SPONGE CITY—BRING THE CITY BACK TO THE NATURE
The process of urbanization has observed considerable changes in city roads, transportation, housing and other infrastructures, and the deteriorated quality of the climate, hydrology, vegetation, and environment. Soil pollution, water contamination, the paralysis of the natural ecological network, the collapse of the cultural ecological system, these issues happened frequently, accompanied with the disordered sprawl in both urban &rural areas. People cannot help but reflect, what a city without social ladders, what a hometown without retrograde steps.
Just as its name implies, the feature of Sponge City should resembled the feature of sponges, which require them to embody enough “flexibility”and “reliance” in face of the climate change and natural hazard, etc. The city can absorb, harvest, filter and purify water when it rains, while “release”the stored rainwater when in need. Its essence lies in solving the disharmony between urbanization and environmental resources. Its goal is to make cities adapted to environmental changes in a flexible manner and confront with natural disasters in a resilient way, to transform the traditional stereotypes on city drainage and waterlogging prevention, and implement low-impact urban development practice, to give a full play on rivers, mountains, urban green spaces, roads, buildings in terms of the function of rainwater absorption, filtration and detain & retain. to reconstruct the natural-like water circulation by employing the landscape elements, such as permeable paving, filtration bio-swale, sunken green space, wetlands and other water bodies, as well as to stabilize the hydraulic characteristics in every urban developing phase, and accumulate, infiltrate and purify the water resource in a natural way.
In the advanced foreign concept, the philosophy of Sponge City initiated by simple and traditional pipe & tube drainage engineering techniques, which are substituted by the ecological landscape design integrated with the idea of ecological storemwater management. Highlighting in employing ecological and biomimetic measures, making full use of the comprehensive service value lies in the natural eco-system, which could carry on the processes like water storage, rainwater regulation, runoff pollutants purification, water quality protection, etc. enhancing natural hydrological cycle in city and maintaining the long-lasting sustainable city development by scientific plan and rational design, and balancing the natural a and artificial landscape. Several developed countries have already formed the comparatively consummate Sponge City management system model, which appropriately suits the in-house technical law & regulation system. Besides, the model was perfectly combined with the plan of urban design and practiced through the design of infrastructure construction. The genuine Sponge City was emerged around the 1980s in China, developed and thrived in the 1990s, and maintained a growing momentum nowadays. The core of the Sponge City focus on reducing pollution, cutting exhausting, retention & detention, recycle & reuse, ecology, etc.
We believe that Sponge City is mainly composed of three parts, namely, natural systems, semi-natural systems and artificial systems. Natural systems mainly include rivers, lakes, wetlands, mountains, forests, and the things alike. Semi-natural systems consist of reservoirs, ponds, country parks, farmlands, urban green belts, shelter forest belts, etc. Artificial system is comprised of rainwater utilization facilities, green roofs, permeable pavement and so on. How to build a Sponge City? How to bring the city back to nature? You may find the answer in the following three main approaches.
(1) To render all-around protection to the original eco-system on target area, repair &restore damaged natural environment and water bodies. First, to proceeds the work on the components of Sponge citiy. Finding out the natural &semi-natural patches, which have significant impact on the surface runoff. Strictly protecting the patches of which could exert great influence on the regional hydrology. Second, to build the ecological corridor. Ecological corridors linked the scattered & fragmented patches together organically. Apart from this, they also formed some scaled and diversified bio-habitats and water conservation areas, which provide the migration route for animals and aquatic network for water regulation. Third, to delineate the regional ecological control lines, and make a clear boundary on urban development, prevent the construction land sprawl in urban& rural areas, and spark the city with sound development and smart growth. Finally, to repair the damaged natural environment and restore the spoiled water bodies ecologically through various technical means, and improve natural water ecosystems' self-healing ability.
(2) Sponge City design & reconstruction in urban planning area.
“Sponge City” demands the control and guide from all levels of cities and all the disciplines of relevant professions.
The phase of comprehensive urban planning should focus on innovative ideas and methods, and on the stormwater management measures which emphasized on low-impact city development accompanied with the related contents of urban ecological protection, land use, hydrographic network, green systems, municipal infrastructure, environmental protection, formulate & regulate the control rate of annual total runoff volume and the corresponsive goal of the annual designed rainfall volume based on the local condition, set out the feasible & practical policies for the low-impact stormwater management system, and select the key implementation area.
Urban subject plan, include the specialized plan in the aspects of water system, green space system, road & transportation systems, and other infrastructure systems in the city. Among them, urban water system planning is intertwined with water supply, water conservation, wasting water (recycle & reuse), drainage (waterlogging prevention), the blue control line and other factors. The green space system planning should meet the basic functional requirements from the precondition of greenery ecology, landscape, recreation and other. Preserve the land and space rationally, as well as provide suitable condition for various species to bread & generate. Infiltrate, regulate and purify the runoff on site & from the surrounding hardened area, and integrate in urban stormwater pipe & channel drainage system and excessive runoff discharge system. As for the specialized plan of road & transportation system, it should not only aim in the coordination between the space layout inside and outside the red control line, but the management of the vertical space layers. We should make full use of the green belt, traffic pass, pedestrian way and the parking lot in different levels of roads, and build stormwater retention & detention facilities to achieve the low-impact development goal.
The phase of regulatory detailed urban plan focues on the implementation of the comprehensive plan and the specialized plan. Set off the controlled goal and standard for the low-impact development. Arrange the lands operated as the stormwater infiltration, detention & retention, purification, utilization and discharge space on the basis of the local condition, and in line with the land use and area layout. Decompose and definitude the low-impact criteria in every modular area, such as the plot ratio, green rate and the depth of the sunken green space, permeable paving rate and green roof rate, etc. all the subordinate plan and land transfer & development should follow these guidelines.
Specifically, to build the low-impact stormwater control & utilization system conjuncted with space carrier such as urban water system, roads, residential areas, green spaces and squares.
Urban water system is the most direct and ideal place to regulate and drainage stormwater. While sufficiently conserving the original water system, taking the site's situation into fully accounts, excavating the ditches and tunnels, connecting all the hydrographic net and forming a complete urban water system. The coast lines design must consider the hard pavement to prevent flood, and give a second thought on the ecological revetment, and improve the water system' capacity in absorbing and purifying storm water.
Urban road is the primary space for rainwater runoff gathering. The pedestrian ways on two sides of the roads could adopt the permeable paving style. The green belt on both sides and the central separation barriers could be properly carved with submergence to convey the stormwater runoff and discharged it into the surrounding green park and other natural environment, for the refined function of stormwater harvesting and infiltration. Urban green space and plaza is the main recreational place for people, and also the main gathering place for rainwater. Green space design should pick a variety of vegetation, while create a favorable natural landscape but also absorb rainwater through the roots of ground cover plants and shrubs. The pavement on the square should use pervious ones to the greatest extent and fully consider the conducting function for stormwater collection and absorption effect, in order to optimize the urban water system.
The roads, sidewalks, leisure squares in the residential areas should use permeable paving and sunken green space during the planning and construction process. The sunken green space below the horizon level could store, harvest, retain & detain stormwater more efficiently, and contribute as a part of hydraulic landscape in the residential zones. It's a smart move to cover the architects with green roofs. This practice harvests and retains stormwater, as well as provides the city with a pleasing landscape and mitigate urban heat island effect.
(3) To establish a assurance mechanism of Sponge City management implementation.
We should promote the standardization and legalization of Sponge City mainly through lawful establishment, institutional reform, regulatory and supervisory management refinement and other measures alike. First, to establish and improve the legal & policy system for Sponge City, and provide an institutional guarantee for Sponge City construction. Second, local governments should reform the current urban stormwater management system, including the establishment of the reward & punishment mechanism associated with the performance assessment and the investment &financial system dedicated in Sponge City construction, and change the current opaque urban plan condition result from lack of social supervision management system. The public supervision from society should be strengthened throughout the process of sponge city construction no matter in which phase, such as project approval and initiation, planning and design, engineering and construction, etc.
The philosophy of Sponge City brings the city back to nature. In this era, nature and humans is an entity. The future is the alternative result of our choice, not our inevitable destiny. Imagine, when the year of 2200 or 2500 approach, our descendent may compare us to aliens who only treated earth as a stopover for refueling. Moreover, our offspring may regard us as barbarians who have destroyed their own homeland. Contemporarily, we are supposed to form a sharing atmosphere instead of an unlimited plundering culture where all the creatures on earth could popularize and generate together. As a newly emerging urban development model, Sponge City theory is still in the stage of exploration and development. We are urged to perceive its concept and content in a broaden horizon and deeper dimension. The practice strategies and standards should be developed and formulated in line with our countries' specific geographical characteristics, catalyze and stimulate the improvement and maturity of the theoretical system, facilitate and prompt cities back to nature. In a nutshell, the outlook of our task is promising but far more than smooth.
He Fang
Sep.2015
(Translated by Zhang Xu)