The change of riverbed elevation in the flow direction caused by scouring and silting is called longitudinal deformation, and the horizontal deformation perpendicular to the water flow is called lateral deformation. Generally speaking, these two kinds of deformation are intertwined. According to the evolution process of riverbed, it can be divided into one-way deformation of riverbed sheets along a certain direction for a long time. For example, some rivers have been silting up and raising their beds for years; Repeated deformation of riverbed with periodic and repeated development, such as shoal scouring in dry season and siltation in flood season. In addition, there are some local deformations. The imbalance of river sediment transport is the fundamental reason for the evolution of river bed. When the amount of upstream sediment is greater than the sediment carrying capacity of the river, the current has no ability to take all the upstream sediment away, resulting in siltation and river bed elevation. When the upstream sediment load is less than the sediment carrying capacity of the river, scouring will occur and the river bed will fall. Under certain conditions, when the riverbed is silted, the siltation speed gradually decreases until it stops, and when the riverbed is scoured, the scouring speed gradually decreases until it stops. This phenomenon is called automatic regulation of river bed and water flow.