scholarly journals Characterization of Preferential Flow in Spatially Variable Unsaturated Field Soils

2001 ◽  
Author(s):  
David Russo ◽  
William A. Jury
Keyword(s):  
Preferential Flow ◽  
Water Saturation ◽  
Ammonium Carbonate ◽  
Lagrangian Description ◽  
Flow Conditions ◽  
Unstable Flow ◽  
Flow And Transport ◽  
Spatial Correlation Structure ◽  
Field Soils ◽  
Clay Lenses

Preferential flow appears to be the rule rather than the exception in field soils and should be considered in the quantitative description of solute transport in the unsaturated zone of heterogeneous formations on the field scale. This study focused on both experimental monitoring and computer simulations to identify important features of preferential flow in the natural environment. The specific objectives of this research were: (1) To conduct dye tracing and multiple tracer experiments on undisturbed field plots to reveal information about the flow velocity, spatial prevalence, and time evolution of a preferential flow event; (2) To conduct numerical experiments to determine (i) whether preferential flow observations are consistent with the Richards flow equation; and (ii) whether volume averaging over a domain experiencing preferential flow is possible; (3) To develop a stochastic or a transfer function model that incorporates preferential flow. Regarding our field work, we succeeded to develop a new method for detecting flow patterns faithfully representing the movement of water flow paths in structured and non-structured soils. The method which is based on application of ammonium carbonate was tested in a laboratory study. Its use to detect preferential flow was also illustrated in a field experiment. It was shown that ammonium carbonate is a more conservative tracer of the water front than the popular Brilliant Blue. In our detailed field experiments we also succeeded to document the occurrence of preferential flow during soil water redistribution following the cessation of precipitation in several structureless field soils. Symptoms of the unstable flow observed included vertical fingers 20 - 60 cm wide, isolated patches, and highly concentrated areas of the tracers in the transmission zone. Soil moisture and tracer measurements revealed that the redistribution flow became fingered following a reversal of matric potential gradient within the wetted area. Regarding our simulation work, we succeeded to develop, implement and test a finite- difference, numerical scheme for solving the equations governing flow and transport in three-dimensional, heterogeneous, bimodal, flow domains with highly contrasting soil materials. Results of our simulations demonstrated that under steady-state flow conditions, the embedded clay lenses (with very low conductivity) in bimodal formations may induce preferential flow, and, consequently, may enhance considerably both the solute spreading and the skewing of the solute breakthrough curves. On the other hand, under transient flow conditions associated with substantial redistribution periods with diminishing water saturation, the effect of the embedded clay lenses on the flow and the transport might diminish substantially. Regarding our stochastic modeling effort, we succeeded to develop a theoretical framework for flow and transport in bimodal, heterogeneous, unsaturated formations, based on a stochastic continuum presentation of the flow and a general Lagrangian description of the transport. Results of our analysis show that, generally, a bimodal distribution of the formation properties, characterized by a relatively complex spatial correlation structure, contributes to the variability in water velocity and, consequently, may considerably enhance solute spreading. This applies especially in formations in which: (i) the correlation length scales and the variances of the soil properties associated with the embedded soil are much larger than those of the background soil; (ii) the contrast between mean properties of the two subdomains is large; (iii) mean water saturation is relatively small; and (iv) the volume fraction of the flow domain occupied by the embedded soil is relatively large.

scholarly journals Preferential Flow Systems Amended with Biogeochemical Components: Imaging of a Two-Dimensional Study

2017 ◽  
Author(s):  
Ashley R. Pales ◽  
Biting Li ◽  
Heather M. Clifford ◽  
Shyla Kupis ◽  
Nimisha Edayilam ◽  
...  
Keyword(s):  
Porous Media ◽  
Preferential Flow ◽  
Light Transmission ◽  
Water Saturation ◽  
Silica Sand ◽  
Two Dimensional ◽  
Unstable Flow ◽  
Transmission Method ◽  
Soil Component ◽  
Plant Exudates

Abstract. The vadose zone is a highly interactive heterogeneous system through which water enters into the subsurface system by infiltration. This paper details the effects of simulated plant exudate and soil component solutions upon unstable flow patterns in a porous media (ASTM silica sand; US Silica, Ottawa, IL, USA) through the use of two-dimensional (2D) tank light transmission method (LTM). The contact angle and surface tension of two simulated plant exudate solutions (i.e. oxalate, and citrate) and two soil component solutions (i.e. tannic acid, and Suwannee River Natural Organic Matter) were analyzed to determine the liquid-gas and liquid-solid interface characteristics of each. To determine if the unstable flow formations were dependent on the type and concentration of the simulated plant exudates and soil components, the analysis of the effects of the simulated plant exudate and soil component solutions were compared to a control rainwater solution. The differences in the fingering flow were quantified with the finger geometries, the velocity of finger propagation, the vertical and horizontal water saturation profiles, and the water saturation at the fingertips. Significant differences in the interface processes indicated a decrease between the control and the plant exudate and soil component solutions tested; specifically, the control at 64.5 θ and 75.75 Nm/m, to the low concentration of citrate at 52.6 θ and 70.8 Nm/m. The changes in finger geometries and velocity of propagation between the control solution and the simulated plant exudate and soil component solutions further demonstrate that the plant exudates increased the wettability and mobility of the solutions during the infiltration process in unsaturated porous media.

Visualizing Preferential Flow Paths using Ammonium Carbonate and a pH Indicator

2002 ◽  
Vol 66 (2) ◽  
pp. 347 ◽  
Author(s):  
Zhi Wang ◽  
Jianhang Lu ◽  
Laosheng Wu ◽  
Thomas Harter ◽  
William A. Jury
Keyword(s):  
Preferential Flow ◽  
Ammonium Carbonate ◽  
Ph Indicator ◽  
Flow Paths ◽  
Preferential Flow Paths

Equation for Describing Solute Transport in Field Soils with Preferential Flow Paths

2005 ◽  
Vol 69 (2) ◽  
pp. 291-300 ◽  
Author(s):  
Young-Jin Kim ◽  
Christophe J. G. Darnault ◽  
Nathan O. Bailey ◽  
J.-Yves Parlange ◽  
Tammo S. Steenhuis
Keyword(s):  
Solute Transport ◽  
Preferential Flow ◽  
Flow Paths ◽  
Preferential Flow Paths ◽  
Field Soils

Visualizing Preferential Flow Paths using Ammonium Carbonate and a pH Indicator

2002 ◽  
Vol 66 (2) ◽  
pp. 347-351 ◽  
Author(s):  
Zhi Wang ◽  
Jianhang Lu ◽  
Laosheng Wu ◽  
Thomas Harter ◽  
William A. Jury
Keyword(s):  
Preferential Flow ◽  
Ammonium Carbonate ◽  
Ph Indicator ◽  
Flow Paths ◽  
Preferential Flow Paths

Preferential Flow and Transport of Cryptosporidium parvum Oocysts through the Vadose Zone: Experiments and Modeling

2004 ◽  
Vol 3 (2) ◽  
pp. 736-736 ◽  
Author(s):  
Christophe J.G. Darnault ◽  
Tammo S. Steenhuis ◽  
Patricia Garnier ◽  
Young-Jin Kim ◽  
Michael Jenkins ◽  
...  
Keyword(s):  
Cryptosporidium Parvum ◽  
Vadose Zone ◽  
Preferential Flow ◽  
Flow And Transport ◽  
Cryptosporidium Parvum Oocysts

Surface fractal characteristics of preferential flow patterns in field soils: evaluation and effect of image processing

Geoderma ◽  
1999 ◽  
Vol 88 (3-4) ◽  
pp. 109-136 ◽  
Author(s):  
Susumu Ogawa ◽  
Philippe Baveye ◽  
Charles W. Boast ◽  
Jean-Yves Parlange ◽  
Tammo Steenhuis
Keyword(s):  
Image Processing ◽  
Preferential Flow ◽  
Flow Patterns ◽  
Surface Fractal ◽  
Field Soils ◽  
Fractal Characteristics

scholarly journals Preferential flow systems amended with biogeochemical components: imaging of a two-dimensional study

2018 ◽  
Vol 22 (4) ◽  
pp. 2487-2509 ◽  
Author(s):  
Ashley R. Pales ◽  
Biting Li ◽  
Heather M. Clifford ◽  
Shyla Kupis ◽  
Nimisha Edayilam ◽  
...  
Keyword(s):  
Light Transmission ◽  
Water Saturation ◽  
Solution Concentration ◽  
Unstable Flow ◽  
Transmission Method ◽  
Control Solution ◽  
Soil Component ◽  
Finger Width ◽  
Plant Exudates ◽  
Soil Components

Abstract. The vadose zone is a highly interactive heterogeneous system through which water enters the subsurface system by infiltration. This paper details the effects of simulated plant exudate and soil component solutions upon unstable flow patterns in a porous medium (ASTM silica sand; US Silica, Ottawa, IL, USA) through the use of two-dimensional tank light transmission method (LTM). The contact angle (θ) and surface tension (γ) of two simulated plant exudate solutions (i.e., oxalate and citrate) and two soil component solutions (i.e., tannic acid and Suwannee River natural organic matter, SRNOM) were analyzed to determine the liquid–gas and liquid–solid interface characteristics of each. To determine if the unstable flow formations were dependent on the type and concentration of the simulated plant exudates and soil components, the analysis of the effects of the simulated plant exudate and soil component solutions were compared to a control solution (Hoagland nutrient solution with 0.01 M NaCl). Fingering flow patterns, vertical and horizontal water saturation profiles, water saturation at the fingertips, finger dimensions and velocity, and number of fingers were obtained using the light transmission method. Significant differences in the interface properties indicated a decrease between the control and the plant exudate and soil component solutions tested; specifically, the control (θ= 64.5∘ and γ= 75.75 mN m−1) samples exhibited a higher contact angle and surface tension than the low concentration of citrate (θ= 52.6∘ and γ= 70.8 mN m−1). Wetting front instability and fingering flow phenomena were reported in all infiltration experiments. The results showed that the plant exudates and soil components influenced the soil infiltration as differences in finger geometries, velocities, and water saturation profiles were detected when compared to the control. Among the tested solutions and concentrations of soil components, the largest finger width (10.19 cm) was generated by the lowest tannic acid solution concentration (0.1 mg L−1), and the lowest finger width (6.00 cm) was induced by the highest SRNOM concentration (10 mg L−1). Similarly, for the plant exudate solutions, the largest finger width (8.36 cm) was generated by the lowest oxalate solution concentration (0.1 mg L−1), and the lowest finger width (6.63 cm) was induced by the lowest citrate concentration (0.1 mg L−1). The control solution produced fingers with average width of 8.30 cm. Additionally, the wettability of the medium for the citrate, oxalate, and SRNOM solutions increased with an increase in concentration. Our research demonstrates that the plant exudates and soil components which are biochemical compounds produced and released in soil are capable of influencing the process of infiltration in soils. The results of this research also indicate that soil wettability, expressed as (cos θ)1∕2, should be included in the scaling of the finger dimension, i.e., finger width, when using the Miller and Miller (1956) scaling theory for the scaling of flow in porous media.

Transport of Nanoplastic under groundwater aquifer flow and transport conditions

2020 ◽  
Author(s):  
Sascha Müller ◽  
Tonci Balic-Zunic ◽  
Nicole R. Posth
Keyword(s):  
Preferential Flow ◽  
Particle Diameter ◽  
Steric Interaction ◽  
Colloidal Transport ◽  
Flow And Transport ◽  
Aquifer Material ◽  
Transport Behavior ◽  
Groundwater Aquifers ◽  
Groundwater Aquifer ◽  
Aquifer Flow

<p>In terrestrial environments soils are hypothesized sinks for plastic particles. Nonetheless, due to the existence of preferential flow paths as well as a variety of geochemical and microbiological processes, this sink may only be temporary. A vertical translocation from soils to groundwater aquifers eventually occurs along different pathways. In these conditions Nanoplastic transport characteristics are similar to colloidal transport behavior. Therby the magnitude of plastic transport is eventually governed by complex interplay between the particle with its surrounding media (particle-particle, particle-solvent, particle- porous media) masked by different hydro-geochemical and microbiological conditions. The physical entrapment of particles (straining) may be significant when the particle diameter exceeds 5% of the median grain size diameter. Below that size additional electrostatic, van der Waals or steric interaction become increasingly important.</p><p>We present a preliminary dataset on the interaction between Nano-sized Polystyrene (PS) with different surface coatings and a variety of common minerals occurring in groundwater aquifers under the presence of Natural Organic Matter (NOM). The reference aquifer material is based on the Danish subsurface structure of Quaternary and Miocene aquifer material, e.g. quartz, calcite and pyrite among others. In our study, batch scale interactions are up-scaled in column flow and transport experiments, simulating different groundwater aquifer flow conditions in the presence of selected minerals and NOM.</p><p>This aims to clarify transport behavior of plastic pollutant in the subsurface environment. Furthermore, it serves as guide in qualitatively assessing and quantifying the vulnerability of groundwater aquifers to Nanoplastic pollution.</p>

scholarly journals Numerical Simulation of the Influence of Taylor Vortex on the Apparent Viscosity Measurement of Semi-Solid Metallic Based On ANSYS Fluent

2022 ◽  
Vol 2152 (1) ◽  
pp. 012061
Author(s):  
Enjie Dong ◽  
Gan Li ◽  
Xiaogang Hu ◽  
Zhong Li ◽  
Juan Chen ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Apparent Viscosity ◽  
Viscosity Measurement ◽  
Taylor Vortex ◽  
Flow State ◽  
Flow Conditions ◽  
Unstable Flow ◽  
Concentric Cylinder ◽  
Ansys Fluent ◽  
Semi Solid

Abstract The apparent viscosity of semi-solid metallic slurry with a low solid fraction, which is one of the most essential parameters for representing the rheological behavior, is mainly measured by the concentric cylinder rotational approach. The principle of this method is based on the assumptions that the fluid is in an ideal laminar flow state and obey the Newton’s internal friction law. However, as the angular velocity ω increases, the fluid undergoes a transition from a stable laminar flow state to a Taylor vortex and turbulent flow state. These unstable flow conditions such as Taylor vortex and turbulence have a severe impact on the accuracy of apparent viscosity measurement. However, these unstable flow conditions are difficult to monitored and analyzed in real time through experimental methods. Computer numerical simulation technology provides the possibility and convenience for the visualization of the flow state of the semi-solid metallic slurry in the measurement system. In this work, ANSYS Fluent was used to simulate the apparent viscosity measurement process of semi-solid slurry, and the flow state transition process of the semi-solid slurry in the measurement system was successfully visualized and analyzed. In order to avoid the influence of Taylor vortex, combined with the measurement principle of the concentric cylinder rotational rheometer and Taylor’s study on flow stability, the empirical equation of limiting speed to avoid Taylor vortex in the process of Searle rheometer viscosity measurement is given.

scholarly journals A simple two layer model for simulation of adsorbing and nonadsorbing solute transport through field soils

2009 ◽  
Vol 6 (5) ◽  
pp. 5631-5664
Author(s):  
M. S. Akhtar ◽  
U. Mohrlok ◽  
D. Stüben
Keyword(s):  
Solute Transport ◽  
Goodness Of Fit ◽  
Preferential Flow ◽  
Sandy Loam ◽  
Flow Equation ◽  
Silty Clay ◽  
Macropore Flow ◽  
Flow Rates ◽  
Retardation Coefficient ◽  
Field Soils

Abstract. While rapid movement of solutes through structured soils constitutes the risk of groundwater contamination, simulation of solute transport in field soils is challenging. A modification in an existing preferential flow model was tested using replicated Chloride and Lithium leachings carried out at constant flow rates through four soils differing in grades and type of structure. Flow rates generated by +10 mm, −10 mm, −40 mm, and −100 mm water heads at the surface of 35 cm diameter 50 cm height field columns. Three well-structured silty clay soils under ponding had concurrent breakthrough of Chloride and Lithium within a few cm of drainage, and a delayed and reduced peak concentration of Lithium with decrease in flow rate controlled by the negative heads. Massive sandy loam soil columns had delayed but uniform breakthrough of the solutes over the flow rates. Macropore flow in well-structured silty clay/clay loam soils reduced retardation, R (1.5 to 4.5) and effective porosity, θe (0.05 to 0.15), and increased macropore velocity, vm (20 to 30 cm cm−1 drainage) compared to the massive sandy soils. The existing simple preferential flow equation (single layer) fitted the data well only when macropore flow was dominant. The modified preferential flow equations (two layers) fitted equally well both for the adsorbing and nonadsorbing solutes. The later had high goodness of fit for a large number of solute breakthroughs, and gave almost identical retardation coefficient R as that calculated by two-domain CDE. With fewer parameters, the modified preferential flow equation after testing on some rigorous model selection criteria may provide a base for future modeling of chemical transport.

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