Dujiangyan in Chengdu Plain and Zheng Guoqu in Shaanxi (predecessor of Jinghui Canal) were irrigation projects built before Qin unified the six countries, in order to increase the strategic material reserve in the unified war. Dujiangyan is a water diversion project on the Minjiang River, which has been successfully operated for 2,250 years, and the irrigation area has also increased to 6,543,800 mu. It is a dam-free water intake hub. The head of the canal mainly depends on the fish mouth to divide water, the flying sand weir overflows the flood, and the treasure bottle mouth controls the water diversion. It has many benefits such as irrigation, flood control and wood release, and is a masterpiece of ancient working people. No water conservancy project in the world has such a large scale and a history of thousands of years. The Zheng Guoqu Du Jiang weir, which was later than 10, was built in 246 BC. At first, Zheng Guoqu took water from a water mirror without a dam. Later, due to the continuous downward cutting of the river bed, the water intake gradually moved up. In the Republic of China, it was presided over by Mr. Li Yizhi and changed to take water from the dam, which is now Jinghui Canal. Sima Qian in the Western Han Dynasty said in Historical Records Biography of Hequ: "Qin Fuqiang died as a vassal." Since then, around 150, a white canal has been built in Zheng Guoqu Irrigation District, which is equally famous with Zheng Guoqu. Ding Yuan built six auxiliary canals in six years (before11), and at the same time formulated the Water Order, which gave birth to the first irrigation management system in China. Later, Longshou Canal irrigated by Luoshui was built in today's Shaanxi. The main canal of Longshou Canal is famous for its thousands of meters long tunnels and unique construction methods. It can be seen that water conservancy construction plays an important role in social development. The construction of irrigation areas in this period was mainly concentrated in the Yellow River and Jianghuai Basin. With the expansion of Han nationality's territory, irrigation areas have been built as far away as Xinjiang, Gansu, Ningxia and Inner Mongolia. Some people think that Karez in Xinjiang was also founded in the Western Han Dynasty.
(c) Establishment of canals and water transport
At the end of the Spring and Autumn Period, Fu Cha, the king of Wu, opened the famous Hangou in order to compete with the vassal states of the Central Plains. From Yangzhou to the north, Hangou reached Huaiyin with the help of natural waterways, and communicated with the Yangtze River and Huaihe River for the first time. In addition, there is a spiritual canal to communicate the gap between Huanghuai and Xiangjiang River, a tributary of the Yangtze River, and Lijiang River in the Pearl River system. Lingqu was built in the 28th year of Qin Shihuang (2 19 BC). Lingqu skillfully uses the topographic features of the upper reaches of Xiang Li, builds a spout, divides the Xiangjiang River into two parts, divides the watershed, introduces a tributary of Nanxi into the Lijiang River, and adjusts the navigable depth in coordination with the overflow balance and the construction of Doumen, so as to achieve the purpose of cross-basin water diversion and navigation. Lingqu played an important role in Qin Shihuang's great cause of unifying Lingnan and promoting its economic and cultural development.
Chang 'an, the capital of the Western Han Dynasty, was built in the sixth year of Yuanguang (BC 129). In order to ensure the capital's material supply and avoid the difficulty of winding the Weihe River, a canal with a length of more than 300 miles was built in the south of the Weihe River from Chang 'an to Tongguan in the west. The grass canal was completed in three years, and at most it transported more than 6 million stones every year, which played an important role in maintaining political stability. The construction of these regional canals laid the foundation for the future construction of the national inland river shipping network. During this period, offshore shipping has also made considerable achievements, reaching Japan in the east and India and Sri Lanka in the south.
(D) the formation of the basic theory of water conservancy science
The active academic atmosphere during the Spring and Autumn Period and the Warring States Period is also manifested in the vigorous rise of basic scientific theories of water conservancy. The climax of water conservancy construction in Qin and Han Dynasties created conditions for the formation of water conservancy discipline. Sima Qian in the Western Han Dynasty first gave the word "water conservancy" a professional meaning in Historical Records. Water conservancy became a scientific and technological discipline related to river regulation, flood control, irrigation and shipping, while professionals engaged in water conservancy engineering technology were called "hydraulic workers" and officials in charge were called "water officials". As a science and technology application discipline closely related to the national economy and people's livelihood, water conservancy was born.
Among the documents in the pre-Qin period, Zhou Li, Shang Yu Shu Gong, Guan Zi and Er Ya were involved in water conservancy science and technology. Basic theories are put forward, which are mainly embodied in water and soil resources planning, flow dynamics, river sediment theory and water cycle theory.
Water and soil resources are the most basic resources in nature. Guan Zi Du Di divides rivers into five types. According to the buried depth, water quality and suitable crops of the corresponding groundwater, the soil in Guanzi, Yuan Di was classified. "Shang Gong" and "Li Zhouzhi's Local Records" have a comprehensive description of the land, rivers and lakes in Kyushu administrative region at that time, which is the beginning of the classification statistics of natural resources.
In the basic theory of water conservancy science, "pipe degree" first proposed the movement law and hydraulic jump phenomenon of open channel flow and pressure pipe flow. The concept of hydraulic gradient of open channel flow was established many years ago, and the phenomenon of pressure pipe flow and hydraulic jump was correctly expounded, which was in a leading position in the world at that time.
Guanzi Yuan Di records the relationship between different soil qualities and groundwater depth and water quality. Xitu, Chilu, Don Juan, Lu Fen and Heilu here are limestone, alluvial soil, yellow soil, saline-alkali soil and black clay, with different soil quality and different water quality. Jin Zhanghua's "Natural History" contains: "Where there is sulfur in the water source, its spring temperature." It records people's early understanding of hydrochemistry.
During the Qin and Han Dynasties, the water conservancy construction reached its first climax in history. At the same time, a large number of records about water conservancy have appeared, and the basic theory of water conservancy science and technology has been further deepened. Historical Records of Rivers and Channels, which had the greatest influence on later generations, came out and became the first general history of water conservancy in China, thus establishing the position of traditional water conservancy as a discipline and an important category of engineering construction.