Overview
Kamiosu Dam is a massive 98-meter-high rockfill dam built across the Neo-Higashidani River, a tributary of the Ibi River in the Kiso River water system, in the Kamiosu district of Neo, Motosu City, Gifu Prefecture. It uses a central earth-core design, in which a clay wall running through the heart of the piled-up rock embankment holds back the water. Rather than existing simply for flood control or irrigation, its defining role is to form the lower reservoir of Chubu Electric Power's Okumino pumped-storage station, making it a place where visitors can take in a quiet mountain lake and a full-scale rockfill embankment while sensing the scale of Japan's power-development sites.
Highlights
- ●The commanding 98-meter central earth-core rockfill embankment
- ●A quiet highland lake forming the lower pool of Okumino station
- ●The dynamic pumped-storage system exchanging water with Kaore Dam lake
- ●A power-development site where six turbines yield up to 1.5 million kilowatts
History
Construction began in 1976 and was completed in 1995, a roughly 20-year undertaking that reflects the difficulty of building a huge artificial lake and generating complex deep in the mountains of Neo. Water is exchanged between the lower reservoir formed by Kamiosu Dam and the upper reservoir formed by the Kaore Dam lake upstream: water is pumped up when electricity demand is low and released to generate power when demand is high, in a classic pumped-storage arrangement. Six turbine generators produce a maximum output of 1.5 million kilowatts, embodying the modern idea of storing energy and using it when needed.
Access
The dam sits in the Kamiosu area of Neo, Motosu City, at roughly 35.74 degrees north and 136.66 degrees east. It lies in mountainous terrain reached by following the Neo River upstream, and public transport is limited, so arriving by car is the practical option. As a highland area prone to snow and icy roads in winter, it is wise to check the season and road conditions before setting out. Because whether visitors may enter and how far they may go can vary by time of year, please confirm the details through official sources.
Best season
The most comfortable time to visit runs from early summer, when fresh greenery dazzles, into autumn, when the surrounding slopes turn color. Autumn is especially rewarding, as the foliage of the nearby peaks is mirrored on the lake surface for a serene highland scene. Winter brings heavy snow and difficult roads, so plan conservatively.
Map
35.7375, 136.6619 · Wikidata
Suggested itinerary
- 1Follow the Neo River upstream to reach the mountain dam site
- 2View the embankment to sense the scale and structure of the rockfill
- 3Photograph the calm scene of the lake surface framed by ridgelines
- 4Reflect on the pumped-storage link between upper and lower pools before heading back
Did you know?
💡 The reservoir formed by Kamiosu Dam has a catchment area of about 12 square kilometers, floods roughly 45 hectares of land when full, and can store about 14.5 million cubic meters of water. Shuttling this water between the upper and lower reservoirs lets the system regulate electricity almost like a giant battery, which is the fascination of pumped-storage generation.
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