modeling pipe into a pond

[sprtsnut5]

Okay, trying to get familiar with pond routing again. I have a detention pond with an outlet structure. The inlet is a storm sewer pipe system. I have used Landdesktop to design the storm sewer and have a flow from the last segment of pipe. How do I model this into my pond? I can't seem to figure out how to enter the flow.

 

[TerryScan]

sprtsnut5,

I do not know the model requirements in your location. However, it is comon for storm sewers to be sized using the rational method and ponds to be routed using SCS methodologies. While there are those with magic formulas to make a correlation...its really apples and oranges.

On a typical project, I will layout my sewer network (without sizing or design yet), I will establish SCS subcatchments that flow to appropriate ponds (larger than 1 per inlet...may even be 1 per pond), I then do the pond design. NOW, I have a tailwater elevation for doing the sewer network design.

The shorter answer: I would create a Subcatchment in Hydrocad and use SCS to establish pond inflow.

 

[sprtsnut5]

This is geeting there... I'm just trying not to have to recreate one or the other, since Hydrocad doesn't model the pipe system. By the way, we do everything with Modified Rational. Any other options out there?

 

[psmart]

You can use a link to introduce the pre-existing hydrograph into your HydroCAD model. For details see

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

As TerryScan suggested, generating the runoff in HydroCAD should also be considered. This will make it much easier to run multiple storms and make other changes. Otherwise you'll have to reload the link with a different Hydrograph each time.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[RWF7437]

" By the way, we do everything with Modified Rational. Any other options out there? "

Yes, there are very many other options "out there"; almost all of them better than "Modified Rational".

There are at least two versions of the modified rational method. Do you mean the one which produces a fictional trapezoidal hydrograph, or do you mean the one developed by Los Angeles County which produces a more realistic hydrograph for an assumed rainfall pattern ?

You can also use the NRCS ( SCS) method, the Santa Barbara Urban Hydrograph method, the Clark Unit hydrograph method, the Snyder Hydrograph method or any of their many local variations.

By far the best method would be one which, unlike these, has been calibrated !

Whichever method you choose, or are required to use, expect errors of estimate of +/- 30% to 100%.

good luck

 

[psmart]

Since you're using HydroCAD, I would definitely recommmend the SCS/NRCS method over Rational method. Although HydroCAD can do both, SCS/NRCS is actually a lot easier to use, and it's much better for any volume sensitive calculations, such as pond routing.

For details on the SCS/NRCS method see

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

If you must use Rational method please read

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

Peter Smart
HydroCAD Software

http://www.hydrocad.net