RECONCILIATION BETWEEN MEASURED AND THEORETICAL TEMPERATURE EFFECTS ON SOIL-WATER RETENTION CURVES

Because temperature has a considerable effect on water retention curve s, it should be accounted for when modeling unsaturated soil water flo w under nonisothermal conditions. Changes are commonly attributed to a lterations in surface tension at the air-water interface, to changes i n the volume of entrapped air, and sometimes to the presence of contam inants at the air-water interface. Predicted changes have, however, al ways fallen short of experimentally determined values reported in the literature. We propose a new theory that considers soil water to be co mposed of continuous water and isolated packets of water. Measured soi l water pressure head values are assumed to be determined by the prope rties of continuous water only. We hypothesize that, when the temperat ure increases, water flows from isolated packets to the continuous wat er phase, thus resulting in an additional temperature effect on the wa ter retention curve. Based on the assumption that the continuous water content changes linearly with the total water content, we derived exp ressions for the change in soil water pressure head with temperature. Calculated changes in points on the water retention curve were subsequ ently much closer to measured values than previously reported. The goo d agreement between measured and predicted results suggests that more definitive experiments be conducted to investigate the role of isolate d water packets on soil water retention curves.