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, p hreatic aquifer have been conducted at the same site before and after the r ainy season. The field site is an uncultivated region located in a citrus o rchard, north of the city of Netanya, on the Coastal Plain aquifer of Israe l. In two single-day campaigns, 13 boreholes were drilled in relatively hom ogeneous sandy sediments in an area subjected to infiltration of rain only. Twelve of the thirteen boreholes were located within a radius of 5 m. Wate r content, as a function of depth, was obtained from continuous cores. We f ound that the distribution of water within the capillary fringe (CF) was co mpact - denoting that there was an abrupt change in water content with incr easing height above the water table. The height of the CF was about 1.4 m a t 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 se ason, respectively. Saturated conditions were detected in some regions of t he CF and unsaturated conditions were found up to 1.5 m below the water tab le. The distribution of water in the capillary fringe remained compact whil e being displaced vertically as the water table rose 35 cm after the winter rains. These observations are consistent with pore level models of the wat er distribution within the capillary fringe in a porous media. (C) 2000 Els evier Science B.V. All lights reserved.