E3S Web of Conferences 415, 06011 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341506011

Analysis of mitigation effect of the open- and closed-type check
damSeungjun Lee1, Hyunuk An1*, and Minseok Kim2
1Chungnam National University, Department of Agricultural and Rural Engineering, 34134 Daejeon, Republic of Korea
2 Korea Institute of Geoscience and Mineral Resources, Geologic Hazards Division, 34132 Daejeon, Republic of Korea

Abstract. Debris flow caused by intense rainfall can damage facilities and endanger human life.
Accordingly, several models have been developed to predict and mitigate the debris flow damage, forwhich check-dam construction is essential. There are two types of check dams: open type and closed
type. The former is suitable for granular debris flow containing little water, whereas the latter issuitable for water-laden debris flows. However, it is challenging to site the check dam to realize
optimal mitigation effects. Therefore, we determined the best check dam location to reduce debris flow
damage considering the two types. In this study, we simulated the Raemian apartment basin for theMt. Umyeon landslides, which occurred in 2011. Constructing the open- and closed type dam at theupper side of the catchment produced the best performance.

1 Introduction
Landslides and debris flows can transport sediment andboulders over long distances and comprise one of themost frequent natural disasters. However, because they
combine water, sediment, boulders, and flotage,simulation and analysis is difficult.
Various methods for analyzing and predicting thedebris flow have been developed, in keeping with thedevelopment of computing power. These can be divided
into numerical modeling and artificial intelligence (AI)machine learning. Further, numerical models aredivided into physical and conceptual–empirical models.
The physical model is advantageous because it
considers physics-based parameters, such as soil depth,
water content in the debris flow, density of particles, andrainfall intensity. Therefore, it may be useful inelucidating the physical mechanism behind debris flow.
However, representing the physical parameters ischallenging. Moreover, applying it to a warning system
is challenging because of the excessive computation
time. In contrast, the statistics-based AI model requiresa short computation time to calculate the debris flow.
However, utilizing it when there records of debris flow
are limited is problematic. Using a numerical model
based on a conceptual–empirical algorithm to figure out
the flow process may be difficult. However, this method
was validated over the past three decades by adequately
simulating debris flow. Further, the simulation time isshort. Therefore, we chose the numerical model basedon a conceptual–empirical algorithm to simulate thedebris flow.
The warning system based on numerical and AImodeling can shorten the evacuation time and lower
casualties. However, it is impossible to reduce property

damage using a warning system. Therefore, constructing
a check dam is essential to mitigating the damage scale(casualties and property damage). However, the optimal
siting conditions for the two types of check dams varies
and is difficult to determine. Therefore, we sought toreduce debris flow damage through optimally siting thetwo types of dams.

2 Material and methods
2.1 Governing equation and numerical modelingIn this study, Deb2D, which was developed by An et al.
[1], was used to simulate the debris flow. This model isbased on a hyperbolic conservation form of the mass
(shallow-water equation). Please refer to An et al. [1]and An et al. [2] for detailed definitions and calculation
methods for discrete terms.
This study focuses on a one-phase modelingapproach due to its simplicity and applicability. Further,
the widely used Voellmy, Bingham, and Coulombviscous rheological models, as well as Takahashi
models, are considered here. The Voellmy friction isexpressed as follows:
S fx  v gh gu2, S fy  v gh gv



2,(3)

where μv is the Coulomb friction coefficient, and ζ isthe turbulent friction coefficient. The Bingham friction
is expressed as follows:S fx b u b v 31
31
 c 
 , S fy    c ,h 
2h (4)2* Corresponding author: hyunuk@cnu.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, 06011 (2023)
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https://doi.org/10.1051/e3sconf/202341506011

where ρ is the mass density, τc is the yield stress, andμb is the Bingham viscosity. The Coulomb-viscous
friction is expressed as follows:S fx  gh tan  c u 
c v 
3131 c 
 , S fy  gh tan     c ,h 
2h (5)2where ϕ is the friction angle between the bed
material and surface, and μc is the Coulomb-viscousviscosity. Finally, the Takahashi model calculates theresistance by classifying the characteristics of debris
flow into 1) stony, 2) immature, and 3) turbulent-muddy
debris flows. The Takahashi friction for a stony debris
Fig. 1. Sun et al.’s (2020) experiment configuration; a) nocheck dam, b) closed-type check dam, c–f) open-type checkdam

flow (C≥0.4C*) is expressed as follows: d   C  1  C   w   d   C  1  C   w  S fx   m u u , S fy   m vv22 h  8  C C 1 3  1
 h  8  C C 1 3  1
12



*

12



*(6)

Immature debris flow occurs when C is less than
0.4C*, and the resistance at the bottom of flow isexpressed as follows:
2S fx 2

1  dm 1  dm u u , S fy vv
0.49  h 0.49  h (7)A turbulent-muddy flow occurs when C is less than0.02, and the bottom flow resistance is expressed asfollows:
S fx w gn2
 gn2
u u , S fy  w 1 3 v v ,T h1 3
T hFig. 2. Experiment vs. simulation results from a–f in Fig. 1(8)4 Study area
Several debris flows occurred (rainfall amount: 500mm/day; maximum rainfall intensity: 80 mm/h) in the
Umyeon Mountain area on July 26 and 27, 2011 due totorrential rainfall. The water-laden debris flows caused
significant property damage in the downtown areas. We
simulate the Raemian apartment basins, for which fielddata are abundant (Fig. 3).
Landslides-debris flows occurred at four points,
marked in red, in the Raemian apartment basin [7]. Theobserved channel lengths in the Raemian basins werereported to be 610 m. The final volume of deposited
sediment was 26 000 m3. The maximum velocity wasdetermined from CCTV footage and dashboard cameras
in cars. It was estimated as 28 m/s in the Raemianapartment blocks. These debris-flow events caused
direct damage to the 3rd floors of the Raemianapartment [7]. In this study, the erodible soil depth is
between 2 m and 5 m [7]. A digital elevation model,utilizing light detection and ranging (1 m × 1 m), wasused to build the terrain. The initial volume of debris
flow was measured as 350 m3.
The check design was divided into 1) closed type:1.1) height (5, 10 m); 1.2) distance from initiation zone
(section 1–7); 2) open type: sections 1–7. However,sections 6 and 7 were too wide for the construction of acheck dam. Therefore, the mitigation effect of the checkdam, located in sections 1–5, was analyzed to identify
the best construction location according to the checkdam design (design type, height, and location). Thethickness of the check dam was fixed at 4 m.

where dm is mean sediment diameter, C is thesediment concentration in the flow, C* is maximum
sediment concentration in the basal, ρw is the density ofwater, σ is the density of the sediment particle, ρT is
mixture density (ρT = σC + (1 − C)ρw), and n is theManning’s roughness coefficient of the channel. Moredetails can be found in the work of Takahashi [3]. We
use the algorithm proposed by Lee et al. [4], which isbased on Lee et al. [5]. It can simulate erosion,entrainment, and deposition. Please refer to [4] fordetails on the algorithm.
Before simulating the debris flow event to analyze
the check dam, we validate the four rheological models
using Sun et al.’s experimental procedure [6].

3 Validation
We compare the simulation results from the fourrheological models with the experiment results. Fig. 1
presents the experimental condition. Using six checkdam designs, we validate the simulation performance ineach case. The simulation and experiment results ofeach rheological model are depicted in Fig. 2. TheVoellmy and Takahashi models exhibit reasonableperformance. The former is advantageous forparameters calibration, so we use it to simulate thedebris flow.

2E3S Web of Conferences 415, 06011 (2023)
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Fig. 3. Study area and events: the 2011 landslide at Mt.
Umyeon, Raemian apartment basin

Fig. 5. Simulation result of final deposited-soil depth when
the check dam is 10 m high and 4 m thick (closed type); a)
without check dam, b) check dam located in section 1, c) insection 2, d) in section 3, e) in section 4, f) in section 5

Fig. 4. Simulation result of final deposited-soil depth when
the designed check dam is 5 m high and 4 m thick (closedtype); a) without check dam, b) with check dam located in
section 1, c) in section 2, d) in section 3, e) in section 4, f) insection 5

Fig. 6. Simulation result of final deposited-soil depth when
the check dam is 10 m high and 4 m thick (open type); a)
without check dam, b) check dam located in section 1, c)
check dam located in section 2, d) check dam located insection 3, e) check dam located in section 4, f) check dam
located in section 55 Results
Fig. 4 presents the simulation results when the closedtype check dam was designed with a height of 5 m. The
damage scale in the absence of the check dam was 26
310 m3 (Fig. 4a), which is close to what was observed(26 000 m3). This finding was used as the standard foranalyzing the mitigation effect. Fig. 4b–f presents thesimulation results. Fig. 4b–d shows that the check dam
located in the upper part of the basin achieved decentperformance. Specifically, the check dams located in
sections 1 and 2 achieved mitigation ratios of 11.35%
and 10.76%, respectively. However, efficiently
reducing the damage due to debris flow using a 5 mcheck dam proved challenging.
The simulation result for a 10 m-high closed-typecheck dam is depicted in Fig. 5. Fig. 5a presents thesimulation result in the absence of a check dam, and Fig.
5b–d shows the results of the check dam being locatedin the upper part of the basin, with decent performance
being realized. Notably, the check dam located in
section 2 achieved a mitigation ratio of 48.71% (Fig. 5c).
The check dams in sections 1 and 3 also realized decent
mitigation effects (44.31% and 42.21% of mitigationratio).
Thus, the mitigation effect was approximately 35%
higher when the check dam was designed with a heightof 10 m rather than 5 m. Figs. 4 and 5 reveal that it ispreferable to construct a closed-type check dam in theupper part of the basin.

Fig. 6 presents the simulation result for a 10 m highopen-type check dam. The open type also achieved
decent performance when the check dam wasconstructed at section 1 (Fig. 6b), which is located in theupper part of the basin. Siting the check dam in section
1 yielded a 12.99% mitigation ratio. However, the checkdam located in section 5 achieved the worst mitigation
effect of approximately -7.89%, implying that installingthe check dam made the damage worse.
According to Figs. 4–6, the mitigation effect wasbest when the check dam was close to the initial dam
area, regardless of the design of the check dam.

6 Conclusions
The two types of check dams were hypothesized in a
debris flow catchment in South Korea to analyze themitigation effect. Although we divided the design of thecheck dam, when we hypothesize the check dam on theupper side of the catchment, it presents the best
performance. However, in order to effectively reduce
debris flow damage, a check dam needs to beconstructed at a height above a certain level. Because theRaemian apartment debris flow was water-landed, theopen-type check dam cannot reveal a decent mitigation
effect. The closed-type check dam presented a highmitigation effect, which has an advantage in effectively
trapping the water-laden debris.

3

E3S Web of Conferences 415, 06011 (2023)
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However, we simulated only one debris flow event(water-laden), so it will be necessary to analyze different
events in the future to precisely and comprehensively
figure out the effect of the check dam.
This work was supported by the National Research Foundationof Korea (NRF) grant funded by the Korea government (MSIT)(No. 2021R1A2C200553012)

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