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PDF files

• Salinity mapping methods in the Australian context - full document (PDF - 2660 KB)
• Foreword, contents and executive summary (PDF - 127 KB)
• Main text - introduction to conclusions (PDF - 1820 KB)
• Appendices (PDF - 630 KB)
• References, glossary and index (PDF - 85 KB)

About this document

Executive Summary

Salt is a hazard when it has the potential to be moved to where it can threaten assets such as agriculture, infrastructure, water resources and biodiversity. Salt stored in the ground may be mobilised by water and transported vertically and horizontally. Australia's growing problem of dryland salinity cannot be reliably assessed without a thorough three-dimensional understanding of the landscape and the hydrological processes that operate within it.

Mapping is the means by which we gain an understanding of what lies on and beneath the Earth's surface. The major uses of mapping in the studies of dryland salinity are to delineate areas affected by surface or vegetation expressions of dryland salinity, and to identify areas not yet affected but at risk of salinisation.

At least 30 satellite, airborne and ground mapping techniques are available for mapping and delineating soils, landforms, water flow and pathways through the subsurface.

• Some can be used to detect or infer the presence of salt at the Earth's surface or contained in the soil profile.
• Satellite and airborne remote sensing techniques can reveal existing surface salinity and can track changes over time.
• Airborne geophysical techniques, combined with ground and borehole control, are important tools in understanding salinity and hydrology at depth at a variety of scales.
• Only borehole sampling and electromagnetics (EM) techniques can detect and resolve salinity in the subsurface at depths in and below the root zone. EM techniques can also give complementary information on palaeochannels and structures which often control groundwater flow.

Salinity risk is a measure of the chance that a salt hazard will cause harm to an asset at some time in the future. Risk should be assessed in the context of the assets to be protected, including agriculture, water quality, infrastructure and the environment. Cost-benefit analyses in salinity management should take into consideration total cost and total benefit in context with the value of all assets.

The optimum strategy for mapping salinity hazard and risk depends on the scale (farm, community or catchment) and resources available to the user. Users need to make best use of existing information and then integrate a range of the available mapping methods so that they best address their specific problem. No single method has primacy, nor is there a ‘magic bullet' for salinity mapping or prediction. Effective use of mapping methods requires expert knowledge or access to trained personnel.

A lot is known about salinity in the top few metres of ground-from dying vegetation , salt scalds and saline water seeps. Each landowner has a good idea of what is visible on their property. A wide range of satellite and airborne techniques can be used to assist in mapping surface expressions of salt and have a useful role in extrapolating from the existing knowledge of surface expression of salinity, obtained by visual inspection and near-surface EM conductivity mapping .

Managing salinity more strategically is hampered by a lack of knowledge about the location of concentrations of salt in the subsurface and whether they are likely to be mobilised by groundwater and pose a risk to assets . Hydrology is the key to understanding how salt stores are mobilised through the earth, both vertically and horizontally. The only broadacre, remote sensing technique that can detect and resolve salinity in the subsurface deeper than the root zone is electromagnetics (EM). Interpretations of EM (and most other techniques) needs to be done by specialists and be checked by targeted ground-truthing, including drill holes and borehole logging. Magnetics can give complementary information on palaeochannels and other structures that could be zones of preferential groundwater flow.

This book covers 26 different methods for mapping salt stores, dryland salinity hazards and risk. It sets out the benefits and limitations of each technique together with useful information on costs, scale, survey design and the depth to which each technique is useful. The book comprehensively summarises the science that justifies the use of each mapping method and refers the reader to a range of references that will provide an even fuller technical explanation if necessary.

This book describes the usefulness of all relevant mapping methods (in use and proposed) for mapping dryland salinity in Australia, and describes their efficacy in the assessment of salinity hazard and risk. The book has the following elements:

• background and context;
• typical questions posed at farm, community, catchment and national scales;
• a description of the interplay of salt and water movement in the landscape that controls salinity (framework factors);
• an assessment of salinity hazard and risk, and costs and benefits of mapping ;
• information on mapping the landscape at different scales to solve salinity-related questions;
• a brief description of methods to map the landscape from the surface, boreholes, aircraft and satellites-salinity mapping methods are categorised as those that directly detect salt and those that use surrogate or indirect attributes to infer the presence of salt and are stratified by the level below the surface at which they operate;
• illustrative case histories describing the process of selecting appropriate mapping techniques for particular problems, including assessment of the future distribution of salinity as it is likely to affect the assets in the landscape such as agricultural production, biodiversity and infrastructure;
• appendices with expanded descriptions of each mapping method; and
• a glossary of key terms.