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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.

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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. 

 

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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?

Example

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?

Solution:

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

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