Detention pond modelling in Hydraflow

[bbengineering]

I am designing a small residential underground detention basin and would like to have the only catch basin also be the outlet in the event of large storms. There is no realistic safe place to discharge it on this small lot, and the existing runoff just flows off the driveway anyway, so this system will greatly improve the situation. The questions is if there is a way to model this in Hydraflow (2012) with the outlet elevation actually above the top of the pond?

 

[beej67]

I haven't messed about with hydraflow in quite a while, but the brute force method would be to calculate your stage-storage relationship yourself in excel, and include the storage in the manhole itself as well as the local gutter storage above the inlet. Then you have a stage storage relationship that does extend above the rim, and your program will work - just enter it manually.

The thing you have to be careful about, when doing things like this, is they're prone to introducing oscillation and continuity error into your model. I don't know if there's a way to check for that in Hydraflow or not. It could be that your model is screwing up without letting you know, which is a bad thing. Consider cross checking its results against another software. The most robust way of modeling something like this would be in SWMM, but the complexity of that model puts it off many first time users.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[bbengineering]

Thanks for your reply. Followup question, how would you determine the flow above the system? I have to compare the storm water flows before and after the development.