1. Freshwater-Saltwater Mixing Zone Biased vs. Reliable Monitoring
in Coastal Aquifers:
Biased vs. Reliable Monitoring
Eyal Shalev
Yossi Yechieli
Haim Gvirtzman – Hebrew University, Jerusalem
} – Geological Survey of Israel

2. Outline Long – screened boreholes Groundwater flow in coastal aquifers
Field data
Numerical simulations
Conclusions

4. Hydraulic Head
Interface
Interface

5. Elci et al., 2003

6. Molz et al., 1994

7. Britt, 2005

8. Konokow and
Hornberger, 2006

9. Konokow and
Hornberger, 2006

11. T/143-4
T/143-3
41.56
81.56
31.57
34.44
73.13
116.00

12. South Korea
Kim et al., 2005
J. Hydrology

13. Kim et al., 2005
J. Hydrology

14. Kim et al., 2005
J. Hydrology

15. Jeju Island
Kim et al., 2006
J. Hydrology

18. Well identification number
Altitude of land surface datum (ft)
Top of screened or open interval (ft)
Bottom of screened or open interval (ft)
Aquifer
18K049
330.00
270
620
Upper Floridan
19E009
217
200
342
21T001
259 89
123
32L015 74
545
750
32L016
320
340
Upper Brunswick
32L017
215
Surficial
32R003
120
134
155
Miocene
35P094
18.7 15
36Q008
9.91
250
406
350 ft = m
142 ft = 43.3 m
205 ft = 62.5 m
Priest, S., 2004, USGS Scientific Investigations Report

25. anisotropy 1:30

26. anisotropic
anisotropic

27. anisotropy 1:30

29. Conclusions Observations monitored in long-screen boreholes do not
accurately represent natural phenomena
Boreholes may act as a “short circuit” along a vertical
gradient, connecting between the higher and lower
hydraulic head zones
This is shown to occur in coastal aquifers both in steady
state and transient (tide) conditions
In steady state conditions, the borehole interference is
higher for the anisotropic case

30. Conclusions (continued)
When tides are introduced, the high amplitude of the
freshwater-saltwater mixing zone occurs only in the
borehole.
In the aquifer, the freshwater-saltwater mixing zone
fluctuations are dampened, and tens of meters inland
from the shoreline the fluctuations are in the order of
few centimeters.
Groundwater flow directions are affected by tides to a
large distance from the shoreline.