Effect of Stones on the Hydraulic Conductivity of Relatively Dry Desert Soils

Abstract

The objective of this study was to determine whether moisture transmission properties of stony soils could be evaluated using samples of the same soil in which the stony fraction (> 2 mm) had been excluded. Experiments were conducted in the laboratory on soil columns with and without stones. Unsaturated hydraulic conductivity (K) was measured with a transient outflow method over the matric potential range of −0.05 to −50 bars using tensiometers and soil psychrometers. The soils studied were Rock Valley gravelly loamy sand (Mojave Desert, Nevada) and Tubac and Rillito gravelly sandy loams (Sonoran Desert, Arizona). On a weight basis, these soils contain up to 40% stones > 2 mm in diameter.If expressed as a function of matric potential, hydraulic conductivity values were similar, with or without stones. Soil water potential as measured by tensiometers or by thermocouple psychrometers is not affected by stones because these instruments respond to moisture changes in the soil portion only. When K was expressed as a function of volumetric water content, the apparent conductivities were higher for a given water content when stones were present. A simple correction of water contents of stone‐free samples, based on the stone volume of each soil, adequately accounted for differenecs observed when water contents were computed on a total volume basis.

Determining the Porosity and Saturated Hydraulic Conductivity of Binary Mixtures

“…Mehuys et al (1975) experimented with stony desert soils (up to 40% by mass of gravels with particle diameter >2 mm) and found that the presence of stones had no appreciable effect on the relationship between unsaturated hydraulic conductivity, K, and pressure head of soil water, ψ. Infiltration in stony soils decreases with increasing rock content because of the less accessible surface for water flow (Valentin 1994). Furthermore, the more spherical rock fragments are, the lower the saturated hydraulic conductivity (Dunn and Mehuys 1984).…”

Evaluation of Hydraulic Parameters Obtained by Different Measurement Methods for Heterogeneous Gravel Soil

“…All of these methods are time and energy consuming and difficult to obtain satisfactory results in a heterogeneous medium. In addition, although the impact of size, content and distribution of rock fragments on soil water movement have been studied by many scholars, conflicting trends often exist in various reports revealing positive correlations, negative correlations, no correlations or a "turning point" between the size/content and infiltration ability (conduction) (Mehuys et al 1975;Bouwer and Rice 1984;Ravina and Magier 1984;Brakensiek et al 1986;Sauer and Logsdon 2002;Khaleel and Heller 2003). Consequently, it has been a challenge to understand the impact of rock fragments on soil hydraulic character, especially at a heterogeneous research site.…”

Variability of Gardner's α for coarse‐textured sediments

“…However, extensive data sets on unsaturated K and its variability are generally not available because of the significant time and effort involved in obtaining accurate measurements, especially in the dry range [e.g., Khaleel et al, 1995]. The problem is further complicated by the frequent presence of a high gravel fraction in vadose zone soils in an arid setting [Mehuys et al, 1975;Russo, 1983b;Bouwer and Rice, 1984;Khaleel and Relyea, 1997].…”