Detention Pond design 1

[SCEngr1]

I have a small subdivision (less than 5 acres) and I need to design an onsite detention pond. Does anyone have any links to design guidelines for either hand calcs or an inexpensive software program? (Is SEDCAD good for detention pond design?)

 

[LHA]

First, download TR-55 here, and use it to estimate volume:

http://www.wcc.nrcs.usda.gov/hydro/hydro-tools-models-tr55.html

Then, HyroCAD here will give you a 5 node sampler. Sounds like you only need 4: Pre, Post, Bypass and Basin. It is very easy to learn.

http://www.hydrocad.net/

I've never heard of SEDCAD.

Engineering is the practice of the art of science - Steve

 

[Maury]

The American Concrete Pipe Association sells a computer program called DASH (Detention and Sewer Hydraulics) that will do detention design by several methods: TR-55, TR-20, HEC-1, and Modified Rational Method. The cost is $10 for members of ACPA and $45 for non-members.

 

[gbam]

Try HEC-1 or HECHMS, both are free downloads and can route inflow hydrographs through a basin. Just import the hydrograph and code the stage storage and discharge.

 

[SCEngr1]

What do you mean by "Just import the hydrograph and code the stage storage and discharge."?

I am a structural engineer who has done civil/site design off an on over my 21 year career; however, I have never designed a detention pond. I know how to use the rational method to develop pre and post-development runoff flows (in cfs) to size storm pipe. But, I don't know how to "route a hydrograph" through a basin (detention pond?).

I know that a hydrograph is Flow (cfs) versus Time (hours). How do you determine what storage volume of pond is required?

 

[cvg]

chapter 8, figure 8.2 in the link below may help

http://www.fcd.maricopa.gov/Resources/DL/Hydraulics Design Manual.pdf

 

[RWF7437]

While none of the reponses above are "bad" advice, your first task is to find out who will review your design. Then get their design standards. Also get an example, if possible. Unless you do this first you can waste a lot of time "designing " this insignificant local detention basin and answering the wrong question.

Good luck

 

[SCEngr1]

Are you suggesting that the Municipality could provide me with an example calc. of a detention pond design? Or, did you have another source in mind?

 

[RWF7437]

Yes SCEngr1 the reviewing agency can and should provide complete criteria and examples. There are so many ways to "design" detention ponds that simply saying design it is meaningless.

good luck

 

[francesca]

I suggest you find a colleague to review your design. You're not supposed to stamp drawings that are outside of your expertise. A 5-acre subdivision isn't worth losing your license over. If you mess up your calculations, you could flood the houses and your calculations will be hauled into court by the insurance company. I'm sure you could find a subby to design that detention basin for you for $500.

 

[RWF7437]

SCEngr1,

Do follow Francesca's advice and have a colleague review your design. You'll be amazed at how silly it all is.

As for, " If you mess up your calculations, you could flood the houses and your calculations will be hauled into court by the insurance company. I'm sure you could find a subby to design that detention basin for you for $500."

I've messed up plenty of calculations in 46 years of engineering but have yet to flood a single house. This is probably because flooding, especially from 5 acre drainage basins, is not caused by messed up calculations. Also such basins are not large enough to cause anybody, not even "the Insurance Company" any great concern. Only local "regulatory agencies" appear to believe that detention basins for these areas are a siginificant factor in any realistic flooding scenario.

good luck

 

[francesca]

This is probably because flooding, especially from 5 acre drainage basins, is not caused by messed up calculations. Also such basins are not large enough to cause anybody, not even "the Insurance Company" any great concern. Only local "regulatory agencies" appear to believe that detention basins for these areas are a siginificant factor in any realistic flooding scenario.

Just because the subdivision is 5-acres, it doesn't mean that the drainage basin is 5-acres! I did once encounter a PE who tried to design a drainage basin for just the area of his subdivision, ignoring the 20+ acres upstream also draining to it, but I corrected him before the drawings were finalized.

Perhaps I was trying to use scare-tactics, but I've seen a few detention basins go to court, in just 18 months of subdivision design.

 

[blueoak]

I think francesca makes a good point, but as to RWF7437 I have always thought that the drainage and storage afforded by roads adds a good safety factor for small watershed areas. This of course assumes that your roads are lower than floor elevations. I sometimes think it is standard road design that keeps people from being flooded and not design engineers.

 

[siteturbo]

You might try

http://www.intelisolve.com/stormsew.html

. It is only $395 and is very easy to use. Also, there are free government sotfware programs such as HEC, TR-55, and HYD. Try doing a search for these on google.