Fresh water lenses on saline groundwater

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Fresh water lenses on saline groundwater

• Dispersive Behavior of the Mixing Zone between a
  Shallow Freshwater Lens and Upward Seeping Saline
  Groundwater
• S.Eeman, A. Leijnse, S.E.A.T.M. van der Zee
• Wageningen UR, Sub-department of Soil Physics,
  Ecohydrology and Groundwater management

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Background

• Low lying areas
• Changing climate
• Non-equilibrium of ground water system
• Influence on land use options?
• Characterization of small scale system

Source G. Oude Essink, Deltares
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Lens on field Scale

• Most relevant for users
• Mixing zone not negligible
• Boundary conditions well defined

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Methods

• Numerical modeling using SUTRA
• Density dependent
• Unsaturated zone
• Analysis of results using spatial moments of
  concentration change with depth

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Results

• Comparison to the analytical solution by Maas
  (2007)
• Analyses of dispersion and diffusion

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Numerical vs Maas(2007)

• First vertical moment dC/dy
• From initially saline towards steady state

Steady state
Max. thickness in time
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Processes contributing to mixing

• Longitudinal dispersion
• Transverse dispersion
• Molecular diffusion

• Different processes
• Different circumstances
• Phase
• Location
• Num. calculations
• Local coordinate system
• Parallel to interface
• Less accurate near ditch

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Contributions to mixing I
Moving interface Steady state conditions
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Contributions to mixing II

• 5m
• 15m
• 25m

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Conclusions

• Steady conditions analytical model of Maas
  (2007) is a very good approximation
• Contribution of dispersion and diffusion to
  mixing depend on phase and location
• Developing lens longitudinal dispersion
• Steady state transverse dispersion / diffusion
• Mid field BC prohibits transverse dispersion
• Near ditch transverse dispersivity

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Current work

• Start of fieldwork in Zeeland with P. de Louw,
  Deltares (thanks!)
• Sensitivity of a fresh water lens for different
  climatic conditions

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Thank You!