Annex_VIII_CaseStudy0302_Funagira_Japan.pdf

IEA Hydropower Implementing Agreement Annex VIII –

Hydropower Good Practices: Environmental Mitigation Measures and Benefits

Case study 03-02: Fish Migration and River Navigation - Funagira Power Plant, Japan

Key Issue:

3-Fish Migration and River Navigation

1-Biological diversity

Climate Zone:

Cf: Temperate Humid Climate

Subject:

- Confirmation of the Effect of the Fish

Ladder in Facilitating Upstream Migration

Funagira Dam

Effects:

- Protection of Fish Resources

Project Name:

Funagira Power Plant

Country:

Shizuoka Pref., Japan (Asia)

Implementing Party & Period

- Project: Electric Power Development Co. Ltd. (J-POWER)

1972 (Commencement of construction) -

- Good Practice: Electric Power Development Co. Ltd. (J-POWER)

1977 -

Keywords:

Fish ladder, Investigation of Upstream Migration, Sweetfish, Fish Straying Prevention

Device, Sodium Lamp Lighting

Abstract:

Following the installation of the fish straying prevention device in the dam and the fish

ladder furnished with sodium lamps in the dam culvert, the investigation of upstream

migration of sweetfish was performed on a continuous basis. Since the investigation

confirmed that a maximum of several hundred thousands of sweetfish were migrating

upstream, the installation of the fish ladder proved effective as part of environmental

impact mitigating measures.

1. Outline of the Project

The Funagira Dam was constructed at the Funagira point along the Tenryu River (Funagira,

Tenryu City, Shizuoka Prefecture: Fig. 1) for the purpose of ensuring water availability for

power generation, irrigation, and city and industrial water supply.

As the most downstream project under the consistently planned development of the Tenryu

River system, investigation and planning had been underway since 1958 for the construction

of the Funagira Power Plant. The Funagira Dam, on the other hand, was planned and designed

as a multi-purpose dam for the purpose of water intake for power generation, irrigation and

city and industrial water supply, as part of

the Tenryu River downstream water

utilization project by the Ministry of

Agriculture, Forestry and Fisheries and

Shizuoka Prefecture. The Funagira Power

Plant began being constructed in 1972 and

started operations in April 1977.

Table 1 shows the specifications of the

Funagira Dam and the Funagira Power Plant.

Shizuoka Pref.

Funagira Dam

Fig. 1 Location Map of the Funagira Dam

Table 1 Specifications of the Funagira Dam and the Funagira Power Plant

Item

Specification

Item

Specification

Name of the power

plant

Name of the dam

Funagira Dam

Funagira Power Plant

Power generation

method

Dam type power

generation

Type of the dam

Concrete gravity

Dam height

24.5 m

Effective head

14.5 m

Maximum water

discharge

270 m 3 /s

Dam length

220.0 m

54,000 m 3

Dam volume

Maximum output

32,000 kW

Annual electric

energy generation

3,600,000 m 3

Effective storage

160,100 MWh

2. Features of the Project Area

The Funagira point is located in the downstream area of the Tenryu River, which runs a total

distance of approx. 250 km (5 th in the national ranking) and has a catchment area of 5,090 km 2

(12 th in the national ranking). Located about 30 km upstream from the estuary of the river, the

Funagira point has a catchment area of as large as 4,895 km 2 .

The Tenryu River originates in Lake Suwa, runs through the Ina Valley that spreads between

the Akashi Mountain Range on the east and the Kiso Mountain Range on the west, and then

flows southward down the Tenryukyo Valley. The river gradually increases in size in its

upstream reaches, by the merging of flood-prone rivers such as the Mibugawa River,

Koshibugawa River and Achigawa River, and further increases in size, in its midstream and

downstream reaches, by the merging of such rivers as the Toyamagawa River, Ochisegawa

River, Mizukubogawa River and Kidagawa River. During this while, the river flows through

midstream and downstream dams, the Hiraoka, Sakuma and Akiba Dam, and flows into the

Enshu Plain from the point about 5 km downstream of the Funagira point.

3. Major Impacts

The downstream reaches of the Tenryu River are one of the best fishing spots for natural

sweetfish in Japan, and are also inhabited by such fish species as landlocked salmon, red

spotted masu trout, carp, big-scaled redfin, crucian carp, tilapia and eel. The river is stocked

with sweetfish, red spotted masu trout, carp, crucian carp and other fish species every year.

There was a concern that the construction of the dam may block upstream migration of fish

species such as sweetfish and thus affect the ecosystem in the river and the fishing industry in

the area.

4. Mitigation Measures

4.1 Structure of the Fish Ladder

The fish ladder was constructed in the excavated foundation of right bank structures, in

consideration of the general layout of structures including the dam and power plant. Its length

was determined according to the water level in the balancing reservoir, the downstream water

level, and the gradient of the water surface in the fish ladder. The 280 m long fish ladder is

comprised of a 71.95 m long downstream entry section, a 38.07 m long upstream exit section

with an open channel structure, and a 169.40 m long intermediate section with a culvert

structure (Fig. 2).

The water channel was 2 m in width and 1/13 degree in angle, considering the swimming

capability of sweetfish. The water channel was made to look very much like a natural riverbed

with a division wall set up every 4.05 m to create a pool and overflow and with several

pebbles laid. A 30 cm x 30 cm opening was also set up in the lower part of the division wall

for the upstream migration of eels.

When the fish ladder was first constructed, 10 cm x 70 cm notches were present alternately on

the right and left sides of the overflow crests (Fig. 3). However, the notches were removed in

1996, based on the observation that the notches caused a disturbance to the surface flow and

thus affected the upstream migration of sweetfish.

Fig. 2 Horizontal and Vertical View

of the Fish Ladder

Fig. 3 Culvert Structure of the Fish Ladder

(When Originally Constructed)

4.2 Accessory Facilities

4.2.1 Fish Ladder Gate

The fish ladder gate is comprised of a reserve gate and a control gate.

The reserve gate, a spindle and slide gate, is used during the inspection of the fish ladder or

the control gate, and has a structure that can block flowing water. The gate has an interlocking

mechanism: the opening of the gate is only enabled when the control gate is in the upright

state in order to prevent quick inflow of water into the fish ladder.

The control gate is structured to automatically rise and fall according to water level

fluctuations in the balancing reservoir with an available depth of 2.2 m used for power

generation, in order to keep the flow rate along the fish ladder steady. The bottom of the door

with a pin structure is made with a watertight rubber seal. The side of the door, in contact

with the door-shaped doorstop, is also made with a watertight rubber seal.

The overflow crest of the control gate has 15 cm of water to maintain the flow rate that meets

the swimming capability of sweetfish in upstream migration and to prevent the interruption of

rapids that makes upstream migration difficult.

Both the reserve and control gate can be operated on-site or remotely from the control office.

The specifications of these gates are shown in Table 2 and their general view is shown in Fig.

Reserve gate Control gate

Horizontal View

Vertical View

high

water

level

connection

rod

Reserve

gate

wire rope

Control gate (No.1)

tail water

level

Fig. 4 General View of the Fish Ladder Gate

Table 2 Specifications of the Reserve and Control Gate

Name

Reserve Gate

Control Gate

Item

Type

Dimensions

Slide gate

Span 2.0 m × Door body 3.1 m

Flap gate

Span 2.0 m × Door body 2.85 m

to 0.75 m

Door body + 0.25 m

Watertight rubber seal on the

three sides

Same as the left

Q’ty

Design water depth

Watertight method

3.7 m

Watertight rubber seal on the

three front sides

1/800 or less relative to the

normal design water depth

1 mm

Door and

Doorstop

Bend in the girder

Buffer thickness of

the skin plate

Doorstop height

1 mm

6.7 m

---

Type

Hoisting by use of an electric

spindle

0.10 to 0.20 m/min.

Wire rope hoisting by use of an

electrically operated drum

0.3 m/min. (Rope hoisting speed)

Hoisting speed

Lift

Operating method

Q’ty

Hoisting load

3.8 m

On-site or remotely

1 unit

Operated under all ranges of

water pressure and automatic

hoisting enabled

210V 60Hz 3f

Enclosed outdoor type,

3-phase, AC, basket induction

motor using magnetic braking

Same as the left

1 unit

Same as the left

Gate

Hoist

Power supply method

Motor

Same as the left

4.2.2 Lighting in the Culvert and Fish Straying Prevention Device

To prevent a delay in upstream migration in the culvert of the fish ladder, and prevent a delay

in the entry into the fish ladder around the entry section in particular, 22 units of yellow

sodium lamps (35 W) were set up every 8 m on the culvert ceiling when the fish ladder was

first constructed, according to the specialist advice that young sweetfish like yellow color.

Then, after the initial construction, additional 20 units were set up between previously

installed lamps (Photo 1).

Since the exit section of the fish ladder from which water flows in is relatively near the head

gate, a 300 W mercury lamp with a red filter with the effect of preventing the straying of fish

was installed in the retaining wall between the water inflow section and the head gate to light

up the water. This helped prevent the entry of fish in upstream migration into the head gate.

Moreover, the head gate in use for city, agricultural and industrial water supply is located

immediately downstream of the water outlet of the Funagira Dam. Water discharge in large

amounts for power generation increases the flow speed, making impossible the upstream

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