How to resolve the "ERROR 141: Outfall has more than 1 inlet link or an outlet link" issue in SWMM 5

How to resolve the "ERROR 141: Outfall has more than 1 inlet link or an outlet link" issue in SWMM 5 

,,,by converting an internal outfall to an external one. Here's a breakdown of the steps, along with some elaborations and considerations:

Understanding the Problem

• Outfall Definition: In SWMM 5 and InfoSWMM, an outfall node is defined as the terminal point of the drainage system. It represents the discharge location to a receiving water body (e.g., river, lake, ocean) or the end of the modeled system.
• Error 141: This error indicates that an outfall node has been incorrectly defined within the network, having more than one incoming link or an outgoing link, which violates the definition of an outfall.

Solution: Converting the Internal Outfall

The solution involves converting the incorrectly defined internal outfall into a regular junction and creating a new, properly defined external outfall downstream.

Steps:

Step 1: Identify the Problem

• Error Message: The error message "ERROR 141: Outfall [Outfall Name] has more than 1 inlet link or an outlet link" clearly identifies the problematic outfall node.
• Model Inspection: Visually inspect the model to confirm the outfall's location and connections.

Step 2: Make a new outfall.

• Location: Create a new node just downstream of the existing (problematic) outfall node. This new node will be your external outfall.
• Tool: Use the "Add Node" or equivalent tool in your SWMM 5 or InfoSWMM interface, and select "Outfall" as the node type.

Step 3: Make the new Outfall have the same invert as the old outfall

• Purpose: To maintain the same hydraulic grade line elevation at the transition.
• How:
  • Note the invert elevation of the original (internal) outfall.
  • Edit the properties of the new outfall node and set its invert elevation to the same value.

Step 4: Convert the older outfall to a Junction using the Pick Axe and the Convert Type tool

• Purpose: To change the internal outfall into a regular node that can have multiple connections.
• Tool: Most software packages have a "Convert Node Type" or similar tool. In InfoSWMM it looks like a Pick Axe.
• Process: Select the original outfall node and use the tool to change its type from "Outfall" to "Junction."

Step 5: Make a new Link connecting the old and the new Outfall

• Purpose: To create a conduit connecting the former outfall (now a junction) to the new external outfall.
• Tool: Use the "Add Link" or equivalent tool.
• Connection: Connect the link from the newly created junction (the old outfall) to the new outfall node.

Step 6: Convert the new Link to an Outlet Type using the Convert Type Tool.

• Purpose: To define the new link as an outlet link, which will allow flow to pass from the junction to the outfall and will model the losses in the new outfall link.
• Tool: Use the "Convert Link Type" or similar tool. In InfoSWMM it is also the Pick Axe tool.
• Process: Select the newly created link and use the tool to change its type to "Outlet."

Step 7: Set up the parameters for the new Outlet Link

• Parameters:
  • Inlet Offset: The elevation difference between the upstream end of the outlet link and the invert of the upstream node (the junction). Set this to be consistent with the elevation of the outlet pipe in the original model.
  • Outlet Offset: The elevation difference between the downstream end of the outlet link and the invert of the downstream node (the outfall). Set this to zero unless there is a reason to have the outlet not at the bottom of the outfall.
  • Flap Gate: Specify whether a flap gate is present (to prevent backflow). Usually, this will be set to "Yes" for an outfall.
  • Outlet Table/Curve: If the outlet's discharge is controlled by a rating curve (e.g., a weir or orifice), you'll need to define the curve. Otherwise, it can often be left blank for a free outfall.
  • Length: You should use a short but positive length for the new Outlet Link.

Step 8: For those outfalls that DO have more than one link you need to make a new Outfall.

• Repeat: Repeat steps 2-7 for any other outfalls in your model that have more than one incoming link or an outgoing link.

Step 9: Run the model.

• Verification: Run the model and check for errors. If the error is resolved and the model runs without further issues, you've successfully converted the internal outfall.
• Results: Analyze the results to ensure the flow is being routed correctly through the new outlet link and outfall.

Important Considerations:

• Hydraulic Equivalence: Ensure the new outlet link and outfall configuration accurately represent the hydraulic behavior of the original, incorrectly defined outfall. If the original outfall had a specific rating curve or control structure, you'll need to replicate that behavior using the outlet link's parameters or a control rule.
• Model Complexity: In complex models, be careful when making changes to the network topology. It's always a good idea to save a backup copy of your model before making significant modifications.
• Node IDs: When you convert node types, the software might automatically assign new IDs. Keep track of these changes, especially if you have control rules or other elements that refer to specific node IDs.
• Outfall Boundary Condition: Make sure the new external outfall has an appropriate boundary condition defined (e.g., free outfall, fixed stage, tidal curve).

.Step 1: Identify the Problem

Step 2:  Make a new outfall.

Step 3:  Make the new Outfall  have the same invert as the old outfall

Step 4:  Convert the older outfall  to a Junction using the Pick Axe and the Convert Type tool

 Step 5:  Make a new Link connecting the old and the new Outfall

 Step 6:  Convert the new Link to an  Outlet Type using the Convert Type Tool.

 Step 7:  Set up the parameters for the new Outlet Link

Step 8:  For those outfalls that DO have more than one link you need to make a new Outfall.

You should be able to run the model now.