Model Dam with Riser in HydroCAD?
Model Dam with Riser in HydroCAD?
(OP)
I am trying to do a dam failure analysis for a small impoundment that has an earthen dam with a riser and conduit. The structure has a 48" inlet pipe, one weir in the riser about 10' above the pipe invert, and a 42" pipe outlet from the riser structure at the same invert as the inlet. I read in a previous post that this cannot be modeled in HEC-RAS but can be modeled in HydroCAD and then put into HEC-RAS to model the rest of the site downstream. How do I model this riser structure in HydroCAD? My only idea right now is to model a 48" culvert going to a "pond" (the riser) with a 42" outlet and a weir designated as Device 1.





RE: Model Dam with Riser in HydroCAD?
Device#1 = 42" culvert, Routing=Primary
Device#2 = Weir, Routing=Device#1
Device#3 = 48" culvert, Routing=Device#1
For illustrated examples please see www.hydrocad.net/pond1.htm
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Model Dam with Riser in HydroCAD?
Here is the other way I tried modeling it. I modeled the lake as one node with two outlets: a weir (the earthen embankment) and the inlet pipe to the riser. That node goes to another node for the riser as a "pond" and entered the volume of the riser as the "pond" volume. The outlets for that node are a sharp-crested weir (Device#1) and the riser outlet pipe (Primary). The result is much different and looks really bad.
What is the difference between these two approaches? Why are the results so different? Would it be more accurate to model it using the second approach I described here because then I can enter a volume for the riser?
RE: Model Dam with Riser in HydroCAD?
For the later case you could use:
Device#1 = 42" outlet culvert, Routing=Primary
Device#2 = Weir/baffle, Routing=Device#1
Device#3 = 48" inlet culvert, Routing=Device#2 (CHANGED routing)
Device#4 = Orifice/riser-top, Routing=Device#1 (NEW device)
This will be analogous to your double-pond scenario. As for the riser volume, the storage is too small to effect the routing, so I would use the zero-storage option for better stability. Of course, the two-pond solution will also require a tailwater-sensitive routing procedure in order for the riser "pond" to influence (reduce) the reservoir discharge.
Peter Smart
HydroCAD Software
www.hydrocad.net