Field observations of a capillary fringe before and after a rainy season

Field measurements of profiles of the water content of a 7-m deep, sandy, phreatic aquifer have been conducted at the same site before and after the rainy season. The field site is an uncultivated region located in a citrus orchard, north of the city of Netanya, on the Coastal Plain aquifer of Israel. In two single-day campaigns, 13 boreholes were drilled in relatively homogeneous sandy sediments in an area subjected to infiltration of rain only. Twelve of the thirteen boreholes were located within a radius of 5 m. Water content, as a function of depth, was obtained from continuous cores. We found that the distribution of water within the capillary fringe (CF) was compact — denoting that there was an abrupt change in water content with increasing height above the water table. The height of the CF was about 1.4 m at each point above the water table, and over a horizontal distance of about 4 m, this height varied by up to 33% and 50% before and after the rainy season, respectively. Saturated conditions were detected in some regions of the CF and unsaturated conditions were found up to 1.5 m below the water table. The distribution of water in the capillary fringe remained compact while being displaced vertically as the water table rose 35 cm after the winter rains. These observations are consistent with pore level models of the water distribution within the capillary fringe in a porous media.