Brief history of dams in Japan

 

From ancient times, the Japanese people have been familiar with irrigation, water supply and flood control facilities. Rice cultivation was introduced to Japan around the 10^th century BC. The earliest rice paddies with civil engineering facilities can be found in south-west of Japan. In the 6th century, the Emperor at that time established centralized government. He prepared irrigation systems for paddies and allocated a certain area of paddy to farmers. A certain portion of the harvest was collected as tax. Sayama-ike, an oldest earth-fill dam for irrigation still in use today, was built in the early 7th century.

 

In the 20^th century, many large dams for flood control and hydropower have been constructed in the central highland, as there are high mountain peaks of over 3,000 meters in elevation and many steep swift-flowing rivers.

 

In 1950, Japan’s first modern rock-fill dam for hydropower in the central highland, Miboro Dam (H=131m) was planned. The project faced with fierce local opposition to construction. The president of the state-owned hydropower company negotiated earnestly, politely, and in good faith with the residents of the proposed submerged area, and after more than 7 years negotiation, finally it reached a settlement on the relocation.

As a token of appreciation for the residents, a 400-year-old large cherry trees (20m high, 6m trunk) in submerged area were transplanted to the dam site. Although this transplanting work was very difficult and challenging, the cherry trees took root and, every spring, they are in full bloom, with petals still scattering into the reservoir. The story related to this transplant work has been adapted into novels and dramatic movies.

In 1963, Kurobe Dam (H=186m), the tallest arch concrete dam was constructed in a nature reserve area. All major facilities as headraces, penstocks, power plants and access roads were underground. Tateyama-Kurobe-Alpine-Route is 40 km sightseeing route by electric bus, ropeway and tunnel cable railway. You can meet spectacular sceneries and alpine fauna and flora, which attracts nearly 1 million visitors a year. (https://www.alpen-route.com/en/)

The story of the various difficulties during construction was made into a blockbuster movie starring Toshiro Mifune, a world-renowned actor in director Akira Kurosawa’s films. Several dramatic movies related to other dams have been also released. These films helps the people to understand the technical and social complexities faced during planning, construction and operation.

 

Experience of Yamba Dam

 

When a dam project is announced, there are usually strong protests. Negotiations for relocation become difficult. The Japanese Government therefore prepare laws and rules for compensation for losses, support for rebuilding livelihoods and the promotion of the welfare of relocated people. However, in the case of the Yamba Dam, it took a long time to conclude negotiations due to stiff resistance.

The Yamba Dam (H=116m) was planned in 1967 in the upper area of Tone River basin in Kanto Plain which area is 17,000 km2 includes Tokyo metropolitan area. When extreme heavy rainfall occurs in this basin, Tokyo may suffer severe flood damage. The government has strengthened the levees of Tone River and constructed several flood control dams. But the Yamba dam could not be constructed, because of hard resistance. After 42 years negotiations, it had almost reached a conclusion by 2009.

Same year, the Liberal Democratic Party (LDP), the governing party for nearly 50 years, lost the general election, and the Democratic Party of Japan (DPJ) administration began. DPJ declared the policy of “from concrete to people”, meaning “value people, not construction project in budget priorities”. The national budget was restructured, resulting the suspension of many large infrastructure projects such as new dams, new highways and new ports.

 

As a symbol of the “concrete to people” policy, the DPJ administration stated, “Yamba Dam project would be suspended and reviewed.” The residents who had made up their minds to accept relocation were surprised at the sudden suspension of the dam project.

From 2009, the Yamba Dam functions’ re-examination based on the current situation was started. The re-examination took more than 2 years and concluded in September 2011. The conclusion was that dam was the most advantageous in flood control, water utilization and hydropower. The policy was changed again and construction project was restarted. In December 2012 DPJ lost the general election.

The contractor was Shimizu corporation, Tekken corporation and IHI infrastructure Joint venture. The contractor then resumed construction of the dam, working day and night.

 

In 2019, the dam construction work was almost finished and it was time for impounding. Initial impoundment was started on 1st October 2019. During initial impoundment, extremely powerful typhoon Hagibis moved northward from the Pacific Ocean and attacked the center of main island in mid-October 2019.

 

 

Tone River basin experienced extreme large volume of rainfall. Despite initial impoundment, Yamba Dam stored the floodwaters from rainfall and prevented flood damage in the downstream areas including Tokyo metropolitan area. Reservoir water level rose 54 meters in two days, which was abnormal speed of water level rising in first impoundment. The flood which maximum inflow was approximately 2,500 m³/sec by accumulated rainfall of 347 mm, was successfully stored and its volume was 75 million m³.

 

Fortunately, there are not any damage on dam, abutments and reservoir.

 

The twists and turns of Yamba Dam project, long-time relocation negotiations, its suspension and restart were well known. The incredible fact that this dam brought flood control benefits to Tone River basin and Tokyo metropolitan area during the initial impoundment was widely reported by medias. This news provided an opportunity to the public to reaffirm the benefits of dams for recent changes in the natural environment, such as increased heavy rainfall.

 

(Those 2 photos are provided by Tone River Dams Integrated Management Office, Ministry of Land, Infrastructure, Transport and Tourism)

 

Tourism around Dam

 

Dam tourism is popular around the large dams in Japan. Many dams allow public access to top of dam and reservoir. Prominent celebrities have claimed to be dam enthusiasts, and TV programs on dam tourism have been often broadcast. These have been very helpful in creating a positive perception of dams. Today, there are not so many objections to dam, although some environmental groups still claim to be against them. JCOLD has supported in editing a 200-page, all-color travel guidebook, “How to Walk Around the Dams”. The authors are eight private dam enthusiasts, who wrote comprehensive information on 200 prominent dams, with beautiful photographs, location maps, dam features and information of nearby attractions such as hot springs.

Oku-Tadami Dam (H=157m, http://okutadami.co.jp/English-okutadami/) has a 560MW hydropower station with one of the largest reservoirs fed by Oze marshland. Oze marshland is in nature reserve area, wetland spreads out at an altitude of 1,700 meters, with streams, small ponds, grasslands, forests and a variety of trekking routes. Skiing and snowboarding slopes are provided with powder snow in winter in the vicinity of the Dam.

 

Oze marshland in winter

 

Conclusion

 

In Japan there used to be negative opinions about dams due to resettlement, environmental destruction, and huge expenditures. However, the people have reaffirmed the benefits of dams, which are the ability of flood control, the ability to produce the renewable energy, and the ability of water storage for tap water. Despite various concerns, dam projects bring value to human society over the long term, 100 years or more, and it should not be discouraged by short-term thinking or opposition and current political situations, which may change in a period of time.

 

 

by Hiroyasu SUGIYAMA Former President of JCOLD (Japan Commission on Large Dams)

 

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