Head within pipe system

[martin888888]

Hello,
We have modeled a sedimentiation pond with a 6" pipe outlet that discahrges 2500' downstream. We have about 40' of drop between the pond and outlet but we do have a few areas of low spots in the pipe (pipe sits on grade). We are trying to analyze if we have enough head to push the stormwater through these lowspots and to the outlet. Will Hydrocad do this analysis?

 

[psmart]

It depends what you mean by "having enough head to push the stormwater through these low-spots." With a 40' drop the pipe will certainly flow, but there will obviously be a permanent pool at any sag, along with the potential for sediment accumulation.

As far as the modeling, using the tube/siphon outlet option should provide a more accurate simulation than the typical culvert outlet.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[martin888888]

Thank you, i have never used the tube/siphon before, will try it. Stupid question as this is outside my expertise but is there a calculation to verify it will flow? I guess I could look at my old Hydro textbooks.

 

[psmart]

I guess I still don't understand your concern. Why - exactly - are you concerned that it might not flow? What mechanism would prevent it from flowing?

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[psmart]

If you're concerned about the general operation and design of the pipe, I would post your question in the storm/flood engineering forum. 2500 feet does seem very long for a 6" stormwater conduit. There are experienced engineers on that forum who will be glad to assist you with your design.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[martin888888]

Thanks for your response, jsut curious, why would the tube/siphon give a more accurate result in this case? We have a 6" pipe (no outlet control) being used as our outlet structure.

 

[psmart]

The two calculations are very different:

A tube/siphon uses the Hazen-Williams coefficient to calculate frictional losses (assuming the tube is full along it's entire length) plus orifice losses at the inlet. This procedure allows for variations in the slope, and even sections with a reverse slope, as long as there in an overall drop. The only parameters are the tube size, length, roughness, and elevation drop.

Culvert flow, on the other hand, assumes a uniform slope, but covers a wider range of inlet and flow conditions, including partial flow in the barrel.

For complete details please see the HydroCAD Owners Manual at

http://www.hydrocad.net/hcmanual.htm

Since you have a very long conduit with variable slope, tube flow seems a better match to your situation. I assume the conduit will be flowing full - any air pockets could be problematic in such a long line. I suggest that you get some feedback on your situation in the storm/flood engineering forum. My comments are limited to the modeling issues under specific conditions, and not to the general operation or suitability of your proposed design.







Peter Smart
HydroCAD Software

http://www.hydrocad.net