The Shanghai Water Authority is planning to build a 25 billion yuan ($3.96 billion) drainage system with wider pipes so the city can better withstand heavy rains and prevent flooding, city officials said Tuesday.

When a heavy downpour hits, these pipelines will serve as an underground reservoir to store large amounts of water, which will eventually be sent on to the city's 50-odd sewage treatment plants.

"When completed, the system will be able store 2.1 million tons of water, enough to fill 1,200 Olympic-size swimming pools," said a press officer surnamed Chen with the Shanghai Urban Construction Design and Research Institute.

The new system will be composed of several main pipelines built under downtown, where the altitude is low, along with 227 underground sub-drainage systems that cover 503.55 square kilometers of the downtown area, Chen said.

In one example, a 15-kilometer-long, 8-meter-wide pipeline built along the Suzhou Creek will connect numerous sub-pipelines designed to collect rain water, according to a press release from the institute.

The project has been designed and is waiting for approval from the local water authority, Chen said.

Ouyang Tianjun, a press officer for the Shanghai Water Authority, confirmed that the project is in progress, but declined to provide further details.

The drainage system of major cities like Beijing, Shanghai and Guangzhou are based on those in the former Soviet Union, where a drier climate made slimmer pipes sufficient, according to a report in the Changjiang Daily.

Shanghai's current drainage system can handle a once-a-year torrential rain, whereas metropolises such as Paris or New York can handle downpours that only occur every five to 10 years, Zhang Zhenyu, spokesperson of the city's flood control administration, told the Shanghai Morning Post.

"The new system will make it so Shanghai can handle a torrential rain that is only supposed to occur every two years," Chen said.