The effects of rock fragment shapes and positions on modeled hydraulic conductivities of stony soils

Abstract

Mountainous soils usually contain a large number of rock fragments, particles with a diameter larger than 2 mm, which can influence soil hydraulic properties that are required to quantitatively describe soil water movement in stony soils. The objective of this study was to numerically estimate both the saturated hydraulic conductivity of a stony soil and its dependence on a relative content of rock fragments (stoniness), and the shape, position and distribution of rock fragments in a soil matrix. The assessment method was based on a numerical version of Darcy's classic experiment that involved steady-state flow through a porous material under a unit hydraulic gradient. Our experiments, involving hypothetical stony soils in this particular case, were simulated using mainly the two-dimensional (2D) numerical model, HYDRUS-2D. A limited number of simulations were carried out using a threedimensional HYDRUS model. Three different shapes of hypothetical rock fragments were used in the study: a sphere, an ellipsoid with two different positions, and a pyramid, all represented by their 2D cross-sections (i.e., a circle, an ellipse, and a triangle, respectively). The mean relative effective saturated hydraulic conductivity (K rs ) for the same stoniness was almost the same for all simulated scenarios and fine soil textures. A stoniness between 0.07 and 0. . Simulated K rs values were underestimated in all scenarios as compared to the Ravina and Magier (1984) function. The smallest differences (−1.1%-2.5%) between numerically simulated and calculated (the Corring and Churchill (1961) method for a cylindrical shape of RFs) K rs values were found for scenario A with its 2D representation of spherical rock fragments. Calculated (the Corring and Churchill (1961) method for a spherical shape of RFs) K rs values corresponded well with those simulated using a 3D representation of spherical rock fragments. Numerical models provide a unique opportunity to evaluate the effects of different factors on the saturated hydraulic conductivity of stony soils that may be nearly impossible to measure in practice.

Influence of Stone Content on Soil Hydraulic Properties: Experimental Investigation and Test of Existing Model Concepts

“…Up to the present, most studies have focused on the volumetric stone content as the most influential factor in estimating the hydraulic properties of stony soils. However, shape, orientation, size distribution, roughness of the stone surface, stone porosity, and placement may also play important roles in changing the effective SHPs (Hlaváčiková et al, 2016). Although the existing work points in the right direction, our results suggest a need for further experimental investigations as a base for developing models that consider more characteristics of the stones.…”

“…In general, the effect of stones on SHPs will depend on the stone content, shape, type, orientation, surface roughness, porosity, position, and size, and this is particularly the case for high stone contents (Zimmerman and Bodvarsson, 1995; Verbist et al, 2009; Ma et al, 2010; Tanino and Blunt, 2012; Hlaváčiková et al, 2016). The simplest model concept is to assume that stones represent just a hydraulically inactive volume fraction that does not alter the local physical properties of the soil and only reduces the water content and hydraulic conductivity of the soil linearly by reducing the (effective) flow cross‐section.…”

Diagnóstico do uso e conservação do solo em região de reforma agrária no semiárido

“…Os solos pedregosos são compostos por pequenas frações de partículas com um diâmetro inferior a 2 mm, e maiores frações de fragmentos de rochas, como por exemplo, cascalho, pedras, pedras e rochas (HLAVÁČIKOVÁ et al, 2016).…”

Thematic Issue on HYDRUS Software Applications to Subsurface Fluid Flow and Contaminant Transport

“…While stony soils have been studied in the past using HYDRUS (2D/3D) (e.g., Hlaváčiková et al, 2016;Novák et al, 2011;Parajuli et al, 2017), those studies considered only hypothetical soil systems with simplified geometries and idealized distributions of stones. Hlaváčiková et al (this issue) in this issue used HYDRUS-1D to assess the impact of stones in real soils of the High Tatras mountains in Slovakia on soil water storage and recharge.…”