E3S Web of Conferences 415, 06007 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341506007

Effect of multiple debris flow countermeasures on flow
characteristics and topographic changes through real-scale
experiment
Woojae Jang2 , Beom-Jun Kim1, Shin-Kyu Choi3, Tae-Hyuk Kwon2 and Chan-Young Yune1*
1Gangneung-Wonju National University, Department of Civil Engineering, 25457 Gangneung, South Korea

2Korea Advanced Institute of Science and Technology, Department of Civil and Environmental Engineering, 34141 Daejeon, SouthKorea

3Korea Electric Power Research Institute, 34056 Daejeon, South KoreaAbstract. In this study, to investigate the effect of multiple countermeasure on the flow characteristics ofdebris flows, a real-scale experiment was conducted in a natural gully by reproducing a debris flow with ainstallation of multiple countermeasures. In addition, the topographic changes before and after experiment
by debris flow were investigated using UAV-LiDAR. Based on the experiment results, the effect of multiple
countermeasures and the topographic changes against the gully erosion and deposition caused by debris flow
were also analyzed. The installation of multiple countermeasures significantly decreased the frontal velocity
of debris flow. Furthermore, the countermeasure induced the deposition of debris material on the back of
the countermeasure.

1 Introduction
Debris flows can lead disastrous consequences todownstream infrastructure of societies because of its
fast-moving characteristics along valleys [3, 4].
Structural countermeasures have been widely utilized toprevent debris flow hazards, which lead to disastrous
consequences to urban area or infrastructure. In
particular, because of advantages of low construction
cost, the ability to screen large boulders, and increased
hydraulic continuity, the use of rigid baffles (cylindricalor rectangular shape) and a flexible barrier with wire
mesh among open-type debris flow countermeasure has
been independently utilized recently. The baffles aim to
decelerate frontal velocity and to reduce dynamic
energy by impeding mobility of debris flow. The
flexible barrier has an advantage in filtering debris
materials and inducing deposition with absorbing
dynamic energy of debris flows. If rigid baffles and aflexible barrier are installed sequentially in the flow pathof debris flows, they can work as effective
countermeasures against debris flows.
Figure 1 shows the concept of the multiple
countermeasures, which combined with arrays of baffles
and a flexible barrier. However, there has been no design
guidelines for the configuration of baffles and they arestill constructed based on empirical approaches byengineers. In particular, not only the appropriate
specification and arrangement for baffle design has still
not been suggested but also the energy reduction due tofrictional loss among grains in design of flexible barrier
has not been considered, which can accordingly lead toexcessive design and increased cost. To understand thedynamic behavior of debris flows, dynamic interactionand energy dissipation caused by debris flow
countermeasures, most of researchers have conducteddebris flow experiments using artificial andminiaturized flumes [1, 5, 9, 12, 15]. The debris flow insmall-scale
flume,
however,mayexhibit
disproportionalities in terms of viscous shear and porepressures due to scale effect of flow [6]. Furthermore,because these flumes were straight and had a constantcross section, it was also difficult to investigate thetopographic changes due to erosion and deposition
during flow process.

Fig. 1. The concept of multiple countermeasures

In this study, to investigate the flow characteristics
by multiple countermeasures, real-scale experiment wasconducted in a natural gully by reproducing a debris
flow with a installation of multiple countermeasures. In* Corresponding author: yune@gwnu.ac.kr© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0(https://creativecommons.org/licenses/by/4.0/).

E3S Web of Conferences 415, 06007 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341506007

addition, topographic changes by the debris flow before
and after experiment were investigated using UAVLiDAR. Video cameras were installed along the flow
path to capture the dynamic behavior of the debris flow.
Load cells were installed in front of the baffles and theflexible barrier to measure the impact load. After theexperiment, the frontal velocity and flow depth wereestimated by the captured image profiles based on thevideo recordings. From the test data, the velocity
reduction characteristics of the flow due to multiple
countermeasure and the topographic changes due to theerosion and deposition of the gully by the debris flow
were analyzed.

installed at the gully of downstream. The multiple
countermeasures consist of rigid hollow cylindricalbaffles with holes and a flexible barrier with wire mesh.
The diameter and height for the cylindrical baffle waswere 0.5 m and 2.0 m, respectively. Each spacing
between successive rows and flexible barrier from baffle
arrays was 12 m. The baffle arrays and flexible barrier
were installed at 188 (first row of baffles) and 212 m,respectively, from the debris flow initiation facility. The
transverse blockage ratio of baffles in the channel wasdetermined as 40 % [7, 13]. The size of flexible barrier
was 6.0 m (top) and 4.0 m (bottom) in width, and 3.0 m
in height. The maximum allowable energy of theflexible barrier was 500 kJ. To measure dynamic impact
load of debris flow, load cells were installed at the top,middle, and bottom of the front baffles. Shackle typetension load cells were installed at the top, middle, andbottom on both sides of the flexible barrier as well. The
detailed design and arrangement of multiple
countermeasures for field experiment were determinedbased on the small-scale experiment [10].

2 Real-scale debris flow experiment
2.1 Test site
Figure 2 shows the study area of the real-scale debris
flow experiment, which is located at Jinbu, Gangwon
province, South Korea. The watershed area of the studysite is 0.28 km2, with a main channel having an overall
length of 824 m and minimum and maximum width of
4.6 and 13.7 m, respectively. The inclination of theinitiation zone and downstream area of the main channel
is 39° and 8°, respectively. It has a similar topographic
characteristics with typical debris hazard sites in South
Korea [14].

Fig. 3. Schematic diagram of debris flow initiation facility.

Fig. 4. Debris flow initiation facility at top view (left) and at
front view (right).
Fig. 2. Study area for the real-scale debris flow experiment.

2.2 Initiation
conditions

facility

andexperimental

Figure 3 shows schematic diagram of the debris flow
initiation facility. The facility was 12.6 m in length and12.0 m in width, consisted of a soil container at the front
and a water container at the back. The height at the front
and back of the facility were 6.5 m and 5.0 m,respectively. The maximum volume of soil and watercontainer was 346 and 268 m3, respectively. In this study,
262 m3 of soil and 202 m3 of water were used. Actual
images of the debris flow initiation facility are shown inFigure. 4. Figure 5 shows the multiple countermeasures

Fig. 5. Real-scale experiment setup.

2

E3S Web of Conferences 415, 06007 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341506007

2.3 UAV-LiDAR survey

release of debris materials from the initiation facility due
to a steep inclination in the initiation zone, and thenslowed down until 140 m from the initiation facility.
From 140 to 210 m, in case of the experiment without
countermeasure, the frontal velocity increased becauseof the straight channel and exposed bed rock having asmooth surface. Thereafter, the slope became gentle
around 8° in average, and accordingly the frontal
velocity of debris flow gradually decreased. According
to the recorded video of the experiment, the debris
eventually stopped at 740 m away from the initiationzone.
By contrast, in the experiment with thecountermeasures, the presence of the countermeasuressignificantly reduced the frontal velocity in the region
between 188 m and 210 m away from the initiation zone.
The frontal velocity was reduced by baffle arrays by 51%
compared with the upstream flow before entering thebaffles. Moreover, the frontal velocity further decreased
as the debris flow passed through the flexible barrier.
After the multiple countermeasures, the frontal velocity
partly regained its speed again. Thus, the installation of
the multiple countermeasures significantly decreased
the dynamic energy of debris flows through suppressionof flow mobility.

To investigate the topographic changes in the channel
due to the debris flow experiment, field surveys using
UAV-LiDAR (DJI Matrice 600 pro; Velodyne VLP-16puck) were performed before and after the experimentover the whole channel. The UAV was flown manuallyat an altitude from 60 m to 80 m above the ground withthe velocity of approximately 0.5 m/s. By means ofsurveys performed two times, the point clouds before
and after the real-scale debris flow experiment wereobtained.
Removal of non-ground points is an essential step tocalculate topographic changes. The non-ground points
include trees and installed man-made structures such as
cylindrical baffles, a closed-type barrier, a flexiblebarrier, and a debris storage container. These nonground points were removed using the cloth simulation
filtering (CSF) plug-in of CloudCompare [2, 16]. The
cloth resolution of 1.0 m and the classification thresholdof 2.0 m were used for the CSF. We chose the multiscalemodel to model cloud comparison (M3C2) method
which is widely used among the point cloud comparison
approaches to detect topographic height changes before
and after the real-scale experiment [11]. In the M3C2
method, the projection scale D was set as 1.7 m. Notethat the normal calculation was not implemented in thisstudy as the orientation for comparison was pre-defined
to be vertical. Figure 6 shows the digital elevation model(DEM) before and after vegetation filtering.

Fig. 7. Debris flow frontal velocity along transportation zone.
Fig. 6. Digital elevation model (DEM) before vegetation
filtering (left) and after vegetation filtering (right).

3.2 Topographic changes
Figure 8 shows the topographic map of the height
alteration in the channel due to the debris flow, which
was obtained by comparing LiDAR 3D point clouds
using the M3C2 method. This two-dimensional
topographic change map was generated through therasterization of M3C2 distance profile with a cell size of
20 cm. Each cell represents elevation change;
accordingly, the erosion and deposition volumes can becalculated at each cell. The total erosion volume wasestimated as 2,872 m3 and the deposition volume as
3,210 m3, respectively. The result depicts the areas withactive basal erosion and the trap and deposition of debris
by the multiple countermeasures including the flexible
barrier and baffles.

3 Experiment results
3.1 Velocity of debris flow
Figure 7 shows the change of frontal velocity along thetransportation zone. The altitude of debris flow initiation
facility was 917m, and it gradually decreased along thechannel as it went downstream. To figure out the effectof the multiple countermeasures on the frontal velocityof the debris flow, the results of the real-scale
experiment conducted in 2012 without debris flow
countermeasures was added in the figure [8]. In here, thesquare symbol (RT) and circle symbol (RT_M) indicate
the case without and with the multiple countermeasures,respectively. The frontal velocity of debris flows for thetwo experiments showed a peak value right after the3E3S Web of Conferences 415, 06007 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341506007

parametric studies and used for numerical modellingdevelopment.
This research was supported by a grant (22RITD-C158631-03)
from the Regional Innovation Technology Development
Program funded by the Ministry of Land, Infrastructure andTransport of the Korean government. Support was also givenby the Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Ministryof Education (2021R1A6A1A03044326) and by "Ministry ofthe Interior and Safety" R&D program (20018265).

References
1.

Chae. B.G, Song, Y.S, Seo. Y.S, Cho. Y.C, Kim.
W.Y, J. E. Geol. 16, 3 (2006), (In Korean)
2. CloudCompare, GPL Software, Version 2.10,(2019)
3. Hübl. J, Suda. J, Proske. D, Kaitna. R, Scheidl. C,
Debris flow impact estimation steep slopes, inProceedings of the 11th International Symposium
on Water Management and Hydraulic Engineering,
WMHE, 1–5 September 2009, Ohrid, Macedonia(2009)
4. Hungr. O, Morgan. G.C, Kellerhals. R, Can
Geotech. J. 21,4 (1984)
5. Iverson. R.M, Reid. M.E, Logan.M, LaHusen. R.G,Godt. J.W, Griswold. J.P, Nat. Geoscience 4 (2011)
6. Iverson, R.M, Denlinger. R.P, J Geophys. Res.
Solid Earth 106 (2001)
7. Ikeya. H, Uehara. S, J. Jpn. Eros. Con. Eng. Soc.
114 (1980), (in Japanese)
8. Jun. K.J, Lee. S.D, Kim. G.H, Lee. S.W, Yune. C.Y,Verification of countermeasures by velocity
estimation of real scale debris flow test, inProceedings of the 6th International Conference on
Debris flow Hazard Mitigation: Mechanics,Prediction and Assessment, DFHM6, 22–25 June
2015, Tsukuba, Japan (2015)
9. Kim. K, Lee. D, Kim. D, Lee. S, J. Kor. Geo.
Environ. Mental. Soc. 9, 5 (2008), (In Korean)
10. Kim. B.J, Kim. Dolla, Yune. C.Y, Korean Societyof Hazard Mitigation, Conference, 9-10, September
2021 (in Korean), (2018)
11. Lague.D, Brodu.N, Leroux.J, Remote sensing J. P
82 (2013)
12. Scheidl. C, Chiari. M, Kaitna. R, Müllegger. M,Krawtschuk. A, Zimmermann, T, Proske. D, Surv.
Geophys. 34, 1 (2013)
13. Watanabe. M, Mizuyama T, Uehara.S, J. Jpn. Eros.
Con. Eng. Soc. 115 (1980), (in Japanese)
14. Yune. C.Y, Kim. K.S, Yoo. N.J, Seo. H.S, Jun. K.J,Italian. J. E. Geol and Environ (2011)
15. Zhou. G.G.D, Li. S, Song. D, Choi, C.E, Chen. X,Landslides 16, 2 (2018)
16. Zhang. W, Qi.J, Wan.P, Wang.H, Xie. D, Wang. X,Yan. G, Remote sensing, 8, 6 (2016)

Fig. 8. Maps of topographic changes by debris flows: (a) theentire channel and (b) an enlarged map of the transportationzone with the countermeasures.

4 Conclusions
In this study, to examine the effect of multiple
countermeasures on the flow characteristics of debris
flow, we conducted a real-scale experiment in a natural
gully with the installation of cylindrical baffles and aflexible barrier. The frontal velocity of the debris flow
showed a significant increase and a maximum value inthe upstream zone due to a high slope angle. But theinstallation of multiple countermeasures significantly
reduced the frontal velocity at the downstream. The
topographic changes by debris flow before and after theexperiment were also investigated using UAV-LiDAR.
The LiDAR results confirmed the effect ofcountermeasures which caused a large amount of results
provide unique data on well-controlled real-scale debris
flow tests, which can be readily extended for various

4