Utilization condition of water wheels and irrigation in Tang dynasty

Water wheel[水車] is largely divided into Fanche(飜車) and TongChe(筒車). Fanche was developed as early as the Eastern han Dynasty, and Tongche seems to have first appeared later, in the Tang Dynasty. In the historical sources of the Tang Dynasty, some records seem to have been found that irrigation was performed by overcoming unfavorable topographical conditions using water wheel. These articles have led some researchers to suggest that water wheels played a very large role in irrigation repairs during the period, but a closer analysis of the sources suggests the opposite. This is because, rather than proving the widespread use of water wheels, Tang Dynasty's sources that specifically mention water wheels suggest their scarcity, and in some cases, the water wheels shown in these sources are merely a representation of the terrain. Meanwhile, TaChe(踏車), a type of Fanche, has been used to some extent in the northern regions. But they were not widely used due to the disadvantages of small irrigation area and large manpower consumption. Besides, NianWei(碾磑), which use falling water to turn the wheel of a cart, were quite common at the time, especially near the capital. They are often confused with Tongche because of their appearance, but their function was different. wealthy ruling families blocked waterways and install Nianwei for their own benefit, interfering with irrigation, and it was not uncommon for decrees to require their removal. Meanwhile, water wheels must be accompanied by reservoirs and canals to achieve a wide range of benefits, so they cannot be used alone to completely overcome terrain conditions or irrigate a small area. In addition, since the production of water wheels requires advanced technology and considerable financial resources, it would not be easy for private or local people to freely produce and utilize water wheels. Furthermore, there are very few literary works from the Tang Dynasty that mention aberrations, but the number of works with aberrations as a theme or subject increases during the Song Dynasty. Therefore, it is reasonable to understand that the operation and spread of water wheels were limited in most areas at that time.