Ancient drainage system ensures Zhangbi Castle weathers the storm

After torrential rainfall swept through the region recently, the ancient drainage system of Zhangbi Castle in Jiexiu city, Shanxi province, continued to function flawlessly — a testament to the ingenuity of craftsmen who worked in harmony with nature and adapted their designs to suit local conditions.

Wang Aiyuan, a 65-year-old researcher on Zhangbi Castle, said that the fortress sits on terrain that slopes downward from south to north, surrounded by ravines on three sides and backed by a mountain on the fourth. This natural elevation difference allows rainwater to flow downhill effortlessly with gravity, providing the ideal topographical conditions for the entire drainage network.

With a history spanning over 1,600 years, Zhangbi Castle was a small military fortress before it was turned into a civilian settlement. In 2012, it was selected as one of China's first "traditional villages".

"The ancient people of Zhangbi followed nature — they channeled water rather than blocking it," said Wang, who has devoted years to studying the fortress' cultural heritage. This time-tested drainage design effectively prevents rainwater from directly eroding building foundations and courtyard walls, significantly reducing water damage to ancient structures and extending the lifespan of traditional dwellings. The result is a remarkable "dry roads as soon as the rain stops" effect.

"Even during heavy flood-season downpours, the walkways on both sides of the fortress remain passable for residents and tourists alike," he added.

In the wake of the Northern Song Dynasty (960-1127), Zhangbi Castle gradually transformed from a military garrison into a village. Over the past millennium, local residents have continuously refined and improved the drainage network during village renovations, ensuring that this ancient hydraulic engineering marvel can remain active.

Currently, 50 to 60 traditional residences within the fortress are awaiting restoration. All renovation work strictly adheres to the original architectural framework — no arbitrary elevation changes or alterations to the existing terrain are permitted, preserving the fortress's authentic appearance to the greatest extent possible.

"Every blade of grass, every tree, every ditch, and every alley in this fortress embodies a thousand years of human settlement wisdom and natural principles. Protecting the original landforms and preserving the ancient layout is the best way to carry forward the castle's cultural legacy," Wang said.

Zhang Guanying, assistant general manager of Zhangbi Castle Eco-Tourism Co, said, "We receive about 400,000 visitors annually, and the unique drainage wisdom has become a major attraction for tourists."

Zhang said that beyond the main drainage system within the village, the fortress' periphery features specially constructed rainwater retention ponds, forming a complementary water regulation network. These ponds buffer the impact of torrential rainfall, regulate water volume in the area, and prevent flooding or water backflow into the village.

During dry periods, the stored water serves agricultural irrigation and emergency firefighting — a perfect example of rainwater resource utilization that combines flood prevention with practical value.

"Many visitors are amazed that this ancient drainage system requires no electricity and no modern equipment — it relies purely on natural terrain and ancient design principles to drain water autonomously, leaving no puddles after the rain. It stands in stark contrast to the urban flooding problems faced by some modern cities during flood season," Zhang said.

Zheng Guanggen, a folk scholar who grew up in Zhangbi Castle, devoted himself to researching the fortress' history and hydraulic engineering after retirement. He interviewed village elders, explored ancient underground tunnel relics, and studied historical stele inscriptions over a 30-year period. His efforts culminated in the book Zheng on Zhangbi, preserving invaluable primary source materials for research on the fortress' construction history and its ancient drainage system.

Having weathered over a thousand years of wind and rain, Zhangbi Castle has never suffered from flood disasters. Wang said that this achievement is not only a remarkable testament to ancient Chinese hydraulic engineering but also offers valuable lessons for addressing modern urban flooding and protecting traditional villages today.