Digital Hillslope Position: A Basis for Consistent Identification of Toposequences.

The lack of a quantitative definition for hillslope position has led to variability in how hillslope elements are defined in various toposequence studies. This shortcoming limits our ability to gain broader understanding of pedologic processes because of the difficulty in comparing studies. A consistent definition of hillslope position would help bring focus to the variation of soil properties observed on hillslopes. We calibrated a model of hillslope position based on the field observations of soil mappers; they regularly make that determination in the context of fieldwork. Despite the variation of hillslope position definitions in research studies, I report on a hillslope position model that was consistent between multiple soil scientists working for two different MLRA offices, across three different Midwestern US landscapes. Because this model is quantitative, it can be easily applied to digitally classify hillslope elements. Use of this digital method for examining toposequences would improve the comparability of different hillslopes, particularly in the context of hydropedology. Although the consistency of position identification between multiple soil scientists suggests that they are keying in on something real in the landscape, more work is needed. Additional data are needed to verify how broadly this model is applicable across different landscapes and among different soil scientists. Also, more research is needed to better understand the processes that produce these thresholds and to similarly quantify the operational scales of other topographic factors not included in hillslope position, such as plan curvature.