Simulate decaying pollutants

Simulate decaying pollutants

Step-by-step guide

Decaying determinants, or non-conservative determinants, are parameters with concentrations that change over time and distance due to both physical transport processes and chemical or biological reactions.

It is possible to model how non-conservative determinants behave in a water system:

  • Degradation over time
  • Reaction to substances

It is important to understand the various decay types and user-defined processes for modeling this behavior.

Non-conservative determinants exist in two primary forms:

  • Dissolved pollutant
  • Attached pollutant

Exceptions to this include parameters such as:

  • Dissolved oxygen
  • Salt
  • pH levels
  • Water temperature

Non-conservative pollutants can also react with other pollutants in the system.

Methods to model the decay of pollutants in InfoWorks ICM:

  • Linear decay: The pollutant decays at a constant rate.
  • Exponential concentration: The decay rate depends on pollutant concentration.
  • Exponential time: Uses a decay rate that is time-dependent.
  • Exponential both: Combines concentration and time factors.

A 'Decaying Pollutants' slide showing the four decay types and their formulas, with a key of variables for the formulas. There are also two images from the ICM interface where they can be found.

To simulate complex pollutant behaviors, custom processes can also be defined using specific equations and parameters. This allows for detailed customization to match real-world scenarios, including:

  • Growth
  • Growth-product
  • Equilibrium

A 'User Defined Processes' slide showing the three types of user-defined processes and their formulas, with a key of variables for the formulas. There are also two images from the ICM interface where they can be found.

To introduce pollutant interactions by using decaying determinants:

  1. Set up scenarios for the four decay options, as shown here in the Scenarios drop-down: Linear decay, Exponential concentration, Exponential time, and Exponential both.

The top-left corner of the ICM interface, with the Scenarios drop-down expanded and the four decay options highlighted in red.

  1. Review the options to define these scenarios. Select Model > Model Parameters > Water quality and sediment parameters.

The top-left corner of the ICM interface, with the Model and Model Parameters menus expanded and Water quality and sediment parameters being selected. All three are highlighted in blue.

  1. In Properties, next to Decaying pollutants, click More (…).

The top-left corner of the ICM interface, with the Properties panel open and the Decaying Pollutions options highlighted in red. The More button has been selected, and the Decaying Pollutants dialog is open to the right over the GeoPlan.

  1. In the Decaying pollutants dialog, in the list of Determinants, expand the Decay type drop-down to review the available types.

The Decaying pollutants dialog, showing a table of determinants, with the Decay type expanded to show all four decay types.

NOTE: For further customization, define the coefficient and equation to meet the needs of the specific scenario.

  1. In Properties, next to User defined processes, click More (…).

The top-left corner of the ICM interface, with the Properties panel open and the User defined process parameters options highlighted in red. The More button has been selected, and the Process Definitions dialog is open to the right over the GeoPlan.

  1. In the Process Definitions dialog, expand the Process type to access the available options: Growth, Growth-product, and Equilibrium.

The Process Definitions dialog, showing a table of definition headers, but no values filled in. Process type is expanded to show the options: Growth, Growth-product, and Equilibrium.

  1. Click OK.

Now, define the four scenarios:

  1. For the Linear decay scenario, open the Decaying pollutants dialog.
  2. Specify the Determinant PL1.
  3. Set the Decay type to Linear.
  4. Enter a Constant decay rate of 100.
  5. Click OK.

The Decaying pollutants dialog, showing a table of determinants, with the first row of cells filled in and the Decay type as Linear.

  1. For Exponential concentration, set the same Determinant and the corresponding Decay type.
  2. Set the Maximum decay rate to 2000.
  3. Set the Exponential decay rate to 0.1.
  4. Click OK.

The Decaying pollutants dialog, showing a table of determinants, with the first row of cells filled in and the Decay type as Exponential concentration.

  1. For Exponential time, set the Exponential decay constant to 10.

The Decaying pollutants dialog, showing a table of determinants, with the first row of cells filled in and the Decay type as Exponential time.

  1. For Exponential both, set the Maximum decay rate to 1000.
  2. Set the Exponential decay to 0.01.
  3. Set the Exponential decay constant to 10.

The Decaying pollutants dialog, showing a table of determinants, with the first row of cells filled in and the Decay type as Exponential both.

  1. Create a pollutograph by setting a value of 100 mg/l for determinant P1D, and then assign it to node 1_S. In this example, the pollutograph is already created:
  2. In the Explorer, right-click P1D and select Open.
  3. To confirm that the 1_S node is assigned, on the P1D tab, right-click one of the profiles and select Profile Properties.

The left side of the ICM interface, with the Browser, Properties panel, and pollutograph window all open. In the pollutograph table, one of the values has been right-clicked, and from the menu, Profile properties is highlighted with a red arrow as being selected.

  1. In the Pollutograph properties dialog, confirm the Object reference.
  2. Click Cancel.

The Pollutograph properties dialog for this example, showing a table of parameters and values. The Object reference parameter is at the top, with its value of 1_S highlighted in orange.

  1. Validate and commit the scenarios.
  2. From the Explorer, select the run to open the Run dialog, then expand it.
  3. If it is not already, drag and drop the P1D pollutograph into the Pollutograph field in the dialog.
  4. Select Use QM.
  5. Click QM Parameters.

The Run dialog, showing the decay pollutant run values for this example. The pollutograph P1D has been dropped into the Pollutograph box, which is highlighted in red. The Use QM option is enabled and also highlighted in red, and the QM parameters button is about to be clicked.

  1. In the QM Parameters dialog, ensure that PL1 is selected.

The QM parameters dialog, showing the table of pollutants and sediment fractions to model, with PL1 enabled in the Dissolved column and highlighted in red, and OK being selected.

  1. Back in the Run dialog, click Run simulations to run all four scenarios.
  2. Open the Linear decay scenario by selecting Results > Graph reports > Simulation report.

The top-left corner of the ICM interface, with the Results and Graph reports menus open and Simulation report being selected from the Graph reports flyout.

  1. From the Explorer, drag and drop the other three scenarios into the Simulations dialog to add them to the list.
  2. Under Selection List, select Current.
  3. Click Produce Graphs.

The Simulations dialog, with the four runs listed in the Sim/SWMM sim box, Current set as the Selection List, and Produce Graphs being selected.

  1. In the Parameter Selection dialog, select Concentration PL1 dissolved.
  2. Click OK.

The graph displays the results of the four decay types changing over time.

The ICM interface, with the Results Report tab open and showing the graphed results for the decaying pollutants run. The blue line shows the Linear decay, the green shows Exponential Both, the red line is for Exponential concentration, and the yellow is for Exponential Time.