Riverbed Evolution in Yangtze River History Ⅰ

Riverbed Evolution in Yangtze River History – Brief Introduction

The part of Yangtze River on the west of Yichang, Hubei Province is the upper reaches of the Yangtze River. It passes by mountains and valleys, and the riverbed was comparatively stable, without obvious changes in Yangtze River history. The Yangtze River below Yichang comes out from the mountains regions and goes into the wide and flat plain area in the middle and down reaches. And the riverbed evolution in this part is very obvious in Yangtze River history.

In early period, the climate in Yangtze River basin was warm and moist. The plants in forests were dense. The riverbed in middle and down reaches of the Yangtze River was wide and shallow, and with many distributaries.

The distributaries on north side of the Yangtze River were gradually disappeared with the development of the Yangtze River in history. Because of the different topographic features, the riverbed evolution in middle and down reaches of the Yangtze River can be divided into two kinds.

Riverbed Evolution in Yangtze River History – Evolution 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 Jingjiang 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.

Riverbed Evolution in Yangtze River History – Evolution of Braided River Course

The river part below down Jingjiang River, from Chenglingji to Jiangyin River estury, about 1600 kilometers long belongs to braided river course, which flows by wide plain with some hills on the way. In this river part, basement rocks and cliffs often can be seen on the river banks. These hills and basement rocks are kinds of fault fractured zone, while the Yangtze Riverbed developed along the fault fractured zone which restricted the free swing of the Yangtze River. So, Yangtze River can't freely wander on the wide fluvial plain as the Yellow River does.