Never flooded for more than 600 years! Why is the Forbidden City not afraid of heavy rain?

Review expert: Wang Shengwei, Senior Engineer, Beijing Municipal Engineering Design and Research Institute Co., Ltd.

On July 27, the 46th World Heritage Conference of UNESCO held in New Delhi, India passed a resolution to include "Beijing Central Axis - a Masterpiece of China's Ideal Capital Order" in the World Heritage List .

Beijing's Central Axis runs through the old city from north to south. After many years, it is still full of vitality and is closely related to people's lives.

View of the gate of the Forbidden City or the Palace Museum from Jingshan Park. Image source: Qianku.com

Among the 15 heritage elements of Beijing's central axis, the Forbidden City is located at the center. As the royal palace of the Ming and Qing dynasties, the Forbidden City has a history of 600 years and is one of the largest and most intact ancient wooden structures in the world. There are many ingenious ideas in the magnificent architectural complex of the Forbidden City, and many devices are still able to operate efficiently. The game between humans and weather has never stopped from ancient times to the present.

Late July to early August every year is the period of most concentrated precipitation in North my country. At this time, urban flooding caused by heavy rainfall always presents a "sea-viewing mode", and how to drain the accumulated water has become a hot topic again and again.

The Forbidden City after the rain, Image source: Weibo @故宫博物院

In terms of drainage and flood prevention, the Forbidden City has demonstrated the wisdom of its predecessors. The Forbidden City's drainage system, which has a history of more than 600 years, has withstood the test of heavy rains time and time again. The design of "dragons emerging from the water" not only ensures the safety of the three main halls, but also creates a magnificent landscape of "thousands of dragons spitting water". How was all this done?

Precision designed drainage system

At the beginning of the construction of the Forbidden City, the drainage system was precisely designed and constructed. The overall trend of the ground of the Forbidden City is high in the north and low in the south. The ground of the Shenwu Gate in the north is about two meters higher than the ground of the Wumen Gate in the south, forming an overall drainage slope of about 2‰. The palace complex with the central axis building as the core makes the overall terrain slightly higher in the middle and slightly lower on both sides, forming a "bear back" style. This slope creates favorable conditions for natural drainage.

The Forbidden City's open and underground ditches are interconnected, with a length of more than 15 kilometers. There are culverts, water ditches, etc., crisscrossing and clearly divided into primary and secondary, all leading to the main canal, the Inner Jinshui River. The Inner Jinshui River is connected to the Outer Jinshui River, the moat, the Zhongnanhai and other water systems outside the Forbidden City wall, so that rainwater flows from high to low terrain to the open and underground ditches, then flows into the main canal, the Inner Jinshui River, and then drains into the river outside the Forbidden City. As long as the river outside the Forbidden City does not overflow, the Forbidden City will not be flooded. The ancients solved the flood problem of the Forbidden City through this complete and systematic drainage system.

The Jinshui River in the Forbidden City on July 31, 2023. Image source: Xinhua News Agency

" Chilong emerging from water " combines beauty and practicality

There is a famous "landscape" in the Forbidden City on rainy days - "Thousand Dragons Spewing Water". The so-called Thousand Dragons actually refers to the drainage devices on the bases of the palaces - Chi (chī) heads. Chi is said to be the ninth son of the dragon, with a big mouth and a belly that can hold water. It is a mythical beast in ancient times. Since the base of the Forbidden City's main hall is relatively high and surrounded by railings, an inner channel will form on the base on rainy days. The water in the channel flows into the Chi head through the bottom of the baluster, and then is discharged from the hole in the mouth of the Chi head, forming the grand scene of "Chi dragons coming out of water".

On July 31, 2023, the 600-year-old drainage system of the Forbidden City resisted the attack of heavy rain, and the dragon head on the base of the Hall of Supreme Harmony in the Forbidden City spit out rainwater. Image source: Xinhua News Agency

The three main halls of the Forbidden City, the Hall of Supreme Harmony, the Hall of Central Harmony and the Hall of Preserving Harmony, are located on an I-shaped platform more than 8 meters high. The platform covers an area of ​​25,000 square meters and is divided into three layers. At the bottom of the railings around the platform, the holes for draining rainwater are connected to exquisitely carved stone dragon heads, and the mouths of the dragon heads are round holes that are also the main drainage outlets. There are 1,142 dragon heads on the three-layer platform. During heavy rains, the scene of "thousands of dragons spitting water" is spectacular. The rainwater from the three platforms flows down layer by layer. There are stone culverts under the steps that connect to the dry ditch, allowing the water to pass smoothly and finally drain into the Inner Jinshui River.

The ingenious design of the drainage system by the ancients, as well as their unique conception and production, protect people from the harm of waterlogging, which makes people sigh at the wisdom of their ancestors. Coupled with the proper maintenance over the years, the Forbidden City has been able to safely survive Beijing's rainy season.

Going further north from the northern section of the central axis, you will arrive at the Beijing Science Center. As a public welfare social science education base serving the public, it has a large science and technology venue open to the public and also provides a variety of novel and interesting science activities.

Photos inside the Beijing Science Center