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.