Dryland salinity is a key Australian natural resource management issue that needs to be addressed to ensure productive and sustainable land use. Dryland Salinity Assessment 2000 is a wake-up call: Australia is a vastly different continent to Europe and we need to change our European-based farming systems to work within the context of Australian soils, water resources and climate.
Dryland salinity provides us with an opportunity to integrate natural resource management into the Australian landscape and to seek new balances: in water quality and quantity, nutrients, vegetation, biodiversity, soil health, and social and economic wellbeing.
Natural resource management requires integrated solutions and therefore, integrated assessments. Australian Dryland Salinity Assessment 2000 does not just concentrate on salinity, but also contributes to the broader land and water management issues.
What is dryland salinity?
Two broad forms of salinity are recognised in Australia.
- Primary or naturally occurring salinity is part of the Australian landscape, and reflects the development of this landscape over time. Examples are the marine plains found around the coastline of Australia, and the salt lakes in central and western Australia.
Salts are distributed widely across the Australian landscapes. They originate mainly from depositions of oceanic salt from rain and wind. Salt stored in the soil or groundwater is concentrated through evaporation and transpiration by plants. In a healthy catchment, salt is slowly leached downwards and stored below the root zone, or out of the system.
- Secondary salinity is the salinisation of land and water resources due to land use impacts by people. It includes salinity that results from watertable rises from irrigation systems-irrigation salinity- and from dryland management systems-dryland salinity. Both forms of salinity are due to accelerated rising watertables mobilising salt in the soil. There is no fundamental difference in the hydrologic process.
Where the water balance has been altered due to changing land use (e.g. clearing of native vegetation for broad acre farming or grazing) the excess water entering the watertable mobilises salt which then rises to the land surface. Movement of water drives salinisation processes and may move the stored salt towards the soil surface or into surface water bodies.
Processes causing stream salinisation
The extent, causes and management options for irrigation salinity are well understood, and have been an important part of Murray-Darling Basin Commission activities for at least two decades. However, in most States and Territories, dryland salinity has received far less attention and resources, and has not been dealt with nationally in any systematic and coordinated manner until very recently. This assessment concentrates on dryland salinity in Australia.
Australian Dryland Salinity Assessment 2000: defining options
It has long been recognised that our land uses-including agricultural development-have significantly changed Australia?s landscapes and natural systems. However, we have not always appreciated the magnitude of change in the soil, water and nutrient balances, the resultant degradation, the timeframe for these changes to be slowed or reversed, and the costs to the wider Australian community.
Changes to the Australian landscape have resulted in the widespread and rapidly growing problem of dryland salinity. Farmers were among the first to be affected, through salinisation of rivers and agricultural land. Biodiversity, as well as regional and urban infrastructure, such as water supply, roads and buildings are now also at risk.
This map represents a compilation of dryland salinity risk and hazard mapping for the year 2050. The map shows the broad distribution of areas considered as having either a high salinity risk or a high salinity hazard. In southern Australia where groundwater level and trend data are available, more confident assessments have been possible. However, in northern Australia groundwater data for trend analysis are very sparse or non-existent. In these regions, salinity assessments have been based on the presence of geological, landscape, regolith, land use and climate attributes which are the prime drivers of salinity. This national map provides a basis for identifying those regions where more detailed assessments are warranted, and where land use changes should be targeted if the risks are to be managed.
Area at risk and impact
The National Land and Water Resources Audit?s (Audit) dryland salinity assessment-Australian Dryland Salinity Assessment 2000-has, in collaboration with the States and Territories, defined the distribution and impacts of dryland salinity across Australia. The aggregate values presented below are the best available estimates within the limits of the methods and data used by the State, Territory and research agencies which undertook this risk assessment.
|New South Wales||181 000||1 300 000|
|Victoria||670 000||3 110 000|
|Queensland||not assessed||3 100 000|
|South Australia||390 000||600 000|
|Western Australia||4 363 000||8 800 000|
|Tasmania||54 000||90 000|
|Total||5 658 000||17 000 000|
* The Northern Territory and the Australian Capital Territory were not included as the dryland salinity problem was considered to be very minor or of moderate to low risk.assessments for more detail.
- The bulk of non-agricultural areas in Western Australia, South Australia and western New South Wales were considered to have a very low salinity risk and were not assessed.
- Approximately 5.7 million hectares are within regions mapped to be at risk or affected by dryland salinity. It has been estimated that in 50 years? time the area of regions with a high risk may increase to 17 million hectares (three times as much as now).
- Some 20 000 km of major road and 1600 km of railways occur in regions mapped to have areas of high risk. Estimates suggest these could be 52 000 km and 3600 km respectively by the year 2050.
- Salt is transported by water. Up to 20 000 km of streams could be significantly salt affected by 2050.
- Areas of remnant native vegetation (630 000 ha) and associated ecosystems are within regions with areas mapped to be at risk. These areas are projected to increase by up to 2 000 000 ha over the next 50 years.
- Australian rural towns are not immune: over 200 towns could suffer damage to infrastructure and other community assets from dryland salinity by 2050.
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 catchments were:
Kamarooka, Victoria - a local flow system in variably weathered fractured rock. Groundwater discharge at break of slope
Lake Warden, Western Australia - a local and regional groundwater flow system in alluvial sediments and deeply weathered rocks
Upper Billabong, New South Wales - a local and intermediate groundwater flow systems in variably weathered fractured rocks in connection to regional flow system in alluvial aquifers
Wanilla, South Australia - a local to intermediate flow system in deeply weathered rock. Groundwater discharge at break of slope and valley floors
The case study region was:
Great Southern, Western Australia - a local and intermediate flow systems in deeply weathered rocks
What are groundwater flow systems?
The Audit?s national dryland salinity assessment has been carried out with the available data on groundwater levels and trends, mapping of lands affected by dryland salinity and knowledge of salt impacts on water resources. It has built on other recent assessments in Western Australia, South Australia and the Murray-Darling Basin. These activities have provided an opportunity to assess the adequacy of data and evaluation approaches and to identify the elements of better collection, analysis and reporting systems.
Constraints to the Analyses
The assessments used existing data held by States and were constrained by the data, timeframes and financial resources available. Difficulties encountered in applying the same landscape analysis approach across States meant that a range of methods and scales were adopted (as described in the National Technical Overview Report).
- Groundwater data limited: In Queensland and Tasmania there are major limitations due to a paucity of groundwater observation bores.
- Groundwater levels: The most reliable estimates come from Victoria and Western Australia where there has been a much better development of monitoring networks. The method used assumes that water table levels continue to change at the assigned rate of rise (or fall) indefinitely into the future. This takes no account of the likely slowing of rates of regional water table rise as the area of active groundwater discharge increases (when groundwater levels are rising). Increased discharge from areas of lower elevation may protect nearby land from the waterlogging and the development of dryland salinity. It is likely that this method overstate the future extent of shallow water tables. The extent to which the area of shallow water tables are overestimated is likely to be greater in more dissected landscapes than those with little vertical relief.
- Groundwater trends: Even where there were perceived to be good quality groundwater data (e.g. in Victoria, south-west Western Australia), the forecasted groundwater levels to 2020 and 2050 are based on straight-line projection of recent trends in groundwater levels. Due to inadequacies in current methods, accurate groundwater surfaces could not be developed with the existing distributed data. This was also an outcome of the Audit?s Salt Scenarios 2020 project (Campbell et al 2000) focused on the Great Southern region of Western Australia.
- Hazard Assessment: In Queensland, the salinity hazard has been estimated using geological and landscape characteristics, climate, land use and knowledge of existing salinity discharge areas. The groundwater information that was appropriate for use in salinity risk assessment is limited to the southeastern part of the State and was used to estimate dryland salinity extent and risk in the Queensland component of the Murray Darling Basin.
- Water resources: Impacts of dryland salinity on water resources were not readily assessable due to the lack of monitoring information at the catchment scale.
- Biodiversity: Few data exist on impacts of dryland salinity on flora, fauna and aquatic ecosystems. Western Australia and Victoria provided the main assessments. Limitations in the estimation of the spatial occurrence of shallow watertables, and the lack of threshold information for species? habitats are important research and development issues.
- Variable methods: The State assessments have identified a number of significant information and method limitations in our ability to evaluate the exact extent of the problem and the likely effectiveness of management responses. Existing monitoring and assessment systems for dryland salinity are inadequate for determining with confidence, the current and future extent of dryland salinity across the continent, or for assessing the effects of any remedial or preventative management responses.
- Lack of comparability: The issues of methods used, reporting scale, monitoring bore distribution and density, data quality and availability need to be considered when interpreting the results of the State assessments.
- Monitoring systems: Major improvements are required in monitoring systems. Improvements include better design and performance indicators appropriate to the questions being asked and the scale being considered.
- Measures of success: Because timeframes for measuring responses for some indicators such as salt trends in streams are long, surrogate measures (such as changes in the levels of perennial vegetation) will be required to assess impacts of land use changes/management responses in the short term.
- Future evaluation: Methods and standards to improve the rigour of subsequent national, regional and local scale audits need to be developed. Future Audits to determine the extent and impact of salinity will require improved data sets from those that were readily available within the given timeframe.
- Australian Dryland Salinity Assessment 2000 report
- National Technical Overview Report of the State-based dryland salinity assessments
- Dryland Salinity Evaluation and Monitoring Report
- Australian Groundwater Flow Systems Technical Report
- National Dryland Salinity Program
- National Action Plan for Salinity and Water Quality
Link to the Map Maker to make a map using this information.
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Key supporting references
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