Q for pond design 1

[7058]

What shall I use as criterion for sizing a pond for develpoment project?

1/Is it Q=CIA/360 (for metric)?
2/If yes, which I? 10min 60min, 120min 1440min?
3/ Or shall I use Rain Hydrograph?
I tried both and results are far apart (20/50%)Generally Rain Hydrograph gives much smaller quantities.
4/ Is the choice dependent of the development area size?

Thank you and have a nice day.
Dragan Andrejevic Civ. Eng.

 

[francesca]

The rational method (Q=CiA) gives a peak flow, not a volume, and therefore cannot be used for pond design. You need to use a hydrograph method, typically a 24-hour storm duration, but check with the review agency.

 

[7058]

Thanks,
I was thinking of Q=CIA/360 and than multiplied by Tc time (say 10min*60s/min) (or may be 2hour with 2hour intensity )for the total quantity, but as I said, it comes far apart with Rain hydrograph.

 

[francesca]

You cannot use the Rational Method in that way. Search the forum for the "Modified Rational Method" which is sometimes applicable, but you can't go wrong with a hydrograph method.

 

[runoff]

You also should check the municipality where you are working. I am finding that in Tennessee and surrounding states are not allowing the Modified Rational Method. I agree with Francesca that the hydrograph method is the way to go.

 

[7058]

Thank you runoff!