Mechanical Engineering - Hydraulics and Fluid Mechanics - Discussion

The water surface profile is a measure of how the flow depth changes longitudinally. The profiles are classified based on the relationship between the actual water depth (y), the normal depth (yn) and the critical depth (yc). Normal depth is the depth of flow that would occur if the flow was uniform and steady, and is usually predicted using the Manning's Equation. Critical depth is defined as the depth of flow where energy is at a minimum for a particular discharge.

Flow profiles are classified by the slope of the channel (So), yn, and yc. There are five slope classifications designated by the letters C, M, S, A, and H (critical, mild, steep, adverse, and horizontal) respectively.

Mild (M) if yn > yc.
Steep (S) if yn < yc.
Critical (C) if yn= yc.
Adverse (A) if So < 0 (if slope is positive in the downstream direction)
Horizontal (H) if So = 0.

Anyone explain it.