Yun Mengze has disappeared in the long river of history. There is Yunmeng County in Xiaogan City, Hubei Province, where the famous Yunmeng Qin bamboo slips were unearthed. This name confirms the former Yunmengze. There are sporadic records of Yun Mengze in historical materials, and Biography of Huo Zhi in Historical Records records: "The old city of Jiangling yǐng ... was spared by Yun Mengze in the East". Pidu Jiangling is now Jingzhou City, and Yunmengze is located in Jianghan Plain east of Jiangling. It is also recorded in Historical Records of Chu Benji: "At that time, Wu people entered Ying. Wang Zhao's death was also a dream. Yunmeng doesn't know his monarch, so he shoots him. " Wang went to Wu Zixu and Sun Wu led Wu soldiers to invade the capital of Chu State, dug the tomb of King Chu Ping, and whipped 300 corpses to avenge his father and brother. King Chu Zhao fled to Yunmengze, was shot by people who didn't know him, and then fled to Yun (now Anlu County).
The formation of Yunmengze is related to the Yangtze River and Hanjiang River. The Yangtze River originates in Qinghai and flows through Qinghai, Tibet, Yunnan, Sichuan, Chongqing, Hubei, Hunan, Jiangxi, Anhui, Jiangsu, Shanghai and other provinces, cities and autonomous regions, with a total length of more than 6,300 kilometers. The upper reaches of the Yangtze River are above Yichang in Hubei, from Yichang to Hukou County in Jiangxi as the middle reaches, and below Hukou County as the downstream. The section from Zhicheng in Yidu City, Hubei Province to Chenglingji in Yueyang City, Hunan Province is called Jingjiang River. Because Jianghan Plain is relatively low and flat, the riverbed in Jingjiang section fluctuates greatly in history, and the river course bends abnormally. During the flood, the river often rushes out of the river and overflows, which is known as "a long river travels a thousand miles, and the danger lies in Jingjiang River".
Jianghan Plain is a continental depression with strong Quaternary subsidence and relatively low terrain. Hundreds of millions of years ago, the whole Jianghan Plain was a huge lake basin, starting from the mountainous area in western Hubei, east to the western foot of Dabie Mountain, south to the Yangtze River and north to Dahongshan. With the siltation of many rivers such as Yangtze River and Hanjiang River, the landscape of Jianghan Delta, lakes and wetlands has gradually formed. According to historical records, two delta plains have been formed in the pre-Qin period. The west is between Jianghan in the east of Jingzhou, and the east is on the west side of the Yangtze River between Chenglingji in Yueyang, Hunan and Wuhan. The great lake between the two places is Yunmengze. In Han Dynasty, the famous Huarong County was located in Jianghan Delta east of Jingzhou. Cao Cao was defeated in Battle of Red Cliffs and fled from Huarong Road, which was muddy and difficult to walk. If he hadn't been lucky, Cao Cao might have been killed and history would have been rewritten.
With the unification of Qin and Han dynasties, the development level of the south has been further improved, human activities have intensified the destruction of natural vegetation, soil erosion has intensified, and there are more and more sediments in rivers. Jianghan Delta has been moving eastward under the action of sediment, and Yunmengze has been squeezed and divided, forming many large and small lakes. These lakes also have a large number of waterways connected with Jingjiang River, which play a natural role in flood season. During the Tang and Song Dynasties, with the increase of population in the south, the activities of reclaiming land by rivers and lakes became more and more frequent. In order to develop the fertile Jianghan Delta and resist floods, people began to build dikes along the Jingjiang River to restrain the river. By the Yuan Dynasty, the Jingjiang section had formed a diversion situation of "nine points and thirteen ports", and the huge amount of water coming from the upstream during the flood period was naturally regulated through these diversion ports.
During the Ming and Qing Dynasties, people's ability to transform nature was further enhanced, and the levees along the river were of higher grade, and the traditional earth and stone dikes were transformed into stone dikes. During the period from Chenghua to Jiaqing in the Ming Dynasty, the caves on the north bank of Jingjiang River were all sealed, and the south bank was Taiping and Tiaoxian, up to Duijintai (more than 60 miles northwest of Jingzhou City) and down to the depilation port in Jianli County. 124 km long dikes are connected into a whole. This is the famous Wancheng levee, also called Wan 'an levee. In order to strengthen the management of Jingjiang Dike, in the first year of Qin Long in the Ming Dynasty (1567), a dike armor method was specially set up, which was maintained by civilian workers, with more than 7,300 people on the north bank and 3,800 people on the south bank.
In the Qing dynasty, following the practice of the Ming dynasty, the dikes on both sides of Jingjiang River were continuously extended and heightened. The dikes in Jiangling, Jianli and Mianyang on the north bank are more than 600 miles long, and those in Jiangling, Gongan and Shishou on the south bank are more than 300 miles long. In the fifty-third year of Qianlong (1788), the Yangtze River flooded, which caused the levee to burst and Jiangling City to be submerged. In order to plug the breach and strengthen the dike body, Emperor Qianlong specially allocated 2 million taels of silver as a special fund, set up stone scales and water standards, stipulated the warranty period of the dike, and changed the civil dike into an official dike.
It is said that life will always find its own way out, in fact, rivers are the same. With the sediment deposition, the terrain of Jianghan Plain gradually rises, and with the obstruction of river banks, the huge amount of river water in flood season can only turn to Dongting Lake Plain with low terrain on the south bank to find new branch canals. Xianfeng two years (1852), Xianfeng ten years (1860), the lotus pond burst; Nine years of tongzhi (1870) and twelve years of tongzhi (1873) were broken. In these floods, the levee burst to form two new tributaries, the Dahe River and Songzi River, and rushed out of the Dahe River and Songzi River. Together with the original Taipingkou and Tiaoxian River, four tributaries on the south bank of Jingjiang River flow into Dongting. With the continuous influx of river water and sediment deposition, Dongting Lake, which was originally small, has become bigger and bigger.
Of course, this process is not overnight, but slow, and the long-term trade-off only accelerated obviously after the Tang and Song Dynasties. Before the Song Dynasty, the Jingjiang River diverted water mainly from the north bank, and after the Yuan and Ming Dynasties, it mainly shifted to the south bank. According to Notes on Water Classics, Dongting Lake was 500 Li in Fiona Fang in the Eastern Jin Dynasty and Southern Dynasties, and it was expanded to "800 Li Dongting" in the Tang and Song Dynasties. Yunmengze also gradually disappeared from the Southern Dynasties to the Tang and Song Dynasties, and was replaced by Jianghan Plain, leaving only sporadic lakes, which also gave Hubei the reputation of "the province of thousands of lakes". After Yunmengze disappeared, Dongting Lake assumed the role of accepting the Yangtze River flood diversion and storage. Because Dongting Lake replaced Yunmengze slowly, and even merged with Jingjiang and Yunmengze in a certain period of time, this is why Dongting Lake was called Yunmengze in ancient times.