A new perspective on water surface profiles is made possible by expressing the gradually varied flow equation in terms of the critical slope S_c. In this way, the flow-depth gradient (dy/dx) is shown to be strictly limited to values outside the range encompassed by S_c and S₀ in which S₀ is the bed slope. This new perspective improves and completes the definition of flow-depth-gradient ranges in the analysis of water surface profiles.