HydroCAD Modeling Question

[owillis28]

For the last 3 months, I have been going round and round with a reviewer on my HydroCAD model of a 5-acre site. Looking for some help on modeling advice from members here so that I can put this project to bed and never sign another proposal for a job within this certain rural water district ever!

Just wanting to figure out the best routing methods to use and make sure that I am doing everything correct. Starting to think that HydroCAD does have a flaw in it after the two hour phone conference I had earlier this week!

If I model the site with subcatchments & a pond (modeled as a catch basin with insignificant storage), the reviewer states that a problem is created because it will "push" through any amount of water (CFSin = CFSout)

If I model the site using a reach in the same situation, tail water conditions, pipe inverts & headwater conditions are ignored and the pipe functions as though there is nothing upstream or downstream. 

I am reading up on the various Reach-Routing Methods and Pond Routing Methods that should be used in certain situations. Any help or assistance would be greatly appreciated. 

(Personally, I feel like the reviewer is trying to keep her consultant job and never let a project die unless she has been looking at it for over a year)

 

[psmart]

When you use a zero-storage pond with a culvert outlet, you are performing a complete culvert analysis including inlet losses, barrel friction, and tailwater effects.  Since there is no storage at the inlet, your will always get Qout=Qin.  However, the simulation will tell you the headwater required for the pipe to handle the flow at each point in time.  This is essentially the WSE inside the catchbasin.  If the WSE rises above the grate, the CB will overflow, and you need to include a suitable overflow device, such as a horizontal orifice.  For details please see www.hydrocad.net/sewers.htm

Note that if you get ponding above the CB, then you are effectively modeling a pond with a culvert outlet, and you should include the above-grade storage volume in the pond.  Once you define the storage, you will see a peak reduction and delay as a result of the hydrograph routing procedure.  Without the storage, you will always get Qout=Qin.

A pipe reach, in contrast, is a simplified procedure that considers only normal Manning's flow within the pipe.  It ignores headwater, inlet losses, and tailwater.  For these reasons, pipes should generally be modeled using the complete pond/culvert process described above.  For further details on pipe modeling options please see www.hydrocad.net/pipes.htm

HydroCAD will model each situation exactly as stated.  It's up to you to choose the procedure that is most appropriate for your particular situation.

 

[owillis28]

Is it possible to model the effects of a flap gate in HydroCAD?

 

[psmart]

Is it possible to model the effects of a flap gate in HydroCAD?

HydroCAD outlets are inherently 1-way devices, automatically behaving as if a 1-way valve were present.  So there is nothing special you need to do to model a flap gate - just define the outlet (such as an orifice or pipe) as usual.