Source provides a variety of catchment constituent generation and filtering options. Channel routing, Reservoir Sedimentation and simple decay are included in the core model, with in-stream processing via specialised plugins.

Constituents in Source refer to materials that are generated, transported and reduced within a catchment and affect water quality. Common examples include sediments, nutrients and contaminants, such as salts or dissolved solids.

Processes that act on these constituents to generate, transport and transform them can be modelled in Source. A constituent can enter or exit the modelled network in several different contexts:

as a concentration at a point
as a diffuse source
- as water travels over a surface
- laterally along a link.

Constituent generation models describe how constituents are generated within a functional unit at sub-catchment level and how the resulting concentrations or loads are delivered to the sub-catchment link. Point concentrations and lateral infiltration are configured within a node or link feature editor, respectively.

Once the constituent is in the system, other processes can act to move or otherwise transform it.

Constituent filtering models represent any constituent reduction between generation by a constituent generation model and arrival at the sub-catchment link.
Constituent routing models describe the movement of constituents along a river channel network, including the exchange of constituents between floodplains, wetlands, irrigation areas and groundwater. Constituent routing models are conservative, meaning that they do not alter the total mass of constituent stored in the system.
Constituent processing models describe processes that can alter the mass of a constituent in a storage or river reach (link), such as via a decay process.

In summary, constituents can be added at:

Links
Functional units and sub-catchments
Inflow nodes
Storage nodes (These model reservoirs, wetlands and re-regulating weirs. Flows and constituents are routed through weirs using the same methodology as links)
Water user nodes and associated demand models
Gauge Nodes

And constituent concentration/mass will be affected at nodes in the model where flow volumes change, such as:

Splitter nodes (Regulated and unregulated)
Confluence nodes
Minimum flow requirement nodes (used to generate orders for dilution flows)
Supply point nodes
Loss nodes
Wetland Hydraulic Connector nodes
Scenario Transfer nodes

Catchment modelling is an ideal tool to investigate constituent budgets and the potential impact of management strategies and it follows that the better a catchment model performs spatially and temporally the greater the confidence in targeted management actions.¹

¹ C. Dougall a and C. Carroll (2013), Great Barrier Reef Source Catchment’s modelling: Enhanced simulation and water quality targeting through event based assessment. Anderssen, R.S. and Boland J. (eds) MODSIM2013, 20th International Congress on Modelling and Simulation. Modelling and Simulation Society of Australia and New Zealand, December 2013. ISBN: 978-0-9872143-3-1.

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