As a demonstration area of the construction of "sponge cities," Tongzhou District in Beijing has recently completed the first batch of 14 pilot projects, with which 70 percent of rainwater could be absorbed and utilized. Ordinary lawns, gardens, cisterns and pavements have been transformed into "sponges" to prevent inundation and water overflow during heavy rains.
Flooding rainwater has become a headache for many cities in recent years. The Water Authority in Tongzhou has specified methods of seeping, holding, reserving, purifying, utilizing, and draining as a package of measures to help resolve the thorny problem and build a sponge city. Different from traditional pipe drainage, the concept of sponge city traces to the source of water with draining mechanism set throughout the course. In this way, the rainwater will be maximally utilized.
Last year Tongzhou was selected to pilot sponge city construction with a total area of 19.36 square kilometers. All the residential communities, public buildings, parks, green lands, municipal roads and watercourses included in the area would be transformed through various facilities such as low elevation greenbelt, rainwater garden, grass belt, permeable pavement, rainwater collector, and eco-detention pond. It is estimated that 70 percent of rainwater could be absorbed and utilized after the transformation.
In Redbud Garden, a pilot community of the project, the sponge transformation covered roads, lawns, and parking lots. Four seepage layers were laid under the road surface, which was paved with water permeable bricks and porous asphalt to quickly absorb and effectively purify rainwater. This summer residents in the community were exhilarated with the disappearance of annoying water puddles on rainy days.
In the BOBO Free City, another pilot community, drainage ditches were transformed into grass belts that could hold, reserve, and purify rainwater. The belts, while rich in flora and fauna, are inlaid with filtration cloth and draining pipelines which help slow down and clarify water flow. In addition, the grass belts are equipped with eco-detention ponds to save rainwater for later uses such as street cleaning and urban irrigation.
After a year of construction, the first batch of 14 sponge projects such as the Redbud Garden, the BOBO Free City, and the Beijing Primary School in Tongzhou have been completed. There are still 40 pilot projects underway. By the end of 2018, the pilot area in Tongzhou is expected to be able to contain 84 percent of rainwater and become a sponge city that is free of ponding and inundation.