Guelph Permeameter Method Research Articles

Determination of canal seepage loss in Arrah Main Canal: A case study*

AbstractIn this study, seepage losses have been determined by the direct inflow–outflow method at four selected reaches of the unlined Arrah Main Canal. Grain size analyses of bed materials of all reaches have been carried out, and in situ hydraulic conductivities have been computed using the Guelph permeameter method in all the reaches. The inflow and outflow discharges of all the reaches have been measured using the area–velocity method. The cross‐section and velocity profiles at the corresponding canal sections have been measured using an echo sounder and a digital current meter, respectively, upstream and downstream of all the selected reaches. Seepage loss in each reach has been computed using the continuity equation assuming the evaporation losses are negligible. Also, the empirical equations (Molesworth, Offengenden, and Moritz) have been used to calculate the seepage losses in these reaches and compared with the seepage losses determined by the experimental observations. The measured seepage losses in the unlined Arrah Main Canal varied from 3.66 to 13.4 m3/s/106 m2. The percentage of seepage losses varied from 2.2% to 8.35%, and seepage losses measured and estimated using empirical equations were comparable.

Peculiarities of Infiltration Measurements in Water-Repellent Forest Soil

The paper deals with measurements of water infiltration carried out on a well-developed forest floor formed by needle-leaf litter of Norway spruce. Three field methods (tension disk permeameter, single-ring infiltrometer and Guelph permeameter) were used to determine the soil hydraulic conductivity. The results were strongly influenced by the water repellency at the interface between the O- and A-horizons. This interface was severely water repellent during the hot and dry summer season, regardless of the generally humid mountain climate of the High Tatras foothill. The single-ring method paradoxically provided lower hydraulic conductivity (3.2 × 10−4 ± 1.3 × 10−4) compared to the tension disk permeameter (8.5 × 10−4 ± 3.3 × 10−4) due to the presence of the water-repellent O/A-interface. This effect was also observed with the Guelph permeameter method, which gave the lowest value (5.6 × 10−5 ± 4.3 × 10−5). Abrupt retardation of infiltration on the water-repellent interface may generate shallow subsurface runoff (as was proved by the irrigation experiment) or litter splash during extreme rainfall events and promote water flow to deeper soil horizons through preferential pathways. The observed effects of the forest floor on rainfall infiltration will depend on the seasonal variability of soil water repellency. Although the forest floor is a source of hydrophobic substances that cause water repellency at the O/A-interface and can trigger runoff generation, at the same time its cohesive duff layer protects the forest soil from erosion.

Analysis of the Physical Integrity of Earth Dams from Electrical Resistivity Tomography (ERT) in Brazil

Dams are structures that barrier rivers and streams for a variety of purposes. The constant maintenance of these structures is essential, since a possible accident can lead to damage of catastrophic proportions. In November 2015 in the city of Mariana, Minas Gerais (MG), Brazil, a tailings dam burst and spilled 56 million cubic meters of tailings. In addition to victimize 19 people, the event caused material, economic and environmental damage—it is considered the largest environmental disaster of Brazil. This research presents a cheap and quickly applied alternative for investigation of seepage of water in earth dams, built with distinct embankment materials—one dam composed of predominantly silt and clay soil and the other predominantly composed of sandy soil. The research methods used were: geotechnical tests as gradation test, permeability test with the Guelph permeameter method and the application of the (DC) resistivity geophysical method from the electrical resistivity tomography (ERT) technique in Wenner array. Three ERT lines were positioned parallel to the longitudinal axis at each dam. The data are presented in 2D and 3D geophysical images with electrical resistivity values modeled. Based on the physical principle of electrolytic conduction, i.e., decrease in electrical resistance in materials or siliceous minerals in moisture conditions compared to the material in the dry state, the results revealed low-resistivity zones restricted to some points, associated with water infiltration in the transverse direction. The results indicate saturation restricted to some points and low permeability, at the present time, an installation of piping processes.

A drive point application of the Guelph Permeameter method for coarse-textured soils

The Guelph Permeameter (GP) is a widely used well/auger-hole method for in-situ determination of field-saturated hydraulic conductivity (Kfs) and sorptive number (α*) in the vadose or unsaturated zone. Its application can be difficult, however, in gravelly materials which are problematic to auger, and in un-cohesive sandy materials which collapse during the augering process or upon wetting of the unlined well. We circumvented these issues, by replacing the GP well with a conically tipped well screen or “drive point” which is pushed, driven, rotated or vibrated to the desired depth. We also developed a steady flow analysis to account for the fact that water discharge through the drive point screen is solely radial, rather than both radial and vertical as in the original GP method. The HYDRUS-2D numerical simulation model was used to determine appropriate shape values (CDP) for the drive point analysis; and an empirical regression equation was developed to convert the discrete CDP values into continuous shape functions for porous materials with negligible-moderate, strong and very strong capillarity. In a well-sorted medium-coarse sand, the drive point method produced Kfs and α* values which were plausible and consistent with other data from the field site. The original GP method, on the other hand, under-estimated the drive point results by factors of 2.1–3.1, which may have been caused by progressive collapse of the unlined GP well, and/or gradual sinking of the GP outflow tip into the unprotected well base. It was concluded that the drive point GP method can provide convenient and accurate estimates of Kfs and α* in materials where hydraulic properties are not substantially altered by the disturbance of drive point installation.

Effects of Measurement Method, Scale, and Landscape Features on Variability of Saturated Hydraulic Conductivity

Knowledge of soil saturated hydraulic conductivity (Ks) and its spatial variation is important to characterize hydrological proc- esses. The objective was to quantify three important variability components, i.e., measurement technique, spatial arrangement in sampling, and differing landscape features (sloped surfaces and gullies), to map Ks distribution in eroded watersheds, such as the Chinese Loess Plateau. Classic and geostatistics were employed to explore the effects of measurement method, sampling scale, and landscape position on the Ks and its spatial variation. In a small watershed with an area of 0.2 km 2 , three techniques, including the soil core (SC), tension infiltration (TI), and Guelph permeameter (GP) methods, were employed to determine the surface Ks at 124 positions on the sloped landscape (minimum sampling space of approximately 10 m). Furthermore, the SC method was applied at 204 positions along four 100-m transects (minimum sampling space of 2 m), and 200 positions along four 10-m transects (minimum sampling space of 0.2 m) on the sloped landscape and 45 positions in the gully areas to determine the surface Ks. The results showed that no significant differences of mean logarithmic value of Ks (Log10 Ks) existed for SC and GP, and the spatial patterns behaved the same for TI and GP. The spatial dependence decreased with a decrease in sampling extent. Structured variability was not observed at the 10-m transect scale. When the minimum sampling space changed from 10 to 2 m, the nugget variance decreased, whereas the structured variance, sill variance, and spatial dependence increased. When minimum sampling space changed from 2 to 0.2 m, the changes in spatial pattern of Ks were negligible, implying that a minimum sampling space of 2 m is needed to capture the spatial pattern of Ks. Ks in the gully areas was significantly less than on the sloped positions. The spatial pattern of Ks changed when the gully positions were included. Gully areas, therefore, should be considered for characterizing the spatial pattern of Ks for watersheds in the Chinese Loess Plateau. DOI: 10.1061/(ASCE)HE.1943-5584.0000630. © 2013 American Society of Civil Engineers. CE Database subject headings: Spatial analysis; Infiltration; Hydraulic conductivity; Measurement. Author keywords: Spatial variability; Gully; Scale; Soil core method; Tension infiltration method; Guelph permeameter method.

Evaluation of Different Methods for Measuring Field Saturated Hydraulic Conductivity under High and Low Water Table

In this research, four methods of in situ measurement of saturated hydraulic conductivity (Ks) including the Guelph permeameter (GP), auger hole (AH), original Porchet (OP), and saturated Porchet methods were compared for a silt loam soil. The representative Ks in a drainage system was also determined as a reference value. The mean values of Ks for the GP, AH, OP, SP, and drainage system methods were 1.18, 1.06, 1.85, 1.18, and 1.08 m d−1, respectively. Furthermore, the GP and OP methods had the highest and lowest coefficients of variation at 42.1 and 24.2%, respectively. The difference in Ks values among all methods except SP and GP and the difference in CV values between GP and OP were statistically significant at the 0.01 level of probability. The direct measurement from the drainage system resulted in Ks values of 0.584, 0.915, 1.019, and 0.915 times that of the OP, SP, AH, and GP methods, respectively. The results of the SP, GP, and AH methods were very similar to that obtained from direct measurement of the drainage system. Results showed that the AH and GP methods are the best methods for measuring Ks in the presence and absence of a water table, respectively, with −1.85 and 9.26% difference, respectively, compared with the reference method. Therefore, in regions with a high water table, the AH method is suitable, and for a low water table, the GP method is recommended.

DISCREPANCIES BETWEEN ANALYTICAL SOLUTIONS OF TWO BOREHOLE PERMEAMETERS FOR ESTIMATING FIELD-SATURATED HYDRAULIC CONDUCTIVITY

Field-saturated hydraulic conductivity (Kfs) is considered the most important parameter for water flow and chemical transport phenomena in soils. The Richards' and Laplace's solutions of the Guelph Permeameter (GP) and the Glover's solution of the Compact Constant Head Permeameter (CCHP) for calculating Kfs were compared. Steady-state flow rates of water into soil at a single constant head infiltration (H = 20 cm) from a borehole measured with the Guelph permeameter method were used to estimate Kfs values using these solutions. The geometric mean values of Kfs calculated using Richards', Laplace's, and Glover's solutions were 0.112, 0.185, and 0.224 cm h −1 , respectively, for a Duffield silt loam soil. The Glover's and Laplace's solutions, neither of which takes into account the effect of unsaturated capillary flow, produce Kfs values approximately 1.5 to 2 times larger than the Kfs values calculated using Richards' solution. While the Glover's solution gives Kfs values nearly 1.4 times larger than those estimated by the Laplace's solution. The student t-test showed that the mean difference (Md) among Richards', Laplace's, and Glover's solutions were significantly different from zero at p < 0.01. Thus, statistical analyses indicated that the three analytical methods result in dissimilar estimates of Kfs values. Negative Kfs values are often obtained using simultaneous equations of Richards' solution approach in heterogeneous soils and the Richards' solution can only be used at one constant water depth when an value must be estimated or assigned based on the soil texture and structure. Both Glover's and Laplace's solutions can be used in coarse textured soils where the capillarity effect is minimal and initial water content in the soil is near the field capacity level. This indicates that the variability in Kfs estimates depend not only on soil structure, texture, and other soil characteristics, but also on the method of estimation imposed by the borehole analytical solution.

A constant-head well permeameter method for measuring field-saturated hydraulic conductivity above an impermeable layer

Hydrologic understanding of mountainous and northern regions of Canada is poor owing to the lack of critical field data such as hydraulic conductivity. A portable field instrument, the Guelph permeameter (GP), is a promising tool for measuring field-saturated hydraulic conductivity in remote watersheds inaccessible by motorized vehicles. In order to extend the applicability of the GP method to relatively thin soils underlain by impermeable bedrock or permafrost, a new set of shape factors was determined by numerical simulation. The new shape factors gave accurate values of field-saturated hydraulic conductivity when tested in the laboratory. The impermeable layer causes flow around the auger hole to be primarily horizontal. Therefore, the GP method measures a predominantly horizontal field-saturated hydraulic conductivity in these thin soils. The measured conductivity represents a weighted average of the soil surrounding the submerged surface of the auger hole. In layered soil, the weight is greater for the layers close to the bottom of the hole than for those close to the top. Key words: Guelph permeameter, hydraulic conductivity, forest hydrology, permafrost, peat

Soil properties and water regime of reclaimed surface dumps in the North Bohemian brown-coal region — a field study

This paper attempts to characterise the water regime of reclaimed surface dumps in connection with their soil physical properties. The results of a research project based on field measurements of moisture content and hydraulic conductivity, supported by analyses of undisturbed soil samples, led to recommendations regarding technological procedures for such dumps. A dielectric soil moisture meter, in an improved version, was successfully used for field monitoring and further evaluation of moisture content. Hydraulic conductivity was also measured in the field (by repeated borehole infiltration) using the Guelph permeameter method. Laplace–Gardner analysis was used for evaluating the field saturated hydraulic conductivity results.

Comparison of Procedures to estimate Steady Flow Rate in Field Measurement of Saturated Hydraulic Conductivity by the Guelph Permeameter Method

Different procedures for estimating steady flow rate during field application of the Guelph permeameter method were compared in terms of field-saturated hydraulic conductivity Kfsand equilibration timets estimates. The steady flow rate was evaluated by the slope of the linear portion of the cumulative drop in water level in the permeameter reservoir versus time plot (reference procedure) and by approximate procedures that use the first three or four consecutive values of the rate of fall of the water level equal or differing by less than a given percentage. The influence of the selected time interval between two successive readings (Δt=2 or 10 min) at the permeameter was also investigated. On average, the approximate procedures were practically equivalent and produced aKfs overestimation for the selected experiments (sample sizeN =81;Δt=2 min; 0·7 mm/h⩽Kfs⩽121·5 mm/h) which was not, however, consistent with the observed, substantial tsunderestimation. TheKfs prediction accuracy varied with soil permeability: in low permeability soil, theKfs overestimation was substantial, being also equal to more than an order of magnitude; in high or relatively high permeability soil (i.e. for reference Kfsvalues greater than about 25 mm/h), the approximate and the reference procedures produced similar results, i.e. differing by a maximum factor of 1·5. The increase in the time interval between two readings of the permeameter gave an improved accuracy of thets and Kfsestimates but also a decrease of the number of successful experiments (i.e. experiments producing estimates of Kfs) within each approximate procedure. An empirical relationship between the minimum equilibration time required to obtain accurate Kfsvalues and the early-time infiltration amount was derived. Using this relationship effectively allowed improvement inKfs estimation accuracy compared to the considered approximate procedures.

MEASURING HYDRAULIC CONDUCTIVITY IN A CRACKING CLAY SOIL USING THE GUELPH PERMEAMETER

Knowing the variation of field-saturated hydraulic conductivity (Kfs) with space, time and antecedent soilmoisture conditions can be important for optimum management of cracking clay soils. The Guelph Permeameter (GP)method is a potentially valuable technique for measuring Kfs and its variation in cracking soils, but concerns existregarding (1) impacts of smearing and compaction in the GP well on the Kfs measurement, (2) accurate detection of whensteady flow from the GP is attained, and (3) time required for the GP to reach steady flow (equilibration time). Theseconcerns were investigated for a series of GP measurements in a cracking clay soil (Vertic Xerochrept) in Sicily by testinga plucking implement for removal of smearing and compaction, and by comparing three approaches for detecting steadyflow and equilibration time. The mean Kfs values (11.4-22.1 mm h1) obtained from the GP measurements were 1-3 ordersof magnitude larger than what might be expected for a clayey texture, indicating that ponded infiltration from the GPwells occurred primarily through highly permeable soil shrinkage cracks, rather than through the low permeability clayeymatrix. Wells that were treated with the plucking implement produced a non-significant (P < 0.05) factor of 1.94 increasein mean Kfs relative to untreated wells, suggesting that this method for removing smearing and compaction functionedprimarily by reopening partially smeared-over shrinkage cracks or other macropores. Relatively short mean equilibrationtimes were obtained for the GP measurements (11-42 min), suggesting that the GP method can measure the soilsantecedent Kfs before wetting from the well causes enough soil swelling to produce a declining permeability. Thetraditional four equal readings (FR) procedure for estimating GP equilibration time substantially underestimated themore recent visual estimation (VE) and the new cumulative drop (CD) procedures. This underestimation by the FRprocedure resulted in overestimates of Kfs relative to the VE and CD procedures for Kfs values less than about 4 mm h1.It was concluded that the GP method can be a viable technique for measuring Kfs in cracking clay soil.

The well-shape factor for the measurement of soil hydraulic properties using the Guelph Permeameter

The Guelph Permeameter method is one of the most frequently used field methods to measure soil hydraulic properties in situ. The well-shape factor which is necessary in the calculation must be obtained visually from a chart. We provide three empirical formulae which can almost perfectly describe the shape factor calculated numerically by Reynolds (see, e.g., Reynolds, 1986. The Guelph Permeameter method for in situ measurement of field-saturated hydraulic conductivity and matric flux potential. Ph.D. Dissertation. University of Guelph, Guelph, Ont.). We conclude that the three empirical formulae can replace the three shape factor curves in the Operating Instructions of Model 2800K1 Guelph Permeameter ( Soil Moisture Corp., 1987).

Hydraulic Conductivity in a Clay Soil: Two Measurement Techniques and Spatial Characterization

AbstractInfiltration, drainage, and chemical leaching are strongly influenced by the magnitude and spatial distribution of the field‐saturated soil hydraulic conductivity (Kfs). The Guelph permeameter (GP) method shows promise as an effective means for field measurement of Kfs and its spatial distribution, but its accuracy in medium‐ and fine‐textured soils is not well established. To further assess its accuracy and effectiveness, the GP method was compared with the auger hole (AH) method at the 0.5‐m depth at 68 grid locations in a texturally uniform silty clay soil that had stable but spatially variable structure. The two methods yielded similar geometric mean Kfs values (P &lt; 0.001), as well as similar semivariograms. The two methods were also positively correlated (r = + 0.6565, P &lt; 0.0001). We therefore concluded that the two methods gave equivalent estimates of Kfs at this field site, and that the GP method is capable of providing valid estimates of Kfs in at least some fine‐textured soils. The Kfs values were not correlated with soil texture, organic C content, or soil surface topography, but were negatively correlated (r = −0.7240 for GP method, r = −0.6070 for AH method, P &lt; 0.0001) with antecedent volumetric water content (θa) measured in situ prior to the GP measurements using a down‐hole time domain reflectometry probe. The semivariogram for θa was similar to those for Kfs. These results suggest that the magnitude, range, and pattern of variability of the Kfs measurements were controlled primarily by the well‐developed and stable soil structure at the field site, rather than by texture, organic C content, or surface topography.

Comparison of Saturated Hydraulic Conductivity Measurement Methods for a Glacial‐Till Soil

AbstractHydraulic conductivity is the single most important hydraulic parameter for flow and transport‐related phenomena in soil, but the results from different measuring methods vary under different field conditions. To evaluate the performance of four in situ saturated hydraulic conductivity (Ks) measuring methods, Ks measurements were made at four depths (15, 30, 60, and 90 cm) and five locations on a glacial‐till soil of Nicollet (fine‐loamy, mixed, mesic Aquic Hapludoll)‐Clarion (fine‐loamy, mixed, mesic Typic Hapludoll) association. The four in situ methods were: (i) Guelph permeameter, (ii) velocity permeameter, (iii) disk permeameter, and (iv) double‐tube method. The Ks was also determined in the laboratory on undisturbed soil cores collected from all the five sites and four depths. The Guelph permeameter method gave the lowest Ks values, possibly because of small sample size, whereas the disk permeameter and double‐tube methods gave maximum values for Ks with minimum variability, possibly because of large sample size. Maximum variability in Ks values for soil cores at shallow depths may have occurred because of the presence or absence of open‐ended macropores. Estimates of Ks, however, are most comparable for the velocity permeameter and the laboratory method using a constant‐head permeameter.

Technical Notes: A Comparison of Two Saturated Hydraulic Conductivity Measuring Techniques in Relation to Drain Installation Methods

Saturated hydraulic conductivity (Ks) is an important parameter influencing subsurface drainage design and performance, and Ks can be affected by subsurface drain installation methods. Ks was measured at a field site at Nashua, Iowa, with 1.2-m (4-ft) deep drain lines installed with a trenchless plow and with a chain trencher at four depths [0 to 150, 150 to 450, 450 to 750, 750 to 1000 mm (0 to 6, 6 to 18, 18 to 30, 30 to 40 in.)] using the Guelph permeameter (in situ technique) and the constant head permeameter method (laboratory technique) on undisturbed soil cores which were removed from the field site. Ks values were 10 to 130 times greater for the constant head permeameter compared to the Guelph permeameter method and were significantly different at all depths for the two measurement methods. The laboratory technique yielded greater standard deviation values for all depths, whereas the coefficient of variation values were greater for the in situ technique. Drain line installation methods did not significantly affect Ks at the 0 to 150 and 150 to 450 mm (0 to 6 and 6 to 18 in.) depths; however, at the 450 to 750 and 750 to 1000 mm (18 to 30 and 30 to 40 in.) depths, the trencher installation method had Ks values two to three times greater than the trenchless installation method and these differences were significantly different. Subsurface drain line installation method can affect the Ks values particularly near the drain line depths; however, these affects did not affect drainage system performance 10 years after installation.

An examination of the Guelph permeameter for measuring the soil's hydraulic properties

The Guelph permeameter method (GPM) is a constant-head well permeameter or shallow well pump-in technique for measuring soil hydraulic properties in the unsaturated zone, i.e., the field-saturated hydraulic conductivity, K fs, and the matric flux potential, φ m. Unfortunately it is not uncommon to obtain negative K fs- and φ m-values with the GPM, especially on heterogeneous soils. The objective of this study was therefore to thoroughly examine the GPM for different soil types over a range of initial soil water content conditions and to evaluate the existence of negative K fs- and φ m-values. Two permeameters of different diameter were constructed to test the GPM. Three sets of 16 wells were prepared at sites of three selected soil types, viz., a Norfolk sandy loam, a Lucedale loam, and a Troup loamy sand, each set having a different well diameter ranging from 36 to 86 mm. Steady state flow in each well was measured at 4 water levels ranging from 50 to 125 mm. For the same wells the measurements were repeated for relatively wet and relatively dry initial soil water content conditions. For yet another site, K fs-values were compared with the saturated hydraulic conductivity values ( K s) obtained by the constant-head method applied to undisturbed soil cores. The in-situ measurements and the undisturbed cores were taken at a depth of 0.34 m at 60 locations on a 50-m × 100-m experimental field. Approximately 40% of the results obtained with the GPM were negative. This was attributed to random heterogeneities and systematic soil textural changes with depth. Fewer negative results were obtained for the coarser soil types. Positive values also seemed to have been affected as indicated by extremely high values of the exponential factor in the hydraulic conductivity-pressure head relation. A regression analysis on the K fs- and K s-values hardly showed any correlation between the results of the GPM and the constant-head method. A co-kriging procedure, using clay content and water content data as covariates, to obtain K s-values for exactly the same locations as where the K fs-values were obtained, gave a slightly higher regression coefficient, but it was still concluded that no significant correlation existed between the two methods.

Laboratory and numerical assessment of the Guelph permeameter method : Reynolds, W D; Elrick, D E Soil SciV144, Oct 1987, P282–299

Laboratory and numerical assessment of the Guelph permeameter method : Reynolds, W D; Elrick, D E Soil SciV144, Oct 1987, P282–299

A LABORATORY AND NUMERICAL ASSESSMENT OF THE GUELPH PERMEAMETER METHOD

The Guelph permeameter method was assessed using laboratory and numerical procedures. Sand tank experiments using air-dry Caledon sand confirmed the theoretical basis of the method, that flow out of a small, uncased well into unsaturated soil rapidly decreases to a steady rate (Qs) and involves a finite wetting region. Saturated flow and field-saturated flow experiments found that the truly saturated hydraulic conductivity Ks, (no entrapped air present) for repacked Caledon sand was approximately a factor of 3.5 greater than the corresponding field-saturated hydraulic conductivity, Kfs (entrapped air present). Horizontal infiltration experiments, which were conducted primarily to measure the metric flux potential (φm) of air-dry Caledon sand, suggested that the discrepancy between Ks and Kfs was the result of an approximate 17% undersaturation due to the entrapped air. Application of the Laplace (K1fs) and Gardner (φ1m) analyses to the sand tank results yields approximately a factor of 12 overestimate of Kfs by K1fs, but only about a 10% overestimate of φm by φlm. This indicates that capillarity (parameterized by φm) dominated field-saturated flow (parameterized by Kfs,) in the sand tank experiments. A numerical model based on Richards' equation was able to accurately simulate the sand tank results using Kfs from the field-saturated flow experiments and φm from the horizontal infiltration experiments. Qs and C values were predicted within ≤2% of the experimental values. The numerical results suggest that Kfs, (rather than Ks) and φm are appropriate parameters for describing flow out of a well into unsaturated, structureless soil; and that the integrally correct representation of the K(ψ) relationship provided by the exponential form of Gardner (1958) and by the method of calculating α, can be adequate for describing both transient and steady flow. A three-member family of numerically derived, unsaturated flow C value curves representing “sand,” “loam and structured clay,” and “unstructured clay” appears to compensate adequately for the neglect of the gravity-capillarity interaction in the Guelph permeameter equations. Sensitivity analyses indicate that for the Richards analysis the correct choice of C value curve from the three-member family of curves is least critical for the hydraulic parameter of primary importance in describing the flow. When field-saturated flow is the dominant component of flow out of the well, the error induced in Kfs, by incorrect choice of C is on the order of ≤30% for the flow conditions analyzed. When capillarity is the dominant component of flow out of the well, the error induced in φm by incorrect choice of C is on the order of ≤10% for the flow conditions analyzed. The sensitivity analyses also confirm that the Laplace analysis is reasonably accurate when the field-saturated component of flow dominates, and that the Gardner analysis is reasonably accurate when the capillarity component of flow dominates.

A Method for Simultaneous In Situ Measurement in the Vadose Zone of Field‐Saturated Hydraulic Conductivity, Sorptivity and the Conductivity‐Pressure Head Relationship

AbstractThe Guelph Permeameter (GP) method for simultaneous, in situ measurement in the vadose zone of field‐saturated hydraulic conductivity (KfS), sorptivity (S) and the conductivity‐pressure head relationship [K(Ψ)] is described and discussed.The method involves measuring the steady‐state liquid recharge, Q, necessary to maintain a constant depth of water, H, in an uncased, cylindrical well of radius, a, finished above the water table. An “in‐hole” Mariotte bottle device is used to maintain H and to measure Q.Step‐by‐step procedures with example calculations are given for obtaining KfS, S and K(Ψ). Techniques for assessing the results are also given.Although detailed field verification of the GP method is still incomplete, the studies conducted so far are quite encouraging.Theoretical and practical advantages afforded by the GP method make it a desirable and cost‐effective means for in situ measurement of Kfs, S and K(Ψ), which are three of the most important parameters governing the flow of water and other wetting liquids in the vadose zone.

IN SITU MEASUREMENT OF FIELD-SATURATED HYDRAULIC CONDUCTIVITY, SORPTIVITY, AND THE α-PARAMETER USING THE GUELPH PERMEAMETER

The Guelph permeameter method is used in 0.02-m- and 0.03-m-radius wells to measure in situ the field-saturated hydraulic conductivity (K10) and matric flux potential (φm) of a heterogeneous, anisotropic, structured loam soil. The K10, estimates, obtained using both Richards (GP-R) and Laplace (GP-L