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Perry de Louw Gualbert Oude Essink Sara Eeman (WUR) Bart Goes

Characterization of local rainwater lenses in agricultural areas with upward saline seepage. Monitoring results Zeeland. Perry de Louw Gualbert Oude Essink Sara Eeman (WUR) Bart Goes. Tomasso Letterio Bastiaan de Veen Corne Prevo Sjors Stevens Valentina Marconi Franceso Sergi

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Perry de Louw Gualbert Oude Essink Sara Eeman (WUR) Bart Goes

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  1. Characterization of local rainwater lenses in agricultural areas with upward saline seepage.Monitoring results Zeeland Perry de Louw Gualbert Oude Essink Sara Eeman (WUR) Bart Goes Tomasso Letterio Bastiaan de Veen Corne Prevo Sjors Stevens Valentina Marconi Franceso Sergi Piet Maljaars

  2. Saline groundwater Max. Holocene Transgression

  3. Factors controlling fresh-salt interface(base for 27 representative monitoring sites) Dynamics Surface water level Drainage Comp. Cover Layer (k,d,S) Salinity of groundwater Seepage intensity

  4. Surface level and position of 27 field sites

  5. Field measurements at 27 sites In-situ, 1D: Temperature and EC with depth with TEC-probe Indirect: formation factor Ex-situ,2D: Continuous Vertical Electrical Sounding (CVES) In-situ,1D: Groundwater sampling at different depth (filters)

  6. Max. Cl-conc (mg/l) Surface Level (cm relative to sea level) TEC-probe results

  7. Site 11 Center ditch Border ditch 1m 7.5m 15m 30m 50m 100m CVES line 200m Fossil Creek ridge 300m Ditch

  8. Site 11 Center ditch Border ditch 1m 7.5m 15m 30m 50m 100m CVES line 200m Fossil Creek ridge 300m Ditch

  9. ECa – depth profiles (TEC-probe) Mixing zone

  10. Characterization using statistical moments (1st, 2th) (5S, 2th) (µ, 1st mom.) (5S, 2th) (µ, 1st mom.)

  11. Fitting on field data 12 16 12 16

  12. Measured and calculated cl-depth profiles 9 10 13 5 2 11

  13. Results: characteristics of fresh-saline interface

  14. Groundwater sampling: filters at different depths 0.3m sloot 0.5m Onverzadigde zone 0.8m 1m Verzadigde zone 4m 1.3m 1.6m 2m 2m 3m 4m

  15. Location of monitoring points 90m 50m 30m 17.5m 7.5m 1m Drain tubes

  16. Cl-conc in parcel and in ditch (sampling)

  17. Cl-conc with depth (sampling) GWL

  18. Unsaturated zone? ? ? ?

  19. Dynamics of Cl-profiles

  20. Dynamics of Cl-profiles T=0 T=2 T=1 T=3

  21. Dynamics of Cl-profiles

  22. Conclusions monitoring results • No sharp interface fresh rainwater-saline groundwater is found; • Mixing zone is found at shallow depth; • Characterization of mixing zone is relevant; • Statistical moments can be used for characterization interface • At seepage sites no fresh groundwater was found (while P-ET >> seepage) • - What happens in the unsaturated zone? • - What is the dynamic of the mixing zone/cl-profile?

  23. THANK YOU

  24. Cl – depth profiles (TEC-probe)

  25. Infiltration and seepage near ditch

  26. Empirical relation: Cl(x) - Electrical Resistance of water(ρw) - HCO3

  27. TEC-probe measurements in parcel (red) and ditch (blue) Depth (m below surface) Cl-conc (mg/l)

  28. Fresh rainwater lens on saline groundwater

  29. Cross section: groundwater systems Zeeland

  30. Composition of cover layer clay peat sand

  31. Seepage intensity: Qs=Δh/c _ Δh = C Seepage intensity (Qs)

  32. Seepage intensity

  33. CVES Principal Continuous Vertical Electrical Sounding (CVES) >80 electrodes at surface 2D elektrical resistance in subsoil Maximum depth (~30 m)

  34. Compensation for soil type: Formation factor FF ECa = EC of water and soil ECw = EC of water • ECw = FF * ECa

  35. Max. Cl-conc (mg/l) Surface Level (cm relative to sea level) Correlation:Char. rainwater lens - factors Depth center of mixing zone (cm below surafec) Seepage intensity (mm/d)

  36. ditch ditch

  37. Lithostratigraphy of Holocene cover layer Hol. cover layer First aquifer

  38. Creek (sand) and reclaimed salt marches (clay-peat)

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