Specific Energy, Critical Flow and Critical Velocity

Specific Energy

It is defined as energy per unit weight of the liquid with respect to the bottom of the channel. The extra information needed to solve the above problem can be provided by the specific energy equation. Specific energy, Es, is defined as the energy of the flow with reference to the channel bed as the datum:

Total Energy on open channel  flow

E= Z+y+ V²/2g

Considering the bed as datum  line , z=0

From Specific Energy curve , Corresponding to  the Minimum specific energy E(min) ,there is only one depth of floe that is called Critical depth.

Critical Flow and Critical Velocity

Critical Flow

Depth of flow of water at which the specific energy. E is minimum is called as critical depth (yc). For rectangular channel, critical depth,

Critical Velocity

Velocity of flow at the critical depth is called critical velocity Vc