River systems are very complex. Modelling is an important tool because it shows the impact of different policies and operational decisions, both for different users and under different conditions. Modelling is one tool among many that river managers use to inform decisions.
The scientific work undertaken to inform the development of the Basin Plan was the best available at the time (2009 to 2012). We need to always work towards building upon our understanding of what climate change and other environmental factors and impacts are likely to mean for the hydrology of our rivers, the way we operate them, the effect on water quality and the Basin’s water-dependent ecosystems.
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Key facts
A ‘model’ is a computer-based representation of a system used to test ideas. Our modelling platform is the best available in Australia.
Modelling is a powerful decision support tool that has helped solve many challenges over the years.
Individual models have been used in Basin water resource management for many years – in some cases, for more than 40 years.
Model results provide a wealth of information which must be considered in context and using expert analysis.
Each individual river system model the MDBA uses is calibrated by its originating agency, most have been rigorously peer reviewed and accredited.
The MDBA uses 24 individual river system models linked together to describe the surface water resources of the Basin.
Modelling is typically undertaken using historical climate data collected over 114 years (from 1895 to 2009) and includes the Federation drought and millenium drought.
Types of modelling and their uses
The Murray–Darling Basin Authority (MDBA) and its river management partners use a variety of models to support the planning and running of the Murray–Darling Basin’s rivers.
Hydrological models
A river model is a computer software tool that simulates the flow and behaviour of water along a river system, taking into account:
- the movement of water through the river channel and associated floodplains, wetlands and anabranches
- losses and gains as water moves through the landscape, and
- how we manage the storage, supply and use of water for various purposes.
These models take a variety of input data such as measured data for rainfall, temperature, evaporation and inflows, for a given period of time.
Scenario modelling
Additional information and conditions are specified for a given scenario, such as water sharing rules, river operating rules and various infrastructure constructed in the system.
These models then use mathematical calculations to simulate the behaviour of a river system for this given set of inputs and conditions, to investigate how consumptive users and the environment are affected as changes occur.
The information output from various modelling scenarios can also be used as input for other models and assessments to allow more detailed environmental, economic and social assessments to further inform decision-making processes and policy development.
The models do not provide a forecast of what might happen in the future. They broadly show the impacts of change in the various scenarios modelled, over the modelling period.
Hydrodynamic modelling
Hydrodynamic models include the topography of the river channel and floodplain, and can incorporate structures such as wetland regulators. Hydrodynamic models are calibrated using the best available data, including measured flows, water levels and satellite images of river flows.
These models help water managers and river operators with:
- predictions of the likely inundated area during environmental watering
- documenting inundated area after watering events
- providing estimates of environmental water use.
This information can also be used in long-term planning. It can be used to compare the advantages and risks of different operating strategies for environmental watering schemes on the River Murray.
National Hydrologic Modelling Strategy
The National Hydrological Modelling Strategy (NHMS) was adopted by the Council of Australian Governments in 2008 to ensure that future water planning is informed by the best modelling practice.
The NHMS was updated and endorsed by the National Reform Committee in 2018.
A key output from the NHMS is the Source Integrated Modelling System (Source IMS).
The Source IMS can simulate the water resource systems at a range of scales, such as urban, catchment and river basin, to support integrated planning, operations and governance including human and ecological influences.
The Source IMS is the product of more than 25 years of collaborative research by the Cooperative Research Centres (CRC) for Catchment Hydrology, CRC for Freshwater Ecology and the eWater CRC.
Development of the Integrated River System Modelling Framework
The Commonwealth Scientific and Industrial Research Organisation (CSIRO) developed an Integrated River System Modelling Framework (IRSMF) that allows 24 river system models to be linked and used.
The Basin states and the MDBA have been developing Source models to support water resource plan development and these improved models will be implemented in the IRSMF.
A review of the current modelling tools with consideration for known future modelling activities is underway to continue to provide a more efficient Integrated River System Modelling Framework.
Upgrading Basin river models
The Australian Government has committed to investing $66 million to upgrade the Murray–Darling Basin's 24 river models to help water managers make timelier, more reliable and transparent water management decisions.
Current models have worked well in the past however governments need to ensure these vital tools are fit for the future climate, are ready to answer future questions and support future decisions by river operators, irrigators and environmental water holders.
The proposed upgrades of the models will:
- increase collaboration and transparency across Basin governments by all having access to the same modelling data
- allow for better management decisions to be made for industries, communities, and the environment
- make evidence, data and knowledge that is used to support decision making more transparent.
Part of the investment will be the development of a public-facing data portal, giving water users access to future-scenario information they can use to plan.
The upgrade will take 4 years, with all the existing MDBA and state government river models expected to be integrated by July 2024.
