Review of methods for mapping dryland salinity

Abstract

Dryland salinity, a growing problem over much of Australia, can only be mapped and predicted with a thorough understanding of the landscape in three dimensions and the hydrological processes that operate within it. Hydrology is the key for understanding how salt stores are mobilised through the Earth, both in a vertical and horizontal sense. Mapping techniques have important roles in delineating soils, landforms, water flow and pathways through subsurface topography, as well as detecting or inferring the presence of salt itself. Satellite and airborne remote sensing techniques are useful in delineating existing surface and near-surface salt, and tracking changes over time. Airborne geophysical techniques, combined with ground and borehole control, are important tools in understanding salinity and hydrology at depth, and essential tools for predicting future changes in salinity. Salt is a hazard when it has the potential to be moved, usually by water, to a location where it can threaten an asset, which may include agriculture, infrastructure, water quality and biodiversity. Salinity risk is a measure of the chance that the salt hazard will cause harm to the asset at some time in the future. Cost-benefit analyses in salinity management should take into consideration total cost and total benefit in context with the value of the asset. The optimum strategy for salinity hazard and risk mapping depends on the scale (farm, community or catchment) and resources available to the user. The best approach makes use of existing information and then integrates a range of the available mapping methods in such a way to best address the specific question at hand. No one 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.