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Hydrological modelling

Computer-based hydrological models are effective tools to help understand, plan and manage river systems. These models have been used in the Murray–Darling Basin for more than 4 decades.

Hydrological models have informed the development and implementation of key water management policies including water sharing arrangements for each valley, the cap on diversions, the Basin salinity management strategy, The Living Murray initiative and the Basin Plan.

What are hydrological models?

A hydrological 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
  • 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 stream flow for a given period of time.

Additional information and conditions are specified for a given scenario — such as diversions, agreed water sharing rules and river operating rules, as well as landscape information for floodplains, wetlands and various works 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, over the specified period of time.

The input parameters can then be changed to investigate how consumptive users and the environment are affected as changes occur.

The models can provide detailed information on river flows, dam levels, losses and water consumption for each scenario.

Statistics can then be used to compare different scenarios and inform robust policy development.

The information output from the model 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.

Importantly, when used this way, the models do not provide a forecast of what might happen in the future, but broadly show the impacts of various scenarios over the range of climatic conditions specified.

How reliable are the models?

The modelling platform used by the MDBA is the best available. However, as they contain assumptions and elements of uncertainty, model results must be considered in content and using expert knowledge.

Individual models have been used in Basin water resource management for many years — in some cases, for more than 40 years.

Each individual river system model is calibrated by its originating agency, with most having been rigorously peer reviewed and accredited.

An independent and comprehensive review of this modelling framework has confirmed the platform constitutes the best available and is fit-for-purpose.

How have they informed the Basin Plan?

We have used 24 individual river system models linked together to describe the surface water resources of the Basin.

These models have been developed in collaboration with the Basin states and Snowy Hydro Limited, and have been run in combination for over 40 years. However, they were first linked by CSIRO as part of its Murray–Darling Basin sustainable yields project.

We have built on the work of CSIRO and adapted the methods and tools for the specific needs of the Basin Plan.

In addition, a number of other modelling tools have bene used in our Basin-wide river systems modelling, including:

  • rainfall-runoff models for creating continuous streamflow records for the period 1895–2009
  • eFLOW Predictor tool developed by eWater Cooperative Research Centre (to assist in creating a series of environmental water requirements)
  • results from floodplain inundations models (to estimate vegetation communities that benefit from different flow rates).

Modelling is undertaken using historical climate data collected over 114 years (from 1895–2009).

This record includes the federation and millennium droughts, as well as very wet periods during the 1950s and 1970s.

It represents a range of of climatic conditions across the Basin that may reoocur in the future, with some uncertainty around the influence of climate change.

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