Digital Classification of Hillslope Position for Defining Soil Map Units.

Classification of hillslope position has a long history in soil geomorphology. Indeed, at the scale of most county-level soil maps, more soil boundaries are based on topography than any other soil-forming factor. However, the inability to accurately and efficiently delineate topographic breaks associated with hillslope elements – either due to lack of sufficient topographic resolution or the proper technology to develop/model them – limits soil mapping accuracy and precision. In this poster, we present modeled data that objectively and quantitatively define the five major hillslope positions, using high resolution elevation data. The model has been calibrated and validated on soil scientists’ observations in the field. The resulting maps of hillslope position represent base maps that can be used to (1) improve research on toposequences by providing explicit definitions of each hillslope element’s location, (2) facilitate the disaggregation of soils currently mapped as complexes, and (3) identify map unit inclusions that exist due to subtle topographic variation. The base maps developed by the model can also help identify areas of possible mismapping, especially where soil boundaries cross topographic breaks. This information can enable the mapper to redefine many existing soil map unit boundaries, placing them more correctly at locations where defendable landscape breaks exist.