Over-allocation in the Murray-Darling Basin
The Murray-Darling Basin is one of the most important catchments in Australia covering over one million square kilometers. It contains numerous wetlands of national and international importance. It is also home to approximately two million people and its water resources have been highly developed for irrigation, industrial and domestic water supply.
To address over-allocation of water and to restore and secure the long-term health of the aquatic ecosystems the Australian Government has focused attention on environmental flow strategies.
Periodic inundation of the floodplain is one such strategy to improve the health of Red Gums and the floodplain and riverine ecosystem and lessen the impact of altered river flows on fish and bird breeding. Quantitative tools are needed to measure environmental benefits from management options.
Modelling the importance of floodplain inundation
The River Murray Floodplain Inundation Model (RiM-FIM) has been produced by CSIRO since 1999, recently in collaboration with the Murray-Darling Basin Authority, to support decision making in environmental flow management in one of Australia's most important water resources.
The tool also provides an information source for developing ecosystem responses to changes in the hydrology of the Basin.
RiM-FIM allows water resource managers to predict the extent and depth of flooding on the floodplain.
The Murray Darling Basin Authority has used the RiM-FIM modeling tool to determine floodplain areas impacted by various management scenarios which has informed the development of the Basin Plan and its implementation strategies.
A number of RiM-FIM versions have been developed over the years for the River Murray and now the modelling tool is being extended to include other reaches of the Murray-Darling Basin including the Lower Darling, Edward-Wakool and Lower Murrumbidgee.
From image to model
RiM-FIM is developed from capturing images of individual flood events and integrating these into a geographical information system (GIS). Over 100 hundred satellite images have been used to map the extent of inundation.
The model is then linked to river flow gauges to provide a predictive tool for flood extent from a range of river flows. The model is also able to predict the depth of flooding and can be used to determine wetting and drying cycles when linked to river flow regimes.
The satellite images are classified to show the observed extent of flooding at a range of flow levels from very dry to fully flooded. The extent of flooding is then interpolated between observations using a digital elevation model.
RiM-FIM was initially developed to cover the River Murray from the South Australian border to the Lower Lakes. It provided water resource managers with cost-effective quality modelling data to support their decision-making.
The RiM-FIM tool was later expanded to include the River Murray up to Hume Dam, near Albury in New South Wales. It has been used in the scientific community to link hydrology to ecological outcomes. The model was enhanced further by the incorporation of digital elevation modelling to provide accurate water depths during flooding events.
The latest version of the RiM-FIM tool was developed for the Murray-Darling Basin Authority and covers the Lower Darling, Edward-Wakool and Lower Murrumbidgee.
Predicting ecosystem benefits
The model has been used to predict inundation extent for various river management scenarios including climate change predictions on the floodplains in the Murray-Darling Basin.
By linking vegetation and wetland maps to the RiM-FIM it is possible to assess changes in ecosystem condition with changes in river flows. The South Australian component of the model links river flow with water height, and can predict the extent of flooding from different river flows and different weir heights.
The tool is used by organisations such as:
- the Murray-Darling Basin Authority
- catchment management and industry groups
- river and ecological scientists
- State and Federal government agencies.
It is used in decision making for river flow and infrastructure management:
- to gauge where flooding may occur
- to research flooding impacts
- to prioritise infrastructure investment
- in the development and implementation of legislation and policy.