Soil Water Distribution and Movement in Layered Soils of a Dam Farmland

In soil profiles, special emphasis has been placed on the migration of agricultural chemicals spread intentionally or accidentally into deep soils or groundwater body. To prevent soil water pollution and estimate the magnitude of the hazard caused by these chemicals, it is necessary to know the processes controlling their movement from the soil surface, through the root zone and eventually to the water table. This paper deals with two-dimensional soil water distribution and movement in sloping layered soils of a dam farmland on the Loess Plateau of China. In the dam farmland, soil water content showed horizontal distribution corresponding to spatial patterns of the particle sizes. The soil water content of deeper soil was relatively stable compared with topsoil. Generally, rainfall infiltration was limited to 0.8 m in the study period. Funnel flows were found in the layered soils of the dam farmland after rainfall proving the existence of this phenomenon which was observed in simulation experiments and field observation by previous researches. In the study area, the wetting front was unstable due to the layered soils. The spatial correlation analysis of the soil water content showed water movement along the layers in the wetting process with 7 m day (-aEuro parts per thousand 1) only on the first day after rainfall. On the vertical direction, the velocity of water movement was 0.3 m day (-aEuro parts per thousand 1) on the first day after rainfall. The results indicated that the quantity of funnel flow increases with distance along the inclined interfaces in the dam farmland which can cause contamination of groundwater. Consequently, future studies should consider the funnel flow and the management of agriculture chemicals in dam farmlands.