An engineering marvel against water
At the confluence of the Min, Dadu, and Qingyi rivers in China's Sichuan province, a 71-meter-tall statue of Maitreya Buddha is carved from a Cretaceous red sandstone cliff. Construction of the Leshan Giant Buddha began in 713 CE and took 90 years to complete, finishing in 803 CE. The project was initiated by a Buddhist monk named Hai Tong, who believed the statue would pacify the turbulent river waters that endangered shipping vessels.
The statue's immense scale is hard to comprehend. Its head is 14.7 meters high and 10 meters wide. The shoulders span 28 meters, and a single instep is large enough to hold over one hundred people. To protect this colossal sandstone figure from the region's heavy rainfall and subsequent water damage, its Tang dynasty builders engineered a sophisticated and hidden drainage system. This network of channels and gutters is integrated directly into the statue's body and is the main reason for its remarkable preservation over twelve centuries.
The drainage system is composed of hidden conduits in the Buddha's hair, collar, chest, and arms. The 1,021 spiraled curls on the Buddha's head, for instance, are not decorative; they part of this system, concealing channels that collect rainwater and direct it away from the face. Cavities behind the 7-meter-long wooden ears connect to pipes that run through the shoulders, guiding water away from the main structure. The system prevents runoff from scouring the statue's surface and minimizes internal moisture, which could otherwise lead to frost cracking and biological growth.
A system tested by time
The statue was carved directly into the Lingyun Mountain cliff face. The construction process itself had an unintended, yet beneficial, side effect. So much rock was removed and deposited into the river below that it altered the currents, making the waters safer for ships, thus fulfilling Hai Tong's original goal.
For its first few centuries, the Buddha was also protected by a 13-story wooden pavilion. This structure sheltered it from direct exposure to the elements until it was destroyed during the Ming Dynasty (1368–1644), leaving the statue exposed. The internal drainage system then became the primary defense against erosion. Its continued function shows a high level of hydrological engineering knowledge during the Tang Dynasty.
The entire Mount Emei Scenic Area, including the Leshan Giant Buddha, was listed as a UNESCO World Heritage Site in 1996. Regular maintenance and research projects continue to study and preserve the statue. Modern techniques, including 3D laser scanning and drone surveys, have been used to assess its condition and inform conservation efforts. These studies confirm the effectiveness of the ancient drainage network, which still helps with the statue's preservation.