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Application of Monte-Carlo Method to Modelling Influence of Selected Soil Heterogeneity on Macrodispersion of Pollutants in Unsaturated Soil Medium

Gorczewska-Langner W.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2011

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Vol. 15, No 3-4

329-337

EN

The influence of soil heterogeneity on miscible solute transport in soil is analyzed. The transport process is simulated numerically using the Monte-Carlo method. This paper shows how different types of soil heterogeneity influence the process of contaminant spreading. If independent flow paths exist in the soil, the degree of the mixing of pollutants in the outflow from the soil profile is larger. If the preferential flow paths are shorter, the degree of mixing, related to the heterogeneity of the velocity field, is smaller. These effects can be captured using the Monte-Carlo method.

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Wpływ niejednorodności pola prędkości na dyspersję hydrodynamiczną w nienasyconym ośrodku gruntowym: badania eksperymentalne i modelowanie numeryczne

Gorczewska-Langner W.

Biuletyn Państwowego Instytutu Geologicznego

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2010

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nr 442 Hydrogeologia z. 11

43--47

PL

Praca dotyczy zjawiska makrodyspersji, czyli rozprzestrzeniania się substancji rozpuszczonej w wodzie gruntowej w skali makro. Przyczyną makrodyspersji są różnice prędkości w poszczególnych ścieżkach przepływu, które mogą występować nawet w pozornie jednorodnym ośrodku gruntowym. Eksperymenty przeprowadzono na makroskopowo jednorodnych i nienasyconych kolumnach gruntowych o trzech różnych długościach. Zawartość wody w kolumnie mierzono metodą radiometryczną, natomiast koncentrację znacznika – na wypływie z kolumny metodą konduktometryczną. Do opisu transportu masy w kolumnie gruntowej wykorzystano model numeryczny umożliwiający symulację przepływu wody gruntowej szeregiem niezależnych, jak i wzajemnie zależnych ścieżek przepływu.

EN

This work concerns the phenomenon of macrodispersion, i.e. large-scale dispersion effect, caused by the local-scale variability of the flow velocity field, which can exist even in apparently homogeneous natural soils. Experiments were performed on macroscopically homogeneous soil columns of three different lengths with steady-state downward unsaturated flow. The water content in the columns was measured using the radiometric method while the tracer concentration was measured at the outflow using the conductometric method. The numerical model was applied to describe mass transport in the columns. The stochastic model of solute transport based on the assumption that the water flows by paths, with no mass exchange between the adjacent paths, but also it accounts for the possible mass exchange between the paths.

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Micro- and macro-dispersive fluxes in canopy flows

Poggi D., Katul G. G.

Acta Geophysica

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2008

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Vol. 56, no. 3

778-799

EN

Resolving every detail of the three-dimensional canopy morphology and its underlying topography remains untenable when modeling high Reynolds number geophysical flows. How to represent the effects of such a complex morphological variability and any concomittant topographic variability into one-dimensional bulk flow representation remains a fundamental challenge to be confronted in canopy turbulence research. Theoretically, planar averaging to the scale of interest should be applied to the time-averaged mean momentum balance; however, such averaging gives rise to covariance or dispersive terms produced by spatial correlations of time-averaged quantities that remain ‘unclosed’ or require parameterization. When the averaging scale is commensurate with few canopy heights, these covariances can be labeled as ‘micro-dispersive’ stresses. When averaging is intended to eliminate low-wavenumber topographic variations, we refer to these covariances as ‘macro-dispersive’ terms. Two flume experiments were used to explore the magnitude and sign of both micro- and macro-dispersive fluxes relative to their conventional Reynolds stresses counterparts: a rod-canopy with variable roughness density and a dense rod canopy situated on gentle hilly terrain. When compared to the conventional momentum flux, the micro-dispersive fluxes in the lowest layers of sparse canopies can be significant (~50%). For dense canopies, the dispersive terms remain negligible when compared to the conventional momentum fluxes throughout. For the macro-dispersive fluxes, model calculations suggest that these terms can be neglected relative to the Reynolds stresses for a deep canopy situated on a narrow hill. For the region in which topographic variations can interact with the pressure, both model calculations and flume experiments suggest that the macro-dispersive fluxes cannot be neglected, and their value can be 20% of the typical Reynolds stresses.