The shuilifa 水利法 "hydraulic works law", also called nongtian shuili fa 農田水利法, was a method to ameliorate local organization of building dykes and dams for irrigating fields. It was part of the reform policy of Wang Anshi 王安石 (1021-1086) during the Northern Song period 宋 (960-1279).
Corvée (yaoyi 徭役) was part of the tax system since ancient times, yet the fairness of the system was at odds in the 11th century, so that irrigation projects were not any more carried out in a reasonable way. The amount of fallow land was considerably high, resulting in low rates of production and reduced tax revenues. In 1069 therefore, in each circuit specially commissioned officials had to adjust the organization of field irrigation, with the support of the local officialdom and their expert staff. The authorities encouraged the people to clear land and to transform it into useable fields and rewarded those who brought forward excellent ideas for advanced methods. At the same time the planting of mulberry trees was recommended, in order to raise the production of silk. For these labour-consuming work it was even allowed to the local treasuries to borrow money to the people so they could hire labour force.
The project, although counting successful work in more than ten thousand places, with 361,000 qing 頃 (see weights and measures) of irrigated land, was aborted with Wang Anshi's downfall in 1078.