While construction of Xuhui Runway Park is underway, our project team shared stories behind its key design feature–the rain gardens. The following piece is written by Sasaki Director Dou Zhang, ASLA, and Associate Yu Zhu in Shanghai office.
Xuhui Riverfront, to the southwest of Downtown Shanghai, is evolving. Previously dominated by industrial uses, the area is swiftly becoming a hub of high end office and commercial development. At the core of this urban renewal is Xuhui Runway Park, a project transforming a 90-year old runway into a green oasis for residents and office workers from the surrounding development.
Fast urbanization in mega cities like Shanghai has brought many consequences. The uptick in severe weather and storm events in recent years can be directly linked to the heat island effect and largely increased impervious surfaces. Additionally, surface runoff from streets—often containing pollutants such as gasoline or heavy metals—often drain into nearby canals without any treatment. This runoff is a major contributor to water quality issues within the entire metropolitan area.
With the Xuhui Runway Park project, we were given a unique opportunity to integrate the stormwater management system into the landscape, by designing the park simultaneously with Yunjin Road; the street parallel to the park. The road surface runoff detention, treatment, and harvesting, as well as habitat creation, are taken as integral parts of the design beyond creating opportunities for leisure and spots for taking in the view.
To address the environmental concerns that Shanghai is facing, we introduced rain gardens as one of the key features of the Runway Park. The stormwater runoff from Yunjin Road is guided into the linear rain gardens that abut the street. As the water passes through the gardens, the solids settle and pollutants are filtered out. The water is then piped into storage tanks for park irrigation, with surplus water draining into the Huangpu River. Various planting themes are proposed at each segment of the rain gardens, responding to the characters of adjacent developments and uses. Boardwalks made of durable bamboo decking are proposed over the gardens, along with native flowering wetland species, to provide a unique opportunity for people to appreciate the plants as well as the diverse insect and bird species living in the garden.
The 700-meter rain gardens, and the 200-meter constructed wetland along the Jichang Canal (which translates literally to “airport canal”), will effectively detain the stormwater and treat all the first-flush runoff from the 1600-meter Yunjin Road in a five-year storm, contributing to the water treatment, and habitat value maximization in the city, as well as long-term cost savings for the operation of the park especially on irrigation.
Early in 2013, the rain garden design concept was presented with the rest of the park design for review to the client and public agencies. Although the overall park design concept, Runway of Urban Life, and the rest of the park features were soon approved, the rain gardens were questioned for its effectiveness, and ease of operation and management. Many stakeholders were unsure about the long-term effectiveness in managing stormwater from the public street, as there is no precedent for such a project in Shanghai. Additionally, the management of streets and parks by different governmental departments raised concerns of liabilities in the event of a street flood resulting from the gardens.
Despite the many successful examples from other parts of the world, not to mention multiple rounds of design refinement of the scheme, the rain gardens were not given the greenlight to move forward until the nationwide advocacy of the Sponge City practice was published in late 2014. The support for low-impact development from central government helped bring that element of the design back to life.
The Sasaki team worked very closely with the local civil engineering team to further improve the drainage path from the road surface to the garden out to the outlet. By breaking the street median at 24 meter intervals, the runoff from car lanes can sheet-flow across bike lanes into the inlets at sidewalk curbs, minimizing piping and eliminating elevation conflicts. A special inlet design allows excessive stormwater to flow directly into the storm sewer main line, minimizing chances for flooding during severe storm events.
After four years of persistent effort from
various parties, the rain gardens in the Runway Park will soon be opened to the
public. It will set a great precedent for integrated landscape design in China,
which will provide aesthetic, recreational, educational, ecological, and economic
benefits for the whole society.