CIV E 530 - OPEN-CHANNEL HYDRAULICS
FALL 2019
PHYSICAL LAB D:  V-NOTCH WEIR

Objective:

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

Procedure:

  1. The formula for the V-notch weir is:

    A. Fully contracted:

    Q = 4.28 Ce tan (θ/2) (H + k)5/2

    A. Partially contracted:

    Q = 4.28 Ce (H + 0.0029)5/2

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

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

  4. Measure the width B of the channel.

  5. With the flume setup running at a given discharge, measure the depth to the water surface upstream of the weir, at a distance at least four times the hydraulic head.

  6. Calculate the hydraulic head H as the depth measured in Step 5.

  7. Check the ratio H/B.

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

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

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