Pollution Index

The Pollution Index is the water quality equivalent of a Runoff Surface:

A Runoff Surface describes the hydraulic properties of an area of the catchment surface
A Pollution Index describes the water quality characteristics of an area of the catchment surface

Runoff Surfaces and Pollution Indices are applied via a Land Use:

For hydraulic runoff, you can divide the subcatchment into up to 12 areas by applying up to 12 Runoff Surfaces to the Land use
The Land Use has just one Pollution Index, defining the water quality parameters of the entire subcatchment

The diagram below shows how a Pollution Index and one or more Runoff Surfaces are used to define subcatchment characteristics.

A Pollution Index or Runoff Surface can be associated with more than one Land Use. A Land Use can be associated with more than one subcatchment.

How Runoff Surfaces and a Pollution Index define subcatchment characteristics

For each Pollution Index the following parameters must be defined in the Surface Pollutant Editor:

Pollution Index ID
a set of equations for potency of attached pollutants (one for each pollutant)
a set of equations for dissolved pollutants in gully pots (one for each pollutant)
a build up factor for surface sediment (based on type of land use)
the gully pot volume

The diagram below shows how the various components combine together to define a Pollution Index.

Components of a Pollution Index Definition