Located on the Longjiang River of Fuqing City, the Tianbao Weir is the oldest comprehensive water conservancy project in the Fujian Province integrating the functions of irrigation, flood control, and fending off sea tides and storing freshwater.

Short and turbulent, the Longjiang River flows directly into the sea and is subject to the influence of sea tides. The biggest challenges faced by Tianbao Weir are floods and sea tides. The body of the weir, arching towards the downstream, forms a funnel with the right bank of the river, while the water intake of the main canal is located right on the mouth of the funnel. Such a structure could help adjust river flow and make water diversion easier in dry seasons. Additionally, this could increase the length of the Weir, hence improving its discharge capacity during flood seasons and reducing the pressure of invading sea tides. Such a design is similar to that of long-axis weirs of modern times, such as duckbill weir and irregular weir. Located at the downstream of a river bend, the Tianbao Weir is in an elevated position, which means it enjoys enough catchment area and water head to store fresh water and resist the intrusion of salt tides. The circulating currents formed at the river bend help separate water from sand and stones. In this way, clean water is diverted from the river for gravity irrigation.

History

Built in the Tianbao Era of the Tang Dynasty (742-756, hence its name of Tianbao), the weir has maintained its original layout. Running from east to west, the weir is 216 m long, 3.5 m tall, 1.5 m wide on the top, and 14-24 m wide at the base. The weir body is built with stone slabs and takes the shape of terraces. 150 m of the weir body is the original structure built in the Tang Dynasty. The water intake, located at the right bank of the river, has a flow rate of 1.5 m3/s and is connected with the 19.4 km-long main canal which irrigates 1267 ha of farmland of 14 villages and two large farms.

In the past 1200 years, the sustainability of the weir also depends on efficient management. Since the Song Dynasty, a special government organization has been set up to manage the weir, and an annual repair system has been in place. According to the Annals of Fuqing County, in 1098-1100, Zhuang Rouzheng, the county magistrate then, established an outdoor law court near the Weir, and the losing party of a lawsuit might be punished to repair the Weir if declared guilty. As a result, the reconstruction was soon completed. In the Ming Dynasty, Ye Xianggao, the Chancellor then, built a stele to memorize the reconstruction of the weir, “as the weir is restored, flood and drought no longer happen. Tens of thousands of people living in the surrounding villages have benefited greatly from the weir.”

The people of Fuqing in ancient times, accumulating experience and learning lessons from practices and failures, tried again and again, and finally created Tianbao Weir, which, with a perfect location and a stable structure, has brought huge benefits to the region. Similarly, the weir has also given birth to the Fuqing spirit of courage and hard work. Although it has been surrounded by the city due to urbanization, the weir continues to perform its irrigation function, and its ecological and landscape functions have been further strengthened.

Irrigation System

The Tianbao Weir itself is composed of three key structures—the barrage, the sluice, and the water intake of the canal. Currently, the weir body, with a trapezoidal cross-section, runs 258 m from east to west (including the sluice and the central bar). On the left side of the barrage stand the sluice and the central bar; the barrage body is 216 m long. The sluice is of three gates, and each opening has a net width of 9 m.

Built close to the Longjiang River, the canal of the Tianbao Weir is 19 km long. When it flows across the irrigation district, it branches to cover the inland. When it meets mountains, stone canals are opened for the water to pass. The stone canals, located at the headwork and the Haikou Township, are called Tang Canals by the locals. Stone canals are structurally stable, so it is possible that these canals were built in the Tang Dynasty when the weir was first constructed, hence their name of Tang Canals.

During the past millennium, the Tianbao Weir has inspired a series of principles and philosophies of water management which have been recorded on ancient steles. The extant steles are the witnesses and relaters of the vicissitudes of the ancient weir.

Water Heritage

The Tianbao Weir was ahead of its times in terms of construction techniques.

During a repair in the Song Dynasty, melted iron was used to reinforce the foundation of the weir and to prevent leaking in the base. This is the earliest record of such practice in China’s history of irrigation project construction.

The Tianbao Weir has made an outstanding contribution to enhancing food production, livelihood opportunities, rural prosperity, and poverty alleviation in the region.

The construction of the weir, having guaranteed local crop yield despite extreme climate events, is the turning point of local agricultural development. For the Fuqing County, the weir has boosted agricultural development, increased crop yield, and raised farmers’ income. In the early Song Dynasty, thanks to the improved irrigation conditions in Fuqing, Champa rice was first planted here and later extended to all over China, leading to the growth of the Chinese population.

The Tianbao Weir was innovative in its ideas at the time of its construction.

Built earlier than the Mulan Weir and the Tuoshan Weir, it is China’s earliest extant water project for fending off sea tides and restoring freshwater.

The Tianbao Weir has contributed to the evolution of efficient and contemporary engineering theories and practices. The body of the weir, arching towards the downstream, forms a funnel with the right bank of the River, while the water intake of the main canal is located right on the mouth of the funnel. Such a structure could help adjust river flow and make water diversion easier in dry seasons. Also, this could increase the length of the Weir, hence improving its discharge capacity during flood seasons and reducing the pressure of invading sea tides. Such a design is similar to that of long-axis weirs of modern times, such as duckbill weir and irregular weir.

The Tianbao Weir is an example of attention to environmental aspects in its design and construction.

Most of the building materials, such as pebbles, stone slabs, and iron, are cheap in cost and easy to get during repairs since they are commonly seen in the region. In addition, the design of long-axis weir could help raise the discharge capacity of the project, which is friendly to the ecosystem of the river.

The Tianbao Weir was an example of engineering marvel at that time.

The Tianbao Weir was first built in the Tang Dynasty. Later during its repair in the Song Dynasty, stone slabs and iron were used. At that time, it was still rare to use these materials in the building of barrages and weirs.

The Tianbao Weir bears the stamp of a civilization of the past.

Its water management follows the ancient Chinese philosophies of the Tao operating naturally and heaven and man being united as one. To commemorate Lang Jian, the county magistrate who presided over the weir’s reconstruction in the Song Dynasty, the locals built a temple for him near the weir. In the Ming Dynasty, Ye Xianggao, the Chancellor then, built a stele to memorize the reconstruction of the weir. Today, the memorial gate for Chancellor Ye is still standing in the old town of Fuqing.

Engineering utility vis-à-vis designed utility

Fuqing County was established in the Tang Dynasty (699). After the An Lushan Rebellion (755-763), the economic centre of China gradually moved to the south. Located in a hilly area, Fuqing needed irrigation projects to boost its crop yields. With the encouragement of the government then, many irrigation and drainage projects were built, and vast wasteland and lowland were turned into fertile farmland with high grain output. Against such background, in the Tianbao Era of the Tang Dynasty, local officials led the people to build the Tianbao Weir. At that time, government officials attached great importance to the construction and repair of water projects. According to the Annals of the Fuqing County, the Tianbao Weir, upon its completion, was of very large scale and irrigates huge tracts of farmland. The weir, by damming water and connecting with the canal, could irrigate both the upstream and downstream farmlands. Despite multiple times of damages and reconstructions, the weir has stayed at its original location and maintained the original structure and form.

In 1099 (the Song Dynasty), Zhuang Rouzheng, the county magistrate of Fuqing, presided over the reconstruction of the Tianbao Weir, during which stone slabs were used to build the weir body, and melted iron was employed to reinforce the base. After the reconstruction, its irrigation area was restored, and it was renamed, Yuanfu Weir. In 1937, the local water authority started to reconstruct the weir once again, and residents of the Haikou Township turned more than 67ha of mudflats by the sea into farmland by irrigating them with water diverted from the Tianbao Weir. In 1959, after the completion of the Dongzhang Reservoir, the upstream basin of the weir shrank by 200km2, leading to the decrease of the water source. In 1963, the local government spent 85000 RMB to heighten the weir (by 0.5m) and extend the canal to Dongge Farm. As a result, the whole Farm (267ha) benefited greatly. Since 2000, the upstream irrigation area of the weir has gradually disappeared due to urbanization. From November 2009 to March 2010, the local government dredged the rivers and canals within the Tianbao Weir irrigation district, and built a new three-gate scouring sluice at the left bank of the Longjaing River, further improving the water-storage and adjusting capacity of the weir. As a result, the storage capacity of the watercourse rose by 151000m3, the irrigation area expanded by 353ha, and disasters of flood and waterlogging were reduced. Currently, the weir irrigates 1267ha of farmland and supply water to hundreds of thousands of residents.

Present State of Conservation

Since its completion in the Tang Dynasty, due to the impact of floods and limited constructing technology and materials, the Tianbao Weir has gone through damages and restorations in Song, Ming and Qing Dynasties and also in the Republic of China era. Currently, the well-preserved weir is still functioning. In addition, it is listed as one of the Officially Protected Cultural Heritages of the Fujian Province.

In recent years, Fuqing County has witnessed rapid economic growth. Economically, it ranks the 18th among the 1000+ counties of China. As urbanization accelerates, irrigated farmland has been shrinking. Hopefully, its nomination for the World Heritage Irrigation Structure could help enhance the protection of the ancient irrigation project by raising the awareness of the local government and residents about its technological, historical, and cultural values.