While Beijing has flooded many times after record rains, the Forbidden City with more than 600 years of history, located a few kilometers from the city center, has always been dry.
According to experts, the secret of the Forbidden City lies in the drainage system designed in the Ming Dynasty, which far exceeds the imagination of modern technology, forcing today’s urban engineers to learn.
Beijing suffered the heaviest rain in 140 years in July 2023, with up to 745 mm of water in some areas, equivalent to nearly two months of average rain. A series of roads were flooded up to 2 meters deep, 33 people died, more than 100,000 people were evacuated, the subway system was paralyzed, and many residential areas lost power for a long time.
The Forbidden City, a UNESCO heritage site located right in the center of a heavy rain zone, only had a few small puddles of water in the courtyard and drained away after 20 minutes. At that time, there were many images circulating on social networks showing water flowing through 600-year-old gutters but not causing prolonged flooding. The palace is still open to welcome tens of thousands of visitors during the day, despite the chaos outside the city.
Forbidden City at sunset. Image: CFP
The Forbidden City was built from 1406-1420 under the reign of King Zhou De (Minh Thanh To), with more than a million workers participating in 14 years. From the beginning, the architects took into account the risk of flooding, a constant threat to Beijing located in the Yellow River Delta, where hundreds of historic floods have occurred.
The drainage system in the palace is designed according to the principle of three intelligent layers, combining topography, architecture and irrigation.
The first layer is sloping terrain and inclined courtyard, the entire palace is built on ground 1-2 m higher than the surrounding road. Each thousands of square meter courtyard is gently tilted in four directions with a precise slope of 1-2%, directing rainwater into central drainage ditches paved with blue stones.
The second layer is a network of gutters and underground drains, under the golden glazed tile roof is a system of 1,142 copper water-spewing dragon heads. Each dragon head is a sophisticated pipe, bringing water from the roof to a system of more than 72 km of underground sewers paved with blue stones, 1-2 m deep, 0.5-1 m wide, arranged in a regular square grid, directly connected to the Kim Thuy River outside.
Dragon head aqueduct in the Forbidden City. Image: CGTN
The last layer is an artificial river and regulating lake, Kim Thuy River – now a moat surrounding the palace, 52 m wide, 6 m deep, acting as a giant regulating tank with a capacity of tens of thousands of cubic meters, receiving excess water from underground sewers and leading to Beijing’s ancient canal system, finally merging into the Vinh Dinh Mon River.
Research by Tsinghua University in 2021 using 3D simulations and field measurements showed that the average drainage speed of the Forbidden City reached 1.5-2 liters/second/m2, higher than the average rainfall during heavy rains in Beijing (1.2 liters/second/m2). Water withdrawal time is only 15-20 minutes after the rain stops, the yard is completely dry, even in extreme rain conditions, the system still ensures that no more than 5 cm of water remains.
“This is an ancient engineering feat. The system not only drains water quickly but also distributes hydraulic pressure evenly, avoiding foundation landslides and protecting long-term wooden structures,” Professor Ly Hieu Dong, an expert in ancient Chinese architecture, commented in the scientific report.
A man rides a motorbike through a flooded street in Miyun district, a suburb of Beijing, July. Photo: Adek Berry/AFP
In the context that China is spending billions of dollars to build a “sponge city” model in more than 30 urban areas to prevent urban flooding, many experts believe that we should learn directly from the Forbidden City. Natural design does not depend on electric pumps or mechanical systems, sustainable for 600 years. The system only needs periodic cleaning and dredging of sewers every 5-10 years, harmoniously integrating drainage function and architectural aesthetics with the image of a dragon head, artificial river, and garden, both preventing floods and creating landscape.
In 2016, after the historic flood that killed 79 people and caused more than 33 billion yuan in damage in Beijing, Chinese netizens once asked a harsh question on Weibo “Why not replicate the Forbidden City model for the whole city instead of building modern concrete culverts that continuously fail?”.
For more than 600 years, through 24 emperors of the Ming and Qing dynasties, the Forbidden City has never recorded a flood that damaged the structure. The secret lies in the “flood prevention from the root” mindset of the ancients – risk prediction, overall design, and taking advantage of nature.