Measurement Of Soil Hydraulic Conductivity Research Articles

Variation in root morphology amongst tree species influences soil hydraulic conductivity and macroporosity

Natural approaches to flood risk management are gaining interest as sustainable flood mitigation options. Targeted tree planting has the potential to reduce local flood risk, however attention is generally focused on the hydrological impacts of catchment afforestation linked to generic tree features, whilst the species-specific impacts of trees on soil hydrology remain poorly understood. This study compared effects of different tree species on soil hydraulic properties. Monocultures of Alnus glutinosa (common alder), Fraxinus excelsior (European ash), Fagus sylvatica (European beech), Betula pendula (silver birch), Castanea sativa (sweet chestnut), Quercus robur (English oak) and Acer pseudoplatanus (sycamore maple) were used to determine effects of tree species identity on soil hydraulic properties (near-saturated K and soil water retention) in a sandy loam soil, North Wales, United Kingdom. The interaction of F. excelsior root properties and soil class on hydraulic conductivity was also examined in four different soils (Rendzic Leptosol, Haplic Luvisol, Dystric Fluvic Cambisol and Dystric Gleysol) across England and Wales. Fine root biomass (FRB) and morphological characteristics were determined at three depths (0–0.1, 0.1–0.2 and 0.2–0.3 m) and complemented by in situ surface measurement of soil hydraulic conductivity. Root morphological traits were closely associated with species identity and pore-size distribution, and FRB was strongly correlated with soil hydraulic conductivity (R2 = 0.64 for 0–0.1 m depth FRB; R2 = 0.69 for 0.1–0.2 m depth FRB). Fine root biomass of F. excelsior was sixfold greater than C. sativa (p < 0.001), and the frequency of 0.01 mm radius soil pores under F. excelsior was twice that of Q. robur. Near-saturated hydraulic conductivity under F. excelsior was 7.91 ± 1.23 cm day−1, double the mean rate of the other species. Soil classification did not significantly influence FRB (p = 0.056) or near-saturated hydraulic conductivity (p = 0.076) in the 0.0–0.1 m depth soil, but soil water retention varied with depth. Species-specific traits of trees should be considered in landscape design to maximise the local hydrological benefits of trees.

Design, Fabrication, Evaluation and Calibration of an Improvised Soil Permeameter for Measurement of Soil Hydraulic Conductivity

This study aimed at the design, fabrication, evaluation and calibration of an improvised soil permeameter for measuring saturated soil hydraulic conductivities. A metal support frame with a permissible strength of 50e-4 N/mm2 was made using steel galvanized pipes of 6 cmØ (internal diameter) and metal flat bars of 8cm long and 0.4cm thick. The water tank (thickness 0.6 cm, height 28 cm, internal diameter 19 cmØ) and permeameter cylinder (thickness 0.6 cm, height 23 cm, internal diameter 19 cmØ) were both made of Perspex glass material. An electromechanical measuring device which was programmed and operated wirelessly was designed and constructed to measure head-in and head-out parameters. To calibrate the improvised soil permeameter, sampled and particle analysed soils from different locations within Zaria metropolis, were a test run on both foreign and improvised soil permeameters and their respective Ksat readings were subjected to regression analysis. According to the R2 values, the generated 3rd order polynomial regression equation from the Ksat readings of both foreign and improvised soil permeameter had a satisfactory R2 value of 0.985.&#x0D; Keywords: Permeameter, Hydraulic Conductivity, Electromechanical, Saturated, Automation

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

AbstractThe 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 (hc) below which thin film flow controls water movement. Soil hydraulic conductivity measurements at matric potential below hc 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.

Impacts of thinning of a Mediterranean oak forest on soil properties influencing water infiltration

AbstractIn Mediterranean ecosystems, special attention needs to be paid to forest–water relationships due to water scarcity. In this context, Adaptive Forest Management (AFM) has the objective to establish how forest resources have to be managed with regards to the efficient use of water, which needs maintaining healthy soil properties even after disturbance. The main objective of this investigation was to understand the effect of one of the AFM methods, namely forest thinning, on soil hydraulic properties. At this aim, soil hydraulic characterization was performed on two contiguous Mediterranean oak forest plots, one of them thinned to reduce the forest density from 861 to 414 tree per ha. Three years after the intervention, thinning had not affected soil water permeability of the studied plots. Both ponding and tension infiltration runs yielded not significantly different saturated,Ks, and unsaturated,K−20, hydraulic conductivity values at the thinned and control plots. Therefore, thinning had no an adverse effect on vertical water fluxes at the soil surface. MeanKsvalues estimated with the ponded ring infiltrometer were two orders of magnitude higher thanK−20values estimated with the minidisk infiltrometer, revealing probably soil structure with macropores and fractures. The input of hydrophobic organic matter, as a consequence of the addition of plant residues after the thinning treatment, resulted in slight differences in terms of both water drop penetration time, WDPT, and the index of water repellency,R, between thinned and control plots. Soil water repellency only affected unsaturated soil hydraulic conductivity measurements. Moreover,K−20values showed a negative correlation with both WDPT andR, whereasKsvalues did not, revealing that the soil hydrophobic behavior has no impact on saturated hydraulic conductivity.

Soil Air Permeability Modeling and Its Use for Predicting Unsaturated Soil Hydraulic Conductivity

Core Ideas Ka(θ) was modeled by considering a similar phenomenon between water and air flows in soil medium. Kw(θ) and Ka(θ) were theoretically linked by considering a similar intrinsic permeabilities for both water and air. The proposed models were tested with laboratory‐measured data showing reasonable accuracy. Since the direct measurement of soil hydraulic conductivity [Kw(θ)] is time consuming and difficult, several methods have been suggested for its prediction. However, their application still requires some kind of direct or experimental measurement, even after calibration. Considering much easier measurement of the air permeability [Ka(θ)] and the water and air flows in the soil medium, several attempts have been made to link Kw(θ) and Ka(θ), most of which have used Ka(θ) to predict the saturated hydraulic conductivity (Ks). The current research was aimed to model the air permeability and evaluate its application for Kw(θ) prediction. In this regard, laboratory measurements were conducted for Kw(θ) and Ka(θ) at different soil moisture contents (θ). Then, we introduced a semitheoretical model and evaluated it using measured data. Results showed that the proposed model can predict Kw(θ), with an average evaluation error of 3.69% and average R2 of 0.88. Regarding the fast and nondestructive measurement of Ka(θ) compared with Kw(θ), the proposed model seems to be more practical to characterize unsaturated soil hydraulic conductivity and can improve the accuracy and efficiency of Kw(θ) estimation.

The effects of stubble retention and tillage practices on surface soil structure and hydraulic conductivity of a loess soil

The current cropping system of excessive tillage and stubble removal in the northwestern Loess Plateau of China is clearly unsustainable. A better understanding of tillage and stubble management on surface soil structure is vital for the development of effective soil conservation practices in the long term. Changes in surface soil structure and hydraulic properties were measured after 4 years of stubble management (stubble retained vs. stubble removed) under contrasting tillage practices (no-tillage vs. conventional tillage) in a silt loam soil (Los Orthic Entisol) in Dingxi, Gansu, the northwestern Loess Plateau, China. Our results indicated that after 4 years small but significant changes in soil properties were observed amongst the different tillage and stubble treatments. Surface soil (0–5 cm) under no-tillage with stubble retention had the highest water stability of macroaggregates (>250 μm), soil organic carbon (SOC) and saturated hydraulic conductivity. Significant correlation was found between water stable macro-aggregates and soil organic carbon content, indicating the importance of the latter on soil structural stability. The improvement in soil structure and stability was confirmed by higher soil hydraulic conductivity measurements. Consistently higher K sat was detected in the no tillage with stubble retained soil compared to other treatments. Therefore, no-tillage with stubble retention practice is an effective management technique for improving physical quality of this fragile soil in the long term.

Water infiltration underneath single-ring permeameters and hydraulic conductivity determination

A single-ring permeameter is suitable for measurement of soil hydraulic conductivity at a large-field scale because of its simple structure, easy operation, portability, small amount of recharging water and particularly because of its variable radius. The authors established a simple single-ring permeameter which consists of a hollow cylinder that is simply inserted into the top soil. Based on the theories of the Philip and Nestingen methods for single-ring permeameter tests, this paper presents new equations for describing 1-D infiltration within the inserted depth of the single-ring infiltrometer and 3-D flow beyond the depth under both gravity and soil suction forces. The soil hydraulic parameters of hydraulic conductivity and soil suction were optimized based on the declines of the ponded water depth within the single-ring cylinder. The new method was validated using numerical simulations of the declines of the water column within the cylinder through the variably saturated flow MODFLOW (VSF-MODFLOW). The new method was then successfully applied in laboratory troughs and on a hillslope in Huanjiang County, northwest Guangxi in southwest China. The results demonstrate that the hydraulic conductivity determined by the new method is more accurate than those from the 1-D Green-Ampt method and the 3-D Nestingen method.

Testing the concentric-disk tension infiltrometer for field measurement of soil hydraulic conductivity

The concentric-disk tension infiltrometer (CDTI) may be used to simultaneously measure the confined ( K c ) and the unconfined ( K u ) soil hydraulic conductivity, but it has received little testing. Comparison between K c and K u can be affected by the calculation approach applied to analyze unconfined steady-state infiltration rates. The objectives of this investigation were to: i) establish the effect of the calculation approach on the estimates of K u ; and ii) compare the K c and K u values measured by the CDTI. A clay soil, a structureless sandy loam soil, and a sandy loam soil with a relatively high gravel content were sampled using a disk of radius equal to 107.5 mm, comprising an inner disk with a radius of 50 mm. Six to 15 multipotential experiments with applied pressure heads, h 0, of −120, −60 and −30 mm, were carried out, depending on the soil. Three different approaches, i.e. the simultaneous equations (SE), piecewise exponential (PE) and regression (RE) methods, were applied to calculate K u . The SE and PE methods yielded equivalent K u results. For the clay soil and the lowest pressure head, the RE method yielded significantly lower K u values as compared with the other methods. The discrepancies were attributed to the influence of the structural pore system in the clay soil that could not be represented by the RE method. The ratio between the mean values of K c and K u varied from 0.96 to 1.45, depending on the considered soil/pressure head combination, and the ratio between the associated coefficients of variation ranged between 0.97 and 2.36. In most cases, K c was higher and more variable than K u . Differences between mean K u and K c results were statistically significant ( P = 0.05) in the structureless sandy loam soil for all h 0 values and in the clay soil for the lowest h 0 value. A statistically significant relationship between ln( K u ) and ln( K c ) was detected in all soils but the regression line differed from the identity line in the sandy loam soil with a high gravel content. Possible factors determining the observed discrepancies were suggested to include: i) overestimation of steady-state, one-dimensional flow rate from the inner disk, and ii) lower ability of the relatively small inner disk to sample a site-representative surface macroporosity as compared with the relatively large disk used for a three-dimensional measurement. It was concluded that differences between K c and K u were small and probably negligible for many practical applications but K c was less reliable than K u . An improved quality of the K c data is expected with a larger inner disk and a longer infiltration run, as compared with the ones considered in this investigation. However, there are practical limits in the possible improvements in terms of both disk size and test duration.

Porosity characterization of Argiudolls under different management systems in the Argentine Flat Pampa

Soil pore network characteristics are influenced by management and tillage practices. The objective of this work was to verify if the simultaneous use of the information obtained from tension infiltrometers and water release curves contribute to a better understanding of the impacts of different long-term management systems on the pore space of agricultural soils. The study was carried out on the Flat Pampa in Santa Fe, Argentina, in two types of typical Argiudolls with a silty-loam surface soil texture. The following treatments were evaluated: a) no-till with corn–wheat/soybean rotation (NT-R), and b) conventional tillage with wheat/soybean sequence (CT-S) at Gálvez; and a) no-till with corn–soybean–wheat/soybean rotation (NT-R), and b) no-till with wheat/soybean sequence (NT-S) at Videla. Tension values of 0, 1.5 and 3 cm were applied using tension infiltrometers with the aim of obtaining soil hydraulic conductivity measurements ( K 0, K 1.5, and K 3), and several hydraulic parameters (pore size, pore number, effective macroporosity, conducting macroporosity ( ε ( a, b) ), water flow and water flow decrease). Undisturbed soil cores were collected to determine water release curves (WRC) and soil bulk density (Db). The total macroporosity (Ma) and pore size frequency curve were determined from the fitted model of the WRC. Macropore connectivity was calculated using ε ( a, b) and Ma. In Gálvez, the Db values, K at all tensions, the number of effective pores, the mean pore radius and the effective macroporosity were significantly higher for NT-R. The conducting and total macroporosity values were similar in NT-R and CT-S, but the pores had better continuity in NT-R. In Videla, only K 0 and K 1.5 showed statistical differences in favor of NT-R. This treatment also had a greater number of effective pores, and higher effective, conducting and total macroporosity values, apart from the overall better pore connectivity. There were no significant differences between the NT-R and CT-S for Db and K 3. The evaluated indicators determined that the pore network characteristics are affected not only by tillage system, but also by the crops chosen for the rotation. When used jointly, tension infiltrometers and water release curves can be very useful tools for monitoring the evolution of the soils physical conditions.

Soil water infiltration measurements using electrical impedance tomography

Characterizing hydraulic properties of different types of soils is of great importance for agricultural and geological studies. In situ measurement of soil hydraulic conductivity is a time-consuming task since data has to be recorded at fixed time intervals over a period of minutes or hours depending on the type of soil. Moreover, it is still necessary to use real data for validating models. This paper presents the design of a multimodal infiltrometer which consists of an automated soil infiltration single-ring measurement device and Electrical Impedance Tomography (EIT) data acquisition system. A data logger measures the liquid level change of the 100cm Marriotte-type column, as the water infiltrates at a rate by maintaining a small positive pressure on the water as it moves out of the infiltrometer. A phantom fitted with 16 plate-type electrodes is embedded in the measurement site underneath the water outlet for EIT measurements. The automated infiltrometer data is used for determining soil saturated hydraulic conductivity whereas the EIT measurement system produces images of the water movement through the material below the land surface whose water saturation fluctuates. The equipment was tested in laboratory and in situ trials on four different types of soil (silt loam, clay loam, silty clay and sandy loam) around the Cuitzeo lake watershed (19°58′N, 101°08′W). The results suggest that EIT can be used to image the dynamics of water infiltration of different types of soils, and the automated infiltrometer can provide better information that visually recorded measurements. Thus, a set of images can be used for measuring drainage properties as well. This has important implications for improving computer modelling and soil characterization.

Unsaturated Hydraulic Conductivity Estimation of a Forest Soil Assuming a Stochastic‐Convective Process

Measurement of soil hydraulic conductivity requires considerable time and effort, which makes it difficult to characterize this important parameter across larger areas, especially remote forest regions. Forest soils are frequently texturally coarser than those in agricultural areas, making them more probable candidates for applications building on the stochastic‐convective hypothesis. We developed a method for measuring unsaturated soil hydraulic conductivity based on the analysis of a dye tracer resident concentration profile. In the experiment, partially saturated, steady‐state water flow was established in a forest allophanic soil by a sprinkler operating at 50 mm h−1, after which the water application was switched to a 10 mg L−1 Brilliant Blue FCF solution. The tracer was applied continuously until its cumulative infiltration reached 125 mm, after which the stained soil profile was exposed and photographed. The picture was subjected to an image analysis procedure designed to obtain the resident concentration profile of the tracer. The concentration was fitted to the solution of the convective lognormal transfer function, whose parameters were used in further calculations using functional relationships derived from the stochastic‐convective framework. The resulting hydraulic conductivity as a function of soil water content agreed within an order of magnitude with the relationship obtained by the instantaneous profile method. While the Mualem–van Genuchten model better reproduced the shape of that relationship, it strongly underestimated the hydraulic conductivity across the soil water content interval of interest (0.1–0.4). Finally, ways to improve the predictive capacity of the stochastic‐convective approach in terms of the general trends of the functional relationship were proposed.

A Study of K Variability and Its Effect on Solute Transport in Subsurface-Flow Sand Filters by Measurement and Modelling

Hydraulics of subsurface flow filters (SSF) was studied by measurement of soil hydraulic conductivity (K) variation and performing tracer tests in two SSF filters consisting of 1–4 mm Ca rich sand (shell sand). Soil samples were carefully taken at several locations in Filter I. A tracer experiment was conducted in the undisturbed Filter II using KI. The measured K variability in Filer I was used to analyze the variations in tracer breakthrough. The spatially distribution of K was obtained by fitting a variogram to observed data and interpolation using Kriging. The tracer residence probability density function (PDF) was determined by modelling the tracer movement with a 3-D groundwater model. The observed and simulated tracer arrival was compared for cases with constant K, constant K and dispersion (D), and for spatially variable K and dispersion. The results show that groundwater models were well suited to simulate solute movement in the SSF system studied. An almost perfect fit to observed tracer PDF was obtained when variable K and dispersion was included in the model. This indicates that information on K variability and dispersion is important for studying solute movement in SSF constructed wetlands.

Predicting Field‐Scale Solute Transport Using In Situ Measurements of Soil Hydraulic Properties

AbstractPredicting unsaturated solute transport using measured hydraulic parameters has been difficult due to the inherent variability of soil properties, and the difficulty in obtaining accurate estimates of hydraulic properties in situ. The objective of this study was to determine if in situ measurement of soil hydraulic conductivity, the α soil parameter, and the water content (θ) vs. pressure head (h) relationship could be used to predict field‐scale solute transport. A series of steady‐state solute transport experiments were conducted on a Fox sand (fine‐loamy over sandy or sandy‐skeletal, mixed, mesic Typic Hapludalf) soil in Ontario, Canada. The transport of Cl− under steady‐state water flux was monitored in three separate experiments using solution samplers. Steady‐state water flux densities applied at the soil surface were 9.72 × 10−6, 1.53 × 10−5, and 8.68 × 10−8 m s−1, respectively, for the three sites. After completion of the transport experiments at Site II, measurements of soil hydraulic conductivity and the α parameter were made using the Guelph pressure infiltrometer (GPI) beside each location and depth where solute breakthrough curves (BTCs) were measured, as well as at the soil surface. Undisturbed soil cores were taken at each location where GPI measurements were made for estimating the parameters in the θ(h) using van Genuchten's equations. The GPI‐ and core‐measured hydraulic parameters obtained at Site II were used to predict the field‐scale solute travel time probability density function (PDF) at the same site, and at Sites I and III using a stochastic‐convective model. Observed solute travel time PDFs were predicted quite well at high surface water fluxes, which were close to the field saturated hydraulic conductivity, Kfs by both the GPI and core methods. Both methods underpredicted the variability of the observed travel time PDF.

Automatic Atomized Water Spray System for Soil Hydraulic Conductivity Measurements

AbstractSoil hydraulic conductivity, K, as function of volumetric water content, θ, must be known accurately for any quantitative investigation of water and solute transport in unsaturated soil. Direct measurements of K(θ) are hampered by lack of a suitable apparatus to apply small and spatially uniform water flux densities to soil surfaces for extended periods of time. We developed an automatic atomized water spray system that meets these requirements. Results indicate that, with this water spray system, soil hydraulic conductivities between saturation and values approaching 0.1 mm/d can be measured easily, quickly, and accurately. Hydraulic conductivities were a single‐valued function of water content, measured simultaneously with time‐domain reflectometry, but not of pressure head.

Effect of Tile Spacing on Crop Yield and Water Table Level in a Planosol Soil

AbstractSix years of data are presented on the effect of tile drainage in a Planosol soil (claypan soils of flat lands) at spacings of 15, 30, and 60 feet. Corn, oats, and hay yields were obtained as well as water table levels, rainfall, tile outflow, soil texture, and soil hydraulic conductivity measurements. Corn and oat yields on the 15‐ and 30‐foot spacings varied from 3.4 to 9.1 bu. per acre higher (significant at 99% probability) than the yields on the 60‐foot spacings. Water table, outflow, and hydraulic conductivity measurements seem to indicate that water movement to the tile is largely through the more permeable backfill over the drains. The initial water table midway between the drains a few hours after a rain is lower for the narrower spacings; subsequently, the rate of drop is nearly the same for all spacings. After the first day following rainfall, evapotranspiration and other losses appear to influence the rate of drop more than the tile. Between the drains the water table is nearly flat. After the soil is saturated, tile outflow increases rapidly within a few minutes after the rain starts and reaches a peak in 2 to 4 hours. Several peak flows of over 1 inch per day were recorded. The maximum tile outflow volume measured for a given storm was 55% of the rainfall; however, this percentage is influenced greatly by antecedent moisture conditions.