Water transport under winter conditions

Winter as well as summer floods result in soil loss and sedimentation. Up to now the winter events cannot be adequately predicted. This paper focuses on the infiltration processes under frozen winter conditions in order to model soil erosion processes in winter by adapting the computer model EROSION 3D [Schmidt, J., Werner, M. v., 2000. Modeling Sediment and Heavy Metal Yields of Drinking Water Reservoirs in the Osterzgebirge Region of Saxony (Germany). In: Soil Erosion - Application of Physically Based Models, Schmidt, J.(Editor). Berlin, Heidelberg, New York., pp. 93-108.].A new snow accumulation and snow melt module has been implemented in order to estimate erosion rates during snowmelt events. Tests show that infiltration still occurs in frozen soils, however, infiltration rates are reduced compared to unfrozen soils [Weigert, A., Wenk, G., Ollesch, G., Fritz, H., 2003. Simulation of snowmelt erosion using the EROSION 3D model. Journal of Plant Nutrition and Soil Sciences, 1/2003.]. In order to improve the EROSION 3D model regarding partly frozen soils a physical based infiltration model extension has been developed and experimentally verified.Processes of infiltration into partly frozen soils are successfully quantified by a newly designed experimental set-up using a soil column (height 50 cm, diameter 21.5 cm). At the bottom of this column a negative pressure can be applied in order to establish unsaturated hydraulic conditions. The volume rate of the percolating water is constantly measured by an online balance. In addition the column is equipped with three TDR and temperature probes.The behaviour of two soil samples (sandy vs. loamy soil) are investigated under saturated, unsaturated and frozen conditions. The improved physical infiltration model based on the combination of Darcy's Law, Hagen-Poiseuille's Law, the capillary-rise equation and the van Genuchten θ(h) function determines with considerable accuracy both the unsaturated hydraulic conductivity and the effective saturated hydraulic conductivity of a partly frozen soil for rigid soil matrix conditions. This approach is compared with the Mualem concept for predicting unsaturated hydraulic conductivities. Fractures were observed due to freezing cracks in case of loamy material. For fractured soils the calibration with a skinfactor is found to be absolutely necessary to give reliable results.     

不同含盐土壤圆盘入渗特征试验

不同含盐土壤水分入渗特征是获得准确的土壤水力参数的基础。该文通过圆盘入渗试验,分析了4种土壤在5个（-1、-3、-6、-9和-12 cm）负水头下的入渗特征。结果表明,随着水头的减小,4种土壤的吸湿率线性减小,稳定入渗率和非饱和导水率呈不同程度减小。随土壤含盐量增加稳定入渗率和导水率呈增大规律。根据实测资料确定了不同负水头下非饱和导水率的Gardner指数模型参数,为盐渍化土壤水力参数的确定提供理论参考。     

Comparison of the soil hydraulic conductivity predicted from its water retention expressed by the equation of Van Genuchten and different capillary models

Knowledge of water retention and conductivity is essential to study water transport in soil. Determination of the conductivity curve is difficult, and it is often predicted by application of a capillary model to the water retention relationship. Three expressions are predicted from the water retention described by the equation of Van Genuchten. Two expressions are obtained in combination with the capillary models of Mualem and Burdine . The third expression is obtained by a combination with the capillary model of Fatt & Dykstra . The three sets of soil properties were applied to clay in order to compute infiltration and infiltration rates according to the series solution of Philip . Comparison with this solution showed that the results of the first two combinations were severely under-estimated, while those of the third were satisfactory. Similar results were obtained for sand by comparison with experimental data. Because conductivity estimated from the capillary model of Fatt & Dykstra is complicated, it was expressed by a power equation, the exponent of which is obtained by applying the Fatt & Dykstra capillary model to the water retention curve expressed according to Brooks & Corey and having the same asymptotic behaviour as the Van Genuchten equation. Application of this procedure to fifty soils selected from a published database gave satisfactory results. It is concluded that the hydraulic conductivity of a soil can be predicted from its water retention as expressed by the equation of Van Genuchten subject to the condition of the capillary model of Fatt & Dykstra and as expressed by the equation of Brooks & Corey, for which the exponent is obtained according to the same capillary model.     

非饱和土壤导水参数的推求

本文根据一维非饱和土壤水分的垂直入渗再分布和水平扩散再分布,采用土壤湿润剖面平均湿度和湿润锋湿度之间函数关系的三种形式,分别推导出非饱和土壤导水率,水分扩散率,比水容量的解析表达式,解析表达式中仅有四个独立参数,均可通过实验数据的简单拟合而得到.与其它方法相比,这种新的推求方法具有花费少、准确度高和测定范围大等特点.     

Water transport under winter conditions

Winter as well as summer floods result in soil loss and sedimentation. Up to now the winter events cannot be adequately predicted. This paper focuses on the infiltration processes under frozen winter conditions in order to model soil erosion processes in winter by adapting the computer model EROSION 3D [Schmidt, J., Werner, M. v., 2000. Modeling Sediment and Heavy Metal Yields of Drinking Water Reservoirs in the Osterzgebirge Region of Saxony (Germany). In: Soil Erosion - Application of Physically Based Models, Schmidt, J.(Editor). Berlin, Heidelberg, New York., pp. 93-108.].A new snow accumulation and snow melt module has been implemented in order to estimate erosion rates during snowmelt events. Tests show that infiltration still occurs in frozen soils, however, infiltration rates are reduced compared to unfrozen soils [Weigert, A., Wenk, G., Ollesch, G., Fritz, H., 2003. Simulation of snowmelt erosion using the EROSION 3D model. Journal of Plant Nutrition and Soil Sciences, 1/2003.]. In order to improve the EROSION 3D model regarding partly frozen soils a physical based infiltration model extension has been developed and experimentally verified.Processes of infiltration into partly frozen soils are successfully quantified by a newly designed experimental set-up using a soil column (height 50 cm, diameter 21.5 cm). At the bottom of this column a negative pressure can be applied in order to establish unsaturated hydraulic conditions. The volume rate of the percolating water is constantly measured by an online balance. In addition the column is equipped with three TDR and temperature probes.The behaviour of two soil samples (sandy vs. loamy soil) are investigated under saturated, unsaturated and frozen conditions. The improved physical infiltration model based on the combination of Darcy's Law, Hagen-Poiseuille's Law, the capillary-rise equation and the van Genuchten θ(h) function determines with considerable accuracy both the unsaturated hydraulic conductivity and the effective saturated hydraulic conductivity of a partly frozen soil for rigid soil matrix conditions. This approach is compared with the Mualem concept for predicting unsaturated hydraulic conductivities. Fractures were observed due to freezing cracks in case of loamy material. For fractured soils the calibration with a skinfactor is found to be absolutely necessary to give reliable results.     

A relatively simple scaling method for describing the unsaturated hydraulic functions of stony soils

Few if any methods exist to estimate the effects of stone content (stoniness) on the unsaturated soil hydraulic properties. A relatively simple scaling method is presented to estimate the hydraulic conductivity of unsaturated stony soils having different stone contents. A key assumption of the method is that van Genuchten's water retention parameters α and n of the fine soil fraction are the same as those of the stony soil. The method further assumes a linearly decreasing relationship between the saturated hydraulic conductivity and the stone content, based on previous numerical simulations. Using the proposed method, it is possible to calculate the hydraulic conductivity of unsaturated stony soils, knowing the saturated hydraulic conductivity of the fine soil fraction, the retention curve of the fine soil fraction, and the particular stoniness of the soil.     

Soil hydraulic properties of two loess soils in China measured by various field-scale and laboratory methods

Knowledge of hydraulic properties is essential for understanding water movement in soil. However, very few data on these properties are available from the Loess Plateau of China. We determined the hydraulic properties of two silty loam soils on agricultural land at sites in Mizhi and Heyang in the region. Undisturbed soil cores were collected from seven layers to one meter depth to determine saturated hydraulic conductivity, soil water retention curves and unsaturated hydraulic conductivity (by the hot-air method). Additional field methods (internal drainage and Guelph permeameter) were applied at the Heyang site to compare differences between methods. Soil water retention curves were flatter at Mizhi than at Heyang. Water contents at saturation and wilting point (1500 kPa) were higher at Heyang than at Mizhi. However, unsaturated hydraulic conductivity was lower at Heyang than at Mizhi, with maximum differences of more than six orders of magnitude. Nevertheless, the two soils had similar saturated hydraulic conductivities of about 60 cm day^− 1. Comparison between the methods showed that soil water retention curves obtained in the laboratory generally agreed well with the field data. Field-saturated conductivities had similar values to those obtained using the soil core method. Unsaturated hydraulic conductivities predicted by the Brooks–Corey model were closer to field data than corresponding values predicted by the van Genuchten model.     

Prediction of hydraulic conductivity and sorptivity in soils at steady-state infiltration

The purpose of this study was (1) to find a matching factor (u) between infiltration rate and hydraulic conductivity during steady-state infiltration, and (2) to propose equations based on infiltration and soil moisture-retention functions for prediction of the hydraulic conductivity K(θ) within the rapidly (non-capillary) drainable pores (RDP) and capillary-matrix pores of soils. The K(θ) of capillary pores was divided into K(θ)_SDP, K(θ)_WHP and K(θ)_FCP within slowly drainable pores (SDP), water-holding pores (WHP) and fine capillary pores (FCP), respectively. Five soil profiles of calcareous sandy loam, alluvial saline and non-saline clay, located at the Nile Delta, were used to apply the proposed equations. The highest and the lowest values of K(θ)_RDP were observed in calcareous and saline clay soil profiles, respectively. Values of K(θ)_RDP remained higher than those for capillary pores in the studied soils. The predicted values of K(θ) in capillary and non-capillary pores classes were in the expected range for unsaturated hydraulic conductivity. Water sorptivity (S) was determined at initial unsaturated soil water conditions and calculated at steady-state infiltration (S _w) using a derived equation. There was a decrease in S with an increase in soil water content; i.e. at steady-state infiltration, S decreased by 35–40% in calcareous soils and by 45–60% in alluvial clay soils. The parameter values of u and S _w tended to be uniform in calcareous soils, but nonuniform in saline and non-saline clay soils.     

Evaluation of porous medium hydraulic properties using experimental methods and RETC code

Two experimental procedures were used to determine both hydraulic properties, soil water retention θ(h) curve and unsaturated hydraulic conductivity K(θ), of a sand sample. Knowledge of hydraulic properties is essential, since they generally control soil water dynamics. A steady-state laboratory method was used for the simultaneous determination of θ(h) and K(θ). A one-step outflow method was used for the determination of diffusivity D(θ) and subsequently K(θ) from soil water retention data which were measured independently on the same sample and using the same apparatus. The comparison of K(θ) measured values from the above-mentioned methods showed very good agreement of the results. Also, the comparison between the experimental K(θ) and θ(h) functions and the predictions obtained using retention curve (RETC) code by simultaneous fit of experimental soil water retention and hydraulic conductivity data from outflow data, assuming the Mualem-van Genuchten model, showed very good agreement. It is noted that the main disadvantage of the one-step outflow method is the weakness to predict K(θ) values near saturation. This disadvantage could be overcome using RETC code with the above procedures, since the K(θ) values between the predictive approach and the steady-state method were similar.     

根据土壤水分特征曲线推求土壤的导水参数

本文中描述了土壤水分特征曲线的一个相对简单的幂函数方程.当把这一方程代入Burdine或Mualem的预报土壤导水率的模式后,可以得到相对导水率的分析解.相对导水率的表达式中仅包含一个参数,该参数用实验资料拟合水分特征曲线模型而得到.并结合特征曲线方程,给出了土壤水分扩散率的表达式.从Burdine和Mualem模式获得分析解的结果,与具有较宽范围导水性质的四种土壤的导水参数实测资料进行了比较.非饱和土壤导水率的预报结果良好;土壤水分扩散率的预报结果对其中三种土壤良好.     

Use of an inverse method and geostatistics to estimate soil hydraulic conductivity for spatial variability analysis

A field method for determining the soil hydraulic properties using a parameter estimation technique is presented. Input data for the inverse problem are soil-water potentials and soil-water contents measured at different soil depths and different times during a field transient drainage experiment. For the water retention function the parametric relation suggested by Van Genuchten was adopted. For the hydraulic conductivity function the relation proposed by Van Genuchten and the exponential relation were adopted.

With the proposed method soil hydraulic properties along a transect of a volcanic Vesuvian soil were determined using as boundary condition the unit gradient of total potential at the bottom of the soil profile. Geostatistics were used to describe the spatial variability of hydraulic conductivity characteristics of the soil here considered.

Finally, results obtained using this method were compared with those of the simplified method suggested by Sisson and Van Genuchten based on a unit gradient water flow model.     

An Analytical Solution of the One-Dimensional Steady-State Van Genuchten-Based Infiltration Equation for a Heterogeneous Soil with a Root-Water Extraction Function

Eurasian Soil Science - An analytical solution is developed for the one-dimensional steady-state infiltration equation for an inclined Van Genuchten heterogeneous soil with a sink term (i.e., with...     

考虑尺度效应的土壤溶质运移动力学特征分析

[目的]为了了解土壤环境中弥散尺度效应、动力学吸附等作用对溶质运移过程的影响。[方法]应用Laplace变换方法和复变函数理论推得溶质运移动力学模型的解析解。利用De Hoog数值反演方法,验证解析解的正确性,利用解析解分析溶质在土壤中的运移特征。[结果]解析解的计算结果与反演函数Fourier级数项数2 N较大(N=500)时的De Hoog数值计算结果吻合很好;土壤溶质浓度随尺度效应的增强、吸附作用及生物降解作用的减弱而增大;分子扩散、一阶动力学吸附以及吸附相溶质降解作用对溶质运移变化影响较小。[结论]所推求解析解是正确的;土壤溶质运移的弥散尺度效应,溶质在液相和吸附相间的线性分配作用及溶质在液相中的降解作用是影响土壤溶质运移过程的主要因素。     

Effects of agricultural practices on hydraulic properties and water movement in soils in Brittany (France)

The intensive agricultural use of soils in the Brittany region (western France) has increased the need for a better understanding of soil water dynamics. The aim of the present study is to compare quantitatively the differences produced by two agricultural practices on soil hydraulic properties (water retention curve and hydraulic conductivity) as well as the infiltration and drainage fluxes in the soils. This study was carried out on two experimental plots managed in the same way for 22 years. The two practices were continuous maize fertilized with mineral fertilizer, denoted as MX, and pasture within a ray-grass/maize rotation (3/1 year) with organic fertilization (pig slurry), denoted as PR. The study consisted of measuring soil physical properties in the laboratory and in the field, and estimating water infiltration in the soil of the two plots by recording water pressure heads after simulation of 2-h artificial rainfall with an intensity of 17 mm/h. We applied the van Genuchten model to describe the water retention and hydraulic conductivity curves (θ(h) and K(h)) for each soil horizon of the two plots. Hydrus-2D and ID softwares were used to construct a numerical model of water movement in the two soils. This model was used to quantify the infiltration rate, deep drainage and actual evaporation fluxes during the artificial rainfall experiment.The vertical influence of agricultural practices in both plots appears to be limited to the uppermost 35 cm. Deeper in the B horizon, there are only very slight differences in the hydraulic properties between the two plots. In the top soil horizons (H1–H5 and H6), the two soil properties mostly affected by practices are the hydraulic conductivity and the α parameter of the van Genuchten model. At the lowest pressure head studied here (−1.5 kPa), hydraulic conductivity in a given horizon differs by more than one order of magnitude between the two plots. The model reproduces quite satisfactorily the observed pressure heads in plot PR at all depths, in the rainy period as well as in the water redistribution period (efficiency >0.77). Results are less good for the MX plot, with efficiency ranging from 0.49 to 0.84 depending on the horizon. The different sources of simulation errors are identified and discussed. For the MX plot, the soil water movement model succeeds in reproducing the infiltration excess runoff observed in the field, allowing us to calculate that it accounts for 9% of the applied rainfall. No surface runoff or ponding appears in the PR plot during the artificial rainfall experiment. In the PR plot, the simulated deep drainage flux increases more rapidly than in the MX plot. The lower hydraulic conductivity in the top soil horizon of the MX plot compared with the PR plot appears to reduce the infiltration rate as well as the deep drainage flux. It also decreases the upward flow of water to the soil surface when the water content in the top soil layer is depleted by evaporation flux. The model simulation could be improved by a more precise representation of the soil structure, particularly the location, size and frequency of clods as well as the variability of hydraulic properties. However, we need to strike a balance between improving the quality of the simulation even further and the practical constraints and efforts involved in measuring the soil hydraulic properties.     

Temporal variation in the hydraulic conductivity of a tilled clay soil as measured by tension infiltrometers

Steady-state infiltration rates from tension infiltrometers were measured on ploughed and unploughed plots in a clay soil during the period June to October. Measurements were made both at the soil surface and at depths of 15 and 25 cm. Hydraulic conductivity in the water potential range zero to ?11 cm was obtained using a piece-wise exponential K(Ψ) function and Wooding's solution for infiltration from a circular source. A two-line regression model showed excellent fits to paired (In KΨ) values on all measurement occasions. This may indicate the existence of a bimodal pore system, reflecting the contributions of macro- and mesopores to the measured K(Ψ) function. The break-point potential dividing the two pore systems varied between c.?4 and ?6cm. Significant variations in the K(Ψ) function between sampling occasions were found at the soil surface, but not at depths of 15 and 25 cm. Measured K(Ψ) values decreased during the growing season, particularly at potentials between ?4 and ?6 cm where reductions were up to one order of magnitude. This was attributed to soil structural breakdown by rain impact and surface capping or sealing. Hydraulic conductivity near the soil surface was significantly increased by disc harrowing in autumn. In contrast, no pronounced difference in the K(Ψ) function between ploughed and unploughed treatments could be discerned at 15 and 25 cm depths in the soil.     

根据土壤水平一维入渗推求紫色土水动力学参数

选择3种不同质地的紫色土,通过室内土壤水平一维入渗试验,探讨简单入渗法和入渗特性法推求水动力学参数对于紫色土的适用性。结果显示,简单入渗法和入渗特性法推求的水动力学参数中,水分特征曲线准确性较高,水分扩散率和非饱和导水率准确性较差。简单入渗法推求的水分扩散率和非饱和导水率均低于实测值1～2个数量级,但推求值与实测值曲线趋势较为一致。入渗特性法推求的水分扩散率和非饱和导水率在高含水量小于实测值,在低含水量大于实测值,推求值随含水量变化趋势响应缓慢。     

Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—2. Application of the methodology

Sarkar et al. (this issue) proposed a laboratory measurement method for obtaining the hydraulic conductivity of soil at near‐saturated moisture conditions, bridging the gap between measurements that can be obtained with the evaporation method in the medium dry region, and measurements of the saturated conductivity by traditional methods. The method is based on a tension infiltration on a limited part of the surface of a soil sample and drainage of the sample at the same tension, leading to a divergent flow field. Despite equal tensions at top and bottom of the sample (“unit gradient”), the water flux in the sample is smaller than the corresponding value of the soil hydraulic conductivity at the applied tension. From numerical analysis of the flow problem, they concluded that unsaturated conductivity can be obtained with an accuracy of 10% for all texture classes of the USDA soil texture triangle. In this paper, we test the methodology for three different soil types using an appropriate apparatus. The results match well with independent saturated conductivity measurements on the wet side, and with unsaturated conductivity measurements in the medium moisture range that were obtained with the evaporation method.     

Influence of water content and soil properties on unsaturated hydraulic conductivity of some red and black soils

The unsaturated hydraulic conductivity was determined in the laboratory for some red and black soils, following water movement into a horizontal column of homogenous soil of uniform packing. A highly significant positive relationship was found between moisture content and hydraulic conductivity values in all the soils studied. Correlation coefficients calculated for the relationships between soil constituents/properties and the change in hydraulic conductivity per unit change in moisture content (regression coefficient between hydraulic conductivity and moisture content) have shown positive relationship to sand and negative relationships to silt, silt + clay, clay, carbonates, aggregates > 0.25 mm and saturated hydraulic conductivity. It is concluded that the unsaturated hydraulic conductivity decreases rapidly with decrease in moisture content and this decrease depends on the soil constituents/properties and differences between soil types are clear.