How to model drainage (Water Overlay)

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When using the Water Overlay to calculate groundwater, the presence of drainages can have a strong impact on the results. Drainages can be modeled using the drainage Construction, and can be configured as either active drainages or passive drainages.

Drainages can be configured

Manually adding a drainage

Editor → Current Situation (Ribbon tab) → Buildings (Ribbon bar)

How to manually create drainages:

  1. Add a new underground Construction to the Project.
  2. Set the Construction's Function to either "Active Drainage" or "Passive Drainage".
  3. Draw the Construction in the 3D World in the location where the drainages are. Ensure the drainages are drawn only under solid land.
  4. Draw another polygon for the Construction in the water where the drainage drains into (without removing the section drawn previously). Ensure it is not drawn over the water's edge.
  5. Open the Water Overlay's Water Overlay Wizard, and continue to the step concerning drainages.
  6. Configure the drainage's attributes as desired.

Preparing and importing drainage data

Editor → Current Situation (Ribbon tab) → Overlays (Ribbon bar) → your Water Overlay (Left panel) → Configuration Wizard (Right panel)

How to prepare and load in drainage data:

  1. Ensure that each drainage has at least 2 polygons: one drawn only under land, and one drawn only in the waterway it should drain into. Ensure no individual polygon overlays with both land and water, or the water's edge.
  2. Ensure all Attributes pertaining to drainages are configured correctly.
  3. Export the data as GeoJSON.
  4. Open the Water Overlay's Water Overlay Wizard, and continue to the step concerning drainages.
  5. Opt to import new data, and import your drainages file.


  • Drainages function across their entire polygon. In real life, drainages are discrete tubes where water can actually flow freely. In between tubes, water actually still only flows with the speed the underground allows. To model this most accurately, the individual drainage tubes should be represented by individual polygons. However, although some detail may be lost by drawing the drainages as a complete and uninterrupted area, functionally the effect of sped up underground flow is still achieved.