Simulating a Blocked Pipe in SWMM5

Simulating a Blocked Pipe in SWMM5

Simulate a blocked pipe in SWMM 5 using a time-dependent control rule and an orifice. 

Method: Using a Control Rule and an Orifice

1. Represent the Pipe with an Orifice:

   • Purpose: Orifices in SWMM 5 can be dynamically controlled, making them suitable for simulating a blockage that occurs during the simulation.
   • Shape: Choose an orifice shape (circular or rectangular) that corresponds to the shape of the pipe you want to simulate as blocked.
   • Size: Set the orifice dimensions (diameter for circular, or width and height for rectangular) to be equivalent to the pipe's dimensions. This ensures that the flow capacity is similar when the orifice is fully open.
   • Location: Place the orifice in the model at the location where you want to simulate the blockage. You will likely need to divide the existing pipe into two links with a new node, and place the orifice at that new node.

2. Create a Time-Dependent Control Rule:

   • Purpose: To close the orifice at a specific time during the simulation, simulating the blockage.
   • Structure:

     RULE Blockage
     IF SIMULATION TIME > [Time of Blockage]
     THEN ORIFICE [Orifice ID] SETTING = 0
     PRIORITY [Priority Number]
     

     • RULE Blockage: Defines the name of the rule.
     • IF SIMULATION TIME > [Time of Blockage]: This is the condition. Replace [Time of Blockage] with the simulation time (in hours or minutes, depending on your model's time units) at which you want the blockage to occur.
     • THEN ORIFICE [Orifice ID] SETTING = 0: This is the action. It sets the orifice's SETTING to 0, effectively closing it completely. Replace [Orifice ID] with the ID of your orifice.
     • PRIORITY [Priority Number]: Assigns a priority to the rule (lower numbers have higher priority).

Example:

Let's say you want to simulate a blockage in pipe P-10 at 2 hours into the simulation. You would:

1. Split P-10 into two links (e.g., P-10A and P-10B) by adding a new junction node.
2. Add a circular orifice (e.g., O-10) at the new junction node, with a diameter equal to the diameter of P-10.
3. Create the following control rule:

RULE Blockage_P10
IF SIMULATION TIME > 2.0
THEN ORIFICE O-10 SETTING = 0
PRIORITY 1

Advantages of this Method:

• Simplicity: It's relatively straightforward to implement using SWMM 5's built-in features.
• Flexibility: You can easily adjust the time of blockage by modifying the control rule.
• Dynamic Control: The use of an orifice allows for more complex blockage scenarios if needed (e.g., partial blockage, gradual blockage).

Additional Considerations:

• Partial Blockage: You can simulate a partial blockage by setting the orifice SETTING to a value between 0 and 1, representing the fraction of the orifice that remains open.
• Gradual Blockage: You can simulate a gradual blockage by creating multiple rules that progressively reduce the orifice SETTING over time.
• Blockage Removal: You can simulate the removal of a blockage by adding another rule that reopens the orifice at a later time. For example:

RULE Unblock_P10
IF SIMULATION TIME > 4.0
THEN ORIFICE O-10 SETTING = 1
PRIORITY 1

• Upstream and Downstream Effects: Carefully consider the potential impacts of the blockage on the upstream and downstream portions of the network. A blockage will likely cause water to back up upstream, potentially leading to flooding or overflows.
• Alternative Blockage Representations:
  • Closed Conduit: You could also simulate a blockage by changing the conduit's status to "Closed" using a control rule. However, using an orifice provides more flexibility for partial or gradual blockages.
  • Pump with Time Series: In InfoSWMM you can use a pump with an on/off time series to simulate the blockage.

Conclusion:

Using a time-dependent control rule and an orifice is an effective and versatile method for simulating a blocked pipe in SWMM 5. It allows for dynamic control over the blockage, enabling you to model various blockage scenarios and analyze their impacts on the hydraulic system. Remember to carefully consider the upstream and downstream effects of the blockage and choose the method that best suits your specific modeling needs.

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.