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

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 ( d θ /d ψ) 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.