A conceptual model to predict the deflation threshold shear velocity as affected by near-surface soil water: II. Calibration and verification

A conceptual model to predict the threshold shear velocity, which should be overcome to initiate deflation of moist sediment, was recently developed by Cornelis et al. The model relates the threshold shear velocity to the ratio between water content and the water content at a matric potential of -1.5 MPa, and contains one proportionality coefficient that accounts for the effect of near-surface wetness. The present study was conducted (i) to determine that proportionality coefficient and hence calibrate the model, and (ii) to verify the calibrated model. The model calibration was achieved through curve fitting the expression against a data set from wind-tunnel experiments that were conducted on different sized sand particles and soil aggregates. Each sediment sample tray was prewetted, and subjected to different shear velocities and hence to different evaporation rates that dried the sediment. Once particle entrainment became sustained as recorded with a saltiphone, samples were taken to a depth of 1 mm to determine water content gravimetrically. To verify the calibrated model, threshold shear velocities simulated with our expression were compared with values obtained with Chepil's model of 1956. It was observed that the soil had to dry out to 75% of the water content at a matric potential of -1.5 MPa for deflation to occur. A single proportionality coefficient value could be used for the different sized sand and soil particles. Very good agreement was observed between our model and the model of Chepil.