You can use a link node to enter flow vs time (to route through your HydroCAD model), or elevation vs. time (to use as a predefined tailwater).  It depends on whether the river represents an inflow to your HydroCAD model or a tailwater condition.
www.hydrocad.net/link.htm

 

Peter Smart
HydroCAD Software
www.hydrocad.net
 

I'm trying to size a broad-crested spillway for flooding, so the river would be an inflow.  Elevation vs. time would be ideal for my situation, but I remember from earlier attempts at some tidal modeling that the link tailwater has a one way flow aspect and can't be used for filling.  Flow vs. time wouldn't allow me to use the node to size the spillway entering the unit since I would have to recalculate the flows by hand for all my spillway iterations.  I tried creating a rain and UH distribution that would match the gage results but didn't know if that was going to be a dead end or not.  Thanks.
  

So the weir is handling overflow from the river?

HydroCAD needs an inflow hydrograph (flow vs. time), which is used to do the routing calculation.  You can't enter elevation vs. time, except in a link, and that's only for used to define a variable tailwater.

You may have to do the weir calculation separately in order to produce an inflow hydrograph for your HydroCAD model.  However, this is pretty easy if you use a weir stage-discharge curve generated by HydroCAD.
 

Peter Smart
HydroCAD Software
www.hydrocad.net
 

Yup, river comes up and I need to fill my wetland at about the same rate.  I'll just go the spreadsheet route.  

I don't know within the computational engine of HydroCAD if it would take much tweaking to allow a link to serve as an input, but it would be handy for our large river and coastal work.  Maybe version 10.5???

Thanks for all the prompt assistance.

The pond inflow is always in the form of flow vs. time, not elevation.  What you need is actually a "pond" where you can set an arbitrary elevation vs. time.  That would allow the flow to be calculated using any of the standard outlet devices.  I'll make sure we add this to the wish-list.

Peter Smart
HydroCAD Software
www.hydrocad.net