This is a poem written by the poet Meng Haoran describing Dongting Lake, which can remind us of the magnificent scenery of the Tang Dynasty. Dongting Lake was called "Cloud Dream" in ancient times, but the original "Cloud Dream osawa" did not refer to Dongting Lake, but the sum swamp in Hubei Province today.
In the late Warring States period, Yunmengze was divided into two due to sediment deposition, and the north of the Yangtze River became a swamp, while the south of the Yangtze River was still a vast lake. From then on, it is no longer called Yunmeng, but this big lake is called Dongting Lake, because there is a Junshan in the lake, formerly known as Dongting Mountain. "A Brief Introduction to ChristianRandPhillips Temple" said: "Dongting is one of the immortal caves, and it is called Dongting. Later generations called Dongting Lake because the flood was terrible and there was no income.
During the Eastern Jin Dynasty and the Southern Dynasties, the Fiona Fang of Dongting Lake was about 500 Li. Due to the backward flow of Jingjiang flood, Dongting Lake has been further expanded, replacing Yunmengze as a natural place to store the Yangtze River flood. Every flood season, more rivers flow into Dongting Lake from Chenglingji, forcing Dongting Lake to "connect grass in the south and red sand in the west, spanning seven or eight hundred miles". During the flood season, the lake area reached more than 6,000 square kilometers, and Dongting Lake entered its heyday.
After the Song Dynasty, the relationship between rivers and lakes, which was originally "the lake Gao Jiang is low, and the lake enters the river", gradually evolved into the pattern of "the river is high and the lake is low, and the river enters the lake", and the flooding of Dongting Lake is becoming more and more serious. During the Yuan, Ming and Qing Dynasties, with the continuous construction of Jingjiang levee and frequent blockage of caves, river disasters intensified, and Jingjiang levee and lake burst frequently. The relationship between rivers and lakes began to be tense, indicating that since the Song Dynasty, the relationship between rivers and lakes began to undergo historic changes, and human factors became an indispensable factor in the variation of the relationship between rivers and lakes.
From 1524, the last "Haodong" on the north bank of Jingjiang River was blocked, and Jingjiang levee was connected into a line. Until 1860, the relationship between rivers and lakes was relatively stable, and the agricultural production in the lake area developed steadily, and the population increased from about 200,000 to about 6,543,800+5,000. In other words, the heyday of Dongting Lake lasted for more than 300 years.
In the second year of Xianfeng in Qing Dynasty (AD 1852), the lotus pond on the south bank of Jingjiang River burst and could not be repaired. In the tenth year of Xianfeng (AD 1860), a great flood occurred, which enlarged the original breach and rushed out of a large inland river. In the ninth year of Tongzhi in Qing Dynasty (AD 1870), another catastrophic flood in history caused the Songzi River on the south bank of Jingjiang River to burst. In the same year, it was blocked, and it broke again in the thirteenth year of Tongzhi, and the flood rushed out of a Songzi River. That is to say, from 1873, Jingjiang flood formed a situation that flowed into Dongting Lake from Songzikou, Taipingkou (Hudukou), Ouchikou and Diaoxiankou.
1860- 1873, 14, which became the turning point of Dongting Lake from prosperity to decline.
The diversion of the four ports not only aggravated the flood disaster in Dongting Lake area, but also brought a lot of sediment into Dongting Lake. The flood in Chenglingji flows into the Yangtze River, but the sediment is deposited in Dongting Lake.
The estuary delta formed by the siltation of four estuaries entering the lake advances from northwest to southeast, which accelerates the development of Dongting Lake beach. Sediment deposition and rapid expansion of beach land lead to a large number of reclamation in the lake area. The lake has become a beach, and the beach has become a ridge soil and a lake field. The retreat of the Lakers in Dongting has begun to appear. The banks of the lake are as big as scales and endless, and there is a great potential for competing with water for land. According to statistics, by the end of the Qing Dynasty, Dongting Lake had a total of dikes 1094.
In the mid-1940s, Dongting Lake was already a vast beach, with fragmented lakes and staggered ports.
According to the actual measurement in recent years, the average annual sediment deposition in Dongting Lake is 98 million cubic meters, and the water surface area is sharply reduced at an average annual rate of about 18 square kilometers. From 1650 to 1852, the lake covers an area of about 6,000 square kilometers with a volume of more than 40 billion cubic meters. By 1949, the lake had shrunk to 4,350 square kilometers with a volume of about 29.3 billion cubic meters. By the early 1990s, the lake had shrunk to 26,965,438+0 square kilometers. China's position as the largest freshwater lake should give way to Poyang Lake (with a surface area of 5,030 square kilometers).
With the decreasing volume of Dongting Lake, its storage capacity for the Yangtze River flood is also weakening. With the passage of time, it is a foregone conclusion that Dongting Lake will shrink further.