Open Channel Flow

Open Channel Flow: 

In open channel flow, water surface is at atmospheric pressure and flow is under gravity.
In case of uniform flow, area of flow is constant, discharge is constant, depth is constant and bottom slope is constant.
Whereas, In Gradually varied flow depth of flow changes in the direction of flow over a large distance and in rapidly varied flow depth of flow changes over a small distance.

Velocity Profile in open channel flow :

Generally an open channel flow is turbulent. Maximum velocity occurs generally at depth of 0.1y-0.25y from the top surface where, 

     y=depth of flow 

Velocity at surface Vo=(0.85-0.95)Vmax

Mean velocity is equal to the point velocity at a depth of 0.6y. 

For greater depth, 

           Vmean=((V0. 2 y+V0. 8y)/2)

Types of flow on the basis of Reynolds Number:
Re=< 500 (Laminar Flow)
500<Re=<2500 (Transitional Flow)
Re>2500 (Turbulent flow)

In open channel flow Re is defined as,
Re=(mean velocity * hydraulic radius*density)/(viscosity)
R=(A/P)

Froud Number : 

It is defined as F=√(inertia force/gravity force) 

                  F=V/√(gD)

Fr<1 (subcritical flow)

Fr=1 (critical flow) 

Fr>1(supercritical flow) 

Uniform Flow:

Uniform flow is said to be uniform if neither the discharge, depth nor velocity of flow changes and channel bottom is also constant. 

Methods to find velocity and discharge:

Chezy's Equation:

V=C√(R.Se)

Where V = mean velocity 

              Se= energy slope

Manning's Equation:

V=(R^(2/3).S^(1/2))/N

               N= Manning's coefficient