# Question on flow rates over a weir.

1. Jan 2, 2009

### jason_mcc

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.

2. Relevant equations

I think it is Q=$$\frac{2}{3}$$b$$\sqrt{2g}$$H$$^{\frac{2}{3}}$$Cd

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

3. The attempt at a solution

Q=$$\frac{2}{3}$$b$$\sqrt{2g}$$H$$^{\frac{2}{3}}$$Cd

0.14=$$\frac{2}{3}$$b$$\sqrt{2g}$$0.23$$^{\frac{2}{3}}$$0.6

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. Jan 2, 2009

### nvn

jason_mcc: There is a typo in your given relevant equation. Change H^0.66667 in your relevant equation to H^1.5.

3. Jan 2, 2009

### jason_mcc

Thanks, got it now.