Posted on October 27, 2022
As an island nation with roughly 30,000 kilometers of coastline, Japan’s connection to the sea is as deep as the ocean itself.
This relationship is one of both of dependence, with most of the country’s population living in coastal areas, and fear, as tsunamis and storm surges periodically threaten communities.
A constant reminder of this complex interplay are the concrete structures that line more than 40% of Japan’s jagged coastline. From seawalls and embankments to wave-dissipating blocks and breakwaters, concrete has been used as the principal line of defense against the forces of the sea throughout the postwar period.
In fact, “Japan’s spending on physical coastal defense has few equals around the world,” researchers from Tohoku University wrote in a 2021 paper titled “Social lives of tsunami walls in Japan.”
On the island of Amami Oshima in Kagoshima Prefecture, a campaign against the construction of a seawall on Katoku Beach is a rare example of opposition to this kind of infrastructure in Japan.
Standing atop the sand dune that separates the beach’s seaward side from the village of Katoku, views of the ocean are unimpeded.
This stretch of sand, unique in its biodiversity, is nicknamed “Jurassic Beach” because its nature recalls that of a prehistoric time. It is the only beach in Japan where a leatherback sea turtle has been recorded laying eggs.
Here, the mouth of the Katoku River, Amami Oshima’s last free-flowing river, shifts naturally, creating a channel that flows parallel to the dune for several months a year and redistributes sand along the beach following a seasonal rhythm.
The beach’s appearance was transformed in October 2014 by two typhoons that uprooted the pandanus trees covering the dune and eroded part of it, leaving the beach thinner and creating a scarp 7 meters from Katoku’s cemetery, which faces the sea.
Residents of Katoku appealed for action to protect the village from future typhoons and a 530-meter-long, 6½-meter-tall seawall was proposed by Kagoshima Prefecture in 2016.
Following a review, the planned structure was shortened to 180 meters. However, the decision remains hotly contested.
Among its fiercest critics is Jean-Marc Takaki, who visited Katoku for the first time in 2010 and moved there two years ago. Takaki is one of 10 plaintiffs engaged in a legal battle with the prefecture to stop the seawall’s construction.
Backed by the Save Katoku conservation group he founded in 2017, Takaki asserts that the beach is the village’s biggest asset and that building a seawall would cause its destruction.
He claims the project also violates Japan’s obligation to preserve Amami Oshima’s environment following the island’s recognition as a UNESCO World Heritage site last year, with Katoku’s beach and river officially designated as a World Heritage “buffer zone.”
Concrete coastline
Of Japan’s many seawalls, the most striking are those lining 430 kilometers of Tohoku’s Pacific coast, some as tall as 15 meters.
Many coastal dikes in the region were damaged during the March 2011 tsunami, failing to stop waves up to 40 meters high from devastating the landscape and taking lives. Even the breakwater in Iwate Prefecture’s Kamaishi Bay, once the world’s tallest, was overwhelmed.
Yet, studies show that without the Kamaishi breakwater, “the tsunami would have been higher and would have arrived earlier,” says Tomoya Shibayama, a coastal engineering professor at Waseda University. The breakwater was destroyed, but it gave people more time to evacuate, he adds.
The government claims that dense structures are an effective defense against natural disasters. However, these barriers have also revealed fundamental weaknesses. In response, new fortifications are being designed so that the structures will survive even in the event of being overwhelmed, Shibayama says.
The government has doubled down on rebuilding barriers in Tohoku, pouring ¥1.3 trillion into coastal armoring capable of withstanding a “level 1” tsunami, expected to occur once every 150 years. To respond to a larger, once-in-a-millennium event of the size of the “level 2” tsunami of 2011, soft strategies such as redrawing hazard maps and improving evacuation plans are in place to save lives where walls can’t.
However, “protecting (communities) against nature is very difficult, and there will always be side effects,” says Koh Furuike, a research engineer at the Tokyo-based Coastal Engineering Laboratory.
Hard structures cause significant erosion of sandy beaches, as a 2019 Ministry of Land, Infrastructure, Transport and Tourism report highlights.
When waves hit a dense surface such as concrete, the reflected force causes the material around the structure to erode.
“If we try to ‘fix’ a coastline in terms of space using hard structures, a beach won’t be allowed to shift backward or forward as it should, being a dynamic ecosystem,” says Giovanni Diego Masucci, a marine biologist at the University of the Ryukyus. “Over time, this can lead to a beach’s erosion and sometimes its complete disappearance.”
In Japan, there are no regulations obliging planners to assess coastal erosion dynamics before fortifications are built, meaning that the long-term effects of construction are often poorly understood.
Similarly, infrastructure’s impact on coastal organisms has been almost completely ignored, says James Davis Reimer, an associate professor in biology at the University of the Ryukyus.
The limited data available suggests that coastal modification leads to biodiversity loss, but Reimer says that little is known about the wider impact.
“How big a footprint do these structures have on the marine environment?” he asks. “No one really knows.”
In addition, removing features such as beaches, dunes and coastal vegetation to make space for artificial revetments negates the role these natural buffers play against disasters.
Conversely, over-relying on concrete barriers may have risks. A 2018 study found that, in certain cases, seawalls made it 30% less likely that Tohoku residents evacuated promptly in the 2011 disaster because they gave them a “false sense of security.” Other analyses have noted that barriers also prevent people from seeing the waves’ arrival.
However, such findings are somewhat misunderstood, according to Shibayama, who points out that, for example, local people are taught to act on the assumption that a tsunami will follow a strong earthquake whether they can see the sea’s surface or not.
Competing claims
Back in Katoku, consensus-building meetings similar to those that had been held in Tohoku were convened to discuss the proposed construction of a seawall, which is estimated to cost around ¥340 million.
The committee that reviewed the initial plan for the seawall and decided to shorten it by two-thirds included engineering and environmental experts, local government officials and a representative of the Katoku community.
“(The committee) weighed the opinions of residents, who were interviewed individually, as well as those opposed to the project,” says Tatsuro Takeshita of the disaster prevention and coastal protection section of Kagoshima Prefecture’s River Division.
The prefectural government says details about the seawall’s construction have been explained to residents at every opportunity.
However, Takaki claims that the consultation process lacked transparency, with many dissenting voices being excluded altogether. The founder of Save Katoku also says residents have been given inaccurate and misleading information.
For example, the prefectural government has distributed a diagram that shows the village will disappear in 50 years’ time if a seawall isn’t built. Takeshita says the illustration is based on national guidelines that analyze the projected cost and benefits of coastal projects.
“We’ve been asking what the scientific basis for the diagram is, and the authorities haven’t produced anything,” Takaki says, something supported by Masumi Serizawa, founder of the Coastal Engineering Laboratory, which has conducted a scientific investigation of Katoku Beach’s dynamics following a request by Takaki’s legal team.
The Coastal Engineering Laboratory’s findings show that no long-term erosion will take place in the next half century “unless sediment is taken from the beach.”
“The committee hasn’t been telling residents properly what would happen once a wall is built,” says Furuike, namely that it would cause coastal erosion and, therefore, limit the beach’s protective impact against incoming waves.
The prefectural government says the dune at Katoku Beach hasn’t recovered despite sand returning in the past eight years since the 2014 typhoons.
However, Coastal Engineering Laboratory found that sandbags placed at the base of the scarp created by the typhoons were almost entirely buried by sand the following year in a natural rebalancing process that has continued ever since.
Mariko Abe, chief of the conservation and education division of the Nature Conservation Society of Japan, agrees.
“The sand has already recovered, so there’s no need to build a seawall,” Abe says.
Together with research organizations such as the Ichthyological Society of Japan, the Nature Conservation Society of Japan has called for the seawall’s construction to be suspended until thorough scientific monitoring can be conducted.
The plaintiffs in the lawsuit against Kagoshima Prefecture also argue that the project violates laws on the use of public funds.
“There’s no reason to build the wall as no long-term erosion is occurring, and the prefecture hasn’t certified any evidence as to why it’s needed,” says legal representative Takaaki Kagohashi of the Japan Environmental Lawyers Federation.
Since March 2019, construction has been delayed by human intervention, including protests and sit-ins, and by nature itself. Sea turtles’ nesting seasons have stopped work from going ahead as these creatures are protected by Kagoshima prefectural law, and the area’s topography limits options for moving concrete blocks to the beach.
However, Takaki says construction is resuming, which violates Japan’s obligations to protect the World Heritage buffer zone. Yet, according to a document published by Kagoshima Prefecture, even though Katoku’s river and beach have been included in the buffer zone, Japan’s Natural Parks Act doesn’t oblige it to abide by any specific regulations.
In applying for Amami Oshima’s inclusion in the World Heritage list, the central government provided details about the Katoku seawall project to the International Union for Conservation of Nature, which plays an advisory role in the process. The organization asked for Katoku’s river and neighboring beach areas to be included in the buffer zone.
The government claimed the seawall will be positioned inland where waves don’t normally reach, therefore preventing erosion, and will be a “buried embankment” covered with sand and plants.
In response to the International Union for Conservation of Nature’s request that Katoku River and estuary be kept “free of infrastructure developments,” assurances were made that neither the wall’s location nor its construction would affect the river, which is home to sensitive species such as the endangered Ryukyu sweetfish and endemic freshwater shrimp.
Takaki argues that the government has made several misleading claims. The seawall is on a dynamic part of the beach where the shoreline fluctuates and plans to cover the structure in vegetation aren’t feasible because no plants grow in that area, he says.
The wall’s concrete blocks have been built on sites further inland, near Katoku River, that lack wildlife protection measures. Furthermore, construction plans require temporarily culverting the river mouth and the seawall’s placement risks interfering with the river’s lateral flow, Takaki claims.
The government did note that Katoku’s dune has a “high disaster prevention function,” but that, following the damage caused in 2014, “natural recovery of the dune is believed to require several decades.”
What it omitted, Takaki says, is that offshore sand dredging and the artificial straightening of the river mouth prior to the typhoons caused the large-scale erosion by impeding the formation of a shoal, which protects the beach from the impact of strong waves.
Furthermore, in the case that the dune has recovered — as some activists and observers claim — it can be said to have resumed its protective function against disasters.
Alternative solutions
In Katoku, several villagers are close to contractors working on the revetment, Takaki says, “so it’s difficult for people in the village who are against the seawall to publicly express their feelings.”
Takaki believes the plan has gone ahead because there is a pervasive fear of speaking out against an orthodox approach to managing coastal environments that is championed by a number of coastal engineers and the government.
Yuzi Tanaka, CEO of the nonprofit Omotehama Network, has witnessed a similar situation elsewhere.
In 2006, the Omotehama Network successfully campaigned for the removal of wave-dissipating blocks from Omotehama Beach in Toyohashi, Aichi Prefecture, to stop sea turtles from dying after getting trapped in them — a breakthrough, though isolated, case in Japan.
In Omotehama, “researchers studying sea turtles were silenced because a lot of importance was put on construction,” Tanaka says.
Alternatives to hard structures do exist, such as creating regulations that prevent people from living too close to the coast or strengthening natural barriers such as vegetation.
In Katoku, for example, activists have replanted pandanus trees on the dune.
In Tohoku, a larger-scale project seeks to plant millions of trees along the coast.
Such methods are gaining traction but fail to attract broad consensus. For many people living in coastal settlements, nature-based solutions “sound like doing nothing,” Abe says.
In addition, while coastal forests may offer some protection, Shibayama says they’re likely to be washed away if a tsunami is extremely large.
By lining the coast with concrete structures, Japan is losing its beaches, especially as it looks to a future of worsening climate impacts, Tanaka of Omotehama Network says.
Tanaka believes Katoku Beach should be protected simply because its self-regulating cycles allow it to survive without the need for concrete.
“If a wall is built there, it could be built anywhere,” he says. “Then all of Japan’s beaches would disappear.”
