Tracer flow model (Water Overlay)

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Tracers can be modeled in the hydrological model, as quantities dissolved in water and transported by flowing water.


The tracer model can be activated and deactivated by adding or removing the appropriate attributes to one or more construction in the project area. If no constructions have attributes configured to interact with the quantities of tracers, then no tracers are created or transported.

Tracers are stored as an exact amount per grid cell, in three different layers: surface, unsaturated ground layer, and saturated ground layer.

The tracers are generically defined and do not have a set unit or magnitude. Furthermore, at most four different tracers can be added and followed.


Conceptually, tracers are added to and removed from the hydrological model by tracer emitters and decomposers. The tracers created are placed on the surface of the grid cells in which the emitters are present.


Tracers can also be decomposed by constructions, if their attributes are configured with a negative value. When tracers are present in a cell which contains a tracer decomposer, the tracers are consequently removed from the hydrological model.


When water moves from a cell which also contains tracers, the tracers are carried along with the water. The tracers are expected to be uniformly distributed within the water. In other words, calculations of tracer movement is done based on the concentration of that tracer in the amount of water that is moved.


  • Tracers can flow along with water into and across the surface, the unsaturated ground layer, and the saturated ground layer.
  • Tracers can flow through hydraulic structures, unless they remove water from the hydrological model entirely, or move it to a location other than the surface, the unsaturated ground layer, or the saturated ground layer. Specifically, tracers can flow through weirs, culverts, pumps, and breaches.
  • It is currently not possible to initialize grid cells with a specific amount for a tracer.
  • It is currently not possible to emit tracers directly into the unsaturated or saturated ground layers.
  • It is currently not possible to decompose tracers in the unsaturated or saturated ground layers.
  • It is currently not possible to let tracers flow into and out of the sewer.
  • Tracers can also be used as a tool to track water flow.

Related formulas

Related models