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Japan Commission on Large Dams
http://www.jcold.or.jp

Dam and Hydropower

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The Roles of Dams and Hydropower

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Sources :1) : “Circumstances of dams in Japan (effective use of existing dams) 2006 (in Japanese)”, Japan Commission on Large Dams
2) : Prepared based on the data of Japan Commission on Large Dams
3) : Prepared based on “ Dam Almanac 2005 (in Japanese) ”, The Japan Dam Foundation 2005. 3
4) : Webpage of the Ministry of Land, Infrastructure, Transport (http://www.mlit.go.jp/river/dam/main/shinngikai/kondankai/dam/pdf2/17-27.pdf) (in Japanese)5) : Prepared based on “Electric Utility Manual (fiscal 2008) (in Japanese) ”, the Federation of Electric Power Companies in Japan (in Japanese)6) : Water Resources in Japan (fiscal 2008), Ministry of Land, Infrastructure and Transport p. 76(in Japanese)7) : Water Resources in Japan (fiscal 2008), Ministry of Land, Infrastructure and Transport p. 90(in Japanese)8) : Prepared based on references 6) and 7) (in Japanese)
9) : Webpage of the Ministry of Education, Culture, Sport’s Science and Technology (http://jcsepa.mri-jma.go.jp/outreach/20070324/Presentations/P2_Yamamoto.pdf)(in Japanese)10) : Webpage of the Chuo Mitsui Trust Holdings, Inc. (http://www.chuomitsui,jp/invest/pdf/repo0503_4.pdf#search=’ Industrial water and industrial production index)(in Japanese)11) : “Earth Dams in Sanuki (in Japanese)”, the prefectural government of Kagawa (March, 2000) (in Japanese)12) : Prepared based on the webpage of the University of Tokyo (http://park.ecc.u-tokyo.ac.jp/irrigationwater/nakashima_071029.pdf) (in Japanese)13) : Webpage of Oki/Kanae Laboratory of the Institute of Industrial Science of the University of Tokyo (http://hydro.iis.u-tokyo.ac.jp/Open House) (in Japanese)
14) : Problems of sand flushing at sedimentation facilities (in Japanese), Electric Power Engineering No. 318, p. 315) : Webpage of the Kansai Electric Power Company, Inc. (http://kepco.co/jp/info/hokuriku/contents/dashi/sougou.htm) (in Japanese)16) : Webpage of Hatsutabara Dam (http://www. cgr.mlit.go.up/hattabara/damsite/facility/keep/keep.htm) (in Japanese)17) : Webpage of the Japan Water Agency (http://www/water/go/jp/honsya/honsya/) (in Japanese)18) : Webpage of Shikoku Regional Development Bureau of the Ministry of Land, Infrastructure, Transport and Tourism(Http://www/skr/mlit.go.jp/kansen/kanri/dam/hozen/html) (in Japanese)
19) : Provided by the Kansai Electric Power Company, Inc .(in Japanese)20) : Provided by the Ministry of Land, Infrastructure, and Transport (in Japanese)21) : Source: The first meeting of the review committee on inadequacy related to water rights for hydropower (in Japanese), River Bureau, Ministry of Land, Infrastructure, and Transport (September, 2007) (in Japanese)22) and 23) : Webpage of the Center for Climate System Research of the University of Tokyo (http://ccsr.u-tokyo.ac.jp/openhouse/2005poster/20050H-K-1/2-5-H-K-1.htm) (in Japanese)24) : Webpage of the Environmental Restoration and Conservation Agency of Japan (http://www/erca/go.jp/ondanka/stop/kikou.html) (in Japanese)25) : Water Resources in Japan (fiscal 2005), Ministry of Land, Infrastructure, and Transport (in Japanese)
26) : Prepared based on ”TEPCO ILLUSTRATED FY2000” (in Japanese)27) : Prepared based on Reservoir Sediment Control in Japan (in Japanese) by Tetsuya Sumi, pp. 108, Fig. 8, 200328) : “Evaluation of Power Generation Technologies based on Life Cycle CO2 Emissions”, the Central Research Institute of Electric Power Industry (in Japanese)29) : Survey by the Agency for Natural Resources and Energy (March 31, 2007) (in Japanese)30) : Prepared based on IEA databases WEC (2004) for hydropower potential (in English)
Image picture ① : Provided by Toden PR Company, Inc . (in Japanese)
Image picture ② : Webpage of Onyado Kawasemi (http://hisuinosato.com) (in Japanese)
Image picture ③ : Webpage of Kurobe Dam (http://iwww.kurobe-dam .com/photo_museum/index.html) (in Japanese)
Image picture ④ : Webpage of the prefectural government of Akita (http:www.pref.akita.lg.jp) (in Japanese)
Image picture ⑤ : Webpage of Onyado Kawasemi (http://hisuinosato.com) (in Japanese)

How Dams and Hydropower Prevent Global Warming.

Japan Commission on Large Dams
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Roles of Dams and Hydropower Today and in the Past

Served as Foundations of Economic Growth and National Land Conservation in Japan*Since the years of the latest data available differ by reference, the values are cited here.

History of Dam Construction

Flood Control

Dams have prevented flood damages
and land slides in their lower regions
by temporarily storing flood waterand discharging it in a controlled way.

In Japan, because of the steep topography, the nation srivers are also very steep. So that the precipitation
immediately runs off land into the rivers, and which causes
floods in a short time as well as rapid water recession.
Therefore, dams store the flood water and this role isinherently effective in mitigating flood damage and utilizing
the water in the season with little rain.
Dams have been constructed for mainly water use such ashydropower since the Meiji era, and after WWII
multipurpose dams for flood control and water use havebeen developed.

1926〜1945

0

2

2

0

10

10

1946〜1955

0

17

17

0

240

240

1956〜1965

2

50

52

1

770

771

1966〜1975

21

62

83

54

860

914

1976〜1985

26

76

102

67

849

916

1986〜1995

13

80

93

34

709

743

1996〜2004

14

84

98

21

747

768

Total

76

371

447

177 4,185 4,362

Dams for hydropower

30

40

50

60

70

80

90

2000

As of fiscal 2004, there are 447 dams in Japan forflood control (excluding dams for agriculturalland disaster prevention), which have a total
flood storage capacity of about 4.4 billion ㎥.

07

Discharge after ﬂood control
by dams

Flood control by dams

Actual flood control by dams and estimated reduction amount of mitigated damage 4）

As of fiscal 2001, there have been 93 dams constructed by the Ministryof Land, Infrastructure and Transport and the Japan Water Agency inJapan. These dams have controlled a total flood discharge of about 340
thousand m3/s in 15 years from 1987 to 2001 and it is estimated thatthe effective reduction amount totaled about 4.2 trillion yen.

Changes in the number of dams according to purpose 2）

Supply of Domestic, Industrial and Agricultural Water〔Improvement of Living Conditions 〕

Dams have supplied water of high quality and assisted immensely in improving people s living conditions and haverespectively increased industrial and agricultural productions.
Hundred million ㎥ /year

Hundred million ㎥

549

126

Hundred million ㎥

Water yield

Hundred million ㎥

Domestic waterIndustrial water

Agricultural water

Municipal water

Total amount of water consumption

40

Hundred million ㎥

Others(rivers, undergroundwater, etc.)
62%

Water yield for municipal use by water resource
development facirlities (the dams, etc.)7）

The total water yield associated with dam construction by the endof fiscal 2005 was 11.84 billion ㎥ for domestic water and 5.92
billion ㎥ for industrial water.
2005 (12.6 billion ㎥)

Dams

Dams

Others(rivers, undergroundwater, etc.)
53%

Others(rivers, undergroundwater, etc.)
74%

102

169
ℓ/person/day

８０

88

69

42

Dams

As of fiscal 2005, water supply produced bywater resource development facilities (thedams, etc.) accounted for 74% of domestic
usage and 47% of industrial usage.

Changes in domestic water consumption in Japan 9）（Domestic water）（Industrial water）
Changes in the contribution ratio of water resource development facilities (the dams, etc.) in industrial water (supplying to water recycling systems)and domestic water 8）（year）〔Increases in Industrial Production〕

The industrial production index was about 25% in fiscal 1965 andabout 90% in fiscal 2001, marking an over threefold increase, with
the increase of industrial water consumption.
Hundred million ㎥

About
90%

About
25%

Recycled industrial water(scale on the left)−１−

144143
142

118

120

4０

141

Supply of fresh water(scale on the left)

1955

1965

1975

Fiscal year

1985

1995

2005

As of fiscal 2005, there are 1,162 hydropower plants in Japan, owned by thenine electric power companies such as TEPCO and J Power. The hydropower
plants which supply 34.27 million kW (17% of the total capacity), play animportant part in securing reliable power supply, cooperating with otherpower sources such as nuclear power plants (46.96 million kW, 23%) andthermal power plants (120.56 million kW, 60%).
The power generated by the hydropower plants, nuclear power plants, andthermal power plants account for 60.0 billion kWh (7%), 287.0 billion kWh(35%) and 462.2 billion kWh (57%), respectively.

【Contribution to Agricultural Water】

According to 2000 data, 98% of agricultural water was taken from rivers and ponds.
National
statistic

89.1

0％

20％

40％

8.9
60％

80％

RiversPonds

Due to the supply of agricultural
water, the irrigation ratio in Japan is
the highest among rice cultivating
nations in Asia.
On the other hand, Japan takes in alarge quantity of water via foodimports. The amount exceeds theannual quantity of water used for
irrigation in Japan in a year. Secured
supply of agricultural water bydams, etc. is important also from theperspective of water security.

2.0
100％

Underground water

Sources of agricultural water 11）

Irrigation ratio in Asian nations 12）

Total assumed amount of imported water to Japan 13）
Assumed water input inimported articles(hundred million ㎥/year)

Others：33

14

Industrial production index

Dams

Others(rivers, undergroundwater, etc.)
26%1975 (16.6 billion ㎥)

135

Hundred million ㎥(year)
Notes: 1. Survey by the Water Resources Department of the Ministry of Land, Infrastructure and Transport
2. The water yield (hundred million m3/year) was calculated by converting the water yield (m3/s) into
its annual value and multiplying by a load factor (day mean supply / day maximum supply) of 5/6.

As of fiscal 2005, the total annual consumption of water in Japan (an estimatebased on intake) accounts for 83.4 billion ㎥, of which 15.9 billion ㎥ (19%) isdomestic water, 12.6 billion ㎥ (15%) is industrial water (to supply to water
recycling systems), and 54.9 billion ㎥ (66%) is agricultural water.
2005 (15.9 billion ㎥)

59.2

Hundred million ㎥

20

Hundred million ㎥(year)

Water consumption in Japan 6）1975 (11.4 billion ㎥)

118.4

Hundred million ㎥

159

Notes: 1. The values are the amounts of water intake estimated by the Water Resources Department of the Ministry ofLand, Infrastructure and Transport and include the water that was returned to rivers after it was used.
2. Industrial water is the amount of fresh water supplied to establishments that had at least four employees. Water
used for public utilities is not included.
3. The estimated amount of agricultural water for 1980 is used for years 1981 and 1982, the estimated amount for1983 is used for years 1984 to 1988, and the estimated amount for 1989 is used for years 1990 to 1993.
4. The sum may not agree with the actual total due to rounding.

160

Mean daily consumption per capita

For tap water
For industrial waterSum

Domestic water consumption
Mean daily consumption per capita

1945

Transition in output from each power resource in Japan 5）ℓ/person/day（ℓ/person/day）（Hundred million ㎥/year）

834

Industrial water consumption

Hundred million ㎥

The domestic water consumption per capita was 169 ℓ/person/day infiscal 1965 and 316 ℓ/person/day in fiscal 2003, showing a twofold
increase, in the background of spread of water service and flush
toilets.
316

Domestic water consumption【Contribution to Domestic and Industrial Water】

1935

Mitigated damage (100 million yen)

Years

Gradients of major rivers in Japan and the world 1）

OthersNuclear power
Thermal power
Hydropower

49

25

22 13
145

36

22
13
3
3

Pork

389
140

89

Total import：640 billion ㎥/year

Source : Industrial Statistics Table and Industrial Production Index of the Ministry of
Economy, Trade and Industry

Maize

Beef

Soy bean

25

121
20

24

Rice

Industrial production index(scale on the right)

Wheat
94

570

Annual water consumption： billion ㎥/year
for irrigation in Japan(Unit yield in Japan: calculated using the data in the food balance table of fiscal 2000)

Changes in industrial water consumption and industrial production index 10）−２−

Vietnam

Total

ThailandMultipurpose
dams

Korea

Singlepurpose
dams

Indonesia

Total

India

Multipurpose
dams

China

Singlepurpose
dams

Japan

Multi-purpose dams including hydropower

Flood control capacity(million ㎥ )Irrigation ratio (%)

Number of dams

Multi-purpose dams excluding hydropower

Number of dams
constructed

Maximum output (MW)Year ofconstruction

Dams for ﬂood control

20

Hydropower was first introduced in the Meiji era to
produce power at spinning mills and mines as independent
power sources. Since then, hydropower has enabled andincreased energy to be produced domestically andsupported its economic growth.

Mitigated damage : 100 million yen［Percentage of output from each power resource］

Dams for supplying irrigation water

1910

Discharge (㎥/s)

Number of dams constructed and flood control capacity 3）

Dams for supplying city and industrial waterRivers in Japan

Power Supply

To sustain the Roles of Dams and Hydropower, constant efforts have been made to mitigate resulting negative environmental impacts

The state of reservoirs involves following environmental issues. To keep fulfilling their roles in dams and hydropower, these issues should be tackled steadily.

Prolonged Turbid Water

Sedimentation

Storing water in a reservoir allows for the capture of sedimentation from the upper regions. Sedimentation reduces theamount of water that can be stored in the reservoir capacity (designed dead storage) and may affect coast formation
around the estuarial regions.
Values within brackets denote the numbers of dams.

1991〜1993 （29）Year of completion

1981〜1990（135）

3.6
12.0

Sedimentations
deposits in somedams in Japan are in
the process of being
exceeded theirdesign values.

23.7

1971〜1980（169）56.2

1961〜1970（158）101.6

1951〜1960（152）
1941〜1950 （27）

58.3
103.4

1931〜1940 （35）

165.0

〜1930

《Example of Improvement》②Bypass tunnel to restrict the inflow of sediments (and supply
sediments to the lower regions to prevent the riverbed fromdegrading and the coastline from recessing)①Forestation of Sediment Sources in the Upper
Regions

Bypassing the turbid waterand sediments during floods
During flood
Prolonged turbid water

59.4

National total（729）
0.0Inflow of sedimentation during floods with prolonged suspended solids causes turbid water. Discharge of the turbid
water may affect the quality of water in the lower regions.

20.0

40.0

60.0

80.0
100.0
120.0
Sedimentation ratio (%)

160.0

Sedimentation conditions 14）《Example of Improvement》

180.0〔Definition of Sedimentation ratio〕(Sedimentation amount ／ The designed dead storage)×100(%)

Dashidaira Dam
Water level during storage

Asahi Dam

Sedimentation

Drawing down
the water level＜Drawing down the water level＞
The water level is lowered in the both dams.

Kurobe River

Unazuki Dam

Flushing and Discharging
Sediment the water level＜Flushing and Discharging Sediment＞
The river is allowed to flow naturally throughboth the dams to discharge sediment from theDashidaira Dam to the lower regions throughthe Unazuki Dam.

Dashidaira Dam
Sediment flushing

Sediment flushing
Kurobe River
Measures after Sediment Flushing and Discharge
Unazuki Dam
Discharge

Dashidaira Dam

Water level during storage Discharge

Recovery of water level

Recovery of water level

Kurobe River

Mechanism of coordinated sediment flushing and discharge＜Measures after Sediment Flushing and Discharge＞
The sand flush gates of the dams are closed torecover the water level. Water from the upper
regions is discharged for a predetermined
period of time.

15）

Eutrophication

Reservoir becomes eutrophic via the inflow of domestic sewage, etc. which may affect the quality of drinking water, etc.

《Example of Improvement》①Purifying Water by Using an Aerating Circulation
Facility②Stopping Expansion of Water bloom by Installinga Cutoff Barrier

Sameura Dam across
Yoshinogawa River 18）

Intake of Surface Water

Selective Intake

Mitigating prolonged turbid
water and sedimentation

Subsequent to bypass operations

Rocks were exposed

Changes in the riverbed at the downstream of the bypass tunnel of Asahi Dam 19）
Hitotsuse Dam across Hitotsusegawa River,Matsubara Dam across Chikugogawa River, etc. 20）

River Environment in the Lower Regions

Hydropower sometimes take in river water in its entirely, which adversely affects the habitats of organisms, water
quality scenery, etc. in the lower regions.

《An Improvement Example》①Appropriate flow at the downstream of the dam to be secured; stated in the
Hydropower Guideline ＊ 21）

Power station

Intake weir

Reduced power generation

Total length of clear stream
restoration: about 6,500 km

Sections outside the scopeof the Guideline Restored

Sections within the scopeof the Guideline Restored

67% of the affected sections
have been restored

Regulating tank
Power station

Total length of affected river sections: about 9,700 km
Sections outside the scopeof the Guideline
Not Restored
Sections within the scopeof the Guideline
Not Restored

Section of reduced water−3−

OutletIntake of Lower Water

Regulating tank

Seirenji Dam across Seirenjigawa River 17）

Prior to bypass operations③Selected intake gate to prevent discharge ofturbid water

Schematic Diagram of Restoring theClear Stream based on the Guideline

Hattabara Dam across Ashidagawa River 16）

Weir

Supplying sediments
to the lower regions

Water level during storage

Drawing down
the water level

Flushing and Discharging Sediment

Intake200.0

Riverbed degradation in
the lower regions

Drawing down the water level
Coordinated sediment flushing torestore the effective capacity and river s
Unazuki Dam
environment in the lower regions

The Dashidaira Dam and the Unazuki Dam,
which is about 7 km downstream across the
Kurobe River, flush and discharge sediments ina mutually coordinated manner. The sedimentthat flowed and was deposited into theDashidaria Dam during the floods isdischarged into the lower regions through the
Unazuki Dam. This coordinated sedimentflushing is implemented by following themethods and the rules that were formulatedwith the purpose of mitigating impacts on theenvironment in the lower regions. An
investigation to evaluate the effects has beenongoing.

140.0

Bypass tunnel to prevent
reservoir sedimentation

Intake weir

Restoration of clear stream

Restoration of clear streams in affected sections

Number of power stations : 699 (52%) out of 1,295
Length of affected sections : about 6,500 km (67%)
out of about 9,700 km＊ Guideline for maintaining the flow of the river at renewing the water rights for power generation enacted by the Ministryof Construction in 1988
−4−

②Revising the Term of
Validity of Water Rights
On April 1, 2009, the term of validityof the water rights for power generation
was revised from 30 years to 20 years(10 years for those that have passed 100
years since the initial permission was
granted) in principle. It is also required
to submit necessary reports every 10
years to evaluate the utilization of riverwater which will be revised for every
fixed period of time from theperspective of public benefits, such asconservation of the river s surrounding
environment.

Predicted Impacts of Global Warming

According to a future climate forecast made by the collaborate study team for the Center for Climate System Research (CCSR),
University of Tokyo and National Institute for Environmental Studies (NIES), Japan Agency for Marine Earth Science and Technology(JAMSTEC), using a global simulator based on the climatic data in the past 100 years, the number of heavy rain days and hot summerdays on which the temperature is 30℃ or above will increase and snow depth will decrease in Japan. Based on the forecast, future
river flows at dam sites were estimated and compared with present values. As the result of the estimations, the number of heavy raindays will increase but the flow of the rivers will drop in general, and the peak of snowmelt discharge will appear in earlier spring than
today, the flow during the wintertime will increase while the flow during the summertime will drop (From reference 22)〜25)). For
effective utilization of rainfall and snow all year round, the results show the increasing importance of securing reservoir capacities.
The number of hot summer days (maximum
temperature of 30℃ or above)

The number of heavy rain days (daily
precipitation of at least 100 mm)

The number ofhot summer days
will increase!

The number ofheavy rain days
will increase!

Roles of Hydropower
The CO2 emissions from hydropower are emitted only forconstruction and facility repair. Hydropower dose not emit CO2 toduring operations.
Approximately 70 million tons of CO2 was reduced via the use ofhydropower in fiscal 2006. Without power supply fromhydropower, the CO2 emissions in Japan would have been about
6% more compared to the level in fiscal 1990.＊
To prevent global warming the Japanese Government sets an aim
to cut CO2 emission by 25% by 2020 respect to1990 levels.
Hydropower is viewed as a clean and renewable energy that emits
zero CO2 and is an effective resource.

Necessity of
an increase

Without new dam
development

Total reservoir
capacity
Total quantity of
sedimentation

Sedimentation
ratio : 0.24%/year

Necessity ofa decrease

Reservoir capacity of dams in Japan and losses in capacity

Year
27）

Development of New Hydropower
For preventing global warming, hydropower is as important assolar and wind. The development of new hydropower with newly
being developed dams is also effective.

In 100 years

Goals for Preventing Global Warming
Based on the G8 Summit in 2008 (held in Toyako, Hokkaido),
Japan set a goal to increase the production of zero emission
energy (renewable energy, nuclear power generation, etc.) so
as account for 50% of the total power generation by 2020.
Today, as of fiscal 2007, the ten electric power companies inJapan produce a total of 1030.3 billion kWh, of which 353.0
billion kWh (35%) are zero emission power. Of this, 78.4
billion kWh (8%) is produced from hydropower, all the morerevealing its importance.

％

％

％

％

％

％

Nuclear power
LNG and LPG
CoalPetroleum
Other gas
New energy
Hydropower

Energy sources of power production by the ten electoric
power companies in Japan (fiscal 2007) 26）−5−

Geothermal

Nuclear

Wind

Solar

LNG (CC)

LNG (steam)

Thermal(petroleum)

Hydropower

Equipment・Operation

Thermal(coal)
December 1

November 1

Flow at Yagisawa Dam 25）

24）

Less than 1,000(unit : kW)

Fuel combustion

Present

October 1

September 1

August 1

July 1

June 1

May 1

April 1March 1

Snow depth (cm)February 1

In 100 years

Global warming is predicted to increase droughts and floods. In
Japan the total reservoir capacity is diminished at a mean ratioof 0.24% a year. To maintain the present reservoir capacity
level, new dams need to be developed while taking measuresagainst sedimentation of existing reservoirs, such as sandflushing described as an improvement example

Flow insummertime
will drop!

Flow in wintertime will
increase!

January 1

Present

The peak willappear early!
Discharge (㎥/s)

The amount of snow
will decrease in allparts of Japan.

Development of New Dams

23）

22）

Snow depth
will drop!

Proposals toward the Future
Capacity (100 million ㎥ )Global Warming Increases the Importance ofSecuring Reservoir Capacities and Hydropower

In Japan, there are potentials
for developing small scalehydropower plants.

Pending development
Developed
Under construction

Hydropower output distribution (number of points) 29）

CO2 emissions per 1 kWh 28）＊Interim Report of Hydropower Study Group (July 2007), Agency for Natural
Resources and Energy

Closing Remarks
In developing countries, the spread of electricity is
indispensable for their growth. Power development
projects are requested to take into consideration
global warming and other environmental issues. In
Japan, not only given that present ongoing measures
but also Kyoto Mechanism, which are supplementarymeasures, have been implemented to achieve the goalsof the Kyoto Protocol. CDM(Clean Development
Mechanism) projects utilizing hydropower via
Japan s advanced and abundant hydropower
technologies will be required to contribute to build aglobal sustainable society. (*Emissions from methaneand other greenhouse gases should be taken into
account in certain tropical regions.)

Developing countries havelarge hydropower potentials.

Development ratio(Advanced nations): about 70%(economical potential)(Other countries): about 20%

Out of the hydropower potential that is
feasibly necessary for global economic
development, only 31% has beendeveloped by 2004.

Hydropower potential feasible for economic development in the world 30）−6−