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.

scholarly journals Interplay between Fingering Instabilities and Initial Soil Moisture in Solute Transport through the Vadose Zone

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 917
Author(s):  
Luis Cueto-Felgueroso ◽  
María José Suarez-Navarro ◽  
Xiaojing Fu ◽  
Ruben Juanes
Keyword(s):  
Spatial Distribution ◽  
Solute Transport ◽  
Soil Water ◽  
Water Flow ◽  
Vadose Zone ◽  
Preferential Flow ◽  
Solute Diffusion ◽  
Wetting Front ◽  
Initial Soil ◽  
The Impact

Modeling water flow and solute transport in the vadose zone is essential to understanding the fate of soil pollutants and their travel times towards groundwater bodies. It also helps design better irrigation strategies to control solute concentrations and fluxes in semiarid and arid regions. Heterogeneity, soil texture and wetting front instabilities determine the flow patterns and solute transport mechanisms in dry soils. When water is already present in the soil, the flow of an infiltration pulse depends on the spatial distribution of soil water and on its mobility. We present numerical simulations of passive solute transport during unstable infiltration of water into sandy soils that are prone to wetting front instability. We study the impact of the initial soil state, in terms of spatial distribution of water content, on the infiltration of a solute-rich water pulse. We generate random fields of initial moisture content with spatial structure, through multigaussian fields with prescribed correlation lengths. We characterize the patterns of water flow and solute transport, as well as the mass fluxes through the soil column. Our results indicate a strong interplay between preferential flow and channeling due to fingering and the spatial distribution of soil water at the beginning of infiltration. Fingering and initial water saturation fields have a strong effect on solute diffusion and dilution into the ambient water during infiltration, suggesting an effective separation between mobile and inmobile transport domains that are controlled by the preferential flow paths due to fingering.

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.

Quantifying the impact of preferential flow on solute transport to tile drains in a sandy field soil

1999 ◽  
Vol 215 (1-4) ◽  
pp. 116-134 ◽  
Author(s):  
M.H Larsson ◽  
N.J Jarvis ◽  
G Torstensson ◽  
R Kasteel
Keyword(s):  
Solute Transport ◽  
Preferential Flow ◽  
Field Soil ◽  
Tile Drains ◽  
The Impact

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 Simulating preferential soil water flow and tracer transport using the Lagrangian Soil Water and Solute Transport Model

2019 ◽  
Vol 23 (10) ◽  
pp. 4249-4267 ◽  
Author(s):  
Alexander Sternagel ◽  
Ralf Loritz ◽  
Wolfgang Wilcke ◽  
Erwin Zehe
Keyword(s):  
Solute Transport ◽  
Soil Water ◽  
Water Flow ◽  
Preferential Flow ◽  
Tracer Transport ◽  
Model Concept ◽  
Soil Matrix ◽  
Matrix Domain ◽  
Flow Domain ◽  
Water And Solute Transport

Abstract. We propose an alternative model concept to represent rainfall-driven soil water dynamics and especially preferential water flow and solute transport in the vadose zone. Our LAST-Model (Lagrangian Soil Water and Solute Transport) is based on a Lagrangian perspective of the movement of water particles (Zehe and Jackisch, 2016) carrying a solute mass through the subsurface which is separated into a soil matrix domain and a preferential flow domain. The preferential flow domain relies on observable field data like the average number of macropores of a given diameter, their hydraulic properties and their vertical length distribution. These data may be derived either from field observations or by inverse modelling using tracer data. Parameterization of the soil matrix domain requires soil hydraulic functions which determine the parameters of the water particle movement and particularly the distribution of flow velocities in different pore sizes. Infiltration into the matrix and the macropores depends on their respective moisture state, and subsequently macropores are gradually filled. Macropores and matrix interact through diffusive mixing of water and solutes between the two flow domains, which again depends on their water content and matric potential at the considered depths. The LAST-Model is evaluated using tracer profiles and macropore data obtained at four different study sites in the Weiherbach catchment in southern Germany and additionally compared against simulations using HYDRUS 1-D as a benchmark model. While both models show qual performance at two matrix-flow-dominated sites, simulations with LAST are in better accordance with the fingerprints of preferential flow at the two other sites compared to HYDRUS 1-D. These findings generally corroborate the feasibility of the model concept and particularly the implemented representation of macropore flow and macropore–matrix exchange. We thus conclude that the LAST-Model approach provides a useful and alternative framework for (a) simulating rainfall-driven soil water and solute dynamics and fingerprints of preferential flow as well as (b) linking model approaches and field experiments. We also suggest that the Lagrangian perspective offers promising opportunities to quantify water ages and to evaluate travel and residence times of water and solutes by a simple age tagging of particles entering and leaving the model domain.

scholarly journals Simulating preferential soil water flow and tracer transport using the Lagrangian Soil Water and Solute Transport Model

2019 ◽  
Author(s):  
Alexander Sternagel ◽  
Ralf Loritz ◽  
Wolfgang Wilcke ◽  
Erwin Zehe
Keyword(s):  
Solute Transport ◽  
Soil Water ◽  
Water Flow ◽  
Field Experiments ◽  
Preferential Flow ◽  
Sensitivity Analyses ◽  
Tracer Transport ◽  
Soil Matrix ◽  
Soil Water Flow ◽  
Water And Solute Transport

Abstract. We propose an alternative model to overcome these weaknesses of the Darcy-Richards approach and to simulate preferential soil water flow and tracer transport in macroporous soils. Our LAST-Model (Lagrangian Soil Water and Solute Transport) relies on a Lagrangian perspective on the movement of water particles carrying a solute mass through the soil matrix and macropores. We advance the model of Zehe and Jackisch (2016) by two main extensions: a) a new routine for solute transport within the soil matrix and b) the implementation of an additional 1-D preferential flow domain which simulates flow and transport in a population of macropores. Infiltration into the matrix and the macropores depends on their moisture state and subsequently macropores are gradually filled. Macropores and matrix interact through diffusive mixing of water and solutes between the two domains which depends on their water content and matric potential at the considered depths. The LAST-Model is then evaluated with sensitivity analyses and tested against tracer field experiments at three different sites. The results show the internal and physical validity of the model and the robustness of our solute transport and the linear mixing approach. Further, the model is able to simulate preferential flow through macropores and to depict well the observed 1-D solute mass profile of a tracer experiment with a high computational efficiency and short simulation times.

scholarly journals High-Resolution Pore-Scale Water Content Measurement in a Translucent Soil Profile from Light Transmission

2021 ◽  
Vol 64 (3) ◽  
pp. 949-962
Author(s):  
Enrique Orozco-López ◽  
Rafael Muñoz-Carpena ◽  
Bin Gao ◽  
Garey Fox
Keyword(s):  
Water Content ◽  
Vadose Zone ◽  
Soil Profile ◽  
Preferential Flow ◽  
Light Transmission ◽  
Water Dynamics ◽  
Soil Profiles ◽  
Pore Scale ◽  
Transmission Method ◽  
Transient Flows

HighlightsResearch methods are needed to study preferential flow processes at pore scale and high temporal resolution.Novel verification of the light transmission method shows high efficiency to measure rapid transient soil water flow.Recast of a previous physical model allows reliable pore-scale water content quantification in translucent soil profiles.Insights from the light transmission method can inform preferential flow modeling efforts.Abstract. Understanding rapid transient flows in the soil unsaturated zone continues to be a major challenge in hydrology and water quality engineering. For example, surface runoff mitigation by riparian buffers can be limited by rapid transient flows due to the natural propensity of these areas for preferential flow pathways (i.e., caused by roots, wormholes, or wetting/drying cycles). However, current monitoring technologies are limited in their ability to capture rapid soil preferential flows at high spatial and temporal resolutions. Among the state-of-the-art technologies to monitor preferential flow, the light transmission method (LTM) has become a promising tool to quantify pore-scale water contents at a laboratory scale, but its reliability and consistency need further study. The objectives of this study are to recast a previously developed LTM physical model, propose a novel verification method to assess LTM reliability to measure pore-scale water dynamics in laboratory translucent soil profiles, and identify the representative pore radius of translucent soil profiles based on their average number of pores. This study found a high measuring efficiency with LTM for soil moisture and drainage estimations (NSE > 0.98, RMSE < 5.4%), showing its potential for use in laboratory analysis of pore-scale rapid transient water dynamics typically found in preferential flow through the vadose zone. This study also shows that the parameter traditionally associated with the number of pores in a translucent soil profile is a fitting parameter with no direct physical meaning. Keywords: Beer-Lambert law, Fresnel law, Light transmission method, Preferential flow, Riparian buffer, Vadose zone.

scholarly journals Regional Aquifer Vulnerability and Pollution Sensitivity Analysis of Drastic Application to Dahomey Basin of Nigeria

2020 ◽  
Vol 17 (7) ◽  
pp. 2609
Author(s):  
Saheed Adeyinka Oke
Keyword(s):  
Sensitivity Analysis ◽  
Vadose Zone ◽  
Shallow Groundwater ◽  
Aquifer Vulnerability ◽  
Single Parameter ◽  
Southwestern Nigeria ◽  
Groundwater Vulnerability Mapping ◽  
Dahomey Basin ◽  
Vulnerability Map ◽  
The Impact

Shallow groundwater vulnerability mapping of the southwestern Nigeria sedimentary basin was assessed in this study with the aim of developing a regional-based vulnerability map for the area based on assessing the intrinsic ability of the aquifer overlying beds to filter and degrade migrating pollutant. The mapping includes using the established seven parameter-based DRASTIC vulnerability methodology. Furthermore, the developed vulnerability map was subjected to sensitivity analysis as a validation approach. This approach includes single-parameter sensitivity, map removal sensitivity, and DRASTIC parameter correlation analysis. Of the Dahomey Basin, 21% was classified as high-vulnerability and at risk of pollution, 61% as moderate vulnerability, and 18% as low vulnerability. Low vulnerability areas of the basin are characterised by thick vadose zones, low precipitation, compacted soils, high slopes, and high depth to groundwater. High-vulnerability areas which are prone to pollution are regions closer to the coast with flat slopes and frequent precipitation. Sensitivity of the vulnerability map show the greatest impact with the removal of topography, soil media, and depth to groundwater and least impact with the removal of the vadose zone. Due to the subjectivity of the DRASTIC method, the most important single parameter affecting the rating system of the Dahomey Basin DRASTIC map is the impact of the vadose zone, followed by the net recharge and hydraulic conductivity. The DRASTIC vulnerability map can be useful in planning and siting activities that generate pollutants (e.g., landfill, soak away, automobile workshops, and petrochemical industries) which pollute the environment, groundwater, and eventually impact the environmental health of the Dahomey Basin’s inhabitants.

Simulating preferential soil water flow and reactive solute transport using the Lagrangian Soil Water and Solute Transport Model (LAST)

2020 ◽  
Author(s):  
Alexander Sternagel ◽  
Ralf Loritz ◽  
Wolfgang Wilcke ◽  
Erwin Zehe
Keyword(s):  
Solute Transport ◽  
Soil Water ◽  
Water Flow ◽  
Preferential Flow ◽  
Transport Model ◽  
Water Dynamics ◽  
Model Concept ◽  
Soil Matrix ◽  
Reactive Solute Transport ◽  
Water And Solute Transport

<p>Recently, we proposed an alternative model concept to represent rainfall-driven soil water dynamics and especially preferential water flow and solute transport in the vadose zone. Our LAST-Model is based on a Lagrangian perspective on the movement of water particles (Zehe and Jackisch, 2016) carrying solute masses through the subsurface which is separated into a soil matrix domain and a preferential flow domain (Sternagel et al., 2019). The preferential flow domain relies on observable field data like the average number of macropores of a given diameter, their hydraulic properties and their vertical length distribution. These data may either be derived from field observations or by inverse modelling using tracer data. Parameterization of the soil matrix domain requires soil hydraulic functions which determine the parameters of the water particle movement and particularly the distribution of flow velocities in different pores sizes. Infiltration into the matrix and the macropores depends on their respective moisture state and subsequently macropores are gradually filled. Macropores and matrix interact through diffusive mixing of water and solutes between the two flow domains which again depends on their water content and matric potential at the considered depths.</p><p>The LAST-Model was evaluated using tracer profiles and macropore data obtained at four different study sites in the Weiherbach catchment in south Germany and additionally compared against simulations using HYDRUS 1-D as benchmark model. The results generally corroborated the feasibility of the model concept and particularly the implemented representation of macropore flow and macropore-matrix exchange. We thus concluded that the LAST-Model approach provides a useful and alternative framework for simulating rainfall-driven soil water and solute dynamics and fingerprints of preferential flow.</p><p>This study presents an extension of the model allowing for the simulation of reactive solute transport. Transformation kinetics are considered by transferring mass from the parent to the child components in each water particle according to the corresponding reaction rates, which is limited by the compound solubility. A retardation coefficient is not helpful in the particle-based framework, as the solute mass is carried by the water particles and travels thus by default at the same velocity. Ad- and desorption are explicit represented through transfer of dissolved mass from the water particles at a given depth to surrounding adsorption sites of the soil solid phase and vice versa. This may either operate under rate-limited or non-limited conditions. Adsorbed solute masses will be considered to be degraded following first-order reaction kinetics. The retardation process delays the solute displacement and enables a suitable time scale for the degradation process, which must be smaller than the time scale for the re-mobilization of the solutes. The proposed extension will be benchmarked against observations of pesticide transport in soil profiles and at tile-drained field sites.</p><p> </p><p>Zehe, E., Jackisch, C.: A Lagrangian model for soil water dynamics during rainfall-driven conditions, Hydrol. Earth Syst. Sci., 20, 3511–3526, https://doi.org/10.5194/hess-20-3511-2016, 2016.</p><p> </p><p>Sternagel, A., Loritz, R., Wilcke, W., and Zehe, E.: Simulating preferential soil water flow and tracer transport using the Lagrangian Soil Water and Solute Transport Model, Hydrol. Earth Syst. Sci., 23, 4249–4267, https://doi.org/10.5194/hess-23-4249-2019, 2019.</p>

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