Entwicklung eines Computerverfahrens zur Berechnung der hydraulischen Leitfähigkeit von wassergesättigten Böden mit der Bohrlochmethode

A computer program for the calculation of the hydraulic conductivity with the auger hole method An iterative procedure is applied for the calculation of the hydraulic conductivity with the auger hole method. Results are compared with data from Ernst (1950) and from Boast and Kirkham (1971). It is found that the achieved results compare well with the data from Boast and Kirkham, but frequently deviate considerably from those of Ernst. It appears that results from Boast and Kirkham are more reliable than those from Ernst. An advantage of the iterative procedure, as compared to the method of Boast and Kirkham, is its simplicity. Calculations are easily performed for sets of data not tabulated by Boast and Kirkham. Calculations can be carried out on a desk-top computer, but do require some computer time. A computer program (in Quick-BASIC) has been developed and can be obtained on request.     

Seasonal variation in field-saturated hydraulic conductivity in two swelling clay soils in Sweden

A simple method (the inversed auger hole method) for measuring field-saturated hydraulic conductivity (K_fs) was investigated. Measurements were carried out in the spring, summer and autumn at three depths in two Swedish clay soils (Ultuna and Limsta, with clay contents of 45–60%0 and 65–80%, under barley and grass/clover ley respectively). Seasonal fluctuations in K_fs at Limsta were more pronounced, and were observed deeper in the profile. This was attributed primarily to larger structural changes due to a higher capacity for swell/shrink (normal shrinkage over the available water range) and an earlier drying up of the soil under grass/clover ley. It was shown that the measured K_fs values were strongly correlated with the total inter aggregate (macro-) porosity (e_t), estimated from a simple model of soil shrinkage. Combining the data from both soils, a single power-law relation was adequate (r= 0.73) to describe the variations in K_fs with e_t     

Ein Vergleich und eine Bewertung von Dränformeln für die Drändistanz von geschichteten Grund- und Stauwasserböden

A comparison and an evaluation of drain spacing equations for layered soils Drain spacings, calculated with different steady-state tile drainage formulas for layered soils, were compared. The formulas under consideration were those of Ernst, van Beers and of Toksöz and Kirkham. It was found that, for certain ranges of the drainage parameters, the drain spacings compare well. For other conditions, differences of over 100 percent did occur. Especially, results obtained with the Ernst equation may deviate considerably from those of the other authors. However, also drain spacings calculated with the van Beers equation do occasionally differ from those of Toksöz and Kirkham. For practical use the equation of Toksöz and Kirkham is recommended.     

Eine Infiltrationsmethode zur Messung der hydraulischen Leitfähigkeit im Felde

An infiltration method for measuring the saturated hydraulic conductivity under field conditions A new field method to measure the hydraulic conductivity under field conditions, developed by Reynolds and Elrick (1985), is presented and compared with a laboratory method using 100 cm³ cylinder cores.     

Bereitstellung von van-Genuchten-Parametern zur Charakterisierung der hydraulischen Bodeneigenschaften

Providing the Parameters of Unsaturated Soil Hydraulic Functions on the Basis of Soil Texture, Bulk Density and Type of Horizon The hydraulic conductivity function can be described by the van Genuchten equation, whereby its parameters are estimated from typical water retention data of soil types and textural classes. The value of saturated hydraulic conductivity can be derived from tables (e.g. Kartieranleitung, 1982) in case measured data are lacking. Especially in well structured or sandy soils saturated conductivity may differ by 1…2 orders of magnitude. This will lead to a shift of the conductivity function. But nevertheless for the first approximation of fluxes in soils such parameters can be used. Thus, soil dependent values of groundwater recharge and pollution can be roughly quantified.     

Prüfung von 3 Verfahren zur Vorhersage der hydraulischen Leitfähigkeit ungesättigter Böden aus Wasserretentionsdaten oder aus der Bodenart

Testing of three methods to predict unsaturated soil hydraulic conductivity from water retention data or from texture class Using 60 soils taken from UNSODA (Leij et al., 1996) the method proposed by Renger et al. (1999) and the prediction according to Mualem (1976)/van Genuchten (1980) were tested. The parameters of the Mualem/vanGenuchten model were estimated either from water retention data or from a table of reference values. Using the reference values requires only the knowledge of texture class (German classification system). An advantage of the method proposed by Renger et al. (1999) is its capability to predict saturated conductivity too. The model of Mualem/vanGenuchten using reference values of parameters yields the best results. The standard deviation between observed and predicted values of unsaturated hydraulic conductivity was 0.93 lg (K) for the Mualem/vanGenuchten model and 1.3 lg (K) for the Renger et al. (1999) predictions.     

THE EFFECT OF HYSTERESIS OF PORE-WATER ON THE HYDRAULIC CONDUCTIVITY

It is pointed out with the help of the Independent Domain Theory, that a fraction of the pore-water constituting a volume ΔV is contained in pores not common to both the wetting and drying states and that this volume in a wetting state is contained in pores whose draining radii are greater than those of the pores containing the water volume ΔV in the drying state. On the above basis it is suggested that hysteresis may affect the hydraulic conductivity: firstly, through differences of the radii of the pores containing the water volume ΔV, which tend to endow a wetting state with a conductivity greater than that of an equally wet but drying state; secondly, through differences of the coordinates of the above-mentioned pores, which may influence the paths of flow and consequently the hydraulic conductivity, and will have either a similar or opposite effect. It is concluded, therefore, that the conductivity in the wetting state can be greater, equal, or even less than that in the drying state, depending on the particular porous body.     

Mualem模型中的饱和导水率修正研究

[目的]提高Mualem模型计算非饱和导水率的准确性。[方法]采用理论推导结合数据统计的方法研究该模型中的饱和导水率ks修正问题。基于Brooks—Corey土壤水分特征曲线模型,建立修正导水率ko与土壤水分特征曲线之间的理论关系式;通过回归分析得到ko与土壤水分特征曲线之间的理论关系式中相关参数。[结果]利用原状黄土的非饱和渗透试验数据,对考虑修正导水率ko的Mualem模型的准确性进行了验证,得到了比较满意的结果。[结论]研究成果可用于依据土壤水分特征曲线直接确定非饱和土导水率,对非饱和导水率预测研究具有一定参考价值。     

陕北水蚀风蚀交错区两种生物结皮对土壤饱和导水率的影响

该文以陕北水蚀风蚀交错区普遍发育的地表和地上两种生物结皮为研究对象，分别以3种非生物结皮（无结皮、物理结皮、去除生物结皮）为对照，使用盘式入渗仪测定其饱和导水率。结果表明：与无结皮土壤相比，两种类型生物结皮均可极显著降低土壤饱和导水率；与去除生物结皮土壤相比，两种类型生物结皮对土壤饱和导水率的降低均不显著；与有物理结皮发育的土壤相比，地表生物结皮对土壤饱和导水率的降低不显著，而地上生物结皮对土壤饱和导水率的降低显著。一方面，两种生物结皮对土壤饱和导水率均有明显降低作用，预示生物结皮在降雨活动中可能会增加径流、降低入渗，阻碍研究区水分亏缺条件下的植被恢复和生态与环境建设。另一方面，与不同的对照相比，生物结皮对土壤饱和导水率的影响截然不同，该结论可在一定程度上解释当前有关生物结皮影响土壤水分入渗方面所存在的分歧。     

Comparison of different measuring and calculating methods to quantify the hydraulic conductivity of unsaturated soil

The double-plate method and the evaporation method provide comparable results on the hydraulic conductivity of soil (K(h_s)). Adaptation of the water retention curve according to the method of Vachaud and Vauclin proved to be very reliable. The course of the K(h_s) function is well shown by all indirect identification methods included in the comparison. In some cases, the absolute deviations of the measured from the calculated values are, however, considerable and primarily determined by the initial value of the hydraulic conductivity. In quantifying the capillary water rise, best approximation to the measured values was reached in 11 of 13 cases with the van Genuchten method.     

Applicability of cavity-throat connecting model for estimating the hydraulic conductivity of fine-grained soils: a geometrical and mathematical approach

Purpose

Determining the hydraulic conductivity of low permeable fine-grained soils is difficult and time-consuming. This work develops a new method with an eye to the pore morphology to correlate hydraulic conductivity with pore-size distribution (PSD) parameters obtained from mercury porosimeter data. In order to realize this method, calculating percolation loss along the flow paths in pore channels and quantifying the spatial morphology of pore channels by proposing a cavity-throat connecting model is necessary.

Materials and methods

In order to establish the standard process of the new method, a kind of sedimentary mucky clay with regular dual-structural PSD has been collected. The samples are divided into three series: (a) vibrated with variable frequencies; (b) frozen at variable temperatures and unfrozen, making the freezing-thawing effect as the variable; and (c) remolded with different water contents. The PSD of freeze-dried samples at the end of each process is obtained by mercury intrusion porosimetry. After that, the method is demonstrated with application to 12 series of fine-grained soils.

Results and discussion

Deduced from mercury porosimeter data, the volume-based PSD curves of fine-grained soils are bimodal, due to the presence of inter-aggregate and intra-aggregate pores. Two important hypotheses have been proposed: (i) one is that in the smaller pore scales, the experimental extrusion curve controlled by the hysteresis loop has a really approximate part compared to the theoretical overall retraction curve, making the experimental extrusion curve characterize the pore cavity size approximately, and (ii) the pore system consists of a series of multistage cavity-throat connections. Accumulating the effects of single connection on the percolation can be used to measure the overall effects of pore system on the percolation. Based on fluid-driven path analysis of percolation, the pore system is quantified by a series of cavity-throat connections and the percolation loss has been derived to estimate the hydraulic conductivity.

Conclusions

The permeable parameter (κ) representing the overall effects of pore connections on the hydraulic conductivity (K) is suited to correlate the microstructure and hydraulic conductivity by the linear relationship with the fixed slope in semilogarithmic coordinate for the fine-grained soils. It is the destruction and recombination of cavity-throat connections that are dominant during the treatments like freezing, remolding, and reinforcing.

     

不同根系构型草本与灌木复合对土壤饱和导水率的影响因素分析及模拟

[目的] 探究不同根系构型草本与灌木复合时的根土性质的差异对土壤饱和导水率的影响,并综合考虑根系和土壤性质建立估算土壤饱和导水率的经验方程,为黄土高原植被恢复后的水文模型建立提供理论参考。[方法] 选取不同根系构型草本与灌木的混合样地,分别为柠条锦鸡儿加冰草(须根系)和柠条锦鸡儿加铁杆蒿(直根系)。采用双环刀法测定不同样地土壤饱和导水率。[结果] 样地类型和土层深度对土壤饱和导水率的影响达到显著水平,两者对土壤饱和导水率影响的因子贡献率分别为26%和52%。直根系铁杆蒿与柠条锦鸡儿混合样地的土壤饱和导水率高于须根系冰草与柠条锦鸡儿混合样地,并且不同样地的土壤饱和导水率随土层深度的增加均表现出降低的趋势。根长密度、团聚体以及土壤容重能够较好地模拟土壤饱和导水率,其拟合精度R²可以达到0.86。[结论] 直根系草本与灌木复合时较须根系草本与灌木复合相比具有更高的饱和导水率。在不同样地中,根长密度、团聚体以及土壤容重是影响饱和导水率的主要因素。     

A new laboratory method to quickly determine the unsaturated hydraulic conductivity of undisturbed soil cores within a wide range of textures

A modified instantaneous profile method is described, which determines the hydraulic conductivity functions of soils with varying textures. Soil suction head as a function of time and depth, rate of outflow as a function of time and the final distribution of moisture content are monitored on undisturbed soil columns. Data is handled following a modification of the procedure of Weeks and Richards (1967). The apparatus consists of five measuring cells, a monitoring unit, five balances and equipment to section the soil columns for the gravimetric determination of soil moisture content. Each measuring cell contains a soil core of 250 cm³, into which five micro-tensiometers are inserted at 2 cm intervals. Exemplary hydraulic conductivity functions are shown for samples taken from an Arenosol, from silty and clayey-silty horizons of a Luvisol and from a clayey Vertisol. The functions showed good agreement with in situ data. Evaluations of variability show the method to be very reliable. On average, the functions of five samples can be determined in one week, making the method quick. At the same time, the method has great potential for the study of effects of soil structure on hydraulic conductivity.     

Vergleich der Verteilungen der Wasserleitfähigkeit und des Porenvolumens von waagrecht und senkrecht entnommenen Stechzylinderproben

Evaluation of the distribution of hydraulic conductivity and porosity measured at horizontally and vertically orientated core samples At 90 core camples taken vertically and 90 taken horizontally from 9 horizons of luvisols from loess hydraulic conductivities (h. c.) and porosities were determined. Frequency distribution of porosity showed but little influence of sample orientation, h. c.-values however showed marked difference. Most frequent values of horizontal distribution was approximated by lowest value of vertical distribution. This result was confirmed by evaluation of measurements given by Bailly (1969) and by Baumgart (1967).     

A Comparison of In Situ Constant and Falling Head Permeameter Tests to Assess the Distribution of Clogging Within Horizontal Subsurface Flow Constructed Wetlands

Clogging is the main operational problem associated with horizontal subsurface flow constructed wetlands (HSSF CWs). The measurement of saturated hydraulic conductivity has proven to be a suitable technique to assess clogging within HSSF CWs. The vertical and horizontal distribution of hydraulic conductivity was assessed in two full-scale HSSF CWs by using two different in situ permeameter methods (falling head (FH) and constant head (CH) methods). Horizontal hydraulic conductivity profiles showed that both methods are correlated by a power function (FH?=?CH^0.7821, r ²?=?0.76) within the recorded range of hydraulic conductivities (0?C70?m/day). However, the FH method provided lower values of hydraulic conductivity than the CH method (one to three times lower). Despite discrepancies between the magnitudes of reported readings, the relative distribution of clogging obtained via both methods was similar. Therefore, both methods are useful when exploring the general distribution of clogging and, specially, the assessment of clogged areas originated from preferential flow paths within full-scale HSSF CWs. Discrepancy between methods (either in magnitude and pattern) aroused from the vertical hydraulic conductivity profiles under highly clogged conditions. It is believed this can be attributed to procedural differences between the methods, such as the method of permeameter insertion (twisting versus hammering). Results from both methods suggest that clogging develops along the shortest distance between water input and output. Results also evidence that the design and maintenance of inlet distributors and outlet collectors appear to have a great influence on the pattern of clogging, and hence the asset lifetime of HSSF CWs.     

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.     

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.     

Comparison of seven water retention functions used for modelling soil hydraulic conductivity due to film flow

The unsaturated soil hydraulic conductivity accounting for film flow is important for understanding soil hydrological and biological processes, especially in arid and semi‐arid regions. Recently, a theoretically based hydraulic conductivity model was developed to describe the hydraulic conductivity as a function of water content. We have used this model to compare seven soil water retention functions commonly used for predicting soil hydraulic conductivity due to film flow. A total of 30 soils, varying in basic properties, were selected from the Unsaturated Soil Hydraulic Database to evaluate the seven functions. The Webb method was applied to identify the critical soil matric potential (h _c) below which thin film flow controls water movement. Soil hydraulic conductivity measurements at matric potential below h _c were then used for curve fitting according to the seven functions. Slight differences were observed among the functions in predicting soil hydraulic conductivity due to film flow. Six of the seven functions in combination with the hydraulic conductivity model described the hydraulic conductivity due to film flow well, according to the terms of the coefficient of efficiency. The relatively poor performance of the one exception was due to the fact that the linear shape of the function made it less flexible at low matric potentials. In addition, the effect of textural class on its performance was substantial, showing a poorer fit for the sand soil compared with the loam and clay soils. These findings have important applications related to soil and water resources conservation especially in arid and semi‐arid regions.     

氮胁迫对玉米单根径、轴向水力导度的影响

氮亏缺影响地上部生长的生理机制之一可能与其对根水力导度的影响有关。为此 ,本文利用蒸腾计法和解剖学方法分别研究了氮亏缺对玉米单根径、轴向水力导度的影响。结果表明 ,氮亏缺条件下 ,玉米单根的径向和轴向导度明显下降 ,其径向导度对水孔蛋白抑制剂HgCl2不敏感。不同氮处理轴向导度差别的主要原因在于成熟的后生木质部导管数目和直径的减少。     

黄土丘陵区典型植被土壤物理性质差异及其对导水特性影响

选取黄土丘陵区12种典型植被样地,通过测定各样地不同土层植物残体生物量、土壤容重、毛管孔隙度、非毛管孔隙度及饱和导水率,研究各指标随土层深度和植被类型的变化规律及其对土壤饱和导水率的影响。结果表明:(1)除容重随土层深度增加外,植物残体、毛管孔隙度、非毛管孔隙度和饱和导水率均随土层深度减少,其中植物残体大多集中于表层土壤(0—10 cm),占总残体生物量的51.4%～85.7%。(2)不同植被类型其植物残体及土壤物理性质存在显著差异,乔木林地植物残体、农耕地土壤容重、灌木林地非毛管孔隙度及饱和导水率均最大,而毛管孔隙度与不同土地利用类型间无显著差异。(3)饱和导水率随植物残体生物量密度(0—10 cm)和土壤容重呈幂函数减小,随毛管孔隙度和非毛管孔隙度呈幂函数增大;土壤容重(BD)和非毛管孔隙度(NCP)是影响土壤饱和导水率(K_s)的主要因素,且土壤饱和导水率可表示为两者的综合非线性方程(K_s=0.6BD~(-4.717)NCP~(0.203),P0.01,R~2=0.63,NSE=0.50)。此外,沙棘灌木林地平均饱和导水率最大,有利于降雨过程中土壤水分入渗,具有较强的水土保持功能。本研究结果可为黄土高原植被恢复生态水文效益评价提供理论依据。