Yes, you could model the forebay as a separate pond with appropriate storage and outlet device(s).  But if the forebay doesn't provide enough storage to create significant detention, there may be no point to including it in the model at all.

Another approach is to model the forebay as part of the storage in the main pond.  Just include it on a separate line in the storage tab.  This is appropriate if the two storage volumes will usually be equalized.  For details see www.hydrocad.net/pondstore.htm

For general modeling tips please see www.hydrocad.net/howto.htm
 

Peter Smart
HydroCAD Software
www.hydrocad.net
 

I wouldn't model the forebay as a separate pond node, it will get confusing when trying to figure out the dry storage area; storage will be across the two nodes, and the outlet behavior may differ from a single-node pond.

Typically I just add the storage in the forebay and micropool together and make sure that the starting elevation is the permanent pool elevation.  If you need to know the permanent pool volume of the sections separately, use Peter's suggestion of adding another line on the storage tab.

I try to stay simple in the model; I wouldn't model the low flow channel.  If anything, you're being more conservative by not accounting for the travel time through the channel.