This summer, many Chinese cities have once again experienced severe flooding during heavy rains, falling back into 'watching the sea' mode, with the 'floods after every rain' issue remaining pressing. At the same time, droughts have been rampant, highlighting the scarcity of water resources. In fact, to address the chronic problem of 'floods after every rain and droughts following immediately', the State Council Office initiated the Sponge City construction program two years ago.
Background and Policy Progress of Sponge Cities
Sponge cities are a new generation of urban rainwater management concepts, referring to cities that have the ability to adapt to environmental changes and mitigate the impact of rain-related natural disasters. They can also be described as 'water-elastic cities,' with the international term being 'Low Impact Development (LID) rainwater systems.' During rainfall, they absorb, store, permeate, and purify water; during times of need, they release and utilize the stored water.
On December 31, 2014, in line with the spirit of the speech on strengthening sponge city construction and the requirements of the Central Economic Work Conference, the Ministry of Finance, Ministry of Housing and Urban-Rural Development, and Ministry of Water Resources decided to launch a pilot program for sponge city construction supported by central fiscal funds. The Guidelines on Promoting Sponge City Construction stipulate that through sponge city construction, the impact of urban development and construction on the ecological environment should be minimized, with 70% of rainfall being locally absorbed and utilized. By 2020, 20% of the built-up area in cities should meet the target requirements; by 2030, 80% of the built-up area in cities should meet the target requirements.
In October 2015, the State Council issued the Guidelines on Promoting Sponge City Construction to advance the work of sponge city construction. It is projected that by 2020, the industry scale will reach 9 trillion yuan, and by 2030, the market scale will reach 70 trillion yuan.
On March 5, 2017, at the Fifth Session of the Twelfth National People's Congress, the government work report clarified the direction for sponge city development, making sponge city construction a priority in all cities, not just pilot cities.
In 2015 and 2016, the country selected 30 cities as pilot projects for sponge city construction in two batches. As of now, the total area covered by sponge city construction pilot projects is 420 square kilometers, with a total investment of approximately 54.4 billion yuan. Among this, central fiscal subsidies amount to 23.34 billion yuan, local government fiscal inputs are 12.9 billion yuan, and social capital investments are around 18.2 billion yuan.
However, the implementation effects of sponge cities seem to be limited. Floods still occur frequently in pilot cities, raising questions such as whether sponge cities are effective and how to address public concerns that 'sponge cities do not absorb water' and 'sponge cities are a waste of money.'
This article offers some perspectives on the critical technical aspects of road permeable paving in sponge cities.
The Functional Requirements of Permeable Paving
China is experiencing rapid urbanization, with significant achievements in city construction. However, issues such as high development intensity and extensive hard surfaces remain. The construction of buildings, roads, and ground surfaces has led to excessive hardening of the underlying surface, altering the natural ecological base and hydrological characteristics of cities. This has resulted in problems such as the urban heat island effect, urban flooding, reduced rainwater infiltration, and deteriorating water ecosystems.
So-called 'sponge cities' aim to fully leverage the absorption, storage, and release functions of various surfaces and retention facilities in buildings, neighborhoods, roads, squares, parks, and green spaces. By adopting a combination of low-impact development measures such as 'permeation, retention, storage, purification, utilization, and discharge,' cities can become more resilient to environmental changes and natural disasters.
Yukuang Yu, Dean of the School of Architecture and Landscape Design at Peking University, stated that 'sponge cities may take 5 to 10 years, or even longer, to address these issues. We cannot conclude that pilot projects for sponge cities have failed just because there was flooding this time. These pilot projects do have demonstrative significance, but it is often localized.'
The challenges faced by sponge cities can be summarized as 'no flooding during light rain, no urban flooding during heavy rain, no black or foul-smelling water bodies, and reduced urban heat island effect.' The importance of building sponge cities to balance the relationship between water and cities is undeniable. However, the effectiveness of sponge cities needs time to be tested.
How can we ensure that sponge cities are implemented effectively and withstand future scrutiny? For permeable road paving, it must not only allow water infiltration and storage but also be environmentally friendly and sustainable. It should consider both product technical performance and urban development issues. Specifically, permeable pavements should have excellent permeability and a certain capacity to retain water, which enables them to alleviate the pressure on drainage systems and reduce urban flooding. Additionally, they should possess high strength, deformation resistance, water stability, good surface smoothness, anti-slip properties, environmental friendliness, and durability.
Historical Release Notes for the Road Permeable System
Driven by technological innovation, DBC Group, a leading new materials company, collaborated with CASU to develop a new permeable pavement technology for sponge city applications. With support from the global chemical giant BASF, Reubao (a permeable pavement system for sponge cities) was born, providing practical solutions for sponge city construction. In actual applications across multiple provinces and cities in Shanghai, Chongqing, Chengdu, Guizhou, and Jiangsu, Reubao demonstrated excellent water permeability, compressive strength, wear resistance, anti-slip properties, as well as environmental aesthetics, colorfulness, ease of maintenance, and sound absorption and noise reduction. It has become a 'breathing' urban landscape pavement, effectively alleviating the urban heat island effect and preventing city roads from overheating.
According to DBC Group's technical lead, the magic of Reubao's structural design lies in its ability not only to drain surface water but also to provide bottom waterproofing or regional water storage. It can filter rainwater through a hierarchical infiltration process, gradually replenishing groundwater while allowing moisture to evaporate from the ground surface during dry periods, thus maintaining a dynamic balance between surface water and groundwater, addressing the ecological issues caused by impermeable surfaces.
Reubao not only allows rainwater to penetrate underground to replenish urban and rural groundwater ecosystems, ensuring the normal growth of surface vegetation. It also blocks rainwater from seeping into the ground to protect against foundation deformation that could affect the structural integrity of urban buildings. By managing water infiltration and drainage in a calculated manner, Reubao ensures the normal cycle of urban water ecology, supporting the healthy growth of surface vegetation and the urban ground ecosystem.
In response to summer heat, Reubao also shows significant effectiveness in mitigating the urban heat island effect. By quickly dispersing stored heat on its breathable surface under intense sunlight, it can also release stored rainwater through evaporation, increasing urban humidity and comfort. This enhances the city's ability to regulate ground temperature and moisture.
Some view sponge cities as a mere embellishment, but I believe they are far from that. The construction of sponge cities is still in its early stages and deserves time for growth. Beyond addressing urban flooding, sponge cities encompass water resources, water environments, water safety, and water ecology. They are genuine 'Beautiful China' projects aimed at benefiting future generations. It is crucial for managers and constructors to adopt a systemic and holistic approach in terms of quality, precision, adaptability to local conditions, and long-term monitoring and evaluation.
Imagine this scene: After a heavy rain, the sky clears up, and the roads and sidewalks are spotlessly clean, gleaming as if washed by rain. Vehicles move orderly, and people step out to enjoy fresh air. Thanks to its advanced permeable pavement system, heavy rain is no longer a disaster but a natural blessing. Reubao, with its integrated water permeability and storage capabilities, has retained the water, showcasing ecological benefits in water conservation and drought resistance.
