Pipe Outlet Inside Catch Basin

[jdd61]

We are seeing more wet detention pond outlet designs with pipe risers and outlets inside the catch basin (as a "protected outlet" alternative to the reverse slope pipe). I have attached photos of two examples - one with vertical low flow and peak discharge outlets; one with vertical low flow outlet but peak discharge outlet in the horizontal plane. I am assuming the outlets will act as weir flow at low heads above outlet invert, but am wondering once the driving head is higher. If the outlet diameter is less than the pipe diameter, it should act as orifice flow. What if the outlet diameter is the same as pipe diameter? What would be the controlling flow? How would it be modeled in HydroCad?

 

[psmart]

You could model this as two separate "ponds": The main storage pond with a culvert outlet, and then a zero-storage pond for the CB structure, including the appropriate weir/orifice details.


Peter Smart
HydroCAD Software

http://www.hydrocad.net