How to add sewer data (Water Overlay)

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For some use cases, it may be important to include sewer functionality in the calculation. Sewers form additional storage for water, and can either store this water indefinitely, slowly remove the water from the hydrological model, or let the water flow in a controlled fashion back onto the surface. Sewers are most relevant for non-sudden excessive water scenarios, such as heavy rainfall.

For the purpose of this instruction, a simple hydrological model will be assumed. We will also assume there is an appropriate amount of water present in or added to the model for the sewer to function in a relevant capacity.


Before adding sewer data, make sure you have a basic water model set up. For the specified scenario, the rainfall overlay will suffice, though any variant will work.

Also ensure the following in your project, if possible:

  • The hydrological system has an excess of water in an urban area. This can be due to rain, inundation, or an inlet.
  • The excess of water is not too excessive, greatly exceeding the reasonable capacity of a potential sewer.
  • The simulation is set up to output a reasonable amount of timeframes. For most simulation durations, 25 to 50 timeframes will suffice.


How to add a sewer to a project:

  1. Configure a base hydrological system.
  2. If you have geo data for sewers, import your sewer area data. If you do not have geo data for sewers, generate sewer area data.
  3. If you have data for sewer overflows, import your sewer overflow data.
  4. Add the SEWER_LAST_VALUE result type to the overlay.
  5. The configuration wizard of the overlay can now be closed.
  6. Recalculate the overlay. The effects of the sewer should now be visible.
  7. Inspect the SEWER_LAST_VALUE results of the overlay. This result shows the amount of water in the sewer.


To see whether the generation or import of the sewer areas completed successfully, you can add a BASE_TYPES result type to the overlay. All cells which are classified as "Sewer" are deemed connected to a sewer. Water ending up on that cell flows into the sewer.

When generating sewer areas via the configuration wizard, the resulting sewer areas are automatically grouped under the SEWER_STORAGE Attribute Filter in the list of areas.

See also