Between the land delta on the east bank of Jingjiang River and the flooded area on the west bank of the Yangtze River from Chenglingji to Wuhan in the pre-Qin period, it is bounded by Hanshui River in the north and "Dajiang River" in the south, that is, about Qianjiang River, south of Mianyang and north to Jianli and Shishou. Notes on Water Classics: "The southeast crosses the east of Jiangxia County, but Yugong said that the dream of the earth is a dream, so the county is named". According to Hanyun County, Jingshan County now governs Yingcheng and Tianmen.
County, it can be seen that the northern boundary of Yunmengze in the pre-Qin period was once far north of Hanshui River. However, after the mid-Warring States period, Yunmengze in Yingcheng and Tianmen was lost by the sediment carried by the Hanshui River, and Yunmengze has been slightly reduced.
During the Western Han Dynasty, due to the siltation of cement sand in the Yangtze River and Han River, the inland deltas of Jingjiang River and Han River were integrated. The Yunmengze area on both sides of the Hanshui River gradually silted up and was divided into Bai Lu Lake, Dongchi Lake, Chuanguan Lake and Nvguan Lake. At that time, the main body of Yunmengze had moved south to Huarong. Later, with the further development of Jianghan Delta, it continued to move to the south and east. The south is blocked by the natural levee on the north bank of the great river, and the east is slightly blocked. By the Eastern Han Dynasty, it had moved to the southeast of Huarong. With the accumulation of sediment transport in Jianghan, the Ze area shrinks and becomes shallow, mainly in swamp form.
Because the neotectonic movement in Jianghan area tends to tilt from north to south, the delta formed by summer flood diversion on the east bank of Jingjiang River also extends to southeast. During the Wei, Jin and Southern Dynasties, with the development of Yunmengze to the southeast, a "700-mile-long" Zhou Xia was formed. During the Southern Dynasties, the main body of Yunmengze gradually moved eastward to the east of Du Yun, Huihuai and Jianli, and extended to the border of Dunyang County on the river (where it is now located in the south of Hanyang County). The only Zhouling county near the river was also flooded and cancelled. The whole Yunmengze is divided into Dachan Lake (now west of Mianyang County), Magu Lake (now equivalent to Honghu Lake in the west of Honghu County), Taibai Lake (now south of Hanyang County) and several ponds of different sizes.
Its scope is only nearly 200 kilometers, less than half of the pre-Qin period.
During the Tang and Song Dynasties, with the further expansion of Jianghan inland delta, the main body of Yunmengze, which is getting shallower and shallower, has been mostly filled with silt and turned into land. There is no record of Huda Lake in Tang and Song Dynasties. According to Yuanhe County Records, Magu Lake "rises in summer and autumn". Although "the water is full", "when the water is dry in spring and summer, it is flat. Zhou Yu is fifteen miles away. " Taibai Lake is also a swamp, where ships from Lu You and Fan Chengda pass. It is already "flourishing" and "infested by giant thieves", and it is known as "a hundred miles shortage". At the beginning of the Northern Song Dynasty, Yushan County was established 60 miles northeast of Jianli County to manage and reclaim the newly generated delta plain. The famous Yunmengze in history has basically disappeared, and large areas of lakes and water bodies have been replaced by scattered lakes and swamps.
During the Ming and Qing Dynasties, due to the blockage of most caves on the north bank of Jingjiang River, Jingjiang River sediment was discharged to the south bank, and many lakes began to appear in Jianghan Plain. During the Ming Dynasty, Maojiangkou (now Xindi Town) was blocked by the construction of a new dike. Most of the surface runoff in Jianghan Plain gathered in Taibai Lake, which had disappeared before, and became a 200-mile shallow lake in Fiona Fang in the late Ming and early Qing Dynasties. During the reign of Qing Qianlong, it was renamed Akano Lake, which was more than 60 kilometers around. During the Guangxu period in the late Qing Dynasty, it was divided into several smaller lakes and marshes due to long-term siltation. At the same time, the deposition of Taibai Lake disappeared, Honghu County began to appear in Jiajing period of Ming Dynasty, but it had expanded into a big lake with a circumference of 200 miles in Guangxu period of the late Qing Dynasty. Up to now, there are still more than 200 shallow lakes called "Ezhu" scattered in Jianghan Plain, which is the remains left by the disintegration of ancient Yunmengze. Due to the strengthening of river accumulation, the gradual expansion of inland delta and the extensive reclamation around lakes, its natural development trend is gradually silting up and dying out.