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DTSTAMP:20190311T155307
UID:61a779fa-440d-11e9-a578-000e0c3db68b
SUMMARY:Influence of connected structures on upscaled models for flow andtransport in the unsaturated zone
DESCRIPTION:Flow velocity of water in the unsaturated zone is described by theRichards equation. Transport of solutes, such as agrochemicals, in thevadose zone is mostly described by an advection-dispersion equation.Soil is in reality highly heterogeneous, so the hydraulic parameters vary in space and their detailed structure is unknown. Heterogeneity ofhydraulic soil parameters has a strong influence on flow and transportprocesses. As an example, it determines dispersion of soluteconcentration. As water and mass fluxes usually have to be predicted onlength scales much larger than the typical length scales ofheterogeneities, flow and transport models have to be upscaled topredict spatial averages of state variables (water content or soluteconcentration). Upscaled models for flow and transport in aquifers arequite well established. In the unsaturated zone, where variances ofhydraulic parameters can be extremely high, assumptions such as smoothlyvarying, moderately heterogeneous hydraulic parameter fields can oftennot be made to derive upscaled models.Heterogeneity of soil is usually captured by modeling hydraulicparameters as correlated random fields. These fields are mostly directlyor indirectly assumed to be multi-Gaussian. This implies that noinformation is used upon whether a certain parameter range is spatiallyconnected or forms isolated clusters. However, connectivity has beenfound to have a strong influence on parameters of upscaled flow models,in particular if the variance of parameters is high.In this presentation, the influence of connected structures ofheterogeneous hydraulic parameter fields on upscaled flow and solutetransport models in the vadose zone will be discussed. Upscaled modelsare derived using homogenization theory. The models are analyzed fordifferent configurations of connected and isolated parameter ranges andfor different parameter contrasts. Homogenization theory is based on anexpansion of the flow- and transport equation in terms of the ratiobetween typical large length scale (for example the medium size) andtypical small length scale (for example the length scale of amacroscopic representative elementary volume). By analyzing differentparameter contrasts, quantified in terms of the expansion parameter, itcan be demonstrated that, for example, the occurrence of non-equilibriumeffects in the upscaled model depends crucially on the information aboutconnectivity of different parameter ranges. Besides the type of upscaledmodel, also the effective model parameters depend on this type ofinformation and can deviate significantly from effective parametersderived under the assumption that parameter fields are multi-Gaussian.
DTSTART;TZID=Europe/Berlin:20071106T160000
DTEND;TZID=Europe/Berlin:20071106T173000
LOCATION:Pfaffenwaldring 61, Raum U1.003 (MML), Universität Stuttgart, , , , 
URL;VALUE=URI:https://www.iws.uni-stuttgart.de/en/institute/events/Influence-of-connected-structures-on-upscaled-models-for-flow-andtransport-in-the-unsaturated-zone/
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