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Flow properties, such as depth of flow area of cross section and velocity of flow vary with respect to distance is called Non-uniform flow.
It is, otherwise, called as varied flow. The varied flow is broadly classified into two
1) Rapidly varied flow (R.V.F)
2) Gradually varied flow (G.V.F)
If the depth of flow changes quickly over a small length of the channel, the flow is said to be gradually varied flow (GVF). Example: Back water in a dam.
The following assumptions are made for analyzing the gradually varied flow:
1. The flow is steady
2. The pressure distribution over the channel section is hydrostatic, i.e., streamlines are practically straight and parallel.
3. The head loss is same as for uniform flow.
4. The channel slope is small, so that the depth measured vertically is the same as depth measured normal to the channel bottom.
5. A channel is prismatic.
6. Kinetic energy correction factor is very close to unity.
7. Roughness coefficient is constant along the channel length
8. The formulae, such as Chezy's formula, Manning's formula which are applicable, to the uniform flow are also applicable for the gradually varied flow for determining slope of energy line.
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