Novel evaporation experiment to determine soil hydraulic properties

Abstract. A novel experimental approach to determine soil hydraulic material properties for the dry and very dry range is presented. Evaporation from the surface of a soil column is controlled by a constant flux of preconditioned air and the resulting vapour flux is measured by infrared absorption spectroscopy. The data are inverted under the assumptions that (i) the simultaneous movement of water in the liquid and vapour is represented by Richards' equation with an effective hydraulic conductivity and that (ii) the coupling between the soil and the well-mixed atmosphere can be modelled by a boundary layer with a constant transfer resistance. The optimised model fits the data exceptionally well. Remaining deviations during the initial phase of an experiment are thought to be well-understood and are attributed to the onset of the heat flow through the column which compensates the latent heat of evaporation.

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Further tests of the HYPROP evaporation method for estimating the unsaturated soil hydraulic properties

Journal of Hydrology and Hydromechanics ◽

10.1515/johh-2017-0046 ◽

2018 ◽

Vol 66 (2) ◽

pp. 161-169 ◽

Cited By ~ 14

Author(s):

Camila R. Bezerra-Coelho ◽

Luwen Zhuang ◽

Maria C. Barbosa ◽

Miguel Alfaro Soto ◽

Martinus Th. van Genuchten

Keyword(s):

Hydraulic Conductivity ◽

Unsaturated Soil ◽

Hydraulic Properties ◽

Water Retention ◽

Measurement Techniques ◽

Richards Equation ◽

Water Retention Curve ◽

Soil Hydraulic Properties ◽

Evaporation Method ◽

Soil Hydraulic

AbstractMany soil, hydrologic and environmental applications require information about the unsaturated soil hydraulic properties. The evaporation method has long been used for estimating the drying branches of the soil hydraulic functions. An increasingly popular version of the evaporation method is the semi-automated HYPROP©measurement system (HMS) commercialized by Decagon Devices (Pullman, WA) and UMS AG (München, Germany). Several studies were previously carried out to test the HMS methodology by using the Richards equation and the van-Genuchten-Mualem (VG) or Kosugi-Mualem soil hydraulic functions to obtain synthetic data for use in the HMS analysis, and then to compare results against the original hydraulic properties. Using HYDRUS-1D, we carried out independent tests of the HYPROP system as applied to the VG functions for a broad range of soil textures. Our results closely agreed with previous findings. Accurate estimates were especially obtained for the soil water retention curve and its parameters, at least over the range of available retention measurements. We also successfully tested a dual-porosity soil, as well as an extremely coarse medium with a very high van Genuchtennvalue. The latter case gave excellent results for water retention, but failed for the hydraulic conductivity. In many cases, especially for soils with intermediate and highnvalues, an independent estimate of the saturated hydraulic conductivity should be obtained. Overall, the HMS methodology performed extremely well and as such constitutes a much-needed addition to current soil hydraulic measurement techniques.

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Effect of stones on soil hydraulic properties: measurement and modeling

10.5194/egusphere-egu2020-670 ◽

2020 ◽

Author(s):

Mahyar Naseri ◽

Sascha C. Iden ◽

Wolfgang Durner

Keyword(s):

Hydraulic Conductivity ◽

Soil Temperature ◽

Hydraulic Properties ◽

Evaporation Rate ◽

Sandy Loam ◽

Stage Ii ◽

Richards Equation ◽

Water Retention Curve ◽

Soil Hydraulic Properties ◽

Soil Hydraulic

Stony soils are soils that contain a high amount of stones and are widespread all over the world. &#160;The effective soil hydraulic properties (SHP), i.e. the water retention curve (WRC) and the hydraulic conductivity curve (HCC) are influenced by the presence of stones in the soil. This influence is normally neglected in vadose zone modeling due to the considerable measurement challenges in stony soils. The available data on the effect of stones on SHP is scarce and there is not a systematic modeling approach to obtain the effective SHP in stony soils. Most of the past studies are limited to the effect of stones on the WRC and saturated hydraulic conductivity and low and medium stone contents (up to 40 % v/v). We investigated the effect of stone content on the effective SHP of stony soils through a series of evaporation experiments. Two soil materials a) sandy loam and b) silt loam as background soils were packed with different volumetric contents (0, 10, 30 and 60 %) of medium stones were in containers with a volume of 5060 cm3. Volumetric stone contents were chosen in a way to present stone-free, moderately stony and highly stony soils. All of the experiments were carried out in two replicate packings with an almost identical bulk density. Packed samples were saturated with water from the bottom and subjected to evaporation in a climate-controlled room. During the evaporation experiments, the pressure head and soil temperature were continuously monitored and the water loss from the soil columns was measured with a balance. The dewpoint method provided additional data on the WRC in the dry soil. The resulting data were evaluated by inverse modeling with the Richards equation to identify effective SHP and to analyze the effect of stone content on the evaporation rate, soil temperature, the effective WRC and the effective HCC. The applied methodology was successful in identifying effective SHP with high precision over the full moisture range. The results reveal a quicker transition from stage I to stage II of evaporation in highly stony soils. Evaporation rate reduces with the increase of the volumetric stone content. The existence of a high amount of stone content shorten stage II of evaporation driven by the vapor diffusion through the restricted soil evaporative surface.

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Direct measurement of the soil water retention curve using X-ray absorption

Hydrology and Earth System Sciences ◽

10.5194/hess-8-2-2004 ◽

2004 ◽

Vol 8 (1) ◽

pp. 2-7 ◽

Cited By ~ 19

Author(s):

A. Bayer ◽

H.-J. Vogel ◽

K. Roth

Keyword(s):

Soil Water ◽

Hydraulic Properties ◽

Capillary Rise ◽

Water Dynamics ◽

Richards Equation ◽

Water Retention Curve ◽

Soil Hydraulic Properties ◽

X Ray ◽

Soil Hydraulic ◽

X Ray Absorption

Abstract. X-ray absorption measurements have been explored as a fast experimental approach to determine soil hydraulic properties and to study rapid dynamic processes. As examples, the pressure-saturation relation θ(Ψ) for a uniform sand column has been considered as has capillary rise in an initially dry sintered glass column. The θ(Ψ)-relation is in reasonable agreement with that obtained by inverting a traditional multi-step outflow experiment. Monitoring the initial phase of capillary rise reveals behaviour that deviates qualitatively from the single-phase, local-equilibrium regime described by Richards’ equation. Keywords: X-ray absorption, soil hydraulic properties, soil water dynamics, Richards’ equation

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Uncertainty in soil hydraulic properties parameterization and its propagation in vadose zone hydrological model output

10.5194/egusphere-egu2020-3716 ◽

2020 ◽

Author(s):

Quirijn de Jong van Lier ◽

Everton Alves Rodrigues Pinheiro

Keyword(s):

Vadose Zone ◽

Correlation Matrix ◽

Hydraulic Properties ◽

Numerical Solutions ◽

Relative Yield ◽

Richards Equation ◽

Model Output ◽

Soil Hydraulic Properties ◽

Deep Drainage ◽

Soil Hydraulic

Vadose zone hydrological models employing finite difference numerical solutions of the Richards equation allow simulating the movement and predicting the state of soil water and associated quantities in the vadose zone. Nowadays, robust algorithms like Hydrus and SWAP are available to perform such simulations. Since most numerical issues with these algorithms have been solved, hydraulic parameters describing the relation between conductivity K, pressure head h and water content &#952; determine the quality of model output. Whichever method is used to obtain soil hydraulic properties, resulting parameters include an uncertainty, which may be expressed as a confidence interval. Existing correlations between parameters may be expressed in a correlation matrix. Using a stochastic approach, uncertainty and correlation may be considered in simulations and their propagation in results can be assessed. We developed a software which generates n stochastic realizations of the hydraulic parameter set considering uncertainty (standard error) and correlation matrix, runs the SWAP model for each realization and extracts the model output of interest. To apply the software and assess the propagation of uncertainties in the model output, hydraulic properties were measured in soils from south-east Brazil using inverse modeling of laboratory evaporation experiments, resulting in Van Genuchten parameter values, respective errors and correlations. These data were used to obtain n (n=104) stochastic realizations of deep drainage, runoff and evaporation in a bare-soil scenario. Similarly, for a pasture cropped scenario the water balance components (including transpiration), and relative yield were evaluated. The effect of uncertainty in these parameters on the mentioned output variables prediction is presented and discussed.

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Sensitivity analysis of unsaturated infiltration flow using head based finite element solution of Richards' equation

MATEMATIKA ◽

10.11113/matematika.v33.n2.915 ◽

2017 ◽

Vol 33 (2) ◽

pp. 131 ◽

Cited By ~ 1

Author(s):

Mohammad Sayful Islam

Keyword(s):

Sensitivity Analysis ◽

Finite Element ◽

Porous Media ◽

Hydraulic Properties ◽

Preferential Flow ◽

Finite Element Solution ◽

Richards Equation ◽

Element Solution ◽

Soil Hydraulic Properties ◽

Soil Hydraulic

Sensitivity analysis is one of the tools available for analyzing the effects of soil parameter on the variably unsaturated flows in porous media, that may easily be implemented into existing conventional Galerkin finite element solution of Richards’ equation based computational fluid dynamics codes. The sensitivity of the model is evaluated on the basis vertical infiltration problem with time dependent boundary condition, sharp gradient in the infiltration front, and discontinuous derivatives in the soil hydraulic properties. Simulation results demonstrate the complicated nature of unsaturated porous media during redistribution water flow. The sample case presented highlight different aspects of the performance of the algorithm and the different factors that can affect their convergence and efficiency, including temporal discretization, convergence error norm, conductivity and moisture content characteristics, boundary conditions, and the extent of fully unsaturated zones in the soil. From the preliminary assessment performed herein, consideration of the number of degrees of freedom used when performing a sensitivity analysis is shown to demand enormous concern, if predicted sensitivities are to have significant physical interpretations. The proposed model is capable of simulating preferential flow situations using parameters which can be related to soil hydraulic properties.

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