The NSW Reconnecting River Country Program aims to improve environmental outcomes using existing water for the environment by increasing flow limits in the Murrumbidgee and Murray rivers. This will enable the release of environmental flows at higher flow rates that can reach wetlands and low-lying floodplain and inundate stranded ecological communities.
To quantify the expected outcomes from such a shift to water management studies were undertaken in fish, vegetation, waterbirds, and energy production, each with a different modelling approach. Each ecohydrological model used timeseries of modelled river flows representing environmental water use under the current operational flow limit and three or four increased flow limit scenarios. Inundation mapping was used to link river flows to floodplain inundation.
Native fish were examined through a series of linked population models and showed the largest environmental benefit in golden perch. A newly developed Floodplain Vegetation Condition Model was built specifically for this project, using a stepwise state and transition architecture, predicting benefits to river red gum and other floodplain communities, but potential declines in black box condition in some areas. Waterbird species richness and abundance were examined through using historical imagery and observed data to build relationships with river flow. The Murray had increased bird density and species richness under relaxed flow limits, whereas the Mid-Murrumbidgee showed little predicted change. To evaluate production, an ‘energetics model’ was developed to track the availability, quality, and movement of energy through aquatic food webs. The study found increased amount of bioavailable energy with increased flow limits. Overall, models predicted net ecological benefits in response to flow regime changes, showing significant benefits of proposed raised flow limits, particularly in drier times.