Modelling pollutant concentration at a node

You can set a time varying pollutant concentration inflow at individual nodes when modelling a water quality event, using a series of date-time / inflow concentration pairs.

Note: There are no water quality controls for hydrant nodes. Hydrant nodes are output-only nodes.

To model pollutant concentration at a node:

1. Open the property sheet for the appropriate node and choose the Water Quality Profile page.

   If the Water Quality Profile page is not visible, you may have to add control parameters for the node. To do this, click the Add Control button

2. Select the Source Type to be used.

   The source type determines the method by which the profile defined in the Water Quality grid is applied to the network during the simulation.

• Fixed Concentration: Concentration profile is applied at the node. For reservoir nodes, concentration profile is applied to water entering the reservoir.

  Tip: Use a concentration value of < 0 in the profile to switch off the concentration source and allow inflow from upstream pipes to set concentration at the node.

• Additional Concentration: Concentration profile is applied to water leaving the node in addition to the calculated concentration.
• Concentration Booster: Concentration at the node is set to the defined profile (provided that the concentration calculated during the simulation is less than the defined concentration).
• Additional Mass Flow: Mass Flow profile is applied to water leaving the node in addition to the calculated concentration.
3. Enter the time varying profile for the inflow pollutant concentration using the grid.

   To do this, enter a series of dates and times in the Date Time column. For each one, set the pollutant concentration / mass flow in the Concentration / Mass Flow column.

4. Check the Linear WQ Profile box for linear interpolation to be used between data points.

   If this box is unchecked, each transfer volume entered is maintained until the next date / time entry, or until the end of the simulation.

5. Select an option for extending the profile before the first time defined in the grid:
• Extend Back - The first value in the grid is extended back to the start of the simulation.
• Extrapolate Back -  Applies to Linear Profiles only: the first two values in the grid are used to extrapolate back to the start of the simulation.

  Note: If Extrapolate Back is selected for a non linear profile, the profile will be extended back.

• Zero/Unchanged - A value of zero or "off" is applied from the start of the simulation until the date / time of the first value in the grid.
6. Select an option for extending the profile after the last time defined in the grid:
• Extend Forward - The last value in the grid is extended to the end of the simulation.
• Extrapolate Forward - Applies to Linear Profiles only: the last two values in the grid are used to extrapolate forward to the end of the simulation.

  Note: If Extrapolate Forward is selected for a non linear profile, the profile will be extended forward.

7. Check the Repeat Profiles box to repeat the first 24 hours of the defined profile for the duration of the simulation.

The Initial Concentration is the concentration of pollutant present at the node at the start of the simulation.