scholarly journals Single and dual-permeability models of chlorotoluron transport in the soil profile

2011 ◽  
Vol 51 (No, 7) ◽  
pp. 310-315 ◽  
Author(s):  
R. Kodešová ◽  
J. Kozák ◽  
J. Šimůnek ◽  
O. Vacek
Keyword(s):  
Solute Transport ◽  
Soil Profile ◽  
Hydraulic Properties ◽  
Preferential Flow ◽  
Water Movement ◽  
Application Rate ◽  
Transport Parameters ◽  
Soil Hydraulic Properties ◽  
Permeability Model ◽  
Herbicide Transport

This study presents the transport of chlorotoluron in the soil profile under field conditions. The herbicide Syncuran was applied on a plot (4 m˛) using an application rate of 2.5 kg/ha of active ingredient. Soil samples were taken after 119 days to study the residual chlorotoluron distribution in the soil profile. The single and dual-permeability models in HYDRUS-1D (Šimůnek et al. 2003) were used to simulate water movement and herbicide transport in the soil profile. Soil hydraulic properties and their variability were previously studied by Kutílek et al. (1989). The solute transport parameters, such as the adsorption isotherm and the degradation rate, were determined in the laboratory. Since the solute transport in the field was probably affected by preferential flow, the chlorotoluron distribution in the soil profile calculated using the single-permeability model had a different character than observed chlorotoluron concentrations. The chlorotoluron distribution within depth calculated using the dual-permeability model was closer to the observed behavior of chlorotoluron. While the herbicide did not reach a depth of 8 cm for the single-porosity system, in the case of the dual-permeability model the solute moved to the depth of 60 cm. The dual-permeability model significantly improved correspondence between calculated and observed herbicide concentrations.

scholarly journals Field and numerical study of chlorotoluron transport in the soil profile

2011 ◽  
Vol 50 (No. 8) ◽  
pp. 333-338 ◽  
Author(s):  
R. Kodešová ◽  
J. Kozák ◽  
O. Vacek
Keyword(s):  
Adsorption Isotherm ◽  
Solute Transport ◽  
Soil Water ◽  
Soil Profile ◽  
Preferential Flow ◽  
Water Movement ◽  
Numerical Study ◽  
Soil Samples ◽  
Transport Parameters ◽  
Four Square

The transport of chlorotoluron in the soil profile under field conditions was studied. The herbicide Syncuran was applied on a four square meter plot using an application rate of 2.5 kg/ha active ingredient. Soil samples were taken after 119 days to study the residual chlorotoluron distribution in the soil profile. HYDRUS-1D (Šimůnek et al. 1998) was used to simulate water movement and herbicide transport in the soil profile. Soil hydraulic properties and their variability were studied previously by Kutílek et al. (1989). The solute transport parameters, like the adsorption isotherm and the degradation rate, were determined in the laboratory. The Freundlich and Langmuir equations were used to fit the experimental data points of the adsorption isotherm, and the affect of each type of adsorption isotherm equation on the solute transport was studied. The chlorotoluron concentrations in soil water tended to be higher for the simulation performed with the Freundlich isotherm then that of the model using the Langmuir isotherm. In both cases, the solution did not pass a depth of8 cm. The simulated chlorotoluron concentrations in soil samples were higher then the observed concentrations when the chlorotoluron degradation was assumed to be in soil water only. Assumption of the solute degradation in both in the solid and the liquid phase significantly improved the accuracy of the solution. The different characters of the simulated and observed chlorotoluron distributions can probably be attributed to the preferential flow of water and solute in the soil profile and by variability of the transport parameters.

Influence of the shape of inter-horizon boundary and size of soil tongues on preferential flow under shallow groundwater conditions: A simulation study

2011 ◽  
Vol 91 (2) ◽  
pp. 211-221 ◽  
Author(s):  
Priyantha B. Kulasekera ◽  
Gary W. Parkin
Keyword(s):  
Solute Transport ◽  
Vadose Zone ◽  
Simulation Study ◽  
Soil Profile ◽  
Preferential Flow ◽  
Shallow Groundwater ◽  
Soil Horizon ◽  
Tongue Length ◽  
The Impact ◽  
Water And Solute Transport

Kulasekera, P. B. and Parkin, G. W. 2011. Influence of the shape of inter-horizon boundary and size of soil tongues on preferential flow under shallow groundwater conditions: A simulation study. Can. J. Soil Sci. 91: 211–221. Detailed studies of the impact of soil tongues at soil horizon interfaces are very important in understanding preferential flow processes through layered soils and in improving the accuracy of models predicting water and solute transport through the vadose zone. The implication of having soil tongues of different shapes and sizes created at the soil horizon interface on solute transport through a layered soil horizon was studied by simulating water and solute transport using the VS2DI model. This 2-D simulation study reconfirmed that soil tongues facilitate preferential flow, and the level of activeness of tongues may depend on the number of soil tongues, their spacing and distribution. Also, the size of the soil tongues (length and diameter at the interface between the soil horizons) and their shape influence the rate of preferential flow. Increasing tongue length consistently resulted in an increase in solute velocity across the entire soil profile regardless of the tongue shape; for example, a soil tongue of 0.25 m length increased solute velocity by about 1.5 times over a soil profile without tongues, but this increase might be different for soil types and groundwater conditions other than those considered in this study. Narrowing of tongues increased solute velocity, whereas increasing the number of tongues in a wider soil profile decreased the solute-front's velocity. As tongue length increased, the area containing solutes at prescribed elapsed times decreased. An implication of this study is that soil horizon tongue shape and spacing reduce pollutant residence times, hence inter-horizon boundary morphology should be considered when modelling transport through the vadose zone. As well, since the solute velocity behaviours of a triangular- and a wider rectangular-shaped tongue were nearly identical, simply measuring solute velocity in the field will reveal little information on the shape of a soil tongue.

Dual permeability soil water dynamics and water uptake by roots in irrigated potato fields

Biologia ◽  
2007 ◽  
Vol 62 (5) ◽  
Author(s):  
František Doležal ◽  
David Zumr ◽  
Josef Vacek ◽  
Josef Zavadil ◽  
Adriano Battilani ◽  
...  
Keyword(s):  
Soil Water ◽  
Field Experiments ◽  
Preferential Flow ◽  
Water Movement ◽  
Root Zone ◽  
Water Pressure ◽  
Boundary Curve ◽  
Water Dynamics ◽  
Permeability Model ◽  
Soil Matrix

AbstractWater movement and uptake by roots in a drip-irrigated potato field was studied by combining field experiments, outputs of numerical simulations and summary results of an EU project (www.fertorganic.org). Detailed measurements of soil suction and weather conditions in the Bohemo-Moravian highland made it possible to derive improved estimates of some parameters for the dual permeability model S1D_DUAL. A reasonably good agreement between the measured and the estimated soil hydraulic properties was obtained. The measured root zone depths were near to those obtained by inverse simulation with S1D _DUAL and to a boundary curve approximation. The measured and S1D _DUAL-simulated soil water pressure heads were comparable with those achieved by simulations with the Daisy model. During dry spells, the measured pressure heads tended to be higher than the simulated ones. In general, the former oscillated between the simulated values for soil matrix and those for the preferential flow (PF) domain. Irrigation facilitated deep seepage after rain events. We conclude that several parallel soil moisture sensors are needed for adequate irrigation control. The sensors cannot detect the time when the irrigation should be stopped.

scholarly journals Comparison between field measurements and numerical simulation of steady-state solute transport in a heterogeneous soil profile

1997 ◽  
Vol 1 (4) ◽  
pp. 853-871 ◽  
Author(s):  
J. Vanderborght ◽  
D. Jacques ◽  
D. Mallants ◽  
P.-H. Tseng ◽  
J. Feyen
Keyword(s):  
Solute Transport ◽  
Water Flow ◽  
Random Fields ◽  
Hydraulic Properties ◽  
Soil Hydraulic Properties ◽  
Field Scale ◽  
Flow Heterogeneity ◽  
Heterogeneous Soil ◽  
Soil Hydraulic ◽  
Second Procedure

Abstract. Abstract: Field-scale solute dispersion is determined by water flow heterogeneity which results from spatial variability of soil hydraulic properties and soil moisture state. Measured variabilities of soil hydraulic properties are highly sensitive to the experimental method. Field-scale dispersion derived from leaching experiments in a macroporous loam soil was compared with field-scale dispersion obtained with numerical simulations in heterogeneous random fields. Four types of random fields of hydraulic properties having statistical properties derived from four different types of laboratory measurements were considered. Based on this comparison, the measurement method depicting heterogeneities of hydraulic properties most relevant to field-scale solute transport was identified. For unsaturated flow, the variability of the hydraulic conductivity characteristic measured on a small soil volume was the most relevant parameter. For saturated flow, simulated dispersion underestimated the measured dispersion and it was concluded that heterogeneity of macroscopic hydraulic properties could not represent solute flow heterogeneity under these flow conditions. Field-scale averaged solute concentrations depend both on the detection method and the averaging procedure. Flux-averaged concentrations (relevant to practical applications) differ from volume-averaged or resident concentrations (easy to measure), especially when water flow is more heterogeneous. Simulated flux and resident concentrations were subsequently used to test two simple one-dimensional transport models in predicting flux concentrations when they are calibrated on resident concentrations. In the first procedure, solute transport in a heterogeneous soil is represented by a 1-D convection dispersion process. The second procedure was based on the relation between flux and resident concentrations for a stochastic convective process. Better predictions of flux concentrations were obtained using the second procedure, especially when water flow and solute transport are very heterogeneous.

scholarly journals In situ Evaluation of Unsaturated Hydraulic Properties Using Subsurface Points

1999 ◽  
Author(s):  
Arthur Warrick ◽  
Uri Shani ◽  
Dani Or ◽  
Muluneh Yitayew
Keyword(s):  
Hydraulic Properties ◽  
Preferential Flow ◽  
Water Pressure ◽  
Point Sources ◽  
Positive Pressure ◽  
Soil Hydraulic Properties ◽  
Undisturbed Soil ◽  
Soil System ◽  
Soil Hydraulic

The primary information for accurately predicting water and solute movement and their impact on water quality is the characterization of soil hydraulic properties. This project was designed to develop methods for rapid and reliable estimates of unsaturated hydraulic properties of the soil. Particularly, in situ methodology is put forth, based on subsurface point sources. Devices were designed to allow introduction of water in subsurface settings at constant negative heads. The ability to operate at a negative head allows a direct method of finding unsaturated soil properties and a mechanism for eliminating extremely rapid preferential flow from the slow matrix flow. The project included field, laboratory and modeling components. By coupling the measurements and the modeling together, a wider range of designs can be examined, while at the same time realistic performance is assured. The developed methodology greatly expands the possibilities for evaluating hydraulic properties in place, especially for measurements in undisturbed soil within plant rooting zones. The objectives of the project were (i) To develop methods for obtaining rapid and reliable estimates of unsaturated hydraulic properties in situ, based on water distribution from subsurface point sources. These can be operated with a constant flow or at a constant head; (ii) To develop methods for distinguishing between matrix and preferential flow using cavities/permeameters under tension; (iii) To evaluate auxiliary measurements such as soil water content or tensions near the operating cavities to improve reliability of results; and (iv: To develop numerical and analytical models for obtaining soil hydraulic properties based on measurements from buried-cavity sources and the auxiliary measurements. The project began in July 1995 and was terminated in November 1998. All of the objectives were pursued. Three new subsurface point sources were designed and tested and two old types were also used. Two of the three new designs used a nylon cloth membrane (30 mm) arranged in a cylindrical geometry and operating at a negative water pressure (tension). A separate bladder arrangement allowed inflation under a positive pressure to maintain contact between the membrane and the soil cavity. The third new design used porous stainless steel (0.5 and 5 mm) arranged in six segments, each with its own water inlet, assembled to form a cylindrical supply surface when inflated in a borehole. The "old" types included an "off-the-shelf" porous cup as well as measurements from a subsurface drip emitter in a small subsurface cavity. Reasonable measurements were made with all systems. Sustained use of the cloth membrane devices were difficult because of leaks and plugging problems. All of the devices require careful consideration to assure contact with the soil system. Steady flow was established which simplified the analysis (except for the drip emitter which used a transient analysis).

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