Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, Japan

LIDAR MEASUREMENT OF
THE BREACHED EARTH-FILL DAM INTHE MARCH 11th GREAT EAST JAPAN
EARTHQUAKE
Hiroyuki KYOKAWA1, Kazuo KONAGAI2, Takashi KIYOTA3, Toshihiko KATAGIRI4 andZaheer Abbas KAZMI5
1

JSPS Postdoctoral Fellow, Institute of Industrial Science, University of Tokyo,
Tokyo, Japan, kyokawa@iis.u-tokyo.ac.jp
2
Professor, Institute of Industrial Science, University of Tokyo,Tokyo, Japan, konagai@iis.u-tokyo.ac.jp
3
Associate Professor, Institute of Industrial Science, University of Tokyo,Tokyo, Japan, kiyota@iis.u-tokyo.ac.jp
4
Technical Assistant, Institute of Industrial Science, University of Tokyo,Tokyo, Japan, toshi@iis.u-tokyo.ac.jp
5
PhD Student, Institute of Industrial Science, University of Tokyo,
Tokyo, Japan, kazmi@iis.u-tokyo.ac.jp

ABSTRACT: Fujinuma dam, an earth-fill dam for irrigation located in Sukagawa City,Fukushima prefecture, was breached in the March 11th Great East Japan Earthquake. The
debris mass from the breached dam flushed a village lying its downstream leaving 8 deadand 1 missing. The authors made a survey along the stream channel of the debris flow.
During their survey, the breached dam body was LiDAR surveyed for its entire 3D image.
With the findings from the survey, this paper discusses a possible mechanism of dambreaching.
Key Words: Great East Japan earthquake, LiDAR, dam breaching, debris flow

INTRODUCTION
The Great East Japan Earthquake measuring Mw 9.0 (USGS, 2010) hit the east Japan at 2:46PM,
March 11th, 2011. The intense shake was followed by tsunami, which engulfed the entire stretch of thePacific coast of east Japan leaving about 20,000 dead or missing. The earthquake-induced liquefaction
had caused severe damage to dwellings, underground facilities in Kanto region, especially, in theTokyo bay area. One of the most serious problems was the disaster at the Fukushima Daiichi nuclear
power plant. This event yielded a long lasting problem of radioactive contamination. With the wide
spreads devastation mentioned above, less attention was paid on landslides including seven slope
failures in Shirakawa region, upstream reaches of the Abukuma River, which slides were responsible973

10mile20km

Epicenter(Mw 9.0)
320

N-S (Max: 309.0Gal)

1600-160-320320

E-W (Max: 294.0Gal)

1600Fujinuma resorvoir-160-320
320

U-D (Max: 117.1Gal)

160

Sukagawa city

0-160

Kik-net(Naganuma)

-320

050

100

150200Time [sec.]

Fig. 1 Location of Fujinuma reservoir and epicenter of the March 11th Great East Japan Earthquake
The recorded strong ground motion at KiK-net Naganuma station (37.2792, 140.2178)

Fig. 2 Survey map (modified from Geospatial Information Authority of Japan, 2011)
for at least 13 deaths (Kiyota, T., 2011). Early Pleistocene no-alkaline pyroclastic flow volcanic rocks
spread in this region (Geological Survey of Japan), and more than 1000 slope failures occurred here
due to a torrential rain back in Aug. 27, 1998. Fujinuma reservoir, located in Sukagawa city,
Fukushima prefecture (37.301944, 140.195278: See Fig. 1) was constructed for irrigation in similargeological condition back in 1949. The northeast earth-fill dam of this reservoir was breached in theGreat East Japan Earthquake with the surface maximum ground acceleration of 309gal recorded by thestrong-motion seismograph at the nearest KiK-net Naganuma station (National Research Institute for
Earth Science and Disaster Prevention), which is located about 2 km away from the Fujinuma lake(37.2792, 140.2178: See Fig. 1). The dam is 18.5m high, 133m long and 99,000m3 in volume, and thefull capacity of its reservoir of 1,504,000m3 (Dam Association of Japan) was reached at that time. The
water from the breached dam eroded its downstream valley and uprooted trees. The debris flow rushed
down the valley and flushed at least 5 houses leaving 8 dead and 1 missing.
Authors surveyed along the stream channel of the debris flow. The breached dam body was
LiDAR surveyed for its entire 3D image. With the findings from the survey, this paper discusses themechanism of dam breaching.

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OUTLINE OF THE SURVEYED AREAAuthors surveyed both breached Fujinuma dam and its downstream reach on April 15th. Fig 2 shows
the survey root along the stream channel of the debris flow and photo-shooting locations. There werelarge and small earth-fill dams stopping the water of the Fujinuma reservoir as shown in Fig. 2.

Photo 1 Sliding failure of small dam (April 15th at 37.299778, 140.195348)

.5
1:1
.5

1:2.
5

L = 5~21m

18.50

1 :2

1:2.
5
1:0.5

Fig. 3 Cross section of original large dam body

Photo 2 Breached dam body of large dam from right abutment (April 15th at 37.301265, 140.195401)

Photo 3 Breached dam body of large dam from left side (April 15th at 37.302465, 140.195223)

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Photo 4 Breached dam body from downstream(April 15th at 37.302661, 140.196055)

Photo 5 Mark of debris flows on valley walls(April 15th at 37.306236, 140.199503)

Photo 6 Breached road embankment(April 15th at 37.305036, 140.198236)

Photo 7 Washed out box culvert(April 15th at 37.304499, 140.197989)

Photo 1 shows the failure of the upstream slope of the small dam (13m high, 55m wide and 108m
long). Almost the entire upstream slope slid down into the reservoir leaving its thin and fragile crest
soil behind the dam body narrowly escaped from breaching probably because the larger dam breachedfirst emptying the water of the reservoir. During the emptying process, the soil mass of the upstream
slope of the small dam may have been carried further down toward the bottom of the reservoir.
Fig. 3 shows the original cross section of the large dam. The large dam is 6 meters wide at its crest,
133 meters long with upstream surface concrete-block-faced. Photo 2 and 3 show the breached large
dam body (Height 18.5m, Length 133m, Volume 99,000m3) from right and left abutments, respectively.
The middle to right part of the dam body was scoured deep by the overtopped water. A clear laminarstructure was seen on the exposed interior of the dam body. Dark-colored mudstone was exposed on
the scoured abutment. 20 to 30 cm-thick Ignimbrite sand layers were also found bedding horizontallyin the exposed dam body (See Photo 2) indicating that the dam body was constructed by compacting
ignimbrite sand. The slide may have been followed by the subsidence of the entire dam body and thus
water-overtopping.
The debris flow from the breached dam eroded its downstream valley and uprooted trees as shownin Photo 4. From mad marks remaining on valley walls, super-elevations were measured at several
locations where the stream channel takes sharp turns, and the debris flow velocity was estimated to bearound 10m/sec. Photo 6 and 7 show the road embankment being across a valley which wasapproximately 300m from the large dam and washed away by the debris flow together with a box
culvert (1.5m-square, 0.14m-thickness).

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Photo 8 Path way of debris flow and downstream stricken area (April 15th at 37.308131, 140.202481)
The box culvert was carried over 48m distance from its original location. Even though the roadembankment was flashed, rocks and trees are found clogging the stream indicating that the debris mass
was temporarily stopped there owing to the presence of the embankment. The debris flow, when it
reached the village, took a sharp 90 degrees clockwise turn along the existing river channel andflushed downstream village (See Photo 8).

LIDAR SURVEY OF THE BREACHED EARTH-FILL DAM
Outline of LIDAR survey
The breached dam body was LiDAR surveyed for its entire 3D image using the laser profile measuringsystem LPM-321 (See Photo 9). LPM-321 is based on the time-of-flight measurement of short laserpulse. It covers 6000m distance without reflector (@ Laser class 1M), with a wide view filed of 150° x360°, an expected maximum error of 25mm and measurement rate of maximum 1000 points / sec.
Using a high resolution digital camera along with it, a RGB color image can be obtained for all
laser-shot points. The authors conducted a LiDAR survey on August 21th. The dam body waslaser-scanned from three different locations: two are on the right abutment; then one on the leftabutment. And then, 3D digital surface models were combined for the 3D LiDAR image of the entire
dam body. Fig.4 shows the obtained 3D image of dam body from the right abutment.

Photo 9 LPM-321 (left: LPM-321, right: laser-scanning scene)

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Reservoir

Downstream

Fig. 4 3D image of the breached dam body using LPM-321

Fig. 5 Bird-eye view of the breached dam
Result of LIDAR survey
Fig. 5 shows a bird-eye view of the breached dam body. There yet remained some areas hidden fromlaser light, which appeared black in this figure. 5 months after the earthquake, the bottom of theemptied reservoir was covered thick with vegetation. Fig. 6 is the contour map of the dam, with thecoordinate origin set at 1.5m above the original dam body crest. This figure also show a longitudinalcross-section of the damaged dam body, where two lines indicate the top and bottom levels of original
dam body, respectively. The top surface of the remaining left dam body is about 50m long, and about
8.5m below the original dam crest. Fig. 7 compares several cross-sections of the damaged dam bodywith their original ones. These cross sections in Fig. 7 respectively correspond to lines A-A', B-B',C-C', D-D', E-E' and F-F' in Fig. 5 and 6. With the presence of vegetation, every cross section after theearthquake shows an increase of the reservoir bottom by about 0 to 0.25m. It can be found from thesefigures that scouring of the soil mass was more serious near the middle to right part of the dam bodythan that near the left abutment. Therefore, it can be deduced that the right dam body, which is thehighest part of the dam body constructed by compaction, slid first, causing either subsidence of thedam crest or razor-sharp earth wall to remain such that the water forced its way through this point. And
then the overflowing water eroded both the upstream and downstream dam body.

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1400120100]
Z [m-5-1060-1 54080 ][mnceDista

20-20
000-5-5Z [m]Z [m]Fig. 6 Contour map of Z-value and the longitudinal section of breached dam-10-154060

Distance [m]

80-15

100

00-5-5-10-15-200204060

Distance [m]8000-5-15-200204060

Distance [m]

8060

80

1002040608010020406080100

Distance [m]Distance [m]-10-15-20010040-15-5-1020-10-200100

Z [m]

Z [m]

20Z [m]Z [m]0-10-200-20inal am
Origpe of dahs

Distance [m]Fig. 7 Comparison of the obtained 3D image of the damaged dam with its original shape979

CONCLUSIONSThe northeast large earth-fill dam of Fujinuma reservoir, located in Sukagawa city, Fukushima
prefecture, was breached in the March 11th Great East Japan Earthquake. Its entire dam body waseroded deep by overflowing water. Particularly soil mass of its right side was completely washed away.
The debris flow, whose speed is estimated to be around 10m/sec from mad marks remaining on valleywalls, rushed down the valley and flushed at least 5 houses leaving 8 dead and 1 missing. Comparing a
3D image of entire dam obtained from LiDAR survey with its original shape, the right dam bodywhose height is 18.5m was completely washed out from its bottom. From the reconnaissance and theLiDAR survey, it was deduced that the upstream slope of right dam body which was the highest pointof the dam body slid first, causing either subsidence of the dam crest or razor-sharp earth wall toremain such that the water forced its way through this point. The numerical simulation will be carriedout for a further discussion about the mechanism of the dam failure in later publications.
REFERENCES
USGS (2011). http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc0001xgp.php
Kiyota, T., Kyokawa, H. and Konagai, K. (2011). “GEO-DISASTER REPORT ON THE 2011
TOHOKU-PACIFIC COAST EARTHQUAKE.” Bulletin of ERS, No. 44, 17-28.
Geological Survey of Japan. “Seamless Digital Geological Map of Japan.”
http://riodb02.ibase.aist.go.jp/db084/zoomify_en.html
National Research Institute for Earth Science and Disaster Prevention. “Digital Strong-Motion
Seismograph Network KiK-net” http://www.kik.bosai.go.jp/kik/index_en.shtml
Dam Association of Japan, “Fujinuma Dam – Dam Handbook”
http://damnet.or.jp/cgi-bin/binranA/All.cgi?db4=0483
Geospatial Information Authority of Japan, “Portal Cyber-japan”
http://portal.cyberjapan.jp/index.html
RIEGL JAPAN, “LPM-321”
http://riegl.com/products/terrestrial-scanning/produktdetail/product/scanner/2/

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