Nakayamagawa Dam

Overview

Nakayamagawa Dam is a gravity concrete dam built on the Nakayamagawa River, part of the Shimatagawa river system, in the city of Iwakuni, Yamaguchi Prefecture. With a height of 37 meters and a crest length of 143 meters, this mid-sized structure blocks a quiet valley and serves two purposes: flood control and municipal water supply for the surrounding area. Ringed by green wooded hills, the dam offers the understated power of civil engineering, its outlet works and reservoir best appreciated as a short stop on a drive through eastern Yamaguchi rather than as a busy tourist site.

Highlights

• ●A 37-meter-high, 143-meter-long gravity dam damming a quiet valley
• ●A mountain reservoir holding up to 7.55 million cubic meters of water
• ●A dual role of flood control and municipal water supply
• ●Calm scenery formed by wooded hills and still water

History

Construction began in 1974 and, after roughly two decades of work, the dam was completed in 1995. Its catchment area is about 15 square kilometers, and when full the reservoir covers around 57 hectares and can store 7.55 million cubic meters of water. The Nakayamagawa had a history of causing flood damage downstream, and the dam was planned to control those floods while meeting the region's growing demand for water. The long construction period reflects the careful surveying and building of its era.

Map

34.0575, 132.0525 · Wikidata

Suggested itinerary

1. 1Set out from central Iwakuni and drive upstream along the Nakayamagawa
2. 2Look up at the dam wall from the downstream side to feel its scale
3. 3Take in the reservoir and ridgelines from the crest or a viewpoint
4. 4Return toward Iwakuni enjoying the riverside countryside on the way back

Did you know?

💡 At 37 meters, the dam is roughly as tall as a mid-rise building of a dozen-plus floors. The span from its 1974 groundbreaking to its 1995 completion—over twenty years—illustrates just how long-term a project balancing flood control and water supply can be.

Nearby spots