Why do rivers produce lateral circulation?

Due to centrifugal force, the surface water flows to the concave bank and the bottom water flows to the convex bank.

The internal spiral motion of curved water flow is annular water flow in cross section. Also known as "lateral circulation" and "curved circulation". When water flows along a curve, centrifugal force will be generated. Under the action of centrifugal force, the water level in concave bank rises and the water level in convex bank falls.

At the same time, due to the high water velocity and centrifugal force, the upper water flow points to the concave shore; The velocity at the bottom of the river is small, and the centrifugal force is small, while the water at the bottom of the river points to the convex bank, forming a lateral circulation. However, there is no transverse circulation in the cross section, and the transverse circulation is combined with the longitudinal flow, showing a spiral downstream.

Rivers:

The reason why the river bends is mainly because the velocity on both sides of the river is different, one side is fast and the other is slow. On the faster side of the river, the impact on the bank is also greater, and the soil is more likely to collapse. When the river bank collapses, it will bend the river.

When the river bends, there will be an S-shaped bank (both banks are like a concave and a convex) and continue to develop. The water will rush to the concave bank, while the water flow on the convex bank is slow, and the gravel and soil brought by the river will slowly deposit. Over the years, the concave bank will become more and more concave, the convex bank will become more and more convex, and the river will show a winding appearance.

Reference to the above content: Baidu Encyclopedia-Horizontal Cycle