What are the limitations of importing/exporting SWMM5 files?


Product(s): CivilStorm, SewerGEMS
Version(s): 08.11.XX.XX and higher
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.

In general, you can import a SWMM INP file from File > Import > SWMM 5, and you can export to the SWMM 5 INP format from File > Export > SWMM.

When an import/export is performed with SWMM5 INP 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 (EPA) is useful for ensuring SWMM Solver results for your model are fully compatible with EPA-SWMM itself. See more information in this article.

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

One other thing that happens when importing SWMM files is that two extra pipes are added for every directed node (ex: pumps).  This is because such elements are treated as link (line) elements in SWMM but nodes (points) in SewerGEMS/CivilStorm.  They are labeled as something similar to "was added during SWMM import", so that 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.

A General Note on Importing SWMM Files Originating from other Modeling Software

Please see the following article for recommendations and troubleshooting issues with importing SWMM INP files that had been exported to INP from another modeling software such as Innovyze/InfoSWMM. You may need to open the file in EPA-SWMM and re-save to INP format as we have found many other modeling software do not properly adhere to SWMM's expected format and the re-save operation will essentially "clean" the file and yield a more successful import into SewerGEMS or CivilStorm.

See: Troubleshooting problems with importing EPANET or EPASWMM files

Special Considerations

Units

EPA-SWMM itself only support limited units based on a selection of "flow unit", so when the model is exporter to SWMM INP, the values for things like length, demand, etc will be converted to a supported units based on the flow unit. For example if the model coordinate or length unit is US Survey Feet, the values will be converted to regular feet on export.

See the SWMM help documentation section "Units of Measurement"

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

Catchbasins that have capture limitations, like maximum capacity, curves or defined by catalog, will be considered as full capture in SWMM5.Catchbasins in the SewerGEMS/CivilStorm model will be exported as Junction nodes in the INP file.

Although HEC-22 inlet capture calculations are supported starting with EPA-SWMM 5.2, SewerGEMS and CivilStorm do not yet support exporting to SWMM 5.2 format, so any catalog inlet information in the SewerGEMS/CivilStorm model will not be exported to SWMM. (as of version 10.03.04.53 -future versions may add support - reference # 869595).

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.

Control Curves

In EPA-SWMM, a model can use a special type of rating curve called a Control Curve. Starting in SewerGEMS and CivilStorm version 10.04.00.158, this is now supported. In EPA-SWMM these are used with pumps, and flow regulators like orifices and weirs. A relationship between the control setting and the controller variable can be specified by using a Control Curve, a Time Series, or a PID Controller. For example for a weir:

RULE MC1
IF NODE N2 DEPTH >= 0
THEN WEIR W25 SETTING = CURVE C25

Or for a pump:

RULE LS034_P1
IF NODE MH034 DEPTH >= 4.000000
THEN PUMP PMP1 SETTING = CURVE VFD_TYPICAL

For a pump, the control curve can be used to simulate a variable speed pump by adjusting the pump outflow flow using the "control setting" multiplier corresponding to the current wet well depth (Controller Value). In older versions of SewerGEMS and CivilStorm, you would need to approximate this type of pump using a Type 4 (depth vs flow, simulated variable speed) pump curve type, or use the built-in variable speed pump functionality with the GVF-Convex solver.

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