Impact Of Preferential Flow Research Articles

An Experimental Study on the Hydromechanical Behaviours of the Evolution of Postearthquake Landslide Deposits

In this study, a series of experiments of the full-scale physical model was employed to investigate the hydromechanical behaviours of the postearthquake landslide evolution, in forms of rill erosion and shallow headward failure on the rill bank slopes under unsaturated conditions. Soil-water characteristic curves (SWCC) were established using the Brooks-Corey (BC) and van Genuchten (VG) models. The stability of the shallow failure was then analyzed via a one-dimensional and unsaturated stability analysis model of the infinite slope. This measurement revealed that the preferential flow and the matrix flow coexisted when infiltration occurred and the VG model performs better in fitting the SWCC than the BC model. Consistent feedback between stability calculations and experimental observations enables the analysis of mechanisms of rill erosion and slope failure of postseismic landslide under the impact of preferential flow. Furthermore, the seepage-induced internal erosion phenomenon was observed in the experiment. This work thus provides a new perspective on the triggering mechanisms of debris flow during the postseismic period.

Impact of preferential flow on soil chemistry of a podzol

Preferential flow paths are thought to affect the patterns of chemical properties of forest soils. However, little is known about their influence on podzols in coniferous forests. In our study we examined how soil chemical properties of a podzol in a Norway spruce stand are affected by preferential flow. We did three tracer experiments with Brilliant Blue FCF and analyzed soil chemical parameters (exchangeable cations, pH, total C, total N and C:N ratio) of preferential flow paths and soil matrix. For statistical analysis, we used mixed-effects models to account for a hierarchical sampling of our data. We found 5.0gkg−1 more C, 0.24gkg−1 more N, a C:N ratio larger by 2, smaller pH values (0.16 pH units), 32% more Ca and 57% more Mg in preferential flow paths than in soil matrix. Compared to the adjacent soil matrix, the content of Al did not differ significantly. However, 67% more Fe were found in preferential flow paths. These distinct chemical properties are probably due to root exudates, transport of solutes and dissolved organic carbon and percolation of acid soil solution from organic horizons along preferential paths. We attribute the increase of Ca and Mg to their transport via preferential flow paths after the application of lime some years ago. We conclude that a lower pH might enhance the release of Fe (and possibly Al) and thus increase podzolisation. In addition, our results show that soil liming could affect both the topsoil and the subsoil via transport of basic cations along preferential flow paths.

Numerical Study of Macropore Impact on Ponded Infiltration in Clay Soils

The single-porosity and dual-permeability models in HYDRUS-1D (Šimůnek et al. 1998, 2003) were used to simulate variably-saturated water movement in clay soils with and without macropores. Numerical simulations of water flow for several scenarios of probable macropore compositions show a considerable impact of preferential flow on water infiltration in such soils. Preferential flow must be considered to predict water recharge in clay soils.

The Impact of Preferential Flow on the Vaporization Barrier Above Waste Emplacement Drifts at Yucca Mountain, Nevada

Predicting the amount of water that may seep into waste emplacement drifts is important for assessing the performance of the proposed geologic repository for spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. The repository would be located in thick, partially saturated, fractured volcanic tuff that will be heated to above-boiling temperatures as a result of heat generation from the decay of nuclear waste. Since infiltrating water will be subject to vigorous boiling for a significant time period, the superheated rock zone (i.e., rock temperature above the boiling point of water) can form an effective vaporization barrier that reduces the possibility of water arrival at emplacement drifts. This paper analyzes the behavior of episodic preferential flow events that penetrate the hot fractured rock, evaluate the impact of such flow behavior on the effectiveness of the vaporization barrier, and discuss the implications for the performance assessment of the repository. Our analysis demonstrates that no liquid water is expected to arrive at emplacement drifts during the first several hundred years after waste emplacement, when the rock temperature is high in the drift vicinity and boiling conditions exist in a sufficiently large region above the drifts.

Impact of preferential flow at varying irrigation rates by quantifying mass fluxes.

Solute concentration and soluble dye studies inferring that preferential flow accelerates field-scale contaminant transport are common but flux measurements quantifying its impact are essentially nonexistent. A tile-drain facility was used to determine the influence of matrix and preferential flow processes on the flux of mobile tracers subjected to different irrigation regimes (4.4 and 0.89 mm h(-1)) in a silt loam soil. After tile outflow reached steady state either bromide (Br; 280 kg ha(-1)) or pentafluorobenzoic acid (PFBA; 121 kg ha(-1)) was applied through the irrigation system inside a shed (3.5 x 24 m). Bromide fluxes were monitored at an irrigation rate of 4.4 mm h(-1) while PFBA fluxes were monitored at an irrigation rate of 0.89 mm h(-1). At 4.4 mm h(-1) nearly one-third of the surface-applied Br was recovered in the tile line after only 124 mm of irrigation and was poorly fit by the one-dimensional convective-dispersive equation (CDE). On the other hand, the one-dimensional CDE fit the main PFBA breakthrough pattern almost perfectly, suggesting the PFBA transport was dominated by matrix flow. Furthermore, after 225 mm of water had been applied, less than 2% of the applied PFBA had been leached through the soil compared with more than 59% of the applied Br. This study demonstrates that the methodology of applying a narrow strip of chemical to a tile drain facility is appropriate for quantifying chemical fluxes at the small-field scale and also suggests that there may be a critical input flux whereby preferential flow is initiated.

Impact of Preferential Flow on Radionuclide Distribution in Soil

Migration of radionuclides in soils and their transfer to edible plants are usually estimated using volume-averaged bulk concentrations. However, radionuclides might not be homogeneously distributed in soils due to heterogeneous water flow and solute transport. One important cause of heterogeneous transport is preferential flow. The aim of this study was to investigate the spatial distribution of radionuclides in the soil in relation to preferential flow paths and to assess the possible consequences for their transfer from soil to plants. We identified the preferential flow paths in a forest soil by staining them with a blue dye, and we compared radionuclide activity in samples from the stained preferential flow paths with those from the unstained soil matrix. The activities of the atmospherically deposited radionuclides 137Cs, 210Pb, 239,240Pu, 238Pu, and 241Am were enriched in the preferential flow paths by a factor of up to 3.5. Despite their different depositional histories, the distribution of the radionuclides between preferential flow paths and matrix was similar. Our findings indicate increased transport of radionuclides through the preferential flow paths, representing a possible risk of groundwater contamination. Furthermore, enrichment of radionuclides in the preferential flow paths might influence the uptake by plants. The heterogeneous radionuclide distribution in the soil and the more intense rooting in the preferential flow paths can be incorporated into soil-to-plant transfer models. Taking the correlated radionuclide and root distribution between the two flow regions into account provides a more physical and biological basis for the calculation of plant activities with transfer models than using the homogeneously mixed bulk soil activities as input parameters.

SIMULATION OF NITROGEN AND PHOSPHORUS LEACHING IN A STRUCTURED SOIL USING GLEAMS AND A NEW SUBMODEL, “PARTLE”

The potential negative impact of agricultural chemicals on the quality of surface and ground water resourcesis a worldwide concern. The complexity of factors affecting nonpoint source pollution makes experimental assessment ofthe environmental consequences of different management strategies laborious and expensive. Therefore, one feasiblemethod is to use the existing research database to validate and modify the computer models, then use the models tosimulate the long-term impact of these systems. In this study the hydrologic and nutrient loss data from a subsurfacedrained, structured clay soil in southwest Sweden was used to examine the applicability of GLEAMS to simulate thedrainage discharge and N and P concentrations in the discharge water. The results indicated that GLEAMS was capableof simulating drainage discharge, nitrate-N and dissolved-P losses reasonably well, but there were no algorithms tosimulate the particulate-P losses via drain tiles. Therefore, a submodel, PARTLE was developed and tested. Our resultsindicate that the PARTLE submodel, in association with the GLEAMS model, provided reasonable estimates ofparticulate-P loss via drainage in this soil. The study concluded that considering the impact of preferential flow and theratio of annual drainage discharge to annual precipitation is necessary for proper predictions of particulate-P instructured soils.