[1] A study on water infiltration and groundwater recharge was conducted in the coastal plain, Israel. The study implemented a novel development, flexible time domain reflectometry sensors (FTDR), which enabled the continuous monitoring of water content at selected points through the entire vadose zone. Data on water content variation with time and depth was collected throughout the rainy season of 2004/2005 at two sites. One site was located in a sand dune area with a 21 m thick vadose zone; the other was located in an undeveloped urban area with an 8.4 m thick vadose zone. The lithology of both sites consisted of unconsolidated sand with silt and clay interbeds. The resultant data allowed tracing of the infiltration progress through the entire vadose zone. Each large rain event initiated an infiltration wave that propagated into the vadose zone and pushed the wetting front farther down. The wetting front appeared to progress in a step-like pattern, controlled by the frequency of large rain events and followed by a slower drainage process. Clay interbeds did not seem to prevent or significantly delay progress of the wetting front down to the groundwater. The apparent wetting front signal reached the groundwater table at 21 m below land surface (bls) only 3 months after the first significant rain event. Groundwater recharge was calculated from the variations in vadose zone water storage. An increase in vadose zone water storage was attributed to an infiltration event, while a reduction in water storage was attributedto a draining process.
Water percolation and solute transport through an unsaturated sandy formation were investigated using a vadose‐zone monitoring system that enables in situ, continuous, real‐time monitoring of the percolating water. Measurements of the temporal variations in vadose‐zone water content as well as continuous monitoring of the vadose‐zone pore water allowed detailed tracking of the propagation velocities of the wetting front and determination of the flow patterns governing solute transport. It has been shown that the chemical composition of mobile flowing water along the vadose zone is not in equilibrium with the total soluble solute potential of the sediment. This phenomenon is usually attributed to a flow mechanism controlled by preferential flow. Wetting‐front propagation patterns, as monitored continuously during four rainy seasons throughout the entire vadose zone, as well as a tracer experiment, showed relatively uniform wetting‐front propagation with no direct evidence for significant preferential flow. Contradictory observations of matrix and preferential flow as governing mechanisms led to conceptualization of the percolation process as pore‐scale dual‐domain flow.
Measurements of vadose zone water pressure using custom‐made tensiometers provided insight into the dynamics of rainfall‐induced infiltration events in a 22‐m‐thick sandy formation. The tensiometers, based on vadose zone sampling ports, were assembled in a vadose zone monitoring system that allowed in situ, real‐time measurements of the temporal variation in vadose zone water content and pore water pressure. Results revealed the critical relationship between temporal variations in vadose zone water content and water pressure, as well as the dynamic connectivity of the vadose zone gas phase to the atmosphere. As expected, variation in the sediment water contents, induced by infiltration events across the vadose zone, resulted in corresponding variations in pore water pressure; however, the measured responses of sediment water pressure to wetting events were delayed compared with the measured variations in water content. The delay in the pressure response to a wetting process varied with location as well as between wetting events. Most of the time, the vadose zone gas phase was well connected to the atmosphere; however, this connectivity was limited during rain events and, therefore, compensation of the measured water pressure variation for the measured atmospheric pressure fluctuation is not straightforward. Connectivity of the vadose zone gas phase to the atmosphere was reestablished simultaneously across the entire vadose zone following redistribution of the percolating water in the upper part of the cross‐section.
A large fraction of the fresh water available for human use is stored in groundwater aquifers. Since human activities such as mining, agriculture, industry and urbanization often result in incursion of various pollutants to groundwater, routine monitoring of water quality is an indispensable component of judicious aquifer management. Unfortunately, groundwater pollution monitoring is expensive and usually cannot cover an aquifer with the spatial resolution necessary for making adequate management decisions. Interpolation of monitoring data between points is thus an important tool for supplementing measured data. However, interpolating routine groundwater pollution data poses a special problem due to the nature of the observations. The data from a producing aquifer usually includes many zero pollution concentration values from the clean parts of the aquifer but may span a wide range (up to a few orders of magnitude) of values in the polluted areas. This manuscript presents a methodology that can cope with such datasets and use them to produce maps that present the pollution plumes but also delineates the clean areas that are fit for production. A method for assessing the quality of mapping in a way which is suitable to the data's dynamic range of values is also presented. Local variant of inverse distance weighting is employed to interpolate the data. Inclusion zones around the interpolation points ensure that only relevant observations contribute to each interpolated concentration. Using inclusion zones improves the accuracy of the mapping but results in interpolation grid points which are not assigned a value. That inherent trade-off between the interpolation accuracy and coverage is demonstrated using both circular and elliptical inclusion zones. A leave-one-out cross testing is used to assess and compare the performance of the interpolations. The methodology is demonstrated using groundwater pollution monitoring data from the Coastal aquifer along the Israeli shoreline
A large fraction of the fresh water available for human use is stored in groundwater aquifers. Since human activities such as mining, agriculture, industry and urbanisation often result in incursion of various pollutants to groundwater, routine monitoring of water quality is an indispensable component of judicious aquifer management. Unfortunately, groundwater pollution monitoring is expensive and usually cannot cover an aquifer with the spatial resolution necessary for making adequate management decisions. Interpolation of monitoring data is thus an important tool for supplementing monitoring observations. However, interpolating routine groundwater pollution data poses a special problem due to the nature of the observations. The data from a producing aquifer usually includes many zero pollution concentration values from the clean parts of the aquifer but may span a wide range of values (up to a few orders of magnitude) in the polluted areas. This manuscript presents a methodology that can cope with such datasets and use them to produce maps that present the pollution plumes but also delineates the clean areas that are fit for production. A method for assessing the quality of mapping in a way which is suitable to the data's dynamic range of values is also presented. A local variant of inverse distance weighting is employed to interpolate the data. Inclusion zones around the interpolation points ensure that only relevant observations contribute to each interpolated concentration. Using inclusion zones improves the accuracy of the mapping but results in interpolation grid points which are not assigned a value. The inherent trade-off between the interpolation accuracy and coverage is demonstrated using both circular and elliptical inclusion zones. A leave-one-out cross testing is used to assess and compare the performance of the interpolations. The methodology is demonstrated using groundwater pollution monitoring data from the coastal aquifer along the Israeli shoreline. The implications for aquifer management are discussed.
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