Assumptions in Gradually Varied Flow

1. The pressure distribution at any section in gradually varied flow is assumed to be hydrostatic. This is because the curvature of stream lines is very small or negligible. The exclusion of the region of high curvature from the analysis of G.V.F is required to meet this assumption.
2. The resistance to flow at any depth is assumed to be given by the corresponding uniform flow equation, such as Manning’s or Chezy’s equation. The only condition is that the slope term to be used in these equations is the slope of energy line (S_f ) instead of bed slope (S₀).

3. Channel is prismatic with small channel bed slope, i.e., Hydraulic Gradient Line (HGL) will lie at free surface.
4. There is no air entrainment.
5. Velocity distribution is invariant, i.e., kinetic energy correction factor, a is 1.
6. Flow is steady, i. e., there is no lateral inflow or outflow from the channel.
7. Resistance coefficient (c and n) are constant with the depth of flow.

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