| 1. |
- Bacher, Matthias, et al.
(författare)
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Three-Dimensional Printing of Macropore Networks of an Undisturbed Soil Sample
- 2015
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 14, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Macropore systems predominantly determine rapid water flow and solute transport in undisturbed soils. Repeated experiments are needed to investigate the relationship between the nature of the macropore network and the resulting water and solute transport under different hydraulic initial and boundary conditions. However, the large heterogeneity in soil macropore network structures renders each soil sample unique and multiple identical samples impossible. In addition, the fragile nature of soil strongly limits the possible number of repeated experiments on one individual sample. Micromodels that mimic the precise shape and location of the macropores in undisturbed soil are therefore necessary to allow repeated experiments. In this study we investigated whether such micromodels can be obtained using contemporary three-dimensional (3-D) printing techniques and materials. We used X-ray computed tomography to digitize the 3-D macropore structure of an undisturbed soil sample. We printed a subsection of this macropore system in five different materials. Four out of the five investigated materials had essential parts of their macropore system clogged with residual printing or printing-aid material. Only one reprint, namely the prime-gray sample that was printed using stereo lithography, exhibited no pore clogging and had the largest hydraulic conductivity of all investigated reprints. Prime gray showed subcritical water repellency with a medium contact angle of approximately 65 degrees, which is similar to contact angles found in natural soil. We conclude that the 3-D printing of undisturbed soil macropore systems is in principle possible with contemporary 3-D printing systems.
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| 2. |
- Beven, K, et al.
(författare)
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On the value of local measurements for prediction of pesticide transport at the field scale
- 2006
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 5:1, s. 222-233
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Tidskriftsartikel (refereegranskat)abstract
- Pesticide transport through the soil profile at the field scale is notoriously difficult to predict because of a lack of appropriate field-scale models and model parameters that take adequate account of heterogeneity in local flow rates and parameters. It is generally impossible to measure all the parameters required to describe that heterogeneity. A way of approximating pesticide transport at the field scale, given uncertainty in the representation of both local characteristics and field-scale distributions, is presented. The methodology allows prior estimates of field-scale distribution parameters to be conditioned on uncertain column-scale measurements. It is shown how this conditioning can drastically constrain steady-state flow predictions of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) transport to groundwater for a site in the Rhone Valley, Switzerland. Some of the simplifying assumptions of the current analysis, in particular, to allow for transient simulations, can be relaxed in the future as more computer power becomes available. The methodology, however, should remain valid.
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| 3. |
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| 4. |
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| 5. |
- Fagerlund, Fritjof, 1974-, et al.
(författare)
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Nonaqueous-phase liquid infiltration and immobilization in heterogeneous media : 2. Application to stochastically heterogeneous formations
- 2007
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 6:3, s. 483-495
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Tidskriftsartikel (refereegranskat)abstract
- We performed a series of well-controlled laboratory experimentsinvestigating the infiltration and subsequent immobilizationof nonaqueous-phase liquid (NAPL) in saturated heterogeneousmedia. A system of two distinct aquifer zones separated by adipping interface was considered. Heterogeneity was representedby a spatially correlated random field with known geostatisticalparameters in one zone in combination with a homogenous packingof the other zone. The effects of heterogeneity on NAPL flowand entrapment in each of the two zones were investigated. Thetime-varying NAPL saturations were continuously monitored inspace and the final static entrapment–saturation distributionwas accurately measured. The immobilized-NAPL distribution contributesto plume generation from source zones. The results show thatcapillary barriers produced by the small-scale heterogeneitystrongly influenced the migration paths and the final distributionof NAPL both in space and across different saturation ranges.The NAPL was immobilized both by snap-off to discontinuous blobsand ganglia and by capillary barriers at textural interfaces.Heterogeneity generally increased entrapment, because spatialvariations in capillary properties caused NAPL to be entrappedat higher saturations. Heterogeneity in the finer formationprovided points of entry into this formation where the NAPLsubsequently could spread as the pressure built up. The NAPLwas immobilized at high saturations because high displacementpressures in the fine materials inhibited flow at low saturations.The accessibility for water flow through NAPL occurrences andthereby also the dissolution of NAPL is limited by (i) highentrapped NAPL saturations that decrease the aqueous-phase relativepermeability and (ii) the location of NAPL inside a formationwith low average permeability.
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| 6. |
- Fagerlund, Fritjof, 1974-, et al.
(författare)
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Nonaqueous-phase liquid infiltration and immobilization in heterogeneous media : 1. Experimental methods and two-layered reference case
- 2007
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 6:3, s. 471-482
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Tidskriftsartikel (refereegranskat)abstract
- Accurate data to understand the migration and entrapment ofnonaqueous-phase liquids (NAPLs) in heterogeneous formationsare presently lacking. A series of well-controlled laboratoryexperiments were conducted to investigate the infiltration andsubsequent immobilization of dense NAPLs in saturated heterogeneousmedia. The focus of this first study was the development ofa special experimental methodology for measuring the dynamicevolution of a NAPL plume in space and time. To demonstratethe method, a reference case of a two-layered formation consistingof two homogeneous sands separated by a dipping interface ispresented. The dipping formation in the reference case allowsthe study of NAPL behavior at texture interfaces under the influenceof both capillary and gravitational forces. The NAPL-saturationmeasurement methodology, based on a multiple-energy x-ray attenuationtechnique, correctly captured the known injected NAPL volumeas well as the general spreading and entrapment behavior inspace and time. Time-continuous measurements of NAPL saturationsallow the study of the history dependence of entrapped saturations.The Land model predicted the observed trend in the entrapmentbehavior well. The entrapment architecture was parameterizedusing spatial moments and moments of mass distribution at differentsaturations. The general features of the NAPL architecture weresuccessfully characterized by a simultaneous interpretationof these moments, while the domination of discontinuous or continuousNAPL was captured by the ganglia/pool ratio.
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| 7. |
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| 8. |
- Hansson, Klas, et al.
(författare)
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Water content reflectometer application to construction materials and its relation to time domain reflectometry
- 2006
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 5:1, s. 459-468
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Tidskriftsartikel (refereegranskat)abstract
- Moisture content measurements using time domain reflectometry (TDR) or water content reflectometry (WCR) are basic in many research areas. The goals of this study were to establish a relation between apparent dielectric number and WCR sensor output, to compare TDR and WCR calibration equations for two coarse road construction materials, and to investigate the influence of sampling volume for horizontally installed sensors. Measurements were performed in fluids of known dielectric number and in two incrementally saturated coarse materials. The effect of sampling volume was evaluated using an electrostatic finite-element model. A two-parameter equation was determined relating the apparent dielectric number to Campbell CS616 ( Campbell Scientific, Logan, UT) WCR output (r(2) > 0.99). A simple calibration can adapt the equation to individual CS616, or similar, sensors. For the finer, coarse material, a three-phase mixing model proved best, while for the coarser material no equation adequately described the measurements. Numerical simulations indicated that limited capillary rise, creating a rapid transition from wet to dry close to saturation, was the explanation, warranting caution when interpreting measurements in nearly saturated coarse materials.
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| 9. |
- Hansson, Klas, et al.
(författare)
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Water flow and heat transport in frozen soil : Numerical solution and freeze-thaw applications
- 2004
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 3:2, s. 693-704
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Tidskriftsartikel (refereegranskat)abstract
- A new method is presented to account for phase changes in a fully implicit numerical model for coupled heat transport and variably saturated water flow involving conditions both above and below zero temperature. The method is based on a mixed formulation for both water flow and heat transport similar to the approach commonly used for the Richards equation. The approach enabled numerically stable, energy- and mass-conservative solutions. The model was evaluated by comparing predictions with data from laboratory column freezing experiments. These experiments involved 20-cm long soil columns with an internal diameter of 8 cm that were exposed at the top to a circulating fluid with a temperature of −6°C. Water and soil in the columns froze from the top down during the experiment, with the freezing process inducing significant water redistribution within the soil. A new function is proposed to better describe the dependency of the thermal conductivity on the ice and water contents of frozen soils. Predicted values of the total water content compared well with measured values. The model proved to be numerically stable also for a hypothetical road problem involving simultaneous heat transport and water flow. The problem was simulated using measured values of the surface temperature for the duration of almost 1 yr. Since the road was snow-plowed during winter, surface temperatures varied more rapidly, and reached much lower values, than would have been the case under a natural snow cover. The numerical experiments demonstrate the ability of the code to cope with rapidly changing boundary conditions and very nonlinear water content and pressure head distributions in the soil profile.
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| 10. |
- Harpold, A, et al.
(författare)
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Effects of preferential hydrological pathways in a galciated watershed in the Northeastern USA
- 2010
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Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 9:2, s. 397-414
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Tidskriftsartikel (refereegranskat)abstract
- Despite observational evidence of lateral preferential flow paths in northeastern U.S. watersheds, their effects on the sources of runoff remain unclear. An intense field survey was undertaken during the 2007 growing season to determine the sources of stream runoff from a 2.51 km2 watershed in the Catskill Mountains, New York State. Lateral preferential flow paths are caused by groundwater springs and soil piping in this region. A two-component hydrograph separation using δ18O showed that event water (rain water) was a significant source of runoff during nine rainfall events (from July to October). With these rainfall events, 14 to 37% of the volume and 18 to 49% of the peak streamflow was attributable to event water. Further, end-member mixing analysis (EMMA), using δ18O, Si, and dissolved organic carbon (DOC), showed that saturated areas accounted for 2 to 24% of the total volume and 4 to 59% of peak streamflow but that groundwater was the dominant source of runoff volume during all events. Field surveys of saturated areas also suggested that near-stream areas were insufficient to generate the observed stream chemistry during rainfall events larger than 8 mm. A connection with the hillside saturated areas was therefore required to explain the results of the hydrograph separations, which were corroborated by the timing of the transient (perched) groundwater and overland flow. The hydrometric measurements confirmed that hillside lateral preferential flow paths rapidly transported water to near-stream saturation areas during runoff events under relatively dry antecedent conditions. A qualitative comparison with conventional techniques for distributing variable saturation areas (VSA) using surface topography and soil transmissivity (i.e., topographic index and soil topographic index), which do not consider the effects of lateral preferential flow paths, demonstrated that typical parameterizations (on the order of <10−1 m) would not have the spatial resolution to represent the measured lateral preferential flow paths (on the order of <10−3 m). Overall, the results suggest that the lateral redistribution of water from hillside areas reduces the influence of surface topography and channel topology on the sources of stream runoff, a finding that is consistent with recent ones from other landscapes where glacial soils have coevolved with the terrestrial hydrology.
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