Jon - recommend you use a type 23 gate on the F1/F4 cards, based on head
on the tidal side of the gate at the downstream side of the junction
structure. The discharge pipe from the junction structure to the pipe
outfall would be modeled as a standard pipe (C1 card), and the exit
would be a "free" outfall. The tide will back up the pipe to the
junction where it controls the gate.

Hope this helps.
Ron Kilmartin
ronkilmartin@attbi.com