CIV E 530 - OPEN-CHANNEL HYDRAULICS
FALL 2011
LAB No. 4 DEMONSTRATION:  BROAD-CRESTED WEIR

Objective: To demonstrate the principles of the broad-crested weir.

  1. Critical depth above weir:  D = (2/3) H

  2. Theoretical formulas for discharge, based on critical flow in the vicinity of the weir:

    Q = (2/3) H [ (2/3) gH ]1/2 L = 3.087 L H3/2         [1]

    Q = (g D3)1/2 L = 5.67 L D3/2         [2]

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

    1. Discharge Qm (cfs)

    2. Head H (ft)

    3. Depth D (ft)

  4. Calculate:

    1. Discharge Q1 based on Equation 1

    2. Discharge Q2 based on Equation 2

  5. Compare Qm with Q1 and Q2.

  6. Determine applicable discharge coefficients:

    1. Cd,1 = Qm/Q1

    2. Cd,2 = Qm/Q2

  7. Calculate ratio H/Dc based on measured values.

  8. Compare calculated H/Dc with theoretical value H/Dc = 1.5

  9. Write a one-page report summarizing the findings.