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**Uniform Flow and Non-uniform Flow**

If for a given length of the channel, the velocity of flow, depth of flow, slope of the channel and cross-section remain constant, the flow is said to be uniform. On the other hand, if for a given length of the channel, the velocity of flow, depth of flow etc., do not remain constant, the flow is said to be non-uniform flow.

Mathematically, uniform and non-uniform flow are written as :

$ \begin{aligned} \frac{\partial y}{\partial S}=0, \frac{\partial V}{\partial S}=0 \end{aligned} $ for uniform flow

$ \begin{aligned}\frac{\partial y}{\partial S} \neq 0, \frac{\partial V}{\partial S} \neq 0 \end{aligned} $ for non-uniform flow.

Non-uniform flow in open channels is also called *varied flow*, which is classified in the following two types as :

Rapidly Varied Flow (R.V.F.), and

Gradually Varied Flow (G.V.F.)

**(i) Rapidly Varied Flow (R.V.F.) :**

Rapidly varied flow is defined as that flow in which depth of flow changes abruptly over a small length of the channel. When there is any obstruction in the path of flow of water, the level of water rises above the obstruction and then falls and again rises over a small length of channel. Thus the depth of flow changes rapidly over a short length of the channel. For this short length of the channel the flow is called rapidly varied flow ( R.V.F ).

**(ii) Gradually Varied Flow (G.V.F.) :**

If the depth of flow in a channel changes gradually over a long length of the channel, the flow is said to be gradually varied flow and is denoted by G.V.F.