Hazem,

The F4 line is called a head dependent gate but the user must enter
opening and closing depths (it does state this in the extran.doc file).
Enter the "Depth at control junction at which the gate is fully open, ft
[m]."

If you substitute the following line for your original F4 line with
elevations the orifice will open and close at the proper depths (from
node 20305).

F4 20305 0.25 3.50 0.00 0.0 0 1

If you use depths then your model will work in any version of swmm44h or
later. BTW, the answers you get with the F3 and F4 lines are the same.

Regards,
Bob Dickinson
DickinsonRE@CDM.COM