Parking Lot Sag Inlet with Ponding

[kevinjackman]

Hi folks,

I am trying to design parking lot drainage using SSA.

I have to restrict flow to 70 l/s/ha which means I will need to have ponds at 2 sag inlets.

To model the ponding at the inlets I have used a storage node with a weir and an orifice.  The orifice connects to a junction and water is outlet to the underground storm pipe.  The weir is at the crest of the ponding area and outlets overland.

I am having trouble with the junction and pond.  The junction seems to be surcharging and shows flooding but the pond is not filling up as desired. The intent is of course to have the junction surcharge, and fill the ponding area over top of it, then take the overland route.

Could someone assist me with modelling this pond / junction?

I have attached the SPF file.

Any help would be appreciated.

Civil 3D 2011.