Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Using Curve Number Method to determine required Detention Storage Volume

Using Curve Number Method to determine required Detention Storage Volume

Using Curve Number Method to determine required Detention Storage Volume

I'm trying to use the Curve Number (CN) Method calculate the required Detention Storage Volume for a pond near the outlet of a 26-ac watershed. I've used NOAA Atlas 14 to find the total rainfall depth (1.83 inches). I'm required to use the Farmer Fletcher 100-year 3-hour Unit Hydrograph for computing required detention volume. I've attempted to do this using the table in the attached JPG. I came up with 125,866 cf of required detention volume. However, I think there must be a flaw in this calculation...

In my example, at t = 90 min, the unit hydrograph yields a total cumulative rainfall of 0.888*1.83 = 1.625 inches. Over the 26.12 acres, this yields a volume of 154,075 cf. Also, at 90 minutes, a release of 0.2 cfs/ac would yield a total release volume of 28,209 cf. Therefore, the volume in the pond should be the difference between the accumulated and released volumes, which is 125,866 cf.

Two problems I'm struggling with...

1) This calculation seems completely independent of CN.
2) The hydrograph is for RAINFALL, NOT RUNOFF. Seems to me that at 90 minutes, not all of the 154,075 cf would have made its way to the detention pond.

Is there a way to incorporate CN? Is there a way to produce a RUNOFF hydrograph? I'd prefer to use my own spreadsheet so that I can follow the calculation from start to finish. (Unlike HEC RAS and other programs where all I can see is my initial input and the final outcome and "hides" the intermediate steps). Any help would be greatly appreciated.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close