The newer option for SWMM 5 culverts uses three culvert classifications and associated equations to compute the inlet controlled flow into a culvert using the FHWA (1985) equations. The culvert code in the culvert.c code of SWMM 5 uses:
1. Two Equations for Unsubmerged culvert flow,
2. One Equation for the Transition flow, and
3. One Equation for Submerged flow.
