Japan’s Ministry of Land, Infrastructure, Transport and Tourism (MLIT) has moved to resurrect the “Kurabuchi Dam” project in Gunma Prefecture, a plan previously abandoned after residents exposed administrative data manipulation. While the government cites “climate change” as the primary reason for revising the Tone River system’s flood control strategy, the lack of resident participation in this sudden reversal has sparked renewed protest.

The “Great Reiwa Renovation” Led by the Ministry

In Japan, the MLIT’s Kanto Regional Development Bureau has initiated procedures to revive dam projects that were once officially cancelled. This move stems from the “Tone River and Edo River System River Improvement Plan” established in March 2025, which aims to radically bolster flood safety in response to the increasing intensity of rainfall linked to climate change. During meetings held with relevant prefectural governments in early 2026, the national government proposed utilizing former dam sites in Gunma Prefecture alongside the heightening of existing dams.

Specifically, at the Yattajima reference point (Isesaki City, Gunma), the “basic high-water discharge”—the estimated maximum flow rate without dam regulation—was raised from 22,000 cubic meters per second to 26,000. Since river widening alone cannot handle the excess, upstream dams must now regulate an additional 4,900 cubic meters per second, leading the government to reconsider “cancelled dams”. The Director-General of the Kanto Regional Development Bureau, Masamichi Hashimoto, has labeled these comprehensive measures the “Great Reiwa Renovation,” signaling a push for rapid development. Please refer to the following diagram.

Why Kurabuchi Dam Became a Priority for Investigation

Among the six cancelled dam projects in Gunma Prefecture considered—including Tokura, Kawago, and Masudagawa—the Kurabuchi Dam in Takasaki City was selected for priority investigation due to its advanced state of prior progress. Originally a Gunma Prefectural project on the Karasu River, construction had reached significant milestones by the time it was suspended in 2003 and officially cancelled in 2015. Notably, 100% of the land acquisition has been completed, and the relocation of surrounding roads is already finished.

According to MLIT estimates, the Kurabuchi Dam has an effective capacity of 10.8 million cubic meters, with approximately 6 million cubic meters dedicated to flood control. Because it can leverage existing infrastructure, the construction period is estimated at 10 years with a cost of approximately 50 billion yen (approx. \$330 million USD)—significantly cheaper and faster than building a new dam from scratch. Along with the Tokura Dam in Katashina Village, it is viewed as an “immediate asset” to strengthen the flood regulation capabilities of the upper Tone River.

History of Cancellation and the Exposed “Lies”

Falsifying Land Prices to Justify Construction

The previous cancellation of the Kurabuchi Dam was not merely due to budget constraints; it was a rare case where residents exposed systematic data falsification by the Japanese local government. In the 2010s, the prefectural government argued that building the dam was more economical than alternative river improvements, claiming costs of 35.7 billion yen for the dam versus 41.1 billion yen for river work. However, when resident groups obtained internal documents through information disclosure requests, they discovered a startling deception.

The residents found that while the actual market value of residential land in the area was between 10,000 and 20,000 yen per square meter, the prefecture had calculated the land acquisition costs for river improvement using an astronomical figure of 200,000 yen per square meter. When residents pointed this out, a panicked prefectural official attempted to reclaim the documents, claiming they were “mistaken,” but the residents had already made copies. The exposure of this organized “lie” was a decisive factor in the then-Governor Hiroyuki Kodera’s decision to cancel the project.

Deception in the 1.37 Cost-Benefit Ratio

The administration also misled the public regarding the project’s cost-benefit ratio (B/C). The prefecture claimed a B/C ratio of 1.37, suggesting that the value of flood damage prevented would outweigh construction costs. However, members of the “Kurabuchi Dam Research Group” personally walked the length of the Karasu River and discovered another fabrication. The prefecture had identified specific areas as “at risk of flooding due to a lack of levees,” but in reality, the embankments of the Shin-etsu Main Line railway functioned as levees, physically preventing water from overflowing.

When residents recalculated the figures based on this reality, the B/C ratio fell well below “1.0,” the standard threshold for public works projects in Japan. It became clear that the administration had fabricated “flooding zones” to create a false necessity for the dam. A lead resident in the effort to stop the dam, Kazuyoshi Otsuka, stated that “the Kurabuchi Dam plan was already a failure as a flood control plan,” expressing deep distrust that a project previously rejected through democratic processes is being revived. Please refer to the following diagram.

Validity of Flood Control Plans Amidst Climate Change

Is “Climate Change” a Scapegoat for Dam Dependency?

The MLIT is now using “climate change” as its primary justification for resurrecting the dam plans. In a 2024 policy update, the Japanese government projected that a 2-degree Celsius rise in global temperatures would increase rainfall by 1.1 times and river discharge by 1.2 times. Based on these scientific forecasts, they argue that existing facilities are insufficient, bringing once-discarded dam plans back into the spotlight. However, experts criticize this move as using climate change as a “free pass” for dam construction.

Takashi Okuma, Professor Emeritus at Niigata University and a specialist in river engineering, has questioned the feasibility of the government’s new flow targets. He noted that while the current seven upstream dams (including the massive Yanba Dam) can only regulate about 2,800 cubic meters per second, the government has set a target nearly three times higher (8,300 cubic meters per second). “To push for the resurrection of the Kurabuchi Dam without showing a realistic final plan for achieving those targets is an irresponsible approach that no river engineer should accept,” Okuma argued.

The Conflict of Sacrificing the Upstream for the Downstream

Flood control for the Tone River system often involves a structural contradiction: imposing burdens on upstream areas like Gunma Prefecture to protect heavily populated downstream regions like Tokyo and Saitama. Although the Takasaki City Council’s petition for restarting construction mentions “protecting the lives of citizens,” the primary objective of the Kurabuchi Dam is actually flood damage reduction in the middle and lower reaches of the Tone and Edo rivers. Local NGOs like “Agreco” point out that official explanations are misleadingly framed to suggest the dam is for the direct benefit of Takasaki residents.

Furthermore, while dams can store floodwaters, they are ineffective if heavy rain falls in the plains downstream of the dam. There is also concern regarding the “Dam Myth”—an over-reliance on infrastructure that may create a false sense of security and delay resident evacuations. Data from the 2019 East Japan Typhoon (Typhoon Hagibis) showed that while existing dams lowered water levels, significant flooding still occurred. Critics argue the debate should move away from just building more dams toward “Basin-wide Flood Management” (Ryuiki Chisui), which focuses on dispersing floodwaters across the entire watershed.

Reigniting Opposition and Citizen Dialogue

A Resurrection Scripted “Without the Residents”

The most criticized aspect of the Kurabuchi Dam’s revival is the lack of public transparency in the decision-making process. The “Tone River System Flood Control Plan Evaluation Committee,” which met between November 2025 and March 2026, consisted only of experts and government officials, with virtually no direct input from watershed residents. In just a few meetings, a dam project that residents had spent years stopping was suddenly deemed “appropriate,” and the start of field surveys was authorized.

In response, the residents who led the original cancellation effort mobilized immediately. On July 11, 2026, a citizen rally titled “Protecting the Clear Streams Without Dams” was held in Takasaki City, drawing over 200 participants. At the gathering, speakers recounted the history of past administrative misconduct and voiced their desire to protect the Karasu River as a natural stream. Residents have submitted inquiries to both the national government and the Takasaki City Council, but responses have remained abstract, citing general “climate change risks” and leaving a widening gap in the dialogue. Please refer to the following diagram.

Political Frictions Within the Takasaki City Council

The resurrection of the dam has also caused sharp divisions within local Japanese politics. A resolution requesting the restart of construction was passed by the Takasaki City Council with the support of the Liberal Democratic Party (LDP)-affiliated “Shinpu-kai” and Komeito. However, all other political factions—including the Communist Party, the Social Democratic Party, and independent members—voted against it. These opposing council members have questioned the ethics of pouring taxpayer money into a project that has never fully accounted for its past data falsification.

Tensions also rose over a public inquiry submitted by the NGO “Agreco” to the city council. Submitted in April 2026, the inquiry asked for the scientific basis of “flood danger levels” and addressed concerns about water quality and the habitat of the endangered Mountain Hawk-Eagle. The council missed its May deadline due to internal disagreements and finally issued a response at the end of June. The citizen group found the response inadequate and intends to continue pushing for deeper deliberation on the government’s survey results.

Ecological Impact and Environmental Protection

The Endangered Mountain Hawk-Eagle and Local Biodiversity

The proposed construction site for the Kurabuchi Dam is in the headwaters of the Karasu River, a region with a rich natural environment that serves as a vital habitat for diverse wildlife. Notably, the area is a confirmed nesting site for the Mountain Hawk-Eagle (Nisaetus nipalensis), an endangered species in Japan. Local conservation groups have conducted long-term monitoring and protection activities for these raptors. Studies from the 1990s already indicated that dam construction would have a devastating impact on their breeding and hunting grounds.

While the MLIT claims it will “consider environmental impacts to avoid adverse effects,” no concrete preservation measures have been presented. The flooding of vast forest areas and the disruption of river continuity would cause irreversible damage to the entire ecosystem. Residents argue that reviving the dam project directly contradicts international and Japanese environmental goals, such as “Nature Positive” and the “30by30” target (protecting 30% of land and sea by 2030).

Threats to the Purity of the Karasu River

Beyond flood control, serious concerns exist regarding water quality and water rights. The Karasu River is known as one of the cleanest streams in Gunma Prefecture, and some of Takasaki City’s tap water is supplied through advanced purification processes that do not use chemicals. However, creating a large stagnant reservoir could lead to summer “blue-green algae” blooms, eutrophication, and downstream turbidity from discharge, significantly risking the city’s water source.

Local citizen groups argue that losing the Karasu River’s clean water is a major issue that threatens the foundation of residents’ lives. While government experts are considering “advanced dam management” by shifting portions of water supply capacity to flood control, it remains unclear how this would impact water availability during droughts. For residents who have lived alongside the river for generations, the dam is seen not just as a civil engineering project, but as an irreversible act that alters the very environment of their hometown.

Future Outlook and Consensus Building

Hurdles from Field Surveys to Official Project Approval

The MLIT plans to move forward quickly with topographical, geological, and fault line surveys at the Kurabuchi and Tokura dam sites. These are necessary because more than 20 years have passed since the original plans were halted, meaning land use and geographical data are outdated. Based on the survey results, the government will officially modify the river improvement plan to include specific dam projects, followed by an evaluation for “new project adoption” before any actual construction begins.

However, the path to project approval is fraught with high hurdles. First, the cost-benefit analysis—the very reason the project was cancelled before—must be re-verified. Due to soaring prices for materials and labor, construction costs are expected to significantly exceed the previous estimate of 50 billion yen, challenging the project’s economic validity. Furthermore, rigorous surveys under Japan’s current Environmental Impact Assessment Law are required. Since the government intends to eventually narrow the list down to about two dam sites, the fate of the Kurabuchi Dam will depend on these surveys and future budget negotiations.

A Shift Toward “Basin-wide Flood Management” or Continued Dam Dependency?

The debate over the resurrection of the Kurabuchi Dam symbolizes a major crossroads for Japan’s water management policy. Will the country continue its “dam dependency,” attempting to suppress the unknown threats of climate change with massive concrete structures? Or will it truly transition to “Basin-wide Flood Management” (Ryuiki Chisui), combining levee reinforcement, flood retention areas, and land-use restrictions to disperse floodwaters across the watershed?.

The most critical factor going forward will be whether the administration engages in sincere dialogue with the residents. If the project is forced through without restoring the trust lost due to past “lies,” a long-term, intense conflict similar to the decade-spanning Yanba Dam controversy is inevitable. Whether a consensus can be reached that respects both the regional environment and the will of the people while balancing the needs of the entire Tone River system remains to be seen. The outcome of this “resurrection drama” will be a litmus test for the future of public works projects in Japan.

Reference Pages

• [Tone River System Flood Control Plan Evaluation Committee (5th Meeting)] https://www.ktr.mlit.go.jp/river/shihon/river_shihon00000499.html

• [Plan-stage Evaluation of Flood Control Measures in the Upper Tone River] https://www.ktr.mlit.go.jp/ktr_content/content/000950074.pdf

• [Kurabuchi Dam Verification Report (March 2015)] https://www.mlit.go.jp/river/shinngikai_blog/tisuinoarikata/dai34kai/dai34kai_siryou3.pdf

• [Petition for Rapid Investigation to Strengthen Flood Control Functions Considering Climate Change (Takasaki City Council)] (MLIT Submission Material)

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