Built during the Ming Dynasty, the Forbidden City has been remarkably well preserved and maintained over the past few centuries. According to the management, floodwaters can be drained in 20 minutes thanks to the complex's excellent drainage system.
The basic principle to avoid flooding is that the amount of water that drains away must be greater than the amount of rain that falls. To do this, the drainage system in the Forbidden City was designed very meticulously, synchronously and comprehensively.
In front of the Thai Hoa Palace square is a three-tiered terrace built of white marble. The terrace has three floors, more than 7 meters high. Around each floor are many elaborately carved dragon heads. Every time it rains, water spurts from 1,142 dragon heads, creating the scene of 'Ten Thousand Dragons Spouting Water', flowing into the Kim Thuy stream, an artificial canal inside the Forbidden City.
The drainage system in the Forbidden City includes both underground sewers and open ponds and ditches, which help drain more than 90 structures over an area of 720,000 square meters. The planning and design of waterways is extremely important.
Outside the Forbidden City, there are at least three waterways to prevent flooding. The first is the outer protective river and the Daming Canal and the Taiping Lake. The second is the Houhai and Taiyi Pond. The third is the Jinshui River and the Tongzihe Canal surrounding the Three Halls. These rivers and canals not only supply water to the capital, but also act as drainage to prevent flooding. All rainwater in the Forbidden City flows into the Jinshui River, which flows to the Donghua Gate and then into the outer canal.
The drainage system of the Forbidden City was also built according to the terrain. The terrain of Beijing is high in the northwest and gradually decreases towards the southeast. Therefore, the water in Beijing drains in a southeast direction. The design of the Forbidden City is based on this terrain, decreasing towards the south, forming a drainage direction from north to south.
The road between the Imperial Palace and the Forbidden City was designed to drain water to the west and south sides of the road into the citadel river.
The Forbidden City has a high construction density, so its self-draining ability is poor. Therefore, the drainage system needs to be calculated accurately and constructed carefully. The system consists of canals, ditches, ponds, and underground pipes that intersect and take on different roles, weaving through the buildings and palaces to form a drainage network.
The sewer system is divided into underground sewers and open sewers. Open sewers are sewers that lead to canals. Underground sewers are located deep underground. When encountering obstacles such as walls or courtyards, water will flow through grooves called Cau Nhan. Water on the surface flows into underground sewers. The surface of the sewer is called Tien Nhan, square, different from the surface of a coin from the Ming and Qing dynasties.
This meticulously designed and comprehensive drainage system, combined with regular maintenance to keep the water flowing smoothly, has helped the Forbidden City not flood for the past 600 years, regardless of the heavy rain and storms. This is considered a miracle of ancient architecture.
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