Exploring the sensitivity on a soil area-slope-grading relationship to changes in process parameters using a pedogenesis model
Abstract. This paper generalises the physical dependence of the relationship between contributing area, local slope, and the surface soil grading first described by Cohen et al, [2009, 2010] using their mARM1D and mARM3D pedogenesis models. A more general computational model, SSSPAM5D, extending the conceptualisation of mARM3D has been developed to further our exploration of soilscape self-organisation. A parametric study was carried out using different parent materials, erosion, and weathering mechanisms. These simulations confirmed the generality of the area-slope-d50 relationship. The relationship is also true for other statistics of soil grading (e.g. d10, d90) and robust for different depths within the profile. For small area-slope regimes (i.e. hillslopes with small areas and/or slopes) only the smallest particles can be mobilised by erosion and the area-slope-d50 relationship appears to reflect the erosion model and its Shields Stress threshold. For higher area-slope regimes, total mobilization of the entire soil grading occurs and self-organisation reflects the relative entrainment of different size fractions. Occasionally the interaction between the in-profile weathering and surface erosion draws the bedrock to the surface and forms a bedrock outcrop. The study also shows the influence on different depth dependent in-profile weathering functions in the formation of the equilibrium soil profile and the grading characteristics of the soil within the profile.