Dams in Japan
Overview 2022

Kanto Regional Development Bureau（https://www.ktr.mlit.go.jp/）

Tokuyama Dam

JAPAN COMMISSION ON LARGE DAMS

Welcome for your
Virtual Visit toDams in Japan

LegendRockfill
Gravity
Earth
OthersDam Maps
200 km
100 mi

JCOLD

Footages

Publications

200 km
100 mi200 km
100 miTechnologies

Source of the base map : Geospatial Information Authority of Japan (GSI)（https://maps.gsi.go.jp/#5/37.932645/138.251953/&base=english&ls=english&disp=1&vs=c1g1j0h0k0l0u0t0z0r0s0m0f1）
Japan And Its Surroundings (Zoom Level 5-8), 1:1,000,000 INTERNATIONAL MAP (Zoom Level 9-11)
The bathymetric contours are derived from those contained within the GEBCO Digital Atlas, published by the BODC on behalf of IOC and IHO (2003) (https://www.gebco.net)
海上保安庁許可第292502号（水路業務法第25条に基づく類似刊行物）
Shoreline data is derived from: United States. National Imagery and Mapping Agency. "Vector Map Level 0 (VMAP0)." Bethesda, MD: Denver, CO: The Agency; USGS Information Services, 1997
Location of the dams on the map is basically derived from MLIT (https://nlftp.mlit.go.jp/ksj/gml/datalist/KsjTmplt-W01.html). Modification and addition of data are conducted by JCOLD andCampo Salado. QR codes on this map are added by JCOLD. Web design and programs are powered by Campo Salado.

CONTENTS
Japan Commission on Large Dams
History … ……………………………………………………………………
Operation … …………………………………………………………………
Organization… ………………………………………………………………
Membership… ………………………………………………………………
Publication… …………………………………………………………………
Annual lecture meeting… ……………………………………………………
Contribution to ICOLD… ……………………………………………………

1
1
1
1
2
2
2

Dams in Japan
Development of dams … …………………………………………………… 3
Major dams in Japan… ……………………………………………………… 4
Hydroelectric power plants in Japan… ……………………………………… 5
Dams completed in 2017 − 2020 in Japan … ……………………………… 6
Asakawa Dam……………………………………………………………… 7
Arase Dam … …………………………………………………………… 9
Apporo Dam… …………………………………………………………… 11
Sanru Dam… ……………………………………………………………… 13
Okutainai Dam… ………………………………………………………… 15
Gokayama Dam… ………………………………………………………… 17
Yokozegawa Dam… ……………………………………………………… 19
Japan Incorporates Climate Change Effects into River and Dam Planning …… 21
Introduction to Dam Technologies in Japan
Trapezoidal CSG dam … …………………………………………………… 24
Sediment bypass tunnel (SBT)… …………………………………………… 24
Preservation measures of dam reservoirs… ………………………………… 24
Advancement of flood control operation… ………………………………… 25
Dam Upgrading Vision… …………………………………………………… 26
Utilization of ICT in construction of dam… ………………………………… 28
Papers in ICOLD & Other Technical Publications
Theme 1 Safety management and rehabilitation of existing dams… ……… 29
Theme 2 New construction technology……………………………………… 30
Theme 3 Spillway and outlet works… ……………………………………… 33
Theme 4 Sophisticated approach for dam operation………………………… 34
Theme 5 Earthquakes and dams… ………………………………………… 37
Theme 6 Reservoir sedimentation and sustainable development…………… 40
Theme 7 Water quality, environmental conservation and social consideration…… 42

1

DAMS IN JAPAN - OVERVIEW 2022

Japan Commission on Large Dams
History

Membership

In 1931, three years after the International Commission
on Large Dams (ICOLD) was established, Japan joined
ICOLD as the Japan National Committee on Large Dams.
In 1944, Japan withdrew from ICOLD during the WorldWar II, then rejoined in March 1953. On September 13,
1962, the Japan Commission on Large Dams (JCOLD)
was established, and in January 2012, it became a General
Incorporated Association.

The members of JCOLD are incorporated bodies
involved in dam construction. They include government
bodies concerned with dam construction, electric powercompanies, survey and research bodies, academic
associations, industrial associations, construction
consultants, construction companies, and manufacturers (77members as of January 2022).

Operation
JCOLD is involved in operations such as surveys, research,
international technology exchanges, etc. concerning large
dams and related facilities (below, “large dams”), in
order to improve the design, construction, maintenance,and operation of large dams and to contribute to thedevelopment of the Japanese economy. Responsibilities
include:(1) C ollection of information, surveying, and researchconcerning large dams(2) Exchange of technology and guidance concerning largedams(3) Participation in ICOLD, assistance to its activities, andinternational exchange of technology concerning large
damsManaging Director
GeneralPresident

Meeting

Vice President(3)Senior Managing Director

AuditorAdvisor/Counselor

Directors

Administrative Oﬃce
Planning Committee(Sub Committees)

Public Relations/ Environment
Editorial

Technical Committee(Sub Committees)-International aﬀairs-Research of actual frost damage of concrete-Rational utilization and operation of existing dams(4) D issemination of and spreading awareness of theachievements of surveys and research concerning largedams(5) O ther activities necessary to achieve the goals of
JCOLD
In recent years, JCOLD has actively conducted a programof surveys and research on methods of harmonizing dam
development with the environment and on ways to mitigate
their environmental impacts to achieve the sustainable
development of dams.

Organization
Under the leadership of the Chairman, there is a Planning
Committee, Technical Committee, and Administrative
Office. These committees undertake work in their respective
areas.

Figure-1 Organization Chart of JCOLDDAMS IN JAPAN - OVERVIEW 2022

2

Publication
JCOLD publishes its Journal, “Large Dams”, four times ayear (January, April, July, October), which is distributed
to members and subscribers. At ICOLD Congresses held
once every three years, JCOLD publishes Dams in Japanin English, which introduces the state of dams and dam
technologies in Japan, and distributes it to Congress
participants (1997, 2000, 2003, 2006, 2009, 2012, 2015 and2018).
Figure-3 Dam Technology Lecture and Discussion Meeting

ISSN 0011-5347

大Study Tour

ダ
ム

第
六
十
四
巻

第
二
五
八
号

巻頭言 年頭のご挨拶

二
〇
二
二
年
一
月

ICOLDをめぐる動き（第57報）〜APG会議（オンライン），
ICOLD第89回年次例会（オンライン）〜
第54回ダム技術講演討論会開催報告
ICOLDフランスマルセイユシンポジウム投稿論文（その2）
随 想 ダムに携わって

一
般
社
団
法
人
日

Dams in Japan
Overview 2018

To increase mutual awareness among engineers, including
JCOLD members and others concerned with dams, on
improving dam and hydroelectric power plant technologies
and the construction of dams, JCOLD holds tours of dams
and hydroelectric power plants still under construction withthe cooperation of various organizations.

No.2582022-1

本大ダ
ム
会

トに社名が変わりました。

電

議

JCOLD

一般社団法人日 本 大 ダ ム 会 議JAPAN COMMISSION ON LARGE DAMS

話（03）5614-0968 FAX（03）
5614-0969

Tokuyama Dam

JAPAN COMMISSION ON LARGE DAMS

Figure-2 Publicaitons of JCOLD

Annual lecture meeting

Figure-4 Tour of the site of the Shin katsurazawa Dam(2019)

Contribution to ICOLD

Dam Technology Lectures and Discussion Meetings

JCOLD submitted 389 ICOLD Congress papers until now.
In addition, Many Japanese engineers participate in ICOLD
Annual Meeting and Congress.

(Held jointly with the Japan Association of Dam & Weir
Equipment Engineering)

JCOLD participates in 22 technical committees at Annual
Meeting and exchanges technical information.

At the meeting, the results of surveys and research by thevarious JCOLD technical sub committees, papers presented
to the ICOLD Congress, and results of activities by theJapan Association of Dam & Weir Equipment Engineering
are reported widely to people concerned with dams. In
addition, the lecturers and participants in the Technology
Lecture and Discussion Meeting discuss the reports in orderto improve the technologies, maintenance, and operation ofdams.

JCOLD held Annual Meeting in 1960(Tokyo) and1984(Tokyo), and Congress in 2012(Kyoto).
Susumu NAGATA(1957-1960), Masayoshi NOSE (19661969), Shigeru ICHIURA (1982-1985), Kyohei BABA
(2001-2004), Norihisa MATSUMOTO(2007-2010) andTadahiko SAKAMOTO(2011-2014) served as a vicepresident of ICOLD.

3

DAMS IN JAPAN - OVERVIEW 2022
Table-1 Number of participants from Japan
Year
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2021
2021

Host country(Host city)
India (New Delhi)
Turkey (Anatolia)
China (Beijing)
Germany (Dresden)
Brazil (Iguazu)
Canada (Montreal)South Korea (Seoul)
Iran (Tehran)
Spain (Barcelona)
Russia (St. Petersburg)
Bulgaria (Sofia)
Brazil (Brasilia)
Vietnam (Hanoi)
Switzerland (Lucerne)Japan (Kyoto)
USA (Seattle)
Indonesia (Bali)
Norway (Stavanger)
South Africa(Johannesburg)
Czech Republic (Prague)
Austria (Vienna)
Canada (Ottawa)India (New Delhi)
France (Marseille)

Number ofparticipantsfrom Japan
43
56
87
60
47
49
143
77
107
79
63
46
75
70
398
73
79
80
58
84
91
85
19
10

Table-2 Number of submitted papers
Year

No.

Host country(Host city)

1933
1936
1955
1958
1961
1964
1967
1970
1973
1976
1979
1982
1985
1988
1991
1994
1997
2000
2003
2006
2009
2012
2015
2018
2022

1
2
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27

Sweden (Stockholm)
USA (Washington)
France (Paris)
USA (New York)
Italy (Rome)
United Kingdom (Edinburg)
Turkey (Istanbul)
Canada (Montreal)
Spain (Madrid)
Mexico (Mexico)
India (New Delhi)
Brazil (Rio de Janeiro)
Switzerland (Lausanne)
United States (San Francisco)
Austria (Vienna)
South Africa (Durban)
Italy (Florence)
China (Beijing)
Canada (Montreal)
Spain (Barcelona)Brazil (Brasilia)
Japan (Kyoto)
Norway (Stavanger)
Austria (Vienna)
France (Marseille)

Number ofsubmitted
papers
3
5
4
13
8
13
11
8
12
9
11
12
17
22
29
25
28
16
20
23
15
37
16
20
12

Dams in Japan
Development of dams
In Japan, the major purpose of dams was irrigation fromancient times to the end of the feudal period in the mid
nineteenth century. The Sayama-ike irrigation pond (Osaka
Prefecture), which is considered to be Japan’s oldest dam,
was completed in 616, and is recorded in the official historic
documents.

in recent years, redevelopment projects, such as raising
the height of dams, excavating reservoirs, and upgrading
discharge facilities, are being carried out more and more.

As Japan was modernized and urbanized after the Meiji
Revolution (1867), Japan started to build dams with modern
technology, to meet the increased demand for water andelectric power. In 1900, the Nunobikigohonmatsu Dam(Hyogo Prefecture) was completed as water supply dam.
As for hydropower, the Chitose No.1 Dam (Hokkaido) was
first completed in 1910. Later, multi-purpose dams withflood control capacity were constructed, with the first, theKodo Dam (Yamaguchi Prefecture), completed in 1940.
To make more efficient use of water resources and control
of flood, comprehensive projects are promoted under theconcept of integrated development of river systems. Also,

Figure-5 Nunobikigohonmatsu Dam

4
DAMS IN JAPAN - OVERVIEW | 2018

Multi-purpose dams
with flood control capacity
Kodo Dam

Hydoro Project

Nunobikigohonmatsu Dam

2000

160,000,000
140,000,000

600,000

120,000,000

500,000

100,000,000

400,000

80,000,000

300,000

60,000,000

200,000

40,000,000

100,000

20,000,000

0

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

Figure-6 Development of Dams, Economy of Japan and Population
Figure-6 Development of Dams, Economy of Japan and Population

2010

0
2020

Major dams in Japan
Major dams in Japan

There are many dams over 100 meters high in Japan, though,There
are many
dams areover
100 meters
highin Japan,their reservoir
capacities
smallerthan thoseof otherdamsthough,theirreservoir
capacities
aresmallerthanthose ofaround the world, reflecting the geographical featuresofotheraroundtheandworld,
Japan dams
(narrowislands
steep reflecting
terrain). the geographicalfeatures of Japan (narrow islands and steep terrain).
Table-3 Ranking of dams by height in Japan
1
2
3
4
5
6
6
6
9
10

Dam name
Kurobe Dam
Takase Dam
Tokuyama Dam
Naramata Dam
Okutadami Dam
Miyagase Dam
Urayama Dam
Nukui Dam
Sakuma Dam
Nagawado Dam

Type
Arch
Rockfill
Rockfill
Rockfill
Gravity
Gravity
GravityArch
GravityArch

Height (m)
186
176
161
158
157
156
156
156
155.5
155

Figure-7 Ｎaramata Dam
Figure-7 Naramata Dam

Table-4 Ranking of dams by reservoir capacity in Japan
Dam name
1
2
3
4
5
6
7
8
9
10

Tokuyama Dam
Okutadami Dam
Tagokura Dam
Yubari Shuparo Dam
Miboro Dam
Kuzuryu Dam
Sakuma Dam
Ikehara Dam
Sameura Dam
Hitotsuse Dam

Reservoir capacity(million m3)
660
601
494
427
370
353
343
338
316
261

200,000,000

Yamba
Dam
180,000,000

Miyagase Dam Tokuyama Dam

Sannoukai Dam

1000

0
1900

Gosho Dam
Takase Dam

Ogouchi Dam

Large Irrigation Project

Municipal water
Irrigation
Flood control
Multipurpose(Hydropower excluded)
Multipurpose(Hydropower included)
Hydropower

3000

Yagisawa Dam

Sakuma Dam Kurobe Dam

Honen-ike Dam

4000

Number of dams

Ikari Dam

Chitose No.1 Dam
Oi DamMunicipal Water Supply

Gross Domestic Product(In billions of yen)

5000

Toubetsu Dam

4

Population of Japan

6000

DAMS IN JAPAN - OVERVIEW 2022

Figure-8 Miyagase Dam
Figure-8 Miyagase Dam

55
DAMS IN JAPAN - OVERVIEW 2022
DAMS IN JAPAN - OVERVIEW | 2018

Hydroelectric power plants in Japan
Hydroelectric power plants in JapanThe output of hydroelectric power plants in Japan accounts
for
about
17%
all electric power
powerplants
sources,and pumped
The
outputof ofhydroelectricin Japanaccounts
storagehydroelectric
power
occupies
top
10sof
for about 19% of all electric power sources, theandelectric
pumpedpower
outputrankings. power occupies top 10s of the electric
storagehydroelectric
power output rankings.

Table-5 Electric power output ranking of Conventional
Table-5ElectricElectricpower
power
outputranking
rankingofofConventional
Conventionalhydropower
plantsTable-5
outputhydropower
plantshydropower
plantsElectric
Electric
Hydroelectric power Electricpower
Dam name
Hydroelectric
power output
power
plant power
power
Hydroelectric
Dam name
Dam name
plant
output(MW)
outputplant(MW) Okutadami Dam
1
Okutadami
560
(MW)
1
Okutadami
560
Okutadami
Dam
Tagokura
400
TagokuraDam
12
Okutadami
560
Okutadami
Dam2
Tagokura
400
Tagokura
Dam
Sakuma350
Sakuma Dam
23
Tagokura
400
Tagokura
Dam
3
Sakuma350
SakumaDam
Dam
Kurobegawa
335
Kurobe34
Sakuma 4
350
SakumaDam
4
Kurobegawa
4335
KurobeDam
Arimine 1 4
265
ArimineDam
45
Kurobegawa
335
Kurobe Dam
5Arimine 1
265
Arimine Dam
Tedorigawa
250
Tedorigawa
Dam
56
Arimine 1 1
265
Arimine Dam
6
Tedorigawa
250
Tedorigawa
Dam
Miboro 1 1
215
Miboro Dam
67
Tedorigawa
250
Tedorigawa
Dam
7
Miboro215
MiboroDam
Shinojiya
206
Miyanaka
Dam
78
Miboro215
Miboro Dam
8Shinojiya
206
MiyanakaDam
Dam
Hitotsuse
180
Hitotsuse
89
Ojiya 2
206
Yamamoto2
9
Hitotsuse
180
Hitotsuse
Dam10
Shinanogawa
177
Nishiotaki
Dam
9
Otori
182
Otori dam
10
Shinanogawa
177
Nishiotaki Dam
10
Hitotsuse
180
Hitotsuse Dam

Figure-9 Okutadami Dam

Table-6 Electric power output ranking of Pumped
Table-6 Electric
power
output ranking
Storagehydropower
plants of Pumped
Storage hydropower plants
Electric
Dam nameElectric
Hydroelectric
power
Dam
name /(upperreservoir
Hydroelectric
power
power
plant
output(upperreservoir
lower reservoir) /power plant
output(MW)lower reservoir)(MW)
Kurogawa Dam /1
Okutataragi
1,932
Kurogawa
Dam /Tataragi Dam
1
Okutataragi
1,932
Tataragi
Dam
Kassa
Dam
/
2
Okukiyotsu
1,600
KassaDam
Dam /
Futai
2
Okukiyotsu
1,600
FutaiDam
Dam/
Kaore
3
Okumino
1,500
Kaore
Dam
Kamiosu Dam/
3
Okumino1,500
Kamiosu
Dam
TakaseDam/
4
Shintakasegawa
1,280
TakaseDam/
Nanakura
Dam
4
Shintakasegawa
1,280
Nanakura
Dam
Ota Dam /4
Okouchi
1,280
Ota Dam
Dam /
Hase
4
Okouchi
1,280
Hase
Dam
Seto Dam/
6
Okuyoshino
1,206
Seto
Dam
Asahi Dam /6
Okuyoshino
1,206
AsahiDam
Dam/
Tambara7
Tambara1,200
Tamahara
Dam /Fujiwara Dam
7
Tamahara
1,200
Fujiwara
Doyo DamDam/
7
Matanogawa
1,200
Doyo Dam/
Matanogawa
Dam7
Matanogawa
1,200Matanogawa
Ouseuchi
DamDam/7
Omarugawa
1,200
Ouseuchi Dam/
IshikawauchiDam
7
Omarugawa
1,200
Ishikawauchi
DamKamihikawaDam/
7
Kazunogawa
1,200
Kamihikawa Dam/
7
Kazunogawa
1,200 Kazunogawa Dam
Kazunogawa Dam

Figure-10 Kurobe Dam

DAMS IN JAPAN - OVERVIEW 2022

6

Dams completed in 2017 - 2020 in Japan
Dams completed in 2017-2020 in Japan are counted in 12 dams. The features are summarized below.
Dam
CompletedNo.

Dam name

Location

PurposeType

Height(m)

Length of
crest
(m)

Reservoir
capacity(103㎥ )

1

Asakawa

Nagano

C

PG

53.0

165

1,100

2

Arase

Kagoshima

I

ER

65.6

407.5

2,580

3

ApporoHokkaido

CSI

CSG

47.2

516

47,400

Hokkaido Pref.

2018

4

Kanaji

Hyogo

C

PG

62.3

184

4,700

Hyogo Pref.

2018

5

Sanru

Hokkaido

CSH

CSG

46.0

350

57,2006

Kochigawa

Fukui

CSI

PG

77.5

202.3

8,000

Fukui Pref.

2019

7

Okutainai

Niigata

CSH

PG

82.0

198.9

10,000Niigata Pref.

2019

8

Ichinoshinden

Niigata

I

ER

26.7

199

1,690

9

Gokayama

Fukuoka

CS

PG

102.5

556

40,20010

Yokozegawa

Kochi

CH

PG

72.1

188.5

7,300

11

Oso

Kumamoto

I

ER

69.9

262.1

4,300

12

Yamba

Gunma

CSH

PG

116.0

290.8

107,500

Owner

Nagano Pref.
Kyushu Regional Agricultural
Administration Office, MAFF*1

Hokkaido Development Bureau,
MLIT*2

Hokuriku Regional Agricultural
Administration Office, MAFF*1
Fukuoka Pref.
Shikoku Regional Development
Bureau, MLIT*2
Kyushu Regional Agricultural
Administration Office, MAFF*1
Kanto Regional Development
Bureau, MLIT*2

2017
2017

2019

2019
2020
2020
2020
2020

Purpose: C - flood control, S - water supply, I - Irrigation, H - hydroelectricity*1 Ministry of Agriculture, Forestry and Fisheries

Type: PG - gravity in masonry or concrete, ER - rock fill, CSG - CSG*2 Ministry of Land, Infrastructure, Transport and Tourism

Several dams are illustrated in the following pages. The key to abbreviations is given below.
DFWL - Design Flood Water Level
HWL - High Water Level
SWL - Surcharge Water Level
NWL - Normal Water Level
LWL - Low Water Level

Figure-1 Plan

0
57

566.6

EL 532.5

93000（13000×6+2000×4+7000）
8@15000=120000
88000

1:1.0

0

J11

31000

7000

0
1:

1:0.8

.8

1:

0.

1:0.8

603.6

593.5

40000

8

1:0.8

Axis of dam

0

1:0.8

60

0.

589.3

1:0.8

EL596

1:

EL586

8

2500

0.

577.5

24800

5000

1:

EL576

8

575.3

598.3

579.2

570.8

5600

544.1

EL54
6

595.6

569.6

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551.2

534.7

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54

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EL546

565.7

5

53

EL520
EL516.5

592.2

619.0

0

608.1

645.9

63

1/18

531.4

0

59

10000

582.5

526.9

1:1.0

539.3

516.5

531.1

EL536

643.8

581.8

532.2

560.3

523.8

523.7

629.4

572.7

599.8

Fishways

Apron L=25000
5500 4000
19400

EL536

545

551.6

Spillways EL515.0 1:1.0

526.5

1:10

532.7

Apron
L=25000

.6

565.3

J9

575.5

J6

573.9

1:1.0

EL564

0.

584.0

563.5

1:

EL566

6

54

EL

6
53
EL

1:0

590.5

581.6

J8

EL556
1:0.6

569.4

568.2

1:1.

568.3

EL555

DC.20.000

EL558

1:0.6

EL561

553.4

547.4

.6

EL556

EL552

EL549

EL540

EL543

EL546

1:0

551.1

546.7

.6

558.3

8

5

1:0.

55

552.4

EL546

5

54

4

528.0

1:0

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548.6

J7

545.7

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EL532.5

EL535.5

線

EL526.5

EL55
6

E.L.147.500

565.4

557.7

0

00

545.6

538.2

川

EL56
6

584.0

583.9

622.3

648.4

539.5

530

586.8

559.8

531.2

617.5

662.7

627.9

1:1.0

5.0

5

54

5

29

L=

EL

el

6000

6

nn

52

530.0

原浅

526.3

EL522

EL516

EL516川

60°

tu

EL

高

531.314000 6000

537.3

飯綱

浅

EL522

EL523.5

573.2

591.4

E.L.147.500

542.8

n

J5

541.7

532.5
道

1:0.8

DC.41.000

543.3

県

528.0

518.4

EL53
6

DC.47.000

53

541.5

533.9

1:0.8

523.4

EL552.5

0

6

96

608.8

640.7

E.L.147.500

538.8

542.7

6

537.1

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538.4

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io

EL516

rs

525

519.9

線

58

86

EL5

604.0

615.7

656.5

629.2

EL516

ve

54

536.4

J4

12800

Di

49000

520.4

田
DC.41.000

531.9

6

500
500
10002000
4000

535

52

EL

6

法
寺・ 534.0

EL526.5

EL529.5

EL532.5

552.2

571.0

EL5
7

0

533.1

6

0.

6

522.5

53

1:

光

532.7

540

EL535.5

EL540

588.5

EL5

598.8

1:1.

1：0.7

6
1:0.8

530.3

6

EL

1:0.

真

J3

521.6

EL

利

7.5

EL543

EL54

5

EL55

EL55
8

00

145

1:1.0

535.1

J2
1:0.8

522.9

56

EL

539.2

.8

1:0

1：1.5

EL

6

1:0.

0.

1:0

1:

537.7

3.5

0.5

EL55

567.2

EL55

0

DC.28.000

535.8

m
8

1:0.

1：1.5

570

537.0

13000
10000

538.8

6

0.

6

500

EL56

66

606.0

622.8

625.2

644.4

665.9

1:1.0

523.5

539.4

542.6

551.1

J1

0.

00
1:1.0

1:

100

559.1

15

6

46

EL5

0

575.3

EL5

0

6

650

EL5
7

86

EL5
96

EL5

6

EL61

5

655.7

0

1:1.

0.

00
1:1.0

1:

180

00
280
1:1.0

1: 563.4
0.
6

J0

54

8

8

1:0.

1:

8

534.0

1:0.

543.8

1:0.8

554.2

R=

EL566

535.0

1:0.8

560.7

592.5

8

574.1

1:0.6

1:1.0

579.1

1:0.6

.8
1:1.0

575

10

0m

564.4

1:0.6

.8

1:0.

586.8

605

541.3

R=

1:0

8

561.3

1:0.8

1:0.

554.5

.8

54
5

569.7

1:0

8

570

8

.
1:0

1:0.

25°

8

561.7

1:0.8

582.3

8

EL586

06

6

EL62

EL6

1:0.

EL576

1

588.2

588.7

8
:0.

554.9

565.1

1:0.8

600.8

634.5

6

EL63

8

6

621.0

650.1

6

EL64

1:0.

EL59

606.8

0.

576.0

572.4

559.5

568.1

630

616.0

641.9

1:0.8

1:1.

1:1.0

7.1

587.5

561.3

584.5

601.5

634.0

6

EL65

667.9

0

00.2

562.6

579.4

591.4

1:0.8

564.4

58
5

1:1.0

579.3

557.7

658.8

1:
0

.0
0

1:1.
EL515.5

0

581.1

657.7

0
1:1.
1:1.0

1.
1:

609.9

617.7

1:1.0

0

0

1:1.0
1:1
0

.0

588.8

1.

1:1.

1:1.0
.0

1:1
1:1.

15005000
10000
500 1900 3500
500

1
1:

592.3

638.5

1

1:
.0
0

8

605.8

1:

.0

0

1:1
1:1.
1:1.0

0.

603.2

1:1.0
1:1.0
.0
1:1.0
514.1

591.0

659.1

566.4

546.8

526.6

0

522.2

永原橋

547.1

574.2

606.2

627.1

642.1

650

522.5

1:1.0

1:

581.1

1:1.0
1:1

0
1.
1:

0

1:1.

am

8

1:1.

1:1.

f d
1:0.

0

s o
0

1:1.

Axi

1:1.

3

641.7

594.

554.7

513.5

523.6

554.4

617.6

625

630.9

7
DAMS IN JAPAN - OVERVIEW 2022

Asakawa Dam

＠ Nagano Prefecture

1:0.8

8

J10

6

DAMS IN JAPAN - OVERVIEW 2022

EL(m)
570.0

5.0

Crest elevation EL566.0

HWL EL563.9
SWL EL562.1

550.0

.8
1:0

1:0.1

560.0

R=1.00EL543.5

540.0

Apron L=25.0

5.0

5.0
10.0

DC.8

DC.7

10.0

1:0
.8

40.0

530.0

1:0.2

NWL EL520.5

510.0

500 1.0

520.0EL513.0
22.4
24.9

42.4

500.0

Figure-2 Typical section
EL（m）
620.0

)

2.0

8@15.0=12.0
Overflow section 93.0

10.0 10.0
13.0

18.0

7.0

31.0

1:0
.8

J0

1:0

J1

J2

J3

6

1:0.

EL550.0

9.6 8.0

J5

J6

J7

J8

J9

J10

J11

NWL EL520.5

1:0.8

540.0

J4

HWL EL563.9
SWL EL562.1.8.8

Crest elevation EL566.0

560.0
550.0

Crest length 165.0

17.6

.8

1.0

1:0

570.0

(1:

.8

580.0

)

1:0

590.0

1.0

1:0

600.0

(1:

1:0.1

610.0

530.0
520.0
510.0
500.0

9.0 6.0

Figure-3 Upstream elevation
EL（m）
620.0
610.0

.8
1:0

J11

J10

J8

J7

J6

J5

J4

J3

J2

.8
J0

6

J1

1:0.

1:0.8

8.0
1.0

1.5

550.0

530.0

18.0

Crest elevation EL566.0

560.0

540.0

1.0

1:0

1.0
13.0

1:0
.8

8@15.0=12.0
Overflow section 93.0

31.0

(1

17.6 2.0

.8

570.0

7.0

1:0

580.0

Crest length 165.0

5.0

590.0

1:0
.8

600.0

0)
:1.

520.0
510.0
500.0

Figure-4 Downstream elevation

9.6

)

1.0

(1:

EL513.400

89DAMS IN JAPAN - OVERVIEW 2022

Arase Dam

＠ Kyushu Regional Agricultural Administration Office

Figure-1 PlanDAMS IN JAPAN - OVERVIEW 2022

EL(m)
160.0

Upstream

10.0

Downstream

150.0

ble

a

e
erm

(P

e4

n
Zo

2.5

e)

zon

1.5
1

Zone3
(Permeable zone)

3.0

Filterzone
1:0.175110.0

1

LWL 123.6

3.0

zone
Filter
1:0.175

130.0
120.0

100.0
90.0

1.5

2.0
1

Zo

ne

Zo

1

ne

4(P

erm
ea
ble
rm
Zone1
zon
ea
ble
Zone2
e)
(Diaphragmz
on(Semi-permeable zone)
zone)
e)

Lowest excavation for foundation elevation
Blanket grouting

70.0

1
1.1

3(

Pe

3.0

80.0

Crest elevation EL 148.6
Non-overflow section EL 148.1
EL 144.0
EL 142.0

NWL 144.0

140.0

Curtain grouting

3.0

26.784

3.0

Figure-2 Typical section

Left bank
EL(m)
175.0
150.0

Right bank

Crest length L=407.5m
Extra banking transitional section L=172.5m
Extra banking transitional section L=200.0m
Maximum extra banking section L=35.0m
Crest elevation EL 148.6

125.0
100.0
75.0
50.0

Figure-3 Longitudinal profile

10

11

DAMS IN JAPAN - OVERVIEW 2022

Apporo Dam

Hokkaido Pref.

spillway

Crest length 516.0m

86.0m

106.0mCrest
spillway

Emergency
spillway

Figure-1 PlanDAMS IN JAPAN - OVERVIEW 2022

Crest length 516.0m
IntakeSWL 88.1m
DFWL 89.1m
NWL 85.4m

Damheight47.2m

Figure-2 Upstream elevetion

Crest length 516.0m
IntakeDamheight47.2m

Figure-3 Downstream elevetion

8.0

Crest elevation EL91.2

3.

0

DFWL EL89.1

Protection concrete

0.

1.75

LWL EL64.0

8
0.

1:

Protection concrete

8

NWL EL85.4

1:

Dam height 47.2m

SWL EL88.1

CSG

EL 56.0

Structural concreteFoundation rockEL 54.5

Energydissipator
EL 49.0
EL 47.5

Seepage control concrete

elevation
EL 44.0

Replacement CSG
Rich - mix CSG
30.0

83.52
shal1

5.6

6.4

42.0
sh1
shal0

Figure-4 Typical section

12

13

DAMS IN JAPAN - OVERVIEW 2022

Sanru Dam

S=1:1,000
Ｔ３１

５

川

Ｗ
１４５．７
１４５．
７

１

０

・

４５．３

Ｔ３４

１５
０

４６．６７

１４

１４５

１４３

４２．９

４６．８

４６．６

５
１５
１５０
１４５

Ｔ２９

０

５

１５

０

５
１８

1:2.0

1:1.5

５
９

1:2.0

１

EL
164
.00
0
154
.00
0
EL

.000
184

EL164.000

０

４

２

２５．２

1:0.8

２３１．２

５

４

６６．１

２級基準点
Ｈ５ＮＯ１

78.0
0

00

１９０

１

EL1

58.0

３

EL1
70.5
00
EL1
68.0
00

EL1

２４

０

EL174.000

１５．１

Ｔ２０

１８９．０６

1:0.8

５

２

２

２１

EL184.000

1:0.8

EL

EL184.000

１３．３

Ｔ１９

EL188.000

1:0.8

５
０
２

０
１
２
５
１
２

０
２

EL194.000

珊 瑠

５

２

２

２０４．５

ＢＴＣ＝１，９２５．０４
Ａ＝２００EL188.000

３
２

１７．０７

２０

０

０

１９００

0

２

０

EL178.00

０２２EL184.000
H.W.L.=182.300
S .W.L.=179.300
N.W.L.=167.400
L.W.L.=158.800

４６．１
Ｔ１

１８９．９

0

Ｔ７

EL143.000

EL168.00
0

０

１８５．２
Ｔ２１
１８８．１４

EL158.00

５
３

１７３．３

EL146.000

Ｔ６

．１９

２２３
Ｔ５
・

Ｔ２

Ｔ２２

９

５

５

EL148.500

0

1
EL

１６７．９

EL149.000

0
74.0

８３．２１

１６０

１７０

１

０

１９

EL146.500

Ｔ２３

１７５

6000

サンル川

１

２

２３
３９．８

15000 6500
1000

1000

道路

用
Ｔ２４工事

道 道 下 川 ・ 雄
武 線

５
０
Ｔ４

１４８．４

１４７．８
Ｔ２５

２
９１．６５

８．００

魚道
工
ＥＰ＝６
Ｘ＝３６
Ｙ＝３０
１４７．８

１４５．６
１４５．４９EL146.500
Ｔ３７
86900

1000
4000
1000

Ｔ２６

１４５．２

４３．４

７３．６２

Ｔ３

４６．７

４５．６９

６

４３．６

１８

８

００

１５０

１７

５

１６０

０

４

金属標

２３０

１６５

１

Ｔ３６

１４５

１７

４６．１

・

１５５

１

４
１７

橋

Ｔ２８

４３．４

４３．３

１４８

０
Ｗ

Ｔ２７

４７．２

一線

７

１

Ｔ３５

９２．００

４８．４

４６．２６

５

４
１

７５．５１

４８．７

４８．４

Hokkaido Development Bureau, MLIT
Ｔ３０

１７６．５８

４７．８

４６．９０

５

１４２．９

４８．７

７

図

１４

１６

０

沢

４３Ｅ

ダム平面

１８

８８．６８

１７．５

0

15.0

４５．２
J8

15.0
J9

15.0
J10

15.0

J13

15.0

J14

15.0

J15

15.0

J16

15.0

J17

15.0

J20

J21

０

ＢＣ＝２，０２５．
Ｒ＝４００
０４ ６１
８６．

８１．７

・

４

１

２４２．０
００

９９

．９

１

５７．２

９０．５

５

８

２０６．６２

６７．５

５

２２

２２

０

１４

５
１

５

１４

１４５．９

１４６．２
１４７．２

・

５

０
１

Ｔ４３

１０．５
７９．２６

６
２３４．３

９

８４．３

１

６

４４．６

２６
０

４

５
１４４．６

２２７．１
２２．２４

，４

８０．３

５

１

１
９

２＝

１４５．２

４３．７

１３．００

０３．１
ＥＣ
＝
０ Ｒ

４５．４

Figure-1 Plan

３０．５

２０６．５

１４６．１５・１４５．７４９

１９７．８９

３

１６５

６７．３

１６０
１５
５
１５
０

J23

２

１７

０

１８
５
１８
０
１７
５

５

０

９

９

18.0

J22

１７０

１

15.0 ２
６６．

６３．０

０２．１
５

７２．４

15.0

J19

５

１８１．１

７７．６

０５．２

15.0

J18

１５

２

15.0

J12

１４
４

０

０

２

１７

２９．８

15.0

Crest length L＝350.0m

１４３．３

５

０

２

１

５

１

２

０

０

２

２

Overflow section L＝78.5m (Eﬀective Width L＝70.5m) Non overflow section L＝129.0m
J11

１５
５

２４０

１

５

０
２

２

３

２

２

３

５

０

15.0

J7

．３
７３

２４

15.0

J6

１７０

２４５

15.0

J5

５

15.0

１９

Non overflow section L＝142.5m
J4

０

15.0
J3

２１

15.0
J2

２４０

15.0
J1

５

17.0
J0

２２

２級基準点
Ｈ５ＮＯ２
２４７．９

・

０

７８．６

ＥＴ

ＡＣ

９４．５８

＝＝

２２

０，

０１

０１．８

３５．７

９９

２１０

Ｔ４４

９３．３２

９４．９

５

１４４．４

１６

５

１４４．９

２５０

１８

４６．６
７３．２

・

５

ｗ

７０

７６．２９

４６．１

の

４９．８５

４６．２

．９

１

DAMS IN JAPAN - OVERVIEW 2022

Crest Length L=350.0
17.0

J1

15.0

J2

15.0

J3

15.0

J4

J5

J6

J7

J8

15.0 15.0 15.0 15.0 15.0
Non overflow section = 142.5

J9

J10

J11

J12

J13

J14

J15

J16

J17

J18

J19

J20

J21

J22

15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0
Non overflow section = 129.0
Overflow section = 78.5 (Effective Width = 70.5)

Water gage

SWL 179.3

Spillways Elevator Intakes
HWL 182.3 (3.5m×5.4m)

1:0.8

Crest elevation EL184.0

18.0

Fish way

1:0.8

J0

NWL 167.4
LWL 158.8

Figure-2 Upstream elevetion

Crest length L=350.0
15.0

J20

15.0

J19

J18

J17

J16

J15

15.0 15.0 15.0 15.0 15.0
Non overflow section = 12.9

J14

15.0

J13

15.0

J12

Intakes Elevator

Fish way

Crest Elevation EL184.0

J11

J10

J9

J8

J7

15.0 15.0 15.0 15.0 15.0 15.0 15.0
Overflow section = 78.5 (Effective Width = 70.5)

SWL 179.300

Spillways(3.5m×5.4m)

J6

J5

J4

J3

J2

15.0 15.0 15.0 15.0 15.0
Non overflow section = 142.5

J1

17.0

HWL 182.300
1:0.8

J21

1:0.8

18.0

J22

1:0.8

Figure-3 Downstream elevetion（Non overflow section）
m
of da
Axis
8.0

HWL
SWL

EL182.3

NWL

EL167.4

Protection concrete

Crest elevation

EL184.0

EL179.3

CSG (C=60kg/m3 )EL158.8

1:

.8

LWL

0.8

1 :0

J23

Protection concrete

CSG (C=80kg/m3 )Protection Concrete

Structural concrete

Protection concrete

Seepage control concrete

11.2

High performance concrete
40.8

Foundation rock elavation EL138.0
Rich Mixed CSG
81.6

Figure-4 Typical section

40.8

J0

J23

14

15

DAMS IN JAPAN - OVERVIEW 2022

Okutainai Dam@ Niigata Pref.

370

425

425

380

375

385

0
43

430

5

N

39

390

440

0
40

4 10

5

5
41

C
L

42
0

0
0
0
EL.349.000
..3
51
L

440

440

40

Crest of Auxiliary dam EL 345.5

435

5
43

15000

42

E

445

LBL-4

1:2.0

0
43

EL.

5

+

450
0
45

5
43

+

44 0

44 5
405

0
46

415

420

425

465

445

48

475

440

0
43

435

370

+EL.340.000

375

LBL-2

0
47

0
38

65
4

385

0

390

46

410

0
40

395

5
45

LBL-3

45 0

5
45

+

470

475

A.D+65.000

356

5.0
37

37
5.
0

360

500

5.0
36

5
49

36
5.
0

.2
:0
1

55
L.3
+E

LBL-1

5
48

450

0

5
48

379

379

Dam Crest length = 198.9

5
43

NO.9

415

5
41
410

O.7
N

Figure-1 Plan

0
45

2200

4

5
5

0
46
4

70

54800

5
47

4

NO.8

0
42

)

11500

0
43
5
42

17 . 64

18400

8

300

0

530

BC7(N
O. 9+

535

25500

520

2000

11＠15000＝165000

0
44

2

510

2000

N
O
. 10

505

2000

12500

50 0

12500

5

39
0

380

375

370

365

12500

495

114000

2000

490

2000

31000

5

485

0
43
420

445

5
43
425

2000

15500

2000

0

435

2000

41000
0
45

12500

4

440
44
5

440

12500

00

425

12500

360

0
5.
34

9725

9000

N
O.
11
＋
5.

N
O
.1
1
4

530

BL-13

430

6500

BL-12

5
39

2000
9725
3550

5
52

N
O
.1
2

BL-11

420

2000

2000

BL-10

J.12

41

445

11500

BL-9

J.11

410

10000

450

1:0.76

5500
5999
5. 0
36

0
5.
38

0
5.
39
0
5.
40

0
5.
35

405. 0

15500
2550
8000

5450
3000

5000
435.0

445.0

455.0

425.0

8000
11000

375.
0

2000

0
5.
34

5
35

455

0
5.
35

BL-8

460

0
5.
36

BL-7

J.10

505.0

C
L

BL-6

J.9

495.0

BL-5

J.8

485.0

BL-4

J.7

475.0

BL-3

J.6

465.0

BL-2

J.5

0
5.
37

J.4

455.0

465

BL-1

J.3

J.13

445.0

J.2

0
52

Crest elevation

435.0

J.1

5
51

425.0

0
47

J.0

510

.0

H

5
50

415.0

Axis of dam

Emergency spillways
H2.4m x B12.5m x 6unit

Control room
Elevator

8000

5

H3.6m x B3.55
Water gage
measuring room

403.0

19000

16.0m×16.0m

495

38

395.
0

385.
0

0
5.
38

spillway

17.5m×19.0m

0
49

525

0
49

A.D+65.000

DAMS IN JAPAN - OVERVIEW 2022

11.5

EL(m)
420
▽ DFWL

410

Control room
▼ Dam Crest EL 415.0

413.4▽ SWL 411.0

400▼399.868

.76
1:0

390
▽ NWL

380

384.0

370
360

▼Guide wall EL 357.0

1:0.3

350
340

▼349.0▼Auxiliary dam EL 345.5
EL340.0▼Apron▼338.0Manmade Rock(Diversion tunnel)▼340.0▼333.0

330

7.0

6.6

35.0

4.0

7.5

2.0

62.32

Figure-2 Typical section

EL(m)
510
500
490

(Rightbank rim tunnel)
54.8

480
470
460

1:

Crest Length = 198.90
43.9

1.

0

31.0

41.5

41.5

EL(m)
470

41.0

460
450

450
Crest Elevation 415.0
Spillway crest 411.0

410
390
380
370

Spillways
H3.6mxB3.55m▼ EL 364.0

320

410
390
380
360
350

350
330

420

370

360
340

Operation room

430

400

Emergency spillways
H2.4m x B12.5m x 6unit

1:0.76

400

440

.6

Control room
Water gage
measuring room▼▼

Elevator

.7

420

1:0

430

1:0

440

▼ Apron elevation 340.0▼41.500

340
330

Diversion tunnel
15.0

Figure-3 Downstream elevation

320

16

DAMS IN JAPAN - OVERVIEW 2022

Gokayama Dam@ Fukuoka Pref.

Diversion tunnel

Valve

ber

cham

.0
EL317

1:0.7617

17.5

t0 EL4

Dam cres7.0
section 21
Non Overflow
Upstream cofferdam

n 113.0
w sectio
6.0
Overfloth L=55
ng
le
Crest

Figure-1 Plan

No

rflow
n Ove

n

sectio226.0

DAMS IN JAPAN - OVERVIEW 2022

0

10

18

20(m)

Axis of dam
11.8
Structual concrete

EL(m)
420.0
410.0

Dam Crest EL 417.5

DFWL EL 415.9
SWL EL 413.4
NWL EL 407.1

400.0
Structual concrete

0

390.0

2.

External concrete

0

3.0

2.

76
0.
1:

380.0
370.0

56.5

84.0

360.0
350.0

External concreteInternal concrete
LWL EL 344.9

High fluidity concrete

Valve chamber

340.0
Structual concrete

EL 318.0

1. .5

320.0

EL 329.0

EL 329.000

330.0

EL 317.0

EL 314.0

310.0

Rocked concrete
13.2

300.0

24.0

116.5

Figure-2 Typical section

In

0

t

in

po

460.0

IntakesElevator

440.0

380.0

EL417.500
Inspection gallery

340.0
320.0
300.0

EL314.0

460.0
440.0
EL417.5

EL413.4

360.0

EL(m)

Dam crest = EL 417.5

1:0.76400.0

1:0.76

420.0

t

in

po

Non overflow section = 217.0

Overflow section = 113.0

Curvilinear section

on
cti

fle

In

Crest length = 556.0

Non overflow section =226.0EL(m)20 40(m)1:0.76

f

lec

n
tio

Inspection gallery

420.0
400.0
380.0
360.0

Downstream passage
20.0 Diversionconduit
B25.0×H30.0

Figure-3 Downstream elevation

340.0
320.0
300.0

19

DAMS IN JAPAN - OVERVIEW 2022

Yokozegawa Dam

Mortar Spraying
15

5

78.68

0

15

5

14

0

14

95

100

@ Shikoku Regional Development Bureau, MLIT

105.11

5

85

90

13

0

80

13

12

5

79.46

0

12

70.49

5

11

22500
110

107.31

3000

105.0

3000

16500

78.04

114.6691.74

6750

105.48

6750

3000

85.27
88.98
95.62

92.75

80.80

82.72

.0

.0
85

83.85

l

110.0

115.0

120.0

125.0

1:0.71

ro

0.

of

0

16

fi

5

ce

8

1:0.

0

5.
.7
46
L1
+E

0.

Outlet and Power generating unit room for site

0

8

.
:0

85.48

16

0

13

1

0

5.

Oomonogawa St.

0

14

130.0

17

nt

15

90.11

Yokoze River

14

135.0

Co

125.0

130.0

87.66

120.0

85.26

5

1:0.8
115.0

1:0.7
1:0.74

17

5

88.93

0.

87.18

110.0

105.0

84.61

84.31

1:

90.05
106.67100.0+EL102.1

7R43352

0.

90

95

10

.0

0.

0

90.0

1:

85.58

8

0.

90.13

1:

15

5

.7

46

L1

98.55

+E

1:0.8

+EL130.900

15

84.20

Elevator+EL124.400
85.90

14

140.0

Water gage room
Plumb line

1:0.8

140

0.

1:

Water gage

8

92.34

88.59

0
17

0

86.87

135

88.72

Crest elevation 152.2

1:

0.

7
1:
0.

0

0
0.
89.17

10

0

125

0.

92.45

10

0
89.24

0

0

95.0

100.

0

Spillways

0

1:

89.59

+EL105.00

11

5

0

0.

12

12

0

5.

10

90.48

92.03

108.08

7

0.

1

13
5

7

0.

1:

110

H
1.55B × 1.8（2gates）
90.49

BL10
10

BL4

BL5

BL6

89.94

BL7

BL9

BL8

130

125

94.51

J3

J4

J9

J5

91.31

J6

120

J2

J7

90.78

96.34

J8
95.20

96.71

17500

115

93.15

Non Overflow section 22000

97.04

Overflow section 96000

87.55

104.55

91.50

91.53
96.00

11@15000=165000

108.36

96.44

93.11

93.17

Figure-1 Plan

Crest length

ow

rfl

Non

95

J1

188500

94.66

94.01

n

tio

5

BL3

0

J0

00

0

J1

99.12

10

BL2

1:

1

J

11

BL

1:1.111

5

0.

BL1

BL

13

90.0

5.

0.

5.

5

140

145

10

11

11

10

5
0.1
1: 20.
0
12
5.
0

1:0.5

150

0

0.
0

0

0

0.

5.
0

155

0

15

5.

14

0.

5.

12

8

5.0

95

13

14

130

+12

160

87.84

12

165

Intakes

13

135.

1:0.5

1:0.71

1:0.8

5Seismometer

90.21

145.0

+EL124.400+EL128.900

145.0

1:0.8

140.0

0

Ove

sec

705

DAMS IN JAPAN - OVERVIEW 2022

Axis of Dam

EL（m）
160

DFWL

150

Crest elevation 152.500

EL150.300

HWL during floods EL145.800
140
HWL in normal times EL131.900

130

120

110

LWL

EL108.600

.71

1:0

100

90

Foundation rock elevation EL80.400

8051.19155.19170

Figure-2 Typical section

Crest length
Non Overflow section 70.5

J12

J11

J10

J9

point

J8

Crest elevation

J7

J6

152.5

Connecting Inspection
gallery for control office
EL130.4

J5

J4Water gage room Elevator
Plumb line

EL 131.9

J2

Intakes

EL 130.9J1J0

Spillways
BH
1.55 × 1.8（2gates）

1:0.71

EL115.458

J3

8

J13

Non Overflow section 22.0

0.

ction

1:

Infle

188.5

Overflow section 96.0

Diversion conduit

EL80.4
Outlet and Power generating room for site
Dewatering outlets

Figure-3 Downstream elevation

20

21

DAMS IN JAPAN - OVERVIEW 2022

Japan Incorporates Climate Change Effects
into River and Dam PlanningYamba Dam was filled up by the rain due to Typhoon Hagibis
in 2019 and saved the Tone River Basin, including part of theTokyo Metropolitan Area, from possible levee failures.
Concerted pre-release from dams on the Nakagawa River
was conducted on September 8, 2020. Nagayasuguchi Dam(this picture) and three other dams joined this operation.

Sakamachi, Hiroshima, just after the 2018
July West Japan Rainfall Disaster. This shows
the vulnerability of a river without dams
against debris from the upper reaches.

Photo by Nakagawa River Office, MLIT
Source:Geospatial Information Authority of Japan (GSI)

Japan Commission on Large Dams

Kyushu has suffered from a spate of severe floods. Damage due to the floods differed substantiallydepending on the availability of flood control dams. For example, in the Chikugo River Basin, tributaries
without major dams, such as the Akatani River in this picture, were severely damaged, while the Sada
River with Terauchi Dam suffered little damage in the 2017 Northern Kyushu Heavy Rain Disaster. In 2020,
a flood in the Kuma River Basin, Kumamoto, Kyushu, caused 50 fatalities and 6,110 houses wereinundated. Kawabegawa Dam, which would have been under operation by the time of this flood if theoriginal plan had gone ahead, was reauthorized to be built after this disaster.

DAMS IN JAPAN - OVERVIEW 2022

The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) manages 109 trunk
rivers in Japan. In 2019, MLIT formalized an increase in the amount of rainfall by 10 to
15% in flood control planning to cope with the effects of climate change in the future. In
2020, the Government also established a general rule to change, as far as it is effective,
the operation rules of reservoirs to allow for pre-release from dams before the arrival ofheavy rains by utilizing weather forecasts. In 2021, “Basin-wide Concerted Measures for
Flood Risk Reduction Acts,” which consists of amendments of nine affiliated acts, wasenacted to tackle the increased rainfall due to climate change.

Japan Incorporates Climate Change
Effects into Dam and River Planning
MLIT employed two climate change models. One is a 4 ℃ global
warming model using the d4PDF (5 km downscaling) dataset
comprising simulated weather data assuming weather in around 2090,
along with the IPCC’s RCP8.5 scenario. The other is a 2 ℃ global
warming model using the d2PDF (5 km downscaling) dataset. It is thesame as d4PDF except that the assumed weather is in around 2040.
With each model, MLIT conducted simulation of rainfall for a duration
ranging from 360 to 5,400 years. MLIT also conducted a simulation
with current conditions (1951 to 2010) to obtain a baseline, which is
not the same as the IPCC’s. Considering uncertainty in the future,
MLIT set the 2 ℃ warming case to be the main case used for dam andriver planning while using the 4 ℃ warming case as a reference case forunmodifiable structures with long-range service duration, for example.
Table 1 shows the projected rate of increase of rainfall. Table 2 shows
how much the flowrate and frequency of severe floods will increase.
The significant increase in the flowrates makes it almost impossible toabsorb the changes within current dam and river planning. Therefore,
alternative methods are to be explored.

Table 1. Projected Increase Rate of Rainfall by Regions
2℃
4℃ Increase
Case
RegionIncrease
Short Range
Hokkaido
1.15
1.4
1.5
North Western Kyushu 1.1
1.4
1.5
Rest of Japan
1.1
1.2
1.3
1. “Short-range” corresponds to rainfall within a range of three to nine hours.
2. This table is not applicable to rainfall within a range of three hours.
3. This table is applicable to a catchment area of no less than 100 km²
although it can be applicable to a smaller catchment area by taking into
consideration the possibility of a higher rate of increase of rainfall.
4. This table is applicable to floods with no more than a 200-year return
period.

Table 2. Projected Increase of Flowrate andFrequency of Severe Floods
Climate Change Scenario Rainfall Flowrate Frequency
2℃ Increase
approx.1.1 approx. 1.2 approx. 2approx. 1.3 approx. 1.4 approx. 4
4℃ Increase
1. The rate of increase of flowrate is the average rate of changes inpeak flowrates of design floods, which correspond to floods with a100- to 200-year return period, at Class A rivers in Japan.
2. The rate of increase of frequency is the average rate of changes in
the probability of design flood level rainfall at Class A rivers in Japan.

Climate change seems to bealreadyaffectingJapanhydrologically.
Improving
concerted pre-release from dams
with more sophisticated use of
weather forecasting, revision ofdesign discharge, and effective
sediment control for sustainable
maintenance of dams are someof the imminent challenges weneed to work hard to resolve.

Prof. Tetsuya SUMI

Ph.D. (Kyoto Univ.)
1985 Public Works Research Inst., MLIT
1998 Associate Prof., Kyoto Univ.
2009 Professor, Kyoto Univ.
2019 Vice-President Candidate at ICOLD
87th General Assembly at Ottawa
2020 Vice President, Japan Society of Dam
Engineers

Northern Hokkaido

Southern Hokkaido

Western Tohoku
San’inSetouchiWestern
Chugoku
NorthWestern
KyushuHokuriku

Eastern Tohoku

Kanto
Chubu
Kinki
Southern Kii
Southern Shikoku
South-eastern Kyushu

Okinawa22

23

DAMS IN JAPAN - OVERVIEW 2022

Basin-Wide Concerted Measures for Flood Risk Reduction
Japan’s response to intensified rainfall is “Basin-wide Concerted Measures for Flood Risk Reduction”(which MLIT refers to as “River Basin Disaster Resilience and Sustainability by All”). With this concept,
all stakeholders related to flood damage reduction are encouraged to work together to reduce flood
disaster risks.
Chisan - Forest
The Taskforce to Promote River Basin
Construction/
Conservation
Sabo Works
Upgradeof
Flood
Disaster Resilience and Sustainability byControl
Dams
Flood Water
Effective Use
All, which includes members from 16
Storage inof Non-Flood
Paddy Fields
Control Dams
ministries and agencies, was established at
Use ofAgricultural
the central government level in 2020. The
Reservoirs for
Urban Flood
Flood Control
Storage
Taskforce drew up the “Action Plan to
Measures against
Backwater Flooding Facilities
Promote River Basin Disaster Resilienceand Sustainability by All” in 2021. It
Relocation to
Pumping Station
Low Risk Areas
comprises various measures such as paddyRetarding Basins
field dams (floodwater storage in paddy
Dredging
High Risk
Flood Defense
fields), relocation to low-risk places,
Area
for Schools
Embankment &delineation of inundation areas by PMF
Reduction of Levee
Fragility(probable maximum flood), and flood
Drainage
Facilities
defense measures for key infrastructure as
Coastal Levees
well as traditional flood control measures
Image of Basin-wide Concerted Measures
such as dams, levees, and retarding basins.
For Flood Risk Reduction

Concerted Pre-release from Dams

A highlight of the basin-wide concerted measures for flood risk reduction is “concerted pre-release fromdams.” Under this scheme, various dam owners such as MLIT, MAFF, prefectures, power generationcompanies and irrigation organizations work together in each river basin to cope with heavy rains in thebasin. By lowering the water level of a dam reservoir further below the top of the conservation pool, in
effect, flood control capacity can be expanded or created. The Government has issued “Basic Policies forEnhancing Flood Control Function of Existing Dams.” Under this new policy, based on “flood control
agreements” among dam owners and river managers, the pre-release operation is conducted when an
expected amount of rainfall in the upper reaches of a dam reaches a threshold beyond which flooding islikely to cause damage downstream. MLIT calculates the expected rainfall with weather forecasts
supplied by the Japan Meteorological Agency (JMA). Larger estimates produced either by an 84-hour
range Global Spectral Model (GSM) or by a 39-hour range Meso-Scale Model (MSM) are used forcomparison with the threshold. MLIT has also formalized a compensation scheme in the event that prerelease operations happen to have adverse impacts on water supply and hydropower.

To see all

200 km
100 miDams Joining Concerted Pre-release Operation
Others
Source of the base map : Geospatial Information Authority of Japan (GSI)
For the details, see the notation at the map on the next page. The same notation applies to this map, too.

Dams Joining Concerted Pre-release Operations Based on Flood Control Agreements

DAMS IN JAPAN - OVERVIEW 2022

24

Introduction
toto
DamTechnologies
in in
Japan
IntroductiontoDamTechnologies
Japan
Introduction
Dam
Technologies
Japan
Trapezoidal
CSG
dam
Trapezoidal
CSG
dam
Trapezoidal
CSGdam

the dammaterials
requireless strength,
the required
the body
dam body
materials
requirelesstherequiredmaterials
requirelessstrength,
the strength,
required
performance
performanceof theof material
is low
are few
performancematerial
is andlow
andare fewonofthe material
isthelowandthere
aretherefew there
restrictions
on theonselectionof materials,”“Rationalization
restrictions
selectionof materials,”“Rationalizationtheselectionofthematerials,”“Rationalizationof design: The
Thetrapezoidal
trapezoidalCSG
CSG damdeveloped
developed
Japan
a new
type restrictions
The
in in
Japan
is aisnew
The trapezoidal dam
CSG dam developedin Japanis atype
new typeof design:
The trapezoidal
shapeshape
improves
seismic
stability,of design:The
trapezoidal
improves
seismic
stability,
trapezoidal
shape
improves
seismic
stability,
andso theofdamwhich
combinesthecharacteristics
ofatrapezoidalof damcombines
the characteristics
of a trapezoidalof which
dam whichcombines
the characteristics
of a trapezoidal
and sothesostrength
requiredofdam
theofbodydammaterials
is andandthestrengthrequiredthe body
dam body
materials
isstrengthrequiredofthematerials
islower,”
Dam
and
the
CSG
(Cemented
Sand
andGravel)construction
Dam Damand andthe CSG(Cemented
Sand Sand
and andGravel)the CSG(Cemented
Gravel)lower,”and “Rationalizationof construction:
Construction
lower,”and “Rationalizationof construction:
Construction“Rationalizationof
construction:
Construction
work
can
be
method.
Itrationalizes
theconstruction
of
dams
in
three
construction
method.
It rationalizes
the construction
of ofconstruction
method.
It rationalizes
the construction
workexecuted
can berapidly
by simplified
construction
work
canexecuted
be executed
rapidly
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ways:damsofmaterials:
because
the
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body
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in“Rationalization
three
ways:
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becausein three ways: “Rationalization of materials: because
facilities.”
facilities.”

ProtectionProtection
concrete concrete

CSG

CSG

ProtectionProtection
concrete concrete

Structural Structuralconcrete concrete
InspectionInspection
gallery gallery
Seepage control
concrete
Seepagecontrol concreteRich mix CSG
Rich mix CSG

Auxiliary curtain
grouting
Auxiliarycurtain grouting
Foundation
drain holedrain hole
Foundation
Curtain grouting
Curtain grouting

Figure-11
Conceptof Trapezoidal
CSG
dam damFigure-11
Conceptof Trapezoidal
CSG
Figure-1
Conceptof Trapezoidal
CSG
dam

Sediment bypass tunnel (SBT)
SBTs are one sustainable and effective strategy against
sedimentation. The SBT connects upstream anddownstream of a dam and bypasses sediment-laden floods
into downstream. They are mainly operated in Japan,
Switzerland and Taiwan.
In Japan, SBTs are operated at the oldest

Figure-12
Tobetsu
DamDamFigure-12
Tobetsu
Dam
Figure-2
Tobetsu
concrete dam in Japan, Nunobikigohonmatsu Dam (1900),
Tachigahata Dam (1905), Asahi Dam (1998), Miwa Dam(2005). Also, they are currently undergoing trial operation
at Koshibu Dam and Matsukawa Dam. The problem of SBTs
is countermeasure against invert abrasion and elucidationof sediment hydrological behavior, and research is currently
under way.

Figure-3 Sediment bypass tunnel (SBT)

Figure-4 Miwa Dam

Preservation measures of dam reservoirs

One of water quality preservation measures for the dam
reservoir is conducted by controlling outflow of pollutant
and nutrient salts from the catchment area.

Water quality issues are closely associated with the size ofthe dam reservoir, and operation of the dam reservoir.

25

DAMS IN JAPAN - OVERVIEW 2022

Fence

Aerating circulation

Fence
Fence

Aerating
circulationTo change water temperature distribution or other
Aerating
circulation
conditions inadequate for algae growth

To prevent the spread of algae or to shift thenutrient flow away from surface to middle layer

To change water temperature distribution or otherTo changewatertemperature
distribution
conditions
inadequate
for algae
growth or otherconditions inadequate for algae growth

No operation

To prevent the spread of algae or to shift the
To preventthe spreadof algaeto shiftthenutrient
flow awayfrom surface
to or
middlelayer

nutrient flow away from surface to middle layer

Operation

No operation
No operation

Operation
Operation
Upper stream
Upper stream

Lower stream Upper stream
(Dam
side)
Lower
stream(Dam
Lowerside)stream(Dam side)

Figure-19
Reservoir
Water quality
facilities
Figure-5
Reservoir
water quality
improvement
facility
Figure-19 Reservoir Water quality facilities
Figure-19
SunlightReservoir Water quality facilities

Inflow ofnutrients
Inflowofnutrients

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Algae blooms

Inflow ofnutrients

Algae blooms

Algae blooms
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To reduce the load of
To reduceload reservoir
ofAuxiliaryDamnutrients
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nutrients to a dam reservoir
with particulate nutrientswith particulate nutrients
To reduce
settledthe load ofsettlednutrients to a dam reservoir
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settledAlgae blooms

Shading

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Auxiliary Dam
Auxiliary Dam

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Selective

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Selective
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To select adequate water depth to
Selective

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selectadequatedepth
tointakebetterwater
qualityof waterintake better quality of water

To select adequate water depth tointake better quality of water

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BypassBypassTocut
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Figure-20Example
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measures
Figure-20
of ofqualityconservation
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Figure-20
of ofqualityconservation
measures
Figure-6Example
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measuresto time.
to time.

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Therefore,
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Actual waterlevel
Nabari River

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Actual water level

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Urban areaof NabariCity

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8.0Design high Water level

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Water level at Nabari City, downstream of 3 dams

Water level at Nabari City, downstream of 3 dams

･Heavy rain due to big typhoon threatened to cause inundation in Nabari River on
Murou
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inundation
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Nabari City,
downstream
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level,
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underitsbelow
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waterlevel atO&M
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of each of the three dams under its integrated control.
flood
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Figure-21
through
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･The above figures
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Figure-21 Flood control through integrated and collaborative operation of three dams

Figure-7
Floodcontrolthrough
integrated
and collaborative
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Figure-21
Floodcontrolthrough
integrated
and collaborative
operationof threeof
damsDAMS IN JAPAN - OVERVIEW 2022

Dam Upgrading Vision
It is important to effectively use existing dams while
controlling total costs. Various technologies will beadvanced as the number of cases of the effective use ofexisting dams grows.
On the other hand, more frequent and intense flood
damage and more frequent droughts are concerns. Under
this context, dam upgrading will be promoted by effectively
using existing dams applying both hard and soft measuresaccording to each basin’s characteristics and issues.
The “Dam Upgrading Vision” which provides a strategy
for the further promotion of dam upgrading efforts that
effectively utilize existing dams has been formulated
in 2017 by MLIT. These strategies for the vision are
categorized below.
1) Dam Life Extension2) Promoting Efficiency and Advancement of Maintenance3) Flexible and Reliable Operation to Optimally Utilize the
Capacity of the Facility4) Improving Facilities for a more Advanced Functionality
5) Responding to Climate Change
6) Addition of Hydropower
7) Protection and Revitalization of River Environment8) Regional Development utilizing the Dams
9) Promoting Dam Upgrading Technologies Overseas
10) Development and Implementation of Technologies toPromote Dam Upgrading
A typical example of utilizing an existing dam is shown in
the figure.
This method is a temporary installation method that canbe used to add penstocks for power generation and flood
discharge pipes to the existing dam body without lowering
the water level of the reservoir.

26“Floating Type Temporary Cofferdam Method”
Conventional cofferdam construction requires long
diving hours at a very deep water depth, large temporary
equipment, and a long construction timeframe.
For the floating type temporary cofferdam method, steel
plates (skin plates) are attached to both the inside andoutside of the bulkhead to make an watertight structure,and this becomes the buoyancy chamber to make thebulkhead float. It is important to maintain the balance
between buoyancy forces and dead weight by filling anddraining the bulkheads blocks in the proper order.
For actual construction, bulkhead blocks made at local
factories will be assembled on the reservoir as a cofferdam
which will be towed to the installation position by a ship,and subsequently pulled by a winch and secured.
And then, water is drained from the cofferdam.
And this new method was used for the first time in the
Tsuruda Dam upgrading.
＜ Efficiencies of this method ＞
This is dependent on scale of the cofferdam andconstruction depth, as large temporary facilities, such aspedestal concrete and support framework, are unnecessary
and diving work can be greatly reduced, costs andprocesses can be reduced, and safety can be improved,
leading to an increase in construction efficiency.
Moreover, when drilling holes in the same dam, it isnecessary with conventional methods to dissemble and thenreassemble the bulkheads, but with this method there is noneed to disassemble the bulkheads; flood the cofferdam anddetach the bulkheads from the dam-body and tow it as is tothe next construction site where it can be installed.

27

DAMS IN JAPAN - OVERVIEW 2022

―New Temporary Cofferdam Methodー

Floating Type Temporary Cofferdam Method
The workability of the temporary cofferdam method can be significantly improvedby watertight structure in each bulkhead to provide buoyancy

1.Loading of Bulkheads on the barge－onto the barge on the reservoir―

2.Transportation of bulkheads toassembling area by the barge－reservoir transportation―

Skin plate

Assembling area

Buoyancy chamber

Bulkhead

Overview of bulkhead

The barge
The barge for transportation【Completion of Installation】
3.Assembling of bulkheads on thereservoir

Bulkheadunderassembling

Bulkheadunderassembling

Lowerbulkhead under thewater-Heighten Workability

Heighten Safety

Shortened Period

Cost Reduction

Overview of assembling

Lowerbulkhead

４．Towing & Installation－dewatering from the temporary cofferdam forfloating and positioning of the temporary cofferdam―

5.Dewatering from the temporary cofferdam－securing a dry working space inside
the temporary cofferdam―

Integrated
temporarycofferdam

Direction dewatering＆Overview of towing

positioning

Dewatering

All work from assembling of bulkheads to installationof temporary cofferdam can be done on the reservoir

DAMS IN JAPAN - OVERVIEW 2022
Utilization
ofin
ICTconstruction
in constructionofof damdam
Utilizationof ICTThe constructionindustry
in in
Japan
aims
at at
drastically
The constructionindustryJapan
aims
drastically
improvingproductivityofall
construction
production
improving productivity of all construction production
processes by utilizing ICT, and its approach is called
processes by utilizing ICT, and its approach is called ii-Construction.
Even Construction.
in the construction of dams, the utilization of ICT
Evenadvancedin the construction
dams, the utilization
ICTsitehas
has been
towardofimproving
quality, ofsafe
advanced
improving
quality,site work,
work,beenshorteningof toward
construction
period,and safe
reductionofconstruction
cost.of construction period, and reduction ofshortening
construction cost.

28

In addition, using ICT to share information in real time andto utilize and accumulate 3-dimensional data can contributetoaddition,a dramatic
rationalization
actions throughout
the damInusing
ICT to shareof
informationin real timelife tocycle
fromdesign stage,
the construction
andutilizeandtheaccumulate
3-dimensional
data canstage tothe operation and maintenance stage.

contribute to a dramatic rationalization of actions
throughout the dam life cycle from the design stage, theconstruction stage to the operation and maintenancestage.

Figure-●ApplicationofofICTICT forfor DamFigure-8
Application
DamConstruction
Construction

29

DAMS IN JAPAN - OVERVIEW 2022

Papers in ICOLD & Other Technical Publications
Papers in ICOLD and EADC
Theme 1

Safety management and rehabilitation of existing dams

A. 10th East Asia Dam Conference in Zhengzhou, October 2018
Issues seen in existing concrete dams as the result ofcomprehensive inspections
K.Yamagishi, S.Takasu
As an effort to extend dam service life, comprehensive
dam inspections were systematized in Japan in 2013,and comprehensive inspections are being carried out ondams that are roughly 30 years old. Comprehensive dam
inspections is carried out by each dam manager applying
technological expertise to perform a comprehensive factfinding survey and evaluation of the soundness of thestate of maintenance and degree of deterioration of civilengineering structures of the dam, which are the constituent

elements of each dam. Comprehensive soundness of civilengineering structures of dams in particular, are evaluatedby additionally performing advanced surveys on items
which cannot be easily surveyed in daily and periodical
inspections for methodological and cost reasons, and items
which could deteriorate over time. This study organizes
the results of comprehensive dam inspections controlled
under the Ministry of Land, Infrastructure, Transport andTourism (MLIT) implemented for dams in Japan in recent
years, looks at issues to note during comprehensive dam
inspections, methods for examining issues, procedures forevaluating examination results, and summarizes the trend inmaintenance issues for concrete gravity dams.

B. ICOLD 87th Annual Meeting International Symposium in Ottawa, June 2019
Design of seismic reinforcement by post-tensioned anchorsin Senbon Dam
H.Kawasaki, S.Ishifuji, and H.Fukumoto
Senbon Dam is a water supply dam with 17 meters highoperated by Matsue City, which was completed in March
1918. Since this dam is an old gravity type masonry dam
and the cross section is also thin, Matsue City will performthe seismic reinforcement with post-tensioned anchors in2019 and 2020.
As for experiences of the reinforcement by post-tensioned
anchors for dams in Japan, there are old cases such as theconstruction of the auxiliary dam in the Fujiwara dam in1955 and the reinforcement of the rock abutment in the
Kawamata arch dam in 1963. However, under the latest
requirement of high durability and high capacity, it is thefirst domestic experience of dam body reinforcement by the
post-tensioned anchor in Japan.
As technical points for applying the post-tensioned anchor
to the Senbon Dam, there are following issues: “copingwith a large load at narrower dam crest, construction
method of the overflow part that occupies 2/3 of the dam
length, solution to partial weak zones in the foundation,
preservation of masonry dam landscape and others”.

C. ICOLD 88th Annual Meeting International Symposium & 5th APG Symposium in New Delhi, February 2021
Japan’s “Follow-up System for Management of Dams”
and its achievements
Y.Mogami, N.Asai, K.Sakamoto, T.Hara and G. Yasuda
The Ministry of Land, Infrastructure, Transport and Tourism(MLIT) of Japan started test operation of the Follow-up
System for Management of Dams (FUSMOD) in 1996 andits regular operation in 2002. FUSMOD aims to facilitate

statutory post-assessments of dam construction projects,
and to improve management of 141 dams and reservoirs
operating under the jurisdiction of MLIT. To comply withFUSMOD, each dam owner is required to perform surveys
for post-environmental assessment as well as for the postassessment of the project in charge. These post-assessments
are not once-and-for-all type but a series of periodical
reviews of dam projects. Using the results of surveys, eachdam owner periodically reviews the hydrological records toDAMS IN JAPAN - OVERVIEW 2022
examine the performance of flood control and water supply,changes on sedimentation, water quality, flora and fauna,demography and regional economic effects. FUSMOD, byanalysing data generated through various surveys and daily
management, provides an opportunity for dam owners torealize how they need to rectify their management of dams.
We demonstrate the benefits of FUSMOD by describing
examples of operations that have been successfully rectified
under FUSMOD. These include improved operation of water
quality control facilities such as selective intake facilities
and aeration facilities based on continuous water quality
survey results. Another example is review of survey plan
for water quality. The changes contributed to more efficient
dam management through acquisition of pivotal data fordam management. Under FUSMOD, measures for controllinginvasive alien species introduced in connection with dam
construction projects, and evaluation of the impact ofdams on local industries through water supply and theirrecreational function, for example, are also studied. The
results lead to rectify related policies and procedures.
FUSMOD enables dam owners to conduct meta-analysis
through analyses and assessment results for various dams.
The achievements thanks to meta-analyses include revisionsof reservoir water quality survey guidelines and reservoir
sediment management guidelines. Moreover, FUSMOD,
through continuously released summaries of analyses andassessments to the general public by MLIT, ensures dam
management is accountable.

Theme 230

Establishment and implementation of the emergency
action plan on the Nam Ngiep 1 Hydropower Project in
Laos
T.Tabuchi, Y.Aosaka, I.Sakai, Y.Yamamoto and S.Tsutsui
A 167 m high roller-compacted concrete (RCC) dam anda 270 MW main power station are being built in the Lao
People’s Democratic Republic (Lao PDR) under the Nam
Ngiep 1 Hydropower Project (NNP1). The large reservoirof 70 km in length, 67 km2 in area and 2 billion m3 involume has such risks as floodwater releases, extraordinary
dam behavior and so on, that may impact human lives andproperties along the downstream river basin. An Emergency
Action Plan (EAP) consisting of dam emergency events,
hazard map, notification, preparedness, and its procedure,
is being established to mitigate issues caused by the aboverisks. So far, actions related to issues of extraordinary dam
behavior have been taken twice during initial impounding.
The reservoir water level was lowered to secure dam
stability when the uplift pressure increased rapidly. A
notification drill for emergency cases is being prepared by
NNP1 and the Lao Government before starting commercial
operation. This paper presents the process of establishing
the EAP and its actions.

New construction technology

A. 10th East Asia Dam Conference in Zhengzhou, October 2018
Countermeasures for shorten the constructionof Yamba dam
M.Kimura, T.Hiratsuka
Yamba concrete gravity dam with a height of 116 m anda volume of about 1,000,000 m³, is under construction on
the Agatsuma River which is a branch of the Tone Riverthat flows through the upstream region of the Tokyo area.
The purpose of the dam is flood control , water supply,and hydro power, which is expected to be completed at
an early period. The concreate placement period is being
greatly reduced by measures as follows; using the Roller
Compacted Dam-concrete (RCD) method for rationalizing

the construction; shortening the construction period byextending the concrete placing facility to improve theplacement speed; shortening the installation period by themethod of preassemble and transfer of the flood discharge
conduits facilities; adoption of precast members for outlet
facilities and gate chamber, diversion which was installedin the dam body, inspection gallery and elevator shaft,overhang zone and changing point of slope gradient; andincreasing the number of days of construction during winterby taking special countermeasures, etc..

31

DAMS IN JAPAN - OVERVIEW 2022

B. ICOLD 87th Annual Meeting International Symposium in Ottawa, June 2019
Development of blasting management system and its
application to verification of ground evaluation using
logging while-drilling
K.Nagai, M.Yamagami and S.Katayama
Concrete aggregate production in dam construction isplanned according to the distribution of good quality
rocks estimated by preliminary surveys such as borehole
exploration and geophysical survey. The accuracy inestimating the distribution of good quality rocks depends
on the quantity of sur- vey and is generally low. This maylead to a limited enhancement in the aggregate production
efficiency. To resolve the problem, we developed arock blasting management system, which consists of arational construction technique with an information andcommunication technology (ICT), and a demonstration
experiment at a dam site. In this report , we will describe
the overviews of the aggregate production work at
the Gokayama Dam and the developed rock blasting
management system with the results of a verification
experiment on the drilling survey and a demonstration
experiment at an aggregate production site.

Tallest RCC gravity dam in Lao PDR - need for high speed
and solutions adopted at the Nam Ngiep 1 Hydropower
Y.Aosaka, T.Seoka, and S.Tsutsui
The high production rate of roller-compacted concrete
placing which achieved during the construction of the main
dam of the Nam Ngiep 1 Hydropower Project in Laos is
outstanding.
The demand for the high pro duct ion required themobilization of materials, equipment, system and humanresources to satisfy the Project’s need for the rapid RCC
placing rates averaging 97,500 m3/month and led the
Project to select the compatible and optimum production,transporting and placing facilities. The optimization andselection of all in relating to RCC facilities are discussed inthis paper. Furthermore, this paper discuss construction
techniques and solutions adopted during construction toachieve the high productivity and efficiency while retaining
the best quality and safety, and which includes the following
6 items,
1) Materials: Supply of materials from outside which are
cement, fly ash and quarry; 2) Equipment: Optimization of all
equipment which are crushing plant, aggregate stockpiling;
RCC batching plant and RCC delivery conveyor belt; 3)
System: Remarkable success of Sloped-Layer Method toachieve high production rates; To obviate manual trimmingof feathered edges; 4) Safety procedure in regard to RCC
placing; 5) Systematization of procedure in regard to dam
zoning; 6) Human resources: Education and establishmentof human relations.

C. ICOLD 88th Annual Meeting International Symposium & 5th APG Symposium in New Delhi, February 2021
Unmanned Maintenance Work with Underwater Remotely
Operated Vehicle (ROV) for Discharge Facilities of Dams

The introduction effects of 3D information models in
Koishiwaragawa Dam Construction Project

S.Uchida, M.Kaida

T.Miyazaki, T.Yoshida

For maintenance work of discharge facilities of dams,manned diving operations have been usually implemented.
And in some cases, they have been carried out in deep waterover 40 meters. However, manned diving puts divers at therisk of fatal accidents. Therefore, the use of an unmanned
underwater Remotely Operated Vehicle (ROV) will makethe maintenance works safe, and also will contribute to cost
reduction by avoiding the use of expensive diving support
equipment.
As a first approach, we developed an underwater ROV tocarry out the work for setting a water shut-off cover at the
tap of water filling pipe facing reservoir water. We tested
this work in a laboratory water tank and then at actual damsites. The evaluation results of the test at actual dam sites
suggest that this work is ready for practical application.

The Construction Project of the Koishiwaragawa Dam,
which is a rockfill dam and is to start operation from
April 2020, is conducted by the Japan Water Agency. This
project is a leading case of applying Three Dimensional (3D)
information models to the design and construction processfrom the early stages of the owner’s work. In Japan, the 3D
information model in the civil engineering field is called
Construction Information Modeling/Management (CIM).3D
graphic models of the dam and surrounding structures
were developed before starting construction of the dam
body. Using Navisworks, an integrated application from
Autodesk, the models incorporated a lot of constructionrelated information such as geological data on dam siteand quarries, quality control data on embankment andmonitoring data of the measuring devices installed in the

DAMS IN JAPAN - OVERVIEW 2022
embankment. This made it easier to recognize each data
spatially and chronologically, to grasp the construction
process, and to share the acquired information among
relevant people, eventually streamlining the entire work
process. Currently, we are planning to upgrade this system32

to make the record management around the dam andreservoir more efficient, by inputting monitoring dataof the displacementdam body, surrounding slopes andpatrolling record data into the 3D models after the initial
impoundment.

E. 27th ICOLD World Congress in Marseille, June 2022
Dam concrete automatic placement system – complete
automation of dan concrete materials supply, production,transport, and placement -Investigation measures and controls against internal
restraint cracks due to thermal stress of RCC dam practice at Nam Ngiep 1 Hydropower project in Lao PDR -N.Yamashita, T.Kase, S.Tachihana, S.Moriyama, and H.Mori

Y.Aosaka, S.Tsutsui, T.Kawata, and B.Egilat

The concrete placement of concrete gravity dams accounts
for about 60% of the construction cost and about 50% of
the construction time. The operations for the concreteof production, transport, and placement are repeated forseveral years. The concrete placement also requires many
experienced skilled workers for the operation of large heavymachines and the compaction work. When rail rope cablecranes are adopted for the concrete transport, the cranemanipulation becomes a complex 3-dimensional operation,
so greater experience and skill than usual are required.
Therefore, we developed a "dam concrete automatic
placement system" that aiming to automate the series ofprocesses of a material supply to the batching plant, a
concrete production, a concrete transport by a transfercar, and a transport and placement using a rail rope cablecrane. This system integrates the automation technologythat has previously been applied to the batching plant andtransfer car, etc., with automation of the rail rope cablecrane. This system was applied to about 40,000 m3 in the
213,000 m3 of total concrete using the rail rope cablecrane on Yanagawa Dam (Morioka City, Iwate Prefecture),
and the following effects were obtained as a result of
its introduction. First, the cycle time per placement was
reduced by about 20 seconds from 3 minutes 40 seconds toabout 3 minutes 20 seconds, a 10% reduction in time. The
placement time for the approximately 40,000 m3 to which
this system was applied was reduced from 533 hours to
494 hours. Secondly, the number of workers required forplacement in the dam was 2 crane operators, 6 batchingplant operators, and 7 for concrete placement, or a total of
15 workers. However, by adopting this system it is expectedthat this conventional number of workers can be reduced
to 2/3, with 1 crane operator, 4 batching plant operators,
and 5 concrete placement workers, or a total of 10 workers.
Thirdly, by automating operation of rail rope cable cranes
with this technology it is possible to automatically andrationally transport the concrete bucket to the placement
position, so the operation can be performed with the same
work efficiency as a proficient operator despite the shortageof experienced operators, so this technology can help torespond to the shortage of proficient operators.

During construction of the Roller Compacted Concrete (RCC)
dam at Nam Ngiep 1 Hydropower Project (NNP1) in Lao
PDR, cracks in the direction of the dam axis emerged on thesurface of the RCC placing on the left bank side where RCC
placing had been suspended in order to install penstocks
that would be embedded in the dam body. The NNP1 Power
Company conducted a crack investigation and thermal stressanalysis by applying the observed ambient temperatureand variation in RCC strength, and was found that the maincause was the difference in concrete temperature between
inner and surface portions of the RCC due to a sudden dropin ambient temperature in the middle of December 2017that was larger than what occurs in an average year. This
paper presents the process of the above investigation,
related root cause analyses, dam stability check and effective
measures taken to control cracks in RCC.

Introduction of 100% inspection based quality control
method in embankment dam construction
H.Sakamoto, K.Someya, and Y.Matsuoka
One of the problems of conventional quality control methodin embankment dam construction is that it is difficult toconfirm the uniformity of quality throughout the entire
embankment. To resolve this issue, we introduced 100%
inspection-based quality control at Koishiwaragawa Dam(an earth core rockfill dam in Japan, H = 139 m). This newquality control comprises two quality control methods. The
first is 100% inspection-based quality control through theapplication of ICT toward three elements that determine
the engineering properties of embankments: (a) grain
size distribution, (b) water content during construction,and (c) compaction energy level. The second is ICDM ofimpermeability performance based on upper boundary
control of compacted soil stiffness .The development ofthese methods makes it possible to gain a understanding of
the spatial and temporal distribution of measured values ofeach control item and substantially streamline the quality
testing process to be performed on compacted embankment
surfaces. This paper described the overview that went into
applying these new quality control methods, as well as theresuts of applyment for Koishiwaragawa dam construction.

33

DAMS IN JAPAN - OVERVIEW 2022

Theme 3Spillway and outlet works

A. 10th East Asia Dam Conference in Zhengzhou, October 2018
Hydraulic design in upgrading dams under operation
T.Sakurai, T.Ishigami
In Japan, the Ministry of Land, Infrastructure, Transport
and Tourism (MLIT) presented a "MLIT's Vision to Upgrade
Dams under Operation" in June 2017. The vision introduces
countermeasures to advance the upgrading of existing dams
by applying both structural and non-structural measures toensure that they are used more effectively than in the past.
There are cases raising the dam body and increasing thedischarge capacity of the discharge facilities etc. in the past.
At some existing dams, improvement projects are currently

under construction.
There are challenges in hydraulic design of improvement
and additional construction of discharge facilities in dam
upgrading different from the construction of a new dam.
Methods to cope with these challenges have been examinedby hydraulic model experiments and so on. In this report,
the outline of three major technologies to increase thedischarge capacity in dam upgrading, cutting dam body,
drilling dam body and tunnel spillway, are introduced.
And taking Nagayasuguchi dam remodeling project as arepresentative example, the contents of the hydraulic designof the existing dam redevelopment project are explained.

B. ICOLD 87th Annual Meeting International Symposium in Ottawa, June 2019
Applying CFD analysis to scouring river bed caused bydischarge flow from the dam and estimating effectivenessof some countermeasures

The method for increasing the waterpower generationby using the storage volume for flood control in themultipurpose dams

K.Hirao, F.Watanabe, S.Ohmori, T. Tsukada, and T. Kurose

H.Takeuchi, T.Ikeda, S.Nagasawa, and S.Tada

Unexpected scour in a river had been observed at thedownstream area nearby the discharge channel of the
dam-type hydropower station of the Tokyo Electric Power
Company Holdings, Inc. We assumed that rotational or
three-dimensional (3-D) water flow induced by complicatedriver bed shape and retaining wall arrangement could
be the cause of the scour described above. Applying 3-Dcomputational fluid dynamics (CFD) analysis, we clarify theflow structure relating the scour and study the main factorof the scour. We also validate the effectiveness of somecountermeasures against the scour by the CFD analysis. In
one countermeasure, we alter the shape of the discharge
channel outlet for the purpose of reducing the flow to theobserved scour area, and results from the 3-D CFD analysis
show the flow accomplished our aim.

In Japan, in recent years, it has become increasingly
important to make the maximum effective use of dams now
in operation. At multipurpose dams managed by the Ministryof Land, Infrastructure, Transport, and Tourism (MLIT) of
Japan, the capacity for water use is clearly discriminatedbetween the capacity for flood control and for water use
such as power generation etc., but storing part of reservoir
capacity for flood control and using it for hydropower
generation etc. is considered as a method of more effective
use of reservoir capacity. In this case, it is necessary to
perform preliminary discharge quickly when flooding ispredicted to ensure capacity for flood control, and when
performing preliminary discharge, it is necessary to avoid
abrupt raise of the water level in the river downstream fromthe dam. Considering such restrictive conditions, possible
capacity for power generation in the capacity for flood
control was calculated at two multipurpose dams on T River
System, M dam and K dam. And the capacity which can be
stored newly in two dams is 27% and between 4 and 6% of
capacity for flood control respectively. And the results ofa simulation have shown that when the new capacity for
power generation has been used up, it is difficult to recover
it because of the small inflow into the reservoirs. And theincrease of power generation obtained from the capacity
newly stored at two dams was small at only about 0.89%.
But, in the future it will be necessary to expand such studies
to cover all dams in Japan in order to consider the feasibilityof increasing generated power.

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34

C. ICOLD 88th Annual Meeting International Symposium & 5th APG Symposium in New Delhi, February 2021
Study of Computational Fluid Dynamics Analysis with
Design on the Spillway of Hydroelectric Power Plant
M.Masuda, F.Watanabe, and S.Takano
In modification of the designing of the spillway used in ourcompany’s hydroelectric power plant, we conducteda hydraulic model experiment based on the conventional
method. Using the results of this experiment, we performed
a reproducibility analysis with the aim of substituting
computational fluid dynamics (CFD) analysis for hydraulic

Theme 4model experiments in further design changes such as cost
reduction studies. Based on the results of our detailed
examination of the analysis model, such as changing
the mesh size or applying an air entrainment model, we
concluded the flow of hydraulic model experiment could
be reproduced with high accuracy by CFD analysis. As aresult, the prospect of substituting the CFD analysis for theexperiment was obtained.

Sophisticated approach for dam operation

B. ICOLD 87th Annual Meeting International Symposium in Ottawa, June 2019
Development of new simulator for training of dam
operation and its future outlook
K.Tamura, S.Kano
In recent years, severe floods caused by super-typhoons,linear rain bands and localized torrential rain, etc. occur
frequently in Japan. Based on this fact, more advanced
and proper dam operation by grasping the water level ofthe downstream rivers of dams is required to minimize
the occurrence of flood damages in downstream of dams,
especially in urban areas etc. Japan Water Agency (JWA) has
developed a new simulator which enables acquisition of skill
for proper dam operation. The developed simulator abounds
in ingenuity for training by reproducing close to reality
situations for flood control operation through changing theriver flow of downstream along with outflow discharge fromthe dam after reflecting the river flow situations caused byrainfall in upstream and downstream areas. Furthermore,
the simulator replicates the transition of rainfall, inflow to
the reservoir and water level in downstream of the dam,in addition to the replication of operational feel of dam
control facilities and has functions which enable to simulate
all of the past floods which have been experienced since
beginning of JWA’s operation.

Improving prediction of river-basin precipitation by
assimilating every-10-minute all-sky Himawari-8 infrared
satellite radiances – a case of Typhoon Malakas (2016)
S.Takino, T.Tsukada, T.Honda, and T.Miyoshi
To operate hydroelectric power dams more effectively,
it is essential to obtain accurate precipitation forecasts.

This study aims to improve precipitation forecasts byassimilating every-10-minute all-sky Himawari-8 infrared
radiance observations. We use an advanced ensemble
data assimilation system developed in RIKEN. This study
focuses on a single case of Typhoon Malakas (2016) which
induced heavy precipitation in the mountain region ofcentral Japan. The results demonstrate that assimilating theHimawari-8 radiance observations significantly improves
the representation of Typhoon Malakas (2016) and cloud
patterns. Moreover, ensemble forecasts initiated fromthe Himawari-8 data assimilation provide more accurate
precipitation forecasts with uncertainty information. In
particular, the forecasts with a longer lead time exhibit abetter forecast skill compared to the Japan Meteorological
Agency’s operational regional model. These promising
results suggest that assimilating the every-10-minute allsky Himawari-8 radiances be effective for improvinghydroelectric power dam operations by providing moreaccurate precipitation forecasts.

Dam operation support system utilizing Artificial
Intelligence (AI)Y.Hida, H.Takiguchi, K.Kudo, and M.Abe
In Japan, droughts and flood damages caused by abnormal
heavy rain have occurred frequently due to the influenceof climate change, so flexible operation that maximizes thefunction of the existing dam is required. With the changeof social situation, efficient dam operation by only a few
operators is required. On the other hand, in recent years, with
the improvement of the processing capacity of computers,
the utilization of artificial intelligence (AI) is becoming
widespread. By recreating the dam operation made by using

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DAMS IN JAPAN - OVERVIEW 2022

human intelligence by computer, it is expected to improve
efficiency and speed up process judgment. Here, in orderto realize the advanced flood routing in dams by only a few
operators, we studied the dam operation support systemutilizing artificial intelligence (AI).

Application of mechanical facilities support system using
tablet terminals for dam management
T.Yoshida, Y.Matsumoto, and K.Sasaki
Activities of operation and maintenance of mechanicalfacilities for dam management are quite diverse, which

include inspection work, support for troubleshooting, andothers. There are many management offices, in which only
one mechanical engineer is assigned. Therefore, needs forsupport in improvement of operation and maintenancework, support for troubleshooting, and technical support
for young mechanical engineers were growing. To copewith those, we are building a management support systemof mechanical facilities using tablet terminals and WEB
applications. It helps works such as inputting inspection
data, accessing various dates through the network, andseveral supports by videophone. This paper reports its
function and the method of the application.

D. ICOLD 89th & 90th Annual Meeting International Symposium in Marseille, November 2021 and May 2022
Decision support for preliminary release of reservoir forflood control using ECMWF medium-range ensemble
rainfall forecast
D.Nohara, K.Kitani, Y.Michihiro, and T.Sumi
developed by considering medium-range ensemble rainfall
forecast provided by European Centre for Medium-Range
Weather Forecasts (ECMWF) to enhance reservoir’s flood
storage capability while maintaining its function for wateruse. Preliminary release operation, in which storage
water for water use is released just before a flood occurs,
is considered here. The desired timing and amount of
preliminary release are estimated from ensemble prediction,
maximizing the flood control capacity while securing storage
recovery after the flood event. The case study with ShinNariwagawa Reservoir in the Takahashi River basin, Japan,
demonstrated the effectiveness of introducing long-range
ensemble prediction in decision making for preliminary
release.

Challenges in flood control operation and dissemination of
information -Lessons from the record-breaking heavy rainin July 2018, JapanT.Sumi, M.Mitsunari, and T.Hamaguchi
In July 2018, a record-breaking heavy rain hit westernpart of Japan, leaving severe damages. 213 dams under
the jurisdiction of the Ministry of Land, Infrastructure,
Transport and Tourism (MLIT) were engaged in flood
control operation, and greatly contributed to the reductionof flood damages. Meanwhile, in case of 8 dams, the amountof rainfall was so huge that the emergency spillway gate
operation by discharging equal to inflow volume wasobliged to execute which caused severe flood damages insome of the downstream areas. In December 2018, Special
Panel set up by MLIT finalized a report urging enhancementof flood control capability of dams and dissemination ofrelated information, in preparation for the risk of extreme
rainfall which may increase under changing climate
condition. This paper briefly introduces the report, outlining
the flood control activities at the 2018 flood event as well as
the contents of the proposal.

Development of effective pre-release method for dams
during super typhoons using long-term ensemble rainfall
forecasts
K.Kido, H.Tano, T.Sumi, D.Nohara, Y.Michihiro, and K.Kitani
Against the background of increasing frequency of heavy
rainfall due to climate change, an analytical approach tomaximize the effective use of the reservoir from both flood
control and water utilization was conducted. Simulations
by applying statistical down-scaling method to the longterm ensemble rainfall forecast by ECMWF on a dam basin
where a large inflow occurred during the Typhoon Hagibis
in 2019 were shown. The results show that it is possible
to use long-term ensemble rainfall forecasts to gain atemporal, stochastic understanding of total rainfall, required
flood storage volumes, and recoverable reserves. Based on
this understanding, a calculation method for setting release
rates that correspond to effective pre-release start times andchanges in rainfall forecasts in order to minimize both flood
control and water service risks was proposed.

DAMS IN JAPAN - OVERVIEW 2022
Development of the snowmelt prediction model using
Artificial Intelligence (AI)36

Study on PMP estimation for the flood risk evaluation ofhydropower dams in consideration of the future climatechangeM. Abe, H.Takiguchi, and Y.Hida1
Droughts and abnormal heavy rains have frequently
occurred in Japan due to the effects of climate change inrecent years, and flexible operations that maximize thefunctions of dams are required. Especially in cold snowy
regions, snowmelt water is stored in a dam to cover water
demand from early spring to early summer, but during thesnowmelt season, a sudden rise in temperature and heavy
rain could cause large-scale floods. Therefore, the highly
accurate prediction of dam inflow during the snowmelt
season is extremely important from the viewpoint ofeffective use of water resources and prevention of snowmelt
floods. On the other hand, in recent years, research utilizing
Artificial Intelligence (AI) has also been promoted in thehydrological field.
This study clarified the problems of the conventional
physical model (rainfall runoff model) and the prediction
model by AI for the inflow of the dam during the snowmelt
season in order to support efficient dam management. Then,by constructing a semi-physical model that complements
the problems of the physical model and the AI model, wedeveloped a more accurate model for predicting the inflow
of snowmelt water during the snowmelt season compared tothe single model.

Y.Kobayashi, E.Nakakita, T.Takemi, Y.Otsuru, and T.Abe
It is important for hydropower dams to estimate PMP(Probable Maximum Precipitation) appropriately and toprepare the plan of facilities modification and operationalchanges in advance, because the future flood risk by
climate change influence is getting higher. In this paper,
we compared three methods of PMP estimation, theconventional method applying DAD (Duration Area andDepth) analysis based on the experienced rain results, theproduct of d4PDF (database for Policy Decision making
for Future climate change) that is the latest climate model
ensemble prediction, and the pseudo-global warming
experimental results on the typhoon.
It was showed that PMP by d4PDF and the pseudo-global
warming experimental results were larger than that by
DAD analysis and fluctuated smoothly and reasonably overtime. It is preferable and reasonable to evaluate the PMP
risk applying DAD analysis at the rough examination, andthe estimations applying d4PDF or pseudo-global warming
experiment is suitable for more detailed examination.

E. 27th ICOLD World Congress in Marseille, June 2022
Dam body behavior monitoring by GNSS on Hachisu dam
and applicability

Benefits of introducing an ICT-based staff support systemfor disaster response work along the lake Biwa shoreline
and its extended uses

K.Tomita, T.Sumi, A.Suzuki ,S.Jikan, S.Noyori, N.Sato, and C.Araya
Hachisu Dam is a concrete gravity dam, 78 m in dam height.
Nearly 30 years have passed since the completion and thedam comprehensive inspection has been implemented. Aspart of the dam comprehensive inspection, a dam bodydeformation monitoring system using GNSS was introduced
in Hachisu Dam in order to clarify the factors of dam bodydeformation measured in the plumb line.
This paper first reviewed the dam safety management
system in Japan and the status of technical developmentin GNSS used in existing dams. Then, this paper studied
the measurement values of GNSS, which is being used formeasurement in Hachisu Dam, and the existing plumbline using multiple regression analysis and verified
the applicability of GNSS in the dam body deformation
measurement of Hachisu Dam and reported issues toaddress in the future concerning GNSS.

M.Nakashima, S.Haruna, Y.Iwamatsu, S.Uchida, A.Goto,and K.Hatano
The Lake Biwa Development Integrated Operation &Maintenance Office (hereinafter "Lake Biwa O&M Office")of the Incorporated Administrative Agency Japan Water
Agency faced the challenge of "to establishing a quick, safeand reliable operational system for all staff, regardless ofjob type" for the operation of drainage pump stations fordisaster response work in 2013 during the incidents suchas the total paralysis of public transport and road closurescaused by flooding. Given the small number of specialized
technical staff, there was a limit to how many of the staff
can respond to pump and other equipment problems during
disaster response work. Thus, it became necessary to makeit possible for "all staff to be competent to handle faults atleast at a minimum level."
To solve these problems, the Lake Biwa O&M Officedeveloped and introduced two systems that utilize ICT(Information and Communication Technology).
One system is the "Drainage Pump Station Operational

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DAMS IN JAPAN - OVERVIEW 2022

Support System". It makes it possible to operate equipment/
facilities by following the image and automated audio
navigation steps displayed on a tablet screen, which shows
the steps required to operate the drainage pump station in
the form of a 'mission card'.
The other system is the "Fault Response Support System". It
allows minor faults to be addressed. It uses head-mounted
display (HMD) that allows the wearer to communicate withaudio and video with support staff using a PC or such froma remote location and receive instructions from them.
The introduction of these two systems (hereinaftercollectively called "Staff Support System") has made it
possible for non-technical staff (i.e., staff not normally
involved in facilities operation/maintenance) who are
unfamiliar with procedures to quickly, safely, and reliably
operate drainage pump stations at the time of actual disaster
response work. These systems have also made it possible torestore the drainage pump station back to normal operation
by an on-site operator sending information such as images
to a remote location which responds with instructions onwhat actions to take.
Furthermore, it has been confirmed that the Staff Support
System is not only capable of solving problems in disaster
response work, but can also be utilized to improve efficiency
in a wide variety of applications.
Although the Staff Support System was developed andintroduced as a result of the issues that arose in disastermanagement operations, thanks to its wide range ofapplications that extend beyond disaster response work, We
can expect its use and application in a wide range of fields
as a means to realize efficient and effective operation andmaintenance using a limited number of staff.

Evaluation of the flood control functions of existing damsin Japan in the context of climate change
H.Kojima, G.Nagatani, M.Kurahashi, I.Kawamura, and T.Sumi

Theme 5In recent years, the frequency of floods in Japan thatexceeded planned scales has been on an increasing trend,
and the development of means for addressing increasing
external forces has become a pressing issue. The purpose ofthis study against this backdrop was to conduct quantitativeevaluations of the current flood control capacity of existingdams against “current probable maximum precipitation,”and to investigate the need for future measures, taking
into account factors such as the roles that each of thesedams play in their respective river systems. As a result, We
have identified differences between major river systems
in Japan as seen in river systems that are equipped witheffective dam-based flood control functions, systems withexisting reservoir functions that are less than adequate,
and systems having water utilization dams which havenot been incorporated in flood regulation regimes underflood control plans. We have also shown that if preliminary
release operations can be performed in Class-A and Class-B
river systems from both existing and hydropower dams, thiscan potentially provide flood control ability improvements
equivalent to that of making dam height extensions.

Development of an advanced operation system forhydroelectric dam using machine learning
S.Takino, Y.Nakada, T.Tsukada, T.Honda, T.Miyoshi
M.Ohhigash, and S.Kotsuki
The operation of a dam at a hydroelectric power plantrequires highly accurate precipitation forecast in the basin
and the inflow discharge to the dam up to about half a daylater. We have developed an operation optimization system
for hydroelectric dams that utilizes machine learning. Usingmachine learning, we were able to predict rainfall andriver discharge with high accuracy. As for dam operation,
dam operation with high power generation efficiency was
performed to keep the dam water level high for a long time
without overflowing.

Earthquakes and dams

A. 10th East Asia Dam Conference in Zhengzhou, October 2018
Dynamic behaviour characteristics of Piano Key Weirs
M.Kashiwayanagi, Z.Cao
A Piano Key Weir (PKW) has been developed as free flowogee crest to provide better hydraulic characteristic thanconventional weirs. A PKW additionally features a small
footprint due to the over-hanged structure, enabling easer
arrangement on the dam crest. Thirty (30) PKWs havebeen operated worldwide as of 2017. Due to the structuralcharacteristics of a PKW, the seismic safety evaluation isan essential issue in order to apply PKWs for dams locatedin earthquake prone area. The dynamic behavior of PKW isinvestigated by numerical simulations using the simple PKW
model and the composite model of the dam and the PKW.
Directional interference of the oscillation of PKW is a key
for the resonance between the dam and the PKW. The waterinteraction on PKW wall is examined.

DAMS IN JAPAN - OVERVIEW 2022

38

B. ICOLD 87th Annual Meeting International Symposium in Ottawa, June 2019
Analytical study on effects of fracture energy for crack
propagation in arch dam during large earthquake

Dynamic analysis of a Piano Key Weir situated on
concrete dams

H.Sato, M.Kondo, T.Sasaki, H.Hiramatsu, and H.Kojima

M.Kashiwayanagi, Z.Cao, and T.Oohashi

In the seismic performance evaluation of concrete dams
against large scale earthquakes, crack propagation analysis
based on smeared crack model is sometimes performed
as a method of nonlinear dynamic analysis to estimate
damage process. But it is not easy to set some parameters
required for the analysis appropriately, such as fractureenergy which is one of the physical properties related to
fracture characteristics of dam concrete, due to shortage ofthe number of full scale experimental tests. In this paper, we
reviewed related past experimental studies including static
and rapid wedge splitting tests with comparatively large
fracture energy, and conducted analytical studies on theeffects of difference in fracture energy for crack propagation
in a concrete arch dam considering such experimental
results data. The results showed that the fracture energy had
an important influence on crack distributions and cracks in
dam body were localized as fracture energy increased.

Piano Key Weirs (PKW) have been developed as spillways
to provide better hydraulic characteristic than conventional
free flow ogee-crest. Due to the structural characteristics
of PKWs, the seismic safety evaluation is an essential issue
in order to apply PKWs for dams located in an earthquake
prone area. To clarify the earthquake-resistant capabilityof PKWs by numerical analyses, the virtual PKW situatingon the concrete dam crest is designed so as to discharge
1200 m3/s. The dynamic characteristics of PKW are
investigated by numerical simulations using the PKW unit
model, not combined in the dam. The behavior during alarge earthquake is analyzed using the PKW model situatedon a concrete dam crest of 100 m high. The conclusions
are as follows. The predominant frequency of the PKW isalmost 10 times of ones of the concrete dam, suggestingthat the behavior of the PKW could be lightly affectedby the interaction between the PKW and the dam. The
investigation of hydrodynamic pressure acting inside of
the PKW is challenging for the better seismic design of the
PKW. The structural investigation such as reinforcement
design and structural detail should be also the challenges toprovide adequate earthquake-resistant capacity of the PKW.

C. ICOLD 88th Annual Meeting International Symposium & 5th APG Symposium in New Delhi, February 2021
A Few Considerations on Earthquake Monitoring of Dams
M.Ka shiwayanagi, Z.Cao, and N.Shimizu
A few considerations on earthquake monitoring of dams
are introduced in terms of enhancement of earthquake
monitoring and safety assessment of dams. These arebased on examinations on thousands of earthquake data
monitored in major dams of J-Power in more than 50 years
in Japan. (1) Transfer function matrix clearly demonstratethat dams under earthquake load behave in a distinctive
manner according to material, configuration and foundation
condition. While concrete gravity dams behave selectively
in upstream-downstream direction as 2D (two-dimensional)
structures due to the high stiffness of dam concrete and rockfoundation, the behavior of embankment dams is 3D (threedimensional), attributing to dilatancy characteristics andthe relatively low stiffness of materials and rock foundation.
(2) Predominant frequencies of dams are various inearthquakes. Analyzing independent monitored data in shorttime segments clarified that the predominant frequencies
decrease relative to the degree of acceleration of dam crest.
It is considered that the interaction between the dam andreservoir works stronger in the higher response accelerationof dam. (3) Spillways arranged in the middle section could
disturb the earthquake monitoring at the highest section of
the dam due to adjoined piers and/or walls of the spillway.
The numerical examinations using numerical models withand without spillway structures suggest that the disturbanceis slight in acceleration response, but crucial in the stressaround spillway. (4) The authors have proposed the new
method of GPS (Global Positioning System) self-relative
single positioning for the dynamic deformation monitoringof dams. When the new method using high frequency GPS
receiver is combined with conventional accelerometers,
earthquake monitoring of dams will be easily upgradedto monitor the deformation process during an earthquake
simultaneously as well as the acceleration response.

Study on the engineering bedrock and seismic motion at itin the earthquake response analysis of a concrete dam
N.Yasuda, Z.Cao
In Japan, the dam safety against large-scale earthquakes isverified by numerical analysis. Seismic motion defined forverification of seismic performance of a dam is set based

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DAMS IN JAPAN - OVERVIEW 2022

on the distance attenuation formula which is obtained bystatistical analysis of the earthquake records of many dams,
the empirical Green’s function method, and a method ofadjusting ground motion record to the stipulated lower-limit
acceleration response spectrum for verification. Generally,
the input seismic motion for the earthquake response
analysis is prepared by pulling the seismic motion back to
the engineering bedrock hypothesized by numerical analysis
method. However, lacking precise criteria for setting
engineering bedrock for earthquake response analysis of adam, the appropriateness of the preparation method of theseismic motion and of the prepared input seismic motion
are not necessarily clarified. This study predicted seismic

motion of deep bedrock using earthquake acceleration
records during the Tokachi-oki Earthquake in 2003 (M. 8.0)
inside bedrock at a depth of 57 m below the bottom of theSatsunaigawa Dam which is equipped with 8 seismographs.
Based on the research results, it was pointed out that in
the case of concrete gravity dams, the engineering bedrock
should be set at a depth equal to about 1.5 times the damheight, and where the shear wave velocity of the bedrock
should be no less than 2,000 m/s. Then, a procedure ofpreparing input seismic motion for earthquake response
analysis is proposed.

E. 27th ICOLD World Congress in Marseille, June 2022
Seismic performance verification of a rockfill dam against
large doublet earthquakes

Investigation of damping characteristics of dams evaluatedby DE/TFM method

N.Yasuda, Z.Cao

M.Kashiwayanagi, Z.Cao

The purpose of this study is to clarify the behavior ofa rockfill dam during large doublet earthquakes and to
propose a procedure for verifying the seismic performanceof rockfill dams during such earthquakes. Impacted bya strong earthquake, the dynamic characteristics of the
Aratozawa Dam significantly changed temporarily. The
behavior of the dam subject to another strong earthquake
before its dynamic characteristics had recovered was
predicted. Based on the analysis results, the seismic
performance of the dam was evaluated. The results clarified
that the change in the dynamic characteristics of the damin response to the first event greatly affected the behaviorof the dam during the second event. In addition, a method
was proposed for predicting the final residual subsidenceof the dam by summing the sliding displacement caused byeach earthquake and the subsidence related to the shaking
and rearrangement of soil particles. It is recommended thatafter a dam experiences a strong earthquake, the reservoir
is adjusted to a safe water level and maintained at that level
for a minimum of one week as an emergency response
measure.

This paper examined the damping characteristics during
earthquakes of 100 m high dams based on the monitored
earthquake behavior using the DE/TFM method, which
is newly invented by authors and uniquely relay on afree vibration extracted from the earthquake response
behavior of the dam. The examination focused on theinternal damping and dissipation (external damping) due
to interaction among dam, foundation and reservoir ofa concrete gravity dam, an arch dam and a rockfill dam.
Following key findings are captured on the damping
characteristics based on the estimated damping ratios ofdams examined. The internal damping of concrete dams thatis essential parameter for the dynamic analysis is identified
as 3 % and 1.5 % for the concrete gravity dam and the arch
dam examined, respectively. An additional internal damping
proportional to the acceleration degree is inevitable for thearch dam to incorporate the non-elastic behavior such as
displacement of transverse joints. Regarding the external
damping of concrete dams, ones due to the interaction withthe reservoir are identified proportional to the water depth
and ones due to the interaction with the foundation are
expected as similar degree as other damping. A non-linear
dependency on an acceleration amplitude is the outstanding
characteristics of the damping of the rockfill dam. It isinterpreted that the non-linear properties of dam material
depending on shear strain of the dam have emerged. The
infiltration of the water into the rockfill dam absorbs theinteraction with the reservoir.

DAMS IN JAPAN - OVERVIEW 2022

Theme 640

Reservoir sedimentation and sustainable development

B. ICOLD 87th Annual Meeting International Symposium in Ottawa, June 2019
Experimental study on effective sediment channel withreservoir topography and morphology
Y.Kitamura, T.Ishino, and T.Okada
Measures to exclude the sedimentation in dam reservoirs areimportant for the sustainable maintenance and operation of
dam reservoirs. There is sediment flushing and pass-throughmethod for measures for reservoir sedimentation. Thismethod is to lower reservoir water level during flooding, toincrease tractive force, to accelerate erosion of sediment,
to form sediment channel, and to pass sediment throughspillway or sediment release gate. This method is economicalmeasure because of utilizing the stream power during
flooding. On the other hand, sediment channel formed in thereservoir has a great change in shape of meander and water
passages depending on the plan shape of reservoir. Flushingefficiency also greatly differs. For this reason, in order to
conduct flushing smoothly sediment in reservoir during
flood period and passing effectively through reservoir, ahydraulic study on the sediment channel formed in reservoir
is important.
In this paper, we report results of consideration about
sediment channel to improve the efficiency of sedimentflushing and pass-through during flooding. We investigate
about characteristics concerning the sediment channels
naturally formed in reservoir and artificially constructed
beforehand by excavating and dredging in dry season
through the mathematical and the hydraulic scale modelling
experiments.

Sediment management plan in Sakawa River – the resultsof the first phase
Y.Fukuda, R.Akita, and K. Doke
Many sediment management plans are being planned inJapan to manage or recover its sediment routing systems.
Among many sediment management plans, one for Sakawa
River is characterized by the long-term environmental
monitoring which consists of biological (vegetation, fish,
benthos, algae) and geological (riverbed materials, riverbed
elevation, suspended sedimentation) data. These data havebeen accumulated in more than 10 years in normal andflood conditions and these are still being accumulated sofar. These longterm data of the sediment routing system
in Sakawa River are very valuable to investigate theenvironmental conditions in the downstream area of the dam.
The results of the investigation of Sakawa River’s geologicaland biological data monitored until 2017 indicate thatcoarsening riverbed was temporarily recovered by sedimentdeposit in upstream area, and the catastrophic damage ofsevere flood caused by Typhoon Malou in 2010 is recoveredin the ecosystem, the condition of riverbed materials and its
elevation.

Turbidity control and sediment management using sluicing
tunnel at hydropower dam
H.Okumura, C.Onda, T.Satoh, and T.Sumi
Hydropower emits no green-house effect gas and isrenewable and domestic energy. It is necessary to solve
the problems around dams and reservoirs which will be
described in this paper to secure the stability of hydropower
supply by effective and sustainable countermeasures.
A dam stores not only clear water but also turbid waterand sediment in a reservoir during flood. Turbid water
stored causes long-term persistence of turbid water in thedownstream area of the dam, because this turbid water isdischarged repeatedly during generation. Sedimentation
causes the loss of the reservoir capacity, obstacle against
intake and outlet function, rising water level in the upperarea of the reservoir and bad influence on river environment
in the downstream area. In this paper, a countermeasureagainst problems at Futatsuno dam located in Kii peninsula,
Japan is studied. It is planned that a sluicing tunnel whichconnects up- and downstream areas of the dam will makevolume of turbid water stored after flood smaller and makesediment bypassing the dam. The numerical simulation
has been implemented for the validation on capability ofthe plan. Then it is concluded that the sluicing tunnel is aneffective countermeasure for turbidity control and sedimentmanagement.

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DAMS IN JAPAN - OVERVIEW 2022

C. ICOLD 88th Annual Meeting International Symposium & 5th APG Symposium in New Delhi, February 2021
Analysis on sediment transport processes around estuary
and coastal shoreline area in the Sagami River Basin topromote reservoir sedimentation countermeasures andintegrated sediment management

Bedload transport and abrasion monitoring at the
Koshibu Dam sediment bypass tunnel and proposing
countermeasures against the abrasion problem
T.Koshiba, T.Sumi

M.Hyodo, K.Horie, T.Kuchiishi, N.Osaki, T.Asaeda, and M.Sasaki
Sagami River Basin is a Class A River with the length of 113
km and basin area of 1,680 km2, coming from the Mount
Fuji and merged with the Nakatsu River into the Sagami Bay
in Kanagawa Prefecture. Several dams (8 dams) and weirs
have been constructed in the Sagami River Basin. Whilethey have provided numerous benefits to society, they also
have negative impacts such as on sediment regimes due toreservoir sedimentation. They have reduced the sedimentsupply to downstream reaches, resulting in coastal erosionof the Chigasaki Coast, riverbed degradation, fixed-river
channels and intensive riparian encroachments, highlighting
the need to adopt integrated sediment management at theriver basin scale. Several measures have been implemented
using removed-sediment from dam reservoirs, such as
direct sediment augmentation on the shorelines eroded,
and indirect one on the riverbed expecting the sediment tobe transported to the coastal shoreline. However, sedimenttransport processes are yet to be revealed, particularlyaround the lower reaches, i.e. from the river mouth andestuary area to coastal shorelines, where sand terrace
around the river mouth has been decreased and may not
be much functional in transporting sediment from fluvial
systems to coastal shorelines. The governmental committee
composed of Ministry of Land, Infrastructure, Transport
and Tourism of Japan (MLIT ), Kanagawa prefectural
governments, and Yamanashi prefectural government, issued
the “Integrated Sediment Management Plan for the Sagami
River Basin” in 2015, in close consultation and collaboration
with the Committee on Integrated Sediment Management
for the Sagami River Basin, in order to efficiently andeffectively promote sediment management in an integrated
and collaborative manner. This paper provides some resultsof quantitative evaluations of the sediment transport
processes in order to develop the Plan and proposes ahypothesis of sediment transport processes in the Sagami
River Basin, analyzing geographical survey data andnumerical simulation results of fluvial and coastal systems,
which is: “sand sediment transported from the Sagami Riverto the estuary area has been transported to the shoreline of
the Chigasaki Coast by coastal waves though slowly”. If thishypothesis is revealed, we can quantitatively evaluate thesediment volume, which is needed to come from the Sagami
River to the estuary area, in order to decelerate the coastal
erosion and sustain the coastal shoreline of the Chigasaki
Coast. This quantitative evaluation enables to determine
goals of sediment transport processes to be achieved
for integrated sediment management involving various
stakeholders.

Sediment bypass tunnels (SBTs) is a leading technique,mainly operated in Japan, Switzerland and Taiwan, tomitigate sedimentation problems in reservoirs. SBT reduces
sedimentation by di-verting sediment laden flood to a tunneland draining directly to the downstream reach. A major
issue in operating SBT is hydro-abrasion on the tunnel
invert caused by a combination of high sediment transport
rate and high flow velocity, whereas the countermeasure is
not well established because the relation between sedimenttransport rate and the abrasion is not clear. Accordingly, at
the Koshibu dam SBT in Japan, sediment transport is being
monitored with a surrogate bedload monitoring systemcalled an impact plate during all the SBT operations since
the SBT completion in 2016. In addition, the abrasion of
the entire tunnel invert is measured once a year using
mobile mapping system (MMS) with a three-dimensionallaser scanner. In this paper, monitoring results including
grain size and transport dynamics, i.e. velocity, transport
rate, spatiotemporal distribu-tion of bypassed sediment, andcurrent progress of abrasion are reported. On the basis of
those observation, design and operation of SBTs that may
reduce invert abrasion with maintaining the suitable bypass
efficiency is proposed.

Sedimentation management utilizing sluicing operation at
the Setoishi dam
H.Okumura, C.Onda, and T.Sumi
The Setoishi hydropower plant on the Kuma River has been
operating since 1958 in Kyushu area, Japan. Sedimentation
rate of the reservoir is under 10%, but the risk ofinundation around the reservoir exists during floods. As
countermeasure, excavations with emptying the reservoir
have been conducted since 2011. However, this is notsustainable: the amount of sediment to be excavated is toolarge, and power generation needs to be shut down. With
this background, sluicing operation which is draw-down
operation during flood to let sediment flow down throughthe spillway has been studied and the operation rules wereaided by nu-merical analysis.
In 2016 and 2017, the test operations were conducted, andit was found that the rules were effective. In June 2018, theregular operation started, and a large flood took place with amaximum dam inflow rate of 4,450m3/s in July, equivalent
to a 10-year flood. In this flood, 154,000m3 of sediment,that is 15% of the reservoir sediment, flowed down throughthe spill-way.

DAMS IN JAPAN - OVERVIEW 2022
The sluicing operation needs improvement to minimize therisk of inundation. We have identified key improvement
factors such as modification of the operation rules and42

removal of large rocks and coarse sediment left in thereservoir.

D. ICOLD 89th & 90th Annual Meeting International Symposium in Marseille, November 2021 and May 2022
Study on the Koshibu Dam sediment bypass tunnel
operation based on sediment transport monitoring in
upstream reaches
T.Koshiba, S.Miura, and T.Sumi
SBTs are a leading technique to mitigate reservoir
sedimentation. SBTs consist of a tunnel connecting the
upstream and downstream areas of a dam and diverting
sediment-laden flood directly during flood events. A
difficulty in operating SBTs is to reduce sediment inflow
into the reservoir effectively, and at the same time, tosustain the dam functions: flood control and hydropower
generation. These requirements settle on an optimization
problem determining the timing to open and close the SBTs

gates with the hydrograph and inflow sediment considered.
Despite many studies on SBTs operation consideringhydrograph, there are few of those on the temporalchange of sediment inflow. Accordingly, this study aims at
improving SBTs operation by understanding sediment inflow
from upstream reaches using an indirect bedload monitoring
system called impact plates. For that, the Koshibu Dam SBT
was picked up because impact plates are already placed inseveral locations in the basin including inside of the SBT.
This observation has revealed the amount of transported
sediment in every season in a year, the relation betweenhydrograph and sediment inflow, and the spatial transient of
sediment transport peaks. According to these observations,desirable rules for SBTs operation are suggested.

E. 27th ICOLD World Congress in Marseille, June 2022
Characteristic Evaluation And Countermeasure Planning
Of Reservoir Sedimentation Utilizing The Long Term
Survey Data In Hydropower Dam
H.Okumura, T.Sumi
The sedimentation management of hydropower dam
reservoir is one of the major problems for the sustainable
operation of the plants in Japan. In order to evaluate thesedimentation characteristics and plan a sedimentation
management, utilizing the results of annual sedimentation
survey data that has been conducted for several decades
and has survey error is studied. It is found that, averaging

Theme 7the survey data is effective to eliminate the error and grasp
the relationship between annual maximum dam inflow andannual sedimentation volume. Utilizing the relationshipand numerical analysis, draw-down operation withspillway remodeling is useful to sustain the function of thehydropower reservoir.

Water quality, environmental conservation and social consideration

B. ICOLD 87th Annual Meeting International Symposium in Ottawa, June 2019
Development of a prediction model used in measures for
reducing mold odor in dam reservoirs
Y.Okada, K.Shima, K.Okabe, N.Arakawa, Y.Watabe,
M.Hongou, and H.Kushibiki
The introduction of water quality conservation facilities
is an effective measure for reducing mold odor in dam
reservoirs. However, depending on the hydraulic and water
quality conditions, the countermeasures of changing thedam operations both by shortening detention time andby lowering surface water temperatures may be efficientand effective. This paper analyzes the results of field
investigation and past surveys, clarifies the mechanismof mold odor occurrence in T dam, and develops a simple
model that enables prediction and prevention of moldodor occurrence. The model makes it possible that dam
administrators pre-vent mold odor by entering daily dam
management data (inflow, outflow, and reservoir watertemperature).Main factor of mold odor occurrence in T

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DAMS IN JAPAN - OVERVIEW 2022

Dam is growth of Cyanobacteria in dam reservoirs. And weclarified Cyanobacteria could grow under certain situation,such as long detention time, a lot of nutrient salts andhigher water temperatures. The developed simple model
can estimate the degree of risk of mold odor. Therefore, it
enables to predict the effects of the countermeasures by therevised dam operation.

Comparison of reproducibility of water temperature andwater temperature stratification formation by different
methods in dam reservoir water quality prediction model
F.Kimura, T.Kitamura, Y.Tsuruta, T.Kanayama, R. Kikuchi,
Y.Kitamura, T.Morikawa, and Y.Okada, Y.Fukuda, T.Shoji,
A.Mieno, T.Suzuki, and M.Kobayashi
In order to properly maintain the water quality of thedam reservoir, it is necessary to properly operate the dam
facility and the water quality preservation facility installed.
In determining these operation methods, simulation using
the water quality prediction method plays an importantrole. However, since there are differences in the basic
formula and the discretization method of each water
quality prediction method, it is inferred that the reservoir
characteristics simulated do not always harmonize onesby other methods from the reproducibility point of view.
In this paper, we focused on the water temperature, whichis the most basic item among water quality predictions of
the dam reservoir. We picked up some methods of water
quality prediction that have been ever applied in dam
reservoirs. The simulation results are compared in term of
the formation conditions of water temperature and watertemperature stratification in three case studies to verify the
reproducibility and the distinction of each method.

National census on river and dam environments in Japanand utilization for appropriate dam management using theresults
T.Osugi, E.Akashi, K.Yamaguchi, H.Kanazawa, and M.Nishikawa
National Census on River and Dam Environments in Japanis a periodical investigation for the purpose of collecting
basic information about the environment of dam reservoirs
and covers biological investigation and investigation on
the number of tourists of the dam reservoir in Japan. This
census targets at eight categories of plants and animals,
such as fish, benthic animal, plankton, birds, etc. for the
purpose of nationwide assaying the environment of a dam
reservoir and its surrounding by accumulating data withkeeping the survey accuracy. It has been carried out morethan 20 years since 1990. In this paper, the objective
species were selected and analyzed among the alien species
expanding these population from the viewpoint of the dam
and its lake management and environmental continuity of
up- and downstream of the dam. For example, it has beenfound that Golden Mussel clogs water pipes and makes
a great influence on hydroelectric power generation andthat other alien species expanding its distribution makes agreat influence on fishery activity. By utilizing this National
Census Data we believe it is possible to upgrade dam
management appropriately.

C. ICOLD 88th Annual Meeting International Symposium & 5th APG Symposium in New Delhi, February 2021
Dam break accident and resulting sediment management
at downstream dams in Lao PDR - Highly turbid flood-flow
and sediment flushing at Nan Ngiep 1 Hydropower Project T.Tabuchi, Y.Aosaka, Y.Murakami, and S.Tsutsui
In September 2017 a dam of the A Project, which islocated 90 km upstream of the Nam Ngiep 1 Hydropower
Project (NNP1) in Lao PDR, collapsed during construction
and partially stored water of around 500,000 m3 in thereservoir was flushed away to the downstream river course.
The highly turbid water had a serious impact on the ecologyof the downstream river course, and sediment of around
700,000m3 was accumulated in main dam and the reregulation dam reservoirs of the NNP1, while the turbid
water flew through the diversion of the main dam of the

NNP1 located 7 km upstream of the re-regulation dam which
was under construction. It was feared from the beginningthat when starting the operation of the re-regulation dam
reservoir, the anaerobic and deteriorated clay and silt could
be released together with the environmental flow throughthe re-regulation dam reservoir, and thus impact theecology of the downstream river basin. In order to mitigate
this harmful impact, the NNP1 determined to implement
sediment flushing in the early dry season of 2017, when
the NNP1 River had a certain volume of the flow before
starting the initial impounding scheduled in May 2018. This
paper presents the dam break impact on the downstream
river course and the resulting sediment management at thedownstream NNP1 reservoirs.

DAMS IN JAPAN - OVERVIEW 2022

44

B a c k w a t e r e ff e c t a n d c o m p e n s a t i o n d u e t o d a mconstruction on Nam Ngiep 1 Hydropower Project in Lao
PDROperation of the selective water intake facility of Sameura
Dam, taking account of downstream water temperatureand turbidity

K.Nakamura, T.Takahashi, K.Tomioka, and S.Tsutsui

M.Tsuda, M.Moriya

A 167 m high concrete dam was constructed related to
the Nam Ngiep 1 Hydropower Project in Lao PDR and,as a result, a reservoir of 67 km2 emerged. At the upper
reaches of the reservoir, local residents enjoyed cultivation
at the flood plain and near the riverbanks and a few houses
existed in the expected inundation area by the reservoir.
The residents feared that they would lose the land where
they bore their lives and further land would be inundated
by the backwater effect of the reservoir. The Nam Ngiep
1 Power Company (NNP1PC) estimated the inundation
area based on a flood mark survey and a flood inundation
simulation; and subsequently installed pegs as a benchmark
for compensation measures and to show the predicted
inundation area to the villagers. In addition, NNP1PC
studied the possibility of drawdown during the rainy season
to achieve an economic balance between minimised need forcompensation and the loss of power generation. This paper
presents the process of survey, study and compensation
related to the backwater effect of the reservoir.

Release of low-temperature water during summer andprolongation of muddy-water discharge from the dam
reservoir after extreme floods have been big challenges
in the operation of the Sameura Dam in Japan since
the beginning of its operations in 1975. Release of lowtemperature and muddy-water has a negative impact on
fisheries and downstream water use. To address theseissues, the surface-water-intake facility was converted to aselective water-intake facility in 1999. Since the conversion,
the level of water withdrawal has been changed according to
the vertical profile of water temperature and turbidity in thedam reservoir as observed by a real-time monitoring system.
The rules of operation were determined through discussions
with academic experts, local people, and river managers.
Water-intake elevation has been set to be relatively low,
and water temperature is cooler than that in the surface
layer while also meeting the target level to conserve
warm water. High-turbidity water is selectively discharged
during flooding for early release of suspended matter. In
our research, we quantified the effect of the operation byusing a two-dimensional vertical water-quality model thatnumerically simulates water temperature and turbidity inthe dam reservoir and downstream.

D. ICOLD 89th & 90th Annual Meeting International Symposium in Marseille, November 2021 and May 2022
Establishment of the comprehensive river environment
conservation system in collaboration with river
stakeholders on the Tenryu River
Y.Kitamura
The sedimentation, turbid water and water quality are
typical environmental issues for dams and reservoirs
which have impact on the reservoir and downstream ofdams. These impacts are influenced from the upstreamof a dam, and influence to the downstream. Therefore, amore integrated environmental management approach andconsideration have been required for the whole river system.
The Tenryu River in Japan flows through the erodible
area near the Median Tectonic Line on Honshu, the mainisland of Japan, and continuously carries a lot of sediment
during floods. The “Tenryu River Natural Resources
Rebirth Promotion Committee” was established in 2012.

The purpose of the committee is to restore fish resources
and improve the river environment. The feature of theliaison committee is that it is composed of the Tenryu Riverfisheries association, academic experts, and dam owner andexchanges knowledge and technology information in spite ofeach interest. The current activities are related to the themeof "attached algae/environmental DNA survey", "turbid watermeasures in reservoir/spawning bed construction technique
at downstream," and "information dissemination". In thispaper, the activities of the comprehensive reservoir andriver environment conservation system in collaboration withriver stakeholders are introduced and described, including
future prospects.

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DAMS IN JAPAN - OVERVIEW 2022

E. 27th ICOLD World Congress in Marseille, June 2022
Simultaneous multi-gate withdrawal with free-selective
air-lock intake equipment in Tono dam, Japan

Mitigation of social impacts by the Yamba dam project
G.Yasuda, K.Watanabe

T.Suzuki, H.Yajima
Simultaneous multi-gate withdrawal (SMGW) with selective
intake equipment in dam reservoir has hardly been reported
in Japan. In this paper, the hydraulic phenomenon andwater intake characteristics of SMGW have been verified
by field observation and numerical analysis for Tono Dam(Tottori Prefecture, Japan) in which SMGW operation has
been conducted. First, as a result of the field observation,
the tendency was confirmed that the amount of water takenfrom each intake pipe by SMGW is not the same whilelarger amount of water is taken from the lower intake pipe
under the condition that thermocline is formed. Next, themixing mechanism of water quality inside the intake tower
was clarified by numerical model that can reproduce theobservation results for the intake tower. Finally, after theestimation of influential factors on the water intake rate of
SMGW by sensitivity analysis, the water intake rate under
SMGW operation can be estimated by applying the waterintake stability factor based on the ratio of the buoyancy
occurring by thermocline to the inertial force induced bywater intake.

The Yamba Dam, located in Gunma Prefecture, central Japan,
was completed in 2020. The construction project has been
opposed by local residents and was deadlocked for morethan 30 years. One of the key devices which helped resolve
the dispute and ensure that the burdens and benefits are
fairly shared between the beneficiaries of the project and the
locals around the dam was Japan’s Act on Special Measuresfor Reservoir Area Development (ASMRAD). This paper first
explains the features of the Yamba Dam and its history,
followed by an outline of the ASMRAD. Applications of the
ASMRAD and its affiliated Reservoir Area Development Fund
(RADF) for the Yamba Dam are explained to highlight theeffectiveness of the ASMRAD and its contribution to theproject. Other measures used to mitigate the social impactsof the project are also described. Unique contributions of
the dam owner and the main contractor to attract social
attention and visitors proved that effective communication
with the public can contribute to the regional economy andhelp mitigate social impacts. Finally, a provisional evaluationof the overall mitigation measures is described.

DAMS IN JAPAN - OVERVIEW 2022

Editorial Committee for Dams in Japan
Chief editor: Goro YASUDA
Advisor: Hideki HIRAI, Ph.D
Member: Chihaya ONDA
Kensuke HAGIWARA
Toru HOSHINO
Yuta KANNO
Shigeru IKEDA, Dr. Eng.
Mitsuhiro YOSHIDA
Tatsuya MIZUNO
Hiroshi KURAHASHI
Junichi FUKUWATARI

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