Torrent of Genius: The Story of Guo Shoujing, the Greatest Hydraulic Engineer

Today, we’ll delve into the life of a prominent hydraulic engineer during the Yuan Dynasty, who over 700 years ago played a pivotal role in Beijing’s water management and made an enduring global impact in the field of astronomical observations and calendar systems.

In the latter half of 2023, China has seen heavy rain and flooding in many areas. A major deluge in late July severely flooded areas of Beijing and Hebei Province, disrupting transportation, damaging infrastructure and adversely affecting residents. Preemptive maintenance of water facilities in these regions can help prevent such tragedies. Water infrastructure is vital for cities, ensuring resident well-being and playing roles in flood control, fire prevention, navigation and irrigation.

During the Yuan Dynasty, which lasted from 1271 to 1368, a great scientist named Guo Shoujing pioneered water diversion schemes like the Yongding River and Baifu Spring, establishing Beijing’s water supply system. Additionally, he planned, designed, and oversaw the construction of projects such as the Shandong section of the Grand Canal and the Tonghui River. His efforts transformed the primarily east-west-oriented canal system from the Sui and Tang dynasties into the north-south-connected Grand Canal, allowing cargo ships to sail directly to Jishuitan within the heart of Yuan Dadu, present-day Beijing, achieving the full linkage of the Beijing-Hangzhou Grand Canal.

In modern-day Beijing, Jishuitan is home to a subway station on Line 2 of the capital’s metro system as well as a well-known hospital. There’s no longer a massive body of water at the site, though it hasn’t completely disappeared. What remains of the Jishuitan of old can be found in the vicinity of Shichahai within Beijing’s Second Ring Road.

Today’s Shichahai has been divided into three separate enclosed lakes: Qianhai, Houhai, and Xihai, where you might occasionally see dragon boat races. However, over 700 years ago, Jishuitan was teeming with numerous vessels of various types. People from that time even described it as “ships connecting end to end, almost covering the entire water surface.” It seems bumper-to-bumper traffic is nothing new to commuters in the capital.

As mentioned earlier, Guo was a great scientist. He not only excelled in water management but also had expertise in astronomy and calendar systems. Many of his inventions had a profound impact on future generations. 

Guo was born in 1231 in Xingtai, Hebei Province. Not much is known about his father, as historical records provide little information, suggesting the possibility of an early death. In any case, Guo was raised to adulthood by his grandfather, Guo Rong.

Guo Shoujing and Kublai Khan, the grandson of Genghis Khan, the founding emperor of the Yuan Dynasty, lived during the same period. When Kublai Khan was constructing the capital city of Dadu, now Beijing, the northern economy was struggling, and the city relied heavily on goods from the southern regions of China. However, at that time, the Grand Canal was no longer navigable. So, an important task undertaken by Guo was to extend the Grand Canal to Dadu, ensuring a vital supply route from the south to the capital.

During the Sui and Tang dynasties from the 6th to 10th century, the Grand Canal was centered on Luoyang in Henan Province, with the Tongji Canal to the north of the Huai River running westward to Luoyang, forming a large bend, along with the Yongji Canal to the north of the Yellow River. This layout of the Grand Canal was advantageous for transporting goods to Luoyang and Chang’an, making it convenient for the Sui and Tang dynasties to control the entire country.

In the early years of the Southern Song Dynasty, which lasted from 1127 to 1279, in an effort to block the advance of the Jin Dynasty troops southward, the Song military deliberately breached the Yellow River, redirecting its flow towards the Huai River and causing it to enter the sea. This diversion led to sedimentation in the Grand Canal, and combined with the prolonged standoff between the Song and Jin dynasties, the northern section of the Grand Canal became unnavigable.

When the Yuan Dynasty established its capital in Dadu, the political center shifted northward, and the importance of dredging the original Grand Canal diminished. Instead, Guo turned his attention to straightening the canal and redirecting it away from Luoyang. In this new configuration, it entered the Hai River basin through Shandong, making it more suitable for the needs of the new capital.

Through the efforts of Guo and countless laborers, the Grand Canal was finally extended to Tongzhou in eastern Beijing. However, the stretch from Tongzhou to Dadu, covering over 20 kilometers, remained challenging due to the significant elevation difference between Dadu and Tongzhou. This presented two key challenges: how to get boats up the incline and how to ensure an adequate water supply for Dadu.

To address the first challenge, Guo improved the design of boat lifts. He installed 24 boat lifts along the canal from Tongzhou to Dadu, using stone gates and a segmented control system to regulate water levels. 

Of course, the most difficult aspect of completing the final 20 kilometers of the waterway wasn’t digging the canal, but sourcing the water. Guo faced immense difficulties in finding a water source. In Dadu, the Yujing Mountain water system existed, but it had insufficient volume, and some of it was reserved for the imperial palace. Guo also considered diverting water from the Yongding River but abandoned this idea due to its turbulent flow.

At the age of 61, Guo tirelessly explored the areas around Beijing. Eventually, he discovered the ideal water source for the Grand Canal in the northeast foothills of Longshan, Changping, northwest of Beijing. As Tongzhou was at a lower elevation than Dadu, the canal needed to carry water from Dadu to Tongzhou. After thorough surveys, Guo determined that the abundant water from Baifu Spring in the Changping Wenyu River system was the perfect source. Subsequently, he oversaw the construction of the Baifu Spring water diversion project.

To ensure the water from Baifu Spring in the Changping mountainous area could reach Dadu, the construction followed a C-shaped route along the foothills. A straight line would have included a low-altitude area in the middle, which the water couldn’t traverse. Baifu Spring water flowed through this canal to reach Wengshan Lake, now Kunming Lake in the Summer Palace, which was then diverted into Dadu.

At the time, Jishuitan, which was a lake within Dadu, served as the endpoint for Baifu Spring’s water, and also marked the termination point of the Beijing-Hangzhou Grand Canal. Therefore, over 700 years ago, Jishuitan was bustling with ships from Jiangsu and Zhejiang provinces, unloading their cargo. As the endpoint of the Grand Canal, Jishuitan also stimulated the commercial prosperity of the Bell and Drum Tower area of the city.

Later, during the construction of Beijing by the Ming Emperor Zhu Di, who ruled in the early 15th century, the northern city wall was moved southward, necessitating the filling of the western section of Jishuitan. Due to the soft ground in this area, they couldn’t build the city wall, leaving a small gap in the northwest corner during the Ming and Qing dynasties. Meanwhile, the eastern section of Jishuitan lost its shipping value and gradually shrank, eventually forming present-day Shichahai.

Guo’s other significant achievement was the management of the Yongding River. The Yongding River, known as the mother river of Beijing, exhibited dramatic seasonal fluctuations and unpredictable behavior. Over 700 years ago, during Kublai Khan’s construction of Dadu, many building materials needed to be transported by water, making the diversion of water from the Yongding River the most feasible option. In fact, during the Jin Dynasty, there had been an attempt to divert water from the Yongding River, which proved unsuccessful due to its turbulent flow and high sediment content. This diversion was called the Jinkou River.

In 1265, Guo proposed to Kublai Khan the reopening of the Jinkou River, which received approval, and he was authorized to oversee all of the Yuan Dynasty’s hydraulic engineering. Guo learned from the Jin Dynasty’s mistakes and, near the Maoyu Village, upstream of Jinkou, pre-excavated a water-reduction channel. From this channel, they dug a deep and wide canal southwestward, reconnecting the Yongding River downstream of Jinkou.

This way, during floods, a portion of the floodwaters could be diverted from the water-reduction channel, allowing them to rejoin the main river downstream of Jinkou, preventing the floodwaters from directly entering Jinkou River and endangering the capital’s safety. This diversion of Yongding River water into the city’s moat provided an important transportation route for the construction of Dadu.

However, the Yongding River during the Yuan Dynasty remained too uncontrollable, and after 35 years, considering the capital’s safety, in 1301 the court eventually decided to close Jinkou once more. 

Today, Beijing’s water systems, aside from natural watercourses, were predominantly constructed under the supervision of Guo. During the construction of these hydraulic projects, he introduced many useful concepts and innovations. For instance, he was the first to propose the concept of “elevation” – that is, he used sea level as the reference point for measuring elevation, a significant contribution to the history of global surveying and mapping.

His other major historical contributions were his astronomical observations.

Guo made significant improvements to astronomical observation instruments. Prior to the Yuan Dynasty, the armillary sphere, an ancient Chinese astronomical observation instrument used to determine celestial coordinates, incorporated mechanisms for measuring equatorial, horizontal, and ecliptic coordinates, among others, all within a single system. This resulted in a cumbersome design with eight or nine concentric rings in a spherical space obstructing the line of sight, making both its manufacture and use inconvenient.

Guo’s invention of the “Jianyi” was a notable advancement. It separated the measurement of horizontal and equatorial coordinates into two independent devices, thus addressing the cumbersome issues associated with the older armillary sphere. He also utilized ball bearings to make the instrument more agile and precise for observations.

Furthermore, Guo improved the ancient instrument used for measuring the length of the sun’s shadow, known as the “gui biao”, a type of gnomon used in ancient China. Ancient people used the length of the sun’s shadow to divide seasons and calculate calendars. To enhance measurement accuracy, Guo increased the height of the gui biao and invented an auxiliary instrument called the “jingfu”. This improved version of the gui biao became known as the “gaobiao” or high-altitude instrument.

Guo also invented instruments like the “Yangyi” and “Kui Ji” for astronomical observations. Utilizing these instruments, Guo observed over 1,000 celestial bodies that were unnamed by previous astronomers.

The Yuan Dynasty had the largest territory of any Chinese dynasty, making it highly conducive for astronomy. In 1279, Guo proposed to Kublai Khan that they should follow the example of the Tang Dynasty astronomer Monk Yixing, who, during the Kaiyuan era, from 713 to 741, conducted astronomical observations at 13 locations throughout the empire. Given that the Yuan’s territory was even larger than that of the Tang, Guo argued that, without conducting measurements across various regions, they couldn’t determine the timing and magnitudes of solar and lunar eclipses, variations in the length of days and nights in different areas, and the positions of bodies on the celestial sphere.

Kublai Khan approved this suggestion, leading to the initiation of a large-scale astronomical observation activity called the “Four Seas Measurement”. Guo established 27 observatories across the vast expanse of the Yuan Dynasty. These observatories were located at different latitudes. By observing the local durations of solar shadows, they could calculate the Earth’s radius.

The only one of those 27 observatories that still exists today is the Guanxing Tower in Dengfeng City in central China’s Henan Province. It consists of two parts: the platform surrounded by winding steps and the stone gnomon that lies flat to the north within a groove on the north wall of the platform. The platform has a square-shaped design with a ridged cover, and its four walls are constructed with water-milled bricks.

Guo’s life journey covered half of China, where he undertook the management of over 100 rivers, canals, and reservoirs. His technological achievements include more than 20 innovations that were far ahead of the global standard. In 1316, at the age of 86 and still actively working, Guo passed away.

As well as his obvious genius, Guo’s transformation into a great scientist can also be attributed to the unique circumstances of his era. During the Yuan Dynasty, the imperial exam system fluctuated: leading scholars of that time were able to focus less on Confucian classics and more on practical sciences, such as hydraulics, astronomy, calendrics, and math – subjects that were beneficial to the state and its people. Furthermore, many of Guo’s proposals received the full support of Kublai Khan, which was a crucial factor in his remarkable achievements.

In honor of Guo’s achievements, several landmarks have been named after him. In 1970, the International Astronomical Union named a lunar crater “Guo Shoujing Crater” on the Moon. In 1977, the Minor Planet Center named an asteroid “2012 Guo Shoujing”. In 2010, the National Astronomical Observatories of the Chinese Academy of Sciences named the LAMOST telescope, the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, the “Guo Shoujing Astronomical Telescope”. In 2019, Guo Shoujing was recognized among the first batch of “Historical Water Control Figures” by the Ministry of Water Resources of China.

Today, there is a Guo Shoujing Memorial Hall in Beijing, located within the Huitong Temple on a small hill north of West Sea in Shichahai. Huitong Temple was originally built during the Yuan Dynasty, and Guo played a significant role in overseeing national hydraulic construction from this location. The memorial hall was constructed in 1986 and covers an area of nearly 800 square meters with a building area of 400 square meters. It features four exhibition halls that provide insights into Guo’s life and his achievements.

Well, that’s the end of our podcast. Our theme music is by the famous film score composer Roc Chen. We want to thank our writer Lü Weitao, translator Du Guodong, and copy editor James McCarthy. And thank you for listening. We hope you enjoyed it, and if you did, please tell a friend so they, too, can understand The Context.