A park in Shanghai, with its water-retention system, is setting an example, Xing Yi reports.

A stainless mirror maze was built in the park with a sculpture sitting on the wall. (XING YI / CHINA DAILY)

When Typhoon In-fa pelted Shanghai with heavy rains in July, Xu Jingxin was worried about the "sponge park" he had been working on for the past two years. Located in the city's Lingang area, the park gets its nickname from the ponds, gardens and a wetland connected by swales and designed to retain water in storms and prevent flooding.

Xu, an engineer with the China Construction Technology Consulting and in charge of the construction of the sponge facilities, was concerned about whether the "sponges" that he helped to design could withstand the test of intense rainfall brought by the typhoon.

"I went to check the site when Typhoon In-fa passed, and to my great relief there were very few pools of water on the ground," Xu says. "The system worked well."

The park was built using permeable material that can absorb and channel water to underground storage units.

Flooding is one of the most serious water-related issues in Chinese cities due to rapid urbanization and the disappearance of natural wetlands. Frequent extreme weather events due to climate change have exacerbated the problem in recent years.

Adjacent to the Shanghai Astronomy Museum, the sponge park in the city's Lingang area is designed to resemble planets that are surrounded by paths. (XING YI / CHINA DAILY)

To cope with the problem, the State Council launched the Sponge City pilot project in 2015, with the aim of having 80 percent of urban areas refitted and embedded with sponge facilities by 2030 to absorb and reuse at least 70 percent of rainwater. More and more "sponge cities" have started to emerge across the country over the past six years. Currently, 30 metropolises are part of the project. Shanghai was selected as one of the pilot cities in 2016.

Rui Dongliang, project manager of Shanghai Lingang New City Investment and Construction, has participated in the construction of the 54-hectare park since it began in 2019. Lingang was a model for the "sponge city" project in Shanghai, and the park an important part of it, he says.

Besides retaining rainwater from runoffs, another function of the facility is to clean and purify water through eco-engineering.

The sponge park was intersected and divided into four parts by two rivers, and the northeast part of the park is a 9.6-hectare wetland with several ponds and floating islands that forms a demonstration zone for the sponge system.

The park entrance with its planetary sculpture. (XING YI / CHINA DAILY)

Xu says the water pumped into the park from the river first goes through a skimmer to remove surface debris before making its way into a pond to sediment. Following that, the water flows through several levels of filtration ponds with aquatic plants such as vallisneria and water lilies.

"The system can purify up to 15,000 cubic meters of water per day, as the water quality rises from Grade V to Grade III when it flows back to the river," Xu says, adding that the system is also connected with the rain drainage so that it can treat the rainwater from the surrounding areas.

Several floating islands of aquatic plants were added to clean the water in the river and serve as a natural habitat for birds.

In order to extend the length of the shoreline so that the river can slow down and be "cleaned" by the floating islands, bends were added to the once straight waterway. The sludge and silt excavated from the riverbed were then used to create landscapes such as little hills on the riverside.

The park provides plenty of fun for visitors. (XING YI / CHINA DAILY)

The park, which opened to the public in August, is becoming a popular spot with residents of nearby areas because of its unique layout.

Adjacent to the Shanghai Astronomy Museum, whose round-shaped futuristic architecture drew crowds when it opened in July, the park has adopted a coherent design－its hills, playgrounds and facilities are designed to resemble planets that are surrounded by circular and curvy paths.

"The sponge technology is at the core of the park, and the starry sky is the theme," says Rui.

"The tourist center was built in the shape of a plane, the 340-meter-long 'infinite bridge' is in the shape of an endless loop. We put a wooden hut on a hill and will organize stargazing tours soon. The open-air auditorium can also hold concerts at night in future."

Rui says the park is currently looking for operators of watersports entertainment, retail stores and restaurants.

A 9.6-hectare wetland with several ponds and floating islands forms a demonstration zone for the sponge system. (XING YI / CHINA DAILY)

Yang Yu, a landscape designer at the China Architecture Design and Research Group, says the overall design of the landscape and buildings was overseen by Li Xinggang, who is best known for being the Chinese chief architect of the National Stadium, or Bird's Nest, the main venue of the Beijing 2008 Olympics.

"We have also built a stainless mirror maze on one of the hills and placed a sculpture of a jade rabbit and an astronomer in it to amuse children. We call it 'Interstellar Maze'," she says, adding that visitors will also get to appreciate plants such as North American crabapple and Japanese evening cherry.

As the land in the Lingang area, which was under water a few decades ago, is made up of saline-alkali soil, a 30-centimeter layer of thick gravel has been placed in the soil to filter salt. Engineers have also chosen plants that can grow in saline soil.

"We hope after several years the 'sponge park' can also treat the soil so that it will become more fertile in future," she adds.

Contact the writer at xingyi@chinadaily.com.cn