Water percolation through the deep vadose zone and groundwater recharge: Preliminary results based on a new vadose zone monitoring system

Abstract

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.