Wakayama Prefecture Dam

1644-Tonoyama Dam a.k.a. Gogawa Dam / Wakayama Prefecture

1644-Tonoyama Dam (Tonoyamadam) a.k.a. Gogawa Dam / Wakayama Prefecture, JapanWakayama Prefecture Dam
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Date of interview: Wednesday, 1/28/2015

The last dam visited that day became the Tonoyama Dam, an arch dam owned by Kansai Electric Power Co (KEPCO). It is also known as the "Gogawa Dam". I don't remember anymore where and how we drove, but it seems that we had traveled quite a distance from the Shimanose Dam.

Gogawa Dam Observation Deck

The first place I arrived at was not the dam site but the Gogawa Dam observation deck. The official name of the dam is Tonoyama Dam, and because the name of the place is Gogawa, it is called Gogawa Dam by the local people. However, the fact that they do not deny the common name and accept the name "Gogawa Dam" is an expression of their kindness in wanting to be close to the people who live there, as well as their consideration for the local community itself.

Gogawa Dam Observation Deck
Gogawa Dam Observation Deck

Otherwise, I don't think they would have put it on the sign. I don't know whether KEPCO or the local community is responsible for the installation of these signs, but at least that is my impression. (The sign on the right looks like it was prepared by KEPCO, while the one on the left looks like it was prepared by the local government.)

Gogawa Dam observatory signboard
Gogawa Dam observatory signboard

As the cross-sectional view on the overview sign indicates, the Tonoyama Dam is a domed arch dam. It is also the first domed arch dam in Japan. It is no exaggeration to say that it is the culmination of Japan's technological prowess, and is said to be the cornerstone of the Kurobe Dam construction.

The Tonoyama Dam seen from the observatory can be captured straight downstream, but the distance makes it look a little small.

Tonoyama Dam (Kappawa Dam) Wide angle
Tonoyama Dam (Kappawa Dam) Wide angle

The mountains are overlapping each other, and the downstream area is just like a beautiful canyon. The Kanden black crest gate and the unique brownish embankment are very tasteful and elegant. It doesn't look much like an arch dam from here, by the way.

Tonoyama Dam (Kappawa Dam)
Tonoyama Dam (Kappawa Dam)

Also in the Kanden Blackorifice gateThe water that is released from it is also very beautiful. The water emanating from it is also very beautiful.

Discharge from orifice gate
Discharge from orifice gate

Incidentally, the Tonoyama Dam has four 7.150 x 5.670 m steel roller gates, two on each side, and two 7.756 x 5.650 m orifice gates in the center. The crest has six 6.770 x 2.279 m steel drop gates.

As the name implies, a drop gate is a gate that is lowered during discharge to allow overflow at the top of the gate. When normally closed, the gate is raised. It looks similar to a roller gate, but the normal and operating times are reversed.

The reason why a drop gate was adopted for the crest gate of the Tonoyama Dam is probably because it is an arch dam with a thin embankment and overflow section because the door body can be contained in a small space.

Dam site of Tonoyama Dam

I moved to the dam site. The dam site does not look like a dam, but just a parking lot, a building, and a crane. I wasn't sure if I could park my car in the parking lot, but since there was no other parking lot, I borrowed it for a while.

Tonoiyama Dam Dam Site
Toyama Damdam-site

A crane for loading and unloading materials.


To my surprise, the Tonoyama Dam is open for tours if you make a reservation in advance. I wonder if it is not possible to visit alone...

To all those wishing to visit the Tono Mountain Dam."
To all those wishing to visit the Tono Mountain Dam."

The top of the Tonoyama Dam and the dam management office are located further down from here, where an incline has been installed on a steep slope.

Inclines and Bogies
Inclines and Bogies

Just by looking at this, you can see that it was built on a very steep terrain.


I moved to the right and left on the right bank to see if I could somehow see the embankment. However, the trees were in the way and this was the best I could do. If I have a chance, I would like to visit the embankment. I would love to see the smoked silver dam at close range...that's what the Tonoyama Dam was like.

View of the top edge from the right bank
View of the top edge from the right bank

(extra) Cape Shiomisaki

Since this was my first visit to Wakayama, I wanted to see the southernmost point of Honshu, so I came to Cape Shiomisaki for the last stop of the day. Normally, you can visit the Shiomisaki Lighthouse, but since it was dusk, I only saw it from outside the gate.

Shio Misaki Lighthouse
Shio Misaki Lighthouse

Cape Tidal Basin is enveloped in evening darkness.

The southernmost stone monument in Honshu
The southernmost stone monument in Honshu

My first visit to Wakayama was very enjoyable as everything I saw was fresh and new. There are many sightseeing spots, such as the ocean, mountains, and of course, many different types of dams to enjoy to the fullest. I left Cape Shiomisaki with a vow to return to Wakayama.

View of the Pacific Ocean from Cape Ushio
View of the Pacific Ocean from Cape Ushio

Tonoyama Dam Specifications

LocationAza-Hinamiguchi, Aza-Agawa, Tanabe City, Wakayama Prefecture
River NameHikigawa River System Hikigawa River
ObjectiveP(Power generation)
ModelA(arch dam)
Bank height64.500m
Bank length128.692m
Dam volume54,100 m3
Watershed Area294km2
Reservoir area137 ha
Total storage capacity21,320,800 m3
Effective water storage capacity13,152,900 m3
Dam operatorKansai Electric Power Co.
Main body constructorMaeda Corporation
Year of launch1955
Year Completed1957
Name of Dam LakeGogawa Reservoir

Other facilities/observations

Parking lot
PR Exhibition Hall×
Viewing platform×

Map around Tonoyama Dam (Gogawa Dam)

Weather around Tonoyam Dam (Gogawa Dam)

Accommodations that may be close to Tonoyama Dam (Gogawa Dam)

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This article was written by.
Shin Jinma

Dam enthusiast who loves Momosuke Fukuzawa / Dampedia and Dam News administrator / Certified Dammeister (01-018) by the Japan Dam Foundation / Started selling discharge caution goods.https://shop.dampedia.com

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