FLAG UPNESS and its application for mapping seasonally wet to waterlogged soils

Abstract

The UPNESS index derived from the Fuzzy Landscape Analysis Geographic information system (FLAG) model was calculated for the Wagga Wagga and Kyeamba Creek Catchments in NSW, Australia. The model uses digital elevation data only to derive UPNESS and several other indices of relative height in the landscape. UPNESS is an index of surface and subsurface water accumulation calculated as the set of cells above any given point in a raster grid that are connected by a continuous monotonic uphill path. Accumulation of groundwater causes increased secondary weathering, solubilisation of rock and soil minerals, and soil pedogenic development. In this paper the UPNESS index is compared with depth to a shallow water table and groundwater electrical conductivity (EC). Reasonable relationships with r² = 0.71 and 0.74 were found between the UPNESS index and depth to watertable and groundwater EC, respectively, in the Wagga Wagga study area.

UPNESS was then used to predict spatial extents of waterlogged to seasonally waterlogged, saline, and sodic soil landscapes within the Kyeamba Catchment, a larger catchment, with soil landscape mapping at a scale of 1:100 000. Most differences between UPNESS and soil landscape mapping occurred in broad valleys where deeply incised channels have caused UPNESS calculations to be more restricted to the stream lines than mapped boundaries. In valley-filled areas with little incision, the UPNESS index derived similar areas but with substantially more detail than the soil landscape mapping. The UPNESS index provides an efficient method to help differentiate seasonally and fully waterlogged, saline, or sodic soils from the drier soils in a catchment. This may aid in objectively establishing initial soil landscape boundaries with detail that would otherwise be too costly to obtain.