Salinity - Overview - Northern Territory
Northern Territory
Introduction
Salinity hazard in the Northern Territory has been assessed (Tickell 1994a, 1994b, 1997) by combining information on various physical parameters that contribute toward the likelihood of dryland salinity. These parameters were then combined in a simple additive model on a geographic information system to map zones of relative hazard.
The most obvious feature of the Northern Territory salinity hazard map is the absence of any areas classified as high hazard. Approximately 6% of the total area has a moderate hazard, 34% is classed as low hazard and 60% as very low.
The salinity hazard of the humid north and the south of the Northern Territory show distinctly different patterns: the humid zone is classified as mainly low and moderate hazard, whereas the arid zone is predominantly very low hazard; lesser areas of low hazard are restricted to the ranges.
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Five indicators used in the hazard assessment were: groundwater salinity, vegetation, median annual rainfall, aquifer yield and the presence or absence of laterite. All were given equal weightings. Each indicator was divided into a range of values and assigned a numerical rating, with the most influential having the highest rating value. A salinity hazard index of a particular area was then computed by adding the rating for each of the five indicators.
Findings
The following findings are based on Tickell 1994.
- Overall salinity hazard for the Northern Territory is relatively low.
- The greatest potential for dryland salinity is in the inland semi-arid areas (particularly on the Sturt Plateau) where conditions are marginally favourable and it would be expected to develop in isolated patches. Other susceptible areas are scattered mainly across the northern part of the Territory.
- If large areas of the Northern Territory were cleared for dryland agriculture, it is unlikely that dryland salinity would become the major problem that it is in southern and eastern Australia. This is because in higher rainfall areas, where deep-rooted vegetation is abundant, salt storages in the ground are small.
- In the more arid areas, where salt storages are often large, deep-rooted vegetation is either sparse or absent. Thus, clearing native vegetation in these areas would be unlikely to alter the water balance sufficiently to raise watertables to dangerously high levels.
- Groundwater monitoring of approximately 50 sites has shown no overall rising trends (Tickell pers. comm.)
Reporting units and case studies
A map overlay technique was used to prepare the Northern Territory salinity hazard map
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.
Further information
- Northern Territory Dryland Salinity Assessment 1994 report
- Australian Dryland Salinity Assessment 2000 report
- National Technical Overview Report of the State-based dryland salinity assessments
- Australian Groundwater Flow Systems Report
- Northern Territory Department of Natural Resources, Environment and the Arts.
- National Dryland Salinity Program
- National Action Plan for Salinity and Water Quality
Key references
Tickell S.J. 1994a, Regional salt storage - Northern Territory, Water Resources Division, Power and Water Authority of the Northern Territory, Report 47/94D.
Tickell S.J. 1994b, Dryland salinity hazard map of the Northern Territory, Water Resources Division, Power and Water Authority of the Northern Territory, Report 54/941.
Tickell S. 1994c, The risk of dryland salinity in the Northern Territory, Northern Territory Department of Land Planning and Environment.
Tickell S.J. 1997, ?Mapping Dryland-Salinity Hazard, Northern Territory, Australia?, Hydrogeology Journal, vol. 5, pp. 109-17.
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