Even in a war that has razed entire cities, the destruction of the Kakhovka hydroelectric dam in southern Ukraine stands out.

Thousands of people were displaced by flooding from one of the world’s largest reservoirs, which was vital for irrigating farmland considered the breadbasket of Europe. The disaster puts global food supplies for millions at risk and could threaten fragile ecosystems for decades.

The dam was visibly scarred by fighting in the months before the breach. Ukrainian strikes had damaged one part of the roadway over the dam, and retreating Russian troops later blew up another. Last month, satellite images showed water flowing uncontrolled over some of the gates.

This has led to suggestions that the dam may have merely fallen victim to the accumulated damage, which Russia has seized on to deny responsibility.

But multiple lines of evidence reviewed by The New York Times, from original engineering plans to interviews with engineers who study dam failures, support a different explanation: that the collapse of the dam was no accident. The catastrophic failure of its underlying concrete foundation was very unlikely to occur on its own.

Given the satellite and seismic detections of explosions in the area, by far the most likely cause of the collapse was an explosive charge placed in the maintenance passageway, or gallery, that runs through the concrete heart of the structure, according to two American engineers, an expert in explosives and a Ukrainian engineer with extensive experience with the dam’s operations.

“If your objective is to destroy the dam itself, a large explosion would be required,” said Michael W. West, a geotechnical engineer and expert in dam safety and failure analysis, who is a retired principal at the engineering firm Wiss, Janney, Elstner. “The gallery is an ideal place to put that explosive charge.”

A satellite image showing the dam three days before its destruction. Pléiades Neo Airbus DS 2023

Engineers cautioned that only a full examination of the dam after the water drains from the reservoir can determine the precise sequence of events leading to the destruction. Erosion from water cascading through the gates could have led to a failure if the dam were poorly designed, or the concrete was substandard, but engineers called that unlikely.

Ihor Strelets, an engineer who served as the deputy head of water resources for the Dnipro River from 2005 until 2018, said that as a Cold War construction project, the dam’s foundation was designed to withstand almost any kind of external attack. Mr. Strelets said he, too, had concluded that an explosion within the gallery destroyed part of the concrete structure, and that other sections then were torn away by the force of the water.

“I do not want my theory to be correct,” Mr. Strelets said. A large explosion in the gallery might mean the total loss of the dam. “But that is the only explanation,” he said.

Waking to Water

In the predawn hours of June 6, residents living close to the dam in both Russian-controlled and Ukrainian-controlled territory heard explosions and strange rumblings, they said later.

They were no strangers to the sounds of fighting. For months, the two armies had traded artillery volleys across the Dnipro River. But this time seemed different — and soon it was clear why.

For those closest to the dam, built in the 1950s by the Soviet state, the rush of water was almost immediate. It took longer for the floods to make their way farther downriver, but when they did, they came fast and then did not begin to subside for more than a week.

“We live on the fourth floor so it didn’t reach our apartment, but the first floor was completely flooded,” said Vasyl, 64, who lives in the Russian-occupied east bank town of Hola Prystan, about 60 miles from the dam, and was reached by phone.

A flooded residential area in the Russian-occupied town of Hola Prystan. Alexander Ermochenko/Reuters

Neighbors and relatives have sought refuge in his apartment. “My sister’s house is completely washed out,” Vasyl said. “It’s just the walls now, nothing inside, no furniture, no appliances.”

Most younger people in the town fled the Russian occupation long ago, he said, leaving behind mostly elderly people, including many with disabilities. “Many of them drowned, as they couldn’t leave their houses or climb to the roofs,” he said. The death toll from the flooding remains unknown; officials say the numbers are likely to rise as the waters recede.

A Prime Target

The relatively spindly sluice gates and cranes and the ribbon of roadway above the water line seemed to offer an easy target for an attack aimed at destroying the Kakhovka dam.

But most of the dam’s enormous mass was hidden below the surface of the water, according to diagrams of the structure obtained by The Times and detailed descriptions by Mr. Strelets, who said he has spent months at the Kakhovka dam and around the reservoir.

Passageway

Passageway

Passageway

That mass consisted of a rounded tower of nearly solid concrete some 20 meters high and as much as 40 meters thick at the bottom, Mr. Strelets said. Built in sections, that colossal barrier ran between earthen embankments on either side of the channel and did much of the work of holding back the waters of the reservoir.

The sluice gates sat atop that barrier, opening and closing to adjust the water level. Visual evidence assembled by The Times shows clear damage to the roadway and to a few of the sluice gates on one side of the channel in the months before the breach of the dam.

Despite that damage and a whitewater cascade tumbling from the vicinity of those gates, engineers said the foundering of an entire section of the dam was more likely to be related to the blasts picked up by seismic sensors and to an infrared signal that U.S. officials said was picked up by a satellite, indicating the heat of an explosion.

The seismic signals were picked up on two sensors, one in Romania and one in Ukraine, and occurred at 2:35 a.m. and 2:54 a.m. Ukraine time, said Ben Dando, a seismologist at Norsar, a Norwegian organization that specializes in seismology and seismic monitoring. The signals were both consistent with an explosion, Dr. Dando said — and not, say, the collapse of the dam on its own.

He said that the network could determine the time of an explosion to within a couple of seconds, but that the location of the blasts was less certain. For example, Norsar could locate the 2:54 a.m. signal to have originated within a zone 20 or 30 kilometers across that included the dam.

A specific time stamp for the infrared signal was not available, but a senior U.S. military official said that it was picked up shortly before the dam collapsed.

A senior American military official said that the United States had ruled out an external attack on the dam, like a missile, bomb or some other projectile, and now assesses that the explosion came from one or more charges set inside it, most likely by Russian operatives.

Floodwaters reached the rooftops of houses in Kherson, about 40 miles downstream from the dam. Daniel Berehulak/The New York Times

Gregory B. Baecher, an engineering professor at the University of Maryland and a member of the National Academy of Engineers, also said the scale of the breach indicated that the underlying concrete barrier had failed, suggesting that charges had been set deep in the structure.

“If they put explosives in the gallery, that would explain a lot,” Professor Baecher said. A large explosion there, he said, “would just rip up all the concrete structure.”

Nick Glumac, an engineering professor and explosives expert at the University of Illinois at Urbana-Champaign, said the size of the necessary charge could vary widely depending on the exact way in which the explosives were set and the precise objective.

“It’s worth remembering that you don’t have to pulverize the dam section, just break it enough such that the water pressure is enough to tear it away,” Professor Glumac said.

Still, Professor Glumac said that based on diagrams of the dam and the latest imagery of the destroyed foundation, “It’s hard for me to see how anything other than an internal explosion in the passageway could account for the damage.” He added, “That’s a massive amount of concrete to move.”

Using the gallery might have another advantage for anyone seeking to hide their tracks. According to Mr. Strelets, the gallery had only two entrances, including one inside the machine room located in a building to one side of the dam.

Dr. West, who is also a former Army combat engineer officer, noted that would allow the dam to be rigged out of sight of spy satellites, drones or witnesses on the ground. Early morning drone footage showed that the initial breach in the dam occurred not far from the machine room.

A satellite image showing the dam a day after its collapse. Maxar Technologies

Professor Baecher said it was possible, though unlikely, that water flow from the damaged gates somehow undermined the concrete structure where it sat on the riverbed. But he said an examination of the drawings indicated that the design had protected against that possibility with standard measures. One of those is a so-called “apron” of concrete on top of the riverbed to the downstream side of the dam.

“This appears to be a well-engineered dam of modern design,” he said.

For its part, the company that operated the dam said in a statement to The Times on June 16 that “Russian forces made an internal explosion which resulted in destroying the dam.” That explosion, the company said, “brought about uncontrolled release of water from the reservoir and disastrous increase of water level in the downstream.”

A Dam in the Cross Hairs

The ravages of the dam since the Russians invaded Ukraine have been captured again and again from overhead and on the ground.

As Russian troops were retreating across the Dnipro River in November 2022, they blew up the roadway atop the structure’s northern end. A surveillance camera captured the powerful nighttime explosion. Satellite images show that the force of the blast destroyed the roadway, but that the dam’s foundation and the walls of the gates at that section of the dam were unaffected. They remain standing today.

The Times obtained very high-resolution satellite imagery that also shows damage to another section of the roadway in the days and weeks before the dam’s collapse. On June 1, or early on June 2, part of the road that runs along the dam collapsed. Ukrainian HIMARS rocket strikes in August 2022 damaged that part of the road but did not hit the dam.

On April 23, a small part of a wall connected to the power plant collapsed — possible evidence of erosion near the dam.

August 2022

November 2022

Ukrainian HIMARS

rocket strikes

Russian destruction

of roadway

Additional roadway

collapse

HELD BY

RUSSIA

HELD BY

RUSSIA

HELD BY

RUSSIA

Location of

damage

Dnipro River

Dnipro River

Dnipro River

HELD BY

UKRAINE

HELD BY

UKRAINE

HELD BY

UKRAINE

August 2022

November 2022

Ukrainian HIMARS

rocket strikes

Russian destruction

of roadway

Additional roadway

collapse

Location of

damage

HELD BY

RUSSIA

HELD BY

RUSSIA

HELD BY

RUSSIA

Dnipro River

Dnipro River

Dnipro River

Dnipro River

HELD BY

UKRAINE

HELD BY

UKRAINE

HELD BY

UKRAINE

August 2022

Ukrainian HIMARS

rocket strikes

HELD BY

RUSSIA

Location of

damage

Dnipro River

HELD BY

UKRAINE

November 2022

Russian destruction

of roadway

HELD BY

RUSSIA

Dnipro River

HELD BY

UKRAINE

Additional roadway

collapse

HELD BY

RUSSIA

Dnipro River

HELD BY

UKRAINE

Sources: Supernova+ via Telegram, Maxar Technologies, Pléiades Neo Airbus DS 2023.

Additionally, the cranes that control the release of water through the dam had not been moved since mid-November, allowing water to flow unchecked out of the same gates over a period of several months. This lack of regulation led the water level of the reservoir to reach its lowest point in decades in February, then hit a 30-year high in May, just weeks before the dam’s destruction.

Neither this previous damage, nor the pressure caused by the high water level or the static position of the cranes is likely to have caused the collapse of the dam’s concrete foundation, experts said, unless the concrete was of low quality and already prone to deteriorate. The large flows would also be insufficient to undermine the dam’s foundation unless, for some reason, the concrete apron — the downstream cover placed over the river bottom — contained flaws or the soil was much softer than accounted for in the design.

A video that emerged this week, after water levels had dropped, provides clear evidence of the catastrophic failure. It shows that the top of the concrete foundation, not just the gates, was destroyed.

Mr. Strelets, the engineer, called the gallery the Achilles’ heel of the Kakhovka dam. He said he hoped a charge had not been put there, because the damage would be irreparable.

“I walked along this dam many times,” he said. “I was proud of it. It is the property of my country. I never even imagined that someone would attempt to destroy it.”