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Freshwater-Saltwater Mixing Zone in Coastal Aquifers: Biased vs. Reliable Monitoring. Eyal Shalev Yossi Yechieli Haim Gvirtzman – Hebrew University, Jerusalem. } – Geological Survey of Israel. Outline. Long – screened boreholes Groundwater flow in coastal aquifers Field data
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Freshwater-Saltwater Mixing Zone in Coastal Aquifers: Biased vs. Reliable Monitoring Eyal Shalev Yossi Yechieli Haim Gvirtzman – Hebrew University, Jerusalem } – Geological Survey of Israel
Outline • Long – screened boreholes • Groundwater flow in coastal aquifers • Field data • Numerical simulations • Conclusions
Hydraulic Head Interface Interface
Konokow and Hornberger, 2006
Konokow and Hornberger, 2006
T/143-3 T/143-4 41.56 81.56 31.57 34.44 73.13 116.00
South Korea Kim et al., 2005 J. Hydrology
Kim et al., 2005 J. Hydrology
Kim et al., 2005 J. Hydrology
Jeju Island Kim et al., 2006 J. Hydrology
350 ft = 106.7 m 142 ft = 43.3 m 205 ft = 62.5 m Priest, S., 2004, USGS Scientific Investigations Report 2004-5265
anisotropic anisotropic
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
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.