E3S Web of Conferences 415, 03020 (2023)
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https://doi.org/10.1051/e3sconf/202341503020

Long-term monitoring of sediment runoff for an active sedimentcontrol in Joganji RiverKenji Miwa1, Koso Mikami2, Takahiko Nagayama3*, Tomohiko Furuya4, Seiya Hayashi4, Masaharu Fujita5, Syusuke
Miyata5, Yoshifumi Satofuka6, Takahisa Mizuyama7, Kuniaki Miyamoto8, Akihiko Ikeda9, and Takahiro Itoh10
1Tateyama Mountain Area Sabo Office, Hokuriku Regional Bureau, Ministry of Land (MLIT), 61 Bunazaka, Ashikuraji, Tateyama-machi, Nakaniikawa-gun, Toyama, Japan
2Ministry of Land, Infrastructure, Transport and Tourism (MLIT), 2-1-3 Kasumigaseki, Chiyoda-ku, Tokyo, Japan
3Osaka Branch Office, Nippon Koei Co., Ltd., 1-2-5Nishitenma, Kuta-ku, Osaka, Japan
4Hokuriku Office, Nippon Koei Co., Ltd., 5-1-43 EkinishiHonmachi, Kanazawa, Ishikawa, Japan
5Disaster Prevention Research Institute, Kyoto University, Shimomitsu, Yoko-oji, Fushimi-ku, Kyoto, Japan
6College of Science and Engineering, Ritsumeikan University, 1-1-1Nojihigashi, Kusatsu, Shiga, Japan
7Professor emeritus, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, Japan
8Technical Adviser, R & D Center, Nippon Koei Co., Ltd., 2304 Inarihara, Tsukuba, Ibaraki, Japan
9Sabo & Landslide Technical Center, 2-7-5 Hirakawacho, Chiyoda-ku, Tokyo, Japan
10Center for Advanced Research, R & D Center, Nippon Koei Co., Ltd., 2304 Inarihara, Tsukuba, Ibaraki, Japan

Abstract. There were huge sediment yielding and deposition due to debris flows by breaking naturallandslide dams which were formed by earthquake in 1858 at upstream reach of Joganji River. Sedimenttransportation is still active by debris flow and flow with bedload due to rainfall, though a lot of erosion
control dams have been constructed. Continuously measuring sediment runoff for long term along a mainriver is necessary to evaluate the propagation of sediment after the huge events for sediment managementin the basin using well hydrological information. Appropriate tools are selected and applied to monitoringin the area managed by Tateyama Mountain Area Sabo Office along Joganji River, using a Reid-type
bedload slot sampler, robust-type hydrophone and velocity meter on the bed for bedload and turbidity meter
for washload. Monitored data is concentratedly collected at the office to apply risk management for sediment
movement due to heavy rainfall and so on. Several typical data and problems to solved were shown because
it passed around twenty years since sediment monitoring started, and those are reported in present study.

1 Introduction
Discontinuous relationships between sediment andwater runoff frequently appear in mountainous regions,through long-term sediment monitoring, and those show
the necessity of sediment monitoring there [1].
Following sensors have been selected and installed as
appropriate tools such as a set of hydrophones forbedloads, pressure meter for the flow depth, turbidity
meter for washloads and an electro-magnetic velocity
meter on the bed for bed shear stress for sedimentmonitoring in Japan [2]. In Joganji River, longitudinalsediment monitoring is carried out using robust-type
sensors, that could prevent from collisions by boulders
along a main river. Because there is huge volume ofdeposited sediment due to debris flows and landslides
by earthquake in 1858 at upstream reach of Joganji
River. Sediment transportation is still active by debris
flows, flow with bedload and so on, though a lot oferosion control works have been constructed.
Additionally, a sabo dam with a movable shutter was
installed for smoothing sediment runoff from a slit dam
and for an effective control of sediment runoff in thebasin. Because it will be important recently for long-term usage of sabo facility and sediment environment to
run out debris from up- to down-stream. Pilot operations
were tried to conduct in flood to flood, and someexamples of sediment controls were obtained
with/without shutter operations during floods [3, 4].
Present study reports monitored data obtained alonga main river of Joganji River such as continuous
measuring and the related system for sediment runoff
along a main river. Hydrological and sediment
information is also applied to sediment management in
the basin. Several matters to be solved are shown
through sediment monitoring such as the limitation for
bedload measurements using acoustic wave and thedifficulty of suspended load in steep torrents of Joganji
River.

2 Monitoring
informationstations

andrelated

Figure 1 shows the observation stations, which arearranged as (A) to (F) from upstream reach and Fig. 2
show sensors installed at Tsunoura-Karyu sabo dam((D) in Fig. 1). Figure 3 is the longitudinal bed profiles* Corresponding author: a4619@n-koei.co.jp© 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, 03020 (2023)
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https://doi.org/10.1051/e3sconf/202341503020

Fig. 1. Sabo dams and monitoring stations along Joganji River.

Fig. 2. Sensors installed at Tsunoura-Karyu sabo dam.

of Joganji River. Bedload monitoring at Hongu sabodam ((F) in Fig.1) started using a pipe hydrophone andpressure meter for the flow depth started on 15thDecember in 2009 and the measurement by turbidity
meter began on 17th December in 2012 [3, 4]. At Hongu
sabo dam, width of spillway is 85 m, flow width is 52 m,
bed slope is 1/90 and drainage area, A, is 193.1km2. Bed
material has a range of diameters such as d60= 30 mm
and d95= 150 mm [2]. At Tsunoura-Karyu sabo dam,concentrated monitoring was carried out at the slit of thesabo dam since June in 2001. The catchment area of thedam, A, is 139.49 km2 and the bed slope near the dam is
1/56 which is measured in 2007. Flow width is 110 m
and bed sediment have a range of diameters such as d60=20 mm and d95= 200 mm [2]. Rainfall is measured atSenjyu-ga-hara Station as shown in Fig. 1. Sedimentmonitoring started with a combination of sensors andReid-type bedload slot there, that was installed inFig. 4. Linear line between impulses of the pipe hydrophone andbedload discharge by the bedload slot at Tsunoura-Karyu sabo dam.

January 2008. The size is 2.0m X 2.0m in plane, 1.5m
in deep and the slit is 0.6m on the bed. Other sensors area pressure meter, a pipe hydrophone (since 2001) and aturbidity meter (since December in 2012).
The calibration line, as shown in Fig. 4, is obtainedand modified year to year between impulses of thehydrophone and bedload discharge by the bedload slot
[3, 4]. Water discharge rate is calculated using a relation
between flow depth, H, and discharge rate, Q, estimatedby surface velocity measurements in floods. Data in Fig.
4 is obtained from pipe hydrophone, and a linear
correlation can be used until 3,000 to 3,500 impulses/5
minutes due to saturation of acoustic wave. In Joganji
River basin, there are a lot of boulders transported byFig. 3. Longitudinal bed profiles along Joganji River.

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E3S Web of Conferences 415, 03020 (2023)
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https://doi.org/10.1051/e3sconf/202341503020(a) Fine sediment discharge(b) Bedload discharge at Hongu sabo dam
Figs. 5. Relation between flow discharge rate and sediment discharge rate at specified stations in Joganji River.

Figs. 6. Relation between flow depth and bedload discharge, that is shown by impulses during 5 minutes, at Karatani sabo dam

and volumetric concentration with Kaolin and water
mixture [4]. In 2021, monitored data does not takenormal values due to failure of turbidity meter atTsunoura-Karyu sabo dam. Two dashed lines identify
the range of fine components of sediment discharge inJapan. Measured value is close to be relatively large inJapan.
Figure 5(b) shows the relation between water
discharge rate and bedload discharge, that is obtained byhydrophone, at Hongu sabo dam. The bedload discharge
is calculated by correlation line shown in Fig. 4. Several
bedload formulas for d60 are compared with previously
measured data. The value of bedload has the limitation
as 0.01 to 0.02 m3/s because the saturation of theacoustic wave takes place for pipe hydrophone.
Runoff of the fine sediment discharge is still active
because a lot of the fine component of sediment isyielded from debris fans, side bank and bed that areformed by previous landslides. However, bedload
discharge is inactive in present bed condition in Joganji
River. Bedload and boulders yielded by previous

floods from sources related to previous landslide. A pipehydrophone is always destroyed due to collisions by
those boulders, and the plate type is mainly used there.
The value increases 4,500 impulses in case of the plate
type hydrophone (the thickness is 12 mm) throughsediment monitoring at Tsunoura-Karyu sabo dam,though the detection for fine component of bedload
becomes dull in comparison with pipe hydrophone.

3 Measured data by sensors
3.1 Bedload and washload
Figure 5(a) shows the relation between water
discharge rate and fine components of sediment
discharge measured by a turbidity meter and direct water
sampling at several observatories. Data measured byturbidity meter at Hongu and Tsunoura-Karyu sabodams is also plotted in the figure, and the data is for thepeak stage in a flood. The linear calibration line is
obtained between the output of turbidity meter (Voltage)

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E3S Web of Conferences 415, 03020 (2023)
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landslides are captured by sabo dams along the mainriver, and result in inactive transport.

though a lot of erosion control works have beenconstructed.
In Joganji River, continuously measuring during
over twenty years and the related system for sediment
runoff along a main river has been carried out toevaluate magnitude of sediment transport since about
150 years after huge sediment disasters according todevelopment of recent sensors for measurements. The
knowledge through long-term monitoring will beconnected to applied sediment management in the basinusing hydrological information in future sabo
management there. Then, one tool was proposed
through sediment monitoring, and that is hysteresis
curve for fine components of sediment and bedload.
Unusual sediment transport could be detected byclockwise and counterclockwise hysteresis curves, due
to debris yielding somewhere. Fine components ofsediment transport are still active, but bedload transports
are inactive due to sabo countermeasure such as sabodams. The several matters to be solved are foundthrough sediment monitoring such as the limitation for
bedload measurements using acoustic wave and thedifficulty of suspended load in steep torrents.

3.2 Hysteresis curves
A sabo dam with a shutter is installed at Myoju sabodam ((B) in Fig. 1) [2, 3, 4] to carry out advanced
sediment runoff control, and that means runoff control
of bedload and boulders during floods. A shutter
operation has almost two roles: One is active sediment
runoff control, and the other is shutter movement control
during operations. Trial attempts for preferable
operation were conducted during floods since 2016.
Figures 6 shows the relation between the flow depth
and bedload discharge measured at Karatani sabo dam((C) in Fig. 1), which is at 3,645 m downstream of
Myoju sabo dam. Those data were obtained during ashutter operation except floods in 2018 without theoperation. Currently, there could be the hysteresis curve
for wash load and bedload through sediment monitoring
using hydrophone [3, 4]. Interesting data is obtained forbedload monitoring such as hysteresis curves, though
the theoretical understanding needs to evaluate thosecurves. There were the clockwise curves for the flow
depth versus the wash load in floods in 2016, 2017 and2018. There were clockwise curves for the flow depth
versus the bedload with the shutter operation in 2016
and 2017. However, there was counterclockwise curve
without the shutter operation in 2018, because thedeposited sediment in the storage area of the Myoju sabo
dam was almost transported during the flood [4]. The
data means that rapid sediment runoff took place in thedecreasing stage of the flood at the slit of Myoju sabo
dam without shutter operation. There are two possibility
that one is sediment runoff deposited in the storage areaof the dam from the slit during the flood, and the otheris unusual sediment transport due to debris flows
occurred somewhere in upstream reach. The hysteresis
curve could be preferable tools to evaluate rapid bedload
runoff in a flood. For example, the curve takes
counterclockwise pattern if sediment transport such asdebris flows takes place during a flood. The data could
be useful for risk management against unusual sedimenttransport.
Bedload and wash load could be monitored well bysediment monitoring using sensors such as hydrophone
and turbidity meter. However, suspended load is still
difficult in mountainous stream. One trial has been
carried out at Tsunoura-Karyu sabo dam as shown in Fig.
2, using vertical installed hydrophones and velocity
meter [2]. Several data were obtained since thosesensors were installed in November 2009. However, thevertical hydrophone was also damaged by collisions ofsuspended sediment particles as shown in Fig. 2.

Authors should be thankful for Tateyama Mountain Area SaboOffice, Hokuriku Regional Development Bureau, Ministry ofLand in Japan (MLIT) for monitoring data useful advice forpresent research.

References
1.

2.

3.

4.

4 Conclusions
At upstream reach of Joganji River, there were huge
sediment yielding and deposition due to debris flows bybreaking natural landslide dams formed by earthquakein 1858. Sediment transportation is quite active bydebris flow and flow with bedload due to rainfall,

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