Abstract
Development-perched watertables and subsurface lateral flows in texture-contrast soils (duplex) are commonly believed to occur as a consequence of the hydraulic discontinuity between the A and B soil horizons. However, in catchments containing shallow bedrock, subsurface lateral flows result from a combination of preferential flow from the soil surface to the soil—bedrock interface, undulations in the bedrock topography, lateral flow through macropore networks at the soil—bedrock interface, and the influence of antecedent soil moisture on macropore connectivity. Review of literature indicates that some of these processes may also be involved in the development of subsurface lateral flow in texture contrast soils. However, the extent to which these mechanisms can be applied to texture contrast soils requires further field studies. Improved process understanding is required for modelling subsurface lateral flows in order to improve the management of waterlogging, drainage, salinity, and offsite agrochemicals movement.
Highlights
Texture-contrast soils cover approximately 20% of the Australian land mass [1] or 2.33 million km2 [2]
The importance of the bedrock properties on subsurface lateral flow development, location, and velocity was further demonstrated by Graham et al [52] who concluded that downslope flow in the Maimai catchment was concentrated at the soil bedrock interface in which flow path location was controlled by small variations in topography and permeability of the bedrock topography
Review of the literature on steep, forested catchments with shallow bedrock indicates that subsurface lateral flow results from a combination of preferential flow from the soil surface to the soil-bedrock surface, variation in the surface topography of the bedrock leading to fill and spill mechanisms which become more connected as antecedent soil moisture increases, and saturated channaelised flow along depressions in the bedrock surface and/or lateral flow through pore networks along the bedrock surface
Summary
Texture-contrast soils (duplex) cover approximately 20% of the Australian land mass [1] or 2.33 million km2 [2]. In “Soil Taxonomy” [10], soils showing characteristics most like those of the duplex soils are classified with the formative element “pale” meaning to show excessive development This includes 15 Great Groups in 3 orders: the Mollisols, Ultisols, and Alfisols. Reduced crop yields in texture-contrast soils result from soil erosion, crusting, limited rooting capacity, poor aeration resulting from the slow movement of soil water through the upper B horizon, and confining of roots to shrinkage cracks and ped faces in the subsoil [19,20,21,22,23,24,25]. Improved process understanding of the mechanisms by which perched water-tables and subsurface lateral develop in texture-contrast soils is required for further model development in order to reduce the incidence of waterlogging, improve irrigation efficiency, and minimise the offsite mobilization of nutrients and agrochemicals to waterways. Differences in process understanding and soil water modelling between the two landscapes are articulated, the transferability of process understanding to texture-contrast soils is discussed, and recommendations for future field research and model development are provided
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