What are the limitations of importing/exporting SWMM5 files?

Product(s): CivilStorm, SewerGEMS
Version(s): 10.XX.XX.XX, 08.11.XX.XX
Area:  Layout and Data Input

Introduction

This article explains the limitations you need to be aware of when importing or exporting EPA SWMM5 INP format.

When an import/export is performed with SWMM5 files the only data that will be retained or unaltered is the data that is supported in both SWMM INP format and CivilStorm or SewerGEMS.

Once constructing models that are intended to be exported to SWMM to be used in other platforms, CivilStorm and SewerGEMS starting with version 10.02.00.55, have an option (in the Calculation Options) to choose the Explicit solver compatibility between two options: SWMM (Bentley 5.1.013) and SWMM (EPA 5.1.013). The second one is useful to ensure SWMM Solver results for your model are fully compatible with EPA-SWMM itself. See more information in this article.

Items in CivilStorm and SewerGEMS that are NOT supported in SWMM 5

  • Sanitary loads collection items (use inflow collection items)
  • Rainfall curves not applicable to the SWMM Runoff Hydrology calculation
  • Continuous patterns
  • User data Extensions
  • Energy costs
  • All presentation settings
  • All ModelBuilder, LoadBuilder, Darwin, TRex settings
  • Pump curves (SWMM exporter generates a CURVE. However such curves are always imported back - during round-trips - as multi-point pump definition. So, if the original pump-definition was a 1-point or 3-point curve the round-trip may not come back to the exact original pump definition type.)
  • Unit Demands
  • Selection Sets
  • Queries
  • Graphs
  • Profiles
  • Tap/Laterals (see adaption below)
  • Headwalls (see adaption below)
  • Node head loss calculation
  • H2S calculation
  • Tractive Stress calculation
  • Scenarios and Alternatives - SWMM does not support scenarios. So, when exporting to SWMM ensure that you have the correct scenario set to current before exporting. See more details in this article.

One other thing that happens when importing SWMM files is that two extra pipes are added for every directed node (ex: pumps).  They are labeled as something similar to "was added during SWMM import".  So when the CivilStorm or SewerGEMS model is exported back to SWMM those extra pipes are removed and the original directed node is rebuilt without the extra pipes.

Modelling adaption considerations

Catchment Polygon Export

CivilStorm or SewerGEMS models that have Catchment polygons that apply the EPA-SWMM Runoff as Runoff Method will have the geometry exported. Catchments that uses other Runoff calculation methods will be converted into Hydrographs ( Time Series) applied to the outflow element.

Ponds and Pond outlet structures with control structures Export

Exported pond polygons will be represented by the Storage Unit SWMM element. Pond Outlet elements that have control structures (Weir, Orifices, etc) are loaded as a single outlet rating curve assuming free outfall.

 

Channels and Gutters

Since SWMM doesn´t directly support channel elements, this kind of element will be exported as conduit links in SWMM. Non-prismatic channels are converted to SWMM style prismatic channels.

While exporting open channels in CiivlStorm and SewerGEMS, its export sets the shape of the SWMM channel based on the start cross section if it exists, otherwise the stop cross section is used.

Catch Basins

Catch Basins that have capture limitation, like maximum capacity, curves or defined by catalog, will be considered as full capture in SWMM5.

Culverts and Headwalls

When modeling a culvert in CivilStorm or SewerGEMS, the SWMM format uses a culvert code for its hydraulic modeling that is applied to each link. CivilStorm and SewerGEMS manage these codes in the Culvert Catalog as follows:

This code is applied to represent the structures at the upstream and downstream edges of the culvert. This code can be referenced to both culvert to headwall elements in CivilStorm or SewerGEMS. After exporting to SWMM, this code is always referenced to the link.

Headwalls are exported to nodes, and if your model has nodes with different Culvert codes, and SWMM only support one code per link, the upstream’ s node code will be used.

Pressure Junctions

Pressure junctions are treated as manholes with a high surcharge depth.

Pumps

Pumps are seen as link elements in SWMM, whereas CivilStorm and SewerGEMS see them as nodes. Therefore, on export to SWMM, a new link element must be created to use as the pump. To do that, two overlapping junctions are created to connect to it. The link in SWMM will have the same name as the pump did in CivilStorm or SewerGEMS. In SWMM, an icon will display for the pump, but when trying to double-click on it, the junction could be selected by mistake.

For Example, take a look the following pump in CivilStorm/SewerGEMS:

 

Here's what it looks like after exporting to and opening in SWMM

A pump’s upstream conduit is considered virtual after exporting to SWMM.

Property Connections, laterals and Taps

Property Connections elements are converted into Junctions, keeping the base load value. Lateral and taps elements are replaced by a link element, connecting the junctions to the connected conduit’s upstream node.

This is an example of two Property Connection elements modeled in CivilStorm/SewerGEMS:

 

And the picture below shows the Export result in SWMM:

Low Impact Development (LID) Control Structures

CivilStorm and SewerGEMS models LID Controls as polygon elements that are referenced to Catchments and to nodes as underdrains. When exporting to SWMM5, LID polygons will be deleted and modeled embedded in the Catchment polygon, working as designed in SWMM.

See Also:

EPA-SWMM Solver Versions Used by SewerGEMS and CivilStorm

Catchments Are Missing After Exporting to EPA SWMM

Recommended
Related