Soil degradation (salinity, sodicity, waterlogging and acidity) in the high rainfall catchments in the Mount Lofty Ranges and Dundas Tablelands is a growing concern to property holders because of the rapid increase in waterlogged saline scalds. The objective of this study was to develop a systematic approach to constructing soil–regolith models that describe, explain and predict soil–water landscape degradation processes in a specific region.

The ‘descriptive model’ uses toposequences (soil landscape cross-sections) to describe the basic soil–regolith features and direction of soil water and solute movement. Here, we suggest that it is also necessary to produce models to explain and predict the relationships and behaviour of the soil–regolith system under study. Such models could explain and predict the processes giving rise to the vast range of complex and poorly understood saline, sodic and acid sulfate soils in catchments. Toposequence and catchment scales are the most suitable for constructing such models because each of the vertical and lateral changes can be linked to hydrological, physicochemical and biomineralogical processes.

This chapter describes several case studies that illustrate how the different types of soil–regolith model have been used to describe and predict degradation processes in salt-affected soils and adjacent stream waters, and to assist in generating maps at catchment and regional scales using geographic information systems. They have also been used to produce soil–landscape and vegetation field keys, which provide details of land-use options that can help to prevent the irreversible spread of saline and sodic conditions.