The current and future extent and impact of shallow water tables and dryland salinity is assessed across the majority of the state of Victoria. Four types of landscape have not been included, namely:
- irrigation areas of the Goulburn, Campaspe, Loddon and Murray valleys of northern Victoria and the Lake Wellington area of Gippsland
- relatively large contiguous areas of native vegetation, mostly on public land
- areas with no suitable groundwater information, which were mostly located in areas of relatively high elevation and rainfall in eastern Victoria
- metropolitan Melbourne and major regional centres.
While dryland salinity is an issue in several major regional centres, the study includes almost all of the land considered to be at potential risk from shallow water tables and dryland salinity in the State.
Area at Risk
The area predicted to be at risk from shallow saline watertables is approximately 670 000 ha. This could increase to over 3 million hectares within 50 years. Between 8% and 18% of the State?s agricultural land is predicted to fall into the high salinity risk category, with up to a further 47% in the moderate-risk category under the worst-case scenario. High-risk areas are concentrated in the Goulburn-Broken and North Central regions in northern Victoria and the Glenelg-Hopkins and Corangamite regions of southern Victoria.
More specifically, the major areas of land that are either currently affected by dryland salinity and/or are predicted to have shallow watertables are:
- the Dundas tablelands of south-west Victoria;
- parts of the western Victorian basalt plains;
- the break of slope between the uplands of the Great Dividing Range and the northern Victorian riverine plain in north-eastern and north-central Victoria;
- the middle and lower reaches of the Loddon riverine plain;
- agricultural land on the eastern fringe of the Sunset Country in north-west Victoria;
- the lower Wimmera river floodplain;
- the floodplains of the Avon and Richardson rivers; and
- coastal areas of south Gippsland.
Current salinity risk areas are based on mapping of land affected by dryland salinity at 1:25 000 scale and analysis of groundwater levels at a scale of approximately 1:250 000. Mapping was based on the nine-second digital elevation model for Victoria and work undertaken for the Murray-Darling Salinity Audit, for much of northern Victoria. Large contiguous areas of forest or woodland (mostly public land) were excluded from the analysis due to the lack of groundwater data and generally low threat of salinisation. Future salinity risk is based on current risk areas and analysis of groundwater trend information. Worst- and best-case trend values were calculated based on relatively wet and dry climatic sequences, respectively. Information on salinity risk and potential impact presented generally represents the worst-case trend scenario.
- Potential future impacts on cropping land are concentrated in the North Central and Goulburn-Broken regions, while impacts on grazing land are greatest in the Glenelg-Hopkins, Goulburn-Broken and Corangamite regions of the State.
- Potential impacts of shallow watertables and dryland salinity on physical infrastructure, particularly roads and rail, are predicted to more than double by 2050. These changes, particularly for the road network, would be expected to greatly increase the maintenance costs incurred by State and local government.
- Shallow watertables are predicted to increase under more than 30 000 ha of land surrounding the Ramsar wetlands of the Western District lakes during the next 20 years.
- Wetlands in the Goulburn-Broken and Corangamite regions are expected to be the most affected, with over 40% of wetlands in each region predicted (in the worst-case scenario) to be in landscapes with shallow watertables by 2050.
- The number of rare or threatened plant and animal species whose habitat is located in shallow watertable areas is expected to increase substantially: plant species from 122 to between 196 and 346, and animal species from 269 to between 317 and 485.
- A two- to three-fold increase in the length of stream or perimeter of reservoir, lake or wetland located in areas of shallow watertable is predicted over the coming 50 years. Much of the increase is predicted for the Goulburn and North Central regions, and under the worst-case trend scenario, for the Glenelg and Corangamite regions. If realised, this change would result in increased groundwater discharge to streams, greater salt wash off and increased stream salinity and salt load.
- Stream salinity increases westwards across northern Victoria (to the Avoca River). Flow-weighted salinity in the lower Loddon and Avoca Rivers either already exceeds or is predicted to exceed Murray-Darling Basin Commission benchmarks for water quality (800 and 1500 ÁS/cm).
- Management of stream salinity is perhaps the most important issue for Victoria. The issue is significant because of the State?s obligations to the Murray-Darling Basin Salinity Strategy as well as potential impacts on irrigation, urban and industrial use and on aquatic ecosystems.
- Implementation targets for the catchment management authorities will require considerable technical support to integrate the latest information from the Audit and Murray-Darling Basin salinity audits, and to set up appropriate monitoring processes.
Catchment Management Authority (CMA) regions have been used to summarise the assessment findings for Victoria.
The salinity extent component of this study is only being undertaken in the southern half of Victoria, in an area comprising the Glenelg-Hopkins, Corangamite, Wimmera, West and East Gippsland Catchment Management Authority (CMA) regions and parts of the Port Philip CaLP area. With the exception of metropolitan Melbourne, salinity extent information from the remainder of the state has been derived from other studies.
What are groundwater flow systems?
To understand salinity across the Australian landscape and through time, we need to understand how groundwater systems respond to changing recharge, and how the excess water that results from increased recharge is distributed. The broad distribution of groundwater flow systems in Australia has been mapped using attributes such as elevation, landscape form and geology. The classification groups groundwater systems with similar recharge and flow behaviour, and other measures such as length of flow paths through aquifers, aquifer permeability and driving pressure gradients for groundwater flow. It identifies groundwater flow systems where particular management activities will lead to similar responses and provides a framework for action.
For more detail: move to the Australia?s Groundwater Flow Systems overview
Case studies were implemented in catchments in southern Australia as part of an evaluation of the groundwater flow systems and a catchment water balance approach to identify:
- areas of the catchment where changes in recharge will most affect catchment salinity;
- how much recharge reduction would be required to reduce salinity by a given percentage in an area of salt-affected land;
- land use and farming system options for reducing recharge enough to manage salinity;
- information for an economic analysis of the costs, benefits and viability of the options for change;
- constraints to achieving required change.
The case study catchment in Victoria was Kamarooka, Victoria - a local flow system in variably weathered fractured rock. Groundwater discharge at break of slope
- Victoria Dryland Salinity Assessment 2000 report
- Australian Dryland Salinity Assessment 2000 report
- National Technical Overview Report of the State-based dryland salinity assessments
- Australian Groundwater Flow Systems Report
- National Dryland Salinity Program
- National Action Plan for Salinity and Water Quality
Government of Victoria 2000, Restoring our Catchments. Victoria?s Salinity Management Framework, Department of Natural Resources and Environment.
Agriculture Western Australia, Department of Conservation and Land Management, Department of Environmental Protection, Water and Rivers Commission (1996) Salinity: a situation statement for Western Australia. A report to the Minister for Primary Industry and the Minister for the Environment.
Allan, M.J. (1994) An assessment of secondary dryland salinity in Victoria. Department of Conservation and Natural Resources, Centre for Land Protection Research. Technical Report No.14.
Allan, M.J. (1996) Method for assessing dryland salinity in Victoria. Department of Natural Resources and Environment, Centre for Land Protection Research. Technical Report No. 34
Beattie, L. and Holden, S. (1998) South-west gross margins 1998-1999. Department of Natural Resources and Environment.
Bond,W.J., Cresswell, H.P., Simpson, R.J., Paydar, Z., Clark, S.G., Moore, A.D., Alcock, D.J., Donnelly, J.R., Freer, M., Keating, B.A., Huth, N.I. and Snow, V.O. (1997) MRC Sustainable Grazing Systems Key Program Project SGS.130. Pre-Experimental water balance investigation. Final Report. CSIRO Land and Water Consultancy Report No. 97-31.
Branson, J., Beswell, D., Hickey, T., Welsh, C. and Mason, L. (1998) Horticultural gross margins for the Kerang/Swan Hill region. Department of Natural Resources and Environment.
Clifton, C. and McGregor, C. (2000) Modelling vegetation systems for the management of dryland salinity in Victoria. Department of Natural Resources and Environment, Centre for Land Protection Research. Technical Report No. 67.
Clifton, C.A. and Schroder, P.M (1997) Perennial pastures use water: fact or fallacy? Paper presented to 38th Grasslands Society of Victoria Annual Conference, Hamilton.
Floyd, P. (1998) North-east gross margins 1998-1999. Department of Natural Resources and Environment.
Government of Victoria (1987) Salt Action. Victoria?s strategy for managing the salinity of land and water resources. Draft.
Government of Victorian (2000) Restoring our Catchments. Victoria?s Salinity Management Framework. Department of Natural Resources and Environment.
Murray Darling Basin Ministerial Council (1999) The salinity audit of the Murray-Darling Basin. Murray-Darling Basin Commission.
O?Brien, K. (1998) Wimmera gross margins 1998-1999. Department of Natural Resources and Environment.
Reid, M.A., Clifton, C.A. and Heislers, D.S. (1998) Dryland salinity management in the Victorian uplands. In Weaver, T.R. and Lawrence, C.R. (ed?s) Groundwater: sustainable solutions. Proceedings of the International Groundwater Conference, Melbourne.
Sinclair Knight Merz (1999a) Ultimate salt loads to the Murray River. Report to the Department of Natural Resources and Environment. Project WC00670.
Sinclair Knight Merz (1999b) Victorian Water Quality Monitoring Network Trend Analysis Report Series. Report to the Department of Natural Resources and Environment.
Sinclair Knight Merz (1999c) South-West Victoria water balance modelling project. Final Report: Assessment of salinity management options for the Glenthompson area. Report to the Department of Natural Resources and Environment. Project WC00822.2
Sinclair Knight Merz (2000) Avon-Richardson Salt and Water Balance Study. Final Report. Report to Department of Natural Resources and Environment. Project WC01234.
Wimalasuriya, R. (1998) North-central gross margins 1998-1999. Department of Natural Resources and Environment.
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