Storm and Sanitary Analysis will not Import Catchment

[info6RUDZ]

I asked a similar question before on this forum, and didn't really get a solution. I am analyzing a natural terrain, and created two Catchments connected to structures. One catchment was imported into SSA as a subbasin but the other did not. There is virtually no difference between the two catchments and i just can't understand why SSA would leave the other one out. Attached is a C3D file with catchments DMA 2 and DMA 3. DMA 2 was imported successfully but DMA 3 was not. Anybody got any ideas? Thanks in advance.

[matt_anderson_pe]

For SSA to recognize a catchment, it needs all of the elements needed to compute runoff.

1. The polygon (by definition - the object)
2. Runoff Coefficient (by default)
3. Time of Concentration (to be calculated or established)

If one is missing, SSA does not import it.  It probably should - but a zero time of concentration (as DMA3 has) would not result in calculated flow.   Now - you have a flow path - but that flow path has a negative slope, and the TR-55 calculation can't handle that, resulting in 0 for your Tc.

[Joe-Bouza · Accepted solution]

Pardon if this is ignorant. Isn't that catchment, curve#, TC and discharge point?

[matt_anderson_pe · Accepted solution]

Yes @Joe-Bouza  you are correct.  Discharge is the element I missed.

The catchment object requires:

1. Runoff Coefficient
2. Tc > 0
3. Discharge Point

and you get a catchment outline.

[info6RUDZ]

That worked. Thanks a lot, @matt_anderson_pe and @Joe-Bouza 

[fcernst]

Are you getting the Catchment boundary vertices importing?

[info6RUDZ]

@fcernst no, since i only imported the pipe networks into SSA, the catchment was imported as a background. It would be great to know if there is a way to be able to directly import the catchment into SSA without having to go through intermediate processes.

[matt_anderson_pe]

Catchment boundaries will only be imported from LandXML parcels - a quirk of SSA from the BOSS days...  They dont add anything to the model beyond the graphic representation of Area.

[fcernst]

You can import and create subcatchments from GIS polygons and map the fields.. but we need SSA to bring in the Catchment vertices in one efficient operation all linked up and ready to go... for sharing SWMM *.inp files to other watershed study team members who expect the vertices to be in the SWMM *.inp file..

[matt_anderson_pe]

@fcernst-

True - but just like Parcels - it's a multi-step process from a Catchment object.

[fcernst]

Yes.. that’s what I’m saying..