Parallel Storm Sewer System Modeling?

[proletariat]

I have an existing storm sewer that I want to leave in service, and supplement with a proposed storm sewer. The two systems will intersect at several points to equalize flows.

They do not follow the same route over a length of about 5000 feet, so I can't just treat them as one pipe. My concern is that the system lower in elevation will surcharge the inlets because it will be overloaded by the higher-elevation system.

Is there any software that will model parallel pipe systems? Hydraflow does not.

 

[RWF7437]

Don't know but three possibilities come to mind:

HydroCAD
HEC-RAS
or even,

EPANet

There may be better alternatives among the many expensive proprietary options but these three are either free or moderately priced.

good luck

 

[Ryb01]

I've had sucess modelling this type of system in SWMM 5.0 or PCSWMM. SWMM 5.0 if a free software and can be downloaded from the EPA website.

 

[beej67]

SWMM, PCSWMM, XP-SWMM. Possibly ICPR, although I've never worked with it so I don't know how it handles pipes.

You want a dynamic model, not one like Hydraflow that likes to ignore what's going on around it.

Or, you could ghetto your way up to a somewhat correct solution. To model something like this in Hydraflow or StormCAD, you could model the lower pipe, vary the flow in it by hand until it surcharges to a particular HGL, then model the upper pipe and vary the flow in it by hand as well until it surcharges to a particular HGL, and vary the flows by hand until you can match the HGLs in the two models. Then add those two flows and that corresponds to the actual flow in the pipes for that combination of models.

Then figure out what your design flow rate is, and keep mucking about with both models until your design flow rate equals the sum of the flow rates in the two models who's HGLs match.

Please note that the above process isn't perfect, because it doesn't really model junction losses at the splits very well, but depending on the application it might get you close enough to where you're comfortable with the design. You'd just have to get a reviewer to buy it.

Of course, by the time you've done all that, and multiplied the time and effort it took times your billing rate, you probably could have bought a license of XP-SWMM.

 

[puzzler77]

It sounds like one system will be shorter than the other creating a higher velocity which would route flow faster than the other system. By routing the two hydrographs, I believe you will find the system will perform for higher flows than merely using super position! Is any of the flow, say for the 100 year event, staying above ground? In that case, you would actually have three systems to deal with. I haven't had the opportunity to try it yet, but I have heard good things about XP-SWMM. Good luck with your endeavor!