Did the ancients have clever ways to drain water? Uncovering the ingenious flood control and drainage systems of ancient buildings

Scientific and sophisticated flood control and drainage system in ancient cities

In recent years, extreme weather has occurred frequently, rainstorms have caused disasters, and floods have raged. Many large and medium-sized cities in China have suffered water disasters of varying degrees. Urban waterlogging has become the weak point of urban development. In late July 2021, Henan Province suffered from extremely heavy rainstorms that were rare in history, especially Zhengzhou City, which suffered heavy casualties and property losses. The issue of urban flood prevention and disaster reduction has once again attracted the attention of society and academia.

In ancient my country, there are many classic examples of urban flood control and drainage systems, which reflect the simple view of nature and dialectics and show the wisdom of the ancient working people. The following examples show the scientific and exquisite urban flood control and drainage systems in ancient my country, such as Fushougou in Ganzhou, Jiangxi, the ancient city wall of Shou County, Anhui, and the Forbidden City in Beijing during the Ming and Qing Dynasties. I hope you can learn from them and gain inspiration.

1. Fushougou:

Underground drainage system that will keep water from flooding for a thousand years

Underground drainage is an important way for cities to reduce flood disasters. In Ganzhou, Jiangxi Province, there is an underground drainage system that was built in the Song Dynasty. It has been used for a thousand years and is still in use today. This is the Fushou Ditch.

Ganzhou, formerly known as Nankang County and Qianzhou, is located in the southern part of Jiangxi Province, at the confluence of the Zhang and Gong rivers in the upper reaches of the Ganjiang River. Ganzhou got its name from this, and is known as the "first city of the thousand-mile Ganjiang River". Ganzhou's terrain is mainly mountainous and hilly, with a subtropical monsoon climate, four distinct seasons, and rain and heat at the same time. Every year, the turn of spring and summer is the peak period for floods and waterlogging disasters in Ganzhou. Historically, flood prevention and drainage have been major issues that Ganzhou City needs to face and solve.

Since the Song Dynasty , Ganzhou has gradually established an underground drainage system with the Fushougou drainage channel as the main body and ponds and water windows supporting each other.

During the Xining period of the Northern Song Dynasty , the then prefect Liu Yi, who served as the "Du Shui Cheng", adopted the principle of zoning drainage based on the turtle-back shaped topography of Ganzhou City, which was high in the southwest and low in the northeast. He built two drainage trunk systems. Because the direction of the two ditches resembled the seal script of the Chinese characters "Fu" and "Shou", they were named Fushou Ditch.

Shougou is located in the northwest of the city, and Fugou is located in the southeast of the city. Rainwater and sewage in the northern area of ​​the city are collected by various ditches into Shougou and discharged from the eastern and northern water windows; rainwater and sewage in the southern area of ​​the city are collected by Fugou and discharged from the southeast water window. In addition to the main drainage channel, many crisscrossing branches and shallow surface drainage ditches are built to connect with it.

The map of Fushougou in the "Ganzhou Prefecture Records" of the Tongzhi Period

The design of the ditch of Fushougou is also very reasonable. First of all, the size of the drainage ditch is quite large, with a trunk width of up to 1 meter and a maximum of 1.6 meters, which can accommodate one person walking. The large size is the key to its large water drainage function and timely outflow of rainwater. Secondly, the lower part of the ditch is built with granite, which is hard, compressive and anti-corrosive, and the upper part is a brick arch structure, which is earthquake-resistant and compressive. This structure is also easy to repair. When a brick is damaged, it can be replaced at any time and continue to function. In addition, the building materials of the ditch are natural and environmentally friendly, mostly using tung oil, yellow mud, sand and stone (commonly known as three-in-one soil), blue bricks, hemp strips and other materials, with strong permeability and sustainability. The total length of Fushougou during the Tongzhi period of the Qing Dynasty was about 12.6 kilometers, and some parts are still in use today.

Brick arch structure inside Fushougou (Photo from the Internet)

The water window is an important part of the flood control and drainage system of Fushougou. According to the principle of hydraulics, the builders built 12 water windows at the outlet of Fushougou. The water windows use the principle of lever and water pressure to effectively avoid the danger of flood backflow. When the flood water level is higher than the water level in the ditch, the pressure of the river water will press the water window. When the river water level is lower than the water level at the outlet, the water window will be flushed open by the water in the ditch. In this way, the river water cannot flood the city through the ditch, and it does not affect the drainage of the water in the ditch.

Ganzhou Fushougou drainage water window

There are also many ponds in Ganzhou City, which play a role in regulating the drainage volume in the entire drainage system. When a large amount of accumulated water in the city cannot be discharged in time, it flows to dozens of ponds connected to Fushougou, such as Phoenix Pond, Goldfish Pond, Hissing Horse Pond, Qingshui Pond, and Hebao Pond. Rainwater and sewage flow to the ponds through Fushougou, forming a huge reservoir. When the river water level drops, the water is slowly discharged, which plays a role in regulating drought and flood.

In addition, the designers of Fushou Ditch also paid great attention to details. In order to avoid mud and sand accumulation, many anti-blockage and easy-to-clear facilities are installed. Copper coin-shaped rainwater grates are installed on the surface. Stone lion claws are built at each turn of Fushou Ditch to dig out garbage in the sewage. Caissons are installed in each inspection well. Mud, sand and garbage flowing through here will be retained in the caissons, which greatly reduces the workload of clearing and maintenance. This shows the creativity and care in the design.

It is worth mentioning that the Fushou Ditch drainage system not only has the function of regulating and storing water during heavy rains, but also shoulders the mission of people's livelihood. The large and small ditches throughout the ancient city are connected to various drainage facilities in residents' courtyards and kitchens. Sewage can be discharged into the Fushou Ditch from residents' homes. Although the mechanism of combining rainwater and sewage does not seem scientific today, more than a thousand years ago, this design and layout enabled the residents of the ancient city to enjoy the convenience brought by the building's water supply and drainage facilities. It was also a great livelihood project.

2. Shou County City Wall:

A model of intelligent water retaining engineering

Shou County is located in the central part of Anhui Province, on the south bank of the middle reaches of the Huai River. It was called Shouyang, Shouchun, and Shouzhou in ancient times and was once the capital of the Chu State. Shou County has a strategic terrain and has been an important water and land transportation hub since ancient times. Due to its natural geographical environment, Shou County has suffered floods and waterlogging disasters many times in history. Its intelligent water retaining system represented by the city wall is impregnable and is a model for urban flood prevention and disaster reduction in my country.

The Shou County city wall water retaining project includes city walls, stone banks, urn cities, culverts, moon dams, as well as ponds and underground drainage systems within the city.

City Wall

The ancient city wall was built during the Xining period of the Northern Song Dynasty and rebuilt during the Jiading period of the Southern Song Dynasty. It is square in shape with four gates: east, west, south and north. The inside of the wall is rammed with clay, the outer wall has a stone foundation and blue bricks on top. The gaps between bricks and stones are slurried with tung oil, glutinous rice juice and lime, making it very strong.

Shou County is surrounded by water on three sides. Whenever the Huai and Fei rivers flood, the ancient city seems to be in the water, so the flood prevention function of the city wall is very important. The ancients took this feature into full consideration when building the city wall, and built the lowest height of the city wall slightly higher than the highest water level of Fengtai Xiashikou, the main stream of the Huai River. When the Huai River flood is about to rise to the top of the city wall, it will flow down from Xiashikou and will not flood into the city, ensuring the safety of Shouzhou City. In addition, in order to reduce the impact of floods, the corners of the city wall are deliberately built in an arc shape.

Shou County Ancient City Wall

Stone bank

The stone bank for protecting the city. It is a 3-meter-high and 8-meter-wide embankment built at the foot of the city wall. It is also called the mooring bank for protecting the city. It was first built during the Jiajing period of the Ming Dynasty. Its inner opening is connected to the foundation of the wall, and its outer opening is built with stone strips. The stone bank for protecting the city adds a solid defense line to the entire city wall, withstanding the direct impact of floods on the foundation of the city wall.

Shou County City Wall Protecting Stone Bank

Barbican

Outside the city gates, there are also urn cities. In ancient times, urn cities were built outside the city gates to strengthen defense or prevent floods. They are semicircular or square. In history, urn cities were built at the four city gates in the east, west, south and north of Shou County, forming an inner and outer gate. If floods enter the urn cities, they will form vortices, which can reduce the pressure of floods on the inner gates and city walls. In the 1960s, due to the inconvenience of municipal transportation, the urn cities at the west and south gates were demolished, and the urn cities at the east and north gates are now preserved.

Shou County Ancient City Wall and Wengcheng

Culvert and Moon Dam

Shou County originally had three culverts, but now only the northeast and northwest culverts remain, which are used to drain the water in the city in time. Yueba is actually a barrel-shaped dam wall with masonry structure built on the culvert, which is higher than the city wall and surrounded by thick embankments. It looks like a small hill from a distance. There are stone steps on the inner wall leading to the culvert at the bottom of the dam. The culvert is sealed with stone slabs and has five gates, which can be opened and closed at any time to control the flow.

The moon dam and culvert work together to prevent floods and drain water. The moon dam protects the culvert and the attached gates to prevent them from being damaged by water from the inner river. The culvert passes through the moon dam and crosses the city wall and the stone bank of the city moat. A wooden plug is installed in the middle, with the small end of the plug facing the city. When the water level in the city is higher than that outside the city, the inner river water will break through the wooden plug through the culvert, enter the culvert body, and drain the water to the moat outside the city. When the water level outside the city is higher than that inside the city, the water from the outer city will plug the wooden plug tightly into the inner river culvert through water pressure, and the water level in the moon dam will also rise, which plays a role in water storage, thereby preventing the water from the outer city from flowing back into the city, which plays an important role in flood prevention and drainage.

Shou County Culverts and Moon Dams In addition to the culverts and moon dams at the city gate, there are water storage ponds for the inner city river at the four corners of the city. There are also many ponds of varying sizes in different areas, such as Nantang, Yazitang, Sajintang, etc. These ponds can store water when water accumulates in the city. Lotus roots and other aquatic plants are planted in them daily to purify water quality, beautify the ecology, and regulate the temperature and humidity in the city. In addition, there are many open ditches and culverts in the city. These open ditches and culverts all flow to the inner rivers in the northwest and northeast corners of the city where the terrain is relatively low, and then drain from the inner city river to the outside of the city through two culverts.

Moon dam and culvert drainage system (when the water level inside the city is higher than outside the city)

Moon dam and culvert drainage system (when the water level inside the city is lower than outside the city)

The Shou County ancient city wall water retaining project has set up numerous barriers, which can be said to be impregnable. It is a valuable experience summed up by the ancient Chinese working people in the long process of fighting flood disasters, and it has important reference significance for modern urban flood control.

3. The Forbidden City of Ming and Qing Dynasties: A unique palace drainage system

Beijing is surrounded by mountains on three sides and has many rivers. In ancient times, every summer, heavy rains and blocked rivers caused floods. However, the Forbidden City, located on the central axis of Beijing, was the royal palace of the Ming and Qing dynasties. Since its construction more than 600 years ago, there has been almost no record of floods caused by heavy rains, thanks to its unique drainage system.

Exquisite measurement, planning and construction

When the Forbidden City was first built, the designers carried out precise measurements, precise design and meticulous construction of the drainage system. The capital is backed by Yanshan Mountain in the north and faces the Bohai Sea in the east. The terrain is high in the north and low in the south, so water flows southeast.

The ground of the Forbidden City conforms to the geographical environment of Beijing. The overall trend is also high in the north and low in the south, high in the middle and low on both sides, and there is a slight slope. The ground elevation of the Shenwu Gate, the north gate of the Forbidden City, is 46.05 meters, and the ground elevation of the Wumen Gate, the south gate, is 44.28 meters. The vertical ground elevation difference is about 2 meters, forming an overall drainage slope of about 2‰, and precipitation is easy to flow to the south. At the same time, the ground design of the palace square is high in the middle and low on both sides, forming a "bear back". When it rains, rainwater from north to south is drained from the middle to the east and west sides. This slope creates favorable conditions for natural drainage.

Scientific and perfect drainage system

The artificial drainage system of the Forbidden City consists of many drainage facilities such as open ditches, underground channels (underground channels also have main and branch ditches), culverts, and ditch eyes. When it rains, rainwater quickly falls to the ground from the sloping roof of the building, flows into the open ditch, and then merges into the underground channel on the ground. Some rainwater that forms surface runoff flows along the ground slope into the rainwater inlets around the courtyard and the foundation (the entrance where water flows from the ground into the underground channel is mostly square stone slabs carved into the shape of Ming and Qing copper coins, also called "money eyes") and stone trough open ditches. If there are steps or buildings, it will pass through the "ditch eye" and merge into the underground ditch (if the open channel encounters obstacles such as steps or walls, a circle of holes will be opened below them, which is called "ditch eyes").

The underground culverts are crisscrossed and connected in all directions. After the rainwater is discharged into the culverts, it is collected by the branch ditches into the main ditch and then discharged into the Inner Golden Water River. The Inner Golden Water River flows out of the Forbidden City from the southeast corner and connects with the 52-meter-wide moat outside the Forbidden City wall. It then connects with the surrounding Outer Golden Water River, Zhongnanhai and other water systems to absorb the rainwater of the Forbidden City.

The Forbidden City's copper coin drain (picture from the Internet)

The wonder of "Thousand Dragons Emerging from Water"

The "Thousand Dragons Emerging from the Water" in the front three halls is the most exciting part of the Forbidden City's drainage system. When the Forbidden City was first designed, in order to prevent water accumulation, 1,142 drainage taps were designed at the bottom of the railings around the three-story base of the Hall of Supreme Harmony, the Hall of Central Harmony, and the Hall of Preserving Harmony. The taps are also called "Chi Shou" and are exquisitely carved with round holes drilled inside, which are the main drainage outlets.

Rainwater falls down the platform layer by layer. The ground of each platform has a slope of 3%-5%. There are stone troughs around the platform for water dispersion. There are also stone culverts under the steps to connect to the dry ditch, so that the water can flow into the ground smoothly and finally drain into the Neijinshui River. In case of heavy rain, the water flowing down from the roof and the rainwater on the platform flow in all directions along the terrain, seeping down from the ditch eyes, spitting out from the faucets, and flowing to the ground layer by layer, presenting a spectacular scene of "thousands of dragons emerging from the water", which is both decorative and practical.

The spectacle of "Thousands of Dragons Emerging from Water" (Photo from the Internet)

The maintenance and upkeep of the Forbidden City's drainage system was also taken very seriously in all dynasties. Every spring, eunuchs would regularly clean and dig to ensure that the Forbidden City's drainage system was unobstructed before the rainy season arrived. During heavy rains, there were special eunuchs responsible for the accumulation of water inside and outside the palace. When necessary, they would open the Jinshui River and release water from the gates to adjust the water volume and level of the Inner Jinshui River in a timely manner.

The achievements of ancient urban flood control and drainage systems are the scientific results of the working people's respect for and use of nature in long-term practice, and have also accumulated rich experience for future generations. Although the flood control problems faced by Chinese cities today are different from those in ancient times, we can still be inspired and learn from the experience of the ancients:

1. Systematic consideration of the relationship between “blocking” and “unblocking”

Do a good job of top-level design at the beginning of urban planning. Water management is a complex system issue. Facing floods is not just a matter of "blocking" or "draining", but requires comprehensive consideration.

2. Coordinated handling of the relationship between “discharge” and “storage”

Urban waterlogging is often related to heavy and concentrated rainfall. While enhancing urban drainage capacity, we must strengthen rainwater and sewage separation, increase the permeability of urban pavements, and increase reservoirs, wetlands and green spaces so that they can fully play their role in conserving water resources and beautifying the ecology, thereby improving the city's ability to store flood water.