XPSWMM Conversion Reconfigure SWMM Junctions Development

Update SWMM Nodes--Junctions Attributes

The following GIS feature updates to the Nodes--Junctions attributes will finalize the SWMM portion of the TUFLOW model. This is typically the final step in the model building process, as the recommended attributes for a junction node vary depending on whether the node is associated with inlet usage connections, 1D/2D culvert connections, and SWMM hydrology sub-catchments.

The recommended configuration for TUFLOW-SWMM junctions uses ponding everywhere and allows SWMM to pond as soon as the water level reaches the highest obvert (ceiling) of the connected conduits. However, this configuration may produce different results compared to the source XPSWMM model especially for deeply buried pipe networks.

The decision to use XPSWMM compatible attributes, or the recommended attributes, should be determined based on how strictly the results need to match previous results and may require client consultation. It is generally recommended to run both configurations to compare between them and the XPSWMM results.

For a summary of the attributes associated with the Nodes--Junctions layer, refer to TUFLOW 2023-03-AD Release Notes (Table A.30) and the SWMM Reference Manual - Volume 2 (Hydraulics).

Nodes--Junctions Attributes XPSWMM Compatible Options

The XPSWMM compatible options leave the maximum depth (Ymax) set by the XPSWMM model which uses the inlet elevation minus the node invert elevation. This approach represents little to no storage between the top of the adjacent conduits and the inlet (ground elevation), which may lead to instabilities. The instabilities may not be identified unless you adjust the output interval to be very small (approx. 5 seconds), but such oscillations can lead to mass errors, and errors in the hydraulic results.

To update the Nodes--Junctions attributes:

1. In the QGIS Layers panel, select (left click) Nodes--Junctions.
2. In the Processing Toolbox, select the 'Edit Features In-Place' tool. This allows the editing of an existing layer, instead of the creation of a new layer.
3. Go to TUFLOW >> SWMM in the processing tool list and select the 'Junctions - Set attributes' processing tool. This opens the dialog shown below.

   • Input Subcatchment layers: If available, select Hydrology--Subcatchments.
   • Input Inlet Usage Layers: If available, select the inlet usage layer (e.g. swmm_iu_XP_001).
   • Input BC Connection Layers: If available, select the 2d_bc connection layer (e.g. 1D2D_Urban_001_2d_bc_L).
   • General Options:

   • Maximum Depth Option (Ymax): 'Leave as is (applies to edit in place only)'
   • Nodes receiving subcatchment flows option (if connected to 2D): 'Based on options selected below'

   • Nodes connected to 2D without Inlets (through embankment culvert):

   • Leave both parameters as the default. These nodes were converted to storage nodes.

   • Nodes connected to 2D with Inlets (underground pipe network):

   • Maximum depth (Ymax) option: 'Use global option'. This will maintain the settings from XPSWMM.
   • Ysur: 0
   • Area of ponding: This value should match the 2D cell area associated with the Inlet Usage connections (25 in the example model).

   • Nodes without 2D Connection (underground pipe network):

   • Surcharge Depth: This value should be a value higher than any expected water level in the model (99 in the example model).
   • Area of ponding: 0

4. Select 'Modify All Features'. Once the tool has finished, click 'Close'.
5. Turn off editing to save the edits.
6. View the attributes within Nodes--Junctions to verify the data processing has been completed correctly.
   
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Nodes--Junctions Attributes Recommended Options

The recommended junction attributes use a maximum depth (Ymax) of 0.0 for all nodes. Ponding is recommended at all nodes connected to the 2D domain. For nodes not connected to the 2D domain, ponding, or the use of a high-surcharge value are both valid options. Setting Ymax to 0.0 and allowing ponding for nodes connected to the 2D domain, ensures storage is represented between the top of adjacent pipes to the ground elevation which greatly stabilizes model simulations and allows water levels in the node between those elevations.

To update the Nodes--Junctions attributes:

1. In the QGIS Layers panel, select (left click) Nodes--Junctions.
2. In the Processing Toolbox, select the 'Edit Features In-Place' tool. This allows the editing of an existing layer, instead of the creation of a new layer.
3. Go to TUFLOW >> SWMM in the processing tool list and select the 'Junctions - Set attributes' processing tool. This opens the dialog shown below.

   • Input Subcatchment layers: Not needed because the attributes will not be dependent on whether this connection exists.
   • Input Inlet Usage Layers: If available, select the inlet usage layer (e.g. swmm_iu_XP_001).
   • Input BC Connection Layers: If available, select the 2d_bc connection layer (e.g. 1D2D_Urban_001_2d_bc_L).
   • General Options:

   • Maximum Depth Option (Ymax): 'Set to 0'
   • Nodes receiving subcatchment flows option (if connected to 2D): 'Based on options selected below'

   • Nodes connected to 2D without Inlets (through embankment culvert):

   • Leave as-is (all of these were converted to storage nodes)

   • Nodes connected to 2D with Inlets (underground pipe network):

   • Maximum depth (Ymax) option: 'Use global option'
   • Ysur: 0
   • Area of ponding: This value should match the 2D cell area associated with the Inlet Usage connections (25 in the example model).

   • Nodes without 2D Connection (underground pipe network):

   • Surcharge Depth: This value should be a value higher than any expected water level in the model (99 in the example model).
   • Area of ponding: 0

4. Select 'Modify All Features'. Once the tool has finished, click 'Close'.
5. Turn off editing to save the edits.
6. View the attributes within Nodes--Junctions to verify the data processing has been completed correctly.
   
   

   
   

Save the QGIS Workspace

In preparation for the next steps of the conversion process, ensure your QGIS workspace has been saved.

1. In QGIS, go to Project > Save from the top dropdown menu options.

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