Best method to use to size detention basin...

[Jambruins]

I used hydrocad about 3 or 4 years ago but I can't remember a whole lot about it. I have a site where I need to size a detention basin to store the 25 year post developed discharge and let it out at the 10 year pre developed rate.

I have entered my area and time of concentration values in my subcat for the predeveloped. What is the best way to come up with the required size of my basin and weir? I have a copy of a project another engineer did and he used the Custom Stage Data method. Is this the method I should use?

Thanks for the help.

 

[psmart]

"Custom stage data" is one of several options for defining the pond storage. How you estimate the storage is another matter.

HydroCAD provides a pond sizing report that will estimate the amount of storage required to attenuate your post-development peak flow down to the target rate, such as the pre-development flow.

Basically, setup the model for the proposed condition, with your flows routed to a new (proposed) pond. The pond does not have to have any data at this point - just route the flows there. Now right-click the pond and open a report window. Select the Sizing tab to see the pond sizing report.

For further details please see

http://www.hydrocad.net/pondsizing.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Jambruins]

Ok, so I enter my post developed areas and TOC in a new subcat. Then I add a pond but do not input anything for the pond. When I right click and select node report and then click sizing it gives me required storage values for corresponding desired-peaks. The desired peak of 0 cfs gives me a required storage of 0.232 acre-feet. So does this mean my detention basin needs to have a volume of 0.232 acre-feet? Thanks for the help.

 

[psmart]

If your goal is to have zero discharge, then yes, you would need 0.232 AF of storage to retain the entire volume. But if some discharge is allowed, less storage is required, as indicated by the graph.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Jambruins]

So if my 10 year pre developed has a peak rate of 0.58 cfs (which is the rate at which I could discharge) I would just need my basin volume to be equal to the volume corresponding to the 0.58 cfs desire peak? Thanks.

 

[psmart]

Yes. That graph will give you an initial estimate for the required storage to achieve any discharge rate. The actual storage requirement will vary somewhat depending on your outlet design.


Peter Smart
HydroCAD Software

http://www.hydrocad.net