Measurement Of Hydraulic Properties Research Articles

Slope stability of bioreactor landfills during leachate injection: Effects of unsaturated hydraulic properties of municipal solid waste

In bioreactor landfill, the leachate flow and moisture distribution depend upon saturated and unsaturated hydraulic properties of municipal solid waste (MSW). The effects of unsaturated parameters have not been studied because of scarcity of the data and variation in unsaturated parameters due to MSW heterogeneity, degree of decomposition, and pore structure. In this study, a numerical two-phase flow model was used to examine the effects of unsaturated hydraulic properties on the moisture distribution, pore fluid pressures, and the stability of a bioreactor landfill slope with horizontal trench as leachate recirculation system. Unsaturated hydraulic parameters were based on the van Genuchten model and obtained from previously published laboratory studies. The unsaturated hydraulic properties of MSW are found to significantly influence the leachate distribution, pore water and capillary pressures, and landfill slope stability during the operations of leachate injection and subsequent gravity drainage. Further research is needed for better understanding and accurate measurement of hydraulic properties and shear strength parameters of unsaturated MSW.

Measurements of stem xylem hydraulic conductivity in the laboratory and field

Summary1. Xylem hydraulic properties play an essential role in supporting growth and photosynthesis and influence sensitivity to environmental conditions such as drought and freezing. Consequently, stem hydraulic conductance can be used as a comparative measure of overall hydraulic adaptation across species and to assess the impact of environmental variation, especially drought, on water transport.2. We summarize the main methods currently in use for measurements of stem xylem hydraulic properties. Measurements can be accomplished in a number of ways, including using a pipette, an analytic balance or a ‘pressure‐drop’ flow meter. We provide new details on the design of a relatively inexpensive and easily field‐deployable flow meter that is flexible for a variety of applications. The biological challenges associated with these measurements arise from the difficulties of working with diverse living tissues of variable geometry.3. We provide a review of best practices and provide technical guidance, emphasizing measurements on detached samples using portable equipment.

Use of the Quantitatively Transformed Field Soil Structure Description of the US National Pedon Characterization Database to Improve Soil Pedotransfer Function

Soil hydraulic properties such as hydraulic conductivity or water retention which are costly to measure can be indirectly generated by soil pedotransfer function (PTF) using easily obtainable soil data. The field soil structure description which is routinely recorded could also be used in PTF as an input to reduce the uncertainty. The purposes of this study were to use qualitative morphological soil structure descriptions and soil structural index into PTF and to evaluate their contribution in the prediction of soil hydraulic properties. We transformed categorical morphological descriptions of soil structure into quantitative values using categorical principal component analysis (CATPCA). This approach was tested with a large data set from the US National Pedon Characterization database with the aid of a categorical regression tree analysis. Six different PTFs were used to predict the saturated hydraulic conductivity and those results were averaged to quantify the uncertainty. Quantified morphological description was successively used in multiple linear regression approach to predict the averaged ensemble saturated conductivity. The selected stepwise regression model with only the transformed morphological variables and structural index as predictors predicted the <TEX>$K_{sat}$</TEX> with <TEX>$r^2$</TEX> = 0.48 (p = 0.018), indicating the feasibility of CATPCA approach. In a regression tree analysis, soil structure index and soil texture turned out to be important factors in the prediction of the hydraulic properties. Among structural descriptions size class turned out to be an important grouping parameter in the regression tree. Bulk density, clay content, W33 and structural index explained clusters selected by a two step clustering technique, implying the morphologically described soil structural features are closely related to soil physical as well as hydraulic properties. Although this study provided relatively new method which related soil structure description to soil structure index, the same approach should be tested using a datasets containing the actual measurement of hydraulic properties. More insight on the predictive power of soil structure index to estimate hydraulic properties would be achieved by considering measured the saturated hydraulic conductivity and the soil water retention.

PROBABILISTIC PREDICTIONS OF INFILTRATION INTO HETEROGENEOUS MEDIA WITH UNCERTAIN HYDRAULIC PARAMETERS

Soil heterogeneity and the lack of detailed site characterization are two ubiquitous factors that render predictions of flow and transport in the vadose zone inherently uncertain. We employ the Green‐Ampt model of infiltration and the Dagan‐ Bresler statistical parameterization of soil properties to compute probability density functions (PDFs) of infiltration rate and infiltration depth. By going beyond uncertainty quantification approaches based on mean and variance of system states, these PDF solutions enable one to evaluate probabilities of rare events that are required for probabilistic risk assessment. We investigate the temporal evolution of the PDFs of infiltration depth and corresponding infiltration rate, the relative importance of uncertainty in various hydraulic parameters and their cross-correlation, and the impact of the choice of a functional form of the hydraulic function. Soil heterogeneity and the lack of detailed site characterization are two ubiquitous factors that hamper one’s ability to predict flow and transport in the vadose zone. The continuing progress in data acquisition notwithstanding, measurements of hydraulic properties of partially saturated media remain scarce and prone to measurement and interpretive errors. Consequently, spatial distributions of hydraulic parameters (saturated and relative hydraulic conductivities, and parameters in retention curves) are typically uncertain and their statistical properties are subject to considerable debate. Despite some reservations, e.g., [1, 2], it has become common to treat saturated hydraulic conductivityK s (x)as a multivariate log-normal random field whose ensemble statistics (e.g., mean, variance, and correlation length) can be inferred from spatially distributed data by means of geostatistics. No such consensus exists about statistical distributions of various hydraulic parameters entering relative hydraulic conductivity and retention curves. For example, various data analyses concluded that spatial variability of a soil parameterα G (x)in the Gardner model of relative conductivity, which is often referred to as the reciprocal of the macroscopic capillary length, exhibits either a normal [3] or log-normal [4] distribution and is either correlated [5] or uncorrelated [3] withK s . We defer a more detailed review of the statistical properties of bothα G (x)and parameters in the van Genuchten model of relative conductivity until Section 2. Here, it suffices to say that any approach to uncertainty quantification for flow and transport in the vadose zone must be flexible enough to accommodate arbitrary statistical distributions of soil properties. Statistical treatment of hydraulic parameters renders corresponding flow equation stochastic. Solutions of these equations are probability density functions (PDFs) of system states (water content, pressure, and macroscopic flow velocity) and can be used not only to predictflowin heterogeneous partially saturated porous media but also to quantify

Shear-Induced Flow Channels in a Single Rock Fracture and Their Effect on Solute Transport

The effect of mechanical shearing on fluid flow anisotropy and solute transport in rough rock fractures was investigated by numerical modeling. Two facing surfaces of a rock fracture of 194 mm × 194 mm in size were laser scanned to generate their respective digital profiles. Fluid flow through the fracture was simulated using a finite element code that solves the Reynolds equation, while incremental relative movement of the upper surface was maintained numerically to simulate a shearing process without normal loading. The motion of solute particles in a rough fracture undergoing shear was studied using a particle tracking code. We found that shearing introduces anisotropy in fracture transmissivity, with a greatly increased flow rate and particle travel velocity in the direction perpendicular to the shearing direction. Shear-induced channels yield a transport behavior in which advection dominates in the direction parallel with shear and dispersion dominates in the direction perpendicular to shear. The shear-induced flow channels not only increase the flow connectivity, but also the transport connectivity in the direction perpendicular to shear. This finding has an important impact on the interpretation of the results of coupled hydromechanical and tracer transport experiments for measurements of hydraulic and transport properties of rock fractures.

Validation of an analytical method for determining soil hydraulic properties of stony soils using experimental data

Soil unsaturated hydraulic properties are an important input for simulations of water and solute movement in the vadose zone. However, in the case of soils containing rock fragments, direct measurement of unsaturated hydraulic properties remains difficult. Recently, an analytical method was proposed (Ma et al., 2009) for determining soil hydraulic properties from horizontal water absorption experiments. Here, we test if this method could be used in the determination of the hydraulic properties of stony soils with a set of experiments. The results show that the method can predict accurately and quickly the hydraulic parameters of stony soils using the cumulative infiltration volume and the rate of wetting front advancement during water absorption into a horizontal soil column. The influence of rock fragment content on some soil hydraulic properties including air entry suction, saturated hydraulic conductivity and the shape coefficients of hydraulic functions was further evaluated. Both air entry suction and shape coefficient show a large range of variation with rock fragment content. Globally, the saturated hydraulic conductivities of stony soils decreased with increasing rock fragment content. However, when the volumetric rock fragment content is about 0.08 cm 3 cm −3, the stony soil displayed a greater saturated hydraulic conductivity compared to the fine earth at 95% confidence level. The relationship between saturated hydraulic conductivity and rock fragment content is not accurately estimated by different equations relating saturated hydraulic conductivity of stony soils to that of non-stony soils. These findings imply that other factors than the reduction of cross sectional area for water flow influence the hydraulic properties of stony soils.

Fault seal calibration: a brief review

Abstract Calibration is a necessary step in the workflow for prediction of fault seal because there is no direct way to detect the hydraulic behaviour of a fault at the scale of a hydrocarbon trap. Over the last 20 years two general approaches have been developed: Measurement of hydraulic properties of fault-zone samples (lab calibration), then mapping these results onto the appropriate parts of trap-bounding faults. Design of simple algorithms which attempt to capture a salient feature of the fault zone (e.g. CSP, SSF, SGR), then looking at known trap-bounding faults to find a relationship between the algorithm and the presence or capacity of a seal (sub-surface calibration). Seal capacity is typically described by Hg–air threshold pressure in the lab or static pressure differences in the subsurface (e.g. hydrocarbon buoyancy pressure). In addition to likely interpretation and geometry errors in approaches (i) and (ii), further uncertainty is introduced when converting the calibrated seal strength to potential hydrocarbon column height, because of the variability of subsurface hydrocarbon fluids (interfacial tension). Despite these potential problems, the different methodologies typically agree reasonably well in their predictions for fault-seal capacity. However, this agreement may be largely coincidental and is likely to be a response to the heterogeneity of fault-zone structure (especially at intermediate ‘compositions’ or SGR).

Simultaneous Laboratory Measurement of Acoustic and Hydraulic Properties of Unsaturated Soils

Complete sets of acoustic properties (compressional and shear wave velocities and attenuations) and hydraulic properties (the soil water characteristic curve and the unsaturated hydraulic conductivity function) were determined across a full range of water contents for two types of soil specimens. The acoustic and hydraulic data were collected using a novel device developed at the University of Vermont. The acoustic data were collected using a Kelly wavelet with a center frequency of 20 kHz. The measured acoustic velocities and attenuations across a full range of water contents were consistent with similar measurements found in the literature and made in rock specimens. The experimental data reported here can be used to verify analytical models that attempt to link acoustic and hydraulic properties of unconsolidated and unsaturated porous media.

Advances in Canadian Peatland Hydrology, 2003-2007

Peatlands represent over 90% of Canadian wetlands and are the focus of considerable hydrological and biogeochemical research. Research on evapotranspiration (ET) has shown that it can exceed annual precipitation (P) where there are replenishing flood events. Evaporation from open water ponds in boreal peatlands exceeds ET from vegetated riparian zones by about two times, but surrounding forests can shelter small ponds by reducing turbulence. In an open bog, evaporation was modelled by separating the surface into vascular vegetation, hummock moss and hollow moss surfaces, and showed that vascular plants contribute 60-80% of ET, mosses making up the remainder with hummock mosses dominant over hollows. Runoff from peatlands is enhanced by features ranging from headwater swamps, ice-cored peat plateaus, patchy arctic wetlands and even sections of riverine peatlands. Groundwater fluxes can be quite erratic, and depend on transient properties of the peat that depend on moisture content (e.g., unsaturated hydraulic conductivity) to unsteady saturated hydraulic properties (e.g., hydraulic conductivity, specific yield) caused by peat compression and dilation associated with water storage changes. Surface elevation adjustments can result in a more stable depth to water table, increase evaporation losses, increase methane emission, and attenuate pore-water concentration of contaminants. Research on Canadian peatlands has also made significant methodological advances, including measurement of hydraulic properties of living mosses and peat pore-water and pore dimension characteristics. A considerable multi-annual effort has also been made in evaluating carbon dynamics from Canadian peatlands. Summer moisture availability is important to determining carbon fluxes with some peatlands experiencing enhanced productivity following drought (water table drawdown). Sudden changes in water table elevation promote DOC production and export. Methane bubbles confound hydraulic gradients and flows by creating local pockets of pressure, which are then released episodically when the entrapped gas reaches a threshold content. Canadian peatland hydrology continues to be actively researched in lab, field and modelling studies.

Direct measurement of hydraulic properties in developing berries of Vitis vinifera L. cv Shiraz and Chardonnay

Berries of Vitis vinifera L. cv Shiraz can undergo weight loss during later stages of ripening. Existing published views on how weight loss occurs are based on changes in capacity of the vascular system to import water during development (McCarthy and Coombe, Australian Journal of Grape and Wine Research, 5, 17–21, 1999). One important element of these views is the proposed cessation of water flow through the xylem after veraison. We have now measured the water flow into berries of Shiraz and Chardonnay as they develop using the pressure probe and the high pressure flow meter (HPFM). The pressure probe connected to the pedicel of individual berries provided measurements of single berry hydraulic conductance. By systematic excision of tissue segments of the berry and pedicel we determined where in the pathway hydraulic conductance changed during development. The HPFM was used on whole bunches showing that berries (including pedicels) represent parallel high hydraulic resistances and that the hydraulic resistance of the bunch axis was rather small. The hydraulic conductance per berry could be determined from excision experiments. There was close agreement between the pressure probe and HPFM measurements. Both showed a ten-fold reduction in hydraulic conductance of whole berries from veraison to full ripeness. Shiraz had hydraulic conductances that were 2- to 5-fold higher than those for Chardonnay. Shiraz maintained a higher hydraulic conductance past 90 days after flowering than Chardonnay. The decrease in hydraulic conductance occurred in both the distal and proximal parts of the berry for both varieties. The pressure probe also provided measurements of the xylem pressure that non-transpiring berries could develop. These pressures were –0.2 to –0.1 MPa until veraison and increased to zero when the juice osmotic potential reached about –3 MPa in Chardonnay and –4 MPa in Shiraz. The results suggest values of the reflection coefficient of the osmotic barrier around the xylem vessels of about 0.1–0.2 at veraison decreasing to 0 at harvest. It is suggested that in addition to changes in xylem anatomy, aquaporins in berry membranes may play a role in regulating hydraulic conductance. Water movement from the berry back to the parent vine via the xylem (backflow) may be an important component of berry weight loss in Shiraz, particularly if the phloem ceases functioning at high osmotic potentials near maximum weight. Backflow could account for a weight loss of 43 mg per day in Shiraz berries for a relatively small gradient of 0.1 MPa.

A Field Application of the Scaled‐Predictive Method for Unsaturated Soil

Unsaturated hydraulic conductivity is important to many vadose zone processes. However, there is uncertainty regarding how laboratory‐ and field‐measured hydraulic property measurements can be combined with soil textural data to improve the description of the unsaturated hydraulic conductivity function at the field scale. In this investigation, we examine a scaled‐predictive method for defining the hydraulic conductivity function. This approach uses field‐measured data to adjust the hydraulic conductivity relationship developed using either laboratory measurements or soil textural data. In addition, both hydraulic property models were scaled using field‐measured data collected during a controlled infiltration experiment. Data from a second controlled infiltration experiment were used to evaluate the hydraulic property models based on accuracy of prediction of the arrival time of a wetting front and the water content distribution with time. The unadjusted laboratory‐derived parameters provide the best first approximation for predicting the wetting front arrival. Both hydraulic property models gave more accurate predictions of the wetting front arrival after adjustment with field‐measured data. Both scaled models predicted the water content distributions poorly. These predictions were improved, especially for the pedotransfer model, if the scaling was applied to only the lower portion of the soil profile.

Deforestation alters the hydraulic and biogeochemical characteristics of small lowland Amazonian streams

AbstractWe investigated how clearing of the tropical rainforest for cattle pasture along small, terra firme lowland streams in the Brazilian Amazon influenced stream hydraulic characteristics, solute concentrations and uptake of dissolved inorganic nitrogen and phosphorus. Measurements of stream channel structure, hydraulic properties and nutrient uptake were obtained from short‐term conservative and non‐conservative solute injections and an in‐stream transport model in two watersheds with pairs of similar‐sized forest and pasture streams in Rondônia. The pasture stream channels were deeper and had a lower cover of sandy bottom habitat and a higher cover of aquatic grass habitat than the forest streams. The pasture streams had larger transient storage zones, higher ratios of transient to channel storage and a shorter hydraulic uptake length than the forest streams. The pasture streams had lower concentrations of dissolved oxygen and NO3− and higher concentrations of dissolved Fe2+. Forest streams exhibited no NO3− uptake, but one pasture stream took up NO3− while the other did not. Uptake of NH4+ was low and variable among streams. Uptake velocities and rates of PO43− were greater in pasture streams compared to those in forest streams. In all streams, uptake lengths for NO3−, NH4+ and PO43− were long and indicated generally lower rates of uptake than in most comparably sized temperate forest streams. Uptake lengths or velocities were not correlated with stream transient storage, suggesting that other factors, such as hypoxia in pasture streams, controlled nutrient uptake. The structural differences are typical for the region, suggesting that deforestation may be altering stream hydrology and biogeochemistry over many thousands of kilometres of primary and secondary stream channels in the Amazon Basin. A better understanding of the extent and distribution of altered hydraulic and biogeochemical function in small streams is required to assess the importance of these changes for larger river networks in the Amazon basin. Copyright © 2006 John Wiley &amp; Sons, Ltd.

English

The accurate determination of saturated and unsaturated hydraulic properties of mine waste and cover material is critical for predicting long-term drainage behavior and closure performance. The rock fragments typically found in mine waste and borrow materials complicate laboratory hydraulic property measurements. Many hydraulic testing laboratories address this issue by removing all material greater than 4.75 mm in diameter, repacking the remaining fine-earth sample in small diameter cores, and “correcting” the resulting measurements for the gravel content using published correction factors. In order to evaluate several of the aforementioned gravel correction and hydraulic property prediction methods, a laboratory experiment was designed to test various well-graded gravelly materials. An alluvial material sample was used to fabricate eight soils with various particle size distributions. The primary sample matrix for all testing was chosen to be the fine-earth fraction, less than 4.75 mm in diameter. Additional soil materials were then fabricated in which either part of the fine-earth fraction was removed, or gravel material ranging from 4.75 mm to 19 mm diameter was added. Test results show that saturated hydraulic conductivity (Ksat) decreased with up to 30% gravel content but increased by orders of magnitude at higher gravel contents. Moisture retention characteristic (MRC) data showed that the air entry value decreased with increasing gravel contents, although the amount of retained water only slightly decreased as gravel content increased. Depending on how the MRC data is interpreted, the predicted unsaturated hydraulic conductivities either showed increasing hydraulic conductivity as gravel contents increased, or the values converge. The measured hydraulic property data could not be accurately predicted using published correction factors, or by other prediction methods that use particle size distribution data. Consequently, removing the gravel fraction could result in significant error in the prediction of mine waste drainage behavior and the performance of cover systems. It is recommended that published correction factors not be used unless the sample is similar in gradation and bulk density to the soils tested by the published method. .

Saturated and Unsaturated Hydraulic Conductivities and Water Retention Characteristics of Weathered Granitic Bedrock

As a first step toward describing water flow processes in bedrock, we determined the hydraulic properties of three trimmed samples of weathered granitic bedrock (referred to as Samples A, B, and C, in order of size) in the laboratory. Silicone rubber was used to fill the space between each sample and the surrounding cylinder wall, ensuring accurate measurement of hydraulic properties of the samples. All samples showed similar saturated hydraulic conductivity values of 1 × 10−4 cm s−1, with the saturated water flow in all samples obeying Darcy's Law. Unsaturated hydraulic conductivity and water retention functions of Sample A were determined by means of a multistep outflow experiment. Parameters in both functions were optimized by comparing observed and computed cumulative outflow rates. The resulting computed cumulative outflow rates using the optimized parameters showed a good match to the observed cumulative outflow data. Moreover, the derived water retention function agreed closely with the function measured by the pressure plate method. We conclude that the methods proposed in this study are effective for determining the hydraulic properties of weathered bedrock. The bedrock water retention curve exhibited small changes in volumetric water content throughout the measurement range where the pressure head, ψ, was greater than −200 cm. The bedrock hydraulic conductivity function showed a small decrease in hydraulic conductivity in the very wet range of ψ greater than −30 cm, and then declined gradually with decreasing ψ.

A dripper-TDR method for in situ determination of hydraulic conductivity and chemical transport properties of surface soils

Field determined hydraulic and chemical transport properties can be useful for the protection of groundwater resources from land-applied chemicals. Most field methods to determine flow and transport parameters are either time or energy consuming and/or they provide a single measurement for a given time period. In this study, we present a dripper-TDR field method that allows measurement of hydraulic conductivity and chemical transport parameters at multiple field locations within a short time period. Specifically, the dripper-TDR determines saturated hydraulic conductivity ( K s), macroscopic capillary length ( λ c), immobile water fraction ( θ im/ θ), mass exchange coefficient ( α) and dispersion coefficient ( D m). Multiple dripper lines were positioned over five crop rows in a field. Background and step solutions were applied through drippers to determine surface hydraulic conductivity parameters at 44 locations and surface transport properties at 38 locations. The hydraulic conductivity parameters ( K s, λ c) were determined by application of three discharge rates from the drippers and measurements of the resultant steady-state flux densities at the soil surface beneath each dripper. Time domain reflectometry (TDR) was used to measure the bulk electrical conductivity of the soil during steady infiltration of a salt solution. Breakthrough curves (BTCs) for all sites were determined from the TDR measurements. The K s and λ c values were found to be lognormally distributed with average values of 31.4 cm h −1 and 6.0 cm, respectively. BTC analysis produced chemical properties, θ im/ θ, α, and D m with average values of 0.23, 0.0036 h −1, and 1220 cm 2 h −1, respectively. The estimated values of the flow and transport parameters were found to be within the ranges of values reported by previous studies conducted at nearby field locations. The dripper TDR method is a rapid and useful technique for in situ measurements of hydraulic conductivity and solute transport properties. The measurements reported in this study give clear evidence to the occurrence of non-equilibrium water and chemical movement in surface soil. The method allows for quantification of non-equilibrium model parameters and preferential flow. Quantifying the parameters is a necessary step toward determining the influences of surface properties on infiltration, runoff, and vadose zone transport.

Numerical simulation of shear-induced flow anisotropy and scale-dependent aperture and transmissivity evolution of rock fracture replicas

Fluid flow anisotropy in a single rock fracture during a shear process is an important issue in rock mechanics and is investigated in this paper using FEM modelling, considering evolutions of aperture and transmissivity with shear displacement history. The distributions of fracture aperture during shearing with large shear displacements were obtained by numerically manipulating relative translational movements between two digitalized surfaces of a rock fracture replica, with changing sample sizes. The scale dependence of the fluid behaviour and properties were also investigated using a fractal approach. The results show that the fracture aperture increases anisotropically during shear with a more pronounced increase in the direction perpendicular to the shear displacement, causing significant fluid flow channelling effect, as also observed by other researchers. This finding may have important impacts on the interpretation of the results of coupled hydro-mechanical experiments for measurements of hydraulic properties of rock fractures because the hydraulic properties are usually calculated from flow test results along the shear directions while ignoring the more significant anisotropic flow perpendicular to the shear direction. This finding indicates that the coupled stress-flow tests of rough rock fractures should be conducted in true three-dimensions if possible. Significant change in fracture aperture/transmissivity in the out-of-plane direction should be properly evaluated if two-dimensional tests are conducted. Results obtained from numerical simulations also show that fluid flow through a single rough fracture changes with increasing sample size and shear displacements, indicating that representative hydro-mechanical properties of the fractures in the field can only be more reliably determined using samples of large enough sizes beyond the stationarity threshold and tested with larger shear displacements.

Estimating soil water retention characteristics from the soil taxonomic classification and mapping informations: Consideration of humus categories

The main limiting factors of soil fertility in Hungary are related to soil water management. For this purpose the water management category systems was elaborated in the scale of 1:100 000 and 1:10 000 (Varallyay et al., 1980, Varallyay, 1989). Soil water-retention characteristics (SWRC) are important factors of that category system, but they can only be measured at limited number of sites in a routine soil survey. From this reason most of the soil survey organizations have established soil information systems for further investigations. Data collected in fields and laboratories, for example soil horizons, texture, structure, organic matter, and carbonate content, etc. are prepared for mapping and for further evaluation, and utilization. Even systematic sampling to obtain spatially distributed hydrophysical input data for simulation models is also practically impossible because direct measurement of soils' hydraulic properties is expensive, time consuming, and labor intensive. Alternatively these properties are predictable from available soil data as bulk density (BD), organic matter (OM) content and particle-size distribution (e.g. Gupta and Larson, 1979; Rawls et al., 1982; Ahuja et al., 1985; Fodor and Rajkai, 2004; Rajkai et al., 2004). Estimating functions of the required parameters from easily obtainable input data are called pedotransfer functions (PTFs) according to Bouma and Van Lanen (1987). Soil maps are visualizing the data collected by the standard soil survey methods. Soil surveys are usually built on soil taxonomic classification and additional data, depending on the special requirement of the survey. Soil maps display not only the soil type, but also other soil attributes with certain categorization. Land evaluation is one of the most widespread applications of soil data for land use planning purposes. For land evaluation purposes maps of a scale of 1:10.000 are required. About 60 % of the agricultural area of Hungary is mapped in this scale (Toth et al., 2004). Many of the maps are digitized, georeferenced and integrated to GIS systems. The 1:10.000 maps in Hungary contain information on soil types (subtypes), parent material and texture. Five additional cartograms complement the basic soil map: (1) humus cartogram (with information on depth of humic layer and humus content of the plough layer); (2) pH and calcium carbonate content cartogram; (3) ground water cartogram (depth of soil water level); (4) cartogram of soil salinity (with information on salt content and distribution in the soil profile) (5) cartogram of soil characteristics those are important in soil fertility and management (rooting depth, erosion, stone content, etc.). The 1:10.000 scale map database is the most extensive and it represents the most soil types in Hungary. Therefore it would be very advantageous to find estimation methods for converting the raw data of soil maps and cartograms as readily available information for determining the soil water management categories. This paper aims to formulate the SWRC dependency of the Hungarian soil taxonomic classification in the case of brown forest soils.

Ground Water Recharge and Discharge in the Central Everglades

AbstractRates of ground water recharge and discharge are not well known in the central Everglades. Here we report estimates of ground water recharge and discharge at 15 sites in the Everglades Nutrient Removal Project and in Water Conservation Area 2A (WCA‐2A), along with measurements of hydraulic properties of peat at 11 sites. A simple hydrogeologic simulation was used to assess how specific factors have influenced recharge and discharge. Simulations and measurements agreed that the highest values of recharge and discharge occur within 600 m of levees, the result of ground water flow beneath levees. There was disagreement in the interior wetlands of WCA‐2A (located &gt; 1000 m from levees) where measurements of recharge and discharge were substantially higher than simulated fluxes. A five‐year time series (1997 to 2002) of measured fluxes indicated that recharge and discharge underwent reversals in direction on weekly, monthly, and annual timescales at interior sites in WCA‐2A. Ground water discharge tended to occur during average to moderately dry conditions when local surface water levels were decreasing. Recharge tended to occur during moderately wet periods or during very dry periods just as water levels began to increase following precipitation or in response to a pulse of surface water released from water‐control structures by water managers. Discharge also tended to occur at sites in the wetland interior for ∼1 week preceding the arrival of the surface water pulse. We conclude that ground water recharge and discharge vary cyclically in the interior wetlands of the central Everglades, driven by the differential responses of surface water and ground water to annual, seasonal, and weekly trends in precipitation and operation of water‐control structures.

Gas-partitioning tracer test to quantify trapped gas during recharge.

Dissolved helium and bromide tracers were used to evaluate trapped gas during an infiltration pond experiment. Dissolved helium preferentially partitioned into trapped gas bubbles, or other pore air, because of its low solubility in water. This produced observed helium retardation factors of as much as 12 relative to bromide. Numerical simulations of helium breakthrough with both equilibrium and kinetically limited advection/dispersion/retardation did not match observed helium concentrations. However, better fits were obtained by including a decay term representing the diffusive loss of helium through interconnected, gas-filled pores. Calculations indicate that 7% to more than 26% of the porosity beneath the pond was filled with gas. Measurements of laboratory hydraulic properties indicate that a 10% decrease in saturation would reduce the hydraulic conductivity by at least one order of magnitude in the well-sorted sandstone, but less in the overlying soils. This is consistent with in situ measurements during the experiment, which show steeper hydraulic gradients in sandstone than in soil. Intrinsic permeability of the soil doubled during the first six months of the experiment, likely caused by a combination of dissolution and thermal contraction of trapped gas. Managers of artificial recharge basins may consider minimizing the amount of trapped gas by using wet, rather than dry, tilling to optimize infiltration rates, particularly in well-sorted porous media in which reintroduced trapped gas may cause substantial reductions in permeability. Trapped gas may also inhibit the amount of focused infiltration that occurs naturally during ephemeral flood events along washes and playas.

Properties of two tropical soils in relation to the transport of radionuclides in the rhizosphere

The uptake of radionuclides by commercial crops is being studied at two sites, Blain and Tippera, in a research farm in the Northern Territory, Australia. Studies have been performed to characterise the properties of the two soils, particularly the hydraulic properties that are considered to significantly influence the transport and plant uptake of these radionuclides in the soils The Blain soil, a sandy loam, has been categorised as SM according to the Unified Soil Classification System. Quartz is the dominant mineral for the Blain soil. The Tippera soil, a kaolinitic clayey loam has been categorised as CL. Chemical analysis results were consistent with these findings. The saturated hydraulic conductivity values were of the order of 10 −4 cm/s for the Blain soil. These values were greater by 3–4 orders of magnitude than those for the Tippera soils. The results obtained from the hydraulic property measurements were used to estimate the unsaturated hydraulic properties. A bimodal description based on van Genuchten-type partial saturation functions was used for the estimation. The estimation was qualitatively consistent with the soil types.