Analysis of Zero Flux Plane Behavior under Periodical Water Supply

Abstract

Zero Flux plane (ZFP) is defined as a plane, which separates two zones of upward and downward movement of water in soil with upward and downward flow occurring simultaneously. In this study, the analysis of the ZFP movements was carried out by two sets of laboratory experiments and numerical simulations, especially paying attention to the effect of the periodical water supply. In the first set of experiment and simulation, surface Andisol soil was used and water was supplied only one time. Evaporation rate was set to 0.15 cm/day, and water was drained from the bottom of the column. The total potential profile and the ZFP movement of experiment and simulation agreed reasonably well. In the second set of experiment and simulation, subsurface Andisol was used and water was supplied periodically. In both experiment and simulation, ZFP appeared at soil surface every time water was supplied, and it gradually moved downward until it reached to the depth of 30 cm, when the ZFP disappeared. We discussed that such disappearance of the ZFP is observed when the initial soil water content at the deep zone is relatively high. In contrast, when the initial soil water content at the deep zone is relatively low, as reported in previous studies, ZFP continues to move downward for a relatively long period. Simulation of ZFP movement was also conducted for different types of soils. Based on the results of this study, a strategy for the periodical water supply in arid and semiarid regions using this ZFP concept was proposed.