Geological factors influencing dryland salinity risk

Dryland salinity has become a major environmental problem in Australia through changes in land management incurred since European settlement. Given appropriate conditions of land management and clin1ate, salinisation follows the advent of discharge areas which arise through rises in groundwater level and/or impediments to groundwater flow. Impediments may be structures such as dams, roads and railway embankments but can also occur naturally through geological features. Geological structures such as dykes, faults and contact zones may be impediments to groundwater flow as can changes to hydraulic conductivity through changes in the permeability of rocks and soils. Geological factors have been incorporated into a predictive model to identify areas at risk to salinisation. The model is a Decision Tree Analysis run via the Knowledge SEEKER computer program. Results from this modelling exercise are comparable with other models based on surface and near-surface flow and topographic indices but suffer from being site specific. The study highlights the need for development of improved methods of mapping subsurface features and for widespread changes to the current system of land management