Photo/IllutrationThe Oura Bay side of the Henoko district where the central government plans to shore up the soft seabed (Eiji Hori)

The government’s plan to relocate a U.S. military base in Okinawa Prefecture is clearly in tatters, despite Prime Minister Shinzo Abe’s insistence that it is the “only solution.”

Despite fierce local opposition, the Abe administration has been forging ahead with the controversial plan to build a new base in the Henoko district of the Okinawan city of Nago to replace the U.S. Marine Corps Air Station Futenma, which sits in the middle of the crowded city of Ginowan within the prefecture.

The Defense Ministry is considering a drastic change in the method of the land reclamation work in response to a serious technical problem that has emerged. The seafloor in some parts of the Henoko reclamation area is “as soft as mayonnaise” to a depth of dozens of meters.

According to details of the new blueprint for the work disclosed by a prefectural government document, the ministry plans to drive 76,699 sand piles into the seabed. This is intended to shore up the soft ground in a 65.4-hectare area that accounts for 60 percent of the side northeast of Camp Schwab (Oura Bay side) where land reclamation work has yet to start.

The volume of sand to be used for the piles will total about 6.51 million cubic meters, which is enough to fill the Tokyo Dome stadium 5.25 times. It also corresponds to the volume of sand collected throughout Okinawa Prefecture for construction and other projects over several years.

Coastal waters in some of the areas in question are as deep as 30 meters. In addition, the soft ground below the seabed extends 60 meters, bringing the total to 90 meters.

In a news conference on Feb. 21, Chief Cabinet Secretary Yoshihide Suga stated: “The method of using sand piles is a conventional one and has been used in many construction projects. It is possible to use it (off Henoko).”

But Defense Minister Takeshi Iwaya has told the Diet that Japanese companies have never used this method for such soil improvement work beyond a depth of 70 meters.

The work is likely to pose unprecedented technical challenges.

Given its impact on the surrounding ecosystem, including precious corals, a fresh environmental assessment will also be necessary.

Other issues that need to be considered include the possibility of subsidence of the envisioned runway and measures to secure the safety of the facility against earthquakes and high tides.

Surprisingly, however, the central government offers no estimates of the period and cost of the soil improvement work.

In a late January Diet session, Abe said it was difficult to make reliable estimates of these factors at the moment. That is an extremely irresponsible position to take.

Pushing through a public works project without estimates of its period or cost is simply unacceptable.

The planned soil improvement work requires a change of the design plan, but Okinawa Governor Denny Tamaki is intent on rejecting the central government’s application for approval of the change.

Proceeding with the Futenma relocation plan after voters in Okinawa have repeatedly expressed their opposition will also be a formidable political challenge.

If the work to build a new base in Henoko is prolonged much longer, the Futenma facility, which poses a safety threat to residents in densely populated areas, will have to remain at its current location.

That situation would also contradict the government’s rationale for pushing through the Henoko project, which is to remove the danger posed by the Futenma base as quickly as possible.

In February 2014, Abe promised Okinawa Prefecture that Futenma operations would be terminated within five years. That deadline expires this month.

The pledge was made in response to a request by then Okinawa Governor Hirokazu Nakaima before giving his approval to the land reclamation work in Henoko. But the promise proved worthless.

In the meantime, the Abe administration did not disclose the existence of the extremely soft seabed despite being aware of the problem. Instead, it has been pouring sand into shallow areas in an attempt to present the project as a fait accompli.

It is now poised to ignore the outcome of a Feb. 24 prefectural referendum on the project.

Clearly, the current Futenma relocation plan has become clearly unworkable. The administration should suspend the work and start talks with the U.S. government on an alternative plan.

It also needs to try to extricate itself from the vicious cycle in which its high-handed approach to this tough policy challenge provoked a local backlash, compounding an already difficult situation.

--The Asahi Shimbun, Feb. 23