The V-notch weir

Today we are going to demonstrate the V-notch weir.

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The width of the flume is 6 inches, or 0.5 ft. [Point to the channel width].

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We turn on the pump.

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We set the bed slope equal to 1% and check the level [Point to the level].

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We set the point gage at zero at the weir crotch [Point to the gage].

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Now we are going to measure the hydraulic head H over the weir.

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The head measurement should be taken at a distance L of at least 4 times the hydraulic head H.

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We try a distance of 150 mm.

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The measured hydraulic head is H = X mm, which is less than 1/4 of 150 mm.

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In U.S. Customary units, the hydraulic head is H = Y ft.

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The ratio of head to width H/B is equal to Y/0.5 = YYY, which is less than 0.2.

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Therefore, the weir is operating under fully contracted conditions.

The discharge through the V-notch weir is:

 Q = 4.28 Ce tan(θ/2) (H + k)5/2

The discharge coefficient Ce is a function of the angle θ of the weir.

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In this case, for θ = 90°, the discharge coefficient Ce is 0.578.

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The head correction k is also a function of the angle θ of the weir [Point to the angle of the weir].

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In this case, for θ = 90°, the head correction k is 0.0029.

 Q = 4.28 Ce tan(θ/2) (Y + k)5/2

 Q = 4.28 × 0.578 × 1 × (Y + 0.0029)5/2

 Q = YY cfs

Therefore, the discharge is YY cfs.

The calculation can be performed using the online calculator

http://ponce.sdsu.edu/onlineveenotch.php