FUKUOKA – A university professor said Monday that restoring tideland at Isahaya Bay in Nagasaki Prefecture by letting seawater back in will make the controversial and now scaled-back land reclamation project far more cost-effective.
Koichi Miyairi of Aichi University estimated that if the national government restores the tideland, which functions as a water purifier, by permanently letting in seawater through the floodgates of a dike traversing the bay, the investment efficiency ratio of the project would exceed 1.0.
The government reclamation project was originally intended to create 1,400 hectares of farmland by filling in the 3,550-hectare reservoir created in the bay by the dike, but the planned area was slashed by half in December after local fishermen said the project is the cause of poor seaweed harvests.
Consequently, the investment efficiency ratio for the revised project fell to 0.83 from 1.01, Miyairi said. He also said it would result in 40 billion yen in overinvestment.
The agriculture ministry is proceeding with the unprofitable project even though the Land Improvement Law requires the investment efficiency ratio of farmland reclamation projects to be more than 1.0, Miyairi said.
The scholar said he calculated the efficiency ratio for restoration of lost tideland on the assumption that some 1,000 hectares of tideland in Aichi Prefecture purify sewage discharged by 100,000 people.
He found that if 1,000 hectares of tideland are restored, the investment effectiveness ratio would rise to 1.15 and that if 2,000 hectares are restored, the figure would reach 1.46.
Miyairi criticized the farm ministry for being “unaccountable to taxpayers” for the reclamation project and said the plan cannot be called a land improvement project because the crop yield increase would account for less than 10 percent of the benefits to be brought about by the project.
“The government should completely give up on the farmland project and instead concentrate on environmental conservation and disaster-prevention measures,” he said.
Isahaya Bay is part of the Ariake Sea, an almost landlocked mass of water encircled by the prefectures of Nagasaki, Kumamoto, Saga and Fukuoka.
A 7,050-meter-long dike with floodgates was built across the bay and the gates closed in 1997 to keep out seawater and thus facilitate reclamation of the land.
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