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Study of debris flow peak discharge at Kamikamihorizawa CreekAkihiko Ikeda1*, Takahiro Itoh2, and Takahisa Mizuyama3
1Sabo & Landslide Technical Center, Volcanic Disaster Prevention Department, 2-7-5 Hirakawacho, Chiyoda-ku, Tokyo, Japan
2Center for Advanced Research, R & D Center, Nippon Koei Co. Ltd., 2304 Inarihara, Tsukuba, Ibaraki, Japan
3Professor emeritus, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, Japan

Abstract. Prediction of the peak discharge of debris flow is one of the most important factors in mitigating
debris flow disasters. Currently, empirical methods based on the relationship between the peak dischargeand total debris flow volume (magnitude) for many debris flow events are used to estimate peak discharge
for planning or designing debris flow countermeasures in Japan. In order to estimate the peak discharge ofdebris flow with high accuracy, the debris flow monitoring sensors with load cell and pressure sensor(hereafter referred to as a DFLP system), was installed to evaluate various characteristics during floods
involving debris flows at Kamikamihorizawa Creek. During the debris flow that occurred on August 29,
2019 at Kamikamihorizawa Creek, seven surges corresponding to debris flow events were monitored by theDFLP system for a 20-minute period. Based on the relationship between the peak discharge and magnitude,
the observation data of Kamikamihorizawa Creek, Illgraben and Schipfenbach has been added to previous
data from the literature and the relationship has been updated. The peak discharge and magnitude of debris
flow on August 29, 2019 at Kamikamihorizawa Creek exhibited distributions similar to past observation
data, which shows that the relationship between peak discharge and magnitude follows a similar trend.

1 Introduction
Prediction of peak discharge of debris flow is one of themost important factors in mitigating debris flow
disasters. In general, the peak discharge of debris flow
has been either measured at observation sites directly orestimated based on debris flow velocity and crosssections (flow depth) derived via field investigations [1,2]. Based on these data, the peak discharge of debris
flow has been estimated from various aspects. Currently,
empirical methods that are based on the relationshipbetween the peak discharge and total debris flow volume(magnitude) of many debris flow events are used toestimate peak discharge for planning or designing debris
flow countermeasures in Japan.
Significant sediment deposition and large numbersof debris flow events have been observed since the1970s at Kamikamihorizawa Creek, which is located on
the eastern side of Mt. Yakedake, an active volcano. Therelationship between the peak discharge and magnitudeat Kamikamihorizawa Creek is used to estimate peakdischarge of debris flow as described above [2, 3]. Inorder to estimate the peak discharge of debris flow withhigh accuracy, it is necessary to acquire a large numberof observation data with better accuracy than thecurrently available data. Therefore, the debris flow
monitoring sensors with load cell and pressure sensor(hereafter referred to as a DFLP system), were installed
to evaluate the characteristics of debris flows atKamikamihorizawa Creek in November 2014 [4].
This study introduces the measured characteristics ofthe debris flow that occurred on August 29, 2019

observed by the DFLP system at Kamikamihorizawa
Creek, and discusses the addition of this observation
data to the past data to improve the accuracy of the peakdischarge estimation based on the relationship between
the peak discharge and magnitude.

2 Outline of Kamikamihorizawa Creek
DFLP system
The Kamikamihorizawa Creek DFLP system wasinstalled at the Kamikamihorizawa No.6 Weir, which isa site where a significant number of debris flow eventsand large amounts of sediment deposition have beenreported previously. At the installation location, an 8°
bed slope was fabricated with a gabion just upstream. Inthe DFLP system, a pin-type load cell was used tomeasure the weight while the vertical force component
was measured by a force plate, thus allowing both thevertical and horizontal components of the force on thebed to be measured at the site.
In addition to the DFLP system components, othersensors installed at the site include closed-circuit
television (CCTV) video cameras, an ultrasonic levelsensor, and a velocity meter. The CCTV video camera
is used to evaluate the flow conditions and flow velocity
on the DFLP plate, while the ultrasonic level andvelocity meters measure the flow depth and surface
velocity of debris flow surges, respectively. Theultrasonic sensors capture data at a resolution of 1.0 m/s
and 0.01 m, and the measured data are recorded at theobservation station at 1-minute intervals without time-* Corresponding author: ikeda@stc.or.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, 03012 (2023)
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averaged processing. The measurement areas on the bed
surface are approximately 0.32 m2 and 0.6 m2 for flow
depth and velocity, respectively. To calculate thesurface velocity, CCTV-captured images are analyzed
manually, primarily by visual inspection, because
observers can more easily pick out objects in the debris
flow and are uninfluenced by splashes near the freesurface.

QpD  Q T 0 .833

(1)

where Qp is the debris-flow peak discharge [m3/s], QT is
the magnitude [m3], and Į = 1.0–0.001. The data shownin Figure 1 vary widely over the range of Į = 0.1–0.001,
principally in the interval Į = 0.1–0.01. The variation inpeak discharge even for the same magnitude is estimatedto be due to differences in sediment supply conditions
and deformation of riverbed.
Monitoring data obtained near the initiation zone ofdebris flows from Kamikamihorizawa Creek areapproximated by (1), where the Į values tend to beapproximately Į = 0.01 if the debris flows are muddy(Nojiri River, Jiangjia creek and Hunshui gully) but
approximately Į = 0.1 if the flows are granular(Kamikamihorizawa Creek, Name River).
The distribution of the debris flow data for the event
on August 29, 2019 at Kamikamihorizawa Creek is near(1) with Į = 0.1, similar to the distributions of the past
data. Hence, although there are differences inobservation method depending on the observation
period, a similar distribution trend was observed at
Kamikamihorizawa Creek.
Illgraben is located in the Southern Alps near Sierrein Canton Wallis, and Schipfenbach is located in theNorthern Alps near Silenen in Canton Uri, Switzerland.
Additional observation data on debris flow collected at
Illgraben and Schipfenbach are also shown in Figure 1.
At Illgraben, on average 3 to 5 debris flows andadditional debris floods are observed every year. The
characteristics of debris flow in Illgraben generally
include coarse granular fronts, although muddy debris
flows also occurs [7]. The distribution of observation
data for 2000, 2008 and 2009 are near power function(1) with Į = 0.01, although debris flows in the interval Į= 0.1–0.01 are classified as the muddy type. At
Schipfenbach, a magnitude of 5,000-5,500m3 debris
flow occurred on 6 August 2000, analyses of the datasuggest the event occurred in two surges separated byabout 1-2 minutes [7]. The distribution of observation
data is near power function (1) with Į = 0.1 is classified
as the granular type similar to Kamikamihorizawa Creek.

3 Debris flows on August 29, 2019
During the massive rainfall that took place from August
27 to 30, 2019, the Mt. Yakedake rainfall station
recorded an accumulated rainfall depth of 217 mm anda maximum rainfall intensity of 35 mm/h at 06:00 on
August 29. Rainfall intensity was based on radarmeasurements, and a heavy magnitude of rainfall wasalso observed at 04:00.
On August 29, 2019, the DFLP system observed andmeasured several debris flow surges resulting from ashort period of rainfall. The rainfall intensity was 12 mm
for a 10-minute period, resulting in an accumulated
depth of 56 mm, and triggering seven debris flow events(surges) within a 20-minute period shortly thereafter.
Sediment concentration was calculated for the debris
flow and the coarse phase by the DFLP system. A
previous study showed that sediment concentrations
could be divided into two components: coarse particle
and mud phases, with the sediment concentration of
mud phase calculated by pressure sensor [5]. Hence,using the DFLP system, the sediment concentration oftime-averaged value of 0.458, can be divided by 0.201
for the coarse phase and by 0.257 for the mud phase. The
sediment runoff volume of whole debris flow wascalculated as 17,017m3 without pore by the DFLP
system analysis [4].

4 Relationship between debris flow
peak discharge and magnitude of
Kamikamihorizawa Creek
The observed debris flow on August 29, 2019 consistedof approximately seven surges, with the duration of theflow being about 17 minutes. The peak of this debris
flow was estimated to have occurred during the second
surge, because the ultrasonic level sensor and the bottompressure sensor showed a maximum flow depth in thefirst surge, but the CCTV-captured images showed amaximum flow depth in the second surge.
The peak discharge of debris flow was estimated to
be 96.1 m3/s based on the flow depth and velocity of thesecond surge from the CCTV-captured images. The
magnitude of the second surge corresponding to themaximum flow depth was estimated to be 5,228m3.
Figure 1 shows the relationship between the peakdischarge and magnitude of debris flow on August 29,
2019 at Kamikamihorizawa Creek alongside past data[5], including recent observed data from Illgraben andSchipfenbach, Switzerland [1, 7]. The line indicates thequasi-theoretical linear relationship represented by thefollowing equation:

5 Conclusions
Characteristics of debris flow that occurred on August29, 2019 at Kamikamihorizawa Creek has been carriedout by the DFLP system that was installed in 2014, andseven surges corresponding to debris flow events weremonitored during a 20-minute period.
To improve the accuracy of the empirical method toestimate peak discharge of debris flow based on therelationship between the peak discharge and magnitude,
the observation data of Kamikamihorizawa Creek,Illgraben and Schipfenbach have been added to datafrom the literature and the relationship has been updated.
The peak discharge and magnitude of debris flow on
August 29, 2019 at Kamikamihorizawa Creek indicatesa similar distribution to past observation data, and therelationship between peak discharge and magnitude also
follows a similar trend as in past data.

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1.0E+05

Qp=΅QT0.833

DebrisȱFlowȱPeakȱDischargeȱQp䠄m3/s䠅

1.0E+04

1.0E+03

1.0E+02

1.0E+01

1.0E+00㻝㻚㻜㻜㻱㻗㻜㻝

㻝㻚㻜㻜㻱㻗㻜㻞

㻝㻚㻜㻜㻱㻗㻜㻟

㻝㻚㻜㻜㻱㻗㻜㻠

㻝㻚㻜㻜㻱㻗㻜㻡

㻝㻚㻜㻜㻱㻗㻜㻢

㻝㻚㻜㻜㻱㻗㻜㻣

㻝㻚㻜㻜㻱㻗㻜㻤

MagnitudeȱofȱDebrisȱFlowȱQT䠄m3䠅
NojiriȱRiverȱ(Japan)䖩*HarumatsuȱRiverȱ(Japan)䖩*ArimuraȱRiverȱ(Japan)䖩*Kamikamihorizawaȱ Creekȱ (Yakedake)䖩*Mt.Tokachidakeȱ (Japan)䖩*JiangjiaȱCreekȱ (China)䖩*AlbretaȱCreekȱ (Canada)䖩*Mt.Nevadoȱ DelȱRuizȱ(Colombia)䖩*ArimuraȱNo.3ȱSaboȱDamȱ(Japan)䖩
DoharaȱRiverȱ(Japan)
OomojiȱRiverȱ(Japan)
ShimogasakoȱRiverȱ(Japan)
SarutakiȱRiverȱ(Japan)
NojiriȱNo.5ȱUpstreamȱ SaboȱDamȱ(Japan)䖩
NojiriȱChannelȱWorksȱ(Japan)䖩
NojiriȱRiverȱMouthȱ(Japan)䖩
IshiharaȱCreekȱ(Japan)
HiiragiȱRiverȱ(Japan)
HariharaȱRiverȱ(Japan)
FunaishiȱRiverȱAȱ(Japan)
NashizawaȱCreekȱ(Japan)
MatanoȱRiverȱ(Japan)
HigashikusuzakiȱRiverȱ(Japan)
MoriyukiȱOhtaniȱRiverȱ(Japan)
Schipfenbachȱ(2000,ȱSwitzerland)

MochikiȱRiverȱ(Japan)䖩*FurusatoȱNo.1ȱRiverȱ (Japan)䖩*KurokamiȱRiverȱ(Sakurajima)䖩*NameȱRiverȱ (Japan)䖩*Mt.Usuzanȱ(Japan)䖩*HunshuiȱGullyȱ(China)䖩*Mt.St.Helensȱ(USA)䖩*NojiriȱNo.8ȱSaboȱDamȱ(Japan)䖩
NameȱRiverȱ (Japan)䖩
YasuȱRiverȱ(Japan)
NarakuraȱRiverȱ(Japan)KonoȱRiverȱ(Japan)
FunaishiȱRiverȱ(Japan)
NojiriȱNo.4ȱSaboȱDamȱ(Japan)䖩
NojiriȱBridgeȱ(Japan)䖩
MizunashiȱNo.1ȱSaboȱDamȱ(Japan)䖩
WadaȱRiverȱ(Japan)
GamaharaȱCreekȱ(Japan)
AtsumariȱRiverȱ(Japan)
TakesawaȱCreekȱ(Japan)
StavaȱRiverȱ(Italy)
NishishirahamaȱRiverȱ(Japan)
KusuzakiȱRiverȱ(Japan)
Illgrabenȱ(2000Ȭ2009,ȱSwitzerland)
KamikamihorizawaȱCreekȱ(2019,ȱJapan)‫ۻ‬:ȱobservation,ȱ ȱOthers:ȱfieldȱinvestigation*)ȱMizuyamaȱ et.al.,ȱ1992

Fig. 1. Relation between peak discharge and magnitude of debris flow.

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The distribution of observation data of 2000, 2008
and 2009 of Illgraben is near power function (1) with Į= 0.01 but falls in the interval Į = 0.1–0.01, which areclassified as muddy type, while the observation data of2000 of Schipfenbach is near power function (1) with Į= 0.1 is classified as granular type debris flow.
Authors are thankful to the Matsumoto Sabo Office, Hokuriku
Regional Development Bureau, Ministry of Land,
Infrastructure, Transport and Tourism in Japan (MLIT) and Dr.
Dieter Rickenmann for monitoring data and for useful advice.
Respectful condolences are extended to the family of Dr.
Hiroshi Suwa, who has passed away on Jan. 14th, 2022, towhom providing us valuable figures and pictures of his fieldobservations at Kamikamihorizawa Creek and for giving us
permission for usage of valuable information.

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