How to tell if single outlet pipe's outlet end is submerged? - Detention Basins 1

[BillsSis]

Hello,
In reviewing a detention basin with a single outlet structure being that of a 18" pipe with no riser attached, how do I analyze the pipe? I'm wanting to use this analysis to put together a table with elevations and discharges of the pipe. Would I analyze it using HY8 or using Orifice Equation?

Thanks!
BillsSis

 

[cvg]

you will need to look at the outfall conditions and estimate tailwater to determine if the tailwater is above the normal depth in the pipe. Orifice equation would only be suitable for higher heads to determine the inlet capacity. you would still need to determine flow characteristics in the pipe and tailwater. you could use HY8

 

[BillsSis]

Thank you very much cvg. Quick and down-to-the-point answer!