In order to control the water flow, maintain the water depth of the waterway and facilitate water diversion, weirs (dikes) have been set up at the north and south ends of this reach to control the water quantity in history. The literature of the initial period of Yanmen is unknown, but the Dingmao Dynasty south of Zhenjiang was set up in the Jin Dynasty at the latest. Before Song Chunhua (990), four weirs, namely Jingkou, Lucheng, Niu Ben and Wangting, had been set up on this section of the canal to store water in stages and maintain navigation.
Since the Tang and Song Dynasties, these weir gates have been built, or dams have been changed or abandoned, and gradually destroyed in the late Qing Dynasty. In the above-mentioned weir gates, especially due to the change of the main channel of the Yangtze River near Zhenjiang, the entrance of the canal is often threatened by the sediment carried by the river tide, so the entrance of the canal has to be replaced frequently.
There are five canals near Zhenjiang in history, namely Dantu Kou, Jianbi Kou, Ganlu Kou, Xiaojingkou and Dajingkou. Before the Sui Dynasty, the entrance to the canal was in Dantu, and the Yangzhou Yangtze River Bridge was opposite the river, with a width of 40 miles. Later, because the river area south of the Yangtze River Bridge is a continent, it was called Guazhou because of its shape like a melon.
After Kaiyuan in the Tang Dynasty, the area of sandbars became wider and wider, and the houses above gradually became the traffic throat of the north and south of the Yangtze River. At this time, the river has shrunk to more than 20 miles. In the twenty-fifth year of Kaiyuan (737), Han Qi moved to Runzhou to make a secretariat, saying, "The north of the state is separated by the river, and the boat is around Guabu, which is 60 miles away, and the wind is high and the waves are urgent." (2) Invite him to cross the river for 20 miles at Jingkou, and open the Yilou River at Zhou Pu Pumpkin in Yangzhou, which is 25 miles long, that is, reach Yangzi Town and set up Yiluodai.
It shows that since the beginning of Kaiyuan, the sandbar on the bank of Yangzhou has been silted and integrated with the north bank. In order to reduce the risk of oil tankers sailing in the river, the estuary of Zhenjiang Canal was moved from Dantukou to Jingkoudai. In the Song Dynasty, the river surface of Guazhou Ferry was still 18 Li. In the early years of Qing Daoguang (1820 or so), the width of the river was only seven or eight miles. At that time, the riverbank was close to the foot of Lushan, Beigushan and Xiangshan in Zhenjiang, and Jinshan and Jiao Shan were isolated islands in the river. However, with the gradual northward movement of the main channel of the Yangtze River, the banks of Guazhou area began to be washed away in the late Ming and early Qing dynasties.
According to the Records of Guazhou, Guazhou City "collapsed year by year" after Daoguang 10 (1830). By the first year of Guangxu (1875), Guazhou City had fallen into the great river and its residents moved to Lisi Port, north of the old city. This is today.