Predicting unsaturated hydraulic conductivity functions of three Indian soils from particle size distribution data

Abstract

The present study compares experimental unsaturated hydraulic conductivity functions, K(θ), of 9 soils of Maharashtra State of India, 3 each in the clay, clay loam, and loam textural classes, all predicted by a particle size distribution (PSD) based model. PSD data were transformed into pore-size distribution using Aryas' modified model. Experimental K(θ) curves were determined by the horizontal infiltration method. Fifteen soils, 5 each with clay, clay loam, and loam texture, were used to evaluate the parameters of flow model (i.e. q_i = cr_i^x) empirically. These parameters deviated from Hagen-Poiseuilles' equation for an idealised porous medium. An effort was made to interpret the deviation in the logc and x values in relation to changes in hydro-physical behaviour of these soils. The model includes packing density and pore tortuosity as a scaling factor, α, of the Arya-Paris model. The model predicted hydraulic conductivity of these soils quite satisfactorily with R² values for log-transformed experimental and predicted hydraulic conductivity being 0.85, 0.97, 0.94, and 0.92 for clay, clay loam, loam, and all textures together, respectively. The root mean square residues for the soils ranged from 0.067 to 0.724, with an average of 0.428. Prediction uncertainties in intra- and inter-textural classes were attributed to differences in hydro-physical behaviour of the soils.