Fluidized Bed Technique for Estimating Soil Critical Shear Stress

Soil erosion models, depending on how they are formulated, always have erodibility parameters in the erosion equations. For a process-based model like the Water Erosion Prediction Project (WEPP) model, the erodibility parameters include rill and interrill erodibility and critical shear stress (τ(cr)). These erodibility parameters are commonly determined from rainfall and runoff experiments. Recent developments in soil erosion research suggest that these experimentally determined parameters are affected by field conditions prevailing during the measurement and therefore are not inherent to the soil. The quest for fast and accurate alternatives to rainfall and runoff experiments for estimating soil erodibility parameters is an active research area. In this study, the fluidized bed technique for intrinsic soil cohesion measurement was improved and tested on four soils with various intrinsic soil properties, along with two low-cohesion materials, sand and glass beads. A strong correlation (R(2) = 0.82) was found between cohesion per unit length C0 and published τ(cr) values. In addition, when the C(0) values were multiplied by a submillimeter dimension equivalent to a hypothetical layer removed at the onset of erosion, the range of stress that was yielded overlapped that of the published τ(cr) values. This method is a simple alternative to rainfall–runoff experiments, with the added advantage of being independent of extrinsic factors.