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July 23, 2012

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Shanghai's drainage system has its limits

SHANGHAI might not be able to cope if it suffers a downpour similar to the one that hit Beijing on Saturday.

Shanghai's drainage system can handle rainfall of up to 36 millimeters per hour, while in some key areas, such as at airports and densely populated areas, the capacity is 55 millimeters per hour, the Shanghai Water Authority said yesterday.

But that would not enable the city to sustain Beijing's weekend downpour when precipitation reached 212 millimeters in urban areas, said Zhuang Minjie, a deputy director.

"The 36 millimeters per hour does not mean 72 millimeters every two hours or 108 millimeters every three hours," Zhuang told Shanghai Daily. "The capacity can not be accumulated as the drainage system might be overwhelmed after hours of rain."

Zhuang described the Beijing downpour as "a disaster."

"In some areas of Beijing the precipitation even reached 400 millimeters. It's not about Beijing, I don't think any city could cope with that rainfall."

But serious flooding might be avoided in Shanghai because of the different geographies.

"The west part of Beijing is higher than the east part, which favors flooding," Zhuang said. "Shanghai is more flat and flooding deeper than 2 meters is unlikely to occur."

Zhuang said Shanghai's drainage system had been steadily improving over the years with comprehensive monitoring and maintenance.

"The maintenance of the underground drainage pipes has been a permanent mechanism. Last year we maintained 8,000 kilometers of pipes and we're about to do more this year."

Zhuang said potential flooding areas were checked before every flood season, enabling problems to be sorted in time.

The department has also set up a citywide monitoring system to alert the relevant authorities once flooding has reached 20 centimeters.

"We have established 157 monitoring spots, of which 125 were at tunnels where floods may easily accumulate," Zhuang said.

"Once the accumulation reaches 20 to 30 centimeters, the police will be alerted to decide whether to close the tunnel," Zhuang said.

Meanwhile, the city has been continuously renovating its drainage system to increase the drainage capacity.

Drainage pipes on 14 roads will be renovated this year and 28 drainage systems established or renovated by 2015.


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