The dam at Dongting Lake lies just 200 meters from Chen Wei’s village home. As soon as he heard about the breach on July 5, he rushed over to find water sprouting from a small hole, like a mountain spring. Within a short while, it was a gushing stream.

The first line of protective embankments lining the lake in Tuanzhou Township in central China’s Hunan province began experiencing a “piping effect” around 4 p.m. Piping is a type of erosion that occurs when the water levels inside and outside a dam vary significantly, which can lead to silt-loaded water from inside a lake or reservoir seeping through weak spots. If not dealt with quickly, it can cause a dam to burst.

According to Zhang Xuanzhuang, a senior environmental safety engineer at China’s Anneng Construction Group, which is responsible for the dam’s maintenance, piping is relatively common in the Dongting Lake region. Since antiquity, locals have used pebbles and fine sand, among other materials, to repair the dams, which are highly penetrable. Damage inflicted by animals can also contribute to potential weaknesses in the dam’s underbelly.

Initially, on July 5, the width of the rupture at Dongting Lake was about 10 meters, but it expanded quickly. The next morning, the gap was almost 150 meters wide, and by afternoon it was 220 meters, resulting in the flooding of nearly 48 square kilometers, 92.5% of the surface area of Tuanzhou Township.

Rescue and disaster relief efforts began immediately. By 9 a.m. on July 8, 138.5 meters of embankments had been shored up, with 87.5 meters remaining. Some 7,680 residents in Tuanzhou Township were evacuated to central Huarong to await transfer to temporary accommodations. No injuries were reported.

High risk

Chen, 62, says the breach was first discovered by a farmer who was grazing cattle beside the lake. “He noticed a hole about the size of a bowl, from which water mixed with silt was pouring out.” The farmer rushed to alert Chen, whose one-story home was just 200 meters from the rupture, and together they went to see where the piping was occurring.

Other villagers soon surrounded the spot and attempted to mitigate the breach, but they lacked enough stones and other materials. Soon, trucks arrived to deliver sand and large stones, while boats were used to deposit sand. “I thought then that we would be able to succeed in our recovery efforts,” Chen says. But around 3 p.m., the hole grew to the size of a household washbasin, and the path to the embankment slowly sank away.

An hour later, massive amounts of water were coming through the dam’s inner slope, and then a split appeared. At that point, there was a 5-meter difference in the water level between the surface of Dongting Lake and outside the dam, resulting in torrents of water bursting forth and flowing south into the village.

As the floodwaters began to surge, Chen recalls that he raced home, collected his 82-year-old mother, put her on the back of his motorbike, and drove her to safer ground. He says his mother had wanted to turn back to rescue some personal items and was worrying about her chickens, geese, and ducks, but he knew it was too dangerous.

After hearing of a “small tear” in the dam, many villagers living in other areas returned to the township for rescue. Hua Yan’s family home is in nearby Tuanrong Village, where three of her grandparents still live. She says she was unable to persuade her paternal grandmother to leave. “Elderly people hate to leave their homes. She also lived through the big flood 28 years ago, which was brought on by a dam break.” The Tuanzhou Township embankment experienced a major rupture in 1996, although the standards for preventative flood measures are much higher today. “She felt it probably wouldn’t be that big of a problem,” Hua says.

However, the situation this time was worse than many had feared. At 5:48 p.m. on July 5, the emergency barriers failed, and the dam burst. Fortunately, by that time, the elderly residents had already been evacuated.

At the top of the dam, Chen saw that the rupture had grown to about 10 meters wide. Emergency services workers were placing large rocks and pouring sand, as well as lining up cars to create a “wall” to stop the water. But the effect was minimal, and soon several trucks were caught in the flooding. The rupture was gradually increasing.

Water damage

Residents living near the Tuanzhou Township embankment know that when Dongting Lake swells, there is always the risk of piping. Each time, patrol officers will conduct inspections; if there’s imminent danger, they will quickly take precautions. After the flood of 1996, Chen had to rebuild his house, and in the 28 intervening years, his home has never flooded.

According to the Hunan Department of Water Resources, Dongting Lake is an important reservoir along the Yangtze River that for generations has been a “battleground” in the fight against flood disasters. Since the beginning of this year’s flood season, Hunan has received 819 millimeters of rainfall, 43.2% more than the average in recent years. Owing to the effects of heavy rainfall and the increase in supplies from the upper reaches of the Yangtze, the water level in Dongting Lake has continued to rise. Since mid-June, the lake had risen by more than 6.5 meters, triggering alarms at 14 monitoring stations in the region.

At 9 a.m. on June 30, the water level at the lake’s hydrometric station at Chenglingji reached the warning level of 33 meters, marking the year’s “first flood of Dongting Lake.”

The rising water level also means a higher risk of piping. Zhang from Anneng Construction says the only way to detect piping is by patrolling the dam. As soon as it’s spotted, “well-like fencing” is erected at the spot of the breach to raise the water level inside the dam. Workers then use sandstone as a filter.

After the alarm was raised on July 5, the fire rescue service and Anneng Construction dispatched teams and vehicles to Huarong County. Armed police officers and civilian rescue teams also arrived at the scene to support the relief efforts.

At 1 a.m. on July 6, a spokesman for Anneng Construction told reporters that the difference in water levels occurring at the breach had been reduced to 10 centimeters from 21 centimeters. By 4 p.m., an endless line of trucks, bulldozers, excavators, and other large vehicles could be seen along the embankment. Rescue workers also used drones to create a 3D model of the breach and collect other data.

The Dongting Lake breach was just over 80 meters in width by about noon the next day. Shortly after, Zhang Yingchun, the executive vice governor of Hunan, said at a news conference that it was hoped the breach would be completely sealed by noon on July 9.

It was also announced that 7,680 people in Tuanzhou Township had been evacuated, including 3,224 who had been temporarily accommodated in four designated locations equipped with daily necessities and medical supplies.

On the morning of July 7, Chen and his family were taking shelter at one of those locations — a vocational school. They had been given a place on the second floor of the school dormitory, with air conditioning and a private bathroom and shower. There was also a well-stocked infirmary.

However, he says he still has concerns. One month after the 1996 flood, Chen had to rebuild his home. Twenty-eight years on, he must do so once again.

Reported by Zheng Ziyu, Zhu Yawen, Zhang Lingyun, Yuan Yangyang, and Wei Yuanqi.

A version of this article originally appeared in Shanghai Observer. It has been translated and edited for brevity and clarity, and is republished here with permission.

Translator: Marianne Gunnarsson; editors: Xue Ni and Hao Qibao.