On the hydraulic properties of coarse-textured sediments at intermediate water contents

Abstract

A modified steady state head control method was used to obtain, on identical samples, direct measurements of soil moisture retention (volumetric water content θ versus matric potential ψ) and unsaturated hydraulic conductivity (K) as a function of both θ and ψ. The minimum ψ values for the undisturbed coarse-textured samples were as low as -400 cm, whereas the θ values were as low as 0.04. Of the 79 samples, 41 contained a high gravel fraction (>2 mm size) that ranged from 20 to 71% by weight. The remaining samples were sandy with very little gravel fraction. We examined similarities and differences between the two soil types in their retention and K(θ) slopes for the intermediate moisture regime. The retention data for the gravelly soils fell within a narrower range than for the sandy type. The water capacity (dθ/dψ) estimates for the two soil types showed similar variability. Although both soils are coarse-textured, important differences were noted in two integral measures for ψ(θ) and K(θ) measurements. The mean and variance for the Campbell pore-size distribution parameter (b) and K(θ) slope (β) estimates for the gravelly type were larger than those for the sandy type. A unique relation was noted between b and β the relationship was similar for the two soil types with a very dissimilar particle-size distribution.