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.
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modeling pipe into a pond
- Thread starter sprtsnut5
- Start date
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.
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.
- Thread starter
- #3
You can use a link to introduce the pre-existing hydrograph into your HydroCAD model. For details see
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
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
" 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
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
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
If you must use Rational method please read
Peter Smart
HydroCAD Software
For details on the SCS/NRCS method see
If you must use Rational method please read
Peter Smart
HydroCAD Software
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