CIV E 530 - OPEN-CHANNEL HYDRAULICS
FALL 2013
LAB No. 12 (PHYSICAL):  V-NOTCH WEIR

Objective:

To demonstrate a discharge measurement using a V-notch weir.

Procedure:

  1. The formula for the V-notch weir is:
    Q = 4.28 Ce tan (θ/2) (H + k)5/2

  2. The discharge coefficient Ce and the head correction k are a function of θ (USBR Measurement Manual).

  3. With the flume setup running at a given discharge:

    1. Set the depth to the weir crotch as 0 on the point gage.

    2. Measure the width B of the channel.

    3. Measure the height P from the bottom of channel to the weir crotch.

    4. Measure the depth to the water surface upstream of the weir, at a distance at least four times the hydraulic head.

  4. Calculate the hydraulic head H as the depth measured in Step 3d.

  5. Check the ratio H/B.

  6. If H/B ≤ 0.2, the weir is fully contracted. Use the formula for fully contracted weir.

  7. If H/B ≤ 0.4, the weir is partially contracted. Use the formula for partially contracted weir.

  8. If H/B ≤ 0.2, compare your results with the Fully contracted V-notch weir calculator.

  9. If H/B ≤ 0.4, compare your results with the Partially contracted V-notch weir calculator.

  10. Write a short report summarizing and commenting on the findings.