Rescue work following the heavy rainstorms that hit Beijing on Saturday is continuing, as the local government pledges to upgrade the poor drainage system.

The floods left at least 37 people dead and caused traffic chaos across the city.

"The rescue and cleanup work is going on, with thousands of people's participation," said Liu Lizhi, a publicity official with Beijing Water Authority.

During the downpour, transportation in the lower areas of the city was paralyzed, especially in some underpasses with poor drainage systems. Deep water was logged at 52 sites in downtown areas, including many underpasses, especially at the Guangqumen Bridge on the East Second Ring Road where a 34-year-old man drowned in a stranded car.

The water was drained by Sunday night, and traffic in the downtown areas has returned to normal.

"The design standards of underpasses are poor because they were constructed in the 1980s," said Zheng Jiang, deputy general manager of Beijing Drainage Group in a press release on Sunday. "It makes our underpass drainage system vulnerable."

Many of the 78 underpasses, which were built lower than surrounding roads, have limited pumping capacity and are capable of draining away water only if the rainfall is less than 30 millimeters an hour, making traffic jams in rainy weather a regular sight, he said.

Pan Anjun, deputy director of the water authority, told China Daily the storms had revealed areas of concern.

"The chaos of transportation due to the summer rainstorms has exposed our weakness in municipal infrastructure," Pan said.

Thorough examinations of underpasses will be conducted, and upgrading plans will be made for every one of them to improve drainage, Pan said. He did not reveal schedule of the upgrading program.

According to a report released by the Beijing Drainage Group in early July, all 78 existing underpasses will be reconstructed by the end of 2015.

More powerful pumps will be installed if water fails to drain from the underpasses when rainfall reaches 50 mm. Adjustable reservoirs will also be built for some underpasses, which will prevent flooding even if the rainfall reaches 70 mm.

"One solution to improve the poor drainage system in Beijing is to gradually upgrade the underground conduits and design standards," said Liu Dongwei, chief architect of the China Institute of Building Standard Design and Research. "But it's not a job that will be completed soon."

The new design standards should be implemented as part of the whole city development plan. In addition, more permeable materials should be adopted in more communities, he said.

"But this upgrading program requires the government to invest more," he said.

The heavy rainfall from the weekend storm drained into rivers running through the capital, which met in the North Canal, the northern part of the Grand Canal and also a branch of Haihe River feeding to the Bohai Sea through Tianjin.

The flood passed through Beijing and arrived in Tianjin on Sunday morning. The water level of the Qinglong and Jianhe rivers, which experienced flooding, peaked at 8.16 meters, 0.06 meters higher than the flood diversion level on Sunday night.

But the flood passed through that section safely, heading to the Bohai Sea on Monday morning.

zhengjinran@chinadaily.com.cn