For introduction to Water Quality in Source, please see Water Quality under fundamental concepts.

Overview of configuring constituents

To configure constituents:

After you have defined constituents, the Constituent Model Configuration dialog is useful for viewing, selecting and editing:

See Constituent Model Configuration for more details.

Defining constituents

The Constituents Configuration dialog (Figure 1; accessible via Edit » Constituents...) is used to enable constituent modelling, and define both constituents and constituent sources:


  • For constituent sources (used only in catchment models), the default source is indicated by a green tick (Figure 1). It cannot be deleted and is automatically assigned to each functional unit/sub-catchment combination. You can change which source is the default using the Set as Default contextual menu.
Figure 1. Configure constituents

Constituent routing

There are two types of constituent routing available, Lumped and Marker routing. (Figure 1). Both of these are conservative routing models, which means that they do not change the total mass of constituent in the system. 

Note: When using lumped routing the following applies for storage routing links, storages and weirs that have volumes close to or equal to zero during the run. The working volume is the sum of the initial storage volume and all input flows, minus evaporation. The minimum volume is 0.01 m3, and is not currently user-configurable. When the working volume drops below the minimum volume, constituents are deposited as mass and removed from the system. The deposited mass is recorded in the Deposited Mass parameter (located at Constituents » <constituent name> » Deposited Mass).

Constituent Model Configuration

You can assign and manage the constituent generation, filter, instream processing and storage processing models for all constituents in the scenario using the Constituent Model Configuration dialog (Figure 2), which is opened by navigating to Edit » Constituent Models.... Before using this dialog, you need to define constituents and constituent sources (as described in Defining constituents) and also either set up your catchment area using the Geographic Wizard for catchments and assigned FU areas and/or add constituents to nodes or links Then, you can use the tree menu on the left to view the filter and generation models for each sub-catchment/FU combination, the instream processing model for each storage routing link, and the storage processing model for each storage node. 

The following operations can be undertaken:

Refer to Working with rainfall-runoff models for more details on assigning a model, adding input data and changing parameters. For more information on using filters see Working with filters in the Feature Table. However, there is also a sub-catchment filter to help you find sub-catchments either by name or by using the sub-catchment map, see Sub-catchment filter.

Figure 2. Constituent Model Configuration


Configuring constituents at nodes

In Source, the behaviour of constituents at each node varies. Select Constituents in the node’s feature editor to configure them. Depending on your requirements and the type of node, you can specify either a constituent’s load or concentration at a node. For example, you can only specify a constituent’s concentration on an inflow node.

Inflow node

In the node's feature editor, specify the inflow constituent data (as a concentration) using the Constituents item (as shown in Figure 3). This behaviour is similar to flow.

Note: Only constituents with units of concentration (mass/volume) can be added or replaced using the Inflow node.
Figure 3. Inflow node (Constituents)

Gauge node

For each constituent, you can specify its observed concentration by entering a value, supplying a time series or defining a function (Figure 4). You can choose to override the modelled constituent concentration with the observed concentration by enabling Set to gauged. Refer to Gauge node - Constituents for more information. 

Figure 4. Gauge node, Constituents

Storage node

For the storage node, you must define the initial concentration of each modelled constituent in the feature editor, under Constituents (Figure 5). You can also change the storage processing model, by clicking the cell with current processing model and selecting the desired model from the drop-down menu (Figure 5). 

Figure 5. Storage node, Constituents

Inlet Channel Mixing allows you to introduce mixing of constituents at a wetland conveyance link (Figure 6). You specify a percentage of the wetland/storage volume that conceptually represents the conveyance link - this is the inlet channel, and the remaining volume represents the main body of the storage/wetland. When water is exchanged between the wetland/river or the wetland/wetland, mixing of constituents is assumed to occur in the inlet channel. If the exchange of water is large enough to flush out the inlet channel, then the constituents will mix with the main body of the wetland, or the river, depending on the direction of water exchange.

Figure 6. Storage node (Inlet channel mixing)

Additionally, for each constituent, you can configure various aspects of its concentration (Figure 7):

Figure 7. Storage node, Constituent concentration

Configuring constituents along links

Constituents can be configured for storage routing links in the feature editor (Figure 7). In this screen, you can specify the link’s constituent concentration when the simulation begins. This parameter assigns a concentration for each modelled constituent in the scenario for the markers created in that link during the model initialisation. You can also specify the instream processing model, the parameters of which can then be configured by selecting Configure

For each constituent, you can specify an increase in concentration from different sources, similar to constituents in the storage node (Figure 8). The parameters are:

Note that both Groundwater and TimeseriesFlux need to be configured on the storage routing link for constituents to enter the link using these sources - see Groundwater and Storage routing - Timeseries Flux.

Note: Unless there is either an initial storage or initial flow defined, there will be no constituent mass in the link at the start of the model simulation.
Figure 8. Storage routing link, constituents

Configuring constituent in catchment models

Constituents in a catchment model have a constituent generation model and a constituent filter model for each sub-catchment/functional unit (FU) combination. To configure these, use the Constituent Model Configuration dialog (Figure 2), which is opened by navigating to Edit » Constituent Models.... You can configure more than one generation and/or filter model for a sub-catchment/FU combination by using constituent sources

Constituent generation models

These describe how constituents (eg. sediments or nutrients) are generated within a functional unit and the resulting concentrations or loads passed to the filter model. Click on any constituent to view the associated FU and generation model for each sub-catchment.

Assign and parameterise generation models for a constituent as follows:

  1. Click on the constituents under Generation Models (in the tree menu).
  2. Assign a model to the sub-catchment/FU combination:
    • Click on the cell in the Model column that you want to change; and
    • Click on the drop-down arrow that appears and choose the required model from the menu;
  3. Assign input data (if relevant) to the model; and
  4. Parameterise the filter model. Depending on the chosen model, the right-side of the table will populate with the associated default parameters. Click on the cells and edit these values.

The available constituent generation models are:

The default constituent generation model is Nil Constituent.

Constituent filter models

Filter models represent any transformation of constituents between generation within the FU and arrival at the link upstream of the sub-catchment node. Filter models process constituents within the FU and as with constituent generation models, are applied to FUs. Follow the same steps outlined for generation models to assign, add input data and parameterise constituent filter models.

The available constituent filter models are:

The default constituent generation model is Pass-through.

Linking constituent generation or filter models

Note: This functionality is currently under development and not all models can be linked. The description that follows is an illustration of what can be undertaken in Source.

Constituent generation and filter models may require one or more of their parameters to originate from another generation or filter model. The load-based nutrient delivery ratio (NDR) filter model depends on the input of the load-based sediment delivery ratio (SDR) filter model. To configure constituent model linking between these two models for a given sub-catchment/FU combination and constituent source, assign an SDR model to the sediment constituent, and an NDR model to each other appropriate constituent. You then need to define a linkage between the SDR quickflowConstistuentIn parameter and the quickflowSedimentIn parameters of the NDR models. Once the linkage is created, the SDR model is run before the NDR models, allowing the correct flow of data at the right point in time.

To link an NDR model to an SDR model, in the Constituent Model Configuration dialog (Edit » Constituent Models...):

Note: Source detects circular dependencies, and will notify you if a defined link needs to be corrected prior to proceeding.

Constituent sources

Constituent sources allow you to configure more than one constituent generation and/or filter model for a given sub-catchment/FU combination. Each constituent source assigned to a constituent/sub-catchment/FU combination allows you to select different constituent models or model parameters. For each source, the selected generation or filter model and its parameters are applied across the entire area of that sub-catchment/FU. An example use for constituent sources is to model the constituents from a fire in the forest and agriculture functional units of SC #1. First, two sources are defined, Default and Fire (Figure 1). Then the default source is used to model the constituent generation and filtering under natural conditions for both the forest and the agriculture FUs in SC#1. Then the fire source is used to model the additional constituent generation and filtering that results from the fire (Figure 2). 

The first step when configuring constituent sources is to add sources to the Constituents Configuration dialog (as described in Defining constituents, Figure 1). There is always at least one constituent source that is the default, it is indicated by a green tick (Figure 1), and cannot be deleted. You can change which source is the default using the Set as Default contextual menu. 

For each constituent, every sub-catchment/FU combination is assigned the default constituent source for both constituent generation and constituent filtering.  You can change the constituent source from the default or add or remove additional constituent sources in the Constituent Model Configuration dialog (Figure 2), which is opened by navigating to Edit » Constituent Models....

To change a constituent source for a constituent generation or filter model:

You can also undertake the following actions using the same contextual menu: