The mother river of China’s Haikou City has suffered water pollution for decades caused by sewage and non-point source pollution urban and suburban runoffs. The landscape architect lead the implementation of nature-based solutions to transforming the gray concrete river into a resilient green infrastructure and integrating the sewage treatment process into an ecological system that revives the river with clean water, rich lives, lush beauty, and social vitalities.
2．Site and Challenges
Haikou is a tourist city in South China’s tropical area with a monsoon climate. In the past four decades, the city has experienced a frenzied ten-times growth in population from a quarter million to 2.3 million. Compared to the sprouting skyscrapers, little attention was paid to the natural water system and the urban water infrastructure which are critical for a city in a monsoon climate. The Meishe River, 23 kilometers long, literally meaning the “beautiful mother river” in local language, which runs through the built up area had become a nightmare for the city, for decades, a sewage dump. The single-minded counter flooding control walls had turned the river into a lifeless concrete channel that people turned their backs on. For many years, piecemeal solutions were attempted such as building walls and locks to control floods and sea tides, river bed dredging, growing flowers and putting lawns at the river bank, locking off the polluted tributaries, etc. But all these measures only worsened the situation. Images of black water, dead fish and concrete flood walls were broadcast nationwide on China’s Central Television. For a tourist beach city, this was shameful.
In 2016, the Haikou government decided to make a change, this time in a holistic and systematic way. The landscape architect was commissioned to lead the mission of recovering the mother river. The project includes a major park, the Fengxiang Park, 80 hectares (about 200 acres) in size and a linear river corridor 13 kilometers long that runs through the densely built area, which makes up the major part of the planned and designed green infrastructure.
3. Objectives and design Strategies
By integrating the works of civil engineering that deal with a gray drainage system of sewage pipes and treatment plants that will collect the sewage of the point sources, and cut off some major pollution sources, the landscape architect designed the river corridor as a comprehensive ecological infrastructure to solve holistically the problems of flood and pollution, recover habitats for biodiversity, create pleasant recreation opportunities, and make it beautiful. Three strategies were adopted:
(1) Planning an ecological infrastructure: Based on terrain, land use, and hydrological process, a stormwater drainage-centered green system, namely the green sponge, was planned to separate the stormwater from the sewage, so as to integrate the river and all its tributaries, wetland, and all built and potential green spaces. The green sponge is also integrated with an inter-connected pedestrian and recreational network.
(2) Transforming grey into green: wherever possible, more green spaces are given to the water: the concrete flood walls were removed and replaced with an eco-friendly river bank. The blocked water way is reconnected to the ocean to allow tides to again enter the city; wetlands and shallow shores along the river were reconstructed so that mangroves could rehabilitate them. Continuous elevated pedestrian paths were designed to create waterfront access.
(3) Integrating grey into green and the terraced wetland park: Interconnected terraces of constructed subsurface flow wetlands are built along the river bank, formerly occupied by a concrete flood wall and garbage dump. The terraces are designed as water cleansing facilities. Two type of water flow into the wetland to be cleansed: The non-point source pollution water runoffs that carry rich nutrients, and sewage from the local urban villages that currently are unable to access the centralized sewage treatment system. In the former case, the wetland can clean 6000 tons of urban runoff daily from grade V to III, which is swimmable; In the latter case, tests show that 3,500 tons of domestic sewage can be cleansed to the same quality daily. For this, mobile pretreatment equipment is installed at the wetland inlet to remove the smell and pathogens that may cause a public health risk, before the grey water is channeled into the wetland. The two flows can be switched alternately or combined according to demands. The biomass from the wetland is harvested and regularly decomposed into fertilizers for use in the landscape.
Integrated into this ecology of resilient water is an interpretative environmental system and resting places to enjoy the landscape services allow visitors to have a unique experience of the designed ecologies.
The project is a great success: the river water has become clean again, fish and birds have returned, mangrove are reestablished, and the water is again the city’s heart; tens of thousands of visitors are attracted to the new landscape. And to celebrate the recovery of the beauty of its mother river which was only a memory for older residents decades ago, Haikou was honored as one of the 18 International Wetland Cities by the Contracting Parties to the Ramsar Convention in 2018.
But what is more significant is that tests prove the nature-based solutions showcased in this project are replicable. Globally, over 85% of sewage in urban areas, mainly in developing countries, is untreated, polluting rivers, lakes and oceans, and worsening the water shortage. 75% of the surface water is polluted in China, mainly caused by non-point source pollution source pollution including urban and suburban runoffs. While centralized sewage treatment systems are economically unfeasible for some urban villages and isolated settlements, nature-based solutions can play an important role in remediating water quality and floods, as well as creating public spaces that provide cultural and social services. It is a whole new territory for the practice and education of landscape architecture.