Evolution of Sinuous River Course in Yangtze River History Ⅱ

In Yangtze River history, the sinuous river course condition was improved by natural cut-off and artificial cut-off. It was beneficial for flood control and navigation.

Evolution of Sinuous River Course in Yangtze River History – Introduction of Sinuous River Course

The four hundreds meters long Jinjiang River, from Zhijiang River to Chenglingji, is the most typical riverbed evolution part in Yangtze Rive history. In the 180 kilometers long upper Jingjiang River, from Zhijiang River to Ouchikou, the construction of riverbed and the flow direction are same. It strengthened the flow rate of water, and the sediments on the both banks are tight. So this part riverbed was comparatively stable. The river part from Ouchikou to Dongting Lake in Hunan Province, extending 240 kilometers, was named down Jinjiang River. At there, the river flow direction meet at right angles, the scouring effect is obvious and the sediments on the banks are loose. So there gradually became typical "free river bend", that is sinuous river course.

Evolution of Sinuous River Course in Yangtze River History – Qing Dynasty

In Tongzhi Period of Qing Dynasty (1862 – 1874), there was only one estuary of the down Jinjiang River was not blocked, while the embankments on the both banks were increasing greatly, even the shoals in the river were included in the embankments. The length of meander belt increased. With the length of river bay increased, the radius of the bend became smaller, and there formed Gourd shaped river course. In high flood seasons, with the work of water in flood plain, the narrow shoals formed ditches. If there were strong floods, these ditches were opened up, and formed new rivers. That's natural cut-off. According to incomplete statistics, in recent 100 years, there happened about ten times natural cut-off. The effect of natural cut-off greatly reduced the length of meander of down Jinjiang River.

Evolution of Sinuous River Course in Yangtze River History – Modern Times

However, with the work of water, the new cut-off riverbeds bend toward new direction again. After Revolution, there carried out twice artificial straightening projects in the down Jinjiang River in 1967 and 1969. In 1972, there happened natural cut-off in Jianli County, which made the bending coefficient of the river course decreased from 3.19 to 2.02. Totally, the river length decreased 80 kilometers, while the flood discharge volume increased five thousand cubic meters per second. They are effective for flood control and the development of the Yangtze Cruise.

As there are many tributaries on the northern bank in history, the alluvial plain on the northern Jinjiang River became high. With the work of neotectonic movement, the increasing rate of north higher than the south. Under the terrain of north side high, while south side low, the cut-off channel of the down Jinjiang River are almost in the south side of bending river course. It made the main river course swing towards right bank, and the range reached ten to twenty kilometers at the largest part.