Beijing gets that sinking feeling

Construction sites, underpasses, roads and even a subway station were flooded after the heaviest rain of the summer wet season so far, stretching the city's drainage systems to capacity.

From 8 am Sunday to 6 am Monday, the average rainfall was 41.4 millimeters over the whole city and 58 millimeters in the downtown, said China Meteorological Administration Monday.

Early on Sunday morning, Jiaomen East Station, Subway Line 10, which is still under construction, was flooded by polluted water from a nearby river. The river burst its banks in the heavy rain. No one was injured during the flood, the Beijing Evening News reported.

Meanwhile, a 10-meter sinkhole, which suddenly opened up in Jiuxianqiao Lu, near the Lido area in Chaoyang district, caused traffic paralysis Monday morning, after a 50-meter section of the road was blocked, the Legal Mirror reported. Construction of Subway Line 14 is ongoing in the area.

A female manager from a nearby food shop, surnamed Zhang, told the Global Times that the hole appeared at around 9 pm on Sunday. Since there were construction workers nearby, the rescue work was quickly started, and workers pumped water out.

"I didn't see any cars stuck in the hole," she said.

According to the Beijing Evening News, at about 11:30 pm on Sunday, a concrete mixer came to pour concrete into the hole. Construction workers helped fill the hole with sand bags, steel tubes and wood, and drainage workers opened the sewage well covers along the road to drain the water out.

"I smelled the stench from the sewers and heard a lot of noise," said a female staff member, surnamed He, from a cigarette store near the hole.

On Monday afternoon, two workers were still guarding the repaired hole with red flags. An anonymous worker, who was directing traffic around the hole, said that the recent torrential rain might have contributed to the sinkhole.

Cai Xianmin, head of the Beijing Institute of Geological Survey, said that as a temporary solution, the measures taken to fill the sinkhole would be effective to solve traffic congestion, but in the long run, the reasons for the sinkhole should be identified before the hole is filled up.

It is not the first time that Beijing's underground construction projects have been connected with sinkholes.

In April 2011, a section of Shiliuzhuang Lu collapsed in Fengtai district and a truck driver and his father were slightly injured after the truck went into the hole. The hole was above a tunnel being dug for Subway Line 10, according to the Legal Mirror.

In nature, sinkholes can occur in landscapes which have limestone karst scenery, like in Guangdong Province or Guangxi Zhuang Autonomous Region, said Cai, but it can also be caused by the construction of underground projects.

"If heavy rain surged into an underground construction site, it may cause a sinkhole," he said.

Zhang Junfeng, founder of the non-government water resource watchdog Happy Water Journeys, said that sinkholes are caused by the excessive extraction of groundwater in the city.

"This extreme groundwater extraction could cause land subsidence, which might crush some underground pipes, causing them to crack," he said.

Zhang said he believes that the Jiuxianqiao Lu sinkhole may be connected with the nearby Jiuxianqiao sewage treatment plant.

"If the pipes are cracked, then soil from above will wash into them," said Zhang. This could cause a sinkhole, he believes, if enough soil is washed away.

Since groundwater accounts for more than half of the amount of water used by people in the city, Zhang said that it is still impossible to stop the extraction of groundwater.

"At present, saving water seems to be the best way to prevent the appearance of more sinkholes," he said.