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In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
Salinity - Risk and Hazard - Northern Territory
Northern Territory
Where is there a dryland salinity risk or hazard and how was this determined?
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.
The most obvious feature of the dryland salinity hazard map for the Northern Territory is the absence of any areas classified as high hazard. Approximately 6% of the total area of the Northern Territory has a moderate hazard, 34% is low and 60% is very low.
The salinity hazard of the humid north and the arid south show distinctly different patterns, with the humid zone classified as mainly low and moderate hazard while the arid zone is predominantly very low hazard, with lesser areas of low hazard restricted to the ranges. The extensive grasslands of the arid zone account for the very low hazard areas while shrublands associated with the ranges raise the hazard of these areas to low.
Assessment methods
The indicators chosen to construct the salinity hazard map are groundwater salinity, vegetation, median annual rainfall, aquifer yield and the presence or absence of laterite. Insufficient information is available to rank these in order of importance, so they have been given equal weighting. Each indicator has been divided into a range of values or types which will have differing influence on the salinity hazard. These were chosen based on the quality of the available data and on a broad knowledge of the values which are likely to be critical to dryland salinity.
For a given indicator, each range has then been compared to the others to determine their relative importance with respect to salinity hazard. They have been assigned a numerical value with the most important having the highest value.
A salinity hazard index of a particular area was then computed by adding the rating for each indicator. The higher the index the greater the salinity hazard.
Ratings from each map were added to produce a salinity hazard index for each sub-area. The map was simplified by grouping ratings into four ranges and assigning hazards of high, moderate, low or very low to each.
High hazard
Only areas with all of the following characteristics are classified as high hazard; groundwater TDS greater than 3000 mg/L, rainfall between 600 and 1400mm, low open woodland to forest vegetation type, aquifer yield less than 0.5 L/s and laterite present. Salinity hazard indices therefore range from 43 to 50.
Moderate hazard
Areas with combinations of physical characteristics which yield salinity hazard indices between 33 and 42 are included in this category. The upper and lower limits are set by the definitions of the high and low hazard categories.
Low hazard
Typical conditions for low hazard are defined here as groundwater TDS less than 1500 mg/L, rainfall less than 600mm or greater than 1400mm and aquifer yields greater than 0.5 L/s. With those three conditions occurring together the maximum possible salinity hazard index is 32. Areas with low hazard therefore have indices 32 or less.
Very low hazard
Areas with grassland or with aquifer yields greater than 5 L/s have been automatically categorised as having very low hazard. The reason for this is that in the case of grassland any alteration to the vegetation is unlikely to result in a significant increase in groundwater recharge and thus in a rise in watertables.
In areas underlain by high yielding aquifers, increases in recharge brought about by clearing will be dissipated by lateral flow through the aquifer and out of the area. Groundwater mounds would thus be unable to form.
The salinity hazard map was published at a scale of 1:2,000,000. The amount of detail and the scale of the component information did not warrant the use of a larger scale.
How can dryland salinity risk change over time?
As the salinity hazard is consider low no assessment of change in dryland salinity over time was required in the Northern Territory.
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
Link to Map maker to make a map using this information.
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