Substance flow model (Water Overlay)

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


The substance 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 substances, then no substances are created or transported.

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

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


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


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


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


  • Substances can flow along with water into and across the surface, the unsaturated underground, and the saturated underground.
  • Water 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 underground, or the saturated underground. Specifically, water can flow through weirs, culverts, pumps, and breaches.
  • It is currently not possible to initialize grid cells with a specific amount for a substance.
  • It is currently not possible to emit substances directly into the unsaturated or saturated underground.
  • It is currently not possible to decompose substances in the unsaturated or saturated underground.
  • It is currently not possible to let substances flow into and out of the sewer.
  • Substances can also be used as a tool to track water flow.

Related formulas

Related models