Question:

Where is a hydraulic seed file and how is it used?

Answer:

The hydraulic seed file is a DGN library which contains all the hydraulic design information you need to start a new drainage design.  For practical purposes, it will usually be the same DGNLIB file which contains your drainage and utility feature definitions.   The hydraulics seed is in fact, a fully functional drainage project that is copied to a new DGN file whenever a SUE command or StormCAD command is first used in in a new DGN file.  

When you see the message box below notifying you that a utility project is being created, it is this hydraulic seed project which is being copied to the active DGN

The hydraulic seed which is used is defined by configuration variables:

SUDA_SEED_FILE = filepath and name
SUDA_SEED_MODEL = model in above file which contains the hydraulic seed project