Tokuyama Dam--The Largest Rockfill Dam in Japan
Creating a Beautiful Reservoir in Harmony with Nature -Commissioned by: the Japan Water Agency

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Tokuyama Dam

Diversion tunnel No.1 L=1,474m
Diversion tunnel No.2 L=1,135m

Upstreamside

Top of dam

Elevator

Selective intake facility

DownstreamsidePower Station

Spillway

Adminisg
BuildintrationNational Highway No.417

Figure 1. PlanEL.(m)Downstream side

Upstream side

Elevation of Crest EL.406.0m

Normal Water Level EL.400.0m

RockCore
Filter161.0mRockFilter
GalleryBlanket grouting
Curtain grouting

Figure 2. Cross Section
EL.(m)

EL.(m)Left bank

Right bank

Length of Crest 427.1m

Elevation of Crest EL.406.0m

Spillway

Low Water Level EL.363.5m

Diversion tunnel No.2
Diversion tunnel No.1

Figure 3. Longitudinal Section of Dam Axis

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Tokuyama Dam

Table 1. SPECIFICATIONSSPECIFICATIONS

ITEM
Purpose(s)Flood control, Nonspecific use/ecological discharge,
Water supply, Irrigation, Power generation

Location

Chubu Region (Ibigawa town, Ibi-gun, Gifu Pref.)River

Ibi River, Kiso River System

Catchment Area

254.5 k m2

Completed2008

ReservoirDam

Spillway

Total Storage Capacity

660,000,000 m3

Effective Storage Capacity

380,400,000 m3

Reservoir AreaApprox. 13 km2

TypeCentral Core Type Rockfill DamHeight161 m

Length of Crest

427.1 mVolumeApprox. 13,700,000 m3

Crest Spillway

Orifice Radial Gates
W 4.1m × H 4.1m × 2 Gates

Emergency Spillway

Radial Gates Overflow
W13.4 m × H10.95 m × 4 Gates

Design Flood

4,200 m3/s

Water Discharge
System for
Utilization

Water discharge Gates

Main Gate: Jet Flow Gate, φ 1,900 mm
Auxiliary Gate: High Pressure Slide Gate, φ 2,150 mm

Intake Equipment

Water Intake Gate
Dam Body

Kumagai Gumi Co.,Ltd, Taisei Corp., Asunaro Aoki
Construction Co.,Ltd.

Spillways

Obayashi Corp., Shimizu Corp., Dainippon Construction

Operator(s)Chubu Electric Power Co., Inc.

Start of commercialoperation

Unit 1：March 24,2016
Unit 2：May 15, 2014

Type

Conventional

Turbines

Francis-type

Installed capacity

Unit 1: 139,000 kW, Unit 2: 24,300 kW
The total output during simultaneous operation amounts to161,900 kW

Primary Firms

Power Station

1.

Straight Multi-step Gate
W 11.0 m × H 45.5 m × 5 Steps-shutters

Background Notes

The upstream basin of the Ibi River, where the Tokuyama Dam was constructed, was designated as a
“survey district” under the Electric Power Development Promotion Act (1957). The Tokuyama Dam Project
started with a pre-execution planning survey held by J-Power in 1971. In 1976 the Project Plan was approvedby the Japanese Government and the Project was taken over from J-Power to the Water Resources Development
Public Corporation (WARDEC) (precursor of today’s Japan Water Agency (JWA)). The relocation of all 466
households in the planned reservoir area was completed in 1989. The construction of the dam body began in2000 and ended in 2006. An initial impoundment followed for 2 years. In 2008 the operation of the dam started
and the Project finally ended.

28Tokuyama Dam

The Tokuyama Dam is the largest rockfill dam in Japan(Top for the reservoir capacity of about 660 million
m3 and dam body of about 13.7 million m3. The third rank for the submerged area of 13 km2 and dam height of161m).
2.

Site Factors

The geology at the dam site has bedrock of Paleozoic/Mesozoic Mino Zone, covered with a Quaternarylayer. The bedrock consists of basalt (lava), tuff, chert, and slate. On the dam axis section, basalt and tuff aredistributed throughout the foundation, with blocks of chert distributed between them. The slate is distributednear the foundation under the spillway overflow part.
In the basement of reservoir, the Ibi River Fault runs continuously NW-SE towards the upstream Ibi River.
Therefore the Neodani Fault which was the epicenter of the massive Nobi Earthquake in 1891 is nearby, thedam’s earthquake safety factor is k = 0.18, for the earth quake safety.
3. Design
3.1 Effective Use of Sand and Gravel from an existing Dam
For construction of Tokuyama Dam, some 840,000 m3 of sand and gravel were collected from thesediments in the reservoir of Yokoyama Dam located further downstream. They were recycled as materials forfilter or concrete aggregate of the dam site. This process resulted in reducing CO2 emissions caused by crushing
new materials, omitting alternation of 17 hectares of quarry sites, and also lowering the cost of materialprocurements. For Yokoyama Dam, the removal of sediment deposits meant a refreshing of the reservoir bed,and recycling them led to lowering the cost for disposing.
3.2 New Technologies and Construction Methods
New technologies and construction methods, such as construction of cofferdam by CFRD (ConcreteFacing Rockfill Dam) method, a submerged fine aggregate weighing system, an automated scanning radio
isotopic densimeter and management of construction process and quality by GPS managing system, were usedthroughout the Project. Safety was enhanced by seismic designs and verifications regarding to the presence ofthe Neodani Fault.
4.

Construction in Practice

4.1 Fast Embanking of the Dam Body (A New Japanese Record for Dam Body Construction)
A quick collection of core materials was implemented by such heavy construction machineries as 12 m3wheel loaders and 46 ton dump trucks. The embankment of core was also carried out speedy by increasing thethickness of each embankment to 30 cm from 25 cm. A number of large heavy machineries such as 90 ton classripper bulldozers, 12 m3 class backhoes, 10.3 m3 class tractor shovels, and 90 ton dump trucks enabled a fastcollection of the massive rock-fill materials. This largest dam in Japan with the volume of 13.7 million m3 wascompleted only within 26 months (excluding a winter break), setting a new Japanese record of 6.2 million m3
embankment in a single year (Photo 1).
At the same time, the spillways were constructed at high speed using slip forms and large sliding forms,etc., and it enabled shortening the execution period and cost reduction (Photos 2 and 3).

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Tokuyama Dam

Photo 1. Tokuyama Dam at the Peak of Embanking (Compaction with 18T class vibrating tamping
rollers, embankment with 90T ripper bulldozers)

Photo 2. Construction of a Training Slip Forms

Photo 3. Construction of a Training Wall with Large Sliding Forms
4.2 Ecological Dam in Harmony with Nature
254 k m2 natural forest, including broadleaved forest by 90%, in the upstream basin was municipalized topreserve the water resource environment. Installation of temporal equipment in the planned reservoir area andmaking 70 % of the access roads (total length of 12.5 km) into tunnels contributed greatly to conserve the28

Tokuyama Dam

natural environment with a rich diversity of flora and fauna. Restricting deforestation and cutting of trees insidethe dam reservoir formed an ecotone, a transition area between two different biomes. This also improved thescenery along the reservoir shoreline, and restricted the discharge of turbid water.
For the Tokuyama Dam Project, a large scale survey of raptors covering the entire basin was carried out. Itwas the first time in Japan that such a large scale survey was held. The result showed 5 pairs of golden eagle
and 17 pairs of mountain hawk eagle were breeding in the basin. The CCD cameras set on the nest trees ofmountain hawk eagle also revealed a number of new biological information. Basing on those findings from thesurvey, adjustments were made to the construction schedule, and methods of construction execution werechanged to reduce noise and vibration.

Range of public forest land
Range land was obtained (about 180 km2)
(excluding national land, prefectural land,and municipal land)
Artificial forests inside the range of the land
obtained(including profit-sharing forests)

Figure 4. Municipalized Forest
5. After the Project
Various environment preservation measures had been implemented during the construction of Tokuyama
Dam. The findings and evaluations gained from monitoring surveys of almost three years after the Projectsurely show the effectiveness of the environmental preservation measures. They also show changes in habitats
coping with new environments created by the reservoir.
References:
1) Tokuyama Dam Management Office web site, http://www.water.go.jp/chubu/tokuyama/(in Japanese)
2) Yoichi Takahashi,Akira Yanagawa,Hiroshi,Matsumori,“Environmental Cocservation Activities atTokuyama Dam in Japan”, 72nd Annual Meeting,2004 ,ICOLD
3) Hideki Soda, Satoyuki Omae, Mikio Nonaka, Nobuteru Sato,“Behavior of slabs of CFRD”, LargeDams, No. 190, January 2005(in Japanese)
4) Masaru Sato, Shigenobu Sakon, Sigeyuki Miyauchi, Masayoshi Kodaniguchi,“Slip form work on thespillway training works at the Tokuyama Dam”, Engineering for dams, No. 230, January 2005(inJapanese)5) Mitsuhiro Oie, Satoshi Kawaji, Mikako Miyahara,“High-speed execution of embanking of the core ofthe Tokuyama Dam”,Dam Engineers, Vol.16 No.2, June 2006(in Japanese)6) Shigeharu Jikan, Kota Murao, Michito. Nakamura, Tadayuki. Nishiyori,“Project to Convert Mountain
Forests to Public Ownership throughout the Entire Upper Catchment Area of the Tokuyama DamReservoir”,3rd Annual Meeting,2006, EADC28Tokuyama Dam

7) Tomonobu Sato, Shigeo Sakon, Shigeharu Jikan, Satoshi Kawaji,“Utilization of Reservoir Sediment ofthe Existing Dam (Yokoyama Dam) for Tokuyama Dam Construction Materials” 4th Annual
Meeting,2007, EADC
8) Shigeharu Jikan, Kota Murao,Takashi Kajitani,Takeshi Suyama,“Environmental Conservation at theTokuyama Dam”, 4th Annual Meeting,2007, EADC
9) Hideki Soda, Mariko Kinoshita, Mikihiro Tanaka, Koji Hino,“Trial ponding at the Tokuyama Dam―Results of monitoring the dam body etc. during trial ponding and response during trial discharge―”,Engineering for dams, , 78th Annual Meeting,2010 ,ICOLD

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Tokuyama Dam