Velocity of approach in fluid mechanics, velocity of approach in notch, velocity of approach in weir, maximum approach velocity.

 Velocity of approach:-

                               Velocity of approach is defined as ther velocity with which the water approaches or reaches ther weir or notch before it flows over it.  

• Thus if Va is the velocity of approach, then an additional head ha equal to Va^2/2g due to velocity if approach, is acting on the water flowing over the notch. 
• Then initial height of water over ther notch become (H + ha ) and ther final height becomes equal to ha.
• Then all the formulae are changed taking into consideration of velocity of approach. 

             Va = Q/ Area of channel

Discharge over a rectangular weir, with the velocity of approach. 

= 2/3 × Cd × L × (2g)^1/2 × [( H1 + ha )^3/2 ha^3/2].

 ☆  ha= Va^2/ 2g.