is storage node required for the inlet HW?
if so...how are they set up?
I looked at the culvert example that comes with SSA, and they use storage curve for the storage shape. Does the storage curve have to hold the flow before it enters the culvert?
If the storage area is not big enough then there is flow loss that doesn't get into the system...I don't remember HEC 5 taking the HW storage area into account for culvert design.
I would recommend using a stoage curve if you believe that a level pool exists above the culvert. This is often the case with small culverts with high head.
If a channel is fairly large and the pool would back up a long ways, make sure you don't include the full length of a channel in the same area where you have created stage-storage data or you are duplicating the storage effect. If you don't expect a level pool, I'd just put the full length of the channel to the culvert and use a junction for the upstream node.