The Development of a Salinity Plugin for the Source Modelling Framework

High salinity in freshwater catchments impacts upon freshwater organisms and ecosystem health, as well as other environmental values such as suitability for drinking water, livestock watering and crop rotation. How saline mine water releases relate to broader catchment salinity issues within the Fitzroy Basin is not well understood.

The development of a salinity plugin for the Source modelling framework has been driven by the need to assess whole of catchment salinity impacts across the Fitzroy catchment, and how these may be influenced by diffuse and point source salt contributions.

Salinity in the Fitzroy catchment has been of considerable interest over the last decade with better understanding of landscape and point sources of salt throughout the region.  Salt in the Fitzroy can come from many sources, including:

• Natural groundwater releases;
• Irrigation activities;
• High groundwater tables due to land clearing;
• Point sources from coal seam gas, power stations, wastewater treatment plants and coal mines.

River salinity impacts the end uses of the water resource for irrigation, industrial use, animal production and human consumption, and increasing salt concentrations can have considerable environmental, economic and social consequences.  One area of focus in recent years has been the contributions of saline discharges from mining operations within the catchment.   

Typically, large open cut mining operations intersect with groundwater flows, but also may require surface water diversions.  During large runoff events, surface waters and groundwaters may combine within open cut mining voids which then need to be dewatered to allow for mining operations to restart.  The discharge of this mining water back into the surface water system may then result in any catchment and groundwater derived salts being put back into receiving waters.  The concentration and loads of salts from such actions should be assessed to ensure that downstream impacts can be appropriately managed, where management outcomes may include cessation of discharge, delay or reduction or discharge or dilution of discharge.

To undertake such assessments, a numerical modelling approach that considers all sources of water and salt across the catchment will need to be implemented.  Fortunately, within the Fitzroy catchment, detailed hydrologic modelling of the region has been undertaken through the state government's Paddock to Reef program (Carroll et al 2012).  This catchment wide hydrologic model was developed in the Source modelling framework (Welsh 2013) and has been used as the basis to understand the hydrologic variability within the Fitzroy system.  This project has focused on developing and coupling a bespoke salinity model (or plugin) to the Fitzroy Source hydrologic model.

Developing a specific salt plugin for the Source model will allow the ongoing use of this platform to assess changes to managing salt loads across the Fitzroy catchment in the future.  This report outlines the development, application and future use of the salt model plugin for the Fitzroy catchment.