The V-notch Weir - CIV E 530 - Open-channel Hydraulics

Summary

This video demonstrates the process of measuring discharge through a v-notch weir. The procedure includes setting the bed slope to 1%, measuring the hydraulic head, and confirming that the weir operates under fully contracted conditions. The video further explains the relationship between the discharge coefficient and the weir's angle, specifically for a 90-degree angle. A detailed formula is provided for calculating discharge, with the final discharge value calculated to be 0.00672 CFS. The video also mentions using an online calculator for further calculations, providing a clear and practical guide for conducting the measurement.

Takeaways

• 😀 The demonstration involves checking the v-notch by turning on the pump and setting the bed slope to 1%.
• 😀 The measurement of the phloem is taken at 6 inches.
• 😀 The point gauge is set to zero at the start of the measurement process.
• 😀 Hydraulic head measurement should be taken at a distance of at least four times the hydraulic head (L = 150mm or 5.905 inches).
• 😀 The measured hydraulic kit is H = 1.0945 inches, which is less than one-fourth of 5.945 inches.
• 😀 The ratio of head to width (H/B) is 0.18, which is less than 0.2, indicating the weir is under fully contracted conditions.
• 😀 The v-notch weir's discharge coefficient (C_sub_E) is 0.578 for an angle (θ) of 90 degrees.
• 😀 The head correction (K) is 0.00029 for an angle (θ) of 90 degrees.
• 😀 The discharge is calculated using the formula: Q = 0.000672 CFS.
• 😀 An online calculator can be used to perform these calculations more easily.

Q & A

What is the purpose of the demonstration in the script?

The purpose of the demonstration is to show how to perform a measurement using a v-notch weir, focusing on setting the bed slope, checking the level, and calculating the discharge.

What is the bed slope set to during the demonstration?

The bed slope is set to 1% during the demonstration.

How is the level checked in the demonstration?

The level is checked by turning on the pump and verifying the bed slope, then adjusting the measurement to ensure accuracy.

What is the phloem height mentioned in the script?

The phloem height is mentioned as six inches.

At what distance should the head measurement be taken?

The head measurement should be taken at a distance of at least four times the hydraulic head, or at a distance of 150 millimeters (approximately 5.9 inches).

What is the measured hydraulic head (H) in the demonstration?

The measured hydraulic head (H) is 1.0945 inches.

What does the ratio of head to width (H/B) represent, and what is its value in this case?

The ratio of head to width (H/B) represents the relationship between the hydraulic head and the width of the weir. In this case, the ratio is 0.18, which is less than 0.2, indicating the weir is operating under fully contracted conditions.

What does it mean for the weir to be operating under fully contracted conditions?

Operating under fully contracted conditions means that the flow is fully confined by the weir, and the discharge is governed by the weir's geometry rather than the flow's free surface.

What are the discharge coefficient and head correction for a v-notch weir with an angle (theta) of 90 degrees?

For a v-notch weir with an angle (theta) of 90 degrees, the discharge coefficient (C_e) is 0.578, and the head correction (K) is 0.0029.

What formula is used to calculate the discharge in the demonstration?

The discharge is calculated using a specific formula that involves the discharge coefficient, head correction, and other parameters of the v-notch weir, yielding a discharge of 0.00672 CFS (cubic feet per second).