V notch Weir Calculator

Enter the values of height and angle of the v-notch in the V-notch weir calculator to calculate its flow rate.


Is This Tool Helpful?


This V Notch calculator computes the flow rate of a triangular weir using the values of its hydraulic head and notch angle. This calculator is used to calculate the discharge of a fully contracted weir flow. 

What is a V-notch weir?

Flow rates of streams and canals are determined usually by installing a weir. 

A V-notch is a triangular weir that has become the standardized weir over time of period. It is used because of the accuracy in head measurements it provides. 


v notch weir

The measurement is taken by the principal that discharge is directly related to the head of the weir. The triangular notch changes the depth of water discharging, providing more accuracy.

A fully contracted weir is one that has H < 2b (b is the distance of the weir from both sides). 

V-notch Formula

The formula used for a fully contracted weir notch is:

 Q = 8/15 × Cd × (2g)1/2 × 12 × tan(θ/2) × H3/2

In this equation:

  • Q stands for flow rate or discharge rate
  • Cd is the discharge constant
  • H is hydraulic head
  • g is gravity constant (9.8 ms-2)

How to find the flow rate of V-notch?


A v-notch of angle 35 degrees and head as 15 was installed on a canal. What will be the flow rate if the discharge constant is 8?


Step 1: Identify the values.

Height = 15

Angle = 35

Cd = 8

Step 2: Write the formula and enter the values.

 Q = 8/15 × 8 × (2g)1/2 × tan(35/2) × 153/2

 Q  =  4.27 × 4.43 × 0.315 × 58.09

 Q = 346.174