HydroCAD calculates the water surface elevation at each node in the system and every time step. The maximum WSE at each node is equivalent to the HGL at that point.
Note that an term HGL generally implies a steady-state analysis, with the entire drainage system at equilibrium, while HydroCAD is a hydrograph routing model, where all the WSE's are continuously changing over time. As such, there is no single HGL for the entire system.
Thanks so much for your response. For a typical storm drain network on a road side, would you recommend modeling each catch basin as a detention pond (storage being the actual volume of the concrete catch basin) with a culvert as primary and an overflow weir as secondary for the water that comes out of the grate in larger storm events?
That's a common approach, but since the storage in each catch basin tends to be negligible we generally recommend that you use the "zero storage" option. For details please see
