% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@BOOK{Bechtold:136391,
      author       = {Bechtold, Michel},
      title        = {{E}xperimental and numerical studies on solute transport in
                      unsaturated heterogeneous porous media under evaporation
                      conditions},
      volume       = {143},
      school       = {Universität Bonn},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-136391},
      isbn         = {978-3-89336-795-5},
      series       = {Schriften des Forschungszentrums Jülich. Reihe Energie und
                      Umwelt / energy and environment},
      pages        = {XVIII, 131 S.},
      year         = {2012},
      note         = {Record converted from JUWEL: 18.07.2013; Universität Bonn,
                      Diss., 2012},
      abstract     = {Groundwater level rise, root water uptake, or evaporation
                      induces local upward water and solute fluxes in soils,
                      causing soil salinization and rise of contaminants to the
                      soil surface, and influencing the migration of solutes to
                      the groundwater. It is known that soil heterogeneity
                      strongly controls transport under infiltration conditions,
                      but its effect on transport under upward flow conditions has
                      barely been investigated. In this thesis, laboratory tracer
                      experiments were conducted in artificial porous media with
                      known heterogeneity under evaporation conditions and
                      observations were compared with numerical simulations in
                      order to improve the understanding of upward flow and
                      transport processes. High concentration gradients due to
                      solute accumulation at the soil surface caused by
                      evaporation are posing very high demands on Eulerian schemes
                      for solving the advection-dispersion equation (ADE), while
                      they have no negative effect on the stability of random walk
                      particle tracking (RWPT) schemes. However, RWPT loses
                      accuracy when the dispersion tensor or the water content is
                      spatially discontinuous, a topic that is frequently-debated
                      in RWPT literature. In this thesis, a new RWPT algorithm is
                      presented that builds on the former concept of representing
                      the discontinuities by partially reflecting barriers. Three
                      improvements were developed that enhance the accuracy and
                      efficiency of this concept by orders of magnitude. In a
                      composite porous medium, consisting of a cylindrical inner
                      core with coarse sand that was surrounded by fine sand, dye
                      and salt tracer experiments were conducted under constant
                      evaporation conditions, and a Gd-DTPA$^{2}$- tracer
                      experiment was monitored with magnetic resonance imaging
                      (MRI) during a cycle of infiltration and evaporation. The
                      key finding of these experiments was the formation of high
                      solute concentration spots at the surface of the coarse
                      material, which is contrary to the general expectation that
                      solutes accumulate and precipitate in regions with finer
                      texture and higher evaporation fluxes. Flow and transport
                      simulations showed that molecular diffusion, which moves
                      solutes away from the evaporating surface back into the
                      porous medium, in combination with lateral water flow
                      redistributes solutes towards locations with the lowest
                      hydraulic head. The formation of high solute concentration
                      spots at the surface of coarser regions, which usually
                      represent preferential flow pathways during strong
                      precipitation, may have an accelerating effect on the
                      leaching of solutes. [...]},
      cin          = {IBG-3},
      ddc          = {500},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      typ          = {PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/136391},
}