The first pilot site for a "sponge city" project in Guangzhou, the capital of Guangdong province, started on July 2. The project, located in the Tianhe district, involves transforming a lake into a wetland park. The move is expected to reduce the volume of stormwater in the city by about 180,000 cubic meters every time a heavy storm occurs.

Torrents descending from the Baiyun Mountain range in the city will be purified and reduced in force after running through vegetation and a dozen ponds in the wetland park. Stormwater will also seep through permeable ground tiles into underground storage spaces and finally run down into a lower reservoir.

"Reducing the buildup of water requires a new way of thinking. We should try to gradually minimize the volume of floodwater at the source rather than trying to drain stormwater quickly by expanding the pipe network without limits," said Kuang Juanjuan, deputy director of the design and research institute at the Guangzhou Water Affairs Bureau.

In urban centers where limited land resources mean there is no space for large wetland parks, Kuang advised the use of permeable paving slabs in parks, public squares and living compounds to reduce surface runoff effectively.

At a conference in January, the water affairs bureau prioritized the plan to build a sponge city this year. On June 29, the standing committee of the city's People's Congress approved the Guangzhou Eco-civilization Development Plan (2016-20), which aims to ensure that the city's downtown can withstand a "once-in-50-years storm" and a "once-in-200-years flood" by 2020.

To achieve that, new construction projects will be required to ensure that at least 40 percent of sidewalks, squares and roads are made from permeable materials. In addition, the city will redesign drainage systems in areas prone to waterlogging and will also study the feasibility of deep-tunnel drainage systems.

xujingxi@chinadaily.com.cn