This word refers to the connection line of the maximum velocity points on the surface of each section of the river.

Middle reaches of the river: the line connecting the maximum velocity points on the surface of each section of the river (water-passing section), also called xi line. Thalweg: the line connecting the maximum water depth points of various sections (cross sections) of the river, also known as streamline. Deep flood point: the maximum water depth of a river section. The section along the Shenhong line is the longitudinal section of the river.