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Water resource modelling

River systems are very complex. Modelling is an important water management tool because it can show the impact of different policies and operational decisions for different users and under different conditions.

A model is a computer based representation of a system and is useful because it allows ideas to be tested first. Modelling provides objective and scientific advice and has helped solve emerging challenges over many years.

The time it takes a computer to run a model can vary from only a few minutes to many days and it can take months to complete a modelling scenario, or a set of modelling scenarios. After a model has been run the results need to be analysed and interpreted. Often this is an iterative process with many versions of a particular scenario being run before the scenario is finalised.

The Murray─Darling Basin Authority collaborates with Basin governments to develop knowledge of how actions taken at individual valleys impact each other. This helps to develop a basin wide response to water management.

Models are more than just about the volume of water flowing in the river (hydrological modelling). Models can be also take into account the topography of the river bed and floodplain (hydrodynamic modelling).

Models are not static and are continuously being developed, improved and extended – new data may become available or conditions may change.

History of water resource modelling and the Murray–Darling Basin Authority

The history of hydrological modelling in the Murray─Darling Basin is closely related to the development and implementation of river management policies and practices.

The evolving challenges and complexity in river management and water sharing has led to more complex models being developed.  The first models were basic and were used for evaluating the locations of major structures on the River Murray, including the Hume and Dartmouth dams. These dams led to a growth in irrigated farms across the Basin - and new models were developed to provide advice on supplying water to irrigators.

As the efficiency of dams increased, the accounting of water became important and models then incorporated water accounting.

Modelling in the 1990s

The next range of models responded to increased salinity and were integral to the development of salinity and drainage strategies. In the 1990s, the results of the rapid development of the previous decade were leading to new challenges. These challenges included increased salinity, algal blooms and impact on reliability of irrigation entitlements. Models were now able to interrogate trends and quantify the risk of over-development. This led to the development of the cap on diversions and The Living Murray program, as a first step to the River Murray returning to a healthy working river.

Since the 1990s, irrigation and environmental water demands have been significantly different in terms of seasonality and the volumes required. Hydrological models were updated to account for environmental demand. As infrastructure was put in place, hydrodynamic modelling has been used in the planning and decision making for irrigation and environmental water delivery.  

2000 onward

While these changes were underway, the Basin faced one of the driest periods in recorded history, from 2001 to 2009.

The Water Act was introduced in 2007. The Act led to the development of the Murray─Darling Basin Plan. This required a whole-of-basin level planning, and the Murray–Darling Basin Authority (MDBA) adapted a CSIRO technology that allowed the different models representing the Basin to be linked.

The Water Act also introduced other requirements in water sharing, such as critical water needs, South Australian storage rights, and the environment’s role as a large water user. These changes are underway and now require models to provide transparent and more detailed advice at an increasing pace.

By 2000, Murray Darling Basin Commission (the predecessor to the MDBA) modellers had seen decades of steadily increasing complexity in managing water resources. Rules and water management were more complex and reporting had become stricter.

The existing models - MSM-BIGMOD - had been in place for more than 40 years and were being limited due to compatibility issues. A lot of the decision making at the time was at a monthly time-step, which meant that the new complex rules could not be implemented as accurately as desired. It was then decided that a River Murray model would be developed using new technology that would represent river flows and management at a daily time-step.

National Hydrological Modelling Strategy

Collaboration between the MDBA, state governments and the eWater Cooperative Research Centre resulted in the adoption of the Source modelling platform (Source).

In 2008, the Council of Australian Governments developed the National Hydrological Modelling Strategy which led to the adoption of Source as the national hydrologic modelling platform. In 2012, the MDBA successfully configured a model in Source that implemented the River Murray flows and operations at a daily time-step.

The Basin Plan’s implementation has only just commenced. Modelling will be instrumental to the successful implementation of the Basin Plan by:

  • representing water sharing plans in a quantifiable way
  • aiding the planning for large environmental water use
  • aiding compliance with the Basin Plan by ensuring transparency.

A timeline of modelling history