While modern Beijing has repeatedly succumbed to the effects of record rainfall and severe flooding, the Forbidden City, a historic treasure spanning over 600 years and located just a few kilometers from the city center, has consistently remained dry.
According to experts, the Forbidden City’s secret lies in its drainage system, an engineering marvel conceived during the Ming Dynasty. Its design, which surpasses modern technical imagination, is now a subject of study for contemporary urban engineers.
In July 2023, Beijing endured its most intense rainfall in 140 years, with water levels reaching up to 745 mm in certain areas—nearly two months’ average rainfall. Major roads were submerged by up to two meters of water, resulting in 33 deaths, the evacuation of over 100,000 people, the paralysis of the subway system, and prolonged power outages in many residential areas.
Yet, the Forbidden City, a UNESCO World Heritage site right in the center of the downpour, only showed a few small puddles in its courtyards. These disappeared completely within 20 minutes. Social media was flooded with images showing torrents of water spilling gracefully from 600-year-old gargoyles, with no prolonged waterlogging. The ancient palace remained open to tens of thousands of visitors that day, a stark contrast to the chaos outside its walls.
The Forbidden City was constructed between 1406 and 1420 under Emperor Zhu Di (Yongle Emperor) of the Ming Dynasty, involving over a million laborers across 14 years. From the outset, architects planned for the perennial flood risk in Beijing, which lies within the Yellow River plain—a region historically prone to flooding.
The palace’s drainage system was ingeniously designed on a three-layered principle, integrating the site’s topography, architecture, and hydrology.
The entire palace complex was built on a raised foundation, elevated 1-2 meters above the surrounding street level. Every inner courtyard, some spanning thousands of square meters, is precisely sloped by 1-2% towards the four cardinal directions. This subtle gradient guides rainwater naturally to central drainage channels paved with bluestone.
Beneath the majestic yellow glazed tile roofs is a system of 1,142 bronze dragon-head waterspouts. Each dragon’s mouth serves as a sophisticated conduit, channeling water from the roofs into an extensive network of over 72 km of underground bluestone sewers. These sewers, typically 1-2 meters deep and 0.5-1 meter wide, are arranged in a regular grid pattern and connect directly to the Golden Water River outside the inner palace.
This combination creates a dramatic scene during heavy rain, often described as “Ten Thousand Dragons Spitting Water,” which efficiently distributes the hydraulic pressure and prevents erosion.
The final layer involves a man-made river and regulating lakes. The Inner Golden Water River flows through the complex before emptying into the outer moat, a 52-meter-wide, 6-meter-deep canal encircling the palace. This moat acts as a massive retention basin with a capacity of tens of thousands of cubic meters. It receives all excess water from the underground sewers and funnels it into Beijing’s ancient canal network, eventually merging with the Yongding River.
A 2021 study by Tsinghua University, utilizing 3D simulation and on-site measurements, determined that the Forbidden City’s average drainage rate reaches 1.5–2 liters per second per square meter ($1.5-2 \, L/s/m^2$). This is significantly higher than the average rainfall rate during Beijing’s major storms, which is about 1.2 liters per second per square meter ($1.2 \, L/s/m^2$). The water clears completely in the courtyards within 15–20 minutes after the rain stops, and the system can ensure water does not accumulate more than 5 cm even during extreme rainfall.
“This is an ancient engineering marvel,” noted Professor Li Xiaodong, an expert in ancient Chinese architecture, in a scientific report. “The system not only drains quickly but also evenly distributes hydraulic pressure, preventing foundation erosion and protecting the long-term integrity of the wooden structures.”
As China invests billions of dollars into its “sponge city” model across more than 30 urban centers to combat urban waterlogging, many experts argue that direct lessons should be drawn from the Forbidden City. Its natural design requires no electric pumps or mechanical systems, and has remained sustainable for 600 years. It only requires periodic cleaning and dredging of the sewers every 5-10 years, harmoniously integrating the practical function of drainage with the architectural aesthetics of dragon gargoyles, man-made rivers, and courtyards—preventing floods while creating beautiful landscapes.
In 2016, following a historic flood that killed 79 people and caused over 33 billion yuan in damage in Beijing, Chinese netizens on Weibo frequently posed a sharp question: “Why not replicate the Forbidden City model for the entire city instead of repeatedly failing with modern concrete sewers?”
For over six centuries, and through the reigns of 24 Ming and Qing emperors, the Forbidden City has never recorded a flood that caused structural damage. The secret lies in the ancient mindset of “flood prevention at the root”—anticipating risk, designing holistically, and utilizing nature’s power.
(According to CNN, The Guardian, CGTN)
