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Water resource modelling

The MDBA uses computer models to help it manage the water in the Murray–Darling Basin. These models help the MDBA to see how different conditions and decisions about water management might affect the river system. They help the MDBA calculate how much water is available, and assist the river operations team to run the river day-to-day as well as plan for the future.

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Computer modelling helps solve water management challenges

Water resource modelling helps the MDBA, governments and water authorities manage water by showing how different decisions, policies or environmental factors could affect our rivers.

By testing different scenarios, computer modelling gives scientists objective information. Modelling can predict effects on:

  • water flows
  • water quality
  • ecosystems.

You should know:

  • A ‘model’ is a computer-based representation of a system.
  • Models are used to test ideas.
  • Different computer models have been used to manage Basin water resources for many years.
  • The MDBA uses 24 individual river system models linked together to describe the surface water resources of the Basin.
  • Each river system model the MDBA uses is calibrated by its originating agency. Most have been rigorously peer reviewed and accredited.
  • Modelling typically uses historical climate data collected over 114 years (from 1895 to 2009) including the federation and millennium droughts
  • The Basin Plan was designed through the use of the long-term water-models described above.

Modelling and water allocations

Computer models (modelling) can show what will happen in different parts of the Basin because of natural events such as high rainfall or drought, or because of water management policies and decisions, such as where to direct water flows. State governments (or state water agencies) use water modelling to determine what size allocation entitlement holders will receive.

Modelling in the past and in the future

Water modelling has driven significant change in the way water is managed in the Basin. It has informed legislation such as the Basin Plan, sustainable diversion limits and the Basin Salinity Management Strategy.

Information from computer models has helped scientists find the best way to approach many challenges over the years, such as:

  • managing salinity and algal blooms
  • deciding whether to allow development near the river
  • developing infrastructure to support The Living Murray program

Now that the Basin Plan is being implemented, modelling will help make it successful by:

  • representing water sharing plans in a quantifiable way so that water users have a clear picture of when and how water will be available to use
  • helping plan for the use of water for the environment
  • helping states to comply with their responsibility to submit water resource plans so that the MDBA can see where water is being used.

When modelling different scenarios, the MDBA can include information like rules about water sharing or river diversions to see how people and the environment are affected as changes occur.

Computer modelling programs take into account:

  • the amount of water flowing in the river (hydrological modelling)
  • the shape of the river bed and floodplain (hydrodynamic modelling)
  • water used for irrigation or town supply
  • other factors such as the impact of climate change.

Modelling programs are always being improved through new technological advances. If conditions change or new data becomes available, this information is also added to the model.

Types of water modelling

The MDBA uses a number of computer models to help it make decisions. These include hydrological models and hydrodynamic models.

Hydrological models

A hydrological model is computer software that mimics the flow and behaviour of water along a river system. It recreates:

  • the movement of water through the river channel and floodplains, wetlands and anabranches (streams that leave the river and rejoin it downstream)
  • losses and gains as water moves through the landscape
  • infrastructure like dams, regulators and weirs
  • the storage, supply and use of water
  • allocation and reserve policies
  • irrigation use and carry over
  • water trade
  • environmental delivery

This information is also used for long-term planning models and helps to compare the advantages and risks of different environmental watering schemes on the River Murray.

The models cover the major floodplain areas along the River Murray including:

  • Hume Dam to Yarrawonga
  • Barmah-Millewa forests
  • Koondrook-Perricoota and Gunbower forests
  • Hattah Lakes
  • Lock 10 to Lock 6 including Lindsay, Mulcra and Wallpolla Islands and the Chowilla floodplain.

Hydrodynamic modelling

Hydrodynamic modelling examines physical processes and creates a picture of the way water is moving in the river system. It uses data about rainfall, temperature, evaporation and stream flow, along with water levels and satellite images of flooding. Hydrodynamic models help water managers and river operators to:

  • predict likely flood behaviour during environmental watering
  • document flooding and estimates of environmental water use.

The River Murray and Lower-Darling River systems model (Source)

Source is a hydrological modelling platform that was built by the MDBA, state governments and the eWater Cooperative Research Centre and is now managed by eWater Ltd.

The MDBA, in conjunction with the states, has created a model of the Murray system, including the Lower Darling using the Source platform. The model assess  information about the River Murray and Lower Darling systems on a daily timestep. The Source model can be used to test different scenarios to help develop policies and make sure the river systems are being operated and managed properly. An operational version of the model can also be used in real time to help river management and river operations.

The Source model includes data on:

  • system inflows
  • flow routing and losses
  • demand for irrigation, stock and domestic uses, town water supply and the environment
  • interstate water sharing, allocation and ownership
  • definition of state’s access rights, allocation and accounting
  • water trade
  • water ordering, and the operation of dams and infrastructure
  • transport of salt.

Connecting different models in the Basin with the Integrated River Systems Modelling Framework

Different areas in the Basin have unique computer models to help manage the water in that particular region. These peer-reviewed and accredited models have been developed by the agencies that govern them, such as the state agencies and the MDBA..

The Integrated River System Modelling Framework (IRSMF) was developed by the CSIRO to link all the different river models into one system.

The IRSMF now connects over 20 different models and was used to guide the Basin Plan and Sustainable Development Limit Adjustment assessments.

Updated: 24 Sep 2020