The Environment of Water Flow and Wei-field System in Wusong River Valley in 10-15 Century

Wei-field systems in Wusongjiang valley in 10-15 century was basically under big wei-field system. The function of this system was to make water in narrow state, raise water level in Tang-Pu system, make water be poured into Wusong river. So the clear stream could intimidate the muddy stream, and the silt of muddy tide could be averted. Due to the agriculture development and the construct of canal bank, Wusong river was become silt from the middle period of Song dynasty, and drainage situation was changed greatly in 15th century. Raising water level of Tang-Pu system is not important, big Wei-field system was not benefit to the function of the new drainage structure, and it was replaced by small Wei-field system. The environment change of the water flow made the changing of wei-field system.