中国古代的潮田

A TENTATIVE DISCUSSION ON ANCIENT CHINA'S FARMLAND IRRIGATED BY TIDE

仰潮水灌溉的潮田是中国古代农业与传统海洋学的一项重大成就。潮田在中国源远流长,水上潮田可追溯到战国,陆上潮田可追溯到三国时的吴国。潮田在中国广泛分布,各海区均有,但相对集中于入海河流的感潮河段。潮田灌溉方式多样,从原始的自流灌溉发展起包括有渠系、潮闸和提水设施的复杂系统。中国古代普遍知道潮灌之水实为河流淡水。人们知道海水成重,所以上潮时,海水沿河床下层上溯形成楔形层,而淡轻的河水则在上层并被抬升,以资灌溉。有关感潮河段河流淡水与海洋成水之间界面的性质和动态的认识,中国比西方早1000多年。

Farmland irrigated by ride was known as Chao Tian. It was a great achievement of agriculture and oceanography in ancient China. The origin of Chao Tian on waters can be traced back to the Warring States period (475—221 B. C.), while its origin on land can be traced back to the Wu Kingdom (A. D. 222—280) of the Three Kingdoms. Cao Tian is scattered all over China's marginal seas (the Bohai Sea, the Yellow Sea, the East China Sea and the South China Sea), but is mainly concentrated on the river's lower reaches where there is tide. In ancient China there had been a complex system of irrigation by tide, which consists of irrigation canals, water gates and pumping means. It had been known in ancient China that the water of irrigation by tide was virtually river water of lower salinity. People knew that sea water of higher salinity is heavier than river water. During tide time, sea water runs inland along the lower layer in the river so that river water remains at the upper layer and thus Can be easily used to irrigate farmland. China is in command of this knowledge earlier than the Western world by over 1,000 years.