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Nil Constituent - SRG

The Nil Constituent model is the default option for constituent generation in Source. It used as a substitute constituent generation model where no constituent load needs to be modelled for a given constituent from a given functional unit (FU).


The Nil Constituent model operates at the functional unit scale at the time-step of the main model.

Principal developer

eWater CRC

Scientific Provenance

The Nil Constituent model is typically applied to functional units that generate only minimal, or zero, amounts of some constituent; or in cases where the constituent load is accounted in some other process, such as being directly applied at a node in the stream network. One example is modelling point sources of nutrients in a model that also includes sediment. In this case, the point source can include a Nil Constituent model for sediment.


Source v2.10


Applies to catchment models built in Source.


Nil Constituent is automatically installed with Source.

Flow phase

This model sets the constituent load at a time-step to 0.

Input data

This model has no input data or parameters. In choosing to apply the Nil Constituent model, the modeller is assumed to have a basis to believe that the given functional unit is not a source of the constituent in question.

Output data

This model sets the constituent output of the target functional unit and, through this, influences the constituent output of the sub-catchment and the downstream node. These influences can be seen by recording constituent output at the functional unit, the surrounding catchment or any point downstream.

Choosing Nil Constituent generation will always result in a time series output of 0 for any functional unit where it is applied.