China's new approach to flood control: Turning cities into sponges

The 'sponge city' model developed to reduce floods and water overflows caused by heavy rainfall in China offers a new approach to urban planning. Instead of quickly channeling rainwater into sewers, the system absorbs it into the ground and stores it in natural areas; it is implemented with permeable roads, green roofs, rain gardens, and artificial ponds. However, experts point out that the method alone will not be sufficient during extreme rainfall.

Cities Absorb Rainwater

In traditional urban infrastructure, rainwater runs off concrete surfaces into sewers and drainage systems. When heavy rains exceed the capacity of these systems, floods can occur on avenues and streets.

The sponge city model follows a different approach. It aims to retain rainwater where it falls, infiltrate it into the ground, and store it for reuse when needed.

In this context, permeable road surfaces, green roofs, rain gardens, and small ponds are employed. Thus, by slowing the direct flow of rainwater into sewers, the aim is to reduce the load on the infrastructure.

Natural Areas Replace Concrete Channels

In the sponge city approach, not only roads and buildings but also urban green spaces play an important role. Alongside concrete channels, watercourses surrounded by plants, wetlands, and green corridors are created.

These areas help reduce the flow rate of rainwater, allowing the water to move in a controlled manner. Plants and soil can also contribute to trapping some pollutants in the water.

The applications also support natural life by increasing the amount of green space in cities and enable more efficient use of rainwater.

Construction is restricted in areas at risk of flooding.

One of the model's core elements is protecting the natural flow paths of water. The approach led by Chinese landscape architect Kongjian Yu argues that the floodplains of rivers and low-lying areas where water accumulates should not be viewed merely as sites for development.

Preserving these areas as natural water storage zones can reduce the risk of excess water reaching settlements during heavy rainfall.

Thus, the goal is for cities to have infrastructure that not only removes rainwater but also retains and manages it.

Systems Can Be Inadequate During Heavy Rainfall

While sponge city measures have the potential to reduce flooding, they do not provide absolute protection against rainfall at all scales.

The flood disaster that struck Zhengzhou, China, in 2021 highlighted the impact of extreme weather events on urban infrastructure. In some parts of the city, more than 200 millimetres of rainfall was recorded within an hour.

Rainfall at this scale can exceed the capacity of systems that absorb and store water. Therefore, experts emphasize that sponge city measures should be implemented alongside traditional drainage infrastructure, flood control systems, and early warning mechanisms.

The sponge city model aims to make cities more resilient to the increasingly frequent extreme rainfall associated with climate change. However, effective results require proper urban planning, regular maintenance, and comprehensive infrastructure investment.