The Experts below are selected from a list of 31116 Experts worldwide ranked by ideXlab platform
Markus Weiler - One of the best experts on this subject based on the ideXlab platform.
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An infiltration model based on flow variability in Macropores: development, sensitivity analysis and applications
Journal of Hydrology, 2005Co-Authors: Markus WeilerAbstract:Simulating infiltration in soils containing Macropores still provides unsatisfactory results, as existing models seem not to capture all relevant processes. Recent studies of macropore flow initiation in natural soils containing earthworm channels revealed a distinct flow rate variability in the Macropores depending on the initiation process. When macropore flow was initiated at the soil surface, most of the Macropores received very little water while a few Macropores received a large proportion of the total inflow. In contrast, when macropore flow was initiated from a saturated or nearly saturated soil layer, macropore flow rate variation was much lower. The objective of this study was to develop, evaluate, and test a model, which combines macropore flow variability with several established approaches to model dual permeability soils. We then evaluate the INfiltration–INitiation–INteraction Model (IN3M) to explore the influence of macropore flow variability on infiltration behavior by performing a sensitivity analysis and applying IN3M to sprinkling and dye tracer experiments at three field sites with different macropore and soil matrix properties. The sensitivity analysis showed that the flow variability in Macropores reduces interaction between the Macropores and the surrounding soil matrix and thus increases bypass flow, especially for surface initiation of macropore flow and at higher rainfall intensities. The model application shows reasonable agreement between IN3M simulations and field data in terms of water balance, water content change, and dye patterns. The influence of macropore flow variability on the hydrological response of the soil was considerable and especially pronounced for soils where initiation occurs at the soil surface. In future, the model could be applied to explore other types of preferential flow and hence to get a generally better understanding of macropore flow.
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simulating surface and subsurface initiation of macropore flow
Journal of Hydrology, 2003Co-Authors: Markus Weiler, Felix NaefAbstract:Abstract Initiation of macropore flow either from the soil surface or from a saturated soil layer at depth is a first order control on water flow in Macropores and water transfer from Macropores into the surrounding soil matrix. Nevertheless, these initiation processes have not been well documented. We surveyed surface topography at four field sites with permanent grass vegetation with grid spacing of 10 cm and applied Kriging to derive the spatial correlation structure. We then simulated the water flux into Macropores based on different combinations of surveyed surface micro-topographies, spatial earthworm burrow distributions, and the soil properties, to examine more fully the role of macropore drainage area (MDA) on macropore flow initiation. The spatial distributions of the earthworm burrows were derived from horizontal soil sections extracted from each study profile. The MDA was calculated for different sets of surface topography and macropore density using a flow accumulation algorithm. The resulting MDA of each macropore was used to calculate the total relative MDA, which is equal to the proportion of overland flow draining into Macropores, and the MDA probability distribution. The results showed that the macropore density primarily controlled the total MDA and that surface micro-topography strongly influenced the probability distribution of the MDA. Only a few Macropores contributed significantly to the total macropore flow whereas the majority of Macropores received little water; a phenomenon especially pronounced for a rough surface topography and for a low soil surface gradient. The simulated probability distribution of subsurface initiation was very different from the distribution derived for surface initiation; more symmetrical, less variable and slightly influenced by the roughness and the gradient of the interface between the saturated and the low permeable soil layer. We conclude that the different amount of water supplied to each macropore further alters the percolation depth and transport of solutes in macroporous soils and should be considered for modelling infiltration in macroporous soils.
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an experimental tracer study of the role of Macropores in infiltration in grassland soils
Hydrological Processes, 2003Co-Authors: Markus Weiler, Felix NaefAbstract:Water flow in Macropores is an important mechanism of infiltration in natural soils and, as such, is crucial for the prediction of runoff generation. The major flow processes controlling macropore flow are the initiation of macropore flow (water supply into Macropores) and the water transfer from the Macropores into the surrounding soil matrix (interaction). The water movement during infiltration and the resulting flow paths were studied with combined sprinkling and dye tracer experiments under different rainfall intensities and initial soil moisture conditions. The dye tracer was continuously applied with the sprinkling water on 1 m2 plots. After the sprinkling, horizontal and vertical soil sections were prepared for surveying dye patterns, which showed the cumulated flow pathways in the soils. These experiments were carried out on four hillslope sites covered with grassland, where earthworms mainly built the macropore system. The evaluation of the flow processes in the soil was based on classified dye patterns and measurements of water content and matric potential. The results illustrate how flow in earthworm channels influences general hydrological flow processes during extreme rainfall events. Macropore flow was initiated from the soil surface or from a saturated or partially saturated soil layer. Transfer of water from the Macropores into the soil matrix was mainly influenced by the soil properties and soil water content. The permeability of the underlying bedrock in combination with this transfer of water controlled the drainage of the Macropores. Finally, major effects of macropore flow processes on the hydrological response were extracted. Infiltration excess overland flow was reduced if water bypassed the less permeable layer through Macropores, saturation excess overland flow was less affected by Macropores, and subsurface flow was activated very rapidly because the infiltrated water bypassed the soil matrix. This study highlights the most important processes that have to be considered in order to understand better and to model infiltration in natural soils in the future. Copyright © 2003 John Wiley & Sons, Ltd.
David C Dunand - One of the best experts on this subject based on the ideXlab platform.
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ti 6al 4v with micro and Macropores produced by powder sintering and electrochemical dissolution of steel wires
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: Daniel J Jorgensen, David C DunandAbstract:Abstract Ti–6Al–4V powder preforms containing parallel layers of steel wire meshes are sintered into composites. Elongated Macropores are created by electrochemical dissolution of the steel wires, and equiaxed micropores by partial powder densification. The macropore diameter and fraction is tailored by the creation of a Fe-containing diffusion zone in the Ti–6Al–4V matrix, which is removed electrochemically together with the wires. Ti–6Al–4V with 21–41% porosity shows compressive stiffness and strength attractive for biomedical implants.
Felix Naef - One of the best experts on this subject based on the ideXlab platform.
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simulating surface and subsurface initiation of macropore flow
Journal of Hydrology, 2003Co-Authors: Markus Weiler, Felix NaefAbstract:Abstract Initiation of macropore flow either from the soil surface or from a saturated soil layer at depth is a first order control on water flow in Macropores and water transfer from Macropores into the surrounding soil matrix. Nevertheless, these initiation processes have not been well documented. We surveyed surface topography at four field sites with permanent grass vegetation with grid spacing of 10 cm and applied Kriging to derive the spatial correlation structure. We then simulated the water flux into Macropores based on different combinations of surveyed surface micro-topographies, spatial earthworm burrow distributions, and the soil properties, to examine more fully the role of macropore drainage area (MDA) on macropore flow initiation. The spatial distributions of the earthworm burrows were derived from horizontal soil sections extracted from each study profile. The MDA was calculated for different sets of surface topography and macropore density using a flow accumulation algorithm. The resulting MDA of each macropore was used to calculate the total relative MDA, which is equal to the proportion of overland flow draining into Macropores, and the MDA probability distribution. The results showed that the macropore density primarily controlled the total MDA and that surface micro-topography strongly influenced the probability distribution of the MDA. Only a few Macropores contributed significantly to the total macropore flow whereas the majority of Macropores received little water; a phenomenon especially pronounced for a rough surface topography and for a low soil surface gradient. The simulated probability distribution of subsurface initiation was very different from the distribution derived for surface initiation; more symmetrical, less variable and slightly influenced by the roughness and the gradient of the interface between the saturated and the low permeable soil layer. We conclude that the different amount of water supplied to each macropore further alters the percolation depth and transport of solutes in macroporous soils and should be considered for modelling infiltration in macroporous soils.
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an experimental tracer study of the role of Macropores in infiltration in grassland soils
Hydrological Processes, 2003Co-Authors: Markus Weiler, Felix NaefAbstract:Water flow in Macropores is an important mechanism of infiltration in natural soils and, as such, is crucial for the prediction of runoff generation. The major flow processes controlling macropore flow are the initiation of macropore flow (water supply into Macropores) and the water transfer from the Macropores into the surrounding soil matrix (interaction). The water movement during infiltration and the resulting flow paths were studied with combined sprinkling and dye tracer experiments under different rainfall intensities and initial soil moisture conditions. The dye tracer was continuously applied with the sprinkling water on 1 m2 plots. After the sprinkling, horizontal and vertical soil sections were prepared for surveying dye patterns, which showed the cumulated flow pathways in the soils. These experiments were carried out on four hillslope sites covered with grassland, where earthworms mainly built the macropore system. The evaluation of the flow processes in the soil was based on classified dye patterns and measurements of water content and matric potential. The results illustrate how flow in earthworm channels influences general hydrological flow processes during extreme rainfall events. Macropore flow was initiated from the soil surface or from a saturated or partially saturated soil layer. Transfer of water from the Macropores into the soil matrix was mainly influenced by the soil properties and soil water content. The permeability of the underlying bedrock in combination with this transfer of water controlled the drainage of the Macropores. Finally, major effects of macropore flow processes on the hydrological response were extracted. Infiltration excess overland flow was reduced if water bypassed the less permeable layer through Macropores, saturation excess overland flow was less affected by Macropores, and subsurface flow was activated very rapidly because the infiltrated water bypassed the soil matrix. This study highlights the most important processes that have to be considered in order to understand better and to model infiltration in natural soils in the future. Copyright © 2003 John Wiley & Sons, Ltd.
Daniel J Jorgensen - One of the best experts on this subject based on the ideXlab platform.
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ti 6al 4v with micro and Macropores produced by powder sintering and electrochemical dissolution of steel wires
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: Daniel J Jorgensen, David C DunandAbstract:Abstract Ti–6Al–4V powder preforms containing parallel layers of steel wire meshes are sintered into composites. Elongated Macropores are created by electrochemical dissolution of the steel wires, and equiaxed micropores by partial powder densification. The macropore diameter and fraction is tailored by the creation of a Fe-containing diffusion zone in the Ti–6Al–4V matrix, which is removed electrochemically together with the wires. Ti–6Al–4V with 21–41% porosity shows compressive stiffness and strength attractive for biomedical implants.
J F Moncrief - One of the best experts on this subject based on the ideXlab platform.
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Role of macropore continuity and tortuosity on solute transport in soils: 2. Interactions with model assumptions for macropore description.
Journal of contaminant hydrology, 2002Co-Authors: S E Allaire, S C Gupta, J Nieber, J F MoncriefAbstract:The impact of macropore description on solute transport predictions in soils is not well understood. A 2-D Galerkin finite element model was used to compare different approaches for describing macropore flow in soil. The approaches were: a modification of the hydraulic conductivity function (Hydraulic function), the lumping of all Macropores into one single straight macropore (Lumping), the use of an exchange factor between microporosities and macroporosities that occupy the same area (Dual porosity), and a detailed description of each macropore (Full description, base case). Simulated breakthrough curves were obtained with domains that contained one or more Macropores of different shapes under both steady state and transient flow conditions. The Hydraulic function approach was not sensitive to macropore continuity and tortuosity. When the Macropores were open at the soil surface and the solute was surface applied, the first three approaches underestimated both breakthrough curves and solute distribution in the profile compared to the Full description approach. When the solute was initially incorporated in the soil, the first three approaches overestimated the breakthrough curves compared to the Full description approach. The first three approaches also underestimated the heterogeneity of solute distribution in the profile compared to the Full description approach, mostly when the Macropores were tortuous. The differences between predicted breakthrough curves with different approaches decreased with an increase in tortuosity and a decrease in surface continuity. To simplify macropore description, the Dual porosity approach was the better of the first three approaches for predicting breakthrough curves provided the exchange factor between Macropores and matrix porosity was available.
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water and solute movement in soil as influenced by macropore characteristics 2 macropore tortuosity
Journal of Contaminant Hydrology, 2000Co-Authors: S E Allaireleung, Satish C Gupta, J F MoncriefAbstract:In most contaminant transport modeling studies, only the Macropores that are visible at the soil surface are considered. Furthermore, it is assumed that these Macropores are straight and continuous throughout the soil profile. Little is known on the importance of other types of macropore continuity and tortuosity on preferential movement of contaminants through soils. This paper describes the results of a laboratory study dealing with macropore continuity effects on breakthrough curves (BTCs) and solute distribution in a Forman loam (fine-loamy mixed Udic Haploborolls) soil. BTCs were obtained under a constant hydraulic head of 0.08 m from a 2-D column (slab) containing artificial Macropores. The input solution contained 1190 mg l−1 KBr, 10 mg l−1 Rhodamine WT, and 100 mg l−1 FD&C Blue #1. The continuity types studied were: macropore open at the soil surface–open at the bottom of the column (O–O), open–closed (O–C), closed–open (C–O), and closed–closed (C–C). A treatment without macropore served as a control. As expected, the solution in the O–O treatment reached the bottom of the macropore about 100 times faster by bypassing most of the soil matrices. As a result, the breakthrough time for O–O treatments was much faster than any other continuity treatments. Both the O–O and O–C type Macropores favored earlier breakthrough, smaller apparent retardation coefficient (R′), deeper center of mass, and higher anisotropy in tracer concentrations in the horizontal direction than the C–O, C–C, and the Control treatment. The C–C macropore was favored in deeper penetration of tracer only when another macropore was present nearby. The importance of macropore continuity increased with an increase in the adsorption coefficient of the tracers.
