TUFLOW SWMM FAQ Draft

Why would someone want to convert existing models from XPSWMM to TUFLOW-SWMM and how hard is it?

TUFLOW-SWMM is a natural choice for migrating existing XPSWMM models. It uses the same 2D engine with SGS and Quadtree and a newer version of the same 1D engine, so generally results should be nearly identical when converted. There may need to be some setup changes that will lead to some differences in results. There are tools to convert existing models that do most of the work during a conversion so it is quite easy. Uncommonly used features may require manual editing. Reach out to support@tuflow.com for assistance.

Does TUFLOW-SWMM require a separate licence?

TUFLOW-SWMM doesn't need separate licence module. It is included in the standard TUFLOW engine licence.

How can I review SWMM results?

The SWMM results can be viewed in the QGIS TUFLOW Viewer in the same way as ESTRY results. Working with the results in the Viewer plot window is no different to ESTRY. SWMM does include some cool Map Window auto scaling display features that ESTRY doesn't.

=Can XP models be converted to TUFLOW-SWMM without an XP licence? XP models can be converted using XPVIEWER to XPX which can import to the TUFLOW-SWMM GPKG format.

Does the GPKG SWMM tools convert all SWMM data?

Everything from the SWMM inp file gets converted except for pollutants and pollutant related information.

Can we use the TUFLOW plugin to work with SWMM data without using TUFLOW?

Yes, of course that is fine. Let us know if you find the plugin useful or give it stars in the plugin repository.

Could TUFLOW-SWMM model be viewed in ArcGIS?

If you want to look at the data in ArcGIS Pro, you could do the convert to/from GeoPackage using QGIS and then work with the data in ArcGIS Pro. This wouldn't be as seamless because you would probably need to close the GeoPackage in QGIS while working in ArcGIS Pro but a workaround until a direct connection is available.

With the ability to work with the files in GIS, is there ever a reason to use the EPA SWMM GUI?

Yes. Rather than think about using the plugin tools or the EPA SWMM GUI, think about how to use the plugin tools and the EPA SWMM GUI. Some features such as Low-Impact-Developments are easier to edit in the EPA SWMM GUI than in GIS tables. Because the systems are interchangeable using SWMM inp files, you can leverage the benefits of both systems.

PCSWMM uses SWMM by itself to run 1D/2D urban drainage models. How is this different from what TUFLOW-SWMM is doing?

Our understanding is it represents the overland flow that it is running the SWMM engine using a lattice of 1D cells in multiple directions. If you look at the 1D SWMM equations and the 2D equations used by TUFLOW, you can see that the 2D equations include additional parameters for things like turbulence and some components in the x direction affect the y direction (and the reverse). Because of this, running a 1D model in multiple directions is not the same as running a full 2D model. Depending on the situation the results may be similar. SWMM is also not optimized to be a 2D solver. I was given a SWMM based 1D and overland flow model that took hours to run. I converted the model to TUFLOW-SWMM with similar resolution and it ran in under 10 minutes. Running both on my laptop.

How would you get data from a non-SWMM GIS format into the SWMM GPKG format?

The plugin can help with converting this data by creating the template for the input layers. You would create the SWMM GPKG file using the plugin tools. You would need to do some data translations to convert the attribute data into the correct fields. Reach out to support@tuflow.com if you need advice on how best to do this.

Do the results generated by the SWMM engine differ much from the ESTRY engine?

Various engines will never produce identical results; however, we would hope that results are generally similar. It will depend a little on the features in the model, for example manhole losses might be treated differently between SWMM and ESTRY / TUFLOW 1D.
With regards to SWMM usage for flood assessments in Australia. Typically, these would require a 2D model component - it is rare to see purely 1D models used for flood assessments in Australia. Therefore, I’m not sure about purely 1D EPA-SWMM models, but SWMM linked to a 2D, for example XP-SWMM then yes there would be occurrences of this.
SWMM does not have an approach specifically for manhole losses and does not support dynamic losses for inlet and exit losses like ESTRY. These are functionalities we would like to add to TUFLOW-SWMM models.
We had a model we converted from TUFLOW-ESTRY to TUFLOW-SWMM and was getting quite different results. However, the ESTRY input files (and therefore the converted SWMM files) used full inlet and outlet losses (0.5 and 1.0). However, because it adjusts these dynamically the applied losses were much lower. Once we used the average applied losses to SWMM, the results became very similar.