In the recent decades, dryland salinity problems associated with the regolith have been of great concern to Australia, as they greatly affect the agricultural industries. A detailed regolith mapping system integrated with geophysics and other mapping techniques has been applied to a project test area on Sandy Creek in the Lockyer district, south-eastern Queensland to relate regolith characters to dryland salinity. Sandy Creek and its catchment in the Helidon Hills is an important water source for the Lockyer Valley which posesses some of the richest agricultural land in Australia. The test area is of particular interest as it includes a water harvesting system and shows evidences of salt and iron leaching.
Considerable progess in regional regolith mapping has been made, but there is also a need for more detailed scale mapping systems to serve management of resources (eg. land, water, foundation resources). Whereas regional mapping has been based on landforms and patterns of landforms, detailed regolith mapping developed in this thesis is based on subdivisions of landforms into 'elements' with corresponding regolith elements differentiated according to toposequences such as in catenas.
Although regolith is surficial, the subsurface characteristics of the regolith are not easily obtained. Geophysical surveys (eg. seismic, resistivity) are useful in that they provide these concealed properties of regolith. A simple resistivity probe was constructed to provide an economical means of assessing shallow regoliths. It was tested in the Sandy Creek test area. However use of the probe proved to be time consuming and limited to pan horizons at Sandy Creek. Thus other geophysical systems were tested. A four-electrode resisitivity technique (employing the Wenner Array) was tried as an alternative electrical method. However this technique proved to be inappropriate for shallow regolith investigation in drought conditions as experienced during this study. An electromagnetic conductivity meter proved to be most effective. It proved substantially quicker and easier to operate as it does not require galvanic contact by ground electrodes. This was an important factor in investigating the regolith under the record drought conditions of 1994.
Domains and discontinuities in apparent conductivity determined by means of a terrain conductivity meter (EM31) manufactured by Geonics Limited of Canada were found to correspond with regolith elements and boundaries based on field mapping. Apparent conductivity is affected by moisture content, clay content and salinity, so that it allows an assessment of many parameters of the regolith. Consequently, it defines the regolith elements which are a basis for a holistic management of landscape, soils, water and vegetation. This is illustrated in an overlay of maps that correlate regolith, geophysical, remote sensing, landscape, and management information. This system of overlays is linked with a drainage model to develop a management strategy with critical location of trees and drainage to control salt and iron leaching.