Regolith-Terrain Analysis and Mapping as a Soil Geomorphological Investigative Methodology for Land Resource Assessment.
Robin N. Thwaites, School of Natural Resource Sciences, Queensland Univ of Technology, Gardens Point Campus, Brisbane, Queensland 4001, Australia
This paper defines the concept of and regolith terrain analysis and mapping (R-TAM) within a regolith pedology context. Regolith pedology encourages a greater geoscience involvement in scientific investigations of soil materials and provides a merger of geoscience and pedological conceptual viewpoints towards solving soil-related natural resource and environmental management problems. Terrain analysis and modelling play key roles in soil-geomorphological landscape mapping. The advent of new technologies and greater modelling applications means that distinctly soil-geomorphological concepts relating to the soil-geomorphological landscape (the ‘geoscape'), and to earth surface processes, can be investigated and applied to land resource management issues. Regolith-terrain mapping is a collection of methods used largely for mineral exploration purposes but has also been applied for land resource evaluation and management purposes. The conceptual approach proposed here entails both the terrain analysis and modelling procedures with those of regolith-terrain mapping as R-TAM. The example presented here of R-TAM is a study to produce continuous data surfaces of the spatial variation of appropriate regolith attributes for forest site-specific management. The approach characterises the soil landscape both from field survey and through digital modelling by initially identifying functional, process-based landscape units termed Regolith-Catenary Units (RCUs). The soil resource is portrayed as a 3-dimensional, soil-geomorphological landscape, and is presented as quantitative regolith-terrain (soil-landscape) information in an explicit and repeatable process through spatial modelling. Fuzzy classification of RCUs then is a basis for the conceptual modelling of the landscape to produce a predicted spatial variation in selected regolith-terrain attributes. Regolith-Catenary Units are taken as the composite regolith-terrain entity, which are described through soil-geomorphic techniques applied to the whole regolith. Observations of the regolith are limited, so conceptual models of the regolith-terrain within the Regolith-Catenary Units are necessary. Spatial expression of landform attributes was achieved through the predictive capabilities of digital terrain analysis using first- and second- derivative functions from a digital elevation model (DEM). Landform attributes are combined through a set of fuzzy rules to form digital Primary Pedogeomorphic Units (PPUs), which are then integrated with the interpreted RCUs. These then serve as decision support ‘maps' of the regolith-terrain attributes that relate directly to site-specific management of the forest resource. These maps are then the basis for site evaluation for general or specific management requirements, e.g. harvesting, establishment, soil conservation and drainage planning. Regolith-Terrain Analysis and Mapping is still an emerging methodology for land resource assessment, and it's application to this purpose is still in need of development.