Showing papers on "Hydraulic conductivity published in 2010"
TL;DR: In this article, the authors reviewed the use of the van Genuchten-Mualem (VGM) model to parameterize soil hydraulic properties and for developing pedotransfer functions (PTFs).
Abstract: We reviewed the use of the van Genuchten–Mualem (VGM) model to parameterize soil hydraulic properties and for developing pedotransfer functions (PTFs). Analysis of literature data showed that the moisture retention characteristic (MRC) parameterization by setting shape parameters m = 1 − 1/ n produced the largest deviations between fitted and measured water contents for pressure head values between 330 (log10 pressure head [pF] 2.5) and 2500 cm (pF 3.4). The Schaap–van Genuchten model performed best in describing the unsaturated hydraulic conductivity, K . The classical VGM model using fixed parameters produced increasingly higher root mean squared residual, RMSR, values when the soil became drier. The most accurate PTFs for estimating the MRC were obtained when using textural properties, bulk density, soil organic matter, and soil moisture content. The RMSR values for these PTFs approached those of the direct fit, thus suggesting a need to improve both PTFs and the MRC parameterization. Inclusion of the soil water content in the PTFs for K only marginally improved their prediction compared with the PTFs that used only textural properties and bulk density. Including soil organic matter to predict K had more effect on the prediction than including soil moisture. To advance the development of PTFs, we advocate the establishment of databases of soil hydraulic properties that (i) are derived from standardized and harmonized measurement procedures, (ii) contain new predictors such as soil structural properties, and (iii) allow the development of time-dependent PTFs. Successful use of structural properties in PTFs will require parameterizations that account for the effect of structural properties on the soil hydraulic functions.
383 citations
238 citations
01 Jan 2010
TL;DR: Independent, albeit closely related, NtAQP1 activities in roots and leaves resulted in improved WUE and contributed to the plant's stress resistance in terms of yield production under all tested conditions, as demonstrated in both tomato and Arabidopsis plants constitutively expressing Nt AqP1.
202 citations
TL;DR: In this article, the authors investigated the frequency of perched water tables, overland flow and stormflow in an Amazon forest and in an adjacent 25-year-old pasture cleared from the same forest, and compared the results with the frequencies of these phenomena estimated from comparisons of rainfall intensity and soil hydraulic conductivity.
177 citations
TL;DR: Lebeau et al. as mentioned in this paper proposed a new model for predicting the hydraulic conductivity of unsaturated porous media, which can be integrated into existing numerical models of water transport in unsaturated soils.
Abstract: [1] Most classical predictive models of unsaturated hydraulic conductivity conceptualize the pore space as either bundles of cylindrical tubes of uniform size or assemblies of cylindrical capillary tubes of various sizes. As such, these models have assumed that liquid configuration isthesameinboththewetanddryrangesandthatasingleconceptcanbeused to describe water transport over the entire range of matric head. Yet theoretical and experimental findings suggest that water transport in wet media, which mostly occurs in water saturated capillaries, is quite different from that in dry media, which occurs in thin liquid films. Following these observations, this paper proposes a new model for predicting thehydraulicconductivityofporousmediathataccountsforbothcapillaryandthinfilmflow processes. As with other predictive models, a mathematical relationship is established between hydraulic conductivity and the water retention function. The model is mathematically simple and can easily be integrated into existing numerical models of water transport in unsaturated soils. In sample calculations, the model provided very good agreement with hydraulic conductivity data over the entire range of matric head. Two other well‐supported models, on the other hand, were unable to conform to the experimental data. Citation: Lebeau, M., and J.‐M. Konrad (2010), A new capillary and thin film flow model for predicting the hydraulic conductivity of unsaturated porous media, Water Resour. Res., 46, W12554, doi:10.1029/2010WR009092.
175 citations
TL;DR: In this article, a new tensiometer design was proposed based on improved tensiometers that resist cavitation to much higher tensions, some reaching values as high as 435 kPa.
Abstract: The evaporation method is frequently used for simultaneous determination of soil water retention and hydraulic conductivity relationships. Tension is measured at two depths within a short soil column as water evaporates from its surface. Water content and flux are determined by weighing the column. Tensions, water contents, and fluxes are used to derive the water retention curve and the unsaturated hydraulic conductivity function. The measurement range of the conventional procedure is limited on the wet end by the inability of pressure transducers to accurately register very small tension differences. Hence, the resulting calculated hydraulic gradient in the vertical direction is associated with large uncertainties. On the dry end, water cavitation in the tensiometer, which typically occurs around 70 to 90 kPa, is the limitation. We present here a new design based on improved tensiometers that resist cavitation to much higher tensions, some reaching values as high as 435 kPa. On the wet end, data from a simple steady-state method were used to supplement the evaporation method. On the dry end, applying the new tensiometers enabled the quantification of hydraulic functions up to 293 kPa average tension. Experimental results and soil water simulation affirmed the validity of the linearization assumption, even on the dry end when nonlinear tension-depth profiles emerge. The application of evaporation functions as a supplement for frequent weighing reduces costs for the equipment and increases the effectiveness of the method. Their validity for deriving fluxes was confirmed for the extended range, too. Results are presented for soil samples of different textures (sand, loam, silt, clay, and peat), various origins, and various dry bulk densities.
171 citations
TL;DR: In this article, the authors measured and instrumented an 11.42km long experimental reach of the Pajaro River, central coastal California, to determine rates of streambed seepage (loss and hyporheic exchange) using reach averaged and point specific methods.
156 citations
TL;DR: In this article, the authors characterize soil physical properties under three land-use classes (forest, pasture, and managed lawn) in the southern Blue Ridge Mountains of southwestern North Carolina, and a total of 90 points were sampled (30 in each land use class) throughout a 983 km 2 study area.
154 citations
01 Jan 2010
TL;DR: In this paper, the authors proposed the concept of "cation ratio of soil structural stability" (CROSS), analogous to SAR, to measure the dispersive effects of Na and K on clay dispersion, and Ca and Mg on flocculation.
Abstract: Sodium salts tend to dominate salt-affected soils and groundwater in Australia; therefore, sodium adsorption ratio (SAR) is used to parameterise soil sodicity and the effects of sodium on soil structure. However, some natural soils in Australia, and others irrigated with recycled water, have elevated concentrations of potassium and/or magnesium. Therefore, there is a need to derive and define a new ratio including these cations in place of SAR, which will indicate the dispersive effects of Na and K on clay dispersion, and Ca and Mg on flocculation. Based on the differential dispersive effects Na and K and the differential flocculation powers of Ca and Mg, we propose the concept of 'cation ratio of soil structural stability' (CROSS), analogous to SAR. This paper also gives the results of a preliminary experiment conducted on three soils varying in soil texture on hydraulic conductivity using percolating waters containing different proportions of the cations Ca, Mg, K, and Na. The relative changes in hydraulic conductivity of these soils, compared with the control treatment using CaCl2 solution, was highly correlated with CROSS. Clay dispersion in 29 soils treated with irrigation waters of varying cationic composition was highly correlated with CROSS rather than SAR. It was also found that CROSS measured in 1:5 soil/water extracts was strongly related to the ratio of exchangeable cations. These results encourage further study to investigate the use of CROSS as an index of soil structural stability in soils with different electrolytes, organic matter, mineralogy, and pH.
151 citations
TL;DR: In this article, the authors used the air-entry pressure of the tensiometer's porous ceramic cup as additional defined tension value, which allowed the quantification of hydraulic functions up to close to the wilting point.
Abstract: Knowledge of hydraulic functions is required for various hydrological and plant-physiologicalstudies. The evaporation method is frequently used for the simultaneous determination ofhydraulic functions of unsaturated soil samples, i.e. , the water-retention curve and hydraulic-conductivity function. All methodic variants of the evaporation method suffer from the limitationthat the hydraulic functions can only be determined to a mean tension of ≈ 60 kPa. This iscaused by the limited measurement range of the tensiometers of typically 80 kPa on the dryend. We present a new, cost- and time-saving approach which overcomes this restriction. Usingthe air-entry pressure of the tensiometer’s porous ceramic cup as additional defined tensionvalue allows the quantification of hydraulic functions up to close to the wilting point. The proce-dure is described, uncertainties are discussed, and measured as well as simulated test resultsare presented for soil samples of various origins, different textures (sand, loam, silt, clay, andpeat) and variable dry bulk density. The experimental setup followed the system HYPROP whichis a commercial device with vertically aligned tensiometers that is optimized to perform evapora-tion measurements. During the experiment leaked water from the tensiometer interior wets thesurrounding soil of the tensiometer cup and can lead to a tension retardation as shown by simu-lation results. This effect is negligible when the tensiometers are embedded vertically. For coar-sely textured soils and horizontal tensiometer alignment, however, the retardation must be con-sidered for data evaluation.
142 citations
TL;DR: In this article, the authors used simulated rainfall experiments to determine whether the varying hydrological effect of ash can be attributed to differences in the underlying soil texture or the ash thickness, and they compared the infiltration rates: (1) before and after controlled burns in 0.5 m2 plots underlain by two sharply contrasting soil textures (sandy loam and gravelly silt loam), and; (2) after the addition of 0.0 cm of ash to the burned sandy loam plots with the original ash layer removed.
TL;DR: The results of a comprehensive testing program conducted to evaluate the hydraulic conductivity of two geosynthetic clay liners (GCLs) considered as a liner component for a tailings impoundment at a proposed zinc and copper mine are reported in this paper.
TL;DR: In this article, the results of a field campaign documenting topsoil hydraulic properties in a small French suburban catchment (7 km 2 ) located near Lyon, France were presented.
Abstract: The hydraulic properties of the topsoil control the partition of rainfall into infiltration and runoff at the soil surface. They must be characterized for distributed hydrological modelling. This study presents the results of a field campaign documenting topsoil hydraulic properties in a small French suburban catchment (7 km 2 ) located near Lyon, France. Two types of infiltration tests were performed: single ring infiltration tests under positive head and tension-disk infiltration using a mini-disk. Both categories were processed using the BEST-Beerkan Estimation of Soil Transfer parameters-method to derive parameters describing the retention and hydraulic conductivity curves. Dry bulk density and particle size data were also sampled. Almost all the topsoils were found to belong to the sandy loam soil class. No significant differences in hydraulic properties were found in terms of pedologic units, but the results showed a high impact of land use on these properties. The lowest dry bulk density values were obtained in forested soils with the highest organic matter content. Permanent pasture soils showed intermediate values, whereas the highest values were encountered in cultivated lands. For saturated hydraulic conductivity, the highest values were found in broad-leaved forests and small woods. The complementary use of tension-disk and positive head infiltration tests highlighted a sharp increase of hydraulic conductivity between near saturation and saturated conditions, attributed to macroporosity effect. The ratio of median saturated hydraulic conductivity to median hydraulic conductivity at a pressure of -20 mm of water was about 50. The study suggests that soil texture, such as used in most pedo-transfer functions, might not be sufficient to properly map the variability of soil hydraulic properties. Land use information should be considered in the parameterizations of topsoil within hydrological models to better represent in situ conditions, as illustrated in the paper. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, the functional significance of microbial activity in the host porous medium in terms of feedback mechanisms instigated by irregular water availability and related physical and chemical conditions that force the organization and formation of unique microbial habitats in unsaturated soils that prompt and potentially perpetuate the formation of preferential flow paths in the vadose zone.
TL;DR: In this article, the effects of soil compaction on macropore parameters measured using X-ray computed tomography (CT) were evaluated on Mexico silt loam (fine, smectitic, mesic Vertic Epiaqualfs) with field treatments.
TL;DR: In this paper, the role of macropore flow and water repellency on spatial and temporal infiltration patterns in a burned soil at plot (0.5 mm), comprising just 5.5% of the soil volume, contributed to 70% and 95%, respectively, of the field-saturated and ponded hydraulic conductivity.
Abstract: Research shows that water repellency is a key hydraulic property that results in reduced infiltration rates in burned soils. However, more work is required in order to link the hydrological behaviour of water repellent soils to observed runoff responses at the plot and hillslope scale. This study used 5 M ethanol and water in disc infiltrometers to quantify the role of macropore flow and water repellency on spatial and temporal infiltration patterns in a burned soil at plot ( 0.5 mm), comprising just 5.5% of the soil volume, contributed to 70% and 95%, respectively, of the field-saturated and ponded hydraulic conductivity (K p ). Because flow occurred almost entirely via macropores in non-repellent areas, this meant that less than 2.5% of the soil surface effectively contributed to infiltration. The hydraulic conductivity increased by a factor of up to 2.5 as the hydraulic head increased from 0 to 5 mm. Due to the synergistic effect of macropore flow and water repellency, the coefficient of variation (CV) in K p was three times higher in the water-repellent soil (CV = 175%) than under the simulated non-repellent conditions (CV = 66%). The high spatial variability in K p would act to reduce the effective infiltration rate during runoff generation at plot scale. Ponding, which tend to increase with increasing scale, activates flow through macropores and would raise the effective infiltration rates at larger scales. Field experiments designed to provide representative measurements of infiltration after fire in these systems must therefore consider both the inherent variability in hydraulic conductivity and the variability in infiltration caused by interactions between surface runoff and hydraulic conductivity. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors quantitatively relate macropore characteristics to saturated hydraulic conductivity (K sat ) and dispersivity (λ) and identify major macropores characteristics useful for estimating soil hydraulic properties under saturated condition.
Abstract: Quantitative relationships between soil structure, especially macropore characteristics, and soil hydraulic properties are essential to improving our ability to predict fl ow and transport in structured soils. Th e objectives of this study were to quantitatively relate macropore characteristics to saturated hydraulic conductivity (K sat ) and dispersivity (λ) and to identify major macropore characteristics useful for estimating soil hydraulic properties under saturated condition. Large intact soil columns were taken from two land uses (cropland and pasture) of the same soil type (a Typic Hapludalf ), with four replicates for each land use. Th e soil columns were scanned using X-ray computed tomography (CT) to obtain macropore parameters including macroporosity, length density, mean tortuosity, network density, hydraulic radius, path number, node density, and mean angle. Th e K sat of the whole soil column, as well as each soil horizon within the column, and solute breakthrough curve (BTC) of CaBr 2 were determined for each column. For all eight soil columns studied, macroporosity and path number (the number of independent macropore paths between two boundaries) explained 71 to 75% of the variability in the natural logarithm of K sat values of the whole soil columns as well as of individual soil horizons. Th e traditional convection–dispersion equation (equilibrium model) simulated the BTCs well for all soil columns except one with an earthworm hole passing through the entire column, for which the two-region model (non-equilibrium model) was required. Th e path number, hydraulic radius, and macropore angle were the best predictors for λ, explaining 97% of its variability. Correlation between λ of the whole soil columns and K sat values of the Bt horizons (but not A horizons) implied that the dispersivity was mainly controlled by the horizon with the lowest K sat in the soil columns. Th ese results indicate that the most useful macropore parameters for predicting fl ow and transport under saturated condition in structured soils included macroporosity, path number, hydraulic radius, and macropore angle.
TL;DR: In this paper, the spatial variability of hydraulic conductivity in a shallow unconfined aquifer located at North Bay, Ontario, composed of glacial-lacustrine and glacialfluvial sands, is examined in exceptional detail and characterized geostatistically.
Abstract: [1] The spatial variability of hydraulic conductivity in a shallow unconfined aquifer located at North Bay, Ontario, composed of glacial-lacustrine and glacial-fluvial sands, is examined in exceptional detail and characterized geostatistically. A total of 1878 permeameter measurements were performed at 0.05 m vertical intervals along cores taken from 20 boreholes along two intersecting transect lines. Simultaneous three-dimensional (3-D) fitting of Ln(K) variogram data to an exponential model yielded geostatistical parameters for the estimation of bulk hydraulic conductivity and solute dispersion parameters. The analysis revealed a Ln(K) variance equal to about 2.0 and 3-D anisotropy of the correlation structure of the heterogeneity (λ1, λ2, and λ3 equal to 17.19, 7.39, and 1.0 m, respectively). Effective values of the hydraulic conductivity tensor and the value of the longitudinal macrodispersivity were calculated using the theoretical expressions of Gelhar and Axness (1983). The magnitude of the longitudinal macrodispersivity is reasonably consistent with the observed degree of longitudinal dispersion of the landfill plume along the principal path of migration. Variably saturated 3-D flow modeling using the statistically derived effective hydraulic conductivity tensor allowed a reasonably close prediction of the measured water table and the observed heads at various depths in an array of piezometers. Concomitant transport modeling using the calculated longitudinal macrodispersivity reasonably predicted the extent and migration rates of the observed contaminant plume that was monitored using a network of multilevel samplers over a period of about 5 years. It was further demonstrated that the length of the plume is relatively insensitive to the value of the longitudinal macrodispersivity under the conditions of a steady flow in 3-D and constant source strength. This study demonstrates that the use of statistically derived parameters based on stochastic theories results in reliable large-scale 3-D flow and transport models for complex hydrogeological systems. This is in agreement with the conclusions reached by Sudicky (1986) at the site of an elaborate tracer test conducted in the aquifer at the Canadian Forces Base Borden.
TL;DR: A modified Green-Ampt model was developed in this paper to describe water infiltration through a 300-cm long and five-layered soil column, and a saturation coefficient was introduced to determine the water content and hydraulic conductivity of the wetted zone.
TL;DR: In this article, the authors evaluated the relative influence of biological, physical and chemical interactions on the percolation of leachate through compacted soil liners and found that the presence of microbial activity was confirmed by direct observations of the microbial population in the permeating liquid, by microbial exopolysaccharides encountered in the soil pores, and from inverse modeling analysis of pore bioclogging.
TL;DR: In this article, the spectral-induced polarization (SIP) response was transformed into a relaxation-time distribution using a Debye decomposition procedure and a strong positive correlation in form of a power law between median relaxation time of the distribution and permeability was observed.
Abstract: The relationship between low-frequency electrical properties and hydraulic permeability of rocks has been the focus of geophysical investigations for a long time because it offers a possibility for an in situ and noninvasive permeability estimation of rocks. We examined the hydraulic and low-frequency (10 mHz to 100 Hz) electrical properties as well as the anisotropic properties of low-permeability sandstones from a tight gas reservoir. Single-frequency electrical properties were found to be of low value for the determination of permeability for the studied samples, whereas a strong link between the spectral-induced polarization (SIP) response and permeability was found. The SIP response was transformed into a relaxation-time distribution using a Debye decomposition procedure. We observed a strong positive correlation in form of a power law between median relaxation time of the distribution and permeability, suggesting that relaxation time is a good measure of the effective hydraulic length scale. From a ...
TL;DR: In this paper, an inverse analysis of Beerkan water infiltration data was performed to characterize unsaturated hydraulic properties of the basic oxygen furnace (BOF) slag and its evolution during a 1-yr period through water infiltration experiments and use of an adapted BEST method for inverse analysis.
Abstract: Newer urban soils, frequently composed of several types of anthropogenic materials, may contain basic oxygen furnace (BOF) slag, which is a steel industry byproduct and considered a potential alternative material for road construction. An understanding of the flow and solute transfer processes through urban soils thus requires hydraulic characterization of these materials. The BEST (Beerkan Estimation of Soil Transfer Parameters) algorithm serves to estimate the full set of unsaturated soil properties by means of conducting an inverse analysis of Beerkan water infiltration data. This study aimed at characterizing unsaturated hydraulic properties of the BOF slag and its evolution during a 1-yr period through water infiltration experiments and use of an adapted BEST method for inverse analysis. Results indicate the evolution with time of BOF slag hydraulic parameters due to their physicochemical changes when exposed to rainfall events. Moreover, the findings of this study highlight the initial spatial variability of hydrodynamic characteristics, which after a certain period shifts to mostly homogeneous behavior. This study has contributed to the hydrodynamic characterization of BOF slag by providing hydraulic conductivity and water retention curves, as required for modeling water and thus solute transfer processes vs. time, which is relevant to BOF slag reuse and environmental considerations.
TL;DR: The role of variations in root and branch maximum hydraulic specific conductivity under high and low soil moisture in determining whole-tree hydraulic conductance and in mediating stomatal control of gas exchange in four contrasting tree species growing under ambient and elevated CO₂ was studied.
Abstract: Summary Anatomical and physiological acclimation to water stress of the tree hydraulic system involves trade-offs between maintenance of stomatal conductance and loss of hydraulic conductivity, with short-term impacts on photosynthesis and long-term consequences to survival and growth. Here, we study the role of variations in root and branch maximum hydraulic specific conductivity (ks-max) under high and low soil moisture in determining whole-tree hydraulic conductance (Ktree) and in mediating stomatal control of gas exchange in four contrasting tree species growing under ambient and elevated CO2 (CO2 a and CO2 e ). We hypothesized that Ktree would adjust to CO2 e through an increase in root and branch ks-max in response to anatomical adjustments. However, physiological changes observed under CO2 e were not clearly related to structural change in the xylem of any of the species. The only large effect of CO2 e occurred in branches of Liquidambar styraciflua L. and Cornus florida L. where an increase in ks-max and a decrease in xylem resistance to embolism (−P50) were measured. Across species, embolism in roots explained the loss of Ktree and therefore indirectly constituted a hydraulic signal involved in stomatal regulation and in the reduction of Gs-ref, the sap-flux-scaled mean canopy stomatal conductance at a reference vapour pressure deficit of 1 kPa. Across roots and branches, the increase in ks-max was associated with a decrease in −P50, a consequence of structural acclimation such as larger conduits, lower pit resistance and lower wood density. Across species, treatment-induced changes in Ktree translated to similar variation in Gs-ref. However, the relationship between Gs-ref and Ktree under CO2 a was steeper than under CO2 e , indicating that CO2 e trees have lower Gs-ref at a given Ktree than CO2 a trees. Under high soil moisture, CO2 e greatly reduced Gs-ref. Under low soil moisture, CO2 e reduced Gs-ref of only L. styraciflua and Ulmus alata. In some species, higher xylem dysfunction under CO2 e might impact tree performance in a future climate when increased evaporative demand could cause a greater loss of hydraulic function. The results contributed to our knowledge of the physiological and anatomical mechanisms underpinning the responses of tree species to drought and more generally to global change.
TL;DR: In this article, the hydraulic properties of fen peat soils from the Biebrza River Valley in the north-east of Poland were investigated using the multi-step outflow method to determine the parameters of the Mualem-van Genuchten model that describes soil moisture retention characteristics and the unsaturated hydraulic conductivity function of each soil sample.
TL;DR: In this article, the authors compare different methods for determining soil hydraulic parameters and evaluate the effect of the uncertainty in these parameters on different variables (i.e. evapotranspiration, average water content in the root zone, flux at the bottom boundary of the root zones) simulated by two hydrological models of different complexity: SWAP, a widely used model of soil moisture dynamics in unsaturated soils based on Richards equation, and ALHyMUS, a conceptual model of the same dynamics based on a reservoir cascade scheme.
Abstract: . Data of soil hydraulic properties forms often a limiting factor in unsaturated zone modelling, especially at the larger scales. Investigations for the hydraulic characterization of soils are time-consuming and costly, and the accuracy of the results obtained by the different methodologies is still debated. However, we may wonder how the uncertainty in soil hydraulic parameters relates to the uncertainty of the selected modelling approach. We performed an intensive monitoring study during the cropping season of a 10 ha maize field in Northern Italy. The data were used to: i) compare different methods for determining soil hydraulic parameters and ii) evaluate the effect of the uncertainty in these parameters on different variables (i.e. evapotranspiration, average water content in the root zone, flux at the bottom boundary of the root zone) simulated by two hydrological models of different complexity: SWAP, a widely used model of soil moisture dynamics in unsaturated soils based on Richards equation, and ALHyMUS, a conceptual model of the same dynamics based on a reservoir cascade scheme. We employed five direct and indirect methods to determine soil hydraulic parameters for each horizon of the experimental profile. Two methods were based on a parameter optimization of: a) laboratory measured retention and hydraulic conductivity data and b) field measured retention and hydraulic conductivity data. The remaining three methods were based on the application of widely used Pedo-Transfer Functions: c) Rawls and Brakensiek, d) HYPRES, and e) ROSETTA. Simulations were performed using meteorological, irrigation and crop data measured at the experimental site during the period June – October 2006. Results showed a wide range of soil hydraulic parameter values generated with the different methods, especially for the saturated hydraulic conductivity Ksat and the shape parameter α of the van Genuchten curve. This is reflected in a variability of the modeling results which is, as expected, different for each model and each variable analysed. The variability of the simulated water content in the root zone and of the bottom flux for different soil hydraulic parameter sets is found to be often larger than the difference between modeling results of the two models using the same soil hydraulic parameter set. Also we found that a good agreement in simulated soil moisture patterns may occur even if evapotranspiration and percolation fluxes are significantly different. Therefore multiple output variables should be considered to test the performances of methods and models.
TL;DR: GCLs containing powdered Na-bentonite treated with different dosages of a proprietary additive intended to reduce the impacts of chemical interactions were permeated with three solutions: a hyperalkaline solution (1/M NaOH and 1.3/mM CsCl) having similar pH to aluminum refining leachate, a 1/3 mCsCl solution (no NaOH), and DI water as mentioned in this paper.
TL;DR: In this article, the authors compared mean K and heterogeneous K fields obtained by various approaches by predicting drawdowns from independent cross-hole pumping tests and total flow rates through a synthetic heterogeneous aquifer from flow-through tests.
Abstract: [1] Groundwater modeling has become a vital component to water supply and contaminant transport investigations. An important component of groundwater modeling under steady state conditions is selecting a representative hydraulic conductivity (K) estimate or set of estimates which defines the K field of the studied region. Currently, there are a number of characterization approaches to obtain K at various scales and in varying degrees of detail, but there is a paucity of information in terms of which characterization approach best predicts flow through aquifers or drawdowns caused by some drawdown inducing events. The main objective of this paper is to assess K estimates obtained by various approaches by predicting drawdowns from independent cross-hole pumping tests and total flow rates through a synthetic heterogeneous aquifer from flow-through tests. Specifically, we (1) characterize a synthetic heterogeneous aquifer built in the sandbox through various techniques (permeameter analyses of core samples, single-hole, cross-hole, and flow-through testing), (2) obtain mean K fields through traditional analysis of test data by treating the medium to be homogeneous, (3) obtain heterogeneous K fields through kriging and steady state hydraulic tomography, and (4) conduct forward simulations of 16 independent pumping tests and six flow-through tests using these homogeneous and heterogeneous K fields and comparing them to actual data. Results show that the mean K and heterogeneous K fields estimated through kriging of small-scale K data (core and single-hole tests) yield biased predictions of drawdowns and flow rates in this synthetic heterogeneous aquifer. In contrast, the heterogeneous K distribution or “K tomogram” estimated via steady state hydraulic tomography yields excellent predictions of drawdowns of pumping tests not used in the construction of the tomogram and very good estimates of total flow rates from the flow-through tests. These results suggest that steady state groundwater model validation is possible in this laboratory sandbox aquifer if the heterogeneous K distribution and forcing functions (boundary conditions and source/sink terms) are characterized sufficiently.
TL;DR: In this article, the effect of the land use change of a Typic Hapludand on some soil structure dependent properties and their variability depending on hydraulic conditions using field, laboratory data and modelling is described.
TL;DR: In this article, the authors investigated electrical and physical-chemical properties of six sandstone samples with contrasting mineralogical characteristics and with hydraulic conductivity varying in a wide range, and they found a positive logarithmic relationship between the relaxation time and the pore throat diameter.
Abstract: SUMMARY
We investigated electrical and physical–chemical properties of six sandstone samples with contrasting mineralogical characteristics and with hydraulic conductivity varying in a wide range. The electrical data were obtained from time domain spectral induced polarization (IP) measurements.
We inverted the IP decays to relaxation time distributions, and then compared the modal relaxation times with the dominant pore throat diameters obtained from the Mercury Injection Capillary Pressure (MICP) data.
We found a positive logarithmic relationship between the relaxation time and the pore throat diameter. Also, we found the normalized chargeability (an integral IP parameter) to be positively correlated with the clay content. These two results suggest that the polarization of our sandstones is controlled by the pore throat distribution, and by the clay content.
The logarithmic relationship contradicts previous theories, and is not universal. Adopting an approach of Kruschwitz and her co-workers, we calculated the effective diffusivity from IP and MICP data, and we found the effective diffusivity values ranging from 2.9 × 10−13 to 1.6 × 10−10 m2 s−1. High diffusivity values, typical of surface diffusion, were obtained for clean sandstones. Low diffusivity values were obtained for clayey sandstones, and they were one to two orders of magnitude lower than those characteristic of the surface diffusion.
We proposed two mechanisms to explain the ‘slow’ diffusion: (1) the effect of surface tortuosity of pore throats filled with clay minerals and (2) the effect of pore geometry. These two effects represent an obstacle in assessing the pore throat diameter and hydraulic conductivity of sandstones with large specific surface and clay content on the basis of spectral IP measurements. However, we believe that the sandstones featuring ‘slow’ diffusion can be discriminated based on the integral polarization parameters, and that the relaxation time remains a valuable parameter for assessing hydraulic properties of clean sandstones.