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. 21 april 2008 Saline groundwater Max. Holocene Transgression

3. 21 april 2008 Factors controlling fresh-salt interface (base for 27 representative monitoring sites) Salinity of groundwater Seepage intensity Surface water level Comp. Cover Layer (k,d,S) Drainage Dynamics

4. 21 april 2008 Surface level and position of 27 field sites

5. 21 april 2008 Field measurements at 27 sites In-situ, 1D: Temperature and EC with depth with TEC-probe Ex-situ,2D: Continuous Vertical Electrical Sounding (CVES) In-situ,1D: Groundwater sampling at different depth (filters) Indirect: formation factor

6. 21 april 2008 TEC-probe results Max. Cl-conc (mg/l) Surface Level (cm relative to sea level)

7. 21 april 2008 Site 11 Center ditch Border ditch 1m 7.5m15m 30m 50m 100m 200m 300m Ditch Fossil Creek ridge CVES line

8. 21 april 2008

9. Site 11 Center ditch Border ditch 1m 7.5m15m 30m 50m 100m 200m 300m Ditch Fossil Creek ridge CVES line

10. 21 april 2008 EC a – depth profiles (TEC-probe) Mixing zone

11. 21 april 2008 Characterization using statistical moments (1 st, 2 th ) (µ, 1 st mom.) (5S, 2 th ) (µ, 1 st mom.) (5S, 2 th )

12. 21 april 2008 Fitting on field data 1216 12

13. 21 april 2008 Measured and calculated cl-depth profiles 2 5 11 9 10 13

14. 21 april 2008 Results: characteristics of fresh-saline interface

15. 21 april 2008 Groundwater sampling: filters at different depths 3m 1.3m 1m 1.6m 2m 0.3m 0.5m 0.8m Verzadigde zone Onverzadigde zone 2m sloot 4m

16. 21 april 2008 Location of monitoring points 90m 50m 30m 17.5m 7.5m 1m Drain tubes

17. 21 april 2008 Cl-conc in parcel and in ditch (sampling)

18. 21 april 2008 Cl-conc with depth (sampling) GWL

19. 21 april 2008 Unsaturated zone? ? ??

20. 21 april 2008 Dynamics of Cl-profiles

21. 21 april 2008 Dynamics of Cl-profiles T=1 T=2 T=3 T=0

22. 21 april 2008 Dynamics of Cl-profiles

23. 21 april 2008 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?

24. 21 april 2008 THANK YOU

25. 21 april 2008 Cl – depth profiles (TEC-probe)

26. 21 april 2008 Infiltration and seepage near ditch

27. 21 april 2008 Empirical relation: Cl(x) - Electrical Resistance of water(ρ w ) - HCO 3

28. 21 april 2008

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

33. 21 april 2008 Fresh rainwater lens on saline groundwater

34. 21 april 2008 Cross section: groundwater systems Zeeland

35. 21 april 2008 Composition of cover layer clay peat sand

36. 21 april 2008 Seepage intensity: Qs=Δh/c _ = Seepage intensity (Q s ) ΔhΔh C

37. 21 april 2008 Seepage intensity

38. 21 april 2008 CVES Principal Continuous Vertical Electrical Sounding (CVES) >80 electrodes at surface 2D elektrical resistance in subsoil Maximum depth (~30 m)

39. 21 april 2008 Compensation for soil type: Formation factor FF EC w = FF * EC a Soil type FF peat1-1.5 clay1.5-3.5 silt2-3.5 sand3.5-5 ECa = EC of water and soil ECw = EC of water Clay%Stan. Err.p-valuem (=FF)FF dev.st.FF var.FF mean Sand<203.94< 2.2e-163.240.4300.1853.285 Clay>203.19< 2.2e-162.080.4040.1631.987

40. 21 april 2008 Correlation:Char. rainwater lens - factors Depth center of mixing zone (cm below surafec) Seepage intensity (mm/d) Max. Cl-conc (mg/l) Surface Level (cm relative to sea level)

41. 21 april 2008 ditch

42. 21 april 2008 Lithostratigraphy of Holocene cover layer Lithostratigraphy (Formation)LayerFacies/ Lithology NaaldwijkSchoorlEolian sand (dunes) ZandvoortMarine sand (beach) WalcherenTidal flats and creeks WormerTidal flats and creeks NieuwkoopHollandveenMarsh (peat) BasisveenMarsh (peat) First aquifer Hol. cover layer

43. 21 april 2008 Creek (sand) and reclaimed salt marches (clay-peat)