UNDERSTANDING THE EFFECTS OF FLOW REGIME ON THE SNOWY RIVER ESTUARY

The construction of the Snowy Mountain Hydro Scheme 1949 - 1974, has resulted in large inter-basin water transfer from the Snowy River to the Murray-Darling Basin, profoundly altering the biophysical condition of the river and its associated estuary and wetlands. The decline in health of the Snowy River system has led to the trial use of environmental water to improve river health. It is only by understanding outcomes of environmental flows, over the entirety of the system, that benefits of the watering scheme may be maximised. An extensive physical monitoring program of the entire estuary system was undertaken. This was coupled with the development of a detailed 3D hydrodynamic model capable of predicting effects of flow on selected water parameters (salinity, temperature and level) in the Snowy River estuary. The monitoring information was used to extend the calibration of the model to a wide range of flow, temperature and salinity conditions so that the model may be used to better determine outcomes of environmental flows on selected biota which use the estuary, either permanently or temporarily. As part of the project, the model was used to determine if suitable water parameters (salinity and temperature) exist within the Snowy River estuary to allow spawning of Australian bass Macquaria novemaculeata, a catadromous native fish species. This information aided the development and implementation of the ecological monitoring part of the project. The ecological monitoring aspect on Australian bass was due to the species being comparatively common (within the catchment), having a life-history completed solely within the catchment (i.e. no known marine phase), a catadromous life-history influenced by flows, and due to it being an iconic target species for recreational anglers.