Detention Question
Detention Question
(OP)
I am modeling a detention pond. The detention is provided by building a dam on a stream. A large diameter culvert is proposed in the stream bed.
This was permitted by the USACE. Two of the conditions of the permit were:
1. The detention time must be less than 2 hours
2. The pipe must be embedded 1 foot below the natural stream bed.
My questions are-
1. What exactly is the definition of detention time; i.e. how do I calculate it? And can someone tell me a publication that addresses this so that I can provide a reference to the local reviewer?
2. What is the best way to model the embedded culvert? I am thinking I should use an equivalent area pipe and model the invert 1' above the actual design invert. Is this correct?
Also, is there any free detention modeling software that allows you to use a rating curve for the pond tailwater depth?
I hope I was clear with my questions. TIA, any help would be appreciated.
This was permitted by the USACE. Two of the conditions of the permit were:
1. The detention time must be less than 2 hours
2. The pipe must be embedded 1 foot below the natural stream bed.
My questions are-
1. What exactly is the definition of detention time; i.e. how do I calculate it? And can someone tell me a publication that addresses this so that I can provide a reference to the local reviewer?
2. What is the best way to model the embedded culvert? I am thinking I should use an equivalent area pipe and model the invert 1' above the actual design invert. Is this correct?
Also, is there any free detention modeling software that allows you to use a rating curve for the pond tailwater depth?
I hope I was clear with my questions. TIA, any help would be appreciated.





RE: Detention Question
For free detention modeling software, use WinTR-55. However, I strongly urge you to also model your culvert in HEC-RAS and check the scour. You will likely need some serious scour protection on the downstream side.
RE: Detention Question
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Detention Question
RE: Detention Question
As far as software, I use PondPack, but that's not free. I think HEC1/HEC-HMS would probably work well and you can use rating curves. EPA-SWMM 5.0 is another good free software. In EPA-SWMM, you can probably model your stream, the dam, outfall, etc.
Hope this helps!
RE: Detention Question
While one can rationalize scenarios other than what is specified regarding embedding the pipe, I would model it as described in the permit. There are several software packages that will model an embedded pipe, including the current version of HY-8:
http://ww
As to last question, I am not personnally familliar with HEC-1. The manual does indicate it can account for tailwater in computations, but I don't know how it's tailwater is established.
I work with HydroCAD (affordable) as well as ICPR (not as affordable). Both of these packages can account for tailwater in calculations and can accept user defined rating curves.
RE: Detention Question
RE: Detention Question
I will give HEC-1 and HEC-HMS a try. I've been using an older version of Hydraflow Hydrographs which only allows a fixed tailwater elevation.
Again thanks for your help