Model dissolved oxygen

Step-by-step guide

Dissolved oxygen (DO) is one of the most common metrics in water quality:

  • Serves as a valuable indicator of river health, since all aquatic life depends on oxygen.
  • The levels of dissolved oxygen in water are influenced by its physical, chemical, and biochemical activities.

A graphical image of a shoreline, lake, and plants in the sun, with arrows demonstrating how oxygen is passed naturally from plants to the air and water through photosynthesis.

  • Oxygen only has solubility in water when it is in equilibrium with air. The saturation value, influenced by temperature (T) and salinity (S), represents the maximum amount of oxygen that can dissolve in water.
  • Oxygen levels in water stabilize based on the surrounding oxygen solubility.

In the absence of a pollutograph profile, saturated DO will be derived from the constant temperature and salinity (salt parameters > Constant Concentration (kg/m³)) values defined in the water quality parameters.

This equation allows for the modeling of dissolved oxygen in a water system:

  • Yields the saturated dissolved oxygen concentration value, or DOS.
  • Applied in ICM by defining the constant salinity and constant temperature values within the Water quality and sediment parameters.

The equation that can be used to calculate dissolved oxygen in the absence of a pollutograph profile.

Dissolved oxygen example scenarios:

  • The first scenario, with a temperature of 20 degrees Celsius and a salinity of 0, yielded a dissolved oxygen saturated value of 0.0093 kilograms per cubic meter.
  • In the second scenario, a temperature of 20 and a salinity of 20 resulted in a DOS of 0.0083 kilograms per cubic meter.
  • And in the third scenario, a temperature of 35 degrees and a salinity of 0 resulted in a DOS of 0.0073 kilograms per cubic meter.

A graphic of the three scenarios that will be studied in this example, colored green, orange, and purple, respectively; as well as a graph of oxygen solubility in water, with dissolved oxygen on the X axis and temperature on the Y axis.

These results demonstrate that dissolved oxygen decreases when the temperature increases. It also shows that the DOS decreases as the salinity increases.

In ICM, to model dissolved oxygen as a function of temperature and salinity in a one-dimensional river:

  1. In the toolbar, expand Scenarios. (Three scenarios are already created for this example.)
  2. Select the Base scenario.

The InfoWorks ICM interface, with the Scenarios drop-down expanded and Base being selected from the highlighted list.

  1. To review the salinity and temperature parameters, navigate to Model > Model parameters > Water quality and sediment parameters.

The top-left corner of the InfoWorks ICM interface, with the Model menu expanded, the Model parameters flyout open, and Water quality and sediment parameters being selected.

  1. In the Object Properties, under Temperature parameters, set the Constant temperature to 20.
  2. Under Salt parameters, set the Constant concentration to 0.

The Properties panel open, with the Salt parameters and Temperature parameters highlighted with a red box.

This creates the first scenario.

  1. Follow the same steps to create the remaining two scenarios, naming them appropriately.
  2. With the three scenarios created, open the Run dialog.

Note that an inflow hydrograph is being used.

  1. Specify the water quality option by ensuring that the Use QM option is enabled.
  2. Click QM parameters.

The Run dialog, with the three scenarios highlighted on the left, the Inflow highlighted in the middle, and the Use QM option highlighted on the right, all in red boxes. The QM parameters button is also highlighted as being selected.

A list of pollutants displays in the QM Parameters dialog.

  1. Select the appropriate pollutants, such as DO, BOD, COD, NO2, NO3, SAL, and TW.
  2. Click OK.

The QM Parameters dialog, with three red boxes highlighting the list of pollutants chosen for this example, including DO, BOD, COD, NO2, NO3, SAL, and TW.

  1. Back in the Run dialog, click Run simulations.
  2. In the Schedule Jobs dialog, confirm that all information is correct for the simulations, and then click OK.

The Run parameters dialog, with the Run simulations button highlighted and the Schedule Job(s) dialog open in front of it.

Once the simulations are complete, analyze the results; focus on dissolved oxygen profiles along the river reach to observe the effects of water solubility on DO concentration.

To plot all three scenarios on a single graph:

  1. Select the river reach.
  2. Navigate to Results > Graph reports > Simulation report.

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

  1. Drag the three scenarios from the Explorer into the Simulations dialog.
  2. Specify the object to be graphed, such as the river reach. Here, Current is selected to include the currently selected object.
  3. Click Produce Graphs.

The top-left corner of the InfoWorks ICM interface, with the Database on the left and the Simulations dialog opened on the right. A red dotted arrow is indicating that the three scenarios have been dragged and dropped into the Sim/SWMM box, and Produce Graphs is highlighted as being selected.

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

The Parameter Selection dialog, showing that the Concentration DO dissolved option has been activated in the Parameters list; the OK button is being selected.

  1. Close the Simulations dialog, if it is still open.

In the graph, the results show that dissolved oxygen decreases as temperature increases. For instance, at 20 degrees Celsius and 0 salinity, DO remains constant at 0.0093 kilograms per cubic meter; and at 35 degrees and 0 salinity, DO is 0.0073 kilograms per cubic meter.

The resulting graph of Concentration DO dissolved, showing that the dissolved oxygen remained constant in all three scenarios.

To reproduce the dissolved oxygen profile using a pollutograph:

  1. In the Explorer, right-click Pollutograph_T, which was created previously, and select Open As.
  2. In the Select Format dialog, select Graph.
  3. Click OK.

In the Database, the context menu for the Pollutograph is expanded and Open As is selected, with a dotted red arrow connecting it to the resulting Select Format dialog, in which the Graph option is being selected.

Set the temperature to vary over time while keeping salinity constant at 20 kilograms per cubic meter. This is done by editing the TW tab within the pollutograph.

  1. Open the Run dialog.
  2. Select Use QM.
  3. Click QM parameters.

The InfoWorks ICM interface, showing the Run dialog for the third scenario set up, with the Use QM option highlighted in a red box.

  1. In the QM Parameters dialog, select the same list of pollutants used previously.
  2. Click OK.

The QM Parameters dialog, showing the same pollutant options selected for the simulation.

  1. Back in the Run dialog, click Run simulations.
  2. Confirm the information in the Schedule Jobs dialog, and then click OK.

The Run Parameters dialog, with the Run simulations button highlighted and the Schedule Job(s) dialog open in front of it.

  1. On the Results toolbar, click Graph.
  2. In the Graph dialog, select Concentration DO dissolved (kg/m³).
  3. Click OK.

The top-left corner of the InfoWorks ICM interface, with the Graph tool highlighted and a red dotted arrow connecting it to the open Graph dialog, where the Concentration DO dissolved (kg/m3) option is selected and highlighted.

The result illustrates how dissolved oxygen decreases as the temperature increases from 20 to 35 degrees Celsius.

The final resulting graph, illustrating how dissolved oxygen decreases as the temperature increases from 20 to 35 degrees Celsius.