Tashan Weir

Prior to the dam's construction, the surrounding area regularly experienced devastating floods due to the torrential rains that would come every summer and autumn due to the local sub-tropical climate. Once it combined with the flat terrain and the high salt content of the Fenghua River, it decimated the crops and made the inhabitants suffer bouts of famine. To remedy this situation, the construction of Tashan Weir was decided by Wang Yuanwei, a magistrate originally from Shandong, and was completed in 833 with the aim of decreasing the risk of flooding and permanently removing salted water from arable land.

The dam was also used to divert water to two different directions. The first stream flows along the Nantang River, serves Dongqiao, Hengzhang, Beidu, Lishe, Shiqi and Duantang, then reaches the city of Ningbo intra-muros before pouring into the man-made Moon Lake (Chinese: 月湖; pinyin: Yuè hú) and Sun Lake (Chinese: 日湖; pinyin: Rì hú) which no longer exists today. The second flow goes up north, serving Xiaoxi, Meiyuan and Shenjiao.

Ancient network of the different Ningbo water courses, with Sun and Moon lakes highlighted

In total, the hydraulic system of Tashan Weir (the dam, the two flows, and the ancillary facilities) has been irrigating nearly 16,000 hectares of land for centuries, and continues to do so even today. The Ningbo area experienced rapid growth due to the stability of water supply that the dam provided.

The dam is about 110 meters long and its top is approximately 5 meters wide. Its outer part is composed of roughly regular stones (2 to 3 meters long and 0.2 to 0.35 meters thick) while its internal part is made of a mixture of stone and wood. In order to consolidate the structure, molten iron was directly injected in some places. The dam was designed in such a way that it adjusts perfectly with the course of the river and is able to withstand risks associated with erosion over time. Maintenance and restructuring work were continuously carried out, from the imperial dynasties to nowadays.

The design of the facility ensured that, in cases of excessive rain, 70 percent of the flood water flows to the Zhang River (inner river) while the remaining 30 percent discharges to the Nantang River (outer river).[3] This proportion in the flow of water is reversed during periods of drought. The Tashan Weir was able to achieve this through the installation of water gates between the inner and outer rivers.

Stela commemorating the accession of Tashan Weir as a Major Historical and Cultural Site Protected at the National Level

Tashan Weir was officially declared on 13 January 1988 as a Major Historical and Cultural Site Protected at the National Level (Number 3-55). It is also recognized as one of the four most important water conservation projects of imperial or pre-imperial China, with the Zhengguo Canal, the Lingqu Canal, as well as Dujiangyan. A temple with a statue representing Wang Yuanwei and ten builders of Tashan Weir was built nearby and important ceremonies and cultural festivities are regularly held there.

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  View from the northern bank of the river
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  First edge of the dam
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  Second edge of the dam
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  View from the west
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  View from the east
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  Holes where molten iron was introduced
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  Temple dedicated to Wang Yuanwei
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  Stele marking the emplacement of the temple
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  Statue of Wang Yuanwei

• Lingqu Canal
• Zhengguo Canal
• Dujiangyan