I am modeling and alternative design with upstream storage of stormwater runoff for the 100 year 6 hr Chicago storm where the outfall pipe runs through private property. I have used box culverts upstream, however, through the property, the pipe sections are 825 mm @ 0.5% grade and 750 mm @ 36% grade respectively. Between the box culvert and the 825 mm pipe, I inserted a 10 m pipe section of 450 mm to act as an orifice. Should I overlay an orifice link on this section of pipe or delete the pipe section and just use an orifice link?