A sensitivity analysis of the Jackson method of predicting unsaturated hydraulic conductivity

Soil Research ◽  
1992 ◽  
Vol 30 (3) ◽  
pp. 285 ◽  
Author(s):  
HP Cresswell
Keyword(s):  
Sensitivity Analysis ◽  
Hydraulic Conductivity ◽  
Water Content ◽  
Volumetric Water Content ◽  
Small Range ◽  
Matric Potential ◽  
Unsaturated Hydraulic Conductivity ◽  
Moisture Characteristic ◽  
Intended Use ◽  
Water Contents

An assessment is made of the sensitivity of the unsaturated hydraulic conductivity predictions from the Jackson model to changes in the measured moisture characteristic and matching factor hydraulic conductivity inputs. The model is shown to be sensitive to the volumetric water content corresponding to the matching factor hydraulic conductivity as well as to the 0 to -1.0 kPa matric potential section of the moisture characteristic input. The significance of this sensitivity is dependent on intended use of the data. Where accurate conductivity prediction is required over a small range of water contents near saturation, the moisture characteristic input used with this model should include measured points between 0 and 1.0 kPa matric potential.

Hyphal colonization of Rhizophagus irregularis increases unsaturated hydraulic conductivity of a loamy sand distant from roots

2021 ◽  
Author(s):  
Michael Bitterlich ◽  
Richard Pauwels
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Hydraulic Properties ◽  
Volumetric Water Content ◽  
Rhizophagus Irregularis ◽  
Loamy Sand ◽  
Soil Hydraulic Properties ◽  
Unsaturated Hydraulic Conductivity ◽  
Soil Hydraulic ◽  
Root Exclusion

<p>Hydraulic properties of mycorrhizal soils have rarely been reported and difficulties in directly assigning potential effects to hyphae of arbuscular mycorrhizal fungi (AMF) arise from other consequences of AMF being present, i.e. their influence on growth and water consumption rates of their host plants that both also influence soil hydraulic properties.</p><p>We assumed that the typical nylon meshes used for root-exclusion experiments in mycorrhizal research can provide a dynamic hydraulic barrier. It is expected that the uniform pore size of the rigid meshes causes a sudden hydraulic decoupling of the enmeshed inner volume from the surrounding soil as soon as the mesh pores become air-filled. Growing plants below the soil moisture threshold for hydraulic decoupling would minimize plant-size effects on root-exclusion compartments and allow for a more direct assignment of hyphal presence to modulations in soil hydraulic properties.</p><p>We carried out water retention and hydraulic conductivity measurements with two tensiometers introduced in two different heights in a cylindrical compartment (250 cm³) containing a loamy sand, either with or without the introduction of a 20 µm nylon mesh equidistantly between the tensiometers. Introduction of a mesh reduced hydraulic conductivity across the soil volumes by two orders of magnitude from 471 to 6 µm d<sup>-1</sup> at 20% volumetric water content.</p><p>We grew maize plants inoculated or not with Rhizophagus irregularis in the same soil in pots that contained root-exclusion compartments while maintaining 20% volumetric water content. When hyphae were present in the compartments, water potential and unsaturated hydraulic conductivity increased for a given water content compared to compartments free of hyphae. These differences increased with progressive soil drying.</p><p>We conclude that water extractability from soils distant to roots can be facilitated under dry conditions when AMF hyphae are present.</p><p> </p>

scholarly journals Determining the Unsaturated Hydraulic Conductivity of Remoulded Loess with Filter Paper Method and Soil Column Seepage Test

2021 ◽  
Author(s):  
Wenwu Chen ◽  
Quanquan Jia ◽  
Peng Liu ◽  
Yanmei Tong
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Filter Paper ◽  
Characteristic Curve ◽  
Soil Column ◽  
Volumetric Water Content ◽  
Experimental Results ◽  
Paper Test ◽  
Unsaturated Hydraulic Conductivity ◽  
The One

Abstract Loess is very widely distributed, and the unsaturated hydraulic conductivity of loess is related to many engineering issues. In order to determine the unsaturated hydraulic conductivity of remolded loess more conveniently and at a lower cost, filter paper test and soil column seepage test were carried out. The results indicate that in the one-dimensional soil column seepage process, the unsaturated hydraulic conductivity of loess increases with the increase of the volumetric water content, and as the seepage time continues, the unsaturated hydraulic conductivity of loess at different depths gradually becomes uniform. The changes in the microstructure indicate that the collapsible settlement will occur during the seepage process, which will reduce the unsaturated hydraulic conductivity of the underlying loess to a certain extent. Compared with the experimental results, the soil hydraulic conductivity curve (SHCC) obtained by the van Genuchten-Mualem model (VG-M model) underestimates the magnitude of unsaturated hydraulic conductivity in the part with a low volumetric water content (< 20%). and the Childs ༆ Collis-George model (CCG model) has more consistent results with the experimental results because it is based on more segments of the soil-water characteristic curve (SWCC).

Measuring unsaturated hydraulic conductivity (K(ψm)) of the F and H soil organic layers at small matric potential (ψm)

2011 ◽  
Vol 91 (6) ◽  
pp. 965-968
Author(s):  
B. Wilske ◽  
E. A. Johnson
Keyword(s):  
Hydraulic Conductivity ◽  
Large Data ◽  
Cold Climate ◽  
Organic Layer ◽  
Matric Potential ◽  
Large Variability ◽  
Organic Layers ◽  
Soil Organic Layer ◽  
Unsaturated Hydraulic Conductivity ◽  
Constant Head

Wilske, B. and Johnson, E. A. 2011. Measuring unsaturated hydraulic conductivity (K(ψm)) of the F and H soil organic layers at small matric potential (ψm). Can. J. Soil Sci. 91: 965–968. K(ψm) of the soil organic layers is a key parameter to assess water redistribution in cold-climate forests. This study tested the twin suction disc apparatus (TSD) as a new method to measure K(ψm) of the F and H layers directly. We compared the results to two studies. One represents a large data base, the other used similar sample locations; but both derived K(ψm) from combining two methods, i.e., pressure plate measurements combined with the instantaneous profile technique or the constant head approach. The TSD data are consistent with previous results considering the large variability in K(ψm) from the combined methods. This suggests that the TSD method represents an alternative to determine K(ψm) of the soil organic layer.

Measurement of unsaturated hydraulic conductivity using tension and drip infiltrometers

Soil Research ◽  
2001 ◽  
Vol 39 (4) ◽  
pp. 823 ◽  
Author(s):  
N. J. McKenzie ◽  
H. P. Cresswell ◽  
H. Rath ◽  
D. Jacquier
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Cores ◽  
Matric Potential ◽  
Constant Flux ◽  
Tension Infiltrometer ◽  
Unsaturated Hydraulic Conductivity ◽  
Wide Range ◽  
Constant Potential ◽  
Potential Methods ◽  
Large Decline

We investigated differences between constant flux and constant potential methods for determining unsaturated hydraulic conductivity in the laboratory. A cheap and robust method was required. The constant flux drip infiltrometer has been used with large intact cores on a wide range of Australian soils. However, the method can be simplified by replacing the drip infiltrometer with a constant potential tension infiltrometer (disc permeameter). We conducted a series of measurements using 9 soil cores to determine whether the measured hydraulic conductivity differed with each method at matric potentials of –10, –20, or –50 mm. Hysteresis effects were also examined because tension infiltrometer measurements are usually made on the adsorption curve of the hydraulic conductivity and matric potential [K(Ψ)] relationship. Drip infiltrometer measurements are often made on the desorption curve. The reproducibility of measurements on a single core was also examined. A large decline in K(Ψ ) was observed on some cores with repeated measurements and this effect was larger than differences between the methods. In the absence of evidence of slaking or dispersion, the suspected cause of the decline in K(Ψ) was clogging of pores from accumulation of microbial biomass and their by-products. The results support the view that K(Ψ) in some soils is a dynamic property. There were consistent differences between the constant flux and constant potential methods on those soil cores not exhibiting a large decline in K(Ψ) (the others were omitted from the method comparison). The tension infiltrometer method indicated greater hydraulic conductivity in soils with well-developed macrostructure when matric potential was greater than –50 mm. Hysteresis effects were significant with both methods and measurements made on desorption and adsorption curves are not considered comparable. Overall, we concluded that the tension infiltrometer method was more suited than the drip method for routine processing of large numbers of samples at low cost.

Soil structure, soil hydraulic properties and the soil water balance

Soil Research ◽  
1992 ◽  
Vol 30 (3) ◽  
pp. 265 ◽  
Author(s):  
HP Cresswell ◽  
DE Smiles ◽  
J Williams
Keyword(s):  
Hydraulic Conductivity ◽  
Water Balance ◽  
Soil Water ◽  
Soil Structure ◽  
Hydraulic Properties ◽  
Rainfall Regime ◽  
Soil Hydraulic Properties ◽  
Matric Potential ◽  
Moisture Characteristic

We review the influence of soil structural change on the fundamental soil hydraulic properties (unsaturated hydraulic conductivity and the soil moisture characteristic) and utilize deterministic modelling to assess subsequent effects on the soil water balance. Soil structure is reflected in the 0 to -100 kPa matric potential section of the soil moisture characteristic with marked changes often occurring in light to medium textured soils' (sands, sandy-loam, loams and clay-loams). The effect of long-term tillage on soil structure may decrease hydraulic conductivity within this matric potential range. The 'SWIM' (Soil Water Infiltration and Movement) simulation model was used to illustrate the effects of long-term conventional tillage and direct drilling systems on the water balance. The effects of plough pans, surface crusts and decreasing surface detention were also investigated. Significant structural deterioration, as evidenced by substantially reduced hydraulic conductivity, is necessary before significant runoff is generated in the low intensity rainfall regime of the Southern Tablelands (6 min rainfall intensity <45 mm h-1). A 10 mm thick plough pan (at a depth of 100 mm) in the A-horizon of a long-term conventionally tilled soil required a saturated hydraulic conductivity (K,) of less than 2.5 mm h-1 before runoff exceeded 10% of incident rainfall in this rainfall regime. Similarly, a crust K, of less than 2.5 mm h-1 was necessary before runoff exceeded 10% of incident rainfall (provided that surface detention was 2 or more). As the crust K, approached the rainfall rate, small decreases in Ks resulted in large increases in runoff. An increase in surface detention of 1 to 3 mm resulted in a large reduction in runoff where crust K, was less than 2-5 mm h-1. Deterministic simulation models incorporating well established physical laws are effective tools in the study of soil structural effects on the field water regime. Their application, however, is constrained by insufficient knowledge of the fundamental hydraulic properties of Australian soils and how they are changing in response to our land management.

Impact of molding water content on hydraulic conductivity of compacted sand-bentonite

1992 ◽  
Vol 29 (2) ◽  
pp. 253-262 ◽  
Author(s):  
Moir D. Haug ◽  
Lionel C. Wong
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Test Program ◽  
Design Factor ◽  
Ottawa Sand ◽  
Critical Design ◽  
Hydraulic Gradients ◽  
To Come ◽  
The Relationship ◽  
Water Contents

The relationship between molding water content and hydraulic conductivity of a compacted sand-bentonite mixture was examined in a laboratory test program. This program involved triaxial permeability testing of nine specimens of 8% bentonite and Ottawa sand, compacted at standard Proctor density using molding water contents ranging from6 to 19%. The permeability tests were conducted using hydraulic gradients ranging from 19 to 40. The specimens were subjected to an average effective stress during testing of 21 kPa. The tests were conducted using continuous back pressure saturation. Each test was run for a minimum of 40 000 min (approximately 28 days) to enable the flow in and out of the specimen to come to equilibrium with respect to each other. The hydraulic conductivity decreased from 6.5 × 10−9 cm/s for a molding water content of 5.9% to 1.4 × 10−9 cm/s for a molding water content of 15.8%. However, although the hydraulic conductivity was related to the molding water content, the variation in hydraulic conductivity was relatively small. Therefore, the low values reported for all hydraulic conductivity tests suggest that molding water content is not a critical design factor in the construction of a low-permeability sand-bentonite liner. Key words : molding water content, bentonite, liners, hydraulic conductivity, triaxial permeability testing, covers, sand.

Estimation of hydraulic conductivity of unsaturated soils using a geotechnical centrifuge

2002 ◽  
Vol 39 (3) ◽  
pp. 684-694 ◽  
Author(s):  
D N Singh ◽  
Sneha J Kuriyan
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Sample ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Hydraulic Conductivity ◽  
Centrifuge Testing ◽  
Geotechnical Centrifuge ◽  
Silty Soil ◽  
Unsaturated Hydraulic Conductivity

A saturated silty soil sample is centrifuged in a geotechnical centrifuge to create an unsaturated state. The change in water content of the soil sample is recorded at different points along the length of the sample to obtain the water-content profile, which is then used to obtain the unsaturated hydraulic conductivity of the soil sample. These hydraulic conductivity values are compared with those obtained and reported by previous researchers by conducting accelerated falling-head tests on this soil sample in a centrifuge. The study demonstrates the use of centrifugation techniques to obtain hydraulic conductivities of unsaturated soils.Key words: silty soil, saturated soil, unsaturated soil, hydraulic conductivity, centrifuge testing.

Tree/pasture interactions at a range of tree densities in an agroforestry experiment. III. Water uptake in relation to soil hydraulic conductivity and rooting patterns

1990 ◽  
Vol 41 (4) ◽  
pp. 709 ◽  
Author(s):  
J Eastham ◽  
CW Rose ◽  
DM Cameron ◽  
SJ Rance ◽  
T Talsma ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Water ◽  
Root Length ◽  
Tree Density ◽  
Soil Hydraulic Conductivity ◽  
Tree Transpiration ◽  
Rooting Patterns ◽  
Soil Hydraulic ◽  
Water Contents

Eucalyptus grandis was planted in a Nelder fan design in November 1983 into a previously established pasture dominated by Setaria sphacelata cv. Kazungula, at the CSIRO Sanford Pasture Research Station, Queensland, Australia. Nine concentric rings of 18 trees were planted at radii of 4.4-61.6 m, giving a range of tree densities which decreased from 3580 to 42 stems/ha. Tree transpiration was studied at three tree densities (2150, 304 and 82 stems/ha, representing high, medium and low densities) over a 'drought' period of approximately 1 yr (Nov. 1985-Sep. 1986) and related to rooting patterns and soil hydraulic properties. Over the range of soil water contents studied, the ratio of tree transpiration rate to equilibrium evaporation rate (T/Esub(eq)) decreased linearly with decreasing mean soil water content at each tree density. To investigate the effects of soil hydraulic conductivity and root length density on the total transpirational flux, overall soil conductances (Ksub(s)) were calculated, with soil conductance in each horizon weighted according to the length of root in that horizon. At each tree density, decreases in the ratio T/Esub(eq) were related to decreases in ln Ksub(s) measured at 1.2 m from the stem. A more rapid decrease in T/Esub(eq) with decrease in water content observed at the low tree density was attributed to a greater decrease in Ksub(s) as mean water contents decreased. The greater decrease in Ksub(s) at low tree densities was associated with a larger proportion of water extracted and a higher proportion of total root length in surface soil horizons, which showed a greater decrease in hydraulic conductivity than subsoil horizons for the same decrease in water content.

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