scholarly journals Modified tension infiltrometer and its use to determine the unsaturated hydraulic conductivity of upper vadose zone

1998 ◽  
Vol 18 ◽  
Author(s):  
Golam Shabbir Sattar
Keyword(s):  
Steady State ◽  
Hydraulic Conductivity ◽  
Vadose Zone ◽  
Water Pressure ◽  
Fundamental Property ◽  
Pressure Head ◽  
Unknown Parameters ◽  
Steady State Condition ◽  
Tension Infiltrometer ◽  
Unsaturated Hydraulic Conductivity

A modification of the CSIRO type tension infiltrometer was designed (designated UNCEL type) and tested. This infiltrometer is considerably cheaper, but more versatile, than any other infiltrometer reported so far. The modified infiltrometer was used in a reconstructed vadose zone to measure the unsaturated hydraulic conductivity and effect of compaction associated with the upper vadose zone. Hydraulic conductivity, a function of matric potential, is a fundamental property for water entry into the soil as well as in the upper vadose zone. Tension infiltrometer technique for determining unsaturated hydraulic conductivity, which is also a function of soil water pressure head, was compared with the existing techniques. The analysis of data from tension infiltrometer is based mainly on flow rate at steady-state condition. The steady-state measurement also enables to determine unknown parameters on the basis of at least two negative heads at the same location. This modified infiltrometer imposes pressure potentials at soil surface from 0.01 to 0.15 m of water, as a result macropores with an air entry value of less than applied tension are excluded. This is practically useful when investigating the influence of structure and compaction of upper vadose zone. Measurement of infiltration at various negative pressure head, with a single disc diameter allowed sensitive measurement of hydraulic properties of upper vadose zone with minimal surface disturbance. The newly designed tension infiltrometer and adopted schemes of calculation enable to determine unsaturated hydraulic conductivity of upper vadose zone with relevance to structural effects more accurately.

scholarly journals Simultaneous Determination of Water Retention Curve and Unsaturated Hydraulic Conductivity of Substrates Using a Steady-state Laboratory Method

HortScience ◽  
2010 ◽  
Vol 45 (7) ◽  
pp. 1106-1112 ◽  
Author(s):  
Paraskevi A. Londra
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Hydraulic Conductivity ◽  
Water Retention ◽  
Water Pressure ◽  
Pressure Head ◽  
Laboratory Method ◽  
Water Retention Curve ◽  
Retention Curve ◽  
Unsaturated Hydraulic Conductivity

For effective irrigation and fertilization management, the knowledge of substrate hydraulic properties is essential. In this study, a steady-state laboratory method was used to determine simultaneously the water retention curve, θ(h), and unsaturated hydraulic conductivity as a function of volumetric water content, K(θ), and water pressure head, K(h), of five substrates used widely in horticulture. The substrates examined were pure peat, 75/25 peat/perlite, 50/50 peat/perlite, 50/50 coir/perlite, and pure perlite. The experimental retention curve results showed that in the case of peat and its mixtures with perlite, there is a hysteresis between drying and wetting branches of the retention curve. Whereas in the case of coir/perlite and perlite, the phenomenon of hysteresis was less pronounced. The increase of perlite proportion in the peat/perlite mixtures led to a decrease of total porosity and water-holding capacity and an increase of air space. Study of the K(θ) and K(h) experimental data showed that the hysteresis phenomenon of K(θ) was negligible compared with the K(h) data for all substrates examined. Within a narrow range of water pressure head (0 to –70 cm H2O) that occurs between two successive irrigations, a sharp decrease of the unsaturated hydraulic conductivity was observed. The comparison of the K(θ) experimental data between the peat-based substrate mixtures and the coir-based substrate mixture showed that for water contents lower than 0.40 m3·m−3, the hydraulic conductivity of the 50/50 coir/perlite mixture was greater. The comparison between experimental water retention curves and predictions using Brooks-Corey and van Genuchten models showed a high correlation (0.992 ≤ R2 ≤ 1) for both models for all substrates examined. On the other hand, in the case of unsaturated hydraulic conductivity, the comparison showed a relatively good correlation (0.951 ≤ R2 ≤ 0.981) for the van Genuchten-Mualem model for all substrates used except perlite and a significant deviation (0.436 ≤ R2 ≤ 0.872) for the Brooks-Corey model for all substrates used.

scholarly journals Examining the effect of pore size distribution and shape on flow through unsaturated peat using computed tomography

2009 ◽  
Vol 13 (10) ◽  
pp. 1993-2002 ◽  
Author(s):  
F. Rezanezhad ◽  
W. L. Quinton ◽  
J. S. Price ◽  
D. Elrick ◽  
T. R. Elliot ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Hydraulic Conductivity ◽  
Pore Structure ◽  
Pore Size ◽  
Soil Water ◽  
Water Pressure ◽  
Peat Soil ◽  
Pressure Head ◽  
Peat Soils ◽  
Unsaturated Hydraulic Conductivity

Abstract. The hydraulic conductivity of unsaturated peat soil is controlled by the air-filled porosity, pore size and geometric distribution as well as other physical properties of peat materials. This study investigates how the size and shape of pores affects the flow of water through peat soils. In this study we used X-ray Computed Tomography (CT), at 45 μm resolution under 5 specific soil-water pressure head levels to provide 3-D, high-resolution images that were used to detect the inner pore structure of peat samples under a changing water regime. Pore structure and configuration were found to be irregular, which affected the rate of water transmission through peat soils. The 3-D analysis suggested that pore distribution is dominated by a single large pore-space. At low pressure head, this single large air-filled pore imparted a more effective flowpath compared to smaller pores. Smaller pores were disconnected and the flowpath was more tortuous than in the single large air-filled pore, and their contribution to flow was negligible when the single large pore was active. We quantify the pore structure of peat soil that affects the hydraulic conductivity in the unsaturated condition, and demonstrate the validity of our estimation of peat unsaturated hydraulic conductivity by making a comparison with a standard permeameter-based method. Estimates of unsaturated hydraulic conductivities were made for the purpose of testing the sensitivity of pore shape and geometry parameters on the hydraulic properties of peats and how to evaluate the structure of the peat and its affects on parameterization. We also studied the ability to quantify these factors for different soil moisture contents in order to define how the factors controlling the shape coefficient vary with changes in soil water pressure head. The relation between measured and estimated unsaturated hydraulic conductivity at various heads shows that rapid initial drainage, that changes the air-filled pore properties, creates a sharp decline in hydraulic conductivity. This is because the large pores readily lose water, the peat rapidly becomes less conductive and the flow path among pores, more tortuous.

Finite formulation for the computation of sorptivity

2020 ◽  
Author(s):  
Pierre-Emmanuel Peyneau ◽  
Laurent Lassabatere ◽  
Joseph Pollacco ◽  
Jesús Fernández-Gálvez ◽  
Borja Latorre ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Water Retention ◽  
Water Pressure ◽  
Pressure Head ◽  
Concentration Function ◽  
Point Of View ◽  
Water Infiltration ◽  
Unsaturated Hydraulic Conductivity ◽  
Flux Concentration

<p>Soil sorptivity is one of the key hydraulic parameters for modelling water infiltration into soil. It quantifies the capacity of a soil to infiltrate water by capillarity. Several formulations, based on various models, have been proposed to compute it from the water retention and the unsaturated hydraulic conductivity functions. All these formulations use the integration of the product of either the hydraulic conductivity or diffusivity function with the flux concentration function. The integration can be performed either over an interval of water pressure head or water content, yielding two equal values. However, the expression of the integral as a function of water pressure head may involve a huge or even infinite interval, which can be numerically difficult to handle. In opposite, the expression of the integral as a function of water content involves the integration of a diverging function (diffusivity) over a large interval, which is also troublesome from a numerical point of view. In this paper, we provide a new expression for sorptivity by cutting the integral in two parts, in order to involve only the integration of a finite function over a finite interval. The dependency of the integral on the flux concentration function is also investigated.</p>

scholarly journals Examining the effect of pore size distribution and shape on flow through unsaturated peat using 3-D computed tomography

2009 ◽  
Vol 6 (3) ◽  
pp. 3835-3862 ◽  
Author(s):  
F. Rezanezhad ◽  
W. L. Quinton ◽  
J. S. Price ◽  
D. Elrick ◽  
T. R. Elliot ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Hydraulic Conductivity ◽  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Water Pressure ◽  
Pressure Head ◽  
Peat Soils ◽  
Unsaturated Hydraulic Conductivity

Abstract. The hydraulic conductivity of unsaturated peat soils is controlled by the peat structure which affects the air-filled porosity, pore size distribution and shape. This study investigates how the size and shape of pores affects the flow of water through peat soils. In this study we used X-ray Computed Tomography (CT), at 45 µm resolution under 5 specific soil-water pressure head levels to provide 3-D, high-resolution images that were used to detect the inner pore structure of peat samples under a changing water regime. Pore structure and configuration were found to be irregular, which affected the rate of water transmission through peat soils. The 3-D analysis suggested that pore distribution is dominated by a single large pore-space. At low pressure head, this single large air-filled pore imparted a more effective flowpath compared to smaller pores. Smaller pores were disconnected and the flowpath was more tortuous than in the single large air-filled pore, and their contribution to flow was negligible when the single large pore was active. We quantify the pore structure of peat soil that affects the hydraulic conductivity in the unsaturated condition, and demonstrate the validity of our estimation of peat unsaturated hydraulic conductivity by making a comparison with a standard permeameter-based method. Estimates of unsaturated hydraulic conductivities were made for the purpose of testing the sensitivity of pore shape and geometry parameters on the hydraulic properties of peats and how to evaluate the structure of the peat and its affects on parameterization. We also studied the ability to quantify these factors for different soil moisture contents in order to define how the factors controlling the shape coefficient vary with changes in soil water pressure head. The relation between measured and estimated unsaturated hydraulic conductivity at various heads shows that rapid initial drainage, that changes the air-filled pore properties, creates a sharp decline in hydraulic conductivity. This is because the large pores readily lose water, the peat rapidly becomes less conductive and the flow path among pores, more tortuous.

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.

scholarly journals Individual Cylinder Air-Fuel Ratio Estimation for a Gasoline Engine with Electromagnetic Valve Train

2018 ◽  
Vol 202 ◽  
pp. 02011
Author(s):  
Yaxuan Xu ◽  
Siqin Chang
Keyword(s):  
Steady State ◽  
Gasoline Engine ◽  
Estimation Algorithm ◽  
Valve Train ◽  
Unknown Parameters ◽  
Steady State Condition ◽  
Electromagnetic Valve ◽  
Fuel Ratio ◽  
De Algorithm ◽  
The Individual

For the multi cylinder gasoline engine, the consistency of each cylinder is an important index to affect the emission and the power. In this paper, in order to reduce the air-fuel ratio (A/F) maldistribution of the engine based on the electromagnetic valve train (EMVT), an individual cylinder A/F estimation algorithm is proposed for the individual cylinder A/F control. Based on the analysis of the hybrid and transfer models of the exhaust of each cylinder in steady state, an individual A/F observer is established by using Kalman filter algorithm. Then the unknown parameters in the observer are identified by the differential evolution(DE) algorithm. Only a single wide area exhaust oxygen(UEGO) sensor is needed to identify the unknown parameters and estimate the A/F of each cylinder. The combined simulation of GT-Power and Simulink validates the effectiveness of the proposed estimation approach. The results show that the proposed method can provide good estimation results under steady-state condition.

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