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Fresh water lenses on saline groundwater

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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Fresh water lenses on saline groundwater

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  1. 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

  2. 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

  3. Lens on field Scale • Most relevant for users • Mixing zone not negligible • Boundary conditions well defined

  4. δc/δz Z Methods • Numerical modeling using SUTRA • Density dependent • Unsaturated zone • Analysis of results using spatial moments of concentration change with depth

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

  6. Numerical vs Maas(2007) • First vertical moment dC/dy • From initially saline towards steady state Steady state Max. thickness in time

  7. 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

  8. Contributions to mixing I Moving ‘interface’ Steady state conditions

  9. 5m 15m 25m Contributions to mixing II

  10. 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

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

  12. Thank You!

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