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Homework Help: Question on flow rates over a weir.

  1. Jan 2, 2009 #1
    1. The problem statement, all variables and given/known data

    Hi everyone. All help is appreciated.

    The discharge over a rectangular notch is to be 0.14m3/sec when the water level is 0.23m above the sill. If the coefficient of discharge is 0.6 calculate the width of notch required.

    Answer: 0.716m

    2. Relevant equations

    I think it is Q=[tex]\frac{2}{3}[/tex]b[tex]\sqrt{2g}[/tex]H[tex]^{\frac{2}{3}}[/tex]Cd

    where Q=flow rate, H=height of water level above bottom of notch, b=width of notch.

    3. The attempt at a solution



    0.14= 2/3 x b x 4.429 x 0.375 x 0.6

    0.14= 0.664 b

    b= 0.21m

    which is wrong. Anyone know what I'm doing wrong?
  2. jcsd
  3. Jan 2, 2009 #2


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    Homework Helper

    jason_mcc: There is a typo in your given relevant equation. Change H^0.66667 in your relevant equation to H^1.5.
  4. Jan 2, 2009 #3
    Thanks, got it now.
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