Weekly Report: Phantom dam is most expensive ever

The Yanba Dam in Naganohara, northwestern Gunma Prefecture, has become a typical example of a public works project that no longer matches the times.

Fifty-seven years have passed since the government floated the idea. During that time, the project has snowballed into the most expensive of its kind in Japan.

Why has the project cost so much? Was it even necessary?

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Question: The cost of the Yanba Dam project in the Agatsumagawa river, a branch of the Tonegawa river, has doubled to 460 billion yen. That means it is the most expensive dam in Japan. Why have project costs snowballed?

Answer: The compensation paid to residents who have to be evicted has increased three and a half times. The construction costs for a new railway and roads to circumvent areas that will eventually be submerged have doubled. It has also become necessary to take precautions against landslides.

It is a typical dam project case, in the sense that the initial cost estimate was far too optimistic. The construction cost of the dam itself is only 62 billion yen.

In addition to the 460 billion yen, 117.5 billion yen has been earmarked for flow-on programs. Part of that money is to be used to build sewerage systems and community halls for residents who moved to substitution land from areas that will be submerged. Those programs are based on the special measures law for areas that serve as sources of water supplies.

The rest of the money will be used to build roadside rest houses, sports gymnasiums and other infrastructure. It has been paid from a fund set up by the governments of prefectures located downstream of the Tonegawa river system. About half of the 117.5 billion yen has already been spent.

Some advocates of the project say 70 percent of the Yanba Dam has been built. Actually, however, 70 percent of the 460 billion yen for the project, or about 321 billion yen, has been spent. That does not mean that construction of the dam itself has progressed to the 70 percent stage.

Of 470 households subject to eviction, about 100 have yet to move to substitution land. Twenty percent of land for a new railway station has not been acquired yet, either. Many local residents are skeptical that the government can complete the dam with the remaining 30 percent of the budget, which is 139 billion yen.

Let's compare how much it would cost to scrap the project with how much it would cost to complete it according to plan.

The governors of prefectural governments that have contributed funds to the project are demanding the central government return the money if it scraps the project. The law on special multipurpose dams stipulates that the government must return money paid for water use.

The governments of Tokyo, Saitama, Chiba, Ibaraki and Gunma prefectures have paid 148.6 billion yen for this purpose. But about 40 percent of the amount was covered by subsidies from the Ministry of Health, Labor and Welfare and other central government bodies. The government would have to return the remaining 60 percent, or about 89 billion yen, to the five local governments if it scrapped the project.

These local governments and the Tochigi prefectural government have also paid 52 billion yen for flood control work. The law does not oblige the central government to return this money.

Of the 460 billion yen budget for the project, 77 billion yen must still be spent to help residents rebuild their lives in new communities. Seiji Maehara, the minister of land, infrastructure, transport and tourism, is determined to spend this money to help residents regardless of what happens to the project.

So if the government canceled the dam project, it would have to pay at least 166 billion yen (89 billion yen and 77 billion yen), on top of the 321 billion yen already spent.

If it continues with the project on the assumption that no additional work is necessary, it will need another 201 billion yen--139 billion yen for the remaining 30 percent of the project cost, plus 62 billion yen for the programs yet to be implemented under the special measures law and with the fund set up by the prefectural governments.

Consequently, it would be cheaper for the government to take the former option.

In that scenario, however, it would need more money if it wanted to implement all the remaining programs which should have been financed by the prefectural governments under the special measures law and with their fund.

Equally, in the event the government decides to press on with the dam project, it could need more money to fund unforeseen additional work.

Maehara said, "We should not think (about which case would require less money) from the viewpoint of the loss and gain of one project."

If the dam was completed, it would stop earth and sand from being carried to downstream areas. As a result, work would be needed to protect shorelines from erosion. Earth and sand accumulated at the bottom of the dam lake would also have to be removed.

Maehara apparently thinks that in an era when the population and the tax revenues are both decreasing, the government must free itself from the costly cycle in which public works projects beget more public works projects.

The collective budget for the construction of all dams around the country exceeds 6 trillion yen. Maehara believes that even if the government incurs a financial burden by scrapping the Yanba Dam project, it would be a necessary cost for the change to the way it uses taxpayer money.

Yanba project not enough for freak storm

Q: To begin with, why did the government want to construct the Yanba Dam?

A: The Kathleen Typhoon that hit Japan in September 1947 triggered mudflows and broke the banks of the Tonegawa river. The natural catastrophe claimed the lives of about 1,100 people in Tokyo and five other prefectures.

In response, the government decided to construct several dams on the upper part of the Tonegawa river system for flood control. One of them was the Yanba Dam. The aim was to build a series of dams that would protect people living along the Tonegawa river from the worst possible storm in 200 years--a torrential downpour that would dump as much as 318 millimeters of rain for three days.

The government made its calculations based on the assumption that 22,000 tons of water would flow per second through the midstream area of the river in Yattajima in Isesaki, southern Gunma Prefecture.

The Yanba Dam would be able to reduce that amount of water flow to some degree. To reduce it sufficiently, however, the government would need to build more than 10 additional dams. At present, there are no plans to construct any more.

Takashi Okuma, a professor emeritus of river engineering at Niigata University, says the assumption that the water flow would reach 22,000 tons a second is excessive. A more reasonable figure, he believes, is about 17,000 tons--in which case the current flood control measures alone would be sufficient to prevent disaster.

Using an even more catastrophic scenario--a once-in-a-millennium storm that would unleash 390 millimeters of rain for three days--the government's Central Disaster Prevention Council calculated a worst-case outcome in which 26,000 tons of water would flow through the Yattajima area every second, causing flooding that would kill 11,000 people.

The calculation was made in view of the increasing incidence of large-scale floods due to global warming.

As long as this way of thinking continues, the government will have to construct dams endlessly.

Hirotake Imamoto, a professor emeritus of river engineering at Kyoto University, has urged Maehara, an old acquaintance, to focus less on dams and more on reinforcing embankments, whose collapse could trigger devastating consequences, and also on strengthening evacuation measures.

Water supply secure even if plans aborted

Q: Some people say that the Yanba Dam is necessary for the stable supply of water to the Tokyo metropolitan area. Is this true?

A: In July last year, the infrastructure ministry revised downward the estimated demand for water from the Tonegawa river system during the period through fiscal 2015. It made the revision to account for the declining population.

Further, the average amount of water one person uses a day has been decreasing since 1997, owing largely to the water-saving functions of toilet bowls and washing machines.

However, the volume of water stored in dam lakes has also been decreasing due to the aging of dams. As a result, the ministry says the dams under construction are necessary. But the governments of Tokyo and the five other prefectures have already secured a water supply sufficient to meet demand in their areas.

The population of Tokyo, for example, used up to 4.92 million tons of water a day in fiscal 2008. The Tokyo metropolitan government has access to 6.3 million tons. If the Yanba Dam is completed, it will have access to an extra 430,000 tons.

Nonetheless, Tokyo, Saitama, Chiba, Ibaraki and Gunma prefectures all took part in the Yanba Dam project with a view to increasing their water supply. That was because they are not allowed to take water from the Tonegawa river unless they shoulder part of the cost of the project.

In the case of Saitama Prefecture, 90 percent of its water supply was underground until 1968. Eventually, however, ground subsidence became a problem. In the 1970s and '80s the prefectural government was forced to take more water from rivers.

At present three-quarters of its water supply comes from the Tonegawa and Arakawa river systems. But because it has contributed money to relatively few dam projects, it can only take water for 1.6 million of its residents as a "temporary measure."

Between April and September each year, the Saitama prefectural government can divert water for agricultural purposes to tap water. Between October and March, however, it cannot. To cover the gap, the prefectural government offered money to the Yanba Dam project.

If the dam is completed, the prefecture will be able to receive water supply preferentially in times of water shortages.

Saitama Prefecture had also taken part in the Tokura Dam construction project in Katashina, northeastern Gunma Prefecture, which was launched by the government-affiliated Japan Water Agency. But in 2003 Saitama Governor Kiyoshi Ueda announced his prefecture would withdraw from the project. Tokyo Governor Shintaro Ishihara followed suit. The Tokura Dam construction project was scrapped as a result.

The principal reason for the Saitama prefectural government's decision to withdraw was that it felt it would secure a stable and sufficient water supply from the Yanba Dam project instead.

The governors of Tokyo and the five other prefectures insist that the Yanba Dam is necessary because there are often water shortages in the Tonegawa river. During the past 20 years, the intake of water from the Tonegawa river has had to be limited six times.

On those six occasions, however, the governments were not required to suspend water supply to households, though they did have to curb the pressure.

Tokyo also takes 70 percent of its water from the Tonegawa river.

If the following measures are taken, it may be possible to deal with water shortages.

・Consider using underground water in a way that will not cause ground subsidence.

・Improve the dams in operation in the upper streams of the Tonegawa river.

・Encourage greater use of water-saving technologies.(IHT/Asahi: November 21,2009)