are the same as those in the existing
KANAKO 2D interface (see n
akatani
et alii, 2010).
SYSTEM APPLICATION TO A REAL DE-
BRIS-FLOW DISASTER
On September 6, 2005, a debris flow occurred on
Miyajima, a small island in Hiroshima Prefecture, Ja-
pan (k
aiboRi
et alii, 2006). Landslides followed heavy
typhoon rains, and the accumulated debris and rocks
gathered and flowed down about 2.6 km, destroying
Fig. 4 - Particle exchange layer for riverbed surfaces
(16)
(17)
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
The total calculated debris-flow volume was 36,000
m
3
, and the peak debris-flow discharge was 360 m
3
/s.
The supplied debris-flow conditions are illustrated in
Fig. 5. Reportedly, 13,000 m
3
of sediment was moved
from the riverbed during the erosion process and trans-
ported downstream. Therefore, we placed 13,000 m
3
(including void) of sediment evenly distributed along
the riverbed. Using the landform data, the calculated
thickness was 0.7 m. The landform conditions were
obtained from topographic maps and reports, and were
prescribed in KANAKO 2D as shown in Fig. 6. We set
the river width for the 1D landform area at a constant
15 m. Other parameters were set as listed in Table 1.
We considered two grain-size conditions in the sup-
plied hydrograph and initial riverbed ratio (see Table 2).
In Case 1, we used ten grain-size classifications with
equal proportions. In Case 2, we set a uniform grain
size of 0.55 m, which was the average diameter for
two existing closed sabo dams and causing sediment
to overflow downstream. We simulated this event us-
ing the developed KANAKO 2D Ver. 2.10 package by
modeling the mixed grain-size sediment debris flow.
SIMULATION CONDITIONS
The total volume of sediment resulting from the
failure was an estimated 18,000 m
3
. Therefore, we sup-
plied this sediment amount as the initial debris flow
volume from the upstream end of the simulation. We
then calculated the sediment concentration of the slope
after applying the Takahashi equation (t
akaHasHi
et alii,
2001) for the equilibrium concentration of debris flow:
where σ is the mass density of the bed material (= 2550
kg/m
3
); ρ is the mass density of the fluid phase includ-
ing water, mud, and silt (= 1180 kg/m
3
); f is the inter-
nal friction angle (= 35°); θ is the angle of the 100-m
slope area (= 4.93°); Cd is the concentration of the
debris flow (0.3 ≤ Cd ≤ 0.9C
*
); and C
*
is the concen-
tration of the movable bed (= 0.6).
We obtained a debris-flow concentration of 30%
from Eq. (18). Then, we calculated the peak debris-flow
discharge using the following equations from the Sabo
Master Plan for Debris Flow (NILIM Japan, 2007):
where Q
sp
is the peak debris-flow discharge (m
3
/s), ΣQ
is the entire debris-flow volume including water and
sediment (m
3
), and Vdqp is the sediment volume (m
3
).
(16)
(20)
(19)
Tab. 2 - Simulation cases
Fig. 5 - Supplied hydrograph for Cases 1 and 2 (left figure) and supplied material conditions for Case 1 (right figure)
Tab. 1 - Simulation parameters
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DEVELOPMENT AND APPLICATION OF GUI EQUIPPED 1-D AND 2-D DEBRIS FLOW SIMULATOR, APPLIED TO MIXED-SIZE GRAINS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
741
than what was observed for the larger sediments.
Therefore, sediment sorting occurred at Obs. 2.
The same tendency was observed at Obs. 3 and 4. A
5.5-m-high closed sabo dam was located between Obs. 2
and 3. This dam was not large enough for the amount of
sediment and was located on a steep gradient, so it was
not very effective. Due to erosion of the initial riverbed
and the sediments flowing over the sabo dam, both Cases
1 and 2 predicted more sediment discharge and total flow
at Obs. 3 than at Obs. 2. The trends for total sediment
discharge, amount of flow, and sediment sorting were
the same as seen at Obs. 2. A 8-m-high closed sabo dam
was located between Obs. 3 and 4. This dam was also
not large enough to catch all the sediment. However, the
dam was located on a small gradient and its capacity was
larger than the upper sabo dam, so it did trap some sedi-
ment. The slope gradient at this point was decreasing;
thus, the sediment discharge and total flow were less at
Obs. 4 compared to Obs. 3. As before, Case 1 predicted
more total sediment discharge and total flow than Case
2, and the peak arrival time was slightly earlier.
The discharge peak of larger sediments 0.6-1.0 m
in diameter was initially larger over short periods of
time, as observed at Obs. 2 and 3. However, medium-
sized sediments 0.3-0.5 m in diameter had a higher
discharge peak than larger sediments over a short pe-
riod of time. For smaller sediments 0.1-0.2 m in diam-
eter, the amount of discharge was initially small, but
this increased after the discharge of the larger and me-
dium-sized sediments decreased and the duration of
the discharge was longer. These phenomena occurred
due to sediment sorting as the debris flow traveled
down the slope, and due to deposition caused by the
sabo dam and the decreasing slope gradient.
Case 1. We included the two existing sabo dams in the
simulations, and assumed that both dams were empty.
SIMULATION RESULTS FOR 1D AREA
We compared the total flow and sediment dis-
charge for both cases at the four observation points
labeled in Fig. 8 as Obs. 1-4. We also examined each
grain size sediment discharge for Case 1 (see Fig.6).
At Obs. 1, the difference between the total flow and
total sediment discharge for the two cases was small.
The grain size distribution for Case 1 indicated that
the discharge of smaller sediments that were 0.1 and
0.2 m in diameter was higher than that of larger diam-
eter sediments due to the selective transport caused by
the flow velocity and flow depth.
At Obs. 1, the distance from the upstream end of the
simulated flow was about 300 m and the gradient was
not large, so the amount of flow was small and the flow
depth was low, therefore sediment sorting did not occur.
At Obs. 2, the distance from the upstream end of
the simulated flow was 600 m and the gradient was
large, so the type of sediment transport was debris
flow. Due to erosion of the initial riverbed, the sedi-
ment discharge in both Cases 1 and 2 increased com-
pared to Obs. 1, and the amount of flow increased.
Case 1 showed slightly more total sediment discharge
and total flow, and the peak arrival time was slightly
earlier than in Case 2. For Case 1, for larger sediments
0.5-1.0 m in diameter, the amount of discharge of
each grain size was initially large over short periods
of time. For smaller sediments 0.1-0.4 m in diameter,
the amount of discharge was initially small, but this
increased after the discharge of larger sediments de-
creased, and the duration of the discharge was longer
Fig. 6 - Miyajima simulation
area shown on kANA-
kO 2D (1D area in the
lower right, 2D area
in the upper right) and
corresponding topog-
raphy map (left)
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
SIMULATION RESULTS FOR 2D AREA
We compared the riverbed variation over the 2D
landform area for Cases 1 and 2 (shown in Fig. 8 cent-
er and right), at 301 s, 426 s, 645 s, and 1799 s. Case 1
with mixed grain-size sediment covered a wider area
and the sediment deposition was thicker. This tenden-
cy was seen all through the simulation period 1800 s.
The transitional change of the average grain-size
diameter is shown for Case 1, at 301 s, 426 s, 645 s,
and 1799 s (shown in Fig. 8 left). The average grain-
size diameter decreased with time due to sediment
sorting. Also, the coarse particles were concentrated
at the front of the debris flow in the 1D landform area,
which affected the discharge flowing to the 2D area.
CONCLUSION
By applying a mixed grain-size sediment model to
debris-flow simulation, now we can describe the flow
and erosion/deposition process of debris flows con-
sidering granularity characteristics. By equipping the
mixed grain-size sediment simulation model with an
efficient GUI, users can run more reasonable debris-
flow simulations without difficulty, and are able to
plan better sabo engineering solutions. We applied our
Fig. 7 - Total flow and total sediment discharge for Cases 1 and 2 (left) and grain size sediment discharge for Case 1 (right)
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DEVELOPMENT AND APPLICATION OF GUI EQUIPPED 1-D AND 2-D DEBRIS FLOW SIMULATOR, APPLIED TO MIXED-SIZE GRAINS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
743
tial areas. However, our proposed mixed grain-size sed-
iment model is limited by the conditions of laboratory
experiments; further studies are required to improve the
parameters we used and check our assumptions. The
proposed model should also be applied to other real
disasters to ensure its accuracy. Furthermore, we must
consider more userfriendly GUIs for the simulations.
system to a real debris-flow disaster that occurred in
Japan and compared the results obtained using mixed
and uniform grain-size sediment.
The results showed that the mixed grain-size sedi-
ment debris-flow predictions had higher discharges
and earlier peak arrival times.
The results also showed differences in the deposi-
tion process in 2D areas, which correspond to residen-
Fig. 8 - Transitional change of average grain-size diameter in the 2D landform area for Case 1(left), riverbed variation in the
2D landform area for Case 1 (center) and Case 2 (right)
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